Showing 1–50 of 107 results for author: Liao, S

Rapid sinking and efficient mergers of supermassive black holes in compact high-redshift galaxies

Authors: Atte Keitaanranta, Peter H. Johansson, Alexander Rawlings, Toni Tuominen, Antti Rantala, Thorsten Naab, Shihong Liao, Bastián Reinoso

Abstract: We present a cosmological zoom-in simulation targeting the high redshift compact progenitor phase of massive galaxies, with the most massive galaxy reaching a stellar mass of $M_{\star}=8.5\times 10^{10} \ M_{\odot}$ at $z=5$. The dynamics of supermassive black holes (SMBHs) is modelled from seeding down to their coalescence at sub-parsec scales due to gravitational wave (GW) emission by utilising… ▽ More We present a cosmological zoom-in simulation targeting the high redshift compact progenitor phase of massive galaxies, with the most massive galaxy reaching a stellar mass of $M_{\star}=8.5\times 10^{10} \ M_{\odot}$ at $z=5$. The dynamics of supermassive black holes (SMBHs) is modelled from seeding down to their coalescence at sub-parsec scales due to gravitational wave (GW) emission by utilising a new version of the KETJU code, which combines regularised integration of sufficiently massive SMBHs with a dynamical friction subgrid model for lower-mass SMBHs. All nine massive galaxies included in this study go through a gas-dominated phase of early compaction in the redshift range of $z\sim 7-9$, starting at stellar masses of $M_\star\gtrsim 10^8\ \mathrm{M}_\odot$ and ending at a few times $M_{\star}\sim 10^9\ \mathrm{M}_\odot$. The sizes, masses and broad band fluxes of these compact systems are in general agreement with the population of systems observed with JWST known as `Little Red Dots'. In the compact phase, the stellar and SMBH masses grow rapidly, leading to a sharp decline in the central gas fractions. The outer regions, however, remain relatively gas-rich, leading to subsequent off-centre star formation and size growth. Due to the very high central stellar densities ($ρ_{\star}\gtrsim 10^{13}\,\mathrm{M_\odot/kpc^3}$), the SMBHs merge rapidly, typically just $\sim 4-35\ \mathrm{Myr}$ after the SMBH binaries have become bound. Combining KETJU with the phenomenological PhenomD model resolves the complete evolution of the GW emission from SMBH binaries through the Pulsar Timing Array frequency waveband up to the final few orbits that produce GWs observable with the future LISA mission. △ Less

Submitted 12 December, 2025; originally announced December 2025.

Comments: 30 pages, 17 figures

Building a Radio AGN Sample from Cosmic Morning -- The Radio High-Redshift Quasar Catalog (RHzQCat): I. Catalog from SDSS Quasars and Radio Surveys at $z > 3$

Authors: Yingkang Zhang, Ruqiu Lin, Krisztina Perger, Sándor Frey, Tao An, Xiang Ji, Qiqi Wu, Shilong Liao

Abstract: Radio-loud high-redshift quasars (RHRQs) provide crucial insights into the evolution of relativistic jets and their connection to the growth of supermassive black holes. Beyond the extensively studied population at $z \ge 5$, the cosmic morning epoch ($3 \lesssim z \lesssim 5$) marks the peak of active galactic nucleus (AGN) activity and black hole accretion, yet remains relatively unexplored. In… ▽ More Radio-loud high-redshift quasars (RHRQs) provide crucial insights into the evolution of relativistic jets and their connection to the growth of supermassive black holes. Beyond the extensively studied population at $z \ge 5$, the cosmic morning epoch ($3 \lesssim z \lesssim 5$) marks the peak of active galactic nucleus (AGN) activity and black hole accretion, yet remains relatively unexplored. In this work, we compiled the radio high-redshift quasar catalog (RHzQCat) by cross-matching the SDSS DR16Q catalog with four major radio surveys -- FIRST,NVSS, RACS, and GLEAM. Our tier-based cross-matching framework and visual validation ensured reliable source identification across surveys with diverse beam sizes. The catalog included 1629 reliable and 315 candidate RHRQs, with radio luminosities uniformly spanning $10^{25.5}$ -- $10^{29.3}$ W Hz$^{-1}$. About 95\% of the confirmed sources exhibited compact morphologies, consistent with Doppler-boosted or young AGN populations at high redshifts. Our catalog increases the number of known RHRQs at $z\ge3$ by an order of magnitude, representing the largest and most homogeneous catalog of radio quasars at cosmic morning, filling the observational gap between the early ($z>6$) and local Universe. It provides a robust reference for future statistical studies of jet evolution, AGN feedback, and cosmic magnetism with next-generation facilities such as the Square Kilometer Array (SKA). △ Less

Submitted 5 December, 2025; v1 submitted 2 December, 2025; originally announced December 2025.

Comments: 26 pages, 9 figures, published by Universe as part of Special Issue: Advances in Studies of Galaxies at High Redshift. Issue website: https://www.mdpi.com/2218-1997/11/12/392 paper link: https://www.mdpi.com/2218-1997/11/12/392/pdf Supplementary data can be found via zenodo: https://doi.org/10.5281/zenodo.17667135

Journal ref: Universe, Vol. 11, No. 12, id. 392 (2025)

HIDES -- I. The population and diversity of HI-rich 'dark' galaxies in the Hestia and Auriga simulations

Authors: Haonan Zheng, Fangzhou Jiang, Shihong Liao, Noam I. Libeskind

Abstract: We present our investigation of HI-rich 'Dark' galaxiEs in Simulations (HIDES), specifically using the Hestia and Auriga simulations in this work. We select galaxies that are faint ($M_g > -10$) and contain sufficient HI ($M_\mathrm{HI} > 10^5\,M_\odot$), and identify 89 such objects, only one of which is completely starless. Their demographics generally converge across simulations of different re… ▽ More We present our investigation of HI-rich 'Dark' galaxiEs in Simulations (HIDES), specifically using the Hestia and Auriga simulations in this work. We select galaxies that are faint ($M_g > -10$) and contain sufficient HI ($M_\mathrm{HI} > 10^5\,M_\odot$), and identify 89 such objects, only one of which is completely starless. Their demographics generally converge across simulations of different resolution, with $M_{200} \sim 10^{9.5}\,M_\odot$, $M_\mathrm{gas} \sim 10^{7.4}\,M_\odot$, $M_\mathrm{HI} \sim 10^{6.5}\,M_\odot$, $M_\mathrm{*} \sim 10^{5.6}\,M_\odot$, low gas metallicity, little or no current star formation, and a mean stellar age of $\sim$ 11 Gyr, and with some of them can survive in dense environments as close as $\sim$ 300 kpc from a Milky-Way mass neighbor. We find a large scatter in their HI density profiles and $M_\mathrm{HI} - M_\mathrm{*}$ relation, which cannot be fully explained by current halo mass or concentration, but can be attributed to ram pressure stripping in dense environments, past mergers, and stellar feedback. In particular, close encounters with massive halos and dense environments can reshape the HI content, which may explain the asymmetric HI map of an intriguing observed analogue, Cloud-9. An empirical fit, $n = 0.25 \left(d_\mathrm{MW}/{1\,\mathrm{Mpc}}\right)^{-1.4}\, \mathrm{Mpc}^{-3}$, based on their number density extended to 3.7 Mpc in constrained local volume simulations, is also provided to aid observational forecasts. We conclude that both mass assembly history and environmental history play a crucial role in the formation and subsequent diversity of these galaxies. △ Less

Submitted 20 November, 2025; originally announced November 2025.

Comments: 11 pages, 6 figures

A pilot VLBI study of the SQUAB quasar sample featuring multiple Gaia detections

Authors: Yingkang Zhang, Tao An, Xiang Ji, Zhenya Zheng, Yuanqi Liu, Qiqi Wu, Ruqiu Lin, Shilong Liao

Abstract: Our previous work identified a class of SDSS quasars exhibiting multiple Gaia detections, classifying them as candidates for various astrophysical systems such as quasar-star pairs, dual quasars, and gravitationally lensed quasars. In this paper, we present a pilot VLBI study targeting a radio-bright subsample and report the first high-resolution imaging results. By leveraging the milliarcsecond-s… ▽ More Our previous work identified a class of SDSS quasars exhibiting multiple Gaia detections, classifying them as candidates for various astrophysical systems such as quasar-star pairs, dual quasars, and gravitationally lensed quasars. In this paper, we present a pilot VLBI study targeting a radio-bright subsample and report the first high-resolution imaging results. By leveraging the milliarcsecond-scale resolution of VLBI and its precise astrometric coordination incorporating with Gaia, we aim to refine the classification of these multiple matched sources, search for potential dual AGNs, and assess the efficacy of the combined Gaia-VLBI approach in resolving ambiguous quasar systems. We cross-matched the SQUAB quasar sample with the FIRST and NVSS catalogs, identifying 18 radio-emitting sources. The three brightest were selected for dual-frequency (1.6 and 4.9 GHz) VLBA observations. We performed VLBI imaging at both Gaia positions, constructed spectral index maps, and estimated brightness temperatures to characterize the radio morphology and physical properties. For the three target sources, our VLBI observations reveal compact radio structures consistent with single AGN at the primary Gaia positions. No significant emission is detected at the secondary Gaia locations. These results support the interpretation of the sources as quasar$-$star pairs, in line with earlier studies. This pilot study demonstrates the value of radio-VLBI high-resolution follow-ups on Gaia-selected quasar systems with multiple counterparts, showing how they can unambiguously reveal the true nature of these systems and help remove contaminants from dual AGN candidate samples. △ Less

Submitted 20 November, 2025; originally announced November 2025.

Comments: 15 pages, 9 figures, accepted by A&A

First Light And Reionisation Epoch Simulations (FLARES) XX: Comparing semi-analytic models at high-redshift

Authors: Louise T. C. Seeyave, Carlton M. Baugh, Angel Chandro-Gomez, Claudia del P. Lagos, Robert M. Yates, L. Y. Aaron Yung, Rachel S. Somerville, Stephen M. Wilkins, Christopher C. Lovell, William J. Roper, Aswin P. Vijayan, Cedric G. Lacey, Chris Power, Shihong Liao, Maxwell G. A. Maltz, Jack C. Turner

Abstract: We explore how the choice of galaxy formation model affects the predicted properties of high-redshift galaxies. Using the FLARES zoom resimulation strategy, we compare the EAGLE hydrodynamics model and the GALFORM, L-Galaxies, SC-SAM and SHARK semi-analytic models (SAMs) at $5\leq z \leq 12$. The first part of our analysis examines the stellar mass functions, stellar-to-halo mass relations, star f… ▽ More We explore how the choice of galaxy formation model affects the predicted properties of high-redshift galaxies. Using the FLARES zoom resimulation strategy, we compare the EAGLE hydrodynamics model and the GALFORM, L-Galaxies, SC-SAM and SHARK semi-analytic models (SAMs) at $5\leq z \leq 12$. The first part of our analysis examines the stellar mass functions, stellar-to-halo mass relations, star formation rates, and supermassive black hole (SMBH) properties predicted by the different models. Comparisons are made with observations, where relevant. We find general agreement between the range of predicted and observed stellar mass functions. The model predictions differ considerably when it comes to SMBH properties, with GALFORM and SHARK predicting between 1.5-3 dex more massive SMBHs ($M_{\rm BH}>10^6\ {\rm M_\odot}$) than L-Galaxies and SC-SAM, depending on redshift. The second half of our analysis focuses on passive galaxies. We show that in L-Galaxies and SC-SAM, environmental quenching of satellites is the prevalent quenching mechanism, with active galactic nuclei (AGN) feedback having little effect at the redshifts probed. On the other hand, $\sim40\%$ of passive galaxies predicted by GALFORM and SHARK are quenched by AGN feedback at $z=5$. The SAMs are an interesting contrast to the EAGLE model, in which AGN feedback is essential for the formation of passive galaxies, in both satellites and centrals, even at high redshift. △ Less

Submitted 14 November, 2025; originally announced November 2025.

Comments: 20 pages, 10 figures, submitted to MNRAS

Particle loads for cosmological simulations with equal-mass dark matter and baryonic particles

Authors: Shihong Liao, Yizhou Liu, Haonan Zheng, Ming Li, Jie Wang, Liang Gao, Bingqing Sun, Shi Shao

Abstract: Traditional cosmological hydrodynamical simulations usually assume equal-numbered but unequal-mass dark matter and baryonic particles, which can lead to spurious collisional heating due to energy equipartition. To avoid such a numerical heating effect, a simulation setup with equal-mass dark matter and baryonic particles, which corresponds to a particle number ratio of… ▽ More Traditional cosmological hydrodynamical simulations usually assume equal-numbered but unequal-mass dark matter and baryonic particles, which can lead to spurious collisional heating due to energy equipartition. To avoid such a numerical heating effect, a simulation setup with equal-mass dark matter and baryonic particles, which corresponds to a particle number ratio of $N_{\rm DM}:N_{\rm gas} = Ω_{\rm cdm} / Ω_{\rm b}$, is preferred. However, previous studies have typically used grid-based particle loads to prepare such initial conditions, which can only reach specific values for $N_{\rm DM}:N_{\rm gas}$ due to symmetry requirements. In this study, we propose a method based on the glass approach that can generate two-component particle loads with more general $N_{\rm DM}:N_{\rm gas}$ ratios. The method simultaneously relaxes two Poisson particle distributions by introducing an additional repulsive force between particles of the same component. We show that the final particle load closely follows the expected minimal power spectrum, $P(k) \propto k^{4}$, exhibits good homogeneity and isotropy properties, and remains sufficiently stable under gravitational interactions. Both the dark matter and gas components individually also exhibit uniform and isotropic distributions. We apply our method to two-component cosmological simulations and demonstrate that an equal-mass particle setup effectively mitigates the spurious collisional heating that arises in unequal-mass simulations. Our method can be extended to generate multi-component uniform and isotropic distributions. Our code based on Gadget-2 is available at https://github.com/liaoshong/gadget-2glass . △ Less

Submitted 8 November, 2025; originally announced November 2025.

