The Diversity and Variability of Star Formation Histories in Models of Galaxy Evolution
Kartheik G. Iyer, Sandro Tacchella, Shy Genel, Christopher C. Hayward, Lars Hernquist, Alyson M. Brooks, Neven Caplar, Romeel Davé, Benedikt Diemer, John C. For… 展开作者
Kartheik G. Iyer, Sandro Tacchella, Shy Genel, Christopher C. Hayward, Lars Hernquist, Alyson M. Brooks, Neven Caplar, Romeel Davé, Benedikt Diemer, John C. Forbes, Eric Gawiser, Rachel S. Somerville, Tjitske K. Starkenburg
备注：
31 pages, 17 figures (+ appendix). Resubmitted to MNRAS after responding to referee's comments. Comments are welcome!
Understanding the variability of galaxy star formation histories (SFHs) across a range of timescales provides insight into the underlying physical processes that regulate star formation within galaxies. We compile the SFHs of galaxies at $z=0$ from an extensive set of models, ranging from cosmological hydrodynamical simulations (Illustris, IllustrisTNG, Mufasa, Simba, EAGLE), zoom simulations (FIRE-2, g14, and Marvel/Justice League), semi-analytic models (Santa Cruz SAM) and empirical models (UniverseMachine), and quantify the variability of these SFHs on different timescales using the power spectral density (PSD) formalism. We find that the PSDs are well described by broken power-laws, and variability on long timescales ($\gtrsim1$ Gyr) accounts for most of the power in galaxy SFHs. Most hydrodynamical models show increased variability on shorter timescales ($\lesssim300$ Myr) with decreasing stellar mass. Quenching can induce $\sim0.4-1$ dex of additional power on timescales $>1$ Gyr. The dark matter accretion histories of galaxies have remarkably self-similar PSDs and are coherent with the in-situ star formation on timescales $>3$ Gyr. There is considerable diversity among the different models in their (i) power due to SFR variability at a given timescale, (ii) amount of correlation with adjacent timescales (PSD slope), (iii) evolution of median PSDs with stellar mass, and (iv) presence and locations of breaks in the PSDs. The PSD framework is a useful space to study the SFHs of galaxies since model predictions vary widely. Observational constraints in this space will help constrain the relative strengths of the physical processes responsible for this variability.
Because the timescale of H$α$ emission (several tens of Myr) following star formation is significantly shorter than that of UV radiation (a few hundred Myr), the H$α$/UV flux ratio provides insight on the star formation histories (SFHs) of galaxies on timescales shorter than $\sim100$ Myr. We present H$α$/UV ratios for galaxies at $z=$ 0.02--0.1 on the familiar star-forming main sequence based on the AKARI-GALEX-SDSS archive dataset. The data provide us with robust measurements of dust-corrected SFRs in both H$α$ and UV for 1,050 galaxies. The results show a correlation between the H$α$/UV rat…
A key uncertainty in galaxy evolution is the physics regulating star formation, ranging from small-scale processes related to the life-cycle of molecular clouds within galaxies to large-scale processes such as gas accretion onto galaxies. We study the imprint of such processes on the time-variability of star formation with an analytical approach tracking the gas mass of galaxies ("regulator model"). Specifically, we quantify the strength of the fluctuation in the star-formation rate (SFR) on different timescales, i.e. the power spectral density (PSD) of the star-formation history, and connect …
We introduce and apply a new approach to probe the response of galactic stellar haloes to the interplay between cosmological merger histories and galaxy formation physics. We perform dark matter-only, zoomed simulations of two Milky Way-mass hosts and make targeted, controlled changes to their cosmological histories using the genetic modification technique. Populating each history's stellar halo with a semi-empirical, particle tagging approach then enables a controlled study, with all instances converging to the same large-scale structure, dynamical and stellar mass at $z=0$ as their reference…
IRAC data have long implied that early ($z\gtrsim6$) galaxies often have very high specific star formation rates (sSFR$\gtrsim$30 Gyr$^{-1}$), but JWST data have shown that at least some early galaxies are forming stars far less vigorously. Here, we systematically analyze the recent star formation histories (SFHs) of a large ($N=368$) sample of $z\sim6$ Lyman-break galaxies (LBGs) spanning $-22\lesssim M_\mathrm{UV}\lesssim-16$ assembled from ACS+NIRCam imaging in the GOODS and Abell 2744 fields. We find that very low H$α$-to-UV luminosity ratios ($L_\mathrm{Hα}/L_\mathrm{UV}$) and strong rece…
