Showing 1–50 of 198 results for author: Kim, T

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

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

Unified Gas Heating Constraints on Extended Dark Matter Compact Objects

Authors: TaeHun Kim, Philip Lu, Volodymyr Takhistov

Abstract: We present the first unified constraints on a broad class of extended dark matter compact objects (EDCOs) from interstellar gas heating. These include axion stars, Q-balls, axion miniclusters, dark fermion stars and primordial black holes surrounded by dark matter halos, which arise in a wide range of theories beyond the Standard Model. As such massive objects traverse the interstellar medium, the… ▽ More We present the first unified constraints on a broad class of extended dark matter compact objects (EDCOs) from interstellar gas heating. These include axion stars, Q-balls, axion miniclusters, dark fermion stars and primordial black holes surrounded by dark matter halos, which arise in a wide range of theories beyond the Standard Model. As such massive objects traverse the interstellar medium, their gravitational influence generates wakes and, if sufficiently compact, drives accretion flows that heat gas in their vicinity. Our general framework extends standard dynamical friction treatments by incorporating finite-size effects, internal density profiles, gas penetration through objects, and criteria for accretion disk formation. We perform detailed numerical calculations of wake formation and gas heating and apply our results to the Leo T dwarf galaxy, establishing new constraints on the dark matter fraction in EDCOs heavier than a solar mass spanning several orders of magnitude in both mass and abundance. △ Less

Submitted 25 August, 2025; originally announced August 2025.

Comments: 44 pages, 11 figures

Report number: KEK-QUP-2025-0018, KEK-TH-2748

Search for Slow Bars in Two Barred Galaxies with Nuclear Structures: NGC 6951 and NGC 7716

Authors: Yun Hee Lee, Ho Seong Hwang, Virginia Cuomo, Myeong-Gu Park, Taehyun Kim, Narae Hwang, Hong Bae Ann, Woong-Tae Kim, Hyun-Jeong Kim, Ji Yeon Seok, Jeong Hwan Lee, Yeon-Ho Choi

Abstract: We investigate two barred galaxies with nuclear structures, NGC 6951 and NGC 7716, to examine whether they host slow bars. Using Gemini/GMOS long-slit spectroscopy, we calculate the bar pattern speed with the Tremaine-Weinberg method and detect kinematically decoupled nuclear disks in both galaxies. We also measure the bar length and strength using Pan-STARRs images and identify a nuclear ring in… ▽ More We investigate two barred galaxies with nuclear structures, NGC 6951 and NGC 7716, to examine whether they host slow bars. Using Gemini/GMOS long-slit spectroscopy, we calculate the bar pattern speed with the Tremaine-Weinberg method and detect kinematically decoupled nuclear disks in both galaxies. We also measure the bar length and strength using Pan-STARRs images and identify a nuclear ring in NGC 6951 and a nuclear bar in NGC 7716 from HST/PC images. Our results indicate that NGC 6951 hosts a slow, long, and strong bar, which likely evolved through interactions with the dark matter halo and contributed to the formation of both the nuclear disk and ring. We also find hints of a rapidly rotating oval structure within the primary bar, although it is not clearly seen in the imaging data. In contrast, the primary bar in NGC 7716 is too weak to be classified as a barred galaxy, while its nuclear disk and nuclear bar are unusually large, possibly due to tidal interactions or the weakness of the primary bar. These findings suggest that slow bars may be more observed in galaxies with nuclear structures and highlight the often underappreciated role of galaxy interactions in bar evolution. △ Less

Submitted 12 August, 2025; originally announced August 2025.

Comments: 25 pages, 11 figures

Journal ref: The Astrophysical Journal, Volume 989, Issue 1, id.55, 19 pp. (2025)

AllBRICQS: The Discovery of Luminous Quasars in the Northern Hemisphere

Authors: Yunyi Choi, Yuming Fu, Myungshin Im, Xue-Bing Wu, Christopher A. Onken, Christian Wolf, Seo-Won Chang, Hyeonho Choi, Mankeun Jeong, Yongjung Kim, Gu Lim, Yuxuan Pang, Taewan Kim, Jubee Sohn, Dohyeong Kim, Ji Hoon Kim, Eunhee Ko, Gregory S. H. Paek, Sungho Jung

Abstract: We present the second catalog of bright quasars from the All-sky BRIght, Complete Quasar Survey (AllBRICQS), focusing on spectroscopically observed quasars in the Northern Hemisphere with Galactic latitude $|b| > 10^\circ$. This catalog includes their spectral data, redshifts, and luminosities. AllBRICQS aims to identify the last remaining optically bright quasars using data from the Wide-field In… ▽ More We present the second catalog of bright quasars from the All-sky BRIght, Complete Quasar Survey (AllBRICQS), focusing on spectroscopically observed quasars in the Northern Hemisphere with Galactic latitude $|b| > 10^\circ$. This catalog includes their spectral data, redshifts, and luminosities. AllBRICQS aims to identify the last remaining optically bright quasars using data from the Wide-field Infrared Survey Explorer (WISE) and Gaia all-sky survey Data Release 3 (DR3). AllBRICQS searches for quasars that are brighter than $B_P = 16.5$ or $R_P = 16$ mag in Gaia DR3, based on simple selection criteria. Here, we report 62 new AllBRICQS quasars spanning various types, which include typical broad emission line quasars and the most luminous iron low-ionization broad absorption line quasars discovered to date. Spectroscopic observations were conducted using the Long-Slit Spectrograph on the 1.8-meter telescope at Bohyunsan Optical Astronomy Observatory, YFOSC on the 2.4-meter telescope at Lijiang Observatory, and BFOSC on the 2.16-meter telescope at Xinglong Observatory. We applied flux calibration using ZTF broadband photometry to correct for attenuation due to intermittent thin clouds during the observations. Redshifts were determined using inverse-variance weighted cross-correlation methods. Our targets span the bolometric luminosity range of $44.9<\log \left( L_{\rm bol} / {\rm erg~s^{-1}} \right)<48.0$ at redshifts between 0.09 and 2.48. These confirmed AllBRICQS quasars provide a valuable resource for future research into quasar evolution, black holes, their environments, and their host galaxies across multiple wavelengths. △ Less

Submitted 16 October, 2025; v1 submitted 8 August, 2025; originally announced August 2025.

Comments: 29 pages, 10 figures, 6 tables. Published in ApJS. This version corresponds to the accepted manuscript and includes all panels of Figure 7, which are presented as a figure set in the published version. The final published version is available via DOI: 10.3847/1538-4365/adf8ed. Spectra and catalog data are publicly available

Journal ref: 2025ApJS..280...73C

The Tremaine-Weinberg method at high redshifts

Authors: Mahmood Roshan, Asiyeh Habibi, J. Alfonso L. Aguerri, Virginia Cuomo, Connor Bottrell, Luca Costantin, Enrico Maria Corsini, Taehyun Kim, Yun Hee Lee, Jairo Mendez-Abreu, Matthew Frosst, Adriana de Lorenzo-Cáceres, Lorenzo Morelli, Alessandro Pizzella

Abstract: This paper examines the reliability of the Tremaine-Weinberg (TW) method in measuring the pattern speed of barred galaxies at high redshifts. Measuring pattern speeds at high redshift may help to shed light on the time evolution of interactions between galactic bars and dark matter halos. The TW method has been extensively employed for nearby galaxies, and its accuracy in determining bar pattern s… ▽ More This paper examines the reliability of the Tremaine-Weinberg (TW) method in measuring the pattern speed of barred galaxies at high redshifts. Measuring pattern speeds at high redshift may help to shed light on the time evolution of interactions between galactic bars and dark matter halos. The TW method has been extensively employed for nearby galaxies, and its accuracy in determining bar pattern speeds has been validated through numerical simulations. For nearby galaxies, the method yields acceptable results when the inclination angle of the galaxy and the position angle of the bar fall within appropriate ranges. However, the application of the TW method to high-redshift galaxies remains unexplored in both observations and simulations. For this study we generated mock observations of barred galaxies from the TNG50 cosmological simulation. These simulated observations were tailored to mimic the integral field unit (IFU) spectroscopy data that the Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST) would capture at a redshift of $z\simeq 1.2$. By applying the TW method to these mock observations and comparing the results with the known pattern speeds, we demonstrate that the TW method performs adequately for barred galaxies whose bars are sufficiently long to be detected by JWST at high redshifts. This work opens a new avenue for applying the TW method to investigate the properties of high-redshift barred galaxies. △ Less

Submitted 21 August, 2025; v1 submitted 24 July, 2025; originally announced July 2025.

Comments: 14 pages (including two appendices), 10 figures; final accepted version for publication in A&A

Dissecting Bar-Induced Stellar Kinematics in Disk Galaxies: The Bisymmetric Model and Rotation Curve Modifications

Authors: Seungwon Baek, Woong-Tae Kim, Dajeong Jang, Taehyun Kim

Abstract: We analyze bars formed in $N$-body simulations to investigate two key aspects of stellar kinematic structure of barred galaxies: the angular distributions of the radial and azimuthal components of stellar velocities, and the impact of bars on rotation curves. We find that stars on bar-supporting $x_1$-like orbits exhibit characteristic sawtooth-like radial velocity patterns and arch-like tangentia… ▽ More We analyze bars formed in $N$-body simulations to investigate two key aspects of stellar kinematic structure of barred galaxies: the angular distributions of the radial and azimuthal components of stellar velocities, and the impact of bars on rotation curves. We find that stars on bar-supporting $x_1$-like orbits exhibit characteristic sawtooth-like radial velocity patterns and arch-like tangential velocity patterns as a function of azimuth. In contrast, stars on box and disk orbits show little azimuthal variation, effectively smoothing the overall velocity distribution. When averaged over all orbital families, the resulting kinematics are broadly consistent with the bisymmetric model of Spekkens & Sellwood, with the amplitudes of bar-induced velocity perturbations increasing with bar strength. In addition, bars amplify the radial pressure gradient associated with enhanced random stellar motions, leading to a noticeable reduction in the mean rotational velocity. This effect becomes more pronounced with increasing bar strength, resulting in a shallower rotation curve within the bar region. We discuss our results in the context of the kinematic properties of observed barred galaxies. △ Less

Submitted 20 July, 2025; originally announced July 2025.