Comments: 16 pages, 11 figures, accepted for publication in The Astrophysical Journal. The code is publicly available at https://github.com/liaoshong/gadget-2glass

Journal ref: The Astrophysical Journal, 995, 147 (2025)

Characterizing the astrometric quality of AGNs in Gaia-CRF3

Authors: Shilong Liao, Qiqi Wu, Ye Ding, Qi Xu, Zhaoxiang Qi

Abstract: Active Galactic Nuclei (AGNs), owing to their great distances and compact sizes, serve as fundamental anchors for defining the celestial reference frame. With about 1.9 million AGNs observed in Gaia DR3 at optical precision comparable to radio wavelengths, Gaia provides a solid foundation for constructing the next-generation, kinematically non-rotating optical reference frame. Accurate assessment… ▽ More Active Galactic Nuclei (AGNs), owing to their great distances and compact sizes, serve as fundamental anchors for defining the celestial reference frame. With about 1.9 million AGNs observed in Gaia DR3 at optical precision comparable to radio wavelengths, Gaia provides a solid foundation for constructing the next-generation, kinematically non-rotating optical reference frame. Accurate assessment of systematic residuals in AGN astrometry is therefore crucial. In this talk, we analysed the parallaxes and proper motions of Gaia DR3 AGNs to characterize systematic errors and their correlations with various physical and observational properties. A subset of Gaia-CRF3 AGNs exhibits significant astrometric offsets, mainly arising from dual or lensed quasars whose structural variations induce photocenter jitter, mimicking parallax and proper motion. Such sources must be carefully excluded from reference frame construction. To this end, we introduce an astrometric quality index for each source to quantify its astrometric reliability. The results reveal a strong correlation between lower quality index values and increasing errors in position, proper motion, and parallax, demonstrating that the proposed index provides an effective metric for selecting high-fidelity AGNs as primary reference sources. △ Less

Submitted 3 November, 2025; originally announced November 2025.

Comments: 6 pages, 3 figures. To be published at PROCEEDINGS of the IAUs 401 "Advancing Reference Systems, Ephemeris, and Standards" held in 04 to 09 August, 2025 at La Plata, Buenos Aires, Argentina

The impact of cosmic filaments on the abundance of satellite galaxies

Authors: Yuxi Meng, Haonan Zheng, Shihong Liao, Lizhi Xie, Lan Wang, Hongxiang Chen, Liang Gao, Quan Guo, Yingjie Jing, Jie Wang, Hang Yang, Guangquan Zeng

Abstract: The impact of cosmic web environments on galaxy properties plays a critical role in understanding galaxy formation. Using the state-of-the-art cosmological simulation IllustrisTNG, we investigate how satellite galaxy abundance differs between filaments and the field, with filaments identified using the DisPerSE algorithm. When filaments are identified using galaxies as tracers, we find that, acros… ▽ More The impact of cosmic web environments on galaxy properties plays a critical role in understanding galaxy formation. Using the state-of-the-art cosmological simulation IllustrisTNG, we investigate how satellite galaxy abundance differs between filaments and the field, with filaments identified using the DisPerSE algorithm. When filaments are identified using galaxies as tracers, we find that, across all magnitude bins, central galaxies in filaments tend to host more satellite galaxies than their counterparts in the field, in qualitative agreement with observational results from the Sloan Digital Sky Survey. The average ratios between satellite luminosity functions in filaments and the field are $3.49$, $2.61$, and $1.90$ in the central galaxy $r$-band magnitude bins of $M_{r, {\rm cen}} \sim -22$, $-21$, and $-20$, respectively. We show that much of this excess can be attributed to the higher host halo masses of galaxies in filaments. After resampling central galaxies in both environments to match the halo mass distributions within each magnitude bin, the satellite abundance enhancement in filaments is reduced by up to $79 \%$. Additionally, the choice of tracers used to identify filaments introduces a significant bias: when filaments are identified using the dark matter density field, the environmental difference in satellite abundance is reduced by more than $70 \%$; after further resampling in both magnitude and halo mass, the difference is further suppressed by another $\sim 60$--$95 \%$. Our results highlight the importance of halo mass differences and tracer choice biases when interpreting and understanding the impact of environment on satellite galaxy properties. △ Less

Submitted 26 September, 2025; originally announced September 2025.

Comments: 16 pages, 7 figures; Submitted to ApJ

The Nature of High-Redshift Massive Quiescent Galaxies -- Searching for RUBIES-UDS-QG-z7 in FLARES

Authors: Jack C. Turner, Will J. Roper, Aswin P. Vijayan, Sophie L. Newman, Stephen M. Wilkins, Christopher C. Lovell, Shihong Liao, Louise T. C. Seeyave

Abstract: RUBIES-UDS-QG-z7 (RQG) is the earliest massive quiescent galaxy identified to date, inferred to have formed its abundant stellar mass in a single burst that ceases rapidly before $z \sim 8$. An object of such extreme nature challenges our understanding of galaxy formation, requiring rapid growth and quenching mechanisms only 0.6 Gyr after the Big Bang and implying number densities 2 dex higher tha… ▽ More RUBIES-UDS-QG-z7 (RQG) is the earliest massive quiescent galaxy identified to date, inferred to have formed its abundant stellar mass in a single burst that ceases rapidly before $z \sim 8$. An object of such extreme nature challenges our understanding of galaxy formation, requiring rapid growth and quenching mechanisms only 0.6 Gyr after the Big Bang and implying number densities 2 dex higher than currently predicted by simulations. We use synthetic observables to identify analogous systems within the First Light And Reionisation Epoch Simulations (FLARES) and find two massive galaxies dominated by rapidly quenched bursts. Beyond demonstrating that the current FLARES model is capable of producing RQG-like systems, these analogues provide a laboratory within which to study the underlying physics. Their active galactic nuclei (AGN) heat and expel gas, inducing rapid quenching and preventing timely rejuvenation. This causes above-average chemical enrichment at a given stellar mass, with super solar levels predicted for RQG. These metallicities are underestimated by spectral energy distribution fitting and we show that $α$-enhancement cannot be solely responsible. Degeneracies with age and dust attenuation appear the more likely causes. Tensions between observed and simulated number densities can be alleviated in part by considering systematics, but adjustments to AGN feedback, such as allowing super-Eddington accretion rates, may be required for full agreement. △ Less

Submitted 19 September, 2025; originally announced September 2025.

Comments: 15 pages, 12 figures, submitted to MNRAS

Discovery of 10,059 new three-dimensional periodic orbits of general three-body problem

Authors: Xiaoming Li, Shijun Liao

Abstract: A very few three-dimensional (3D) periodic orbits of general three-body problem (with three finite masses) have been discovered since Newton mentioned it in 1680s. Using a high-accuracy numerical strategy we discovered 10,059 three-dimensional periodic orbits of the three-body problem in the cases of $m_{1}=m_{2}=1$ and $m_{3}=0.1n$ where $1\leq n\leq 20$ is an integer, among which 1,996 (about 20… ▽ More A very few three-dimensional (3D) periodic orbits of general three-body problem (with three finite masses) have been discovered since Newton mentioned it in 1680s. Using a high-accuracy numerical strategy we discovered 10,059 three-dimensional periodic orbits of the three-body problem in the cases of $m_{1}=m_{2}=1$ and $m_{3}=0.1n$ where $1\leq n\leq 20$ is an integer, among which 1,996 (about 20\%) are linearly stable. Note that our approach is valid for arbitrary mass $m_{3}$ so that in theory we can gain an arbitrarily large amount of 3D periodic orbits of the three-body problem. In the case of three equal masses, we discovered twenty-one 3D ``choerographical'' periodic orbits whose three bodies move periodically in a single closed orbit. It is very interesting that, in the case of two equal masses, we discovered 273 three-dimensional periodic orbits with the two bodies ($m_{1}=m_{2}=1$) moving along a single closed orbit and the third ($m_{3}\neq 1$) along a different one: we name them ``piano-trio'' orbits, like a trio for two violins and one piano. To the best of our knowledge, all of these 3D periodic orbits have never been reported, indicating the novelty of this work. The large amount of these new 3D periodic orbits are helpful for us to have better understandings about chaotic properties of the famous three-body problem, which ``are, so to say, the only opening through which we can try to penetrate in a place which, up to now, was supposed to be inaccessible'', as pointed out by Poincaré, the founder of chaos theory. △ Less

Submitted 11 August, 2025; originally announced August 2025.

Comments: 9 pages, 4 figures and 4 tables

Interpreting nebular emission lines in the high-redshift Universe

Authors: Aswin P. Vijayan, Robert M. Yates, Christopher C. Lovell, William J. Roper, Stephen M. Wilkins, Hiddo S. B. Algera, Shihong Liao, Paurush Punyasheel, Lucie E. Rowland, Louise T. C. Seeyave

Abstract: One of the most remarkable outcomes from JWST has been the exquisite UV-optical spectroscopic data for galaxies in the high-redshift Universe ($z \geq 5$), enabling the use of various nebular emission lines to infer conditions of the interstellar medium. In this work, we evaluate the reliability of these diagnostics, specifically those used to recover the star formation rate (SFR), the ionising ph… ▽ More One of the most remarkable outcomes from JWST has been the exquisite UV-optical spectroscopic data for galaxies in the high-redshift Universe ($z \geq 5$), enabling the use of various nebular emission lines to infer conditions of the interstellar medium. In this work, we evaluate the reliability of these diagnostics, specifically those used to recover the star formation rate (SFR), the ionising photon production efficiency, and the gas-phase oxygen abundance. We use forward-modelled galaxy spectra from idealised toy models and the FLARES cosmological hydrodynamical simulations to assess how these diagnostic lines respond to variations in the underlying stellar populations and star-dust geometry. We find that due to the clumpy nature of FLARES galaxies, they exhibit strong internal variation in age, metallicity and dust attenuation, biasing the interpretation using these diagnostics. In FLARES, the SFRD at the bright-end of the SFR function can be underestimated by as much as $30 \%$ compared to the true values. Similarly, the true ionising photon production efficiency in FLARES remains almost constant with stellar mass, while estimates using H$α$ or H$β$ can underestimate it by more than 0.5 dex at the massive end ($>10^{9.5}$ M$_{\odot}$), introducing an artificial declining trend. The FLARES mass-metallicity relation derived from line ratios (dust corrected) exhibits a flat trend, whereas the intrinsic mass-weighted relation shows a strong positive correlation. These findings highlight the critical importance of understanding the biases introduced due to the coupling of star-dust geometry and heterogeneous stellar population when interpreting nebular emission lines at high redshift. Hence the accurate interpretation of high-redshift galaxy spectra requires careful forward modelling that accounts for realistic star-dust geometry and population variations. △ Less

Submitted 27 July, 2025; originally announced July 2025.

Comments: 23 pages and 16 figures. Submitted to the Open Journal of Astrophysics

Introduction to the Chinese Space Station Survey Telescope (CSST)

Authors: CSST Collaboration, Yan Gong, Haitao Miao, Hu Zhan, Zhao-Yu Li, Jinyi Shangguan, Haining Li, Chao Liu, Xuefei Chen, Haibo Yuan, Jilin Zhou, Hui-Gen Liu, Cong Yu, Jianghui Ji, Zhaoxiang Qi, Jiacheng Liu, Zigao Dai, Xiaofeng Wang, Zhenya Zheng, Lei Hao, Jiangpei Dou, Yiping Ao, Zhenhui Lin, Kun Zhang, Wei Wang , et al. (97 additional authors not shown)

Abstract: The Chinese Space Station Survey Telescope (CSST) is an upcoming Stage-IV sky survey telescope, distinguished by its large field of view (FoV), high image quality, and multi-band observation capabilities. It can simultaneously conduct precise measurements of the Universe by performing multi-color photometric imaging and slitless spectroscopic surveys. The CSST is equipped with five scientific inst… ▽ More The Chinese Space Station Survey Telescope (CSST) is an upcoming Stage-IV sky survey telescope, distinguished by its large field of view (FoV), high image quality, and multi-band observation capabilities. It can simultaneously conduct precise measurements of the Universe by performing multi-color photometric imaging and slitless spectroscopic surveys. The CSST is equipped with five scientific instruments, i.e. Multi-band Imaging and Slitless Spectroscopy Survey Camera (SC), Multi-Channel Imager (MCI), Integral Field Spectrograph (IFS), Cool Planet Imaging Coronagraph (CPI-C), and THz Spectrometer (TS). Using these instruments, CSST is expected to make significant contributions and discoveries across various astronomical fields, including cosmology, galaxies and active galactic nuclei (AGN), the Milky Way and nearby galaxies, stars, exoplanets, Solar System objects, astrometry, and transients and variable sources. This review aims to provide a comprehensive overview of the CSST instruments, observational capabilities, data products, and scientific potential. △ Less

Submitted 19 September, 2025; v1 submitted 6 July, 2025; originally announced July 2025.