SIRIUS: The relation between the diversity of dwarf galaxies and their formation histories
The University of Tokyo（东京大学）；Kobe University（神户大学）；Center for Planetary Science (CPS), Graduate School of Science, Kobe University（神户大学行星科学中心）；Tohoku University of Community Service and Science（东北社区服务科学大学）
To investigate the variability of the star formation rate (SFR) of galaxies, we define a star formation change parameter, SFR$_{\rm 5Myr}$/SFR$_{\rm 800Myr}$ which is the ratio of the SFR averaged within the last 5 Myr to the SFR averaged within the last 800 Myr. We show that this parameter can be determined from a combination of H$α$ emission and H$δ$ absorption, plus the 4000 A break, with an uncertainty of $\sim$0.07 dex for star-forming galaxies. We then apply this estimator to MaNGA galaxies, both globally within Re and within radial annuli. We find that galaxies with higher global SFR$_{…
Nuclear star clusters (NSCs) are the densest stellar systems in the Universe and are found in the centres of all types of galaxies. They are thought to form via mergers of star clusters such as ancient globular clusters (GCs) that spiral to the centre as a result of dynamical friction or through in-situ star formation directly at the galaxy centre. There is evidence that both paths occur, but the relative contribution of either channel and their correlation with galaxy properties are not yet constrained observationally. We aim to derive the dominant NSC formation channel for a sample of 25 nuc…
Modern spectroscopic surveys of galaxies such as MaNGA consist of millions of diverse spectra covering different regions of thousands of galaxies. We propose and implement a deep unsupervised machine learning method to summarize the entire diversity of MaNGA spectra onto a 15x15 map (DESOM-1), where neighbouring points on the map represent similar spectra. We demonstrate our method as an alternative to conventional full spectral fitting for deriving physical quantities, as well as their full probability distributions, much more efficiently than traditional resource-intensive Bayesian methods. …
We investigate whether the considerable diversity in the satellite populations of nearby Milky Way (MW)-mass galaxies is connected with the diversity in their host's merger histories. Analyzing 8 nearby galaxies with extensive observations of their satellite populations and stellar halos, we characterize each galaxy's merger history using the metric of its most dominant merger, $M_{\rm \star,Dom}$, defined as the greater of either its total accreted stellar mass or most massive current satellite. We find an unexpectedly tight relationship between these galaxies' number of $M_{V}\,{<}\,{-}9$ sa…
Multiple investigations support describing galaxy growth as a stochastic process with correlations over a range of timescales governed by a parameter, $H$, empirically and theoretically constrained to be near unity. Here, we show that the distribution of UV-slopes, $β$, derived from an ensemble of theoretical $H=1$ star formation histories (SFHs) is consistent with data at all redshifts $z\le 16$. At $z=0$, the median value $\langleβ_{H=1}\rangle=-2.27$ agrees well with the canonical $β_0=-2.23$ for local starbursts \citep{meurer1999}. At $4\lesssim z\lesssim16$, JWST data span the model distr…
This article focuses on certain variability and emission characteristics of Active Galactic Nuclei (AGN), especially their radio-loud subset consisting of quasars, BL Lacs and $γ$-ray detected narrow-line Seyfert 1 galaxies, all of which exhibit relativistically beamed jets of nonthermal radiation. Several striking trends and correlations, including some that have received scant attention, drawn from the available comparatively recent literature are highlighted. These can provide very useful inputs to models of AGN and be probed at a deeper level using the optical telescopes recently set up at…
We present the cumulative star-formation histories (SFHs) of >15000 dwarf galaxies ($M_{*}=10^{7-10}M_{\odot}$) from the TNG50 run of the IllustrisTNG suite across a vast range of environments. The key factors determining the dwarfs' SFHs are their status as central or satellite and their stellar mass, with centrals and more massive dwarfs assembling their stellar mass at later times on average compared to satellites and lower mass dwarfs. The satellites (in hosts of total mass $M_{200c,\,host}=10^{12-14.3}M_{\odot}$) assembled 90% of their z=0 stellar mass ~$7.0_{-5.5}^{+3.3}$ Gyr ago, while …