Comments: 19 pages, 21 figures, 1 table, accepted for publication in ApJ

Impostor Among $ν$s: Dark Radiation Masquerading as Self-Interacting Neutrinos

Authors: Anirban Das, P. S. Bhupal Dev, Christina Gao, Subhajit Ghosh, Taegyun Kim

Abstract: Multiple cosmological observations hint at neutrino self-interactions beyond the Standard Model, yet such interactions face severe constraints from terrestrial experiments. We resolve this tension by introducing a model where active neutrinos resonantly convert to self-interacting dark radiation after BBN but before CMB epoch. This exploits the fact that cosmological observables cannot distinguish… ▽ More Multiple cosmological observations hint at neutrino self-interactions beyond the Standard Model, yet such interactions face severe constraints from terrestrial experiments. We resolve this tension by introducing a model where active neutrinos resonantly convert to self-interacting dark radiation after BBN but before CMB epoch. This exploits the fact that cosmological observables cannot distinguish between neutrinos and dark radiation with the same abundance and free-streaming properties. Our mechanism, based on a simple Type-I seesaw framework along with a keV-scale scalar mediator, achieves two objectives: (1) it produces strongly self-interacting dark radiation that imitates neutrino self-interactions favored by cosmological data, and (2) it depletes the active neutrino energy density, relaxing cosmological neutrino mass bounds and easing the tension with neutrino oscillation data. The model naturally evades laboratory constraints through suppression of the neutrino-mediator coupling by the squared mass ratio of active and sterile neutrinos. We demonstrate how this scenario is favored over $Λ$CDM by the combined Planck and DESI data, while being consistent with all other constraints. Our mechanism is testable in future laboratory probes of absolute neutrino mass and searches for sterile neutrinos. △ Less

Submitted 9 June, 2025; originally announced June 2025.

Comments: 5+14 pages, 3+7 captioned figures and 1+4 tables

Ensemble Modeling of the Solar Wind Flow with Boundary Conditions Governed by Synchronic Photospheric Magnetograms. I. Multi-point Validation in the Inner Heliosphere

Authors: Dinesha V. Hegde, Tae K. Kim, Nikolai V. Pogorelov, Shaela I. Jones, Charles N. Arge

Abstract: The solar wind (SW) is a vital component of space weather, providing a background for solar transients such as coronal mass ejections, stream interaction regions, and energetic particles propagating toward Earth. Accurate prediction of space weather events requires a precise description and thorough understanding of physical processes occurring in the ambient SW plasma. Ensemble simulations of the… ▽ More The solar wind (SW) is a vital component of space weather, providing a background for solar transients such as coronal mass ejections, stream interaction regions, and energetic particles propagating toward Earth. Accurate prediction of space weather events requires a precise description and thorough understanding of physical processes occurring in the ambient SW plasma. Ensemble simulations of the three-dimensional SW flow are performed using an empirically-driven magnetohydrodynamic heliosphere model implemented in the Multi-Scale Fluid-Kinetic Simulation Suite (MS-FLUKSS). The effect of uncertainties in the photospheric boundary conditions on the simulation outcome is investigated. The results are in good overall agreement with the observations from the Parker Solar Probe, Solar Orbiter, Solar Terrestrial Relations Observatory, and OMNI data at Earth, specifically during 2020-2021. This makes it possible to shed more light on the properties of the SW propagating through the heliosphere and perspectives for improving space weather forecasts. △ Less

Submitted 28 May, 2025; originally announced May 2025.

Comments: 36 Pages, 12 Figures, Accepted for publication in The Astrophysical Journal (ApJ)

Journal ref: The Astrophysical Journal, Volume 988, Number 2,154,2025

DarkNESS: A skipper-CCD NanoSatellite for Dark Matter Searches

Authors: Phoenix Alpine, Samriddhi Bhatia, Ana M. Botti, Brenda A. Cervantes-Vergara, Claudio R. Chavez, Fernando Chierchie, Alex Drlica-Wagner, Rouven Essig, Juan Estrada, Erez Etzion, Roni Harnik, Terry Kim, Michael Lembeck, Qi Lim, Bernard J. Rauscher, Nathan Saffold, Javier Tiffenberg, Sho Uemura, Hailin Xu

Abstract: The Dark matter Nanosatellite Equipped with Skipper Sensors (DarkNESS) deploys a recently developed skipper-CCD architecture with sub-electron readout noise in low Earth orbit (LEO) to investigate potential signatures of dark matter (DM). The mission addresses two interaction channels: electron recoils from strongly interacting sub-GeV DM and X-rays produced through decaying DM. Orbital observatio… ▽ More The Dark matter Nanosatellite Equipped with Skipper Sensors (DarkNESS) deploys a recently developed skipper-CCD architecture with sub-electron readout noise in low Earth orbit (LEO) to investigate potential signatures of dark matter (DM). The mission addresses two interaction channels: electron recoils from strongly interacting sub-GeV DM and X-rays produced through decaying DM. Orbital observations avoid attenuation that limits ground-based measurements, extending sensitivity reach for both channels. The mission proceeds toward launch following laboratory validation of the instrument. A launch opportunity has been secured through Firefly Aerospace's DREAM 2.0 program, awarded to the University of Illinois Urbana-Champaign (UIUC). This will constitute the first use of skipper-CCDs in space and evaluate their suitability for low-noise X-ray and single-photon detection in future space observatories. △ Less

Submitted 22 May, 2025; originally announced May 2025.

Comments: Submitted to Advances in Space Research. arXiv admin note: text overlap with arXiv:2412.12084

Report number: FERMILAB-PUB-25-0354-PPD

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

RVSNUpy: A Python Package for Spectroscopic Redshift Measurement Based on Cross-Correlation

Authors: Taewan Kim, Jubee Sohn, Ho Seong Hwang

Abstract: We introduce RVSNUpy, a new Python package designed to measure spectroscopic redshifts. Based on inverse-variance weighted cross-correlation, RVSNUpy determines the redshifts by comparing observed spectra with various rest-frame template spectra. We test the performance of RVSNUpy based on ~ 6000 objects in the HectoMAP redshift survey observed with both SDSS and MMT/Hectospec. We demonstrate that… ▽ More We introduce RVSNUpy, a new Python package designed to measure spectroscopic redshifts. Based on inverse-variance weighted cross-correlation, RVSNUpy determines the redshifts by comparing observed spectra with various rest-frame template spectra. We test the performance of RVSNUpy based on ~ 6000 objects in the HectoMAP redshift survey observed with both SDSS and MMT/Hectospec. We demonstrate that a slight redshift offset (~ 40 km/s) between SDSS and MMT/Hectospec measurements reported from previous studies results from the small offsets in the redshift template spectra used for SDSS and Hectospec reductions. We construct the universal set of template spectra, including empirical SDSS template spectra, carefully calibrated to the rest frame. Our test for the HectoMAP objects with duplicated observations shows that RVSNUpy with the universal template spectra yields the homogeneous redshift from the spectra obtained with different spectrographs. We highlight that RVSNUpy is a powerful redshift measurement tool for current and future large-scale spectroscopy surveys, including A-SPEC, DESI, 4MOST, and Subaru/PFS. △ Less

Submitted 3 May, 2025; originally announced May 2025.

Comments: 12 figures

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)

Planck isocurvature constraint on primordial black holes lighter than a kiloton

Authors: TaeHun Kim, Jinn-Ouk Gong, Donghui Jeong, Dong-Won Jung, Yeong Gyun Kim, Kang Young Lee

Abstract: We demonstrate that primordial black holes (PBHs) lighter than $10^9 \, \text{g}$, which evaporated before the Big Bang nucleosynthesis, can induce significant isocurvature perturbations due to their biased clustering amplitude and the branching ratio of the Hawking radiation differing from the abundance ratio. By leveraging the upper bound on the isocurvature perturbations from the cosmic microwa… ▽ More We demonstrate that primordial black holes (PBHs) lighter than $10^9 \, \text{g}$, which evaporated before the Big Bang nucleosynthesis, can induce significant isocurvature perturbations due to their biased clustering amplitude and the branching ratio of the Hawking radiation differing from the abundance ratio. By leveraging the upper bound on the isocurvature perturbations from the cosmic microwave background anisotropies reported by the Planck collaboration, we derive a new upper bound on the abundance of these light PBHs. △ Less

Submitted 5 July, 2025; v1 submitted 18 March, 2025; originally announced March 2025.

Comments: Discussions added and improved; 10 pages, 2 figures

Report number: APCTP-Pre2025-005

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)

ALMAGAL I. The ALMA evolutionary study of high-mass protocluster formation in the Galaxy. Presentation of the survey and early results

Authors: S. Molinari, P. Schilke, C. Battersby, P. T. P. Ho, A. Sanchez-Monge, A. Traficante, B. Jones, M. T. Beltran, H. Beuther, G. A. Fuller, Q. Zhang, R. S. Klessen, S. Walch, Y. -W. Tang, M. Benedettini, D. Elia, A. Coletta, C. Mininni, E. Schisano, A. Avison, C. Y. Law, A. Nucara, J. D. Soler, G. Stroud, J. Wallace , et al. (51 additional authors not shown)

Abstract: Fundamental questions about the physics responsible for fragmenting molecular parsec-scale clumps into cores of ~1000 au are still open, that only a statistically significant investigation with ALMA is able to address: what are the dominant agents that determine the core demographics, mass, and spatial distribution as a function of the physical properties of the hosting clumps, their evolutionary… ▽ More Fundamental questions about the physics responsible for fragmenting molecular parsec-scale clumps into cores of ~1000 au are still open, that only a statistically significant investigation with ALMA is able to address: what are the dominant agents that determine the core demographics, mass, and spatial distribution as a function of the physical properties of the hosting clumps, their evolutionary stage and the different Galactic environments in which they reside? To what extent extent is fragmentation driven by clumps dynamics or mass transport in filaments? With ALMAGAL we observed the 1.38 mm continuum and lines toward more than 1000 dense clumps in our Galaxy, with M>500M_sun, surface density > 0.1 g/cm2 and d<7.5 kpc. The ACA and two 12-m array setups were used to deliver a minimum resolution of ~1000 au over the entire sample distance range. The sample covers all evolutionary stages from infrared dark clouds (IRDCs) to HII regions from the tip of the Galactic bar to the outskirts of the Galaxy. The spectral setup includes several molecular lines to trace the multiscale physics and dynamics of gas, notably CH3CN, H2CO, SiO, CH3OH, DCN, HC3N, SO etc. We present an initial overview of the observations and the early science product and results, with a first characterization of the morphological properties of the continuum emission. We use "perimeter-versus-area" and convex hull-versus-area metrics to classify the different morphologies. More extended and morphologically complex shapes are found toward clumps that are relatively more evolved and have higher surface densities. △ Less

Submitted 7 March, 2025; originally announced March 2025.