Comments: 48 pages, 12 figures, 1 table. Accepted for publication in SCIENCE CHINA Physics, Mechanics & Astronomy

A Be star-black hole binary with a wide orbit from LAMOST time-domain survey

Authors: Qian-Yu An, Yang Huang, Wei-Min Gu, Yong Shao, Zhi-Xiang Zhang, Tuan Yi, B. D. Lailey, T. A. A. Sigut, Kyle Akira Rocha, Meng Sun, Seth Gossage, Shi-Jie Gao, Shan-Shan Weng, Song Wang, Bowen Zhang, Xinlin Zhao, Senyu Qi, Shilong Liao, Jianghui Ji, Junfeng Wang, Jianfeng Wu, Mouyuan Sun, Xiang-Dong Li, Jifeng Liu

Abstract: Binary systems consisting of an early type star and a black hole (BH) are crucial for understanding various astrophysical phenomena, particularly the origins of detected gravitational wave sources. Be binary systems are expected to represent a key evolutionary stage in hosting BHs. However, while hundreds of Be X-ray binaries are known, the only confirmed BH candidate in a Be binary remains highly… ▽ More Binary systems consisting of an early type star and a black hole (BH) are crucial for understanding various astrophysical phenomena, particularly the origins of detected gravitational wave sources. Be binary systems are expected to represent a key evolutionary stage in hosting BHs. However, while hundreds of Be X-ray binaries are known, the only confirmed BH candidate in a Be binary remains highly controversial. We report the discovery of ALS 8814, a Be star-BH binary with a moderately eccentric ($e = 0.23$) and wide orbit ($P = 176.6$ days), revealed by the radial velocity (RV) measurement of the visible Be star. Our analysis, combining flux-calibrated spectra in the Balmer discontinuity region and spectral template matching, yields a mass of $11.2^{+1.4}_{-1.2}$ $M_\odot$ for the Be star. The minimum mass of the unseen companion, assuming an edge-on inclination ($i = 90^{\circ}$), is $9.8\pm 0.7\,M_\odot$. We rule out the presence of non-degenerate companions in ALS 8814, indicating that it can only be a BH. This discovery represents a robust case of a Be-BH binary, identified purely through precise RV measurements from a single set of lines. The extremely low peculiar velocity of ALS 8814 suggests that the BH is formed via a direct core-collapse with a negligible natal kick, implying an almost perfect alignment between the Be star's spin and the orbital plane. In this context, the binary's inclination angle is estimated to be 22$^{\circ}$-49$^{\circ}$ by analyzing the shallow double-peaked profile of the H$α$ emission line. This inclination range corresponds to a BH mass estimate between $15\,M_\odot$ and $58\,M_\odot$. As the only unambiguous Be-BH binary system known to date, ALS 8814 provides valuable constraints on the BH formation in a binary system with a high-mass companion. △ Less

Submitted 29 May, 2025; originally announced May 2025.

Comments: 76 pages, 29 figures, to be submitted

First Light And Reionization Epoch Simulations (FLARES) -- XIX: Supermassive black hole mergers in the early Universe and their environmental dependence

Authors: Shihong Liao, Dimitrios Irodotou, Maxwell G. A. Maltz, Christopher C. Lovell, Zhen Jiang, Sophie L. Newman, Aswin P. Vijayan, Paurush Punyasheel, William J. Roper, Louise T. C. Seeyave, Sonja Soininen, Peter A. Thomas, Stephen M. Wilkins

Abstract: The upcoming space-based gravitational wave (GW) observatory, LISA, is expected to detect GW signals from supermassive black hole (SMBH) mergers occurring at high redshifts. However, understanding the origin and growth of SMBHs in the early Universe remains an open problem in astrophysics. In this work, we utilize the First Light And Reionization Epoch Simulations (FLARES), a suite of cosmological… ▽ More The upcoming space-based gravitational wave (GW) observatory, LISA, is expected to detect GW signals from supermassive black hole (SMBH) mergers occurring at high redshifts. However, understanding the origin and growth of SMBHs in the early Universe remains an open problem in astrophysics. In this work, we utilize the First Light And Reionization Epoch Simulations (FLARES), a suite of cosmological hydrodynamical zoom-in simulations, to study SMBH mergers at $5 \lesssim z \lesssim 10$ across a wide range of environments. Most mergers in FLARES involve secondary SMBHs near the seed mass ($m_{\rm seed} \approx 1.5 \times 10^{5}~{\rm M}_{\odot}$) while primary SMBHs span up to $10^{9}~{\rm M}_{\odot}$, resulting in mass ratios from $q \sim 10^{-4}$ to $1$, with a peak at $q \sim 1$. The number of mergers increases rapidly towards lower redshifts, and the comoving total number density scales with overdensity as $n_{\rm merger} = 10^{-3.81} (1 + δ)^{4.78}$. Denser regions host more massive mergers, with higher merger redshifts and lower mass ratios. Within the FLARES redshift range, LISA is expected to detect mergers with $10^{5} \lesssim M_{\rm tot}/{\rm M}_{\odot} \lesssim 10^{8}$ and $q \gtrsim 10^{-2}$, corresponding to a detection rate of $0.030~{\rm yr}^{-1}$ for events with signal-to-noise ratio ${\rm SNR} \geq 10$. Our study demonstrates the sensitivity of GW predictions at high redshifts to SMBH seed models and merger time delays, highlighting the need for improved modeling in future cosmological simulations to maximize LISA's scientific return. △ Less

Submitted 20 October, 2025; v1 submitted 18 May, 2025; originally announced May 2025.

Comments: 16 pages, 13 figures, accepted for publication in MNRAS

Journal ref: Mon Not R Astron Soc (2025) 3055-3070

Ultra-diffuse galaxies in the EAGLE simulation

Authors: Haonan Zheng, Shihong Liao, Liang Gao, Fangzhou Jiang

Abstract: We use the highest-resolution EAGLE simulation, Recal-L025N0752, to study the properties and formation of ultra-diffuse galaxies (UDGs). We identify 181 UDGs and find their properties closely match observations. The total masses of EAGLE UDGs range from ${\sim}5\times 10^{8}~M_{\odot}$ to ${\sim}2\times 10^{11}~M_{\odot}$, indicating that they are dwarf galaxies rather than failed $L_\star$ galaxi… ▽ More We use the highest-resolution EAGLE simulation, Recal-L025N0752, to study the properties and formation of ultra-diffuse galaxies (UDGs). We identify 181 UDGs and find their properties closely match observations. The total masses of EAGLE UDGs range from ${\sim}5\times 10^{8}~M_{\odot}$ to ${\sim}2\times 10^{11}~M_{\odot}$, indicating that they are dwarf galaxies rather than failed $L_\star$ galaxies. EAGLE UDGs are not a distinct population, but rather a subset of dwarf galaxies, as their properties generally form a continuous distribution with those of normal dwarf galaxies. Unlike the situations in previous studies, the extended sizes of field UDGs in EAGLE are not driven by high halos spin or by supernova-induced stellar expansion, but instead largely arise from high spins in their star-forming gas and thus the newly formed stars at large radii. This might be attributed to galactic fountains, by which star-forming gas are launched to large halo-centric distances and acquire additional angular momentum through interactions with the circumgalactic medium. For satellite UDGs, ${\sim} 60 \%$ of them were already UDGs before falling into the host galaxy, while the remaining ${\sim} 40\%$ were normal galaxies prior to infall and subsequently transformed into UDGs due to tidal effects after infall. △ Less

Submitted 27 November, 2025; v1 submitted 21 April, 2025; originally announced April 2025.

Comments: 16 pages, 9 figures, accepted by ApJ

Analysis of the Gaia Data Release 3 parallax bias at bright magnitudes

Authors: Ye Ding, Shilong Liao, Shangyu Wen, Zhaoxiang Qi

Abstract: The combination of visual and spectroscopic orbits in binary systems enables precise distance measurements without additional assumptions, making them ideal for examining the parallax zero-point offset (PZPO) at bright magnitudes (G < 13) in Gaia. We compiled 249 orbital parallaxes from 246 binary systems and used Markov Chain Monte Carlo (MCMC) simulations to exclude binaries where orbital motion… ▽ More The combination of visual and spectroscopic orbits in binary systems enables precise distance measurements without additional assumptions, making them ideal for examining the parallax zero-point offset (PZPO) at bright magnitudes (G < 13) in Gaia. We compiled 249 orbital parallaxes from 246 binary systems and used Markov Chain Monte Carlo (MCMC) simulations to exclude binaries where orbital motion significantly impacts parallaxes. After removing systems with substantial parallax errors, large discrepancies between orbital and Gaia parallaxes, and selecting systems with orbital periods under 100 days, a final sample of 44 binaries was retained.The weighted mean PZPO for this sample is -38.9 $\pm$ 10.3 $μ$as, compared to -58.0 $\pm$ 10.1 $μ$as for the remaining systems, suggesting that orbital motion significantly affects parallax measurements. These formal uncertainties of the PZPO appear to be underestimated by a factor of approximately 2.0. For bright stars with independent trigonometric parallaxes from VLBI and HST, the weighted mean PZPOs are -14.8 $\pm$ 10.6 and -31.9 $\pm$ 14.1 $μ$as, respectively. Stars with $G \leq 8$ exhibit a more pronounced parallax bias, with some targets showing unusually large deviations, likely due to systematic calibration errors in Gaia for bright stars. The orbital parallaxes dataset compiled in this work serves as a vital resource for validating parallaxes in future Gaia data releases. △ Less

Submitted 13 February, 2025; v1 submitted 11 February, 2025; originally announced February 2025.

Comments: 11 pages, 8 figures, accepted by AJ

Measuring the Hubble constant through the galaxy pairwise peculiar velocity

Authors: Wangzheng Zhang, Ming-chung Chu, Shihong Liao, Shek Yeung, Hui-Jie Hu

Abstract: The Hubble constant $H_0$, the current expansion rate of the universe, is one of the most important parameters in cosmology. The cosmic expansion regulates the mutually approaching motion of a pair of celestial objects due to their gravity. Therefore, the mean pairwise peculiar velocity of celestial objects, which quantifies their relative motion, is sensitive to both $H_0$ and the dimensionless t… ▽ More The Hubble constant $H_0$, the current expansion rate of the universe, is one of the most important parameters in cosmology. The cosmic expansion regulates the mutually approaching motion of a pair of celestial objects due to their gravity. Therefore, the mean pairwise peculiar velocity of celestial objects, which quantifies their relative motion, is sensitive to both $H_0$ and the dimensionless total matter density $Ω_m$. Based on this, using the Cosmicflows-4 data, we measured $H_0$ for the first time via the galaxy pairwise velocity in the nonlinear and quasi-linear range. Our results yield $H_0=75.5\pm1.4$ km s$^{-1}$ Mpc$^{-1}$ and $Ω_m=0.311^{+0.029}_{-0.028}$ . The uncertainties of $H_0$ and $Ω_m$ can be improved to around 0.6% and 2%, respectively, if the statistical errors become negligible in the future. △ Less

Submitted 5 December, 2024; originally announced December 2024.

Comments: 10 pages, 3 main + 2 appendix figures, accepted for publication in ApJL

Journal ref: ApJ Letters 978, 1 (2025)

DULAG: A DUal and Lensed AGN candidate catalog with GMP method

Authors: Qiqi Wu, M. Scialpi, Shilong Liao, F. Mannucci, Zhaoxiang Qi

Abstract: Context. A series of studies have demonstrated that the Gaia multipeak method (GMP) is a very efficient technique to select active galactic nucleus (AGN) pair candidates. The number of candidates is determined by the size of the input AGN catalogs, usually limited to spectroscopically-confirmed objects. Aims. The objective of this work is to compile a larger and highly reliable catalog of GMP pair… ▽ More Context. A series of studies have demonstrated that the Gaia multipeak method (GMP) is a very efficient technique to select active galactic nucleus (AGN) pair candidates. The number of candidates is determined by the size of the input AGN catalogs, usually limited to spectroscopically-confirmed objects. Aims. The objective of this work is to compile a larger and highly reliable catalog of GMP pair candidates extracted from the six million objects the Gaia AGN catalog, the majority of which lack spectroscopic information. Methods. In order to ascertain the differences in the properties of GMP pair candidates compared to normal AGN, we conducted an investigation utilising samples of GMP AGN. These differences were employed to establish the optimal selecting criteria, which ultimately led to the identification of a highly reliable candidate catalog. Results. We found significant differences in astrometry and multi-band colour distribution between normal AGN and GMP pair candidates. A DUal and Lensed AGN candidate catalog with GMP method (DULAG) comprising 5,286 sources was ultimately compiled, accompanied by a highly reliable Golden sample of 1,867 sources. A total of 37 sources in the Golden sample have been identified as dual AGN or lensed AGN. For the majority of sources in the Golden sample, we provide reference redshifts and find three close AGN pair candidates among them. △ Less

Submitted 8 November, 2024; originally announced November 2024.

Comments: 13 pages, 13 figures, 6tables, A&A accepted

Journal ref: A&A 692, A154 (2024)

First Light and Reionisation Epoch Simulations (FLARES) XVII: Learning the galaxy-halo connection at high redshifts

Authors: Maxwell G. A. Maltz, Peter A. Thomas, Christoper C. Lovell, William J. Roper, Aswin P. Vijayan, Dimitrios Irodotou, Shihong Liao, Louise T. C. Seeyave, Stephen M. Wilkins

Abstract: Understanding the galaxy-halo relationship is not only key for elucidating the interplay between baryonic and dark matter, it is essential for creating large mock galaxy catalogues from N-body simulations. High-resolution hydrodynamical simulations are limited to small volumes by their large computational demands, hindering their use for comparisons with wide-field observational surveys. We overco… ▽ More Understanding the galaxy-halo relationship is not only key for elucidating the interplay between baryonic and dark matter, it is essential for creating large mock galaxy catalogues from N-body simulations. High-resolution hydrodynamical simulations are limited to small volumes by their large computational demands, hindering their use for comparisons with wide-field observational surveys. We overcome this limitation by using the First Light and Reionisation Epoch Simulations (FLARES), a suite of high-resolution (M_gas = 1.8 x 10^6 M_Sun) zoom simulations drawn from a large, (3.2 cGpc)^3 box. We use an extremely randomised trees machine learning approach to model the relationship between galaxies and their subhaloes in a wide range of environments. This allows us to build mock catalogues with dynamic ranges that surpass those obtainable through periodic simulations. The low cost of the zoom simulations facilitates multiple runs of the same regions, differing only in the random number seed of the subgrid models; changing this seed introduces a butterfly effect, leading to random differences in the properties of matching galaxies. This randomness cannot be learnt by a deterministic machine learning model, but by sampling the noise and adding it post-facto to our predictions, we are able to recover the distributions of the galaxy properties we predict (stellar mass, star formation rate, metallicity, and size) remarkably well. We also explore the resolution-dependence of our models' performances and find minimal depreciation down to particle resolutions of order M_DM ~ 10^8 M_Sun, enabling the future application of our models to large dark matter-only boxes. △ Less

Submitted 31 October, 2024; originally announced October 2024.

