Showing 1–50 of 154 results for author: Gadotti, D

The GECKOS Survey: Extraplanar ionised gas in star-forming galaxies from eDIG to galaxy-scale winds

Authors: R. Elliott, D. B. Fisher, B. Mazzilli Ciraulo, A. Fraser-McKelvie, M. R. Hayden, M. Martig, J. van de Sande, A. J. Battisti, J. Bland-Hawthorn, A. D. Bolatto, T. H. Brown, B. Catinella, F. Combes, L. Cortese, T. A. Davis, E. Emsellem, D. A. Gadotti, F. Pinna, T. H. Puzia, L. A. Silva-Lima, L. M. Valenzuela, G. van de Ven

Abstract: We map the extraplanar gas, with $\sim$50-200 pc resolution, in nine star-forming galaxies using Multi-Unit Spectroscopic Explorer (MUSE) observations from the GECKOS VLT Large Program targeting edge-on galaxies with similar stellar mass as the Milky Way. The narrow range in stellar mass ($\pm0.35$ dex) of the GECKOS sample makes it ideal for studying trends with star formation rate (SFR). We find… ▽ More We map the extraplanar gas, with $\sim$50-200 pc resolution, in nine star-forming galaxies using Multi-Unit Spectroscopic Explorer (MUSE) observations from the GECKOS VLT Large Program targeting edge-on galaxies with similar stellar mass as the Milky Way. The narrow range in stellar mass ($\pm0.35$ dex) of the GECKOS sample makes it ideal for studying trends with star formation rate (SFR). We find strong extraplanar emission reaching $\sim$2-8 kpc from the disk midplane in all targets with $\rm{SFR}\geq$1 M$_{\odot}$ yr$^{-1}$. Targets with SFR$\,\geq\,$5 M$_{\odot}$ yr$^{-1}$ have brighter, more extended H$α$ emission compared to lower SFR targets. In high-SFR systems, the gas velocity dispersion ($σ_{\rm Hα}$) shows a biconical morphology, consistent with the expectation of outflows. This agrees with previous works suggesting high velocity dispersion in a biconical shape is a good means to identify outflows. We find mixed results using line diagnostics ([OIII]$_{5007}$/H$β$ - [NII]/H$α$ and $σ_{\rm Hα}$ - [SII]/H$α$) to spatially resolve ionisation mechanisms across the extraplanar gas. The highest [NII]/H$α$ are the extraplanar gas of the highest SFR systems, yet main-sequence galaxies have the highest [OIII]/H$β$. While the morphology of [NII]/H$α$ may be useful to identify outflows, the absolute value of the line ratio alone may not distinguish strong outflows from extraplanar gas of main-sequence galaxies. The ubiquitous extraplanar emission can be interpreted as the result of feedback, in the form of large-scale winds for starbursts or smaller-scale galactic fountains for main-sequence galaxies. Moreover, shock-heating may ionise gas at the interface of the disk and the circumgalactic medium, independent of the source of the gas. △ Less

Submitted 29 January, 2026; originally announced January 2026.

Comments: 24 Pages and 18 figures. Submitted to MNRAS

A nuclear disc at Cosmic Noon: evidence of early bar-driven galaxy evolution

Authors: Zoe A. Le Conte, Dimitri A. Gadotti, Thomas Harvey, Leonardo Ferreira, Christopher J. Conselice, Taehyun Kim, Camila de Sá-Freitas, Francesca Fragkoudi, Justus Neumann, E. Athanassoula

Abstract: Recent studies have revealed that bars can form as early as a few billion years after the Big Bang, already displaying characteristics similar to those of evolved bars in the Local Universe. Bars redistribute angular momentum throughout the galaxy, regulating star formation, AGN activity, and the formation of new stellar structures such as nuclear discs. However, the effects of bar-driven evolutio… ▽ More Recent studies have revealed that bars can form as early as a few billion years after the Big Bang, already displaying characteristics similar to those of evolved bars in the Local Universe. Bars redistribute angular momentum throughout the galaxy, regulating star formation, AGN activity, and the formation of new stellar structures such as nuclear discs. However, the effects of bar-driven evolution on young galaxies are not yet known, as no evidence of bar-built stellar structures has ever been found beyond $z = 1$, until now. In this work, we present evidence for a bar-built, star-forming nuclear disc already present at redshift $z = 1.5$. This is the first evidence of a bar-built stellar structure at Cosmic Noon. We find that this nuclear disc is actively forming stars and is of similar size to some nuclear discs in nearby galaxies. This evidence solidifies the now emerging picture in which bars are fundamental not only in the late evolution of galaxies, but also in their early evolutionary stages. It changes the current paradigm by urging a revision of our picture of galaxy evolution beyond redshift one to include new considerations of the role of bars as early as a few billion years after the Big Bang. △ Less

Submitted 27 July, 2026; v1 submitted 26 January, 2026; originally announced January 2026.

Comments: 7 pages, 3 figures, accepted for publication in MNRAS

Journal ref: Mon Not R Astron Soc (2026)

Composite Bulges -- V. Detecting signatures of gas inflows in IFU data: The MUSE view of ionised gas kinematics in nearby galaxies

Authors: Tutku Kolcu, Witold Maciejewski, Peter Erwin, Dimitri A. Gadotti, Francesca Fragkoudi, Paula R. T. Coelho, Victor P. Debattista, Adriana de Lorenzo-Cáceres, Camila de Sá-Freitas, Patricia Sánchez-Blázquez

Abstract: Using VLT/MUSE data, we study the ionised-gas kinematics in a mass- and volume-limited ($M_* \geq 10^{10} M_\odot$, $D \leq 20$\,Mpc) sample of 21 nearby galaxies to identify signatures of extended shocks within their inner kiloparsec, which appear as coherent velocity jumps in kinematic maps. By removing angular momentum, shocks in gas cause inflows, which can trigger nuclear star formation and f… ▽ More Using VLT/MUSE data, we study the ionised-gas kinematics in a mass- and volume-limited ($M_* \geq 10^{10} M_\odot$, $D \leq 20$\,Mpc) sample of 21 nearby galaxies to identify signatures of extended shocks within their inner kiloparsec, which appear as coherent velocity jumps in kinematic maps. By removing angular momentum, shocks in gas cause inflows, which can trigger nuclear star formation and fuel AGN activity. To identify the signatures of extended shocks, we examine residual velocity fields after subtracting a modelled rotating disc, and we study velocity difference between various gas tracers. Combining our kinematic analysis with BPT ionisation diagnostic maps and dust morphology, we find that 12 of 21 galaxies ($\sim$57%) show extended shock signatures with velocity jumps consistent with models of bar-driven shocks. This is likely a lower limit, as three additional galaxies ($\sim$14%) exhibit shocks along bars, potentially reaching the nucleus but obscured by AGN outflows. We trace shock signatures inwards close to the resolution limit, which suggests that shocks may be the prevailing mechanism of inflow in the central kpc of galaxies. The only two unbarred galaxies in our sample are also the only systems with unperturbed kinematics and no shocks, strongly linking the perturbed gas dynamics in centres of galaxies to the presence of bars. All galaxies with inner bars show LINER- or Seyfert-like nuclear emission, whereas galaxies without inner bars exhibit all emission types, indicating that regardless of gas supply, inner bars suppress star formation in galactic nuclei. △ Less

Submitted 21 June, 2026; v1 submitted 5 January, 2026; originally announced January 2026.

Comments: 22 pages, 9 figures (Appendices: 40 pages with figures), accepted for publication in MNRAS, V2 (includes referee comments)

The impact of bars on the properties of HII regions in the TIMER survey

Authors: Laura Sánchez-Menguiano, Dimitri A. Gadotti, Almudena Zurita, Estrella Florido, Isabel Pérez, Paula Coelho, Jesús Falcón-Barroso, Taehyun Kim, Adriana de Lorenzo-Cáceres, Alejandra Z. Lugo-Aranda, Justus Neumann, Camila de Sá-Freitas, Patricia Sánchez-Blázquez

Abstract: In this study we perform a comparative analysis of the properties of the HII regions located in different areas of barred galaxies, with the aim of investigating the impact of bars on the physical properties of the ionised gas. Based on integral field spectroscopy data for 17 barred galaxies covering approximately the central 6x6 kpc, we detect a total of 2200 HII regions, of which 331 are located… ▽ More In this study we perform a comparative analysis of the properties of the HII regions located in different areas of barred galaxies, with the aim of investigating the impact of bars on the physical properties of the ionised gas. Based on integral field spectroscopy data for 17 barred galaxies covering approximately the central 6x6 kpc, we detect a total of 2200 HII regions, of which 331 are located within the nuclear disc (also known as circumnuclear regions), 661 in the bar region, and 1208 in the disc. Among the physical properties of the HII regions, we explore the O/H and N/O abundances, H$α$ luminosity, dust extinction, electron density, and H$α$ equivalent width. We find clear differences in the properties of the HII regions between the nuclear disc, the bar and the disc, that could be explained by an enhancement in the molecular gas concentration in the central parts driven by bar-induced gas flows. As this gas is channelled towards the galaxy centre, the most extreme values in the analysed properties are found for the circumnuclear HII regions. Unlike the bar strength, galaxy mass does seem to affect the properties of the HII regions, with massive galaxies presenting higher values in most of the properties, possibly due to the increased amount of gas in these systems. This study provides evidence that the bar-driven redistribution of material within the galaxy inner parts causes significant differences in the HII region properties depending on their location within the galaxies. △ Less

Submitted 17 December, 2025; originally announced December 2025.

Comments: Published in MNRAS

Journal ref: 2026, Volume 545, Issue 1, 23 pp

Robust galaxy image decompositions with Differential Evolution optimisation and the problem of classical bulges in and beyond the nearby Universe

Authors: Dimitri A. Gadotti

Abstract: Deconstructing galaxies through two-dimensional decompositions has been shown to be a powerful technique to derive the physical properties of stellar structures in galaxies. However, most studies employ fitting algorithms that are prone to be trapped in local minima, or involve subjective choices. Furthermore, when applied on samples beyond the nearby Universe, results on the fraction of classical… ▽ More Deconstructing galaxies through two-dimensional decompositions has been shown to be a powerful technique to derive the physical properties of stellar structures in galaxies. However, most studies employ fitting algorithms that are prone to be trapped in local minima, or involve subjective choices. Furthermore, when applied on samples beyond the nearby Universe, results on the fraction of classical bulges in disc galaxies do not agree with studies on nearby galaxies. The latter studies point to a small fraction of classical bulges, possibly challenging our merger-driven picture of galaxy formation. Therefore, understanding the discrepancy between observations in and beyond the nearby Universe is of paramount importance. In this paper, I use a sample of 16 nearby galaxies drawn from the TIMER project, which previously have been shown to not host classical bulges, and perform decompositions applying different methodologies and employing the original images as well as artificially redshifted images. I show that the Differential Evolution algorithm is able to provide accurate measurements of structural properties with little subjective intervention, correctly indicating the presence of nuclear discs (not classical bulges). However, I also show that when the physical spatial resolution is not adequate, a systematic overestimation of the photometric bulge Sérsic index leads to the false conclusion of the presence of classical bulges. I discuss how this may be the root cause of the discrepancy mentioned above, and point out how this issue may be a problem even with data from facilities such as Euclid, HST and JWST. △ Less

Submitted 17 November, 2025; originally announced November 2025.

Comments: Accepted for publication in MNRAS (31 pages, including 14 figures, 7 tables and 3 appendices); Fig. A1 will appear in full resolution in the journal version (allowing to better visualise central details in the isophotal contours and ellipse fits)

Dark gaps and resonances in barred galaxies

Authors: Taehyun Kim, Dimitri A. Gadotti, Myeong-gu Park, Yun Hee Lee, Francesca Fragkoudi, Minjin Kim, Woong-Tae Kim

Abstract: Dark gaps, low surface brightness regions along the bar minor axis, are expected to form as a consequence of secular evolution in barred galaxies. Although several studies have proposed links between dark gap locations and dynamical resonances, the results remain inconclusive. Using DESI Legacy Imaging Survey data, we find that approximately 61% of barred galaxies exhibit pronounced dark gaps. We… ▽ More Dark gaps, low surface brightness regions along the bar minor axis, are expected to form as a consequence of secular evolution in barred galaxies. Although several studies have proposed links between dark gap locations and dynamical resonances, the results remain inconclusive. Using DESI Legacy Imaging Survey data, we find that approximately 61% of barred galaxies exhibit pronounced dark gaps. We compare the location of dark gaps with resonance radii derived from the Tremaine-Weinberg method applied to MaNGA data for the same galaxies. Our analysis shows that dark gaps do not preferentially form at specific resonances. Instead, their locations correlate with $\mathcal{R}$ $\equiv$ $R_{CR}/R_{Bar}$: slow bars tend to show shorter dark gap radii, while fast bars show longer ones. This trend reflects a tight relation between bar length and dark gap radius. However, when barred galaxies are classified by their ring morphology, certain types exhibit dark gaps that align with specific resonances. Notably, dark gaps located between the inner and outer rings are closely associated with the corotation radius. In galaxies with two dark gaps along the bar minor axis profile, the inner dark gap typically aligns with the ultraharmonic resonance, and the outer dark gap corresponds to the corotation radius. These findings suggest that some morphological types share similar $\mathcal{R}$ values and exhibit dark gaps near specific resonances. Thus, dark gaps may serve as proxies for dynamical resonances only in certain systems. Our findings may help explain the discrepancies observed in earlier studies. △ Less

Submitted 11 October, 2025; originally announced October 2025.