Comments: 21 pages, 18 figures plus appendices. Astronomy & Astrophysics, accepted

Resolved Stellar Mass Estimation of Nearby Late-type Galaxies for the SPHEREx Era: Dependence on Stellar Population Synthesis Models

Authors: Jeong Hwan Lee, Minjin Kim, Taehyun Kim, Hyunjin Shim, Luis C. Ho, Ho Seong Hwang, Hyunmi Song, Dohyeong Kim, Yujin Yang, Woong-Seob Jeong

Abstract: The upcoming all-sky infrared spectrophotometric SPHEREx mission is set to provide spatially resolved stellar mass maps of nearby galaxies, offering more detailed insights than integrated light observations. In this study, we develop a strategy for estimating stellar mass using SPHEREx by examining the dependence on different stellar population synthesis (SPS) models and proposing new scaling rela… ▽ More The upcoming all-sky infrared spectrophotometric SPHEREx mission is set to provide spatially resolved stellar mass maps of nearby galaxies, offering more detailed insights than integrated light observations. In this study, we develop a strategy for estimating stellar mass using SPHEREx by examining the dependence on different stellar population synthesis (SPS) models and proposing new scaling relations based on simulated SPHEREx data. We estimate the resolved stellar masses of 19 nearby late-type galaxies from the PHANGS-MUSE survey, treating these as fiducial masses. By testing four SPS models covering infrared wavelengths, i.e., E-MILES, Bruzual \& Charlot 2003 (BC03), Charlot \& Bruzual 2019 (CB19), and FSPS, we find systematic differences in mass-to-light ratios at $3.6~{\rm μm}$ ($M_{\ast}/L_{\rm 3.6μm}$) among the SPS models. In particular, BC03 and CB19 yield mass-to-light ratios on average $\sim0.2-0.3~{\rm dex}$ lower than those from E-MILES and FSPS. These mass-to-light ratios strongly correlate with stellar age, indicating a significant impact of young stellar populations on stellar mass measurements. Our analysis, incorporating fiducial masses and simulated SPHEREx data, identifies the $1.6~{\rm μm}$ band as the optimal wavelength for stellar mass estimation, with the lowest scatter ($0.15-0.20~{\rm dex}$) of the stellar mass. This scatter can be further reduced to $0.10-0.12~{\rm dex}$ across all SPS models by incorporating optical and SPHEREx colors. These results can provide guidance for measuring the stellar masses of the numerous nearby galaxies that SPHEREx will survey. △ Less

Submitted 3 February, 2025; originally announced February 2025.

Comments: Accepted for publication in AJ, 29 pages, 14 figures, 2 tables, 1 appendix

Machine learning based Photometric Redshifts for Galaxies in the North Ecliptic Pole Wide field: catalogs of spectroscopic and photometric redshifts

Authors: Taewan Kim, Jubee Sohn, Ho Seong Hwang, Simon C. -C. Ho, Denis Burgarella, Tomotsugu Goto, Tetsuya Hashimoto, Woong-Seob Jeong, Seong Jin Kim, Matthew A. Malkan, Takamitsu Miyaji, Nagisa Oi, Hyunjin Shim, Hyunmi Song, Narae Hwang, Byeong-Gon Park

Abstract: We perform an MMT/Hectospec redshift survey of the North Ecliptic Pole Wide (NEPW) field covering 5.4 square degrees, and use it to estimate the photometric redshifts for the sources without spectroscopic redshifts. By combining 2572 newly measured redshifts from our survey with existing data from the literature, we create a large sample of 4421 galaxies with spectroscopic redshifts in the NEPW fi… ▽ More We perform an MMT/Hectospec redshift survey of the North Ecliptic Pole Wide (NEPW) field covering 5.4 square degrees, and use it to estimate the photometric redshifts for the sources without spectroscopic redshifts. By combining 2572 newly measured redshifts from our survey with existing data from the literature, we create a large sample of 4421 galaxies with spectroscopic redshifts in the NEPW field. Using this sample, we estimate photometric redshifts of 77755 sources in the band-merged catalog of the NEPW field with a random forest model. The estimated photometric redshifts are generally consistent with the spectroscopic redshifts, with a dispersion of 0.028, an outlier fraction of 7.3%, and a bias of -0.01. We find that the standard deviation of the prediction from each decision tree in the random forest model can be used to infer the fraction of catastrophic outliers and the measurement uncertainties. We test various combinations of input observables, including colors and magnitude uncertainties, and find that the details of these various combinations do not change the prediction accuracy much. As a result, we provide a catalog of 77755 sources in the NEPW field, which includes both spectroscopic and photometric redshifts up to z~2. This dataset has significant legacy value for studies in the NEPW region, especially with upcoming space missions such as JWST, Euclid, and SPHEREx. △ Less

Submitted 2 February, 2025; originally announced February 2025.

Comments: 18 pagees, 12 figures, 4 tables

Magnetohydrodynamic Simulation of a Coronal Mass Ejection Observed During the Near-radial Alignment of Solar Orbiter and Earth

Authors: Talwinder Singh, Dinesha V. Hegde, Tae K. Kim, Nikolai V. Pogorelov

Abstract: Interplanetary Coronal Mass Ejections (ICMEs) are the primary sources of geomagnetic storms at Earth. Negative out-of-ecliptic component (Bz) of magnetic field in the ICME or its associated sheath region is necessary for it to be geo-effective. For this reason, magnetohydrodynamic simulations of CMEs containing data-constrained flux ropes are more suitable for forecasting their geo-effectiveness a… ▽ More Interplanetary Coronal Mass Ejections (ICMEs) are the primary sources of geomagnetic storms at Earth. Negative out-of-ecliptic component (Bz) of magnetic field in the ICME or its associated sheath region is necessary for it to be geo-effective. For this reason, magnetohydrodynamic simulations of CMEs containing data-constrained flux ropes are more suitable for forecasting their geo-effectiveness as compared to hydrodynamic models of the CME. ICMEs observed in situ by radially aligned spacecraft can provide an important setup to validate the physics-based heliospheric modeling of CMEs. In this work, we use the constant-turn flux rope (CTFR) model to study an ICME that was observed in situ by Solar Orbiter (SolO) and at Earth, when they were in a near-radial alignment. This was a stealth CME that erupted on 2020 April 14 and reached Earth on 2020 April 20 with a weak shock and a smoothly rotating magnetic field signature. We found that the CTFR model was able to reproduce the rotating magnetic field signature at both SolO and Earth with very good accuracy. The simulated ICME arrived 5 hours late at SolO and 5 hours ahead at Earth, when compared to the observed ICME. We compare the propagation of the CME front through the inner heliosphere using synthetic J-maps and those observed in the heliospheric imager data and discuss the role of incorrect ambient SW background on kinematics of the simulated CME. This study supports the choice of the CTFR model for reproducing the magnetic field of ICMEs. △ Less

Submitted 31 January, 2025; originally announced February 2025.

Multiple Populations of the Large Magellanic Cloud Globular Cluster NGC 2257: No Major Environmental Effect on the Formation of Multiple Populations of the Old Globular Clusters in Large Magellanic Cloud

Authors: Jae-Woo Lee, Tae-Hyeong Kim, Hak-Sub Kim, Hyun-Il Sung, Hwihyun Kim, Francesco Di Mille

Abstract: How the environment of the host galaxy affects the formation of multiple populations (MPs) in globular clusters (GCs) is one of the outstanding questions in the near-field cosmology. To understand the true nature of the old GC MPs in the Large Magellanic Cloud (LMC), we study the Ca--CN--CH photometry of the old metal-poor LMC GC NGC 2257. We find the predominantly FG-dominated populational number… ▽ More How the environment of the host galaxy affects the formation of multiple populations (MPs) in globular clusters (GCs) is one of the outstanding questions in the near-field cosmology. To understand the true nature of the old GC MPs in the Large Magellanic Cloud (LMC), we study the Ca--CN--CH photometry of the old metal-poor LMC GC NGC 2257. We find the predominantly FG-dominated populational number ratio of $n$(FG):$n$(SG) = 61:39($\pm$4), where the FG and SG denote the first and second generations. Both the FG and SG have similar cumulative radial distributions, consistent with the idea that NGC 2257 is dynamically old. We obtain [Fe/H] = $-$1.78$\pm$0.00 dex($σ$=0.05 dex) and our metallicity is $\sim$0.2 dex larger than that from the high-resolution spectroscopy by other, due to their significantly lower temperatures by $\sim$ $-$200 K. The NGC 2257 FG shows a somewhat larger metallicity variation than the SG, the first detection of such phenomenon in an old LMC GC, similar to Galactic GCs with MPs, strongly suggesting that it is a general characteristic of GCs with MPs. Interestingly, the NGC 2257 SG does not show a helium enhancement compared to the FG. Our results for the Galactic normal GCs exhibit that the degree of carbon and nitrogen variations are tightly correlated with the GC mass, while NGC 2257 exhibits slightly smaller variations for its mass. We show that old LMC GCs follow the same trends as the Galactic normal GCs in the $Δ$W$_{\rm CF336W,F438W,F814W}$, $N_{\rm FG}/N_{\rm tot}$, and $\log M/M_{\rm \odot}$ domains. Our result indicates that the environment of the host galaxy did not play a major role in the formation and evolution of GC MPs. △ Less

Submitted 9 January, 2025; originally announced January 2025.