Comments: 19 pages, 12 figures. Submitted to MNRAS

Identifying supermassive black hole recoil in elliptical galaxies

Authors: Alexander Rawlings, Atte Keitaanranta, Max Mattero, Sonja Soininen, Ruby J. Wright, Noa Kallioinen, Shihong Liao, Antti Rantala, Peter H. Johansson, Thorsten Naab, Dimitrios Irodotou

Abstract: We study stellar core growth in simulations of merging massive ($M_\star>10^{11}\,\mathrm{M}_\odot$) elliptical galaxies by a supermassive black hole (SMBH) displaced by gravitational wave induced recoil velocity. With controlled, dense sampling of the SMBH recoil velocity, we find the core radius originally formed by SMBH binary scouring can grow by a factor of 2-3 when the recoil velocity exceed… ▽ More We study stellar core growth in simulations of merging massive ($M_\star>10^{11}\,\mathrm{M}_\odot$) elliptical galaxies by a supermassive black hole (SMBH) displaced by gravitational wave induced recoil velocity. With controlled, dense sampling of the SMBH recoil velocity, we find the core radius originally formed by SMBH binary scouring can grow by a factor of 2-3 when the recoil velocity exceeds $\sim50$ per cent of the central escape velocity, and the mass deficit grows by up to a factor of $\sim4$. Using Bayesian inference we predict the distribution of stellar core sizes formed through this process to peak at $\sim1\,\mathrm{kpc}$. An orbital decomposition of stellar particles within the core reveals that radial orbits dominate over tube orbits when the recoil velocity exceeds the velocity dispersion of the core, whereas tube orbits dominate for the lowest recoil kicks. A change in orbital structure is reflected in the anisotropy parameter, with a central tangential bias present only for recoil velocities less than the local stellar velocity dispersion. Emulating current integral field unit observations of the stellar line-of-sight velocity distribution, we uncover a distinct signature in the Gauss-Hermite symmetric deviation coefficient $h_4$ that uniquely constrains the core size due to binary scouring. This signature is insensitive to the later evolution of the stellar mass distribution due to SMBH recoil. Our results provide a novel method to estimate the SMBH recoil magnitude from observations of local elliptical galaxies, and implies these galaxies primarily experienced recoil velocities less than the stellar velocity dispersion of the core. △ Less

Submitted 26 February, 2025; v1 submitted 17 October, 2024; originally announced October 2024.

Comments: 27 pages, 21 figures, as accepted

Analysis of Gaia Data Release 3 Parallax bias in the Galactic plane

Authors: Ye Ding, Shilong Liao, Qiqi Wu, Zhaoxiang Qi, Zhenghong Tang

Abstract: The systematic errors are inevitable in Gaia published astrometric data. Lindegren et al. (L21) proposed a global recipe to correct for the GEDR3 parallax zero point offset, which did not consider the Galactic plane. The applicability of their correction model to the Galactic plane remains uncertain. We attempt to have an independent investigation into the sample dependence of the L21 correction,… ▽ More The systematic errors are inevitable in Gaia published astrometric data. Lindegren et al. (L21) proposed a global recipe to correct for the GEDR3 parallax zero point offset, which did not consider the Galactic plane. The applicability of their correction model to the Galactic plane remains uncertain. We attempt to have an independent investigation into the sample dependence of the L21 correction, and its applicability to the Galactic plane. We collect various samples, including quasars, binaries, and sources with parallaxes from other surveys or methods, to validate the L21 correction, especially in the Galactic plane. We conclude that the L21 correction exhibits sample dependence, and does not apply effectively to the Galactic plane. We present a new parallax bias correction applying to the Galactic plane, offering improvements over the existing L21 correction. The correction difference between L21 and this work can go up to 0.01 mas within certain ranges of magnitude and colour. This work provides an additional recipe for users of Gaia parallaxes, especially for sources located near the Galactic plane. △ Less

Submitted 23 September, 2024; originally announced September 2024.

Comments: 16 pages, 17 figures, have been accepted by A&A

Prospects for detecting cosmic filaments in Lyman-alpha emission across redshifts $z=2-5$

Authors: Yizhou Liu, Liang Gao, Shihong Liao, Kai Zhu

Abstract: The standard $\rm Λ$CDM cosmological model predicts that a large amount of diffuse neutral hydrogen distributes in cosmic filaments, which could be mapped through Lyman-alpha (Ly$α$) emission observations. We use the hydrodynamical simulation Illustris-TNG50 to investigate the evolution of surface brightness and detectability of neutral hydrogen in cosmic filaments across redshifts $z=2-5$. While… ▽ More The standard $\rm Λ$CDM cosmological model predicts that a large amount of diffuse neutral hydrogen distributes in cosmic filaments, which could be mapped through Lyman-alpha (Ly$α$) emission observations. We use the hydrodynamical simulation Illustris-TNG50 to investigate the evolution of surface brightness and detectability of neutral hydrogen in cosmic filaments across redshifts $z=2-5$. While the HI column density of cosmic filaments decreases with redshift, due to the rising temperature with cosmic time in filaments, the surface brightness of Ly$α$ emission in filaments is brighter at lower redshifts, suggesting that the detection of cosmic filaments is more feasible at lower redshifts. However, most of the Ly$α$ emission from cosmic filaments is around $10^{-21}$ $\rm erg\ s^{-1}cm^{-2}arsec^{-2}$, making it extremely challenging to detect with current observational instruments. We further generate mock images using the Multi-Unit Spectroscopic Explorer (MUSE) spectrograph installed on the Very Large Telescope (VLT) and a MUSE-like spectrograph on the upcoming Extremely Large Telescope (ELT). Our finding indicates that while the VLT can only detect filamentary structures made of dense gas in galactic centers, the ELT is expected to reveal much finer filamentary structures from diffuse neutral hydrogen outside of galaxies. Compared to the VLT, both the number density and the longest length of filaments are greatly boosted with the ELT. Hence the forthcoming ELT is highly promising to provide a clearer view of cosmic filaments in Ly$α$ emission. △ Less

Submitted 3 April, 2025; v1 submitted 17 September, 2024; originally announced September 2024.

Comments: 12 pages, 7 figures, accepted for publication in APJ

Journal ref: ApJ, 2025, 984, 55

Apostle--Auriga: Effects of stellar feedback subgrid models on the evolution of angular momentum in disc galaxies

Authors: Hang Yang, Shihong Liao, Azadeh Fattahi, Carlos S. Frenk, Liang Gao, Qi Guo, Shi Shao, Lan Wang, Ruby J. Wright, Guangquan Zeng

Abstract: Utilizing the Apostle--Auriga simulations, which start from the same zoom-in initial conditions of Local Group-like systems but run with different galaxy formation subgrid models and hydrodynamic solvers, we study the impact of stellar feedback models on the evolution of angular momentum in disc galaxies. At $z = 0$, Auriga disc galaxies tend to exhibit higher specific angular momenta compared to… ▽ More Utilizing the Apostle--Auriga simulations, which start from the same zoom-in initial conditions of Local Group-like systems but run with different galaxy formation subgrid models and hydrodynamic solvers, we study the impact of stellar feedback models on the evolution of angular momentum in disc galaxies. At $z = 0$, Auriga disc galaxies tend to exhibit higher specific angular momenta compared to their cross-matched Apostle counterparts. By tracing the evolution history of the Lagrangian mass tracers of the in-situ star particles in the $z = 0$ galaxies, we find that the specific angular momentum distributions of the gas tracers from the two simulations at the halo accretion time are relatively similar. The present-day angular momentum difference is mainly driven by the physical processes occurring inside dark matter haloes, especially galactic fountains. Due to the different subgrid implementations of stellar feedback processes, Auriga galaxies contain a high fraction of gas that has gone through recycled fountain (${\sim} 65$ per cent) which could acquire angular momentum through mixing with the high angular momentum circumgalactic medium (CGM). In Apostle, however, the fraction of gas that has undergone the recycled fountain process is significantly lower (down to ${\sim} 20$ per cent for Milky Way-sized galaxies) and the angular momentum acquisition from the CGM is marginal. As a result, the present-day Auriga galaxies overall have higher specific angular momenta. △ Less

Submitted 19 October, 2024; v1 submitted 19 August, 2024; originally announced August 2024.

Comments: after revised, accepted for publication in MNRAS

Assembly History and Internal Structure of Cluster Cold Dark Matter Haloes

Authors: Qingxiang Chen, Shihong Liao, Jie Wang, Liang Gao

Abstract: We use the Phoenix simulations to study the mass assembly history and internal structures of cluster dark matter haloes ($M_{200} \gtrsim 5\times 10^{14} h^{-1}{\rm M}_\odot$). We confirm that cluster haloes grow inside-out, similar to galactic haloes. Major merger events dominate the growth of the internal region and minor mergers/diffuse accretion shape the outskirts. However, compared to galact… ▽ More We use the Phoenix simulations to study the mass assembly history and internal structures of cluster dark matter haloes ($M_{200} \gtrsim 5\times 10^{14} h^{-1}{\rm M}_\odot$). We confirm that cluster haloes grow inside-out, similar to galactic haloes. Major merger events dominate the growth of the internal region and minor mergers/diffuse accretion shape the outskirts. However, compared to galactic haloes, cluster haloes tend to have a younger and more actively evolving inner region. On average, the majority of mass (> 80%) in the inner region ($R< 0.1 r_{200}$) of Phoenix haloes is accreted after $z = 3$, while for galactic haloes, most mass in the central region has already been accreted before $z=6$. The density profiles of cluster haloes are less stable than those of galactic haloes over different radii. The enclosed mass within $50$ or $150$ kpc of all Phoenix haloes evolves substantially in the past ${\sim} 7$ Gyr, while galactic haloes remained stable during the same period. We suggest that the relatively younger and more active state explains the various observations of cluster haloes, especially in central regions. △ Less

Submitted 9 August, 2024; originally announced August 2024.

Comments: 12 pages, 11 figures, accepted for publication in MNRAS

Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry

Authors: Gaia Collaboration, P. Panuzzo, T. Mazeh, F. Arenou, B. Holl, E. Caffau, A. Jorissen, C. Babusiaux, P. Gavras, J. Sahlmann, U. Bastian, Ł. Wyrzykowski, L. Eyer, N. Leclerc, N. Bauchet, A. Bombrun, N. Mowlavi, G. M. Seabroke, D. Teyssier, E. Balbinot, A. Helmi, A. G. A. Brown, A. Vallenari, T. Prusti, J. H. J. de Bruijne , et al. (390 additional authors not shown)

Abstract: Gravitational waves from black-hole merging events have revealed a population of extra-galactic BHs residing in short-period binaries with masses that are higher than expected based on most stellar evolution models - and also higher than known stellar-origin black holes in our Galaxy. It has been proposed that those high-mass BHs are the remnants of massive metal-poor stars. Gaia astrometry is exp… ▽ More Gravitational waves from black-hole merging events have revealed a population of extra-galactic BHs residing in short-period binaries with masses that are higher than expected based on most stellar evolution models - and also higher than known stellar-origin black holes in our Galaxy. It has been proposed that those high-mass BHs are the remnants of massive metal-poor stars. Gaia astrometry is expected to uncover many Galactic wide-binary systems containing dormant BHs, which may not have been detected before. The study of this population will provide new information on the BH-mass distribution in binaries and shed light on their formation mechanisms and progenitors. As part of the validation efforts in preparation for the fourth Gaia data release (DR4), we analysed the preliminary astrometric binary solutions, obtained by the Gaia Non-Single Star pipeline, to verify their significance and to minimise false-detection rates in high-mass-function orbital solutions. The astrometric binary solution of one source, Gaia BH3, implies the presence of a 32.70 \pm 0.82 M\odot BH in a binary system with a period of 11.6 yr. Gaia radial velocities independently validate the astrometric orbit. Broad-band photometric and spectroscopic data show that the visible component is an old, very metal-poor giant of the Galactic halo, at a distance of 590 pc. The BH in the Gaia BH3 system is more massive than any other Galactic stellar-origin BH known thus far. The low metallicity of the star companion supports the scenario that metal-poor massive stars are progenitors of the high-mass BHs detected by gravitational-wave telescopes. The Galactic orbit of the system and its metallicity indicate that it might belong to the Sequoia halo substructure. Alternatively, and more plausibly, it could belong to the ED-2 stream, which likely originated from a globular cluster that had been disrupted by the Milky Way. △ Less

Submitted 19 April, 2024; v1 submitted 16 April, 2024; originally announced April 2024.