Comments: Accepted for publication in ApJ, 16 pages, 8 figures

The evolution of the bar fraction and bar lengths in the last 12 billion years

Authors: Zoe A. Le Conte, Dimitri A. Gadotti, Leonardo Ferreira, Christopher J. Conselice, Camila de Sá-Freitas, Taehyun Kim, Justus Neumann, Francesca Fragkoudi, E. Athanassoula, Nathan J. Adams

Abstract: We investigate the evolution of the bar fraction and length using an extended JWST NIRCam imaging dataset of galaxies at $1 \leq z \leq 4$. We assess the wavelength dependence of the bar fraction and bar length evolution by selecting a nearly mass-complete CEERS disc sample and performing visual classifications on the short (F200W) and long (F356W+F444W) wavelength channels. A similar bar fraction… ▽ More We investigate the evolution of the bar fraction and length using an extended JWST NIRCam imaging dataset of galaxies at $1 \leq z \leq 4$. We assess the wavelength dependence of the bar fraction and bar length evolution by selecting a nearly mass-complete CEERS disc sample and performing visual classifications on the short (F200W) and long (F356W+F444W) wavelength channels. A similar bar fraction is observed for both samples, and combined, we find a declining bar fraction from $0.16^{+0.03}_{-0.03}$ to $0.07^{+0.03}_{-0.01}$ over the redshift range. No evolution in the F356W+F444W bar length is measured, with a mean of 3.6 kpc. A slight increase of $\sim 1$ kpc towards $z = 1$ is measured in the F200W sample, with a mean of 2.9 kpc. We find that the correlation between bar length and galaxy mass, for massive galaxies at $z < 1$, is unseen at $z > 1$. By incorporating barred galaxies at $z<1$, we show that there is a modest increase in the bar length ($\approx 2$ kpc) towards $z=0$, but bars longer than $\approx8$ kpc are only found at $z<1$. We show that bars and discs grow in tandem, for the bar length normalised by disc size does not evolve. Not only is a significant population of bars forming beyond $z = 1$, but our results also show that some of these bars are as long and strong as the average bar at $z\approx0$. △ Less

Submitted 14 November, 2025; v1 submitted 8 October, 2025; originally announced October 2025.

Comments: 18 pages, 12 figures. Accepted in MNRAS

Journal ref: MNRAS, 2025, staf2010, 10.1093/mnras/staf2010

The GECKOS Survey: Resolved, multiphase observations of mass-loading and gas density in the galactic wind of NGC 4666

Authors: Barbara Mazzilli Ciraulo, D. B. Fisher, R. Elliott, A. Fraser-McKelvie, M. R. Hayden, M. Martig, J. van de Sande, A. J. Battisti, J. Bland-Hawthorn, A. D. Bolatto, T. H. Brown, B. Catinella, F. Combes, L. Cortese, T. A. Davis, E. Emsellem, D. A. Gadotti, C. del P. Lagos, X. Lin, A. Marasco, E. Peng, F. Pinna, T. H. Puzia, L. A. Silva-Lima, L. M. Valenzuela , et al. (2 additional authors not shown)

Abstract: We present a multiphase, resolved study of the galactic wind extending from the nearby starburst galaxy NGC 4666. For this we use VLT/MUSE observations from the GECKOS program and HI data from the WALLABY survey. We identify both ionised and HI gas in a biconical structure extending to at least $z\sim$8 kpc from the galaxy disk, with increasing velocity offsets above the midplane in both phases, c… ▽ More We present a multiphase, resolved study of the galactic wind extending from the nearby starburst galaxy NGC 4666. For this we use VLT/MUSE observations from the GECKOS program and HI data from the WALLABY survey. We identify both ionised and HI gas in a biconical structure extending to at least $z\sim$8 kpc from the galaxy disk, with increasing velocity offsets above the midplane in both phases, consistent with a multiphase wind. The measured electron density, using [SII], differs significantly from standard expectations of galactic winds. We find electron density declines from the galaxy centre to $\sim2$ kpc, then rises again, remaining high ($\sim100-300$ cm$^{-3}$) out to $\sim$5 kpc. We find that HI dominates the mass loading. The total HI mass outflow rate (above $z~>2$ kpc) is between $5-13~M_{\odot}~\rm yr^{-1}$, accounting for uncertainties from disk-blurring and group interactions. The total ionised mass outflow rate (traced by H$α$) is between $0.5~M_{\odot}~\rm yr^{-1}$ and $5~M_{\odot}~\rm yr^{-1}$, depending on $n_e(z)$ assumptions. From ALMA/ACA observations, we place an upper-limit on CO flux in the outflow which correlates to $\lesssim2.9~M_{\odot}~\rm yr^{-1}$. We also show that the entire outflow is not limited to the bicone, but a secondary starburst at the edge generates a more widespread outflow, which should be included in simulations. The cool gas in NGC 4666 wind has insufficient velocity to escape the halo of a galaxy of its mass, especially because most of the mass is present in the slower atomic phase. This strong biconical wind contributes to gas cycling around the galaxy. △ Less

Submitted 26 October, 2025; v1 submitted 22 September, 2025; originally announced September 2025.

Comments: 19 pages, 13 figures (+ appendices). Accepted 24/10/2025 to MNRAS

Journal ref: Mon Not R Astron Soc (2025) 3290-3311

The GECKOS Survey: revealing the formation history of a barred galaxy via structural decomposition and resolved spectroscopy

Authors: A. Fraser-McKelvie, D. A. Gadotti, F. Fragkoudi, C. de Sá-Freitas, M. Martig, M. Bureau, T. Davis, R. Elliott, E. Emsellem, D. Fisher, M. R. Hayden, J. van de Sande, A. B. Watts

Abstract: Disentangling the (co-)evolution of individual galaxy structural components remains a difficult task, owing to the inability to cleanly isolate light from spatially overlapping components. In this pilot study of PGC\,044931, observed as part of the GECKOS survey, we utilise a VIRCAM $H$-band image to decompose the galaxy into five photometric components, three of which dominate by contributing… ▽ More Disentangling the (co-)evolution of individual galaxy structural components remains a difficult task, owing to the inability to cleanly isolate light from spatially overlapping components. In this pilot study of PGC\,044931, observed as part of the GECKOS survey, we utilise a VIRCAM $H$-band image to decompose the galaxy into five photometric components, three of which dominate by contributing $>50\%$ of light in specific regions: a main disc, a boxy/peanut bulge, and a nuclear disc. When the photometric decompositions are mapped onto MUSE observations, we find remarkably good separation in stellar kinematic space. All three structures occupy unique locations in the parameter space of the ratio of the light-weighted stellar line-of-sight mean velocity and velocity dispersion ($\rm{V}_{\star}/σ_{\star}$), and the high-order stellar skew ($h_{3}$). These clear and distinct kinematic behaviours allow us to make inferences about the formation histories of the individual components from observations of the mean stellar ages and metallicities of the three components. A clear story emerges: the main disc built over a sustained and extended star formation phase, possibly partly fuelled by gas from a low-metallicity reservoir. Early on, that disc formed a bar that buckled and subsequently formed a nuclear disc in multiple and enriched star-formation episodes. This result is an example of how careful photometric decompositions, combined with spatially well-resolved stellar kinematic information, can help separate out age-metallicity relations of different components and therefore disentangle the formation history of a galaxy. The results of this pilot study can be extended to a differential study of all GECKOS survey galaxies to assert the true diversity of Milky Way-like galaxies. △ Less

Submitted 5 November, 2025; v1 submitted 19 September, 2025; originally announced September 2025.

Comments: 5 pages, 3 figures, accepted by A&A

Journal ref: A&A 705, A1 (2026)

Nuclear discs in disc galaxies: structural properties and scaling relations

Authors: Dimitri A. Gadotti, Camila de Sá-Freitas

Abstract: The presence of nuclear discs in barred disc galaxies has been demonstrated in studies on stellar structures and kinematics. It is thus imperative to establish their fundamental properties and scaling relations, which can help understanding their connection to other central stellar structures, including nuclear star clusters. In this Letter, we use results from the structural analysis and star for… ▽ More The presence of nuclear discs in barred disc galaxies has been demonstrated in studies on stellar structures and kinematics. It is thus imperative to establish their fundamental properties and scaling relations, which can help understanding their connection to other central stellar structures, including nuclear star clusters. In this Letter, we use results from the structural analysis and star formation histories of a sample of galaxies with nuclear discs to show the distributions of fundamental parameters and scaling relations. Our analysis shows that the nuclear disc mass-size relation, and the relation between the nuclear disc mass and the stellar mass of its host galaxy, are - at face value - different from the corresponding relations for nuclear star clusters, but marginally compatible given the uncertainties. This sets constraints to scenarios in which their formation is connected. We also find that the nuclear disc in the Milky Way is on the shorter end of the distribution of sizes set by nuclear discs in other galaxies. This is the first analysis of this kind for kinematically confirmed nuclear discs, and further understanding of the properties of the nuclear disc in the Milky Way and other galaxies is necessary to corroborate these results. △ Less

Submitted 17 September, 2025; originally announced September 2025.

Comments: To appear in MNRAS Letters

The GECKOS survey: Jeans anisotropic models of edge-on discs uncover the impact of dust and kinematic structures

Authors: T. H. Rutherford, A. Fraser-McKelvie, E. Emsellem, J. van de Sande, S. M. Croom, A. Poci, M. Martig, D. A. Gadotti, F. Pinna, L. M. Valenzuela, G. van de Ven, J. Bland-Hawthorn, P. Das, T. A. Davis, R. Elliott, D. B. Fisher, M. R. Hayden, A. Mailvaganam, S. Sharma, T. Zafar

Abstract: The central regions of disc galaxies host a rich variety of stellar structures: nuclear discs, bars, bulges, and boxy-peanut (BP) bulges. These components are often difficult to disentangle, both photometrically and kinematically, particularly in star-forming galaxies where dust obscuration and complex stellar motions complicate interpretation. In this work, we use data from the GECKOS-MUSE survey… ▽ More The central regions of disc galaxies host a rich variety of stellar structures: nuclear discs, bars, bulges, and boxy-peanut (BP) bulges. These components are often difficult to disentangle, both photometrically and kinematically, particularly in star-forming galaxies where dust obscuration and complex stellar motions complicate interpretation. In this work, we use data from the GECKOS-MUSE survey to investigate the impact of dust on axisymmetric Jeans Anisotropic Multi-Gaussian Expansion (JAM) models, and assess their ability to recover kinematic structure in edge-on disc galaxies. We construct JAM models for a sample of seven edge-on ($i \gtrapprox 85^\circ$) galaxies that span a range of star formation rates, dust content, and kinematic complexity. We find that when dust is appropriately masked, the disc regions of each galaxy are fit to $χ^2_{\text{reduced}}\leq 5$. We analyse two-dimensional residual velocity fields to identify signatures of non-axisymmetric structure. We find that derived dynamical masses are constant within 10% for each galaxy across all dust masking levels. In NGC 3957, a barred boxy galaxy in our sample, we identify velocity residuals that persist even under aggressive dust masking, aligned with bar orbits and supported by photometric bar signatures. We extend this analysis to reveal a bar in IC 1711 and a possible side-on bar in NGC 0522. Our results highlight both the capabilities and limitations of JAM in dusty, edge-on systems and attempt to link residual velocities to known non-axisymmetric kinematic structure. △ Less

Submitted 10 September, 2025; originally announced September 2025.

Comments: 13 pages, 13 figures, accepted for publication in Astronomy and Astrophysics

Journal ref: A&A 703, A206 (2025)

Nuclear Stellar Discs

Authors: Mathias Schultheis, Mattia C. Sormani, Dimitri A. Gadotti

Abstract: We review our current understanding of nuclear stellar discs (NSDs), rotating, and flattened stellar structures found in the central regions of both early- and late-type galaxies. We examine their demographics, kinematics, stellar populations, metallicity gradients and star formation histories. We derive scaling relations linking NSDs to properties of their host galaxies, and compare them with ana… ▽ More We review our current understanding of nuclear stellar discs (NSDs), rotating, and flattened stellar structures found in the central regions of both early- and late-type galaxies. We examine their demographics, kinematics, stellar populations, metallicity gradients and star formation histories. We derive scaling relations linking NSDs to properties of their host galaxies, and compare them with analogous relations for nuclear star clusters. The relationship between NSDs and other central galactic components, including nuclear rings, nuclear bars, and nuclear star clusters, is explored. The role of NSDs as tracers of the secular evolution of barred galaxies is highlighted, emphasising how they can be used to constrain properties of galactic bars such as their ages. Special attention is given to the Milky Way's NSD, which serves as a unique case study thanks to its proximity and the ability to resolve individual stars. The review covers the Milky Way's NSD structure, kinematics, dynamics and stellar content, addressing ongoing debates about the presence of a nuclear bar and implications of the latter for central gas dynamics. We argue that NSDs form by in-situ star formation, most of them because of bar-driven gas inflow, but possibly in some cases because of external acquisition of gas during a gas-rich merger. The review concludes by outlining open questions, future research directions and the exciting prospects provided by upcoming observational facilities. △ Less

Submitted 15 September, 2025; v1 submitted 4 September, 2025; originally announced September 2025.

Comments: To appear in The Astronomy and Astrophysics Review; v2 has updates to Fig. 4 and Sect. 4.5 (Scaling relations) and one reference

Optimising the analysis of emission lines in galaxies: the case of the MUSE TIMER galaxy NGC 613

Authors: Luiz A. Silva-Lima, Dimitri A. Gadotti, Lucimara P. Martins, Tutku Kolcu, Paula R. T. Coelho, Francesca Fragkoudi, Taehyun Kim, Camila de Sá-Freitas, Jesús Falcón-Barroso, Adriana de Lorenzo-Cáceres, Jairo Méndez-Abreu, Justus Neumann, Miguel Querejeta, Patricia Sánchez-Blázquez

Abstract: Galaxy evolution is driven by spatially distributed processes with varying timescales. Integral field spectroscopy provides spatially-resolved information about these processes. Nevertheless, disentangling these processes, which are related to both the underlying stellar populations and the interstellar medium can be challenging. We present a case study on NGC~613, observed with MUSE (Multi-Unit S… ▽ More Galaxy evolution is driven by spatially distributed processes with varying timescales. Integral field spectroscopy provides spatially-resolved information about these processes. Nevertheless, disentangling these processes, which are related to both the underlying stellar populations and the interstellar medium can be challenging. We present a case study on NGC~613, observed with MUSE (Multi-Unit Spectroscopic Explorer) for the TIMER (Time Inference with MUSE in Extragalactic Rings) project, a local barred galaxy, which shows several gas ionisation mechanisms and is rich in both large and inner-scale stellar structures. We develop a set of steps to overcome fundamental problems in the modelling of emission lines with multiple components, together with the characterisation of the stellar populations. That results in the disentanglement of the gas ionisation mechanisms and kinematics, along with an optimal parametrisation for star formation history recovery. Our analysis reveals evidence of gas inflows, which are associated with the bar dust lanes traced with \textit{Hubble} Space Telescope (HST). In addition, we show the gas kinematics in a central biconical outflow, which is aligned with a radio jet observed with Very Large Array (VLA). The emission line provides estimates of electron density, gas-phase metallicity, and the mass outflow rate, allowing us to distinguish intertwined ionisation mechanisms and to identify a part of the multiphase gas cycle in NGC 613. It traces the gas kinematics from the bar lanes to inner scale gas reservoirs, where it can eventually trigger star formation or AGN activity, as observed in the outflow. △ Less

Submitted 20 May, 2025; originally announced May 2025.