Comments: Accepted for publication in The Astronomical Journal; 19 figures and 1 table

Prediction of Star Formation Rates Using an Artificial Neural Network

Authors: Ashraf Ayubinia, Jong-hak Woo, Fatemeh Hafezianzadeh, Taehwan Kim, Changseok Kim

Abstract: In this study, we develop an artificial neural network to estimate the infrared (IR) luminosity and star formation rates (SFR) of galaxies. Our network is trained using 'true' IR luminosity values derived from modeling the IR spectral energy distributions (SEDs) of FIR-detected galaxies. We explore five different sets of input features, each incorporating optical, mid-infrared (MIR), near-infrared… ▽ More In this study, we develop an artificial neural network to estimate the infrared (IR) luminosity and star formation rates (SFR) of galaxies. Our network is trained using 'true' IR luminosity values derived from modeling the IR spectral energy distributions (SEDs) of FIR-detected galaxies. We explore five different sets of input features, each incorporating optical, mid-infrared (MIR), near-infrared (NIR), ultraviolet (UV), and emission line data, along with spectroscopic redshifts and uncertainties. All feature sets yield similar IR luminosity predictions, but including all photometric data leads to slightly improved performance. This suggests that comprehensive photometric information enhances the accuracy of our predictions. Our network is applied to a sample of SDSS galaxies defined as unseen data, and the results are compared with three published catalogs of SFRs. Overall, our network demonstrates excellent performance for star-forming galaxies while we observe discrepancies in composite and AGN samples. These inconsistencies may stem from uncertainties inherent in the compared catalogs or potential limitations in the performance of our network. △ Less

Submitted 23 December, 2024; originally announced December 2024.

Comments: 13 pages, 7 figures, and 2 tables. Accepted for publication in ApJ

Accuracy of Stellar Mass-to-light Ratios of Nearby Galaxies in the Near-Infrared

Authors: Taehyun Kim, Minjin Kim, Luis C. Ho, Yang A. Li, Woong-Seob Jeong, Dohyeong Kim, Yongjung Kim, Bomee Lee, Dongseob Lee, Jeong Hwan Lee, Jeonghyun Pyo, Hyunjin Shim, Suyeon Son, Hyunmi Song, Yujin Yang

Abstract: Future satellite missions are expected to perform all-sky surveys, thus providing the entire sky near-infrared spectral data and consequently opening a new window to investigate the evolution of galaxies. Specifically, the infrared spectral data facilitate the precise estimation of stellar masses of numerous low-redshift galaxies. We utilize the synthetic spectral energy distribution (SED) of 2853… ▽ More Future satellite missions are expected to perform all-sky surveys, thus providing the entire sky near-infrared spectral data and consequently opening a new window to investigate the evolution of galaxies. Specifically, the infrared spectral data facilitate the precise estimation of stellar masses of numerous low-redshift galaxies. We utilize the synthetic spectral energy distribution (SED) of 2853 nearby galaxies drawn from the DustPedia (435) and Stripe 82 regions (2418). The stellar mass-to-light ratio ($M_*/L$) estimation accuracy over a wavelength range of $0.75-5.0$ $μ$m is computed through the SED fitting of the multi-wavelength photometric dataset, which has not yet been intensively explored in previous studies. We find that the scatter in $M_*/L$ is significantly larger in the shorter and longer wavelength regimes due to the effect of the young stellar population and the dust contribution, respectively. While the scatter in $M_*/L$ approaches its minimum ($\sim0.10$ dex) at $\sim1.6$ $μ$m, it remains sensitive to the adopted star formation history model. Furthermore, $M_*/L$ demonstrates weak and strong correlations with the stellar mass and the specific star formation rate (SFR), respectively. Upon adequately correcting the dependence of $M_*/L$ on the specific SFR, the scatter in the $M_*/L$ further reduces to $0.02$ dex at $\sim1.6$ $μ$m. This indicates that the stellar mass can be estimated with an accuracy of $\sim0.02$ dex with a prior knowledge of SFR, which can be estimated using the infrared spectra obtained with future survey missions. △ Less

Submitted 17 November, 2024; originally announced November 2024.

Comments: Accepted for publication in AJ. 19 pages, 14 figures

Primordial Black Hole Reformation in the Early Universe

Authors: Taehun Kim, Philip Lu

Abstract: Primordial black holes (PBH) can arise in a wide range of scenarios, from inflation to first-order phase transitions. Light PBHs, such as those produced during preheating, in bounce cosmologies, or at the GUT scale, could induce an early matter-dominated phase given a moderate initial abundance. During the early matter domination, the growth of initial PBH density perturbations can trigger collaps… ▽ More Primordial black holes (PBH) can arise in a wide range of scenarios, from inflation to first-order phase transitions. Light PBHs, such as those produced during preheating, in bounce cosmologies, or at the GUT scale, could induce an early matter-dominated phase given a moderate initial abundance. During the early matter domination, the growth of initial PBH density perturbations can trigger collapse on horizon scales, producing much heavier PBHs. While the remaining original PBHs evaporate and reheat the Universe, these massive reformed PBHs survive for an extended period of time, producing potentially observable signatures at the present. We study this PBH reformation scenario and show that those reformed PBHs can emit significant quantities of gamma rays detectable by the next generation of experiments. The rapid reheating after matter domination generates a coincident stochastic gravitational wave background, which could be within the range of the upcoming CMB-S4 experiment. The PBH reformation scenario provides an intriguing possibility of decoupling the current PBH population and the initial formation mechanism from early Universe physics, while providing opportunities for observation through multi-messenger astronomy. △ Less

Submitted 16 April, 2025; v1 submitted 11 November, 2024; originally announced November 2024.

Comments: 10 pages, 5 figures

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

Weak-lensing Mass Reconstruction of Galaxy Clusters with a Convolutional Neural Network -- II: Application to Next-Generation Wide-Field Surveys

Authors: Sangjun Cha, M. James Jee, Sungwook E. Hong, Sangnam Park, Dongsu Bak, Taehwan kim

Abstract: Traditional weak-lensing mass reconstruction techniques suffer from various artifacts, including noise amplification and the mass-sheet degeneracy. In Hong et al. (2021), we demonstrated that many of these pitfalls of traditional mass reconstruction can be mitigated using a deep learning approach based on a convolutional neural network (CNN). In this paper, we present our improvements and report o… ▽ More Traditional weak-lensing mass reconstruction techniques suffer from various artifacts, including noise amplification and the mass-sheet degeneracy. In Hong et al. (2021), we demonstrated that many of these pitfalls of traditional mass reconstruction can be mitigated using a deep learning approach based on a convolutional neural network (CNN). In this paper, we present our improvements and report on the detailed performance of our CNN algorithm applied to next-generation wide-field observations. Assuming the field of view ($3°.5 \times 3°.5$) and depth (27 mag at $5σ$) of the Vera C. Rubin Observatory, we generated training datasets of mock shear catalogs with a source density of 33 arcmin$^{-2}$ from cosmological simulation ray-tracing data. We find that the current CNN method provides high-fidelity reconstructions consistent with the true convergence field, restoring both small and large-scale structures. In addition, the cluster detection utilizing our CNN reconstruction achieves $\sim75$% completeness down to $\sim 10^{14}M_{\odot}$. We anticipate that this CNN-based mass reconstruction will be a powerful tool in the Rubin era, enabling fast and robust wide-field mass reconstructions on a routine basis. △ Less

Submitted 26 February, 2025; v1 submitted 25 October, 2024; originally announced October 2024.

Comments: 11 pages, 8 figures. Published in ApJ

Journal ref: 2025 ApJ 981 52

Chandra Survey in the AKARI North Ecliptic Pole Deep Field Optical/Infrared Identifications of X-ray Sources

Authors: T. Miyaji, B. A. Bravo-Navarro, J. Díaz Tello, M. Krumpe, M. Herrera-Endoqui, H. Ikeda, T. Takagi, N. Oi, A. Shogaki, S. Matsuura, H. Kim, M. A. Malkan, H. S. Hwang, T. Kim, T. Ishigaki, H. Hanami, S. J. Kim, Y. Ohyama, T. Goto, H. Matsuhara

Abstract: We present a catalog of optical and infrared identifications (ID) of X-ray sources in the AKARI North Ecliptic Pole (NEP) Deep field detected with Chandra covering $\sim 0.34\,{\rm deg^{2}}$ with 0.5-2 keV flux limits ranging $\sim 2 \mathrm{-} 20\times 10^{-16}\,{\rm erg\,s^{-1}\,cm^{-2}}$. The optical/near-infrared counterparts of the X-ray sources are taken from our Hyper Suprime Cam (HSC)/Suba… ▽ More We present a catalog of optical and infrared identifications (ID) of X-ray sources in the AKARI North Ecliptic Pole (NEP) Deep field detected with Chandra covering $\sim 0.34\,{\rm deg^{2}}$ with 0.5-2 keV flux limits ranging $\sim 2 \mathrm{-} 20\times 10^{-16}\,{\rm erg\,s^{-1}\,cm^{-2}}$. The optical/near-infrared counterparts of the X-ray sources are taken from our Hyper Suprime Cam (HSC)/Subaru and Wide-Field InfraRed Camera (WIRCam)/Canada-France-Hawaii Telescope (CFHT) data because these have much more accurate source positions due to their spatial resolution than that of {Chandra} and longer wavelength infrared data. We concentrate our identifications in the HSC $g$ band and WIRCam $K_{\rm s}$ band-based catalogs. To select the best counterpart, we utilize a novel extension of the likelihood-ratio (LR) analysis, where we use the X-ray flux as well as $g - K_{\rm s}$ colors to calculate the likelihood ratio. Spectroscopic and photometric redshifts of the counterparts are summarized. Also, simple X-ray spectroscopy is made on the sources with sufficient source counts. We present the resulting catalog in an electronic form. The main ID catalog contains 403 X-ray sources and includes X-ray fluxes, luminosities, $g$ and $K_{\rm s}$ band magnitudes, redshifts, and their sources, optical spectroscopic properties, as well as intrinsic absorption column densities and power-law indices from simple X-ray spectroscopy. The identified X-ray sources include 27 Milky-Way objects, 57 type I AGNs, 131 other AGNs, and 15 galaxies. The catalog serves as a basis for further investigations of the properties of the X-ray and near-infrared sources in this field. (Abridged) △ Less

Submitted 22 July, 2024; v1 submitted 18 July, 2024; originally announced July 2024.