Comments: 23 pages, accepted fro publication in A&A Letters. New version with small fixes

The evolutionary pathways of disk galaxies with different sizes

Authors: Hong-Chuan Ma, Min Du, Luis C. Ho, Ming-jie Sheng, Shihong Liao

Abstract: From the IllustrisTNG-50 simulation, a sample of 836 central disk galaxies with tiny stellar halos is chosen to study the inherent evolution of galaxies driven by nature. These galaxies are classified as compact, normal, or extended by referencing their locations on the mass-size ($M_\star-R_{\rm 1/2}$) diagram. This research demonstrates the distinctive evolutionary pathways of galaxies with diff… ▽ More From the IllustrisTNG-50 simulation, a sample of 836 central disk galaxies with tiny stellar halos is chosen to study the inherent evolution of galaxies driven by nature. These galaxies are classified as compact, normal, or extended by referencing their locations on the mass-size ($M_\star-R_{\rm 1/2}$) diagram. This research demonstrates the distinctive evolutionary pathways of galaxies with different sizes in IllustrisTNG simulations, primarily driven by nature. It is confirmed that disk galaxies inherit the angular momentum of their parent dark matter halos. More compact galaxies form earlier within halos possessing lower specific angular momentum through heightened star formation during the early phase at redshifts above 2. During the later phase, the size of extended galaxies experiences more pronounced growth by accreting gas with high angular momentum. Additionally, we reveal that many key characteristics of galaxies are linked to their mass and size: (1) compact galaxies tend to exhibit higher metal content, proportional to the potential well $\frac{M_\star}{R_{\rm 1/2}}$, (2) compact galaxies host more massive bulges and black holes, and higher central concentration. Furthermore, our analysis indicates that galaxies of all types continue to actively engage in star formation, with no evident signs of quenching attributed to their varying sizes and angular momenta. △ Less

Submitted 2 July, 2024; v1 submitted 16 April, 2024; originally announced April 2024.

Comments: 11 pages, 11 figures. Accepted for publication in A&A

Journal ref: A&A 689, A293 (2024)

First Light and Reionization Epoch Simulations (FLARES) -- XV: The physical properties of super-massive black holes and their impact on galaxies in the early universe

Authors: Stephen M. Wilkins, Jussi K. Kuusisto, Dimitrios Irodotou, Shihong Liao, Christopher C. Lovell, Sonja Soininen, Sabrina C. Berger, Sophie L. Newman, William J. Roper, Louise T. C. Seeyave, Peter A. Thomas, Aswin P. Vijayan

Abstract: Understanding the co-evolution of super-massive black holes (SMBHs) and their host galaxies remains a key challenge of extragalactic astrophysics, particularly the earliest stages at high-redshift. However, studying SMBHs at high-redshift with cosmological simulations, is challenging due to the large volumes and high-resolution required. Through its innovative simulation strategy, the First Light… ▽ More Understanding the co-evolution of super-massive black holes (SMBHs) and their host galaxies remains a key challenge of extragalactic astrophysics, particularly the earliest stages at high-redshift. However, studying SMBHs at high-redshift with cosmological simulations, is challenging due to the large volumes and high-resolution required. Through its innovative simulation strategy, the First Light And Reionisation Epoch Simulations (FLARES) suite of cosmological hydrodynamical zoom simulations allows us to simulate a much wider range of environments which contain SMBHs with masses extending to $M_{\bullet}>10^{9}\ M_{\odot}$ at $z=5$. In this paper, we use FLARES to study the physical properties of SMBHs and their hosts in the early Universe ($5\le\, z \le10$). FLARES predicts a sharply declining density with increasing redshift, decreasing by a factor of 100 over the range $z=5\to 10$. Comparison between our predicted bolometric luminosity function and pre-\emph{JWST} observations yield a good match. However, recent \emph{JWST} observations appear to suggest a larger contribution of SMBHs than previously observed, or predicted by FLARES. Finally, by using a re-simulation with AGN feedback disabled, we explore the impact of AGN feedback on their host galaxies. This reveals that AGN feedback results in a reduction of star formation activity, even at $z>5$, but only in the most massive galaxies. A deeper analysis reveals that AGN are also the cause of suppressed star formation in passive galaxies but that the presence of an AGN doesn't necessarily result in the suppression of star formation. △ Less

Submitted 18 March, 2025; v1 submitted 3 April, 2024; originally announced April 2024.

Comments: 17 pages, 13 figures, accepted for publication in the Open Journal of Astrophysics. The first two authors are joint primary authors

The Physical Origin of the Mass-Size Relation and Its Scatter of Disk Galaxies

Authors: Min Du, Hong-Chuan Ma, Wen-Yu Zhong, Luis C. Ho, Shihong Liao, Yingjie Peng

Abstract: Utilizing a kinematic decomposition of simulated galaxies, we focus on galaxies with tiny kinematically inferred stellar halos, indicative of weak external influences. We investigate the intricate interplay between internal (natural) and external (nurture) processes in shaping the scaling relationships of specific angular momentum ($j_\star$), stellar mass ($M_\star$), and size of disk galaxies wi… ▽ More Utilizing a kinematic decomposition of simulated galaxies, we focus on galaxies with tiny kinematically inferred stellar halos, indicative of weak external influences. We investigate the intricate interplay between internal (natural) and external (nurture) processes in shaping the scaling relationships of specific angular momentum ($j_\star$), stellar mass ($M_\star$), and size of disk galaxies within the IllustrisTNG simulation. The correlation among mass, size, and angular momentum of galaxies is examined by comparing simulations with observations and the theoretical predictions of the exponential hypothesis. Galaxies with tiny stellar halos exhibit a large scatter in the $j_\star$-$M_\star$ relation, which suggests that it is inherently present in their initial conditions. The analysis reveals that the disks of these galaxies adhere to the exponential hypothesis, resulting in a tight fiducial $j_\star$-$M_\star$-scale length (size) relation that is qualitatively consistent with observations. The inherent scatter in $j_\star$ provides a robust explanation for the mass-size relation and its substantial variability. Notably, galaxies that are moderately influenced by external processes closely adhere to a scaling relation akin to that of galaxies with tiny stellar halos. This result underscores the dominant role of internal processes in shaping the overall $j_\star$-$M_\star$ and mass-size relation, with external effects playing a relatively minor role in disk galaxies. Furthermore, the correlation between galaxy size and the virial radius of the dark matter halo exists but fails to provide strong evidence of the connection between galaxies and their parent dark matter halos. △ Less

Submitted 25 March, 2024; originally announced March 2024.

Comments: 11 pages, 9 figures, accepted for publication in A&A

Journal ref: A&A 686, A168 (2024)

The influence of baryons on low-mass haloes

Authors: Haonan Zheng, Sownak Bose, Carlos S. Frenk, Liang Gao, Adrian Jenkins, Shihong Liao, Volker Springel, Jie Wang, Simon D. M. White

Abstract: The Voids-within-Voids-within-Voids (VVV) project used dark-matter-only simulations to study the abundance and structure of dark matter haloes over the full mass range populated in the standard $Λ\mathrm{CDM}$ cosmology. Here we explore how baryonic effects modify these results for $z=0$ halo masses in the range $10^4$ to $10^7~\mathrm{M_\odot}$, below the threshold for galaxy formation. Our main… ▽ More The Voids-within-Voids-within-Voids (VVV) project used dark-matter-only simulations to study the abundance and structure of dark matter haloes over the full mass range populated in the standard $Λ\mathrm{CDM}$ cosmology. Here we explore how baryonic effects modify these results for $z=0$ halo masses in the range $10^4$ to $10^7~\mathrm{M_\odot}$, below the threshold for galaxy formation. Our main study focuses on three simulations from identical initial conditions at $z=127$, one following dark matter only, one including non-radiative gas, and one additionally including the baryonic physics relevant in this halo mass range (cooling and photoheating). In the non-radiative simulation, above $10^{5.5}~\mathrm{M_\odot}$, halo abundance and internal structure are very similar to the dark-matter-only simulation, and the baryon to dark matter ratio is everywhere close to the cosmic value. At lower mass, this ratio drops and haloes are less concentrated and less massive in the non-radiative case. Test simulations at higher resolution show this to be mainly a resolution effect; the expected drop in baryon content due to residual pressure effects only becomes substantial for $z=0$ haloes below $\sim 10^{2.7}~\mathrm{M_\odot}$. However, gas is heated by reionization at $z=6$ in our "full physics" run, and this results in almost complete expulsion of gas from all haloes in our simulated mass range. This suppresses the halo mass function by $\sim 30 \%$, lowers halo concentration, and consequently weakens the dark matter annihilation signal by $\sim 40-60 \%$. △ Less

Submitted 9 August, 2024; v1 submitted 25 March, 2024; originally announced March 2024.

Comments: 12+2 pages, 9 figures

Journal ref: Monthly Notices of the Royal Astronomical Society, Volume 532, Issue 3, August 2024, Pages 3151-3165

The Present-Day Mass Function of Star Clusters in the Solar Neighborhood

Authors: Xiaoying Pang, Siqi Liao, Jiadong Li, Zhiqiang Yan, Mingjie Jian, M. B. N. Kouwenhoven, Shih-Yun Tang, Yifan Wang

Abstract: This work analyses the present-day mass function (PDMF) of 93~star clusters utilizing Gaia DR3 data, with membership determined by the StarGo machine learning algorithm. The impact of unresolved binary systems on mass estimation is rigorously assessed, adopting three mass ratio profiles for correction. The PDMF is characterized by the power-law index, $α$, derived through a robust maximum likeliho… ▽ More This work analyses the present-day mass function (PDMF) of 93~star clusters utilizing Gaia DR3 data, with membership determined by the StarGo machine learning algorithm. The impact of unresolved binary systems on mass estimation is rigorously assessed, adopting three mass ratio profiles for correction. The PDMF is characterized by the power-law index, $α$, derived through a robust maximum likelihood method that avoids biases associated with data binning. The value of $α$ for stars between the completeness limited mass of Gaia with a mean 0.3 $M_\odot$ for our cluster samples and 2 $M_\odot$, exhibits stability for clusters younger than 200 Myr, decreasing for older clusters, particularly when considering stars within the half-mass radius. The PDMF of these star clusters is consistent with a dynamically evolved Kroupa IMF via the loss of low-mass stars. Cluster morphology shows a correlation with $α$, as $α$ values exhibit a decreasing trend from filamentary to tidal-tail clusters, mirroring the sequence of increasing cluster age. The dependence of $α$ on total cluster mass is weak, with a subtle increase for higher-mass clusters, especially outside the half-mass radius. We do not observe a correlation between $α$ and the mean metallicity of the clusters. Younger clusters have lower metallicity compared to their older counterparts, which indicates that the older clusters might have migrated to the solar neighbourhood from the inner disk. A comparison with numerical models incorporating a black hole population suggests the need for observations of distant, older, massive open clusters to determine whether or not they contain black holes. △ Less

Submitted 13 March, 2024; originally announced March 2024.

Comments: 19 pages, 10 figures, accepted to ApJ

Measuring neutrino mass and asymmetry with matter pairwise velocities

Authors: Wangzheng Zhang, Ming-chung Chu, Rui Hu, Shihong Liao, Shek Yeung

Abstract: Neutrinos are believed to be the most abundant fermions in the Universe, but their masses are unknown, except for being non-zero but much smaller than other fermions. Cosmological relic neutrinos could also have non-zero chemical potentials (or asymmetries). Using neutrino-involved N-body simulations, we investigate the neutrino effects on the matter pairwise velocity, which itself is an interesti… ▽ More Neutrinos are believed to be the most abundant fermions in the Universe, but their masses are unknown, except for being non-zero but much smaller than other fermions. Cosmological relic neutrinos could also have non-zero chemical potentials (or asymmetries). Using neutrino-involved N-body simulations, we investigate the neutrino effects on the matter pairwise velocity, which itself is an interesting probe of cosmology. We find that for light-halo ($[10^{11},10^{13}]\ M_\odot$) mean pairwise velocity, in the transition range ($[4,15]\ \mathrm{Mpc}$), the effects of neutrino masses overwhelm the effects of neutrino asymmetries, while in the two-halo-group range ($[25,50]\ \mathrm{Mpc}$), for both light and heavy haloes ($[10^{13},10^{15}]\ M_\odot$), the effects of neutrino asymmetries dominate, making it possible to disentangle the two effects. We provide fitting formulae to quantify the effects of neutrino mass and asymmetry on halo-halo pairwise velocities. △ Less

Submitted 27 August, 2025; v1 submitted 7 December, 2023; originally announced December 2023.

Comments: 15 pages, 4 main + 3 appendix figures, accepted for publication in MNRAS; v3: fix symbol typo in Eq. (10)

Journal ref: MNRAS 529, 360 (2024)

RABBITS -- I. The crucial role of nuclear star formation in driving the coalescence of supermassive black hole binaries

Authors: Shihong Liao, Dimitrios Irodotou, Peter H. Johansson, Thorsten Naab, Francesco Paolo Rizzuto, Jessica M. Hislop, Alexander Rawlings, Ruby J. Wright

Abstract: In this study of the `Resolving supermAssive Black hole Binaries In galacTic hydrodynamical Simulations' (RABBITS) series, we focus on the hardening and coalescing process of supermassive black hole (SMBH) binaries in galaxy mergers. For simulations including different galaxy formation processes (i.e. gas cooling, star formation, SMBH accretion, stellar and AGN feedback), we systematically control… ▽ More In this study of the `Resolving supermAssive Black hole Binaries In galacTic hydrodynamical Simulations' (RABBITS) series, we focus on the hardening and coalescing process of supermassive black hole (SMBH) binaries in galaxy mergers. For simulations including different galaxy formation processes (i.e. gas cooling, star formation, SMBH accretion, stellar and AGN feedback), we systematically control the effect of stochastic eccentricity by fixing it to similar values during the SMBH hardening phase. We find a strong correlation between the SMBH merger time-scales and the presence of nuclear star formation. Throughout the galaxy merging process, gas condenses at the centre due to cooling and tidal torques, leading to nuclear star formation. These recently formed stars, which inherit low angular momenta from the gas, contribute to the loss cone and assist in the SMBH hardening via three-body interactions. Compared to non-radiative hydrodynamical runs, the SMBH merger time-scales measured from the runs including cooling, stellar and SMBH physical processes tend to be shortened by a factor of ${\sim}1.7$. After fixing the eccentricity to the range of $e \sim 0.6$--$0.8$ during the hardening phase, the simulations with AGN feedback reveal merger time-scales of ${\sim} 100$--$500$ Myr for disc mergers and ${\sim} 1$--$2$ Gyr for elliptical mergers. With a semi-analytical approach, we find that the torque interaction between the binary and its circumbinary disc has minimal impact on the shrinking of the binary orbit in our retrograde galaxy merger. Our results are useful in improving the modelling of SMBH merger time-scales and gravitational wave event rates. △ Less

Submitted 1 February, 2024; v1 submitted 2 November, 2023; originally announced November 2023.