Comments: Accepted for publication in MNRAS; 23 pages, 16 figures, 1 table, 1 Appendix

Bar ages derived for the first time in nearby galaxies: Insights on secular evolution from the TIMER sample

Authors: Camila de Sá-Freitas, Dimitri A. Gadotti, Francesca Fragkoudi, Paula Coelho, Adriana de Lorenzo-Cáceres, Jesús Falcón-Barroso, Patricia Sánchez-Blázquez, Taehyun Kim, Jairo Mendez-Abreu, Justus Neumann, Miguel Querejeta, Glenn van de Ven

Abstract: Once galaxies settle their discs and become self-gravitating, stellar bars can form, driving the subsequent evolution of their host galaxy. Determining the ages of bars can therefore shed light on the epoch of the onset of secular evolution. In this work, we apply the first broadly applicable methodology to derive bar ages to a sample of 20 nearby galaxies. The method is based on the co-eval build… ▽ More Once galaxies settle their discs and become self-gravitating, stellar bars can form, driving the subsequent evolution of their host galaxy. Determining the ages of bars can therefore shed light on the epoch of the onset of secular evolution. In this work, we apply the first broadly applicable methodology to derive bar ages to a sample of 20 nearby galaxies. The method is based on the co-eval build-up of nuclear structures and bars and involves using IFS data from the MUSE instrument on VLT to disentangle the SFH of the nuclear disc from the background population. This allows us to derive the formation epoch of the nuclear disc and, thus, of the bar. We estimate the bar formation epoch of nearby galaxies - mostly from the TIMER survey-, creating the largest sample of galaxies with known bar ages to date. We find bar formation epochs between 1 and 13 Gyr ago, illustrating how disc-settling and bar formation are processes that first took place in the early Universe and are still taking place in some galaxies. We infer the bar fraction over cosmological time with our sample, finding remarkable agreement with that obtained from direct studies of galaxies at high redshifts. Additionally, for the first time, we can investigate secular evolution processes taking into account the ages of bars. Our results agree with the scenario in which bars aid the quenching of the host galaxy, with galaxies hosting older bars tending to be more "quenched". We also find that older bars tend to be longer, stronger, and host larger nuclear discs. Furthermore, we find evidence of the nuclear disc stellar mass build-up over time. On the other hand, we find no evidence of downsizing playing a role in bar formation, since we find that bar age is independent of galaxy stellar mass. With the means to estimate bar ages, we can begin to understand better when and how bars shape the observed properties of disc galaxies. △ Less

Submitted 16 December, 2025; v1 submitted 26 March, 2025; originally announced March 2025.

Comments: Accepted for publication in Astronomy & Astrophysics (A&A), 20 pages, 13 Figures, 3 Appendice Figures. See erratum in 10.1051/0004-6361/202557798e (results and discussion are unchanged)

Journal ref: A&A 698, A5 (2025)

The Complete Spitzer Survey of Stellar Structure in Galaxies (CS$^4$G)

Authors: P. M. Sánchez-Alarcón, H. Salo, J. H. Knapen, S. Comerón, J. Román, A. E. Watkins, R. J. Buta, S. Laine, J. M. Falcón-Ramírez, M. Anetjärvi, E. Athanassoula, A. Bosma, D. A. Gadotti, J. L. Hinz, L. C. Ho, B. W. Holwerda, J. Janz, T. Kim, J. Koda, J. Laine, E. Laurikainen, B. F. Madore, K. Menéndez-Delmestre, R. F. Peletier, M. Querejeta , et al. (3 additional authors not shown)

Abstract: The Spitzer Survey of Stellar Structure in Galaxies (S$^4$G), together with its Early Type Galaxy (ETG) extension, stand as the most extensive dataset of deep, uniform mid-infrared (mid-IR; 3.6 and 4.5$\,μ$m) imaging for a sample of $2817$ nearby ($d<40 \,$Mpc) galaxies. However, the velocity criterion used to select the original sample results in an additional 422 galaxies without HI detection th… ▽ More The Spitzer Survey of Stellar Structure in Galaxies (S$^4$G), together with its Early Type Galaxy (ETG) extension, stand as the most extensive dataset of deep, uniform mid-infrared (mid-IR; 3.6 and 4.5$\,μ$m) imaging for a sample of $2817$ nearby ($d<40 \,$Mpc) galaxies. However, the velocity criterion used to select the original sample results in an additional 422 galaxies without HI detection that ought to have been included in the S$^4$G on the basis of their optical recession velocities. In order to create a complete magnitude-, size- and volume-limited sample of nearby galaxies, we collect $3.6\,μ$m and $i$-band images using archival data from different surveys and complement it with new observations for the missing galaxies. We denote the sample of these additional galaxies as Disc Galaxy (DG) extension. We present the Complete Spitzer Survey of Stellar Structure in Galaxies (CS$^4$G), encompassing a sample of $3239$ galaxies with consistent imaging, surface brightness profiles, photometric parameters, and revised morphological classification. Following the original strategy of the S$^4$G survey, we produce masks, surface brightness profiles, and curves of growth using masked $3.6\,μ$m and $i$-band images. From these profiles, we derive the integrated quantities: total magnitude, stellar mass, concentration parameter, and galaxy size, converting to $3.6\,μ$m. We re-measure these parameters also for the S$^4$G and ETG to create a homogenous sample. We present new morphological revised $T$-types, and we showcase mid-IR scaling relations for the photometric parameters. We complete the S$^4$G sample by incorporating 422 galaxies. The CS$^4$G includes at least 99.94\% of the complete sample of nearby galaxies, meeting the original selection criteria, and it will enable a wide set of investigations into galaxy structure and evolution. △ Less

Submitted 12 March, 2025; originally announced March 2025.

Comments: 22 pages, 11 figures, 3 tables, 3 appendices. Accepted for publication in A&A

Journal ref: A&A 697, A38 (2025)

Large-Scale Stellar Age-Velocity Spiral Pattern in NGC 4030

Authors: Iris Breda, Glenn van de Ven, Sabine Thater, J. Falcón-Barroso, Prashin Jethwa, Dimitri A. Gadotti, Masato Onodera, Ismael Pessa, Joop Schaye, Gerhard Hensler, Jarle Brinchmann, Anja F. -Krause, Davor Krajnović, Bodo Ziegler

Abstract: The processes driving the formation and evolution of late-type galaxies (LTGs) continue to be a debated subject in extragalactic astronomy. Investigating stellar kinematics, especially when combined with age estimates, provides crucial insights into the formation and subsequent development of galactic discs. Post-processing of exceptionally high-quality Integral Field Spectroscopy (IFS) data of NG… ▽ More The processes driving the formation and evolution of late-type galaxies (LTGs) continue to be a debated subject in extragalactic astronomy. Investigating stellar kinematics, especially when combined with age estimates, provides crucial insights into the formation and subsequent development of galactic discs. Post-processing of exceptionally high-quality Integral Field Spectroscopy (IFS) data of NGC 4030 acquired with the Multi Unit Spectroscopic Explorer (MUSE), clearly reveals a striking grand design spiral pattern in the velocity dispersion map not previously detected in other galaxies. This pattern spatially correlates with HII regions, suggesting that stars currently being born exhibit lower velocity dispersion as compared to surrounding areas where star formation (SF) is less active. We examine the age-velocity relation (AVR) and propose that its configuration might be shaped by a combination of heating mechanisms, seemingly consistent with findings from recent high-resolution cosmological zoom-in simulations. The complex structure of the uncovered AVR of NGC 4030 support the hypothesis that stellar populations initially inherit the velocity dispersion σ of the progenitor cold molecular gas, which depends on formation time and galactocentric distance, subsequently experiencing kinematic heating by cumulative gravitational interactions during their lifetime. While advancing our understanding of the AVR, these findings offer a new framework for investigating disk heating mechanisms, and their role in the evolution of galactic disks. △ Less

Submitted 25 November, 2024; originally announced November 2024.

Comments: accepted for publication in A&A letters

Journal ref: A&A 692, L10 (2024)

The GECKOS Survey: Identifying kinematic sub-structures in edge-on galaxies

Authors: A. Fraser-McKelvie, J. van de Sande, D. A. Gadotti, E. Emsellem, T. Brown, D. B. Fisher, M. Martig, M. Bureau, O. Gerhard, A. J. Battisti, J. Bland-Hawthorn, A. Boecker, B. Catinella, F. Combes, L. Cortese, S. M. Croom, T. A. Davis, J. Falcón-Barroso, F. Fragkoudi, K. C. Freeman, M. R. Hayden, R. McDermid, B. Mazzilli Ciraulo, J. T. Mendel, F. Pinna , et al. (8 additional authors not shown)

Abstract: The vertical evolution of galactic discs is governed by the sub-structures within them. We examine the diversity of kinematic sub-structure present in the first 12 galaxies observed from the GECKOS survey, a VLT/MUSE large programme providing a systematic study of 36 edge-on, Milky Way-mass disc galaxies. Employing the nGIST analysis pipeline, we derive the mean line-of-sight stellar velocity (… ▽ More The vertical evolution of galactic discs is governed by the sub-structures within them. We examine the diversity of kinematic sub-structure present in the first 12 galaxies observed from the GECKOS survey, a VLT/MUSE large programme providing a systematic study of 36 edge-on, Milky Way-mass disc galaxies. Employing the nGIST analysis pipeline, we derive the mean line-of-sight stellar velocity ($V_{\star}$), velocity dispersion ($σ_{\star}$), skew ($h_{3}$), and kurtosis ($h_{4}$) for the sample, and examine 2D maps and 1D line profiles. Visually, the majority of this sample (8/12) are found to possess boxy-peanut bulges and host the corresponding kinematic structure predicted for stellar bars viewed in projection. Four galaxies exhibit strong evidence for the presence of nuclear discs, including central $h_{3}$-$V_{\star}$ sign mismatch, `croissant'-shaped central depressions in $σ_{\star}$ maps, strong gradients in $h_{3}$, and positive $h_{4}$ plateaus over the expected nuclear disc extent. The strength of the $h_{3}$ feature corresponds to the size of the nuclear disc, measured from the $h_{3}$ turnover radius. We can explain the features within the kinematic maps of all sample galaxies via disc structure(s) alone. We do not find any need to invoke the existence of dispersion-dominated bulges. Obtaining the specialised data products for this paper and the broader GECKOS survey required significant development of existing integral field spectroscopic (IFS) analysis tools. Therefore, we also present the nGIST pipeline: a modern, sophisticated, and easy-to-use pipeline for the analysis of galaxy IFS data. We conclude that the variety of kinematic sub-structures seen in GECKOS galaxies requires a contemporary view of galaxy morphology, expanding on the traditional view of galaxy structure, and uniting the kinematic complexity observed in the Milky Way with the extragalactic. △ Less

Submitted 24 June, 2025; v1 submitted 5 November, 2024; originally announced November 2024.

Comments: 32 pages (9 of which are appendix), 26 figures, accepted 12/06/2025 to A&A

Journal ref: A&A 700, A237 (2025)

Towards Understanding the Milky Way's Typicality: Assessing the Chemodynamics of M31's Bulge & Bar, Thick & Thin Discs

Authors: Benjamin J. Gibson, Gail Zasowski, Anil Seth, Dimitri A. Gadotti, Zixian Wang, Dmitry Bizyaev, Steven R. Majewski, Jon Holtzmann, Sanjib Sharma

Abstract: We describe a novel framework to model galaxy spectra with two cospatial stellar populations, such as may represent a bulge & bar or thick & thin disc, and apply it to APOGEE spectra in the inner $\sim$2 kpc of M31, as well as to stacked spectra representative of the northern and southern parts of M31's disc ($R\sim4-7$ kpc). We use a custom M31 photometric decomposition and A-LIST spectral templa… ▽ More We describe a novel framework to model galaxy spectra with two cospatial stellar populations, such as may represent a bulge & bar or thick & thin disc, and apply it to APOGEE spectra in the inner $\sim$2 kpc of M31, as well as to stacked spectra representative of the northern and southern parts of M31's disc ($R\sim4-7$ kpc). We use a custom M31 photometric decomposition and A-LIST spectral templates to derive the radial velocity, velocity dispersion, metallicity, and $α$ abundance for both components in each spectrum. In the bulge, one component exhibits little net rotation, high velocity dispersion ($\sim$170 km s$^{-1}$), near-solar metallicity, and high $α$ abundance ([$α$/M] = 0.28), while the second component shows structured rotation, lower velocity dispersion ($\sim$121 km s$^{-1}$), and slightly higher abundances ([M/H] = 0.09, [$α$/M] = 0.3). We tentatively associate the first component with the classical bulge and the second with the bar. In the north disc we identify two distinct components: the first with hotter kinematics, lower metallicity, and higher $α$ abundance than the second ([M/H] = 0.1 and 0.39, [$α$/M] = 0.29 and 0.07). These discs appear comparable to the Milky Way's ''thick'' and ''thin'' discs, providing the first evidence that M31's inner disc has a similar chemodynamical structure. We do not identify two distinct components in the south, potentially due to effects from recent interactions. Such multi-population analysis is crucial to constrain galaxy evolution models that strive to recreate the complex stellar populations found in the Milky Way. △ Less

Submitted 30 October, 2024; originally announced October 2024.

Comments: 16 pages, 9 figures

Journal ref: Mon Not R Astron Soc (2025) 669-687

Do strong bars exhibit strong non-circular motions?

Authors: Taehyun Kim, Dimitri A. Gadotti, Yun Hee Lee, Carlos López-Cobá, Woong-Tae Kim, Minjin Kim, Myeong-gu Park

Abstract: Galactic bars induce characteristic motions deviating from pure circular rotation, known as non-circular motions. As bars are non-axisymmetric structures, stronger bars are expected to show stronger non-circular motions. However, this has not yet been confirmed by observations. We use a bisymmetric model to account for the stellar kinematics of 14 barred galaxies obtained with the Multi-Unit Spect… ▽ More Galactic bars induce characteristic motions deviating from pure circular rotation, known as non-circular motions. As bars are non-axisymmetric structures, stronger bars are expected to show stronger non-circular motions. However, this has not yet been confirmed by observations. We use a bisymmetric model to account for the stellar kinematics of 14 barred galaxies obtained with the Multi-Unit Spectroscopic Explorer (MUSE) and characterize the degree of bar-driven non-circular motions. For the first time, we find tight relations between the bar strength (bar ellipticity and torque parameter) and the degree of stellar non-circular motions. We also find that bar strength is strongly associated with the stellar radial velocity driven by bars. Our results imply that stronger bars exhibit stronger non-circular motions. Non-circular motions beyond the bar are found to be weak, comprising less than 10% of the strength of the circular motions. We find that galaxies with a boxy/peanut (B/P) bulge exhibit a higher degree of non-circular motions and higher stellar radial velocity compared to galaxies without a B/P bulge, by 30-50%. However, this effect could be attributed to the presence of strong bars in galaxies with a B/P feature in our sample, which would naturally result in higher radial motions, rather than to B/P bulges themselves inducing stronger radial motions. More observational studies, utilizing both stellar and gaseous kinematics on statistically complete samples, along with numerical studies, are necessary to draw a comprehensive view of the impact that B/P bulges have on bar-driven non-circular motions. △ Less

Submitted 27 October, 2024; originally announced October 2024.