Comments: 16 pages, 9 figures, Three electronic (fits) tables are included in src. Accepted to Astronomy and Astrophysics

Journal ref: A&A 689, A83 (2024)

Development of MMC-based lithium molybdate cryogenic calorimeters for AMoRE-II

Authors: A. Agrawal, V. V. Alenkov, P. Aryal, H. Bae, J. Beyer, B. Bhandari, R. S. Boiko, K. Boonin, O. Buzanov, C. R. Byeon, N. Chanthima, M. K. Cheoun, J. S. Choe, S. Choi, S. Choudhury, J. S. Chung, F. A. Danevich, M. Djamal, D. Drung, C. Enss, A. Fleischmann, A. M. Gangapshev, L. Gastaldo, Y. M. Gavrilyuk, A. M. Gezhaev , et al. (84 additional authors not shown)

Abstract: The AMoRE collaboration searches for neutrinoless double beta decay of $^{100}$Mo using molybdate scintillating crystals via low temperature thermal calorimetric detection. The early phases of the experiment, AMoRE-pilot and AMoRE-I, have demonstrated competitive discovery potential. Presently, the AMoRE-II experiment, featuring a large detector array with about 90 kg of $^{100}$Mo isotope, is und… ▽ More The AMoRE collaboration searches for neutrinoless double beta decay of $^{100}$Mo using molybdate scintillating crystals via low temperature thermal calorimetric detection. The early phases of the experiment, AMoRE-pilot and AMoRE-I, have demonstrated competitive discovery potential. Presently, the AMoRE-II experiment, featuring a large detector array with about 90 kg of $^{100}$Mo isotope, is under construction. This paper discusses the baseline design and characterization of the lithium molybdate cryogenic calorimeters to be used in the AMoRE-II detector modules. The results from prototype setups that incorporate new housing structures and two different crystal masses (316 g and 517 - 521 g), operated at 10 mK temperature, show energy resolutions (FWHM) of 7.55 - 8.82 keV at the 2.615 MeV $^{208}$Tl $γ$ line, and effective light detection of 0.79 - 0.96 keV/MeV. The simultaneous heat and light detection enables clear separation of alpha particles with a discrimination power of 12.37 - 19.50 at the energy region around $^6$Li(n, $α$)$^3$H with Q-value = 4.785 MeV. Promising detector performances were demonstrated at temperatures as high as 30 mK, which relaxes the temperature constraints for operating the large AMoRE-II array. △ Less

Submitted 3 March, 2025; v1 submitted 16 July, 2024; originally announced July 2024.

Journal ref: Eur. Phys. J. C 85, 172 (2025)

Q-Balls in the presence of attractive force

Authors: Yu Hamada, Kiyoharu Kawana, TaeHun Kim, Philip Lu

Abstract: Q-balls are non-topological solitons in field theories whose stability is typically guaranteed by the existence of a global conserved charge. A classic realization is the Friedberg-Lee-Sirlin (FLS) Q-ball in a two-scalar system where a real scalar $χ$ triggers symmetry breaking and confines a complex scalar $Φ$ with a global $U(1)$ symmetry. A quartic interaction $κχ^2|Φ|^2$ with $κ>0$ is usually… ▽ More Q-balls are non-topological solitons in field theories whose stability is typically guaranteed by the existence of a global conserved charge. A classic realization is the Friedberg-Lee-Sirlin (FLS) Q-ball in a two-scalar system where a real scalar $χ$ triggers symmetry breaking and confines a complex scalar $Φ$ with a global $U(1)$ symmetry. A quartic interaction $κχ^2|Φ|^2$ with $κ>0$ is usually considered to produce a nontrivial Q-ball configuration, and this repulsive force contributes to its stability. On the other hand, the attractive cubic interaction $Λχ|Φ|^2$ is generally allowed in a renormalizable theory and could induce an instability. In this paper, we study the behavior of the Q-ball under the influence of this attractive force which has been overlooked. We find approximate Q-ball solutions in the limit of weak and moderate force couplings using the thin-wall and thick-wall approximations respectively. Our analytical results are consistent with numerical simulations and predict the parameter dependencies of the maximum charge. A crucial difference with the ordinary FLS Q-ball is the existence of the maximum charge beyond which the Q-ball solution is classically unstable. Such a limitation of the charge fundamentally affects Q-ball formation in the early Universe and could plausibly lead to the formation of primordial black holes. △ Less

Submitted 1 September, 2024; v1 submitted 15 July, 2024; originally announced July 2024.

Comments: Matches with the published version; 30 pages, 6 figures

Report number: DESY-24-102

Journal ref: JHEP 08 (2024) 242

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

Deeper, Sharper, Faster: Application of Efficient Transformer to Galaxy Image Restoration

Authors: Hyosun Park, Yongsik Jo, Seokun Kang, Taehwan Kim, M. James Jee

Abstract: The Transformer architecture has revolutionized the field of deep learning over the past several years in diverse areas, including natural language processing, code generation, image recognition, time series forecasting, etc. We propose to apply Zamir et al.'s efficient transformer to perform deconvolution and denoising to enhance astronomical images. We conducted experiments using pairs of high-q… ▽ More The Transformer architecture has revolutionized the field of deep learning over the past several years in diverse areas, including natural language processing, code generation, image recognition, time series forecasting, etc. We propose to apply Zamir et al.'s efficient transformer to perform deconvolution and denoising to enhance astronomical images. We conducted experiments using pairs of high-quality images and their degraded versions, and our deep learning model demonstrates exceptional restoration of photometric, structural, and morphological information. When compared with the ground-truth JWST images, the enhanced versions of our HST-quality images reduce the scatter of isophotal photometry, Sersic index, and half-light radius by factors of 4.4, 3.6, and 4.7, respectively, with Pearson correlation coefficients approaching unity. The performance is observed to degrade when input images exhibit correlated noise, point-like sources, and artifacts. We anticipate that this deep learning model will prove valuable for a number of scientific applications, including precision photometry, morphological analysis, and shear calibration. △ Less

Submitted 29 May, 2024; v1 submitted 29 March, 2024; originally announced April 2024.

Comments: 18 pages, 14 figures, 1 table, Resubmitted to ApJ after the first revision

Maunakea Spectroscopic Explorer exposure time calculator for end-to-end simulator: to optimizing spectrograph design and observing simulation

Authors: Tae-Geun Ji, Jennifer Sobeck, Changgon Kim, Hojae Ahn, Mingyeong Yang, Taeeun Kim, Sungwook E. Hong, Kei Szeto, Jennifer L. Marshall, Christian Surace, Soojong Pak

Abstract: The Maunakea Spectroscopic Explorer (MSE) project will provide multi-object spectroscopy in the optical and near-infrared bands using an 11.25-m aperture telescope, repurposing the original Canada-France-Hawaii Telescope (CFHT) site. MSE will observe 4,332 objects per single exposure with a field of view of 1.5 square degrees, utilizing two spectrographs with low-moderate (R$\sim$3,000, 6,000) and… ▽ More The Maunakea Spectroscopic Explorer (MSE) project will provide multi-object spectroscopy in the optical and near-infrared bands using an 11.25-m aperture telescope, repurposing the original Canada-France-Hawaii Telescope (CFHT) site. MSE will observe 4,332 objects per single exposure with a field of view of 1.5 square degrees, utilizing two spectrographs with low-moderate (R$\sim$3,000, 6,000) and high (R$\approx$30,000) spectral resolution. In general, an exposure time calculator (ETC) is used to estimate the performance of an observing system by calculating a signal-to-noise ratio (S/N) and exposure time. We present the design of the MSE exposure time calculator (ETC), which has four calculation modes (S/N, exposure time, S/N trend with wavelength, and S/N trend with magnitude) and incorporates the MSE system requirements as specified in the Conceptual Design. The MSE ETC currently allows for user-defined inputs of target AB magnitude, water vapor, airmass, and sky brightness AB magnitude (additional user inputs can be provided depending on computational mode). The ETC is built using Python 3.7 and features a graphical user interface that allows for cross-platform use. The development process of the ETC software follows an Agile methodology and utilizes the Unified Modeling Language (UML) diagrams to visualize the software architecture. We also describe the testing and verification of the MSE ETC. △ Less

Submitted 16 January, 2024; originally announced January 2024.