Comments: 18 pages, 8 main + 3 appendix figures, renamed as RABBITS I, accepted for publication in MNRAS

Journal ref: MNRAS 528, 5080 (2024)

RABBITS -- II. The impact of AGN feedback on coalescing supermassive black holes in disc and elliptical galaxy mergers

Authors: Shihong Liao, Dimitrios Irodotou, Peter H. Johansson, Thorsten Naab, Francesco Paolo Rizzuto, Jessica M. Hislop, Ruby J. Wright, Alexander Rawlings

Abstract: In this study of the `Resolving supermAssive Black hole Binaries In galacTic hydrodynamical Simulations' (RABBITS) series, we investigate the orbital evolution of supermassive black holes (SMBHs) during galaxy mergers. We simulate both disc and elliptical galaxy mergers using the KETJU code, which can simultaneously follow galaxy (hydro-)dynamics and small-scale SMBH dynamics with post-Newtonian c… ▽ More In this study of the `Resolving supermAssive Black hole Binaries In galacTic hydrodynamical Simulations' (RABBITS) series, we investigate the orbital evolution of supermassive black holes (SMBHs) during galaxy mergers. We simulate both disc and elliptical galaxy mergers using the KETJU code, which can simultaneously follow galaxy (hydro-)dynamics and small-scale SMBH dynamics with post-Newtonian corrections. With our SMBH binary subgrid model, we show how active galactic nuclei (AGNs) feedback affects galaxy properties and SMBH coalescence. We find that simulations without AGN feedback exhibit excessive star formation, resulting in merger remnants that deviate from observed properties. Kinetic AGN feedback proves more effective than thermal AGN feedback in expelling gas from the centre and quenching star formation. The different central galaxy properties, which are a result of distinct AGN feedback models, lead to varying rates of SMBH orbital decay. In the dynamical friction phase, galaxies with higher star formation and higher SMBH masses possess denser centres, become more resistant to tidal stripping, experience greater dynamical friction, and consequently form SMBH binaries earlier. As AGN feedback reduces gas densities in the centres, dynamical friction by stars dominates over gas. In the SMBH hardening phase, compared to elliptical mergers, disc mergers exhibit higher central densities of newly formed stars, resulting in accelerated SMBH hardening and shorter merger time-scales (i.e. $\lesssim 500$ Myr versus $\gtrsim 1$ Gyr). Our findings highlight the importance of AGN feedback and its numerical implementation in understanding the SMBH coalescing process, a key focus for low-frequency gravitational wave observatories. △ Less

Submitted 24 April, 2024; v1 submitted 2 November, 2023; originally announced November 2023.

Comments: 24 pages, 10 main + 4 appendix figures, renamed as RABBITS II, accepted for publication in MNRAS

Journal ref: MNRAS 530, 4058 (2024)

The abundance of dark matter haloes down to Earth mass

Authors: Haonan Zheng, Sownak Bose, Carlos S. Frenk, Liang Gao, Adrian Jenkins, Shihong Liao, Yizhou Liu, Jie Wang

Abstract: We use the Voids-within-Voids-within-Voids (VVV) simulations, a suite of successive nested N-body simulations with extremely high resolution (denoted, from low to high resolution, by L0 to L7), to test the Press-Schechter (PS), Sheth-Tormen (ST), and extended Press-Schechter (EPS) formulae for the halo abundance over the entire mass range, from mini-haloes of $10^{-6}\ \mathrm{M_\odot}$, to cluste… ▽ More We use the Voids-within-Voids-within-Voids (VVV) simulations, a suite of successive nested N-body simulations with extremely high resolution (denoted, from low to high resolution, by L0 to L7), to test the Press-Schechter (PS), Sheth-Tormen (ST), and extended Press-Schechter (EPS) formulae for the halo abundance over the entire mass range, from mini-haloes of $10^{-6}\ \mathrm{M_\odot}$, to cluster haloes of $10^{15}\ \mathrm{M_\odot}$, at different redshifts, from $z=30$ to the present. We find that at $z=0$ and $z=2$, ST best reproduces the results of L0, which has the mean cosmic density (overdensity $δ=0$), at $10^{11-15} ~\mathrm{M_\odot}$. The higher resolution levels (L1-L7) are biased underdense regions ($δ<-0.6$). The EPS formalism takes this into account since it gives the mass function of a region conditioned, in this case, on having a given underdensity. EPS provides good matches to these higher levels, with deviations $\lesssim 20\%$, at $10^{-6-12.5} ~\mathrm{M_\odot}$. At $z \sim 7-15$, the ST predictions for L0 and the EPS for L1-L7 show somewhat larger deviations from the simulation results. However, at even higher redshifts, $z \sim 30$, EPS fits the simulations well again. We confirm our results by picking more subvolumes from the L0 simulation, finding that our conclusions depend only weakly on the size and overdensity of the region. The good agreement of EPS with the higher-level simulations implies that PS (or ST) gives an accurate description of the total halo mass function in representative regions of the universe. △ Less

Submitted 10 April, 2024; v1 submitted 24 October, 2023; originally announced October 2023.

Comments: 10 pages, 5 figures (additional 2 figures in the appendix)

Journal ref: Monthly Notices of the Royal Astronomical Society, Volume 528, Issue 4, March 2024, Pages 7300-7309

Gaia Focused Product Release: Sources from Service Interface Function image analysis -- Half a million new sources in omega Centauri

Authors: Gaia Collaboration, K. Weingrill, A. Mints, J. Castañeda, Z. Kostrzewa-Rutkowska, M. Davidson, F. De Angeli, J. Hernández, F. Torra, M. Ramos-Lerate, C. Babusiaux, M. Biermann, C. Crowley, D. W. Evans, L. Lindegren, J. M. Martín-Fleitas, L. Palaversa, D. Ruz Mieres, K. Tisanić, A. G. A. Brown, A. Vallenari, T. Prusti, J. H. J. de Bruijne, F. Arenou, A. Barbier , et al. (378 additional authors not shown)

Abstract: Gaia's readout window strategy is challenged by very dense fields in the sky. Therefore, in addition to standard Gaia observations, full Sky Mapper (SM) images were recorded for nine selected regions in the sky. A new software pipeline exploits these Service Interface Function (SIF) images of crowded fields (CFs), making use of the availability of the full two-dimensional (2D) information. This ne… ▽ More Gaia's readout window strategy is challenged by very dense fields in the sky. Therefore, in addition to standard Gaia observations, full Sky Mapper (SM) images were recorded for nine selected regions in the sky. A new software pipeline exploits these Service Interface Function (SIF) images of crowded fields (CFs), making use of the availability of the full two-dimensional (2D) information. This new pipeline produced half a million additional Gaia sources in the region of the omega Centauri ($ω$ Cen) cluster, which are published with this Focused Product Release. We discuss the dedicated SIF CF data reduction pipeline, validate its data products, and introduce their Gaia archive table. Our aim is to improve the completeness of the {\it Gaia} source inventory in a very dense region in the sky, $ω$ Cen. An adapted version of {\it Gaia}'s Source Detection and Image Parameter Determination software located sources in the 2D SIF CF images. We validated the results by comparing them to the public {\it Gaia} DR3 catalogue and external Hubble Space Telescope data. With this Focused Product Release, 526\,587 new sources have been added to the {\it Gaia} catalogue in $ω$ Cen. Apart from positions and brightnesses, the additional catalogue contains parallaxes and proper motions, but no meaningful colour information. While SIF CF source parameters generally have a lower precision than nominal {\it Gaia} sources, in the cluster centre they increase the depth of the combined catalogue by three magnitudes and improve the source density by a factor of ten. This first SIF CF data publication already adds great value to the {\it Gaia} catalogue. It demonstrates what to expect for the fourth {\it Gaia} catalogue, which will contain additional sources for all nine SIF CF regions. △ Less

Submitted 8 November, 2023; v1 submitted 10 October, 2023; originally announced October 2023.

Journal ref: A&A 680, A35 (2023)

Gaia Focused Product Release: A catalogue of sources around quasars to search for strongly lensed quasars

Authors: Gaia Collaboration, A. Krone-Martins, C. Ducourant, L. Galluccio, L. Delchambre, I. Oreshina-Slezak, R. Teixeira, J. Braine, J. -F. Le Campion, F. Mignard, W. Roux, A. Blazere, L. Pegoraro, A. G. A. Brown, A. Vallenari, T. Prusti, J. H. J. de Bruijne, F. Arenou, C. Babusiaux, A. Barbier, M. Biermann, O. L. Creevey, D. W. Evans, L. Eyer, R. Guerra , et al. (376 additional authors not shown)

Abstract: Context. Strongly lensed quasars are fundamental sources for cosmology. The Gaia space mission covers the entire sky with the unprecedented resolution of $0.18$" in the optical, making it an ideal instrument to search for gravitational lenses down to the limiting magnitude of 21. Nevertheless, the previous Gaia Data Releases are known to be incomplete for small angular separations such as those ex… ▽ More Context. Strongly lensed quasars are fundamental sources for cosmology. The Gaia space mission covers the entire sky with the unprecedented resolution of $0.18$" in the optical, making it an ideal instrument to search for gravitational lenses down to the limiting magnitude of 21. Nevertheless, the previous Gaia Data Releases are known to be incomplete for small angular separations such as those expected for most lenses. Aims. We present the Data Processing and Analysis Consortium GravLens pipeline, which was built to analyse all Gaia detections around quasars and to cluster them into sources, thus producing a catalogue of secondary sources around each quasar. We analysed the resulting catalogue to produce scores that indicate source configurations that are compatible with strongly lensed quasars. Methods. GravLens uses the DBSCAN unsupervised clustering algorithm to detect sources around quasars. The resulting catalogue of multiplets is then analysed with several methods to identify potential gravitational lenses. We developed and applied an outlier scoring method, a comparison between the average BP and RP spectra of the components, and we also used an extremely randomised tree algorithm. These methods produce scores to identify the most probable configurations and to establish a list of lens candidates. Results. We analysed the environment of 3 760 032 quasars. A total of 4 760 920 sources, including the quasars, were found within 6" of the quasar positions. This list is given in the Gaia archive. In 87\% of cases, the quasar remains a single source, and in 501 385 cases neighbouring sources were detected. We propose a list of 381 lensed candidates, of which we identified 49 as the most promising. Beyond these candidates, the associate tables in this Focused Product Release allow the entire community to explore the unique Gaia data for strong lensing studies further. △ Less

Submitted 10 October, 2023; originally announced October 2023.

Comments: 35 pages, 60 figures, accepted for publication by Astronomy and Astrophysics

Journal ref: A&A 685, A130 (2024)

Gaia Focused Product Release: Radial velocity time series of long-period variables

Authors: Gaia Collaboration, Gaia Collaboration, M. Trabucchi, N. Mowlavi, T. Lebzelter, I. Lecoeur-Taibi, M. Audard, L. Eyer, P. García-Lario, P. Gavras, B. Holl, G. Jevardat de Fombelle, K. Nienartowicz, L. Rimoldini, P. Sartoretti, R. Blomme, Y. Frémat, O. Marchal, Y. Damerdji, A. G. A. Brown, A. Guerrier, P. Panuzzo, D. Katz, G. M. Seabroke, K. Benson , et al. (382 additional authors not shown)

Abstract: The third Gaia Data Release (DR3) provided photometric time series of more than 2 million long-period variable (LPV) candidates. Anticipating the publication of full radial-velocity (RV) in DR4, this Focused Product Release (FPR) provides RV time series for a selection of LPVs with high-quality observations. We describe the production and content of the Gaia catalog of LPV RV time series, and the… ▽ More The third Gaia Data Release (DR3) provided photometric time series of more than 2 million long-period variable (LPV) candidates. Anticipating the publication of full radial-velocity (RV) in DR4, this Focused Product Release (FPR) provides RV time series for a selection of LPVs with high-quality observations. We describe the production and content of the Gaia catalog of LPV RV time series, and the methods used to compute variability parameters published in the Gaia FPR. Starting from the DR3 LPVs catalog, we applied filters to construct a sample of sources with high-quality RV measurements. We modeled their RV and photometric time series to derive their periods and amplitudes, and further refined the sample by requiring compatibility between the RV period and at least one of the $G$, $G_{\rm BP}$, or $G_{\rm RP}$ photometric periods. The catalog includes RV time series and variability parameters for 9\,614 sources in the magnitude range $6\lesssim G/{\rm mag}\lesssim 14$, including a flagged top-quality subsample of 6\,093 stars whose RV periods are fully compatible with the values derived from the $G$, $G_{\rm BP}$, and $G_{\rm RP}$ photometric time series. The RV time series contain a mean of 24 measurements per source taken unevenly over a duration of about three years. We identify the great most sources (88%) as genuine LPVs, with about half of them showing a pulsation period and the other half displaying a long secondary period. The remaining 12% consists of candidate ellipsoidal binaries. Quality checks against RVs available in the literature show excellent agreement. We provide illustrative examples and cautionary remarks. The publication of RV time series for almost 10\,000 LPVs constitutes, by far, the largest such database available to date in the literature. The availability of simultaneous photometric measurements gives a unique added value to the Gaia catalog (abridged) △ Less

Submitted 9 October, 2023; originally announced October 2023.