Comments: Accepted for publications Astrophysical Journal (ApJ). 23 pages, 10 figure, 1 table

Closing the gap: secular evolution of bar-induced dark gaps in presence of thick discs

Authors: Soumavo Ghosh, Dimitri A. Gadotti, Francesca Fragkoudi, Vighnesh Nagpal, Paola Di Matteo, Virginia Cuomo

Abstract: The presence of dark gaps, a preferential light deficit along the bar minor axis, is observationally well known. The properties of dark gaps are thought to be associated with the properties of bars, and their spatial locations are often associated with bar resonances. However, a systematic study, testing the robustness and universality of these assumptions, is still largely missing. Here, we inves… ▽ More The presence of dark gaps, a preferential light deficit along the bar minor axis, is observationally well known. The properties of dark gaps are thought to be associated with the properties of bars, and their spatial locations are often associated with bar resonances. However, a systematic study, testing the robustness and universality of these assumptions, is still largely missing. Here, we investigate the formation and evolution of bar-induced dark gaps using a suite of N-body models of (kinematically cold) thin and (kinematically hot) thick discs with varying thick disc mass fraction, and different thin-to-thick disc geometry. We find that dark gaps are a natural consequence of the trapping of disc stars by the bar. The properties of dark gaps (such as strength and extent) are well correlated with the properties of bars. For stronger dark gaps, the fractional mass loss along the bar minor axis can reach up to ~60-80 percent of the initial mass contained, which is redistributed within the bar. These trends hold true irrespective of the mass fraction in the thick disc and the assumed disc geometry. In all our models harbouring slow bars, none of the resonances (corotation, Inner Lindblad resonance, and 4:1 ultra-harmonic resonance) associated with the bar correspond to the location of dark gaps, thereby suggesting that the location of dark gaps is not a universal proxy for these bar resonances, in contrast with earlier studies. △ Less

Submitted 22 July, 2024; originally announced July 2024.

Comments: 13 pages, 12 figures, 1 table (including appendix), accepted for publication in MNRAS

Impacts of bar-driven shear and shocks on star formation

Authors: Taehyun Kim, Dimitri A. Gadotti, Miguel Querejeta, Isabel Pérez, Almudena Zurita, Justus Neumann, Glenn van de Ven, Jairo Méndez-Abreu, Adriana de Lorenzo-Cáceres, Patricia Sánchez-Blázquez, Francesca Fragkoudi, Lucimara P. Martins, Luiz A. Silva-Lima, Woong-Tae Kim, Myeong-gu Park

Abstract: Bars drive gas inflow. As the gas flows inwards, shocks and shear occur along the bar dust lanes. Such shocks and shear can affect the star formation and change the gas properties. For four barred galaxies, we present Hα velocity gradient maps that highlight bar-driven shocks and shear using data from the PHANGS-MUSE and PHANGS-ALMA surveys which allow us to study bar kinematics in unprecedented d… ▽ More Bars drive gas inflow. As the gas flows inwards, shocks and shear occur along the bar dust lanes. Such shocks and shear can affect the star formation and change the gas properties. For four barred galaxies, we present Hα velocity gradient maps that highlight bar-driven shocks and shear using data from the PHANGS-MUSE and PHANGS-ALMA surveys which allow us to study bar kinematics in unprecedented detail. Velocity gradients are enhanced along the bar dust lanes, where shocks and shear are shown to occur in numerical simulations. Velocity gradient maps also efficiently pick up expanding shells around HII regions. We put pseudo slits on the regions where velocity gradients are enhanced and find that Hα and CO velocities jump up to ~170 km/s, even after removing the effects of circular motions due to the galaxy rotation. Enhanced velocity gradients either coincide with the peak of CO intensity along the bar dust lanes or are slightly offset from CO intensity peaks, depending on the objects. Using the BPT diagnostic, we identify the source of ionization on each spaxel and find that star formation is inhibited in the high velocity gradient regions of the bar, and the majority of those regions are classified as LINER or composite. This implies that star formation is inhibited where bar-driven shear and shocks are strong. Our results are consistent with the results from the numerical simulations that show star formation is inhibited in the bar where shear force is strong. △ Less

Submitted 30 April, 2024; originally announced May 2024.

Comments: 26 pages, Accepted for publication in ApJ

The onset of bar formation in a massive galaxy at $z \sim 3.8$

Authors: Aristeidis Amvrosiadis, Samuel Lange, James Nightingale, Qiuhan He, Carlos S. Frenk, Kyle A. Oman, Ian Smail, Mark A. Swinbank, Francesca Fragkoudi, Dimitri A. Gadotti, Shaun Cole, Edoardo Borsato, Andrew Robertson, Richard Massey, Xiaoyue Cao, Ran Li

Abstract: We examine the morphological and kinematical properties of SPT-2147, a strongly lensed, massive, dusty, star-forming galaxy at $z = 3.762$. Combining data from JWST, HST, and ALMA, we study the galaxy's stellar emission, dust continuum and gas properties. The imaging reveals a central bar structure in the stars and gas embedded within an extended disc with a spiral arm-like feature. The kinematics… ▽ More We examine the morphological and kinematical properties of SPT-2147, a strongly lensed, massive, dusty, star-forming galaxy at $z = 3.762$. Combining data from JWST, HST, and ALMA, we study the galaxy's stellar emission, dust continuum and gas properties. The imaging reveals a central bar structure in the stars and gas embedded within an extended disc with a spiral arm-like feature. The kinematics confirm the presence of the bar and of the regularly rotating disc. Dynamical modeling yields a dynamical mass, ${M}_{\rm dyn} = (9.7 \pm 2.0) \times 10^{10}$ ${\rm M}_{\odot}$, and a maximum rotational velocity to velocity dispersion ratio, $V / σ= 9.8 \pm 1.2$. From multi-band imaging we infer, via SED fitting, a stellar mass, ${M}_{\star} = (6.3 \pm 0.9) \times 10^{10}$ $\rm{M}_{\odot}$, and a star formation rate, ${\rm SFR} = 781 \pm 99$ ${\rm M_{\odot} yr^{-1}}$, after correcting for magnification. Combining these measurements with the molecular gas mass, we derive a baryonic-to-total mass ratio of ${M}_{\rm bar} / {M}_{\rm dyn} = 0.9 \pm 0.2$ within 4.0 kpc. This finding suggests that the formation of bars in galaxies begins earlier in the history of the Universe than previously thought and can also occur in galaxies with elevated gas fractions. △ Less

Submitted 2 April, 2024; originally announced April 2024.

Comments: 19 pages, 11 figures. Submitted to MNRAS

The universal variability of the stellar initial mass function probed by the TIMER survey

Authors: Ignacio Martín-Navarro, Adriana de Lorenzo-Cáceres, Dimitri A. Gadotti, Jairo Méndez-Abreu, Jesús Falcón-Barroso, Patricia Sánchez-Blázquez, Paula Coelho, Justus Neumann, Glenn van de Ven, Isabel Pérez

Abstract: The debate about the universality of the stellar initial mass function (IMF) revolves around two competing lines of evidence. While measurements in the Milky Way, an archetypal spiral galaxy, seem to support an invariant IMF, the observed properties of massive early-type galaxies (ETGs) favor an IMF somehow sensitive to the local star formation conditions. The fundamental methodological and physic… ▽ More The debate about the universality of the stellar initial mass function (IMF) revolves around two competing lines of evidence. While measurements in the Milky Way, an archetypal spiral galaxy, seem to support an invariant IMF, the observed properties of massive early-type galaxies (ETGs) favor an IMF somehow sensitive to the local star formation conditions. The fundamental methodological and physical differences between both approaches have hampered, however, a comprehensive understanding of IMF variations. We describe here an improved modelling scheme that allows for the first time consistent IMF measurements across stellar populations with different ages and complex star formation histories. Making use of the exquisite MUSE optical data from the TIMER survey and powered by the MILES stellar population models, we show the age, metallicity, [Mg/Fe], and IMF slope maps of the inner regions of NGC 3351, a spiral galaxy with a mass similar to that of the Milky Way. The measured IMF values in NGC3351 follow the expectations from a Milky Way-like IMF, although they simultaneously show systematic and spatially coherent variations, particularly for low-mass stars. In addition, our stellar population analysis reveals the presence of metal-poor and Mg-enhanced star-forming regions that appear to be predominantly enriched by the stellar ejecta of core-collapse supernovae. Our findings showcase therefore the potential of detailed studies of young stellar populations to better understand the early stages of galaxy evolution and, in particular, the origin of the observed IMF variations beyond and within the Milky Way. △ Less

Submitted 20 December, 2023; originally announced December 2023.

Comments: 16 pages, 11 figures. Accepted for publication in Astronomy and Astrophysics

Bar Properties as a Function of Wavelength: A Local Baseline with S4G for High-Redshift Studies

Authors: Karín Menéndez-Delmestre, Thiago S. Gonçalves, Kartik Sheth, Tomás Düringer Jacques de Lima, Taehyun Kim, Dimitri A. Gadotti, Eva Schinnerer, E. Athanassoula, Albert Bosma, Debra Meloy Elmegreen, Johan H. Knapen, Rubens E. G. Machado, Heikki Salo

Abstract: The redshift evolution of bars is an important signpost of the dynamic maturity of disk galaxies. To characterize the intrinsic evolution safe from band-shifting effects, it is necessary to gauge how bar properties vary locally as a function of wavelength. We investigate bar properties in 16 nearby galaxies from the Spitzer Survey of Stellar Structure in Galaxies (S4G) at ultraviolet, optical and… ▽ More The redshift evolution of bars is an important signpost of the dynamic maturity of disk galaxies. To characterize the intrinsic evolution safe from band-shifting effects, it is necessary to gauge how bar properties vary locally as a function of wavelength. We investigate bar properties in 16 nearby galaxies from the Spitzer Survey of Stellar Structure in Galaxies (S4G) at ultraviolet, optical and mid-infrared wavebands. Based on the ellipticity and position angle profiles from fitting elliptical isophotes to the two-dimensional light distribution, we find that both bar length and ellipticity - the latter often used as a proxy for bar strength - increase at bluer wavebands. Bars are 9% longer in the B-band than at 3.6 um. Their ellipticity increases typically by 8% in the B-band, with a significant fraction (>40%) displaying an increase up to 35%. We attribute the increase in bar length to the presence of star forming knots at the end of bars: these regions are brighter in bluer bands, stretching the bar signature further out. The increase in bar ellipticity could be driven by the apparent bulge size: the bulge is less prominent at bluer bands, allowing for thinner ellipses within the bar region. Alternatively, it could be due to younger stellar populations associated to the bar. The resulting effect is that bars appear longer and thinner at bluer wavebands. This indicates that band-shifting effects are significant and need to be corrected for high-redshift studies to reliably gauge any intrinsic evolution of the bar properties with redshift. △ Less

Submitted 7 December, 2023; originally announced December 2023.

Comments: Accepted to MNRAS

The JWST Galactic Center Survey -- A White Paper

Authors: Rainer Schoedel, Steve Longmore, Jonny Henshaw, Adam Ginsburg, John Bally, Anja Feldmeier, Matt Hosek, Francisco Nogueras Lara, Anna Ciurlo, Mélanie Chevance, J. M. Diederik Kruijssen, Ralf Klessen, Gabriele Ponti, Pau Amaro-Seoane, Konstantina Anastasopoulou, Jay Anderson, Maria Arias, Ashley T. Barnes, Cara Battersby, Giuseppe Bono, Lucía Bravo Ferres, Aaron Bryant, Miguel Cano Gonzáalez, Santi Cassisi, Leonardo Chaves-Velasquez , et al. (89 additional authors not shown)

Abstract: The inner hundred parsecs of the Milky Way hosts the nearest supermassive black hole, largest reservoir of dense gas, greatest stellar density, hundreds of massive main and post main sequence stars, and the highest volume density of supernovae in the Galaxy. As the nearest environment in which it is possible to simultaneously observe many of the extreme processes shaping the Universe, it is one of… ▽ More The inner hundred parsecs of the Milky Way hosts the nearest supermassive black hole, largest reservoir of dense gas, greatest stellar density, hundreds of massive main and post main sequence stars, and the highest volume density of supernovae in the Galaxy. As the nearest environment in which it is possible to simultaneously observe many of the extreme processes shaping the Universe, it is one of the most well-studied regions in astrophysics. Due to its proximity, we can study the center of our Galaxy on scales down to a few hundred AU, a hundred times better than in similar Local Group galaxies and thousands of times better than in the nearest active galaxies. The Galactic Center (GC) is therefore of outstanding astrophysical interest. However, in spite of intense observational work over the past decades, there are still fundamental things unknown about the GC. JWST has the unique capability to provide us with the necessary, game-changing data. In this White Paper, we advocate for a JWST NIRCam survey that aims at solving central questions, that we have identified as a community: i) the 3D structure and kinematics of gas and stars; ii) ancient star formation and its relation with the overall history of the Milky Way, as well as recent star formation and its implications for the overall energetics of our galaxy's nucleus; and iii) the (non-)universality of star formation and the stellar initial mass function. We advocate for a large-area, multi-epoch, multi-wavelength NIRCam survey of the inner 100\,pc of the Galaxy in the form of a Treasury GO JWST Large Program that is open to the community. We describe how this survey will derive the physical and kinematic properties of ~10,000,000 stars, how this will solve the key unknowns and provide a valuable resource for the community with long-lasting legacy value. △ Less

Submitted 14 October, 2025; v1 submitted 18 October, 2023; originally announced October 2023.