Comments: 30 pages, 13 figures

Journal ref: J. Astron. Telesc. Instrum. Syst., Vol. 10, Issue 01, 018001 (2024)

Stability of Hydrides in Sub-Neptune Exoplanets with Thick Hydrogen-Rich Atmospheres

Authors: Taehyun Kim, Xuehui Wei, Stella Chariton, Vitali B. Prakapenka, Young-Jay Ryu, Shize Yang, Sang-Heon Shim

Abstract: Many sub-Neptune exoplanets have been believed to be composed of a thick hydrogen-dominated atmosphere and a high-temperature heavier-element-dominant core. From an assumption that there is no chemical reaction between hydrogen and silicates/metals at the atmosphere-interior boundary, the cores of sub-Neptunes have been modeled with molten silicates and metals (magma) in previous studies. In large… ▽ More Many sub-Neptune exoplanets have been believed to be composed of a thick hydrogen-dominated atmosphere and a high-temperature heavier-element-dominant core. From an assumption that there is no chemical reaction between hydrogen and silicates/metals at the atmosphere-interior boundary, the cores of sub-Neptunes have been modeled with molten silicates and metals (magma) in previous studies. In large sub-Neptunes, pressure at the atmosphere-magma boundary can reach tens of gigapascals where hydrogen is a dense liquid. A recent experiment showed that hydrogen can induce the reduction of Fe$^{2+}$ in (Mg,Fe)O to Fe$^0$ metal at the pressure-temperature conditions relevant to the atmosphere-interior boundary. However, it is unclear if Mg, one of the abundant heavy elements in the planetary interiors, remains oxidized or can be reduced by H. Our experiments in the laser-heated diamond-anvil cell found that heating of MgO + Fe to 3500-4900 K (close to or above their melting temperatures) in a H medium leads to the formation of Mg$_2$FeH$_6$ and H$_2$O at 8-13 GPa. At 26-29 GPa, the behavior of the system changes, and Mg-H in an H fluid and H$_2$O were detected with separate FeH$_x$. The observations indicate the dissociation of the Mg-O bond by H and subsequent production of hydride and water. Therefore, the atmosphere-magma interaction can lead to a fundamentally different mineralogy for sub-Neptune exoplanets compared with rocky planets. The change in the chemical reaction at the higher pressures can also affect the size demographics (i.e., "radius cliff") and the atmosphere chemistry of sub-Neptune exoplanets. △ Less

Submitted 5 January, 2024; originally announced January 2024.

Journal ref: Proceedings of the National Academy of Sciences 120, no. 52 (2023): e2309786120

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 Seoul National University AGN Monitoring Project III: H$β$ lag measurements of 32 luminous AGNs and the high-luminosity end of the size--luminosity relation

Authors: Jong-Hak Woo, Shu Wang, Suvendu Rakshit, Hojin Cho, Donghoon Son, Vardha N. Bennert, Elena Gallo, Edmund Hodges-Kluck, Tommaso Treu, Aaron J. Barth, Wanjin Cho, Adi Foord, Jaehyuk Geum, Hengxiao Guo, Yashashree Jadhav, Yiseul Jeon, Kyle M. Kabasares, Won-Suk Kang, Changseok Kim, Minjin Kim, Tae-Woo Kim, Huynh Anh N. Le, Matthew A. Malkan, Amit Kumar Mandal, Daeseong Park , et al. (6 additional authors not shown)

Abstract: We present the main results from a long-term reverberation mapping campaign carried out for the Seoul National University Active Galactic Nuclei (AGN) Monitoring Project. High-quality data were obtained during 2015-2021 for 32 luminous AGNs (i.e., continuum luminosity in the range of $10^{44-46}$ erg s$^{-1}$) at a regular cadence, of 20-30 days for spectroscopy and 3-5 days for photometry. We obt… ▽ More We present the main results from a long-term reverberation mapping campaign carried out for the Seoul National University Active Galactic Nuclei (AGN) Monitoring Project. High-quality data were obtained during 2015-2021 for 32 luminous AGNs (i.e., continuum luminosity in the range of $10^{44-46}$ erg s$^{-1}$) at a regular cadence, of 20-30 days for spectroscopy and 3-5 days for photometry. We obtain time lag measurements between the variability in the H$β$ emission and the continuum for 32 AGNs; twenty-five of those have the best lag measurements based on our quality assessment, examining correlation strength, and the posterior lag distribution. Our study significantly increases the current sample of reverberation-mapped AGNs, particularly at the moderate to high luminosity end. Combining our results with literature measurements, we derive a H$β$ broad line region size--luminosity relation with a shallower slope than reported in the literature. For a given luminosity, most of our measured lags are shorter than the expectation, implying that single-epoch black hole mass estimators based on previous calibrations could suffer large systematic uncertainties. △ Less

Submitted 26 November, 2023; originally announced November 2023.

Comments: Accepted by ApJ; 39 pages, 22 figures

Emergent particles of de Sitter: thermal interpretation of the stochastic formalism and beyond

Authors: TaeHun Kim

Abstract: A thermal interpretation of the stochastic formalism of a slow-rolling scalar field in de Sitter (dS) is given. We construct a correspondence between Hubble patches of dS and particles living in another space called an abstract space. By assuming a dual description of scalar fields and classical mechanics in the abstract space, we show that the stochastic evolution of the infrared part of the fiel… ▽ More A thermal interpretation of the stochastic formalism of a slow-rolling scalar field in de Sitter (dS) is given. We construct a correspondence between Hubble patches of dS and particles living in another space called an abstract space. By assuming a dual description of scalar fields and classical mechanics in the abstract space, we show that the stochastic evolution of the infrared part of the field is equivalent to the Brownian motion in the abstract space filled with a heat bath of massless particles. The 1st slow-roll condition and the Hubble expansion are also reinterpreted in the abstract space as the speed of light and a transfer of conserved energy, respectively. Inspired by this, we sketch quantum emergent particles, which may realize the Hubble expansion by an exponential particle production. This gives another meaning of dS entropy as entropy per Hubble volume. △ Less

Submitted 6 August, 2024; v1 submitted 23 October, 2023; originally announced October 2023.

Comments: Discussions added and improved; matches with the published version; 28 pages, 2 figures

Journal ref: JCAP 08 (2024) 009

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

Regurgitated Dark Matter

Authors: TaeHun Kim, Philip Lu, Danny Marfatia, Volodymyr Takhistov

Abstract: We present a new paradigm for the production of the dark matter (DM) relic abundance based on the evaporation of early Universe primordial black holes (PBHs) themselves formed from DM particles. As a concrete realization, we consider a minimal model of the dark sector in which a first-order phase transition results in the formation of Fermiball remnants that collapse to PBHs, which then emit DM pa… ▽ More We present a new paradigm for the production of the dark matter (DM) relic abundance based on the evaporation of early Universe primordial black holes (PBHs) themselves formed from DM particles. As a concrete realization, we consider a minimal model of the dark sector in which a first-order phase transition results in the formation of Fermiball remnants that collapse to PBHs, which then emit DM particles. We show that the regurgitated DM scenario allows for DM in the mass range $\sim1$ GeV $- \,10^{16}$ GeV, thereby unlocking parameter space considered excluded. △ Less

Submitted 26 August, 2024; v1 submitted 11 September, 2023; originally announced September 2023.

Comments: 12 pages, 2 figures; matches publication as Letter in Physical Review D

Report number: KEK-QUP-2023-0019, KEK-TH-2550, KEK-Cosmo-0321, IPMU23-0029

Journal ref: Phys. Rev. D 110, L051702 (2024)

The Seoul National University AGN Monitoring Project IV: H$α$ reverberation mapping of 6 AGNs and the H$α$ Size-Luminosity Relation

Authors: Hojin Cho, Jong-Hak Woo, Shu Wang, Donghoon Son, Jaejin Shin, Suvendu Rakshit, Aaron J. Barth, Vardha N. Bennert, Elena Gallo, Edmund Hodges-Kluck, Tommaso Treu, Hyun-Jin Bae, Wanjin Cho, Adi Foord, Jaehyuk Geum, Yashashree Jadhav, Yiseul Jeon, Kyle M. Kabasares, Daeun Kang, Wonseok Kang, Changseok Kim, Donghwa Kim, Minjin Kim, Taewoo Kim, Huynh Anh N. Le , et al. (7 additional authors not shown)

Abstract: The broad line region (BLR) size-luminosity relation has paramount importance for estimating the mass of black holes in active galactic nuclei (AGNs). Traditionally, the size of the H$β$ BLR is often estimated from the optical continuum luminosity at 5100\angstrom{} , while the size of the H$α$ BLR and its correlation with the luminosity is much less constrained. As a part of the Seoul National Un… ▽ More The broad line region (BLR) size-luminosity relation has paramount importance for estimating the mass of black holes in active galactic nuclei (AGNs). Traditionally, the size of the H$β$ BLR is often estimated from the optical continuum luminosity at 5100\angstrom{} , while the size of the H$α$ BLR and its correlation with the luminosity is much less constrained. As a part of the Seoul National University AGN Monitoring Project (SAMP) which provides six-year photometric and spectroscopic monitoring data, we present our measurements of the H$α$ lags of 6 high-luminosity AGNs. Combined with the measurements for 42 AGNs from the literature, we derive the size-luminosity relations of H$α$ BLR against broad H$α$ and 5100\angstrom{} continuum luminosities. We find the slope of the relations to be $0.61\pm0.04$ and $0.59\pm0.04$, respectively, which are consistent with the \hb{} size-luminosity relation. Moreover, we find a linear relation between the 5100\angstrom{} continuum luminosity and the broad H$α$ luminosity across 7 orders of magnitude. Using these results, we propose a new virial mass estimator based on the H$α$ broad emission line, finding that the previous mass estimates based on the scaling relations in the literature are overestimated by up to 0.7 dex at masses lower than $10^7$~M$_{\odot}$. △ Less

Submitted 29 June, 2023; originally announced June 2023.