Upcoming galaxy surveys and 21-cm experiments targeting high redshifts $z\gtrsim 6$ are highly complementary probes of galaxy formation and reionization. However, in order to expedite the large volume simulations relevant for 21-cm observations, many models of galaxies within reionization codes are entirely subgrid and/or rely on halo abundances only. In this work, we explore the extent to which resolving and modeling individual galaxy formation histories affects predictions both for the galaxy populations detectable by upcoming surveys and the signatures of reionization accessible to upcoming…
Untangling Similarities and Differences in Star Formation Histories Across Cosmological Simulations
Canadian Institute for Theoretical Astrophysics, University of Toronto（多伦多大学理论天体物理研究所）；David A. Dunlap Department of Astronomy & Astrophysics, University of Toronto（多伦多大学大卫·邓普克天文与天体物理系）；Department of Statistical Sciences, University of Toronto（多伦多大学统计科学系）；Dunlap Institute for Astronomy & Astrophysics, University of Toronto（多伦多大学邓普克天文与天体物理研究所）；Data Sciences Institute, University of Toronto（多伦多大学数据科学研究所）；Institute for Astronomy, University of Hawaiʻi（夏威夷大学天体物理研究所）
We investigate the orbital motions of dwarf spheroidal galaxies (dSphs) in the halo of the Milky Way (MW) to understand their possible effects on the diversity of the star formation histories seen in these MW satellites. In this work, we explicitly consider a time-varying gravitational potential due to the growth of the MW's dark halo mass to calculate the long-term orbital evolutions of the dSphs, guided with {\it Gaia} DR2 proper motions, over the past 13.5 billion years. We find that the infall time of a satellite, defined at which the galaxy first crosses within the growing virial radius o…
We present constraints on the timescale of star formation variability and the correlation between star formation and host halo accretion histories of star-forming (SF) central galaxies from the scatter of the stellar-to-halo mass relation (SHMR). SF galaxies are found to have a tight relationship between their star formation rates and stellar masses on the so-called "star-forming sequence" (SFS), which characterizes their SF histories and $M_*$ growths. Meanwhile, observed SHMR constraints connect $M_*$ growth to halo accretion history. Combining these observed trends with a cosmological $N$-b…
Sub-Gyr variability around the SFMS and its contribution to the scatter
Universidad Complutense de Madrid（马德里康普顿斯大学）；Instituto de Física de Partículas y del Cosmos, Universidad Complutense de Madrid（马德里康普顿斯大学粒子与宇宙物理研究所）；Universidad Nacional Autónoma de México（墨西哥国立自治大学）；Instituto de Astronomía, Universidad Nacional Autónoma de México（墨西哥国立自治大学天文学研究所）；Instituto de Astrofísica de Canarias（加那利群岛天体物理学研究所）
In the era of large-scale spectroscopic surveys in the Local Group (LG), we can explore using chemical abundances of halo stars to study the star formation and chemical enrichment histories of the dwarf galaxy progenitors of the Milky Way (MW) and M31 stellar halos. In this paper, we investigate using the Chemical Abundance Ratio Distributions (CARDs) of seven stellar halos from the Latte suite of FIRE-2 simulations. We attempt to infer galaxies' assembly histories by modelling the CARDs of the stellar halos of the Latte galaxies as a linear combination of template CARDs from disrupted dwarfs,…
A systematic analysis of star cluster disruption by tidal shocks -- II. Predicting star cluster dissolution rates from a time-series analysis of their tidal histories
Nonparametric star formation histories (SFHs) have long promised to be the `gold standard' for galaxy spectral energy distribution (SED) modeling as they are flexible enough to describe the full diversity of SFH shapes, whereas parametric models rule out a significant fraction of these shapes {\it a priori}. However, this flexibility is not fully constrained even with high-quality observations, making it critical to choose a well-motivated prior. Here, we use the SED-fitting code \texttt{Prospector} to explore the effect of different nonparametric priors by fitting SFHs to mock UV-IR photometr…