Comments: This White Paper will be updated when required (e.g. new authors joining, editing of content). Most recent update: 14 Oct 2025

Schwarzschild Modeling of Barred S0 Galaxy NGC 4371

Authors: Behzad Tahmasebzadeh, Ling Zhu, Juntai Shen, Dimitri A. Gadotti, Monica Valluri, Sabine Thater, Glenn van de Ven, Yunpeng Jin, Ortwin Gerhard, Peter Erwin, Prashin Jethwa, Alice Zocchi, Edward J. Lilley, Francesca Fragkoudi, Adriana de Lorenzo-Cáceres, Jairo Méndez-Abreu, Justus Neumann, Rui Guo

Abstract: We apply the barred Schwarzschild method developed by Tahmasebzadeh et al. (2022) to a barred S0 galaxy, NGC 4371, observed by IFU instruments from the TIMER and ATLAS3D projects. We construct the gravitational potential by combining a fixed black hole mass, a spherical dark matter halo, and stellar mass distribution deprojected from $3.6$ $μ$m S$^4$G image considering an axisymmetric disk and a t… ▽ More We apply the barred Schwarzschild method developed by Tahmasebzadeh et al. (2022) to a barred S0 galaxy, NGC 4371, observed by IFU instruments from the TIMER and ATLAS3D projects. We construct the gravitational potential by combining a fixed black hole mass, a spherical dark matter halo, and stellar mass distribution deprojected from $3.6$ $μ$m S$^4$G image considering an axisymmetric disk and a triaxial bar. We independently modelled kinematic data from TIMER and ATLAS3D. Both models fit the data remarkably well. We find a consistent bar pattern speed from the two sets of models with $Ω_{\rm p} = 23.6 \pm 2.8 \hspace{.08cm} \mathrm{km \hspace{.04cm} s^{-1} \hspace{.04cm} kpc^{-1} }$ and $Ω_{\rm p} = 22.4 \pm 3.5 \hspace{.08cm} \mathrm{km \hspace{.04cm} s^{-1} \hspace{.04cm} kpc^{-1} }$, respectively. The dimensionless bar rotation parameter is determined to be $ 1.88 \pm 0.37$, indicating a likely slow bar in NGC 4371. Additionally, our model predicts a high amount of dark matter within the bar region ($M_{\rm DM}/ M_{\rm total}$ $\sim 0.51 \pm 0.06$), which, aligned with the predictions of cosmological simulations, indicates that fast bars are generally found in baryon-dominated disks. Based on the best-fitting model, we further decompose the galaxy into multiple 3D orbital structures, including a BP/X bar, a classical bulge, a nuclear disk, and a main disk. The BP/X bar is not perfectly included in the input 3D density model, but BP/X-supporting orbits are picked through the fitting to the kinematic data. This is the first time a real barred galaxy has been modelled utilizing the Schwarzschild method including a 3D bar. △ Less

Submitted 4 September, 2024; v1 submitted 30 September, 2023; originally announced October 2023.

Comments: 25 pages, 19 figures, Accepted for publication in MNRAS

A JWST investigation into the bar fraction at redshifts 1 < z < 3

Authors: Zoe A. Le Conte, Dimitri A. Gadotti, Leonardo Ferreira, Christopher J. Conselice, Camila de Sá-Freitas, Taehyun Kim, Justus Neumann, Francesca Fragkoudi, E. Athanassoula, Nathan J. Adams

Abstract: The presence of a stellar bar in a disc galaxy indicates that the galaxy hosts in its main part a dynamically settled disc and that bar-driven processes are taking place in shaping its evolution. Studying the cosmic evolution of the bar fraction in disc galaxies is therefore essential to understand galaxy evolution in general. Previous studies have found, using the Hubble Space Telescope (HST), th… ▽ More The presence of a stellar bar in a disc galaxy indicates that the galaxy hosts in its main part a dynamically settled disc and that bar-driven processes are taking place in shaping its evolution. Studying the cosmic evolution of the bar fraction in disc galaxies is therefore essential to understand galaxy evolution in general. Previous studies have found, using the Hubble Space Telescope (HST), that the bar fraction significantly declines from the local Universe to redshifts near one. Using the first four pointings from the James Webb Space Telescope (JWST) Cosmic Evolution Early Release Science Survey (CEERS) and the initial public observations for the Public Release Imaging for Extragalactic Research (PRIMER), we extend the studies of the bar fraction in disc galaxies to redshifts $1 \leq z \leq 3$, i.e., for the first time beyond redshift two. We only use galaxies that are also present in the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) on the Extended Groth Strip (EGS) and Ultra Deep Survey (UDS) HST observations. An optimised sample of 368 close-to-face-on galaxies is visually classified to find the fraction of bars in disc galaxies in two redshift bins: $1 \leq z \leq 2$ and $2 < z \leq 3$. The bar fraction decreases from $\approx 17.8^{+ 5.1}_{- 4.8}$ per cent to $\approx 13.8^{+ 6.5}_{- 5.8}$ per cent (from the lower to the higher redshift bin), but is about twice the bar fraction found using bluer HST filters. Our results show that bar-driven evolution might commence at early cosmic times and that dynamically settled discs are already present at a lookback time of $\sim 11$ Gyrs. △ Less

Submitted 23 April, 2024; v1 submitted 18 September, 2023; originally announced September 2023.

Comments: Accepted for publication in MNRAS; 18 pages, 10 figures; final version includes new disc classification and mass cut, but results remain the same; Figs. 6 and 7 summarise the main results

On the accretion of a new group of galaxies onto Virgo: III. The stellar population radial gradients of dEs

Authors: Bahar Bidaran, Francesco La Barbera, Anna Pasquali, Glenn van de Ven, Reynier Peletier, Jesus Falcón-Barroso, Dimitri A. Gadotti, Agnieszka Sybilska, Eva K. Grebel

Abstract: Using MUSE data, we investigate the radial gradients of stellar population properties (namely age, [M/H], and the abundance ratio of $α$ elements [$α$/Fe]) for a sample of nine dwarf early-type (dE) galaxies with log(M$_{\star}$/M$_{\odot}$) $\sim$ 9.0 and an infall time onto the Virgo cluster of 2-3Gyr ago. We followed a similar approach as in Bidaran et al. (2022) to derive their stellar populat… ▽ More Using MUSE data, we investigate the radial gradients of stellar population properties (namely age, [M/H], and the abundance ratio of $α$ elements [$α$/Fe]) for a sample of nine dwarf early-type (dE) galaxies with log(M$_{\star}$/M$_{\odot}$) $\sim$ 9.0 and an infall time onto the Virgo cluster of 2-3Gyr ago. We followed a similar approach as in Bidaran et al. (2022) to derive their stellar population properties and star formation histories (SFHs) through fitting observed spectral indices and full spectral fitting, respectively. We find that these nine dE galaxies have truncated [Mg/Fe]vs.[Fe/H] profiles than equally-massive Virgo dE galaxies with longer past infall times. Short profiles of three dE galaxies are the result of their intense star formation which has been quenched long before their accretion onto the Virgo cluster, possibly as a result of their group environment. In the remaining six dE galaxies, profiles mainly trace a recent episode of star burst within 0.4R$_{\rm e}$ which results in higher light-weighted [$α$/Fe] values. The latter SFH peak can be due to ram pressure exerted by the Virgo cluster at the time of the accretion of the dE galaxies. Also, we show that younger, more metal-rich and less $α$-enhanced stellar populations dominate their inner regions (i.e., < 0.4R$_{\rm e}$) resulting in mainly flat $\nabla_{\rm age}$, negative $\nabla_{\rm [M/H]}$ and positive $\nabla_{\rm [α/Fe]}$. We find that with increasing log($σ_{\rm Re}$) of dE galaxies, $\nabla_{\rm age}$ and $\nabla_{\rm [α/Fe]}$ flatten, and the latter correlation persists even after including early-type galaxies up to log($σ_{\rm Re}$ $\sim$ 2.5), possibly due to the more extended star formation activity in the inner regions of dEs, as opposed to more massive early-type galaxies. △ Less

Submitted 31 August, 2023; originally announced August 2023.

Comments: 18 pages, 8 figures, accepted in MNRAS

Disc galaxies are still settling: The discovery of the smallest nuclear discs and their young stellar bars

Authors: Camila de Sá-Freitas, Dimitri A. Gadotti, Francesca Fragkoudi, Lodovico Coccato, Paula Coelho, Adriana de Lorenzo-Cáceres, Jesús Falcón-Barroso, Tutku Kolcu, Ignacio Martín-Navarro, Jairo Mendez-Abreu, Justus Neumann, Patricia Sanchez Blazquez, Miguel Querejeta, Glenn van de Ven

Abstract: When galactic discs settle and become massive enough, they are able to form stellar bars. These non-axisymmetric structures induce shocks in the gas, causing it to flow to the centre where nuclear structures, such as nuclear discs and rings, are formed. Previous theoretical and observational studies have hinted at the co-evolution of bars and nuclear discs, suggesting that nuclear discs grow "insi… ▽ More When galactic discs settle and become massive enough, they are able to form stellar bars. These non-axisymmetric structures induce shocks in the gas, causing it to flow to the centre where nuclear structures, such as nuclear discs and rings, are formed. Previous theoretical and observational studies have hinted at the co-evolution of bars and nuclear discs, suggesting that nuclear discs grow "inside-out", thereby proposing that smaller discs live in younger bars. Nevertheless, it remains unclear how the bar and the nuclear structures form and evolve with time. The smallest nuclear discs discovered to date tend to be larger than $\sim200~\rm{pc}$, even though some theoretical studies find that when nuclear discs form they can be much smaller. Using MUSE archival data, we report for the first time two extragalactic nuclear discs with radius sizes below $100~\rm{pc}$. Additionally, our estimations reveal the youngest bars found to date. We estimate that the bars in these galaxies formed $4.50^{+1.60}_{-1.10}\rm{(sys)}^{+1.00}_{-0.75}\rm{(stat)}$ and $0.7^{+2.60}\rm{(sys)}^{+0.05}_{-0.05}\rm{(stat)}~\rm{Gyr}$ ago, for NGC\,289 and NGC\,1566, respectively. This suggests that at least some disc galaxies in the Local Universe may still be dynamically settling. By adding these results to previous findings in the literature, we retrieve a stronger correlation between nuclear disc size and bar length and we derive a tentative exponential growth scenario for nuclear discs. △ Less

Submitted 8 August, 2023; originally announced August 2023.

Comments: Accepted in A&A (in press), 13 pages, 5 figures, 2 tabels

Journal ref: A&A 678, A202 (2023)

Composite Bulges -- III. A Study of Nuclear Star Clusters in Nearby Spiral Galaxies

Authors: Aishwarya Ashok, Anil Seth, Peter Erwin, Victor P. Debattista, Adriana de Lorenzo-Cáceres, Dmitri A. Gadotti, Jairo Méndez-Abreu, John E. Beckman, Ralf Bender, Niv Drory, Deanne Fisher, Ulrich Hopp, Matthias Kluge, Tutku Kolcu, Witold Maciejewski, Kianusch Mehrgan, Taniya Parikh, Roberto Saglia, Marja Seidel, Jens Thomas

Abstract: We present photometric and morphological analyses of nuclear star clusters (NSCs) -- very dense, massive star clusters present in the central regions of most galaxies -- in a sample of 33 massive disk galaxies within 20 Mpc, part of the "Composite Bulges Survey." We use data from the Hubble Space Telescope including optical (F475W and F814W) and near-IR (F160W) images from the Wide Field Camera 3.… ▽ More We present photometric and morphological analyses of nuclear star clusters (NSCs) -- very dense, massive star clusters present in the central regions of most galaxies -- in a sample of 33 massive disk galaxies within 20 Mpc, part of the "Composite Bulges Survey." We use data from the Hubble Space Telescope including optical (F475W and F814W) and near-IR (F160W) images from the Wide Field Camera 3. We fit the images in 2D to take into account the full complexity of the inner regions of these galaxies (including the contributions of nuclear disks and bars), isolating the nuclear star cluster and bulge components. We derive NSC radii and magnitudes in all 3 bands, which we then use to estimate NSC masses. Our sample significantly expands the sample of massive late-type galaxies with measured NSC properties. We clearly identify nuclear star clusters in nearly 80% of our galaxies, putting a lower limit on the nucleation fraction in these galaxies that is higher than previous estimates. We find that the NSCs in our massive disk galaxies are consistent with previous NSC mass-NSC radius and Galaxy Mass-NSC Mass relations. However, we also find a large spread in NSC masses, with a handful of galaxies hosting very low-mass, compact clusters. Our NSCs are aligned in PA with their host galaxy disks but are less flattened. They show no correlations with bar or bulge properties. Finally, we find the ratio of NSC to BH mass in our massive disk galaxy sample spans a factor of $\sim$300. △ Less

Submitted 7 August, 2023; originally announced August 2023.

Comments: Accepted to The Astrophysical Journal

Composite Bulges -- IV. Detecting Signatures of Gas Inflows in the IFU data: The MUSE View of Ionized Gas Kinematics in NGC 1097

Authors: Tutku Kolcu, Witold Maciejewski, Dimitri A. Gadotti, Francesca Fragkoudi, Peter Erwin, Patricia Sánchez-Blázquez, Justus Neumann, Glenn Van de Ven, Camila de Sá-Freitas, Steven Longmore, Victor P. Debattista

Abstract: Using VLT/MUSE integral-field spectroscopic data for the barred spiral galaxy NGC 1097, we explore techniques that can be used to search for extended coherent shocks that can drive gas inflows in centres of galaxies. Such shocks should appear as coherent velocity jumps in gas kinematic maps, but this appearance can be distorted by inaccurate extraction of the velocity values and dominated by the g… ▽ More Using VLT/MUSE integral-field spectroscopic data for the barred spiral galaxy NGC 1097, we explore techniques that can be used to search for extended coherent shocks that can drive gas inflows in centres of galaxies. Such shocks should appear as coherent velocity jumps in gas kinematic maps, but this appearance can be distorted by inaccurate extraction of the velocity values and dominated by the global rotational flow and local perturbations like stellar outflows. We include multiple components in the emission-line fits, which corrects the extracted velocity values and reveals emission associated with AGN outflows. We show that removal of the global rotational flow by subtracting the circular velocity of a fitted flat disk can produce artefacts that obscure signatures of the shocks in the residual velocities if the inner part of the disk is warped or if gas is moving around the centre on elongated (non-circular) trajectories. As an alternative, we propose a model-independent method which examines differences in the LOSVD moments of H$α$ and [N II]$λ$6583. This new method successfully reveals the presence of continuous shocks in the regions inward from the nuclear ring of NGC 1097, in agreement with nuclear spiral models. △ Less

Submitted 19 June, 2023; originally announced June 2023.