Comments: Accepted for publication in ApJ (Jun. 25th, 2023). 21 pages, 12 figures

Coronal Heating as Determined by the Solar Flare Frequency Distribution Obtained by Aggregating Case Studies

Authors: James Paul Mason, Alexandra Werth, Colin G. West, Allison A. Youngblood, Donald L. Woodraska, Courtney Peck, Kevin Lacjak, Florian G. Frick, Moutamen Gabir, Reema A. Alsinan, Thomas Jacobsen, Mohammad Alrubaie, Kayla M. Chizmar, Benjamin P. Lau, Lizbeth Montoya Dominguez, David Price, Dylan R. Butler, Connor J. Biron, Nikita Feoktistov, Kai Dewey, N. E. Loomis, Michal Bodzianowski, Connor Kuybus, Henry Dietrick, Aubrey M. Wolfe , et al. (977 additional authors not shown)

Abstract: Flare frequency distributions represent a key approach to addressing one of the largest problems in solar and stellar physics: determining the mechanism that counter-intuitively heats coronae to temperatures that are orders of magnitude hotter than the corresponding photospheres. It is widely accepted that the magnetic field is responsible for the heating, but there are two competing mechanisms th… ▽ More Flare frequency distributions represent a key approach to addressing one of the largest problems in solar and stellar physics: determining the mechanism that counter-intuitively heats coronae to temperatures that are orders of magnitude hotter than the corresponding photospheres. It is widely accepted that the magnetic field is responsible for the heating, but there are two competing mechanisms that could explain it: nanoflares or Alfvén waves. To date, neither can be directly observed. Nanoflares are, by definition, extremely small, but their aggregate energy release could represent a substantial heating mechanism, presuming they are sufficiently abundant. One way to test this presumption is via the flare frequency distribution, which describes how often flares of various energies occur. If the slope of the power law fitting the flare frequency distribution is above a critical threshold, $α=2$ as established in prior literature, then there should be a sufficient abundance of nanoflares to explain coronal heating. We performed $>$600 case studies of solar flares, made possible by an unprecedented number of data analysts via three semesters of an undergraduate physics laboratory course. This allowed us to include two crucial, but nontrivial, analysis methods: pre-flare baseline subtraction and computation of the flare energy, which requires determining flare start and stop times. We aggregated the results of these analyses into a statistical study to determine that $α= 1.63 \pm 0.03$. This is below the critical threshold, suggesting that Alfvén waves are an important driver of coronal heating. △ Less

Submitted 9 May, 2023; originally announced May 2023.

Comments: 1,002 authors, 14 pages, 4 figures, 3 tables, published by The Astrophysical Journal on 2023-05-09, volume 948, page 71

Onboard Science Instrument Autonomy for the Detection of Microscopy Biosignatures on the Ocean Worlds Life Surveyor

Authors: Mark Wronkiewicz, Jake Lee, Lukas Mandrake, Jack Lightholder, Gary Doran, Steffen Mauceri, Taewoo Kim, Nathan Oborny, Thomas Schibler, Jay Nadeau, James K. Wallace, Eshaan Moorjani, Chris Lindensmith

Abstract: The quest to find extraterrestrial life is a critical scientific endeavor with civilization-level implications. Icy moons in our solar system are promising targets for exploration because their liquid oceans make them potential habitats for microscopic life. However, the lack of a precise definition of life poses a fundamental challenge to formulating detection strategies. To increase the chances… ▽ More The quest to find extraterrestrial life is a critical scientific endeavor with civilization-level implications. Icy moons in our solar system are promising targets for exploration because their liquid oceans make them potential habitats for microscopic life. However, the lack of a precise definition of life poses a fundamental challenge to formulating detection strategies. To increase the chances of unambiguous detection, a suite of complementary instruments must sample multiple independent biosignatures (e.g., composition, motility/behavior, and visible structure). Such an instrument suite could generate 10,000x more raw data than is possible to transmit from distant ocean worlds like Enceladus or Europa. To address this bandwidth limitation, Onboard Science Instrument Autonomy (OSIA) is an emerging discipline of flight systems capable of evaluating, summarizing, and prioritizing observational instrument data to maximize science return. We describe two OSIA implementations developed as part of the Ocean Worlds Life Surveyor (OWLS) prototype instrument suite at the Jet Propulsion Laboratory. The first identifies life-like motion in digital holographic microscopy videos, and the second identifies cellular structure and composition via innate and dye-induced fluorescence. Flight-like requirements and computational constraints were used to lower barriers to infusion, similar to those available on the Mars helicopter, "Ingenuity." We evaluated the OSIA's performance using simulated and laboratory data and conducted a live field test at the hypersaline Mono Lake planetary analog site. Our study demonstrates the potential of OSIA for enabling biosignature detection and provides insights and lessons learned for future mission concepts aimed at exploring the outer solar system. △ Less

Submitted 18 January, 2024; v1 submitted 25 April, 2023; originally announced April 2023.

Comments: 56 pages, 18 figures, accepted by The Planetary Science Journal on 2023-10-09

Journal ref: Planet. Sci. J. 5 (2024) 19

Probing Cosmological Particle Production and Pairwise Hotspots with Deep Neural Networks

Authors: Taegyun Kim, Jeong Han Kim, Soubhik Kumar, Adam Martin, Moritz Münchmeyer, Yuhsin Tsai

Abstract: Particles with masses much larger than the inflationary Hubble scale, $H_I$, can be pair-produced non-adiabatically during inflation. Due to their large masses, the produced particles modify the curvature perturbation around their locations. These localized perturbations eventually give rise to localized signatures on the Cosmic Microwave Background (CMB), in particular, pairwise hotspots (PHS). I… ▽ More Particles with masses much larger than the inflationary Hubble scale, $H_I$, can be pair-produced non-adiabatically during inflation. Due to their large masses, the produced particles modify the curvature perturbation around their locations. These localized perturbations eventually give rise to localized signatures on the Cosmic Microwave Background (CMB), in particular, pairwise hotspots (PHS). In this work, we show that Convolutional Neural Networks (CNN) provide a powerful tool for identifying PHS on the CMB. While for a given hotspot profile a traditional Matched Filter Analysis is known to be optimal, a Neural Network learns to effectively detect the large variety of shapes that can arise in realistic models of particle production. Considering an idealized situation where the dominant background to the PHS signal comes from the standard CMB fluctuations, we show that a CNN can isolate the PHS with $\mathcal{O}(10)\%$ efficiency even if the hotspot temperature is $\mathcal{O}(10)$ times smaller than the average CMB fluctuations. Overall, the CNN search is sensitive to heavy particle masses $M_0/H_I=\mathcal{O}(200)$, and constitutes one of the unique probes of very high energy particle physics. △ Less

Submitted 15 March, 2023; originally announced March 2023.

The Early Light Curve of a Type Ia Supernova 2021hpr in NGC 3147: Progenitor Constraints with the Companion Interaction Model

Authors: Gu Lim, Myungshin Im, Gregory S. H. Paek, Sung-Chul Yoon, Changsu Choi, Sophia Kim, J. Craig Wheeler, Benjamin P. Thomas, Jozsef Vinkó, Dohyeong Kim, Jinguk Seo, Wonseok Kang, Taewoo Kim, Hyun-Il Sung, Yonggi Kim, Joh-Na Yoon, Haeun Kim, Jeongmook Kim, Hana Bae, Shuhrat Ehgamberdiev, Otabek Burhonov, Davron Mirzaqulov

Abstract: The progenitor system of Type Ia supernovae (SNe Ia) is expected to be a close binary system of a carbon/oxygen white dwarf (WD) and a non-degenerate star or another WD. Here, we present results from a high-cadence monitoring observation of SN 2021hpr in a spiral galaxy, NGC 3147, and constraints on the progenitor system based on its early multi-color light curve data. First, we classify SN 2021hp… ▽ More The progenitor system of Type Ia supernovae (SNe Ia) is expected to be a close binary system of a carbon/oxygen white dwarf (WD) and a non-degenerate star or another WD. Here, we present results from a high-cadence monitoring observation of SN 2021hpr in a spiral galaxy, NGC 3147, and constraints on the progenitor system based on its early multi-color light curve data. First, we classify SN 2021hpr as a normal SN Ia from its long-term photometric and spectroscopic data. More interestingly, we found a significant "early excess" in the light curve over a simple power-law $\sim t^{2}$ evolution. The early light curve evolves from blue to red and blue during the first week. To explain this, we fitted the early part of $BVRI$-band light curves with a two-component model of the ejecta-companion interaction and a simple power-law model. The early excess and its color can be explained by shock cooling emission due to a companion star having a radius of $8.84\pm0.58$$R_{\odot}$. We also examined HST pre-explosion images with no detection of a progenitor candidate, consistent with the above result. However, we could not detect signs of a significant amount of the stripped mass from a non-degenerate companion star ($\lesssim0.003\,M_{\odot}$ for H$α$ emission). The early excess light in the multi-band light curve supports a non-degenerate companion in the progenitor system of SN 2021hpr. At the same time, the non-detection of emission lines opens a door for other methods to explain this event. △ Less

Submitted 9 March, 2023; originally announced March 2023.

Comments: 26 pages, 13 figures + appendix, Accepted for publication in ApJ

Prediction and Verification of Parker Solar Probe Solar Wind Sources at 13.3 R$_\odot$

Authors: Samuel T. Badman, Pete Riley, Shaela I. Jones, Tae K. Kim, Robert C. Allen, C. Nick Arge, Stuart D. Bale, Carl J. Henney, Justin C. Kasper, Parisa Mostafavi, Nikolai V. Pogorelov, Nour E. Raouafi, Michael L. Stevens, J. L. Verniero

Abstract: Drawing connections between heliospheric spacecraft and solar wind sources is a vital step in understanding the evolution of the solar corona into the solar wind and contextualizing \textit{in situ} timeseries. Furthermore, making advanced predictions of this linkage for ongoing heliospheric missions, such as Parker Solar Probe (PSP), is necessary for achieving useful coordinated remote observatio… ▽ More Drawing connections between heliospheric spacecraft and solar wind sources is a vital step in understanding the evolution of the solar corona into the solar wind and contextualizing \textit{in situ} timeseries. Furthermore, making advanced predictions of this linkage for ongoing heliospheric missions, such as Parker Solar Probe (PSP), is necessary for achieving useful coordinated remote observations and maximizing scientific return. The general procedure for estimating such connectivity is straightforward (i.e. magnetic field line tracing in a coronal model) but validating the resulting estimates difficult due to the lack of an independent ground truth and limited model constraints. In its most recent orbits, PSP has reached perihelia of 13.3$R_\odot$ and moreover travels extremely fast prograde relative to the solar surface, covering over 120 degrees longitude in three days. Here we present footpoint predictions and subsequent validation efforts for PSP Encounter 10, the first of the 13.3$R_\odot$ orbits, which occurred in November 2021. We show that the longitudinal dependence of \textit{in situ} plasma data from these novel orbits provides a powerful method of footpoint validation. With reference to other encounters, we also illustrate that the conditions under which source mapping is most accurate for near-ecliptic spacecraft (such as PSP) occur when solar activity is low, but also requires that the heliospheric current sheet is strongly warped by mid-latitude or equatorial coronal holes. Lastly, we comment on the large-scale coronal structure implied by the Encounter 10 mapping, highlighting an empirical equatorial cut of the Alfvèn surface consisting of localized protrusions above unipolar magnetic separatrices. △ Less

Submitted 29 March, 2023; v1 submitted 8 March, 2023; originally announced March 2023.