Comments: 36 pages, 38 figures

The Timeless Timing Argument and the Mass of the Local Group

Authors: Till Sawala, Jorge Peñarrubia, Shihong Liao, Peter H. Johansson

Abstract: The Timing Argument connects the motion of a two-body system to its mass in an expanding Universe with a finite age, under the assumption that it has evolved on a self-gravitating orbit. It is commonly applied to the present-day Milky Way-M31 system in order to infer its unknown mass from the measured kinematics. We use a set of Local Group analogues from the Uchuu simulation to investigate the Ti… ▽ More The Timing Argument connects the motion of a two-body system to its mass in an expanding Universe with a finite age, under the assumption that it has evolved on a self-gravitating orbit. It is commonly applied to the present-day Milky Way-M31 system in order to infer its unknown mass from the measured kinematics. We use a set of Local Group analogues from the Uchuu simulation to investigate the Timing Argument over cosmic time. We find that the median inferred mass remains almost constant over the past 12 Gyr, even while the haloes themselves grew in mass by more than an order of magnitude. By contrast, we find a closer, and nearly time-invariant agreement between the Timing Argument value and the mass within a sphere of radius equal to the MW-M31 separation, and we identify this as the total mass of the system. We conclude that the comparatively close present-day agreement between the Timing Argument and the sum of the halo masses reflects no underlying relation, but merely echoes the fact that the MW and M31 now contain most (but not all) of the mass of the Local Group system. △ Less

Submitted 18 August, 2023; v1 submitted 25 July, 2023; originally announced July 2023.

Comments: 6 pages, 4 figures, this version accepted to MNRAS Letters

Astrometric mass measurement of compact companions in binary systems with Gaia

Authors: Yilun Wang, Shilong Liao, Nicola Giacobbo, Aleksandra Olejak, Jian Gao, Jifeng Liu

Abstract: For binary systems with an unseen primary and a luminous secondary, the astrometric wobble of the secondary could be used to study the primary. With Gaia, it is possible to measure the mass of the black hole or neutron star with a luminous companion (hereafter BH/NS-LC). Our aim is to provide a method for predicting Gaia's ability in measuring the mass of BH/NS-LCs. We also tried to estimate the n… ▽ More For binary systems with an unseen primary and a luminous secondary, the astrometric wobble of the secondary could be used to study the primary. With Gaia, it is possible to measure the mass of the black hole or neutron star with a luminous companion (hereafter BH/NS-LC). Our aim is to provide a method for predicting Gaia's ability in measuring the mass of BH/NS-LCs. We also tried to estimate the number of solvable BH/NS-LCs using Gaia. We used a realistic Markov chain Monte Carlo simulation of mock Gaia observations to obtain a relation between the uncertainty of mass measurement of the primary in BH/NS-LCs with the observable variables of the secondary astrometric orbit. Furthermore, we used the MOBSE code to evolve a Galactic BH/NS-LC sample with a combined Milky Way model. Our relation is applied to this sample to estimate the number of solvable BH/NS-LCs. We derived a good relation between the mass uncertainty and the binary parameters. For the first time, we show the quantitive influence of the period P, inclination i, eccentricity e, and ecliptic latitude $β$ to the mass measurement. Our results suggest that $48^{+7}_{-7}$ BH-LCs and $102^{+11}_{10}$ NS-LCs are solvable during a 5 yr Gaia mission. We also give the distribution of the distance and apparent magnitude of the Gaia solvable BH/NS-LCs. This solvable sample would be increased by additional spectroscopic data or a prolonged Gaia mission. The mass uncertainty relation could be used in future simulations of BH/NS-LCs observed by Gaia. The prediction of the solvable BH/NS-LCs is not only influenced by the process in generating the Galactic BH/NS-LC sample, but is also affected by our uncertainty relation. In particular, the relations of parameters such as $[P, e, i, β]$ are very useful to correct the selection effect in the statistic results of the future BH/NS-LC sample observed by Gaia. △ Less

Submitted 24 July, 2023; originally announced July 2023.

Journal ref: A&A, 665 (2022) A111

Strange Quasar Candidates with Abnormal Astrometric Characteristics from Gaia EDR3 and SDSS (SQUAB-II): Optical Identifications

Authors: Xiang Ji, Zhen-Ya Zheng, Qiqi Wu, Ruqiu Lin, P. T. Rahna, Yingkang Zhang, Shuairu Zhu, Shilong Liao, Zhaoxiang Qi, Tao An

Abstract: There are some strange quasars with multiple Gaia detections or observed with abnormal astrometric characteristics, such as with large proper motions or significant astrometric noises. Those strange quasars could be potential candidates of quasar-star pairs, dual quasars (DQs), or lensed quasars (LQs). Searching for both DQs and LQs is of great importance in many fields of astrophysics. Here in th… ▽ More There are some strange quasars with multiple Gaia detections or observed with abnormal astrometric characteristics, such as with large proper motions or significant astrometric noises. Those strange quasars could be potential candidates of quasar-star pairs, dual quasars (DQs), or lensed quasars (LQs). Searching for both DQs and LQs is of great importance in many fields of astrophysics. Here in this work, we select 143 SDSS spectroscopically confirmed quasars that have multiple Gaia EDR3 detections within 1 arcsec of the SDSS quasar' position. We apply several optical identification methods to classify this sample. We firstly exclude 65 quasar-star pairs via their stellar features including their parallaxes and proper motions, stellar features in the SDSS spectra, or via the colour-colour diagram. Based on the spectral-fitting results, we find 2 DQ candidates, one of which presents a double-peaked [O III] emission line feature and the other shows a broad $H_β$ velocity offset ($\sim$ 870 $ km s^{-1} $) relative to the [O III] $λ$5007 line. Via the colour difference method, we further find 56 LQ candidates with similar colours in their multiple images. We also cross-match 143 objects with the HST archive and find 19 targets with archival HST images. Our classification results of those 19 targets are mainly consistent with previous works. △ Less

Submitted 7 July, 2023; v1 submitted 14 June, 2023; originally announced June 2023.

Comments: 18 pages, 11figures, accepted for publication in MNRAS

KETJU -- resolving small-scale supermassive black hole dynamics in GADGET-4

Authors: Matias Mannerkoski, Alexander Rawlings, Peter H. Johansson, Thorsten Naab, Antti Rantala, Volker Springel, Dimitrios Irodotou, Shihong Liao

Abstract: We present the new public version of the KETJU supermassive black hole (SMBH) dynamics module, as implemented into GADGET-4. KETJU adds a small region around each SMBH where the dynamics of the SMBHs and stellar particles are integrated using an algorithmically regularised integrator instead of the leapfrog integrator with gravitational softening used by GADGET-4. This enables modelling SMBHs as p… ▽ More We present the new public version of the KETJU supermassive black hole (SMBH) dynamics module, as implemented into GADGET-4. KETJU adds a small region around each SMBH where the dynamics of the SMBHs and stellar particles are integrated using an algorithmically regularised integrator instead of the leapfrog integrator with gravitational softening used by GADGET-4. This enables modelling SMBHs as point particles even during close interactions with stellar particles or other SMBHs, effectively removing the spatial resolution limitation caused by gravitational softening. KETJU also includes post-Newtonian corrections, which allows following the dynamics of SMBH binaries to sub-parsec scales and down to tens of Schwarzschild radii. Systems with multiple SMBHs are also supported, with the code also including the leading non-linear cross terms that appear in the post-Newtonian equations for such systems. We present tests of the code showing that it correctly captures, at sufficient mass resolution, the sinking driven by dynamical friction and binary hardening driven by stellar scattering. We also present an example application demonstrating how the code can be applied to study the dynamics of SMBHs in mergers of multiple galaxies and the effect they have on the properties of the surrounding galaxy. We expect that the presented KETJU SMBH dynamics module can also be straightforwardly incorporated into other codes similar to GADGET-4, which would allow coupling small-scale SMBH dynamics to the rich variety of galactic physics models that exist in the literature. △ Less

Submitted 8 June, 2023; originally announced June 2023.

Comments: 21 pages, 19 figures. Code available from https://www.mv.helsinki.fi/home/phjohans/ketju

Simulation of CSSTs astrometric capability

Authors: Zhensen Fu, Zhaoxiang Qi, Shilong Liao, Xiyan Peng, Yong Yu, Qiqi Wu, Li Shao, Youhua Xu

Abstract: The China Space Station Telescope (CSST) will enter a low Earth orbit around 2024 and operate for 10 years, with seven of those years devoted to surveying the area of the median-to-high Galactic latitude and median-to-high Ecliptic latitude of the sky. To maximize the scientific output of CSST, it is important to optimize the survey schedule. We aim to evaluate the astrometric capability of CSST f… ▽ More The China Space Station Telescope (CSST) will enter a low Earth orbit around 2024 and operate for 10 years, with seven of those years devoted to surveying the area of the median-to-high Galactic latitude and median-to-high Ecliptic latitude of the sky. To maximize the scientific output of CSST, it is important to optimize the survey schedule. We aim to evaluate the astrometric capability of CSST for a given survey schedule and to provide independent suggestions for the optimization of the survey strategy. For this purpose, we first construct the astrometric model and then conduct simulated observations based on the given survey schedule. The astrometric solution is obtained by analyzing the simulated observation data. And then we evaluate the astrometric capability of CSST by analyzing the properties of the astrometric solution. We find that the accuracy of parallax and proper motion of CSST is better than 1 mas( yr1) for the sources of 18-22 mag in g band, and about 1-10 mas( yr1) for the sources of 22-26 mag in g band, respectively. The results from real survey could be worse since the assumptions are optimistic and simple. We find that optimizing the survey schedule can improve the astrometric accuracy of CSST. In the future, we will improve the astrometric capability of CSST by continuously iterating and optimizing the survey schedule. △ Less

Submitted 4 April, 2023; originally announced April 2023.

Comments: 17 pages, 10 figures

Constraining interacting dark energy models with the halo concentration-mass relation

Authors: Yu Zhao, Yun Liu, Shihong Liao, Jiajun Zhang, Xiangkun Liu, Wei Du

Abstract: The interacting dark energy (IDE) model is a promising alternative cosmological model which has the potential to solve the fine-tuning and coincidence problems by considering the interaction between dark matter and dark energy. Previous studies have shown that the energy exchange between the dark sectors in this model can significantly affect the dark matter halo properties. In this study, utilisi… ▽ More The interacting dark energy (IDE) model is a promising alternative cosmological model which has the potential to solve the fine-tuning and coincidence problems by considering the interaction between dark matter and dark energy. Previous studies have shown that the energy exchange between the dark sectors in this model can significantly affect the dark matter halo properties. In this study, utilising a large set of cosmological $N$-body simulations, we analyse the redshift evolution of the halo concentration-mass ($c$-$M$) relation in the IDE model, and show that the $c$-$M$ relation is a sensitive proxy of the interaction strength parameter $ξ_2$, especially at lower redshifts. Furthermore, we construct parametrized formulae to quantify the dependence of the $c$-$M$ relation on $ξ_2$ at redshifts ranging from $z=0$ to $0.6$. Our parametrized formulae provide a useful tool in constraining $ξ_2$ with the observational $c$-$M$ relation. As a first attempt, we use the data from X-ray, gravitational lensing, and galaxy rotational curve observations and obtain a tight constraint on $ξ_2$, i.e. $ξ_2 = 0.071 \pm 0.034$. Our work demonstrates that the halo $c$-$M$ relation, which reflects the halo assembly history, is a powerful probe to constrain the IDE model. △ Less

Submitted 29 August, 2025; v1 submitted 5 December, 2022; originally announced December 2022.

Comments: 9 pages, 5 figures, 5 tables

The growth of intermediate mass black holes through tidal captures and tidal disruption events

Authors: Francesco Paolo Rizzuto, Thorsten Naab, Antti Rantala, Peter H. Johansson, Jeremiah P. Ostriker, Nicholas C. Stone, Shihong Liao, Dimitrios Irodotou

Abstract: We present $N\mathrm{-body} $ simulations, including post-Newtonian dynamics, of dense clusters of low-mass stars harbouring central black holes (BHs) with initial masses of 50, 300, and 2000 $\mathrm{M_{\odot}}$. The models are evolved with the $N\mathrm{-body} $ code \textsc{bifrost} to investigate the possible formation and growth of massive BHs by the tidal capture of stars and tidal disruptio… ▽ More We present $N\mathrm{-body} $ simulations, including post-Newtonian dynamics, of dense clusters of low-mass stars harbouring central black holes (BHs) with initial masses of 50, 300, and 2000 $\mathrm{M_{\odot}}$. The models are evolved with the $N\mathrm{-body} $ code \textsc{bifrost} to investigate the possible formation and growth of massive BHs by the tidal capture of stars and tidal disruption events (TDEs). We model star-BH tidal interactions using a velocity-dependent drag force, which causes orbital energy and angular momentum loss near the BH. About $\sim 20-30$ per cent of the stars within the spheres of influence of the black holes form Bahcall-Wolf cusps and prevent the systems from core collapse. Within the first 40 Myr of evolution, the systems experience 500 up to 1300 TDEs, depending on the initial cluster structure. Most ($> 95$ per cent) of the TDEs originate from stars in the Bahcall-Wolf cusp. We derive an analytical formula for the TDE rate as a function of the central BH mass, density and velocity dispersion of the clusters ($\dot{N}_{\mathrm{TDE}} \propto M\mathrm{_{BH}} ρσ^{-3}$). We find that TDEs can lead a 300 $\mathrm{M_{\odot}}$ BH to reach $\sim 7000 \mathrm{M_{\odot}}$ within a Gyr. This indicates that TDEs can drive the formation and growth of massive BHs in sufficiently dense environments, which might be present in the central regions of nuclear star clusters. △ Less

Submitted 23 November, 2022; originally announced November 2022.