Comments: MNRAS accepted (19 pages, 18 figures, 1 table)

Evidence of an age gradient along the line of sight in the nuclear stellar disc of the Milky Way

Authors: F. Nogueras-Lara, M. Schultheis, F. Najarro, M. C. Sormani, D. A. Gadotti, R. M. Rich

Abstract: The nuclear stellar disc (NSD) is a flat dense stellar structure at the heart of the Milky Way. Recent work has shown that analogous structures are common in the nuclei of external spiral galaxies, where there is evidence of an age gradient that indicates that they form inside-out. However, the characterisation of the age of the NSD stellar population along the line of sight is still missing due t… ▽ More The nuclear stellar disc (NSD) is a flat dense stellar structure at the heart of the Milky Way. Recent work has shown that analogous structures are common in the nuclei of external spiral galaxies, where there is evidence of an age gradient that indicates that they form inside-out. However, the characterisation of the age of the NSD stellar population along the line of sight is still missing due to its extreme source crowding and the high interstellar extinction towards the Galactic centre. We aim to characterise the age of the stellar population at different average Galactocentric NSD radii to investigate for the first time the presence of an age gradient along the line of sight. We selected two groups of stars at different NSD radii via their different extinction and proper motion distribution. We analysed their stellar population by fitting their de-reddened $K_s$ luminosity functions with a linear combination of theoretical models. We find significant differences in the stellar population at different NSD radii, indicating the presence of an age gradient along the line of sight. Our sample from the closest edge of the NSD contains a significant fraction ($\sim40 \%$ of its total stellar mass) of intermediate-age stars (2-7 Gyr) that is not present in the sample from stars deeper inside the NSD, in which $\sim90 \%$ of the stellar mass is older than 7 Gyr. Our results suggest that the NSD age distribution is similar to the one found in external galaxies and they imply that bar-driven processes observed in external galaxies are similarly at play in the Milky Way. △ Less

Submitted 5 March, 2023; v1 submitted 6 February, 2023; originally announced February 2023.

Comments: Accepted for publication in A&A. 7 pages, 6 figures

Journal ref: A&A 671, L10 (2023)

Inward Bound: Bulges from High Redshifts to the Milky Way

Authors: Dimitri A. Gadotti, Elena Valenti, Francesca Fragkoudi, Anita Zanella, Lodovico Coccato, Camila de Sá-Freitas, Stella-Maria Chasiotis-Klingner

Abstract: With over 200 registered participants, this fully online conference allowed theorists and observers across the globe to discuss recent findings on the central structures of disc galaxies. By design, this conference included experts on the Milky Way, local and high-redshift galaxies, and theoretical aspects of galaxy formation and evolution. The need for such a broad range of expertise stems from t… ▽ More With over 200 registered participants, this fully online conference allowed theorists and observers across the globe to discuss recent findings on the central structures of disc galaxies. By design, this conference included experts on the Milky Way, local and high-redshift galaxies, and theoretical aspects of galaxy formation and evolution. The need for such a broad range of expertise stems from the important advances that have been made on all fronts in recent years. One of the main goals of this meeting was accordingly to bring together these different communities, to find a common ground for discussion and mutual understanding, to exchange ideas, and to efficiently communicate progress. △ Less

Submitted 31 October, 2022; originally announced January 2023.

Comments: Report on ESO Conference held online on 2-6 May 2022, published on The Messenger; talks and discussion sessions are available at https://www.eso.org/sci/meetings/2022/BULGES2022/restricted.html

The vertical structure of the spiral galaxy NGC 3501: first stages of the formation of a thin metal-rich disc

Authors: Natascha Sattler, Francesca Pinna, Nadine Neumayer, Jesus Falcón-Barroso, Marie Martig, Dimitri A. Gadotti, Glenn van de Ven, Ivan Minchev

Abstract: We trace the evolution of the edge-on spiral galaxy NGC 3501, making use of its stellar populations extracted from deep integral-field spectroscopy MUSE observations. We present stellar kinematic and population maps, as well as the star formation history, of the south-western half of the galaxy. The derived maps of the stellar line-of-sight velocity and velocity dispersion are quite regular, show… ▽ More We trace the evolution of the edge-on spiral galaxy NGC 3501, making use of its stellar populations extracted from deep integral-field spectroscopy MUSE observations. We present stellar kinematic and population maps, as well as the star formation history, of the south-western half of the galaxy. The derived maps of the stellar line-of-sight velocity and velocity dispersion are quite regular, show disc-like rotation, and no other structural component of the galaxy. However, maps of the stellar populations exhibit structures in the mass-weighted and light-weighted age, total metallicity and [Mg/Fe] abundance. These maps indicate that NGC 3501 is a young galaxy, consisting mostly of stars with ages between 2 to 8 Gyr. Also, they show a thicker more extended structure that is metal-poor and $α$-rich, and another inner metal-rich and $α$-poor one with smaller radial extension. While previous studies revealed that NGC 3501 shows only one morphological disc component in its vertical structure, we divided the galaxy into two regions: an inner metal-rich midplane and a metal-poor thicker envelope. Comparing the star formation history of the inner thinner metal-rich disc and the thicker metal-poor disc, we see that the metal-rich component evolved more steadily, while the metal-poor one experienced several bursts of star formation. We propose this spiral galaxy is being observed in an early evolutionary phase, with a thicker disc already in place and an inner thin disc in an early formation stage. So we are probably witnessing the birth of a future massive thin disc, continuously growing embedded in a preexisting thicker disc. △ Less

Submitted 23 January, 2023; originally announced January 2023.

Comments: 15 pages, 12 figures. Accepted for publication in MNRAS

The Fornax3D project: Environmental effects on the assembly of dynamically cold disks in Fornax cluster galaxies

Authors: Y. Ding, L. Zhu, G. van de Ven, L. Coccato, E. M. Corsini, L. Costantin, K. Fahrion, J. Falcón-Barroso, D. A. Gadotti, E. Iodice, M. Lyubenova, I. Martín-Navarro, R. M. McDermid, F. Pinna, M. Sarzi

Abstract: We apply a population-orbit superposition method to 16 galaxies in the Fornax cluster observed with MUSE/VLT in the context of the Fornax3D project. By fitting the luminosity distribution, stellar kinematics, and age and metallicity maps simultaneously, we obtained the internal stellar orbit distribution, as well as the age and metallicity distribution of stars on different orbits for each galaxy.… ▽ More We apply a population-orbit superposition method to 16 galaxies in the Fornax cluster observed with MUSE/VLT in the context of the Fornax3D project. By fitting the luminosity distribution, stellar kinematics, and age and metallicity maps simultaneously, we obtained the internal stellar orbit distribution, as well as the age and metallicity distribution of stars on different orbits for each galaxy. Based on the model, we decompose each galaxy into a dynamically cold disk (orbital circularity $λ_z\ge0.8$) and a dynamically hot non-disk component (orbital circularity $λ_z<0.8$), and obtain the surface-brightness, age, and metallicity radial profiles of each component. The galaxy infall time into the cluster is strongly correlated with galaxy cold-disk age with older cold disks in ancient infallers. We quantify the infall time $t_{\rm infall}$ of each galaxy with its cold-disk age using a correlation calibrated with TNG50 cosmological simulations. For galaxies in the Fornax cluster, we found that the luminosity fraction of cold disk in galaxies with $t_{\rm infall}>8$ Gyr are a factor of $\sim 4$ lower than in more recent infallers while controlling for total stellar mass. Nine of the 16 galaxies have spatially extended cold disks, and most of them show positive or zero age gradients; stars in the inner disk are $\sim 2-5$ Gyr younger than that in the outer disk, in contrast to the expectation of inside-out growth. Our results indicate that the assembly of cold disks in galaxies is strongly affected by their infall into clusters, by either removal of gas in outer regions or even tidally stripping or heating part of the pre-existing disks. Star formation in outer disks can stop quickly after the galaxy falls into the cluster, while star formation in the inner disks can last for a few Gyrs more, building the positive age gradient measured in cold disks. △ Less

Submitted 15 February, 2023; v1 submitted 13 January, 2023; originally announced January 2023.

Comments: 31 pages, 32 figures, Accepted to A&A

Journal ref: A&A 672, A84 (2023)

A new method for age-dating the formation of bars in disc galaxies: The TIMER view on NGC1433's old bar and the inside-out growth of its nuclear disc

Authors: Camila de Sá-Freitas, Francesca Fragkoudi, Dimitri A. Gadotti, Jesús Falcón-Barroso, Adrian Bittner, Patricia Sánchez-Blázquez, Glenn van de Ven, Rebekka Bieri, Lodovico Coccato, Paula Coelho, Katja Fahrion, Geraldo Gonçalves, Taehyun Kim, Adriana de Lorenzo-Cáceres, Marie Martig, Ignacio Martín-Navarro, Jairo Mendez-Abreu, Justus Neumann, Miguel Querejeta

Abstract: The epoch in which galactic discs settle is a major benchmark to test models of galaxy formation and evolution but is as yet largely unknown. Once discs settle and become self-gravitating enough, stellar bars are able to form; therefore, determining the ages of bars can shed light on the epoch of disc settling, and on the onset of secular evolution. Nevertheless, until now, timing when the bar for… ▽ More The epoch in which galactic discs settle is a major benchmark to test models of galaxy formation and evolution but is as yet largely unknown. Once discs settle and become self-gravitating enough, stellar bars are able to form; therefore, determining the ages of bars can shed light on the epoch of disc settling, and on the onset of secular evolution. Nevertheless, until now, timing when the bar formed has proven challenging. In this work, we present a new methodology for obtaining the bar age, using the star formation history of nuclear discs. Nuclear discs are rotation-supported structures, built by gas pushed to the centre via bar-induced torques, and their formation is thus coincident with bar formation. In particular, we use integral field spectroscopic (IFS) data from the TIMER survey to disentangle the star formation history of the nuclear disc from that of the underlying main disc, which enables us to more accurately determine when the nuclear disc forms. We demonstrate the methodology on the galaxy NGC 1433 -- which we find to host an old bar that is $8.0^{+1.6}_{-1.1}\rm{(sys)}^{+0.2}_{-0.5}\rm{(stat)}$ Gyr old -- and describe a number of tests carried out on both the observational data and numerical simulations. In addition, we present evidence that the nuclear disc of NGC 1433 grows in accordance with an inside-out formation scenario. This methodology is applicable to high-resolution IFS data of barred galaxies with nuclear discs, making it ideally suited for the TIMER survey sample. In the future we will thus be able to determine the bar age for a large sample of galaxies, shedding light on the epoch of disc settling and bar formation. △ Less

Submitted 14 November, 2022; originally announced November 2022.

Comments: Accepted for Publication by A&A, 18 pages, 14 figures

The survival of stellar discs in Fornax-like environments, from TNG50 to real galaxies

Authors: Pablo M. Galán-de Anta, M. Sarzi, A. Pillepich, Y. Ding, L. Zhu, L. Coccato, E. M. Corsini, K. Fahrion, J. Falcón-Barroso, D. A. Gadotti, E. Iodice, M. Lyubenova, I. Martín-Navarro, R. M. McDermid, F. Pinna, G. van de Ven, P. T. de Zeeuw

Abstract: We study the evolution of kinematically-defined stellar discs in 10 Fornax-like clusters identified in the TNG50 run from the IllustrisTNG suite of cosmological simulations. We considered disc galaxies with present-day stellar mass $M_{\star}\geq 3 \times 10^{8} M_{\odot}$ and follow their evolution since first entering their host cluster. Very few stellar discs survive since falling in such dense… ▽ More We study the evolution of kinematically-defined stellar discs in 10 Fornax-like clusters identified in the TNG50 run from the IllustrisTNG suite of cosmological simulations. We considered disc galaxies with present-day stellar mass $M_{\star}\geq 3 \times 10^{8} M_{\odot}$ and follow their evolution since first entering their host cluster. Very few stellar discs survive since falling in such dense environments, ranging from 40% surviving to all being disrupted. Such survival rates are consistent with what reported earlier for the two more massive, Virgo-like clusters in TNG50. In absolute terms, however, the low number of present-day disc galaxies in Fornax-like clusters could be at odds with the presence of three edge-on disc galaxies in the central regions of the actual Fornax cluster, as delineated by the Fornax3D survey. When looking at the Fornax analogues from random directions and with the same selection function of Fornax3D, the probability of finding three edge-on disc galaxies in any one Fornax-like cluster in TNG50 is rather low, albeit not impossible. We also compared the stellar-population properties near the equatorial plane derived from integral-field spectroscopy for the three edge-ons in Fornax to similar line-of-sight integrated values for present-day disc galaxies in TNG50. For one of these, the very old and metal-rich stellar population of its disc cannot be matched by any the disc galaxies in TNG50, including objects in the field. We discuss possible interpretations of these findings, while pointing to future studies on passive cluster spirals as a way to further test state-of-the-art cosmological simulations. △ Less

Submitted 2 November, 2022; v1 submitted 1 November, 2022; originally announced November 2022.

Comments: 12 pages, 7 figures. Accepted on 21 of October, published on 25 of October

On the accretion of a new group of galaxies onto Virgo: II. The effect of pre-processing on the stellar population content of dEs

Authors: Bahar Bidaran, Francesco La Barbera, Anna Pasquali, Reynier Peletier, Glenn van de Ven, Eva K. Grebel, Jesus Falcón-Barroso, Agnieszka Sybilska, Dimitri A. Gadotti, Lodovico Coccato

Abstract: Using MUSE spectra, we investigate how pre-processing and accretion onto a galaxy cluster affect the integrated stellar population properties of dwarf early-type galaxies (dEs). We analyze a sample of nine dEs with stellar masses of $\rm \sim 10^9 \, M_\odot$, which were accreted ($\sim$ 2-3 Gyr ago) onto the Virgo cluster as members of a massive galaxy group. We derive their stellar population pr… ▽ More Using MUSE spectra, we investigate how pre-processing and accretion onto a galaxy cluster affect the integrated stellar population properties of dwarf early-type galaxies (dEs). We analyze a sample of nine dEs with stellar masses of $\rm \sim 10^9 \, M_\odot$, which were accreted ($\sim$ 2-3 Gyr ago) onto the Virgo cluster as members of a massive galaxy group. We derive their stellar population properties, namely age, metallicity ([M/H]), and the abundance ratio of $α$ elements ([$α$/Fe]), by fitting observed spectral indices with a robust, iterative procedure, and infer their star formation history (SFH) by means of full spectral fitting. We find that these nine dEs are more metal-poor (at the 2-3$σ$ level) and significantly more $α$-enhanced than dEs in the Virgo and Coma clusters with similar stellar mass, cluster-centric distance, and infall time. Moreover, for six dEs, we find evidence for a recent episode of star formation during or right after the time of accretion onto Virgo. We interpret the high [$α$/Fe] of our sample of dEs as the result of the previous exposure of these galaxies to an environment hostile to star formation, and/or the putative short burst of star formation they underwent after infall into Virgo. Our results suggest that the stellar population properties of low-mass galaxies may be the result of the combined effect of pre-processing in galaxy groups and environmental processes (such as ram-pressure triggering star formation) acting during the early phases of accretion onto a cluster. △ Less

Submitted 14 July, 2022; originally announced July 2022.