Comments: 33 Pages, 7 Figures, JGR Space Physics, Published Online 2023/3/28, In Final Production

Improving the Arrival Time Estimates of Coronal Mass Ejections by Using Magnetohydrodynamic Ensemble Modeling, Heliospheric Imager data, and Machine Learning

Authors: Talwinder Singh, Bernard Benson, Syed A. Z. Raza, Tae K. Kim, Nikolai V. Pogorelov, William P. Smith, Charles N. Arge

Abstract: The arrival time prediction of Coronal mass ejections (CMEs) is an area of active research. Many methods with varying levels of complexity have been developed to predict CME arrival. However, the mean absolute error (MAE) of predictions remains above 12 hours, even with the increasing complexity of methods. In this work we develop a new method for CME arrival time prediction that uses magnetohydro… ▽ More The arrival time prediction of Coronal mass ejections (CMEs) is an area of active research. Many methods with varying levels of complexity have been developed to predict CME arrival. However, the mean absolute error (MAE) of predictions remains above 12 hours, even with the increasing complexity of methods. In this work we develop a new method for CME arrival time prediction that uses magnetohydrodynamic simulations involving data-constrained flux-rope-based CMEs, which are introduced in a data-driven solar wind background. We found that, for 6 CMEs studied in this work, the MAE in arrival time was ~8 hours. We further improved our arrival time predictions by using ensemble modeling and comparing the ensemble solutions with STEREO-A&B heliospheric imager data. This was done by using our simulations to create synthetic J-maps. A machine learning (ML) method called the lasso regression was used for this comparison. Using this approach, we could reduce the MAE to ~4 hours. Another ML method based on the neural networks (NNs) made it possible to reduce the MAE to ~5 hours for the cases when HI data from both STEREO-A&B were available. NNs are capable of providing similar MAE when only the STEREO-A data is used. Our methods also resulted in very encouraging values of standard deviation (precision) of arrival time. The methods discussed in this paper demonstrate significant improvements in the CME arrival time predictions. Our work highlights the importance of using ML techniques in combination with data-constrained magnetohydrodynamic modeling to improve space weather predictions. △ Less

Submitted 10 February, 2023; originally announced February 2023.

Constraining the Temperature-Density Relation of the Inter-Galactic Medium from Analytically Modeling Lyman-alpha Forest Absorbers

Authors: Li Yang, Zheng Zheng, T. -S. Kim

Abstract: The absorption by neutral hydrogen in the intergalactic medium (IGM) produces the Ly$α$ forest in the spectra of quasars. The Ly$α$ forest absorbers have a broad distribution of neutral hydrogen column density $N_{\rm HI}$ and Doppler $b$ parameter. The narrowest Ly$α$ absorption lines (of lowest $b$) with neutral hydrogen column density above $\sim 10^{13}{\rm cm^{-2}}$ are dominated by thermal b… ▽ More The absorption by neutral hydrogen in the intergalactic medium (IGM) produces the Ly$α$ forest in the spectra of quasars. The Ly$α$ forest absorbers have a broad distribution of neutral hydrogen column density $N_{\rm HI}$ and Doppler $b$ parameter. The narrowest Ly$α$ absorption lines (of lowest $b$) with neutral hydrogen column density above $\sim 10^{13}{\rm cm^{-2}}$ are dominated by thermal broadening, which can be used to constrain the thermal state of the IGM. Here we constrain the temperature-density relation $T=T_0(ρ/\barρ)^{γ-1}$ of the IGM at $1.6<z<3.6$ by using $N_{\rm HI}$ and $b$ parameters measured from 24 high-resolution and high-signal-to-noise quasar spectra and by employing an analytic model to model the $N_{\rm HI}$-dependent low-$b$ cutoff in the $b$ distribution. In each $N_{\rm HI}$ bin, the $b$ cutoff is estimated using two methods, one non-parametric method from computing the cumulative $b$ distribution and a parametric method from fitting the full $b$ distribution. We find that the IGM temperature $T_0$ at the mean gas density $\barρ$ shows a peak of $\sim 1.5\times 10^4$K at $z\sim $2.7-2.9. At redshift higher than this, the index $γ$ approximately remains constant, and it starts to increase toward lower redshifts. The evolution in both parameters is in good agreement with constraints from completely different approaches, which signals that He II reionization completes around $z\sim 3$. △ Less

Submitted 9 February, 2023; originally announced February 2023.

Comments: 18 pages, 5 figures

PBH formation from overdensities in delayed vacuum transitions

Authors: Kiyoharu Kawana, TaeHun Kim, Philip Lu

Abstract: Primordial black hole (PBH) formation from first-order phase transitions (FOPTs) combines two prevalent elements of beyond the Standard Model physics with wide-ranging consequences. We elaborate on a recently proposed scenario in which inhomogeneities in vacuum energy decay seed the overdensities that collapse to PBHs. In this scenario, the PBH mass is determined by the Hubble mass as in conventio… ▽ More Primordial black hole (PBH) formation from first-order phase transitions (FOPTs) combines two prevalent elements of beyond the Standard Model physics with wide-ranging consequences. We elaborate on a recently proposed scenario in which inhomogeneities in vacuum energy decay seed the overdensities that collapse to PBHs. In this scenario, the PBH mass is determined by the Hubble mass as in conventional formation scenarios, while its number density is determined by the nucleation dynamics of the FOPT. We present a detailed study of the formation probability including parameter dependencies. In addition, we generate populations in the open mass window as well as for the HSC and OGLE candidate microlensing events. This mechanism inevitably creates PBHs in generic FOPTs, with significant populations produced in slow and moderately strong phase transitions. △ Less

Submitted 28 November, 2023; v1 submitted 28 December, 2022; originally announced December 2022.

Comments: 11 pages, 7 figures; matches with the published version; discussions significantly improved

Journal ref: Phys. Rev. D 108, 103531 (2023)

Primordial Black Holes as a Factory of Axions: Extragalactic Photons from Axions

Authors: Yongsoo Jho, Tae-Geun Kim, Jong-Chul Park, Seong Chan Park, Yeji Park

Abstract: Primordial black holes (PBHs) are significant sources of axions and axion-like particles (ALPs), provided their Hawking temperature exceeds the particles' masses. Given the predominant decay of axions into photons, the enhanced photon spectrum they generate can be feasibly detected using sensitive detectors. This paper introduces a novel methodology that elucidates the decay process for particles… ▽ More Primordial black holes (PBHs) are significant sources of axions and axion-like particles (ALPs), provided their Hawking temperature exceeds the particles' masses. Given the predominant decay of axions into photons, the enhanced photon spectrum they generate can be feasibly detected using sensitive detectors. This paper introduces a novel methodology that elucidates the decay process for particles to traverse and decay over cosmological timescales. Specifically, we derive estimations for the photon spectrum and flux, assuming a monochromatic mass spectrum and isotropic distribution for PBHs. Encouragingly, forthcoming detectors like e-ASTROGAM are well positioned to capture this signal. △ Less

Submitted 5 April, 2025; v1 submitted 22 December, 2022; originally announced December 2022.

Comments: 13 pages, 7 figures; title changed, updated figures

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

Caught in the Act: A Metal-Rich High-Velocity Cloud in the Inner Galaxy

Authors: Frances H. Cashman, Andrew J. Fox, Bart P. Wakker, Trisha Ashley, Derck Massa, Edward B. Jenkins, Dhanesh Krishnarao, Felix J. Lockman, Robert A. Benjamin, Rongmon Bordoloi, Tae-Sun Kim

Abstract: We characterize the chemical and physical conditions in an outflowing high-velocity cloud in the inner Galaxy. We report a super-solar metallicity of [O/H] = $+0.36\pm0.12$ for the high-velocity cloud at $v_\mathrm{LSR}$ = 125.6 km s$^{-1}$ toward the star HD 156359 ($l$ = 328.$^{\circ}$7, $b$ = $-$14.$^{\circ}$5, $d$ = 9 kpc, $z$ = $-$2.3 kpc). Using archival observations from FUSE, HST STIS, and… ▽ More We characterize the chemical and physical conditions in an outflowing high-velocity cloud in the inner Galaxy. We report a super-solar metallicity of [O/H] = $+0.36\pm0.12$ for the high-velocity cloud at $v_\mathrm{LSR}$ = 125.6 km s$^{-1}$ toward the star HD 156359 ($l$ = 328.$^{\circ}$7, $b$ = $-$14.$^{\circ}$5, $d$ = 9 kpc, $z$ = $-$2.3 kpc). Using archival observations from FUSE, HST STIS, and ESO FEROS we measure high-velocity absorption in H I, O I, C II, N II, Si II, Ca II, Si III, Fe III, C IV, Si IV, N V, and O VI. We measure a low H I column density of log $N$(H I) = $15.54\pm0.05$ in the HVC from multiple unsaturated H I Lyman series lines in the FUSE data. We determine a low dust depletion level in the HVC from the relative strength of silicon, iron, and calcium absorption relative to oxygen, with [Si/O]=$-0.33\pm0.14$, [Fe/O]=$-0.30\pm0.20$, and [Ca/O] =$-0.56\pm0.16$. Analysis of the high-ion absorption using collisional ionization models indicates that the hot plasma is multi-phase, with the C IV and Si IV tracing 10$^{4.9}$ K gas and N V and O VI tracing 10$^{5.4}$ K gas. The cloud's metallicity, dust content, kinematics, and close proximity to the disk are all consistent with a Galactic wind origin. As the HD 156359 line of sight probes the inner Galaxy, the HVC appears to be a young cloud caught in the act of being entrained in a multi-phase Galactic outflow and driven out into the halo. △ Less

Submitted 20 October, 2022; originally announced October 2022.

Comments: Submitted to ApJ, 18 pages, 13 figures, comments welcome