Comments: 17 pages, 18 figures

Modelling the accretion and feedback of supermassive black hole binaries in gas-rich galaxy mergers

Authors: Shihong Liao, Peter H. Johansson, Matias Mannerkoski, Dimitrios Irodotou, Francesco Paolo Rizzuto, Stuart McAlpine, Antti Rantala, Alexander Rawlings, Till Sawala

Abstract: We introduce a new model for the accretion and feedback of supermassive black hole (SMBH) binaries to the KETJU code, which enables us to resolve the evolution of SMBH binaries down to separations of tens of Schwarzschild radii in gas-rich galaxy mergers. Our subgrid binary accretion model extends the widely used Bondi--Hoyle--Lyttleton accretion into the binary phase and incorporates preferential… ▽ More We introduce a new model for the accretion and feedback of supermassive black hole (SMBH) binaries to the KETJU code, which enables us to resolve the evolution of SMBH binaries down to separations of tens of Schwarzschild radii in gas-rich galaxy mergers. Our subgrid binary accretion model extends the widely used Bondi--Hoyle--Lyttleton accretion into the binary phase and incorporates preferential mass accretion onto the secondary SMBH, which is motivated by results from small-scale hydrodynamical circumbinary disc simulations. We perform idealised gas-rich disc galaxy merger simulations using pure thermal or pure kinetic active galactic nuclei (AGN) feedback. Our binary accretion model provides more physically motivated SMBH mass ratios, which are one of the key parameters for computing gravitational wave (GW) induced recoil velocities. The merger time-scales of our simulated SMBH binaries are in the range $t_{\rm merge}{\sim} 10$--$400$ Myr. Prograde in-plane equal-mass galaxy mergers lead to the shortest merger time-scales, as they experience the strongest starbursts, with the ensuing high stellar density resulting in a rapid SMBH coalescence. Compared to the thermal AGN feedback, the kinetic AGN feedback predicts longer merger time-scales and results in more core-like stellar profiles, as it is more effective in removing gas from the galaxy centre and quenching star formation. This suggests that the AGN feedback implementation plays a critical role in modelling SMBH coalescences. Our model will be useful for improving the modelling of SMBH mergers in gas-rich galaxies, the prime targets for the upcoming LISA GW observatory. △ Less

Submitted 18 February, 2023; v1 submitted 21 November, 2022; originally announced November 2022.

Comments: 28 pages, 13 main + 6 appendix figures, accepted for publication in MNRAS

Journal ref: MNRAS 520, 4463 (2023)

Baryonic Effects on Lagrangian Clustering and Angular Momentum Reconstruction

Authors: Ming-Jie Sheng, Hao-Ran Yu, Sijia Li, Shihong Liao, Min Du, Yunchong Wang, Peng Wang, Kun Xu, Shy Genel, Dimitrios Irodotou

Abstract: Recent studies illustrate the correlation between the angular momenta of cosmic structures and their Lagrangian properties. However, only baryons are observable and it is unclear whether they reliably trace the cosmic angular momenta. We study the Lagrangian mass distribution, spin correlation, and predictability of dark matter, gas, and stellar components of galaxy-halo systems using IllustrisTNG… ▽ More Recent studies illustrate the correlation between the angular momenta of cosmic structures and their Lagrangian properties. However, only baryons are observable and it is unclear whether they reliably trace the cosmic angular momenta. We study the Lagrangian mass distribution, spin correlation, and predictability of dark matter, gas, and stellar components of galaxy-halo systems using IllustrisTNG, and show that the primordial segregations between components are typically small. Their protoshapes are also similar in terms of the statistics of moment of inertia tensors. Under the common gravitational potential they are expected to exert the same tidal torque and the strong spin correlations are not destroyed by the nonlinear evolution and complicated baryonic effects, as confirmed by the high-resolution hydrodynamic simulations. We further show that their late-time angular momenta traced by total gas, stars, or the central galaxies, can be reliably reconstructed by the initial perturbations. These results suggest that baryonic angular momenta can potentially be used in reconstructing the parameters and models related to the initial perturbations. △ Less

Submitted 4 February, 2023; v1 submitted 9 October, 2022; originally announced October 2022.

Comments: 8 pages, 5 figures, 1 table. Matches the accepted version in ApJ

Journal ref: The Astrophysical Journal, Volume 943, Number 2, 2023

Gaia Data Release 3: Summary of the content and survey properties

Authors: Gaia Collaboration, A. Vallenari, A. G. A. Brown, T. Prusti, J. H. J. de Bruijne, F. Arenou, C. Babusiaux, M. Biermann, O. L. Creevey, C. Ducourant, D. W. Evans, L. Eyer, R. Guerra, A. Hutton, C. Jordi, S. A. Klioner, U. L. Lammers, L. Lindegren, X. Luri, F. Mignard, C. Panem, D. Pourbaix, S. Randich, P. Sartoretti, C. Soubiran , et al. (431 additional authors not shown)

Abstract: We present the third data release of the European Space Agency's Gaia mission, GDR3. The GDR3 catalogue is the outcome of the processing of raw data collected with the Gaia instruments during the first 34 months of the mission by the Gaia Data Processing and Analysis Consortium. The GDR3 catalogue contains the same source list, celestial positions, proper motions, parallaxes, and broad band photom… ▽ More We present the third data release of the European Space Agency's Gaia mission, GDR3. The GDR3 catalogue is the outcome of the processing of raw data collected with the Gaia instruments during the first 34 months of the mission by the Gaia Data Processing and Analysis Consortium. The GDR3 catalogue contains the same source list, celestial positions, proper motions, parallaxes, and broad band photometry in the G, G$_{BP}$, and G$_{RP}$ pass-bands already present in the Early Third Data Release. GDR3 introduces an impressive wealth of new data products. More than 33 million objects in the ranges $G_{rvs} < 14$ and $3100 <T_{eff} <14500 $, have new determinations of their mean radial velocities based on data collected by Gaia. We provide G$_{rvs}$ magnitudes for most sources with radial velocities, and a line broadening parameter is listed for a subset of these. Mean Gaia spectra are made available to the community. The GDR3 catalogue includes about 1 million mean spectra from the radial velocity spectrometer, and about 220 million low-resolution blue and red prism photometer BPRP mean spectra. The results of the analysis of epoch photometry are provided for some 10 million sources across 24 variability types. GDR3 includes astrophysical parameters and source class probabilities for about 470 million and 1500 million sources, respectively, including stars, galaxies, and quasars. Orbital elements and trend parameters are provided for some $800\,000$ astrometric, spectroscopic and eclipsing binaries. More than $150\,000$ Solar System objects, including new discoveries, with preliminary orbital solutions and individual epoch observations are part of this release. Reflectance spectra derived from the epoch BPRP spectral data are published for about 60\,000 asteroids. Finally, an additional data set is provided, namely the Gaia Andromeda Photometric Survey (abridged) △ Less

Submitted 30 July, 2022; originally announced August 2022.

Comments: 23 pages, 2 figures

Gaia Data Release 3: Reflectance spectra of Solar System small bodies

Authors: Gaia Collaboration, L. Galluccio, M. Delbo, F. De Angeli, T. Pauwels, P. Tanga, F. Mignard, A. Cellino, A. G. A. Brown, K. Muinonen, A. Penttila, S. Jordan, A. Vallenari, T. Prusti, J. H. J. de Bruijne, F. Arenou, C. Babusiaux, M. Biermann, O. L. Creevey, C. Ducourant, D. W. Evans, L. Eyer, R. Guerra, A. Hutton, C. Jordi , et al. (422 additional authors not shown)

Abstract: The Gaia mission of the European Space Agency (ESA) has been routinely observing Solar System objects (SSOs) since the beginning of its operations in August 2014. The Gaia data release three (DR3) includes, for the first time, the mean reflectance spectra of a selected sample of 60 518 SSOs, primarily asteroids, observed between August 5, 2014, and May 28, 2017. Each reflectance spectrum was deriv… ▽ More The Gaia mission of the European Space Agency (ESA) has been routinely observing Solar System objects (SSOs) since the beginning of its operations in August 2014. The Gaia data release three (DR3) includes, for the first time, the mean reflectance spectra of a selected sample of 60 518 SSOs, primarily asteroids, observed between August 5, 2014, and May 28, 2017. Each reflectance spectrum was derived from measurements obtained by means of the Blue and Red photometers (BP/RP), which were binned in 16 discrete wavelength bands. We describe the processing of the Gaia spectral data of SSOs, explaining both the criteria used to select the subset of asteroid spectra published in Gaia DR3, and the different steps of our internal validation procedures. In order to further assess the quality of Gaia SSO reflectance spectra, we carried out external validation against SSO reflectance spectra obtained from ground-based and space-borne telescopes and available in the literature. For each selected SSO, an epoch reflectance was computed by dividing the calibrated spectrum observed by the BP/RP at each transit on the focal plane by the mean spectrum of a solar analogue. The latter was obtained by averaging the Gaia spectral measurements of a selected sample of stars known to have very similar spectra to that of the Sun. Finally, a mean of the epoch reflectance spectra was calculated in 16 spectral bands for each SSO. The agreement between Gaia mean reflectance spectra and those available in the literature is good for bright SSOs, regardless of their taxonomic spectral class. We identify an increase in the spectral slope of S-type SSOs with increasing phase angle. Moreover, we show that the spectral slope increases and the depth of the 1 um absorption band decreases for increasing ages of S-type asteroid families. △ Less

Submitted 24 June, 2022; originally announced June 2022.

Comments: 30 pages, 26 figures

ET White Paper: To Find the First Earth 2.0

Authors: Jian Ge, Hui Zhang, Weicheng Zang, Hongping Deng, Shude Mao, Ji-Wei Xie, Hui-Gen Liu, Ji-Lin Zhou, Kevin Willis, Chelsea Huang, Steve B. Howell, Fabo Feng, Jiapeng Zhu, Xinyu Yao, Beibei Liu, Masataka Aizawa, Wei Zhu, Ya-Ping Li, Bo Ma, Quanzhi Ye, Jie Yu, Maosheng Xiang, Cong Yu, Shangfei Liu, Ming Yang , et al. (142 additional authors not shown)

Abstract: We propose to develop a wide-field and ultra-high-precision photometric survey mission, temporarily named "Earth 2.0 (ET)". This mission is designed to measure, for the first time, the occurrence rate and the orbital distributions of Earth-sized planets. ET consists of seven 30cm telescopes, to be launched to the Earth-Sun's L2 point. Six of these are transit telescopes with a field of view of 500… ▽ More We propose to develop a wide-field and ultra-high-precision photometric survey mission, temporarily named "Earth 2.0 (ET)". This mission is designed to measure, for the first time, the occurrence rate and the orbital distributions of Earth-sized planets. ET consists of seven 30cm telescopes, to be launched to the Earth-Sun's L2 point. Six of these are transit telescopes with a field of view of 500 square degrees. Staring in the direction that encompasses the original Kepler field for four continuous years, this monitoring will return tens of thousands of transiting planets, including the elusive Earth twins orbiting solar-type stars. The seventh telescope is a 30cm microlensing telescope that will monitor an area of 4 square degrees toward the galactic bulge. This, combined with simultaneous ground-based KMTNet observations, will measure masses for hundreds of long-period and free-floating planets. Together, the transit and the microlensing telescopes will revolutionize our understandings of terrestrial planets across a large swath of orbital distances and free space. In addition, the survey data will also facilitate studies in the fields of asteroseismology, Galactic archeology, time-domain sciences, and black holes in binaries. △ Less

Submitted 14 June, 2022; originally announced June 2022.

Comments: 116 pages,79 figures

Gaia Data Release 3: Mapping the asymmetric disc of the Milky Way

Authors: Gaia Collaboration, R. Drimmel, M. Romero-Gomez, L. Chemin, P. Ramos, E. Poggio, V. Ripepi, R. Andrae, R. Blomme, T. Cantat-Gaudin, A. Castro-Ginard, G. Clementini, F. Figueras, M. Fouesneau, Y. Fremat, K. Jardine, S. Khanna, A. Lobel, D. J. Marshall, T. Muraveva, A. G. A. Brown, A. Vallenari, T. Prusti, J. H. J. de Bruijne, F. Arenou , et al. (431 additional authors not shown)

Abstract: With the most recent Gaia data release the number of sources with complete 6D phase space information (position and velocity) has increased to well over 33 million stars, while stellar astrophysical parameters are provided for more than 470 million sources, in addition to the identification of over 11 million variable stars. Using the astrophysical parameters and variability classifications provid… ▽ More With the most recent Gaia data release the number of sources with complete 6D phase space information (position and velocity) has increased to well over 33 million stars, while stellar astrophysical parameters are provided for more than 470 million sources, in addition to the identification of over 11 million variable stars. Using the astrophysical parameters and variability classifications provided in Gaia DR3, we select various stellar populations to explore and identify non-axisymmetric features in the disc of the Milky Way in both configuration and velocity space. Using more about 580 thousand sources identified as hot OB stars, together with 988 known open clusters younger than 100 million years, we map the spiral structure associated with star formation 4-5 kpc from the Sun. We select over 2800 Classical Cepheids younger than 200 million years, which show spiral features extending as far as 10 kpc from the Sun in the outer disc. We also identify more than 8.7 million sources on the red giant branch (RGB), of which 5.7 million have line-of-sight velocities, allowing the velocity field of the Milky Way to be mapped as far as 8 kpc from the Sun, including the inner disc. The spiral structure revealed by the young populations is consistent with recent results using Gaia EDR3 astrometry and source lists based on near infrared photometry, showing the Local (Orion) arm to be at least 8 kpc long, and an outer arm consistent with what is seen in HI surveys, which seems to be a continuation of the Perseus arm into the third quadrant. Meanwhile, the subset of RGB stars with velocities clearly reveals the large scale kinematic signature of the bar in the inner disc, as well as evidence of streaming motions in the outer disc that might be associated with spiral arms or bar resonances. (abridged) △ Less

Submitted 5 August, 2022; v1 submitted 13 June, 2022; originally announced June 2022.

Comments: 35 pages, 27 figures, accepted for publication in A&A special Gaia DR3 issue. V2: abstract completed. V3: complete author list and link to data: https://drive.google.com/drive/u/1/folders/1yOJPjYmM7QK5XVsqaiSOTuwDQNti2LlZ

Journal ref: A&A 674, A37 (2023)