Comments: 17 pages, 10 figures, Accepted for publication in MNRAS

The Fornax3D project: The assembly history of massive early-type galaxies in the Fornax cluster from deep imaging and integral field spectroscopy

Authors: M. Spavone, E. Iodice, G. D'Ago, G. van de Ven, L. Morelli, E. M. Corsini, M. Sarzi, L. Coccato, K. Fahrion, J. Falcón-Barroso, D. A. Gadotti, M. Lyubenova, I. Martín-Navarro, R. M. McDermid, F. Pinna, A. Pizzella, A. Poci, P. T. de Zeeuw, L. Zhu

Abstract: This work is based on high quality integral-field spectroscopic data obtained with the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT). The 21 brightest ($m_B\leq 15$ mag) early-type galaxies (ETGs) inside the virial radius of the Fornax cluster are observed out to distances of $\sim2-3\ R_{\rm e}$. Deep imaging from the VLT Survey Telescope (VST) is also available for t… ▽ More This work is based on high quality integral-field spectroscopic data obtained with the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT). The 21 brightest ($m_B\leq 15$ mag) early-type galaxies (ETGs) inside the virial radius of the Fornax cluster are observed out to distances of $\sim2-3\ R_{\rm e}$. Deep imaging from the VLT Survey Telescope (VST) is also available for the sample ETGs. We investigate the variation of the galaxy structural properties as a function of the total stellar mass and cluster environment. Moreover, we correlate the size scales of the luminous components derived from a multi-component decomposition of the VST surface-brightness radial profiles of the sample ETGs with the MUSE radial profiles of stellar kinematic and population properties. The results are compared with both theoretical predictions and previous observational studies and used to address the assembly history of the massive ETGs of the Fornax cluster. We find that galaxies in the core and north-south clump of the cluster, which have the highest accreted mass fraction, show milder metallicity gradients in their outskirts than the galaxies infalling into the cluster. We also find a segregation in both age and metallicity between the galaxies belonging to the core and north-south clump and the infalling galaxies. The new findings fit well within the general framework for the assembly history of the Fornax cluster. △ Less

Submitted 30 May, 2022; originally announced May 2022.

Comments: 23 pages, 7 figures, 3 tables. Accepted for publication in A&A

Journal ref: A&A 663, A135 (2022)

The Fornax3D project: Intrinsic Correlations between Orbital Properties and the Stellar Initial Mass Function

Authors: A. Poci, R. M. McDermid, M. Lyubenova, I. Martin-Navarro, G. van de Ven, L. Coccato, E. M. Corsini, K. Fahrion, J. Falcon-Barroso, D. A. Gadotti, E. Iodice, F. Pinna, M. Sarzi, P. T. de Zeeuw, L. Zhu

Abstract: [arXiv Abridged] In this work, we explore new spatially-resolved measurements of the IMF for three edge-on lenticular galaxies in the Fornax cluster. Specifically, we utilise existing orbit-based dynamical models, which re-produce the measured stellar kinematics, in order to fit the new IMF maps within this orbital framework. We then investigate correlations between intrinsic orbital properties an… ▽ More [arXiv Abridged] In this work, we explore new spatially-resolved measurements of the IMF for three edge-on lenticular galaxies in the Fornax cluster. Specifically, we utilise existing orbit-based dynamical models, which re-produce the measured stellar kinematics, in order to fit the new IMF maps within this orbital framework. We then investigate correlations between intrinsic orbital properties and the local IMF. We find that, within each galaxy, the high-angular-momentum, disk-like stars exhibit an IMF which is rich in dwarf stars. The centrally-concentrated pressure-supported orbits have IMF which are similarly rich in dwarf stars. Conversely, orbits at large radius which have intermediate angular momentum exhibit IMF which are markedly less dwarf-rich relative to the other regions of the same galaxy. Assuming that the stars which, in the present-day, reside on dynamically-hot orbits at large radii are dominated by accreted populations, we can interpret these findings as a correlation between the dwarf-richness of a population of stars, and the mass of the host in which it formed. Specifically, deeper gravitational potentials would produce more dwarf-rich populations, resulting in the relative deficiency of dwarf stars which originated in the lower-mass accreted satellites. Conversely, the central and high angular-momentum populations are likely dominated by in-situ stars, which were formed in the more massive host itself. There are also global differences between the three galaxies studied here, of up to $\sim 0.3\ \mathrm{dex}$ in the IMF parameter $ξ$. We find no local dynamical or chemical property which alone can fully account for the IMF variations. △ Less

Submitted 25 May, 2022; originally announced May 2022.

Comments: 11 pages. Accepted to MNRAS

The Fornax3D project: discovery of ancient massive merger events in the Fornax cluster galaxies NGC 1380 and NGC 1427

Authors: Ling Zhu, Glenn van de Ven, Ryan Leaman, Annalisa Pillepich, Lodovico Coccato, Yuchen Ding, Jesús Falcón-Barroso, Enrichetta Iodice, Ignacio Martin Navarro, Francesca Pinna, Enrico Maria Corsini, Dimitri A. Gadotti, Katja Fahrion, Mariya Lyubenova, Shude Mao, Richard McDermid, Adriano Poci, Marc Sarzi, Tim de Zeeuw

Abstract: We report the discovery of ancient massive merger events in the early-type galaxies NGC 1380 and NGC 1427, members of the Fornax galaxy cluster. Both galaxies have been observed by the MUSE IFU instrument on the VLT, as part of the Fornax3D project. By fitting recently-developed population-orbital superposition models to the observed surface brightness as well as stellar kinematic, age, and metall… ▽ More We report the discovery of ancient massive merger events in the early-type galaxies NGC 1380 and NGC 1427, members of the Fornax galaxy cluster. Both galaxies have been observed by the MUSE IFU instrument on the VLT, as part of the Fornax3D project. By fitting recently-developed population-orbital superposition models to the observed surface brightness as well as stellar kinematic, age, and metallicity maps, we obtain the stellar orbits, age and metallicity distributions of each galaxy. We then decompose each galaxy into multiple orbital-based components, including a dynamically hot inner stellar halo component which is identified as the relic of past massive mergers. By comparing to analogues from cosmological galaxy simulations, chiefly TNG50, we find that the formation of such a hot inner stellar halo requires the merger with a now-destroyed massive satellite galaxy of $3.7_{-1.5}^{+2.7} \times 10^{10}$ Msun (about $1/5$ of its current stellar mass) in the case of NGC 1380 and of $1.5_{-0.7}^{+1.6} \times10^{10}$ Msun (about $1/4$ of its current stellar mass) in the case of NGC 1427. Moreover, we infer that the last massive merger in NGC 1380 happened $\sim10$ Gyr ago based on the stellar age distribution of the re-grown dynamically cold disk, whereas the merger in NGC 1427 ended $t\lesssim 8$ Gyr ago based on the stellar populations in its hot inner stellar halo. The major merger event in NGC 1380 is the first one with both merger mass and merger time quantitatively inferred in a galaxy beyond the Local Volume. Moreover, it is the oldest and most massive merger uncovered in nearby galaxies so far. △ Less

Submitted 13 April, 2022; v1 submitted 29 March, 2022; originally announced March 2022.

Comments: A&A accepted, 19 pages, 16 figures

Journal ref: A&A 664, A115 (2022)

Revisiting the role of bars in AGN fuelling with propensity score sample matching

Authors: Luiz A. Silva-Lima, Lucimara P. Martins, Paula R. T. Coelho, Dimitri A. Gadotti

Abstract: The high luminosity displayed by an active galactic nucleus (AGN) requires that gas be transported to the centre of the galaxy by some mechanism. Bar-driven processes are often pointed out in this context and a number of studies have addressed the bar-AGN connection, but with conflicting results. Some of the inconsistencies can be explained by the different spatial- and timescales involved in bar-… ▽ More The high luminosity displayed by an active galactic nucleus (AGN) requires that gas be transported to the centre of the galaxy by some mechanism. Bar-driven processes are often pointed out in this context and a number of studies have addressed the bar-AGN connection, but with conflicting results. Some of the inconsistencies can be explained by the different spatial- and timescales involved in bar-driven gas inflows, accretion by the central black hole, and AGN emission. However, the discrepant results could also be due to sample biases, because both the AGN activity determination and the bar detection are influenced by the method employed. We revisit the bar-AGN connection in a sample of galaxies from SDSS, looking for evidence of the influence of bars on AGN activity. We determine AGN activity by emission line diagnostics and the properties of the bar were previously estimated with \texttt{BUDDA}, which performs 2D bulge-bar-disk decomposition. Before comparing active and inactive galaxies, we made a careful selection of the sample to minimise selection biases. We created control samples by matching them with the AGN sample using propensity score matching. This technique offers an analytical approach for creating control samples given some object parameters. We find that AGN are preferentially found in barred galaxies and that the accretion rate is higher in barred galaxies, but only when different M-$σ$ relations are used to estimate the black hole mass M$_\bullet$ in barred and unbarred galaxies (from the central velocity dispersion $σ$). On the other hand, we find no correlation between activity level and bar strength. Altogether, our results strengthen theoretical predictions that the bar is an important mechanism in disc galaxies, creating a gas reservoir to feed AGN, but they also indicate that other mechanisms can play a major role, particularly at scales <~100 pc. △ Less

Submitted 15 March, 2022; originally announced March 2022.

Journal ref: A&A 661, A105 (2022)

The Fornax3D project: The environmental impact on gas metallicity gradients in Fornax cluster galaxies

Authors: M. A. Lara-Lopez, P. M. Galan-de Anta, M. Sarzi, E. Iodice, T. A. Davis, N. Zabel, E. M. Corsini, P. T. de Zeeuw, K. Fahrion, J. Falcon-Barroso, D. A. Gadotti, R. M. McDermid, F. Pinna, V. Rodriguez-Gomez, G. van de Ven, L. Zhu, L. Coccato, M. Lyubenova, I. Martin-Navarro

Abstract: The role played by environment in galaxy evolution is a current debate in astronomy. The degree to which environment can alter, re-shape, or drive galaxy evolution is a topic of discussion in both fronts, observations and simulations. This paper analyses the gas metallicity gradients for a sample of 10 Fornax cluster galaxies observed with MUSE as part of the Fornax3D project. Detailed maps of emi… ▽ More The role played by environment in galaxy evolution is a current debate in astronomy. The degree to which environment can alter, re-shape, or drive galaxy evolution is a topic of discussion in both fronts, observations and simulations. This paper analyses the gas metallicity gradients for a sample of 10 Fornax cluster galaxies observed with MUSE as part of the Fornax3D project. Detailed maps of emission lines allowed a precise determination of gas metallicity and metallicity gradients. The integrated gas metallicity of our Fornax cluster galaxies show slightly higher metallicities (~0.045 dex) in comparison to a control sample. In addition, we find signs of a mass and metallicity segregation from the center to the outskirts of the cluster. By comparing our Fornax cluster metallicity gradients with a control sample we find a general median offset of ~0.04 dex/Re, with 8 of our galaxies showing flatter or more positive gradients. We find no systematic difference between the gradients of recent and intermediate infallers when considering the projected distance of each galaxy to the cluster center. To identify the origin of the observed offset in the metallicity gradients, we perform a similar analysis with data from the TNG50 simulation. We identify 12 subhalos in Fornax-like clusters and compare their metallicity gradients with a control sample of field subhalos. This exercise also shows a flattening in the metallicity gradients for galaxies in Fornax-like halos, with a median offset of ~0.05 dex/Re We also analyse the merger history, Mach numbers (M), and ram pressure stripping of our TNG50 sample. We conclude that the observed flattening in metallicity gradients is likely due to a combination of galaxies traveling at supersonic velocities (M>1) that are experiencing high ram pressure stripping and flybys. △ Less

Submitted 8 February, 2022; originally announced February 2022.

Comments: Accepted by A&A

Journal ref: A&A 660, A105 (2022)

The effects of AGN feedback on the structural and dynamical properties of Milky Way-mass galaxies in cosmological simulations

Authors: Dimitrios Irodotou, Francesca Fragkoudi, Ruediger Pakmor, Robert J. J. Grand, Dimitri A. Gadotti, Tiago Costa, Volker Springel, Facundo A. Gómez, Federico Marinacci

Abstract: Feedback from active galactic nuclei (AGN) has become established as a fundamental process in the evolution of the most massive galaxies. Its impact on Milky Way (MW)-mass systems, however, remains comparatively unexplored. In this work, we use the Auriga simulations to probe the impact of AGN feedback on the dynamical and structural properties of galaxies, focussing on the bar, bulge, and disc. W… ▽ More Feedback from active galactic nuclei (AGN) has become established as a fundamental process in the evolution of the most massive galaxies. Its impact on Milky Way (MW)-mass systems, however, remains comparatively unexplored. In this work, we use the Auriga simulations to probe the impact of AGN feedback on the dynamical and structural properties of galaxies, focussing on the bar, bulge, and disc. We analyse three galaxies -- two strongly and one unbarred/weakly barred -- using three setups: (i) the fiducial Auriga model, which includes both radio and quasar mode feedback, (ii) a setup with no radio mode, and (iii) one with neither the radio nor the quasar mode. When removing the radio mode, gas in the circumgalactic medium cools more efficiently and subsequently settles in an extended disc, with little effect on the inner disc. Contrary to previous studies, we find that although the removal of the quasar mode results in more massive central components, these are in the form of compact discs, rather than spheroidal bulges. Therefore, galaxies without quasar mode feedback are more baryon-dominated and thus prone to forming stronger and shorter bars, which reveals an anti-correlation between the ejective nature of AGN feedback and bar strength. Hence, we report that the effect of AGN feedback (i.e. ejective or preventive) can significantly alter the dynamical properties of MW-like galaxies. Therefore, the observed dynamical and structural properties of MW-mass galaxies can be used as additional constraints for calibrating the efficiency of AGN feedback models. △ Less

Submitted 11 May, 2022; v1 submitted 21 October, 2021; originally announced October 2021.