Understanding the rate at which stars form is central to studies of galaxy formation. Observationally, the star formation rates (SFRs) of galaxies are measured using the luminosity in different frequency bands, often under the assumption of a time-steady SFR in the recent past. We use star formation histories (SFHs) extracted from cosmological simulations of star-forming galaxies from the FIRE project to analyze the time-scales to which the H$α$ and far-ultraviolet (FUV) continuum SFR indicators are sensitive. In these simulations, the SFRs are highly time variable for all galaxies at high red…
The primary method for inferring the stellar mass ($M_*$) of a galaxy is through spectral energy distribution (SED) modeling. However, the technique rests on assumptions such as the galaxy star formation history and dust attenuation law that can severely impact the accuracy of derived physical properties from SED modeling. Here, we examine the effect that the assumed star formation history (SFH) has on the stellar properties inferred from SED fitting by ground truthing them against mock observations of high-resolution cosmological hydrodynamic galaxy formation simulations. Classically, SFHs ar…
We present a new approach to understanding star-to-star helium abundance variations within globular clusters. We begin with detailed radiation hydrodynamics simulations of cluster formation within giant molecular clouds, and investigate the conditions under which multiple populations could be created. Chemical enrichment occurs dynamically as the cluster is assembled. We test two extreme mechanisms for injection of enriched gas within the clusters, and find that realistic multiple populations can be formed in both mechanisms. The stochastic cluster formation histories are dictated by the inher…
We investigate the stellar populations for a sample of 161 massive, mainly quiescent galaxies at $\langle z_{\rm obs} \rangle=0.8$ with deep Keck/DEIMOS rest-frame optical spectroscopy (HALO7D survey). With the fully Bayesian framework Prospector, we simultaneously fit the spectroscopic and photometric data with an advanced physical model (including non-parametric star-formation histories, emission lines, variable dust attenuation law, and dust and AGN emission) together with an uncertainty and outlier model. We show that both spectroscopy and photometry are needed to break the dust-age-metall…
DeepDive: Tracing the early quenching pathways of massive quiescent galaxies at $z>3$ from their star-formation histories and chemical abundances
University of Massachusetts, Amherst（马萨诸塞大学阿默斯特分校）；Cosmic Dawn Center (DAWN)（宇宙黎明中心）；DTU Space, Technical University of Denmark（丹麦技术大学空间科学与技术中心）；David A. Dunlap Department of Astronomy & Astrophysics, University of Toronto（多伦多大学戴维·A·邓普尔天文与天体物理系）；Dunlap Institute for Astronomy & Astrophysics, University of Toronto（多伦多大学邓普尔天文与天体物理研究所）；Observatories of the Carnegie Institution for Science（卡内基科学机构天文台）
The Local Ultraviolet to Infrared Treasury II. Refining Star Formation Histories of Ten Metal-Poor Dwarf Galaxies with Simultaneous UV-Optical Two-CMD Fitting
AGN in massive galaxies identified via optical broadband variability: lessons from VST-COSMOS for future LSST science
University of Hertfordshire（赫特福德大学）；Department of Physics, University of Napoli “Federico II”（那不勒斯费德里科二世大学物理系）；Millennium Institute of Astrophysics (MAS)（天体物理学千年研究所）；INAF - Osservatorio Astronomico di Capodimonte（意大利国家天体物理研究所卡波迪蒙特天文台）；School of Physics and Astronomy, University of Nottingham（诺丁汉大学物理与天文学学院）
Measurements of the rotation curves of dwarf galaxies are often interpreted as requiring a constant density core at the centre, at odds with the "cuspy" inner profiles predicted by $N$-body simulations of cold dark matter (CDM) haloes. It has been suggested that this conflict could be resolved by fluctuations in the inner gravitational potential caused by the periodic removal of gas following bursts of star formation. Earlier work has suggested that core formation requires a bursty and extended star formation history (SFH). Here we investigate the structure of CDM haloes of dwarf galaxies ($M_…
The short-term X-ray variability of tidal disruption events (TDEs) and its similarities with active galactic nuclei (AGN) are poorly understood. In this work, we show the diversity of TDE's short-term X-ray variability, and take Swift J1644+57 as an example to study the evolution of various properties related to the short-term X-ray variability, such as the X-ray flux distribution, power spectral density (PSD), rms variability, time lag and coherence spectra. We find that the flux distribution of Swift J1644+57 has a lognormal form in the normal state, but deviates from it significantly in the…