Comments: 21 pages, 11 main (9 old and 2 new) + 5 Appendix figures. Accepted for publications by MNRAS

NGC 5746: formation history of a massive disc-dominated galaxy

Authors: Marie Martig, Francesca Pinna, Jesús Falcón-Barroso, Dimitri Gadotti, Bernd Husemann, Ivan Minchev, Justus Neumann, Tomás Ruiz-Lara, Glenn van de Ven

Abstract: The existence of massive galaxies lacking a classical bulge has often been proposed as a challenge to $Λ$CDM. However, recent simulations propose that a fraction of massive disc galaxies might have had very quiescent merger histories, and also that mergers do not necessarily build classical bulges. We test these ideas with deep MUSE observations of NGC 5746, a massive ($\sim 10^{11}$ M$_\odot$) ed… ▽ More The existence of massive galaxies lacking a classical bulge has often been proposed as a challenge to $Λ$CDM. However, recent simulations propose that a fraction of massive disc galaxies might have had very quiescent merger histories, and also that mergers do not necessarily build classical bulges. We test these ideas with deep MUSE observations of NGC 5746, a massive ($\sim 10^{11}$ M$_\odot$) edge-on disc galaxy with no classical bulge. We analyse its stellar kinematics and stellar populations, and infer that a massive and extended disc formed very early: 80% of the galaxy's stellar mass formed more than 10 Gyr ago. Most of the thick disc and the bar formed during that early phase. The bar drove gas towards the center and triggered the formation of the nuclear disc followed by the growth of a boxy/peanut-shaped bulge. Around $\sim$ 8 Gyr ago, a $\sim$1:10 merger happened, possibly on a low-inclination orbit. The satellite did not cause significant vertical heating, did not contribute to the growth of a classical bulge, and did not destroy the bar and the nuclear disc. It was however an important event for the galaxy: by depositing its stars throughout the whole galaxy it contributed $\sim 30$% of accreted stars to the thick disc. NGC 5746 thus did not completely escape mergers, but the only relatively recent significant merger did not damage the galaxy and did not create a classical bulge. Future observations will reveal if this is representative of the formation histories of massive disc galaxies. △ Less

Submitted 20 September, 2021; originally announced September 2021.

Comments: Accepted for publication in MNRAS. 22 pages, 21 figures (including appendix)

Fornax 3D project: assessing the diversity of IMF and stellar population maps within the Fornax Cluster

Authors: I. Martín-Navarro, F. Pinna, L. Coccato, J. Falcón-Barroso, G. van de Ven, M. Lyubenova, E. M. Corsini, K. Fahrion, D. A. Gadotti, E. Iodice, R. M. McDermid, A. Poci, M. Sarzi, T. W. Spriggs, S. Viaene, P. T. de Zeeuw, L. Zhu

Abstract: The stellar initial mass function (IMF) is central to our interpretation of astronomical observables and to our understanding of most baryonic processes within galaxies. The universality of the IMF, suggested by observations in our own Milky Way, has been thoroughly revisited due to the apparent excess of low-mass stars in the central regions of massive quiescent galaxies. As part of the efforts w… ▽ More The stellar initial mass function (IMF) is central to our interpretation of astronomical observables and to our understanding of most baryonic processes within galaxies. The universality of the IMF, suggested by observations in our own Milky Way, has been thoroughly revisited due to the apparent excess of low-mass stars in the central regions of massive quiescent galaxies. As part of the efforts within the Fornax 3D project, we aim to characterize the two-dimensional IMF variations in a sample of 23 quiescent galaxies within the Fornax cluster. For each galaxy in the sample, we measured the mean age, metallicity, [Mg/Fe], and IMF slope maps from spatially resolved integrated spectra. The IMF maps show a variety of behaviors and internal substructures, roughly following metallicity variations. However, metallicity alone is not able to fully explain the complexity exhibited by the IMF maps. In particular, for relatively metal-poor stellar populations, the slope of the IMF seems to depend on the (specific) star formation rate at which stars were formed. Moreover, metallicity maps have systematically higher ellipticities than IMF slope ones. At the same time, both metallicity and IMF slope maps have at the same time higher ellipticities than the stellar light distribution in our sample of galaxies. In addition we find that, regardless of the stellar mass, every galaxy in our sample shows a positive radial [Mg/Fe] gradient. This results in a strong [Fe/H]-[Mg/Fe] relation, similar to what is observed in nearby, resolved galaxies. Since the formation history and chemical enrichment of galaxies are causally driven by changes in the IMF, our findings call for a physically motivated interpretation of stellar population measurements based on integrated spectra that take into account any possible time evolution of the stellar populations. △ Less

Submitted 29 July, 2021; originally announced July 2021.

Comments: 14 pages and 10 figures (plus Appendix including all the stellar population maps). Accepted for publication in Astronomy and Astrophysics

Journal ref: A&A 654, A59 (2021)

The Fornax3D project: Planetary nebulae catalogue and independent distance measurements to Fornax cluster galaxies

Authors: T. W. Spriggs, M. Sarz, P. M. Galán-de Anta, R. Napiwotzki, S. Viaene, B. Nedelchev, L. Coccato, E. M. Corsini, K. Fahrion, J. Falcón-Barroso, D. A. Gadotti, E. Iodice, M. Lyubenova, I. Martín-Navarro, R. M. McDermid, L. Morelli, F. Pinna, G. van de Ven, P. T. de Zeeuw, L. Zhu

Abstract: Extragalactic planetary nebulae (PNe) offer a way to determine the distance to their host galaxies thanks to the nearly universal shape of the planetary nebulae luminosity function (PNLF). Accurate PNe distance measurements rely on obtaining well-sampled PNLFs and the number of observed PNe scales with the encompassed stellar mass. This means either disposing of wide-field observations or focusing… ▽ More Extragalactic planetary nebulae (PNe) offer a way to determine the distance to their host galaxies thanks to the nearly universal shape of the planetary nebulae luminosity function (PNLF). Accurate PNe distance measurements rely on obtaining well-sampled PNLFs and the number of observed PNe scales with the encompassed stellar mass. This means either disposing of wide-field observations or focusing on the bright central regions of galaxies. In this work we take this second approach and conduct a census of the PNe population in the central regions of galaxies in the Fornax cluster, using VLT/MUSE data for the early-type galaxies observed over the course of the Fornax3D survey. Using such integral-field spectroscopic observations to carefully separate the nebular emission from the stellar continuum, we isolated [OIII] 5007 Å sources of interest, filtered out unresolved impostor sources or kinematic outliers, and present a catalogue of 1350 unique PNe sources across 21 early-type galaxies, which includes their positions, [OIII] 5007 Å line magnitudes, and line-of-sight velocities. Using the PNe catalogued within each galaxy, we present independently derived distance estimates based on the fit to the entire observed PNLF observed while carefully accounting for the PNe detection incompleteness. With these individual measurements, we arrive at an average distance to the Fornax cluster itself of 19.86 $\pm$ 0.32 Mpc ($μ_{PNLF}$ = 31.49 $\pm$ 0.04 mag). Our PNLF distance measurements agree well with previous distances based on surface brightness fluctuations, finding no significant systematic offsets between the two methods as otherwise reported in previous studies. △ Less

Submitted 22 July, 2021; v1 submitted 20 July, 2021; originally announced July 2021.

Comments: 26 pages, 16 figures, 3 tables. Accepted for publication in Astronomy and Astrophysics Journal. Corrected Fig. 7 legend

Journal ref: A&A 653, A167 (2021)

The Fornax 3D project: PNe populations and stellar metallicity in edge-on galaxies

Authors: P. M. Galán-de Anta, M. Sarzi, T. W. Spriggs, B. Nedelchev, F. Pinna, I. Martín-Navarro, L. Coccato, E. M. Corsini, P. T. de Zeeuw, J. Falcón-Barroso, D. A. Gadotti, E. Iodice, R. J. J. Grand, K. Fahrion, M. Lyubenova, R. M. McDermid, L. Morelli, G. van de Ven, S. Viaene, L. Zhu

Abstract: Context. Extragalactic Planetary Nebulae (PNe) are useful distance indicators and are often used to trace the dark-matter content in external galaxies. At the same time, PNe can also be used as probes of their host galaxy stellar populations and to help understanding the later stages of stellar evolution. Previous works have indicated that specific number of PNe per stellar luminosity can vary acr… ▽ More Context. Extragalactic Planetary Nebulae (PNe) are useful distance indicators and are often used to trace the dark-matter content in external galaxies. At the same time, PNe can also be used as probes of their host galaxy stellar populations and to help understanding the later stages of stellar evolution. Previous works have indicated that specific number of PNe per stellar luminosity can vary across different galaxies and as a function of stellar-population properties, for instance increasing with decreasing stellar metallicity. Aims. In this study we further explore the importance of stellar metallicity in driving the properties of the PNe population in early-type galaxies, using three edge-on galaxies in the Fornax cluster offering a clear view into their predominantly metal-rich and metal-poor regions near the equatorial plane or both below and above it, respectively . Methods. Using VLT-MUSE integral-field observations and dedicated PNe detection procedures, we construct the PNe luminosity function and compute the luminosity-specific number of PNe alpha in both in- and off-plane regions of our edge-on systems. Results. Comparing these alpha values with metallicity measurements also based on the same MUSE data, we find no evidence for an increase in the specific abundance of PNe when transitioning between metal-rich and metal-poor regions. Conclusions. Our analysis highlights the importance of ensuring spatial consistency to avoid misleading results when investigating the link between PNe and their parent stellar populations and suggest that in passively-evolving systems variations in the specific number of PNe may pertain to rather extreme metallicity regimes found either in the innermost or outermost regions of galaxies. △ Less

Submitted 22 June, 2021; originally announced June 2021.

Journal ref: A&A 652, A109 (2021)

Diversity of nuclear star cluster formation mechanisms revealed by their star formation histories

Authors: K. Fahrion, M. Lyubenova, G. van de Ven, M. Hilker, R. Leaman, J. Falcón-Barroso, A. Bittner, L. Coccato, E. M. Corsini, D. A. Gadotti, E. Iodice, R. M. McDermid, I. Martín-Navarro, F. Pinna, A. Poci, M. Sarzi, P. T. de Zeeuw, L. Zhu

Abstract: Nuclear star clusters (NSCs) are the densest stellar systems in the Universe and are found in the centres of all types of galaxies. They are thought to form via mergers of star clusters such as ancient globular clusters (GCs) that spiral to the centre as a result of dynamical friction or through in-situ star formation directly at the galaxy centre. There is evidence that both paths occur, but the… ▽ More Nuclear star clusters (NSCs) are the densest stellar systems in the Universe and are found in the centres of all types of galaxies. They are thought to form via mergers of star clusters such as ancient globular clusters (GCs) that spiral to the centre as a result of dynamical friction or through in-situ star formation directly at the galaxy centre. There is evidence that both paths occur, but the relative contribution of either channel and their correlation with galaxy properties are not yet constrained observationally. We aim to derive the dominant NSC formation channel for a sample of 25 nucleated galaxies, mostly in the Fornax galaxy cluster, with stellar masses between $M_\rm{gal} \sim 10^8$ and $10^{10.5} M_\odot$ and NSC masses between $M_\rm{NSC} \sim 10^5$ and $10^{8.5} M_\odot$. Using Multi-Unit Spectroscopic Explorer (MUSE) data from the Fornax 3D survey and the ESO archive, we derive star formation histories, mean ages and metallicities of NSCs, and compare them to the host galaxies. In many low-mass galaxies, the NSCs are significantly more metal-poor than the hosts with properties similar to GCs. In contrast, in the massive galaxies, we find diverse star formation histories and cases of ongoing or recent in-situ star formation. Massive NSCs ($> 10^7 M_\odot$) occupy a different region in the mass-metallicity diagram than lower mass NSCs and GCs, indicating a different enrichment history. We find a clear transition of the dominant NSC formation channel with both galaxy and NSC mass. We hypothesise that while GC-accretion forms the NSCs of the dwarf galaxies, central star formation is responsible for the efficient mass build up in the most massive NSCs in our sample. At intermediate masses, both channels can contribute. The transition between these formation channels seems to occur at galaxy masses $M_\rm{gal} \sim 10^9 M_\odot$ and NSC masses $M_\rm{NSC} \sim 10^7 M_\odot$. △ Less

Submitted 13 April, 2021; originally announced April 2021.

Comments: accepted for publication in Astronomy & Astrophysics, 18 pages, 10 figures (including appendix)

Journal ref: A&A 650, A137 (2021)

The Fornax3D project: Assembly histories of lenticular galaxies from a combined dynamical and population orbital analysis

Authors: A. Poci, R. M. McDermid, M. Lyubenova, L. Zhu, G. van de ven, E. Iodice, L. Coccato, F. Pinna, E. M. Corsini, J. Falcón-Barroso, D. A. Gadotti, R. J. J. Grand, K. Fahrion, I. Martín-Navarro, M. Sarzi, S. Viaene, P. T. de Zeeuw

Abstract: Abridged for arXiv: In this work, we apply a powerful new technique in order to observationally derive accurate assembly histories through a self-consistent combined stellar dynamical and population galaxy model. We present this approach for three edge-on lenticular galaxies from the Fornax3D project -- FCC 153, FCC 170, and FCC 177 -- in order to infer their mass assembly histories individually a… ▽ More Abridged for arXiv: In this work, we apply a powerful new technique in order to observationally derive accurate assembly histories through a self-consistent combined stellar dynamical and population galaxy model. We present this approach for three edge-on lenticular galaxies from the Fornax3D project -- FCC 153, FCC 170, and FCC 177 -- in order to infer their mass assembly histories individually and in the context of the Fornax cluster. The method was tested on mock data from simulations to quantify its reliability. We find that the galaxies studied here have all been able to form dynamically-cold (intrinsic vertical velocity dispersion $σ_z \lesssim 50\ {\rm km}\ {\rm s}^{-1}$) stellar disks after cluster infall. Moreover, the pre-existing (old) high angular momentum components have retained their angular momentum (orbital circularity $λ_z > 0.8$) through to the present day. Comparing the derived assembly histories with a comparable galaxy in a low-density environment -- NGC 3115 -- we find evidence for cluster-driven suppression of stellar accretion and merging. We measured the intrinsic stellar age--velocity-dispersion relation and find that the shape of the relation is consistent with galaxies in the literature across redshift. There is tentative evidence for enhancement in the luminosity-weighted intrinsic vertical velocity dispersion due to the cluster environment. But importantly, there is an indication that metallicity may be a key driver of this relation. We finally speculate that the cluster environment is responsible for the S0 morphology of these galaxies via the gradual external perturbations, or `harassment', generated within the cluster. △ Less

Submitted 7 February, 2021; v1 submitted 4 February, 2021; originally announced February 2021.

Comments: Accepted for publication in A&A

Journal ref: A&A 647, A145 (2021)