The time-scales probed by star formation rate indicators for realistic, bursty star formation histories from the FIRE simulations
José A. Flores Velázquez, Alexander B. Gurvich, Claude-André Faucher-Giguère, James S. Bullock, Tjitske K. Starkenburg, Jorge Moreno, Alexandres Lazar, Francisc… 展开作者
José A. Flores Velázquez, Alexander B. Gurvich, Claude-André Faucher-Giguère, James S. Bullock, Tjitske K. Starkenburg, Jorge Moreno, Alexandres Lazar, Francisco J. Mercado, Jonathan Stern, Martin Sparre, Christopher C. Hayward, Andrew Wetzel, Kareem El-Badry
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 redshift, and continue to be bursty to z=0 in dwarf galaxies. When FIRE SFHs are partitioned into their bursty and time-steady phases, the best-fitting FUV time-scale fluctuates from its ~10 Myr value when the SFR is time-steady to >~100 Myr immediately following particularly extreme bursts of star formation during the bursty phase. On the other hand, the best-fitting averaging time-scale for H$α$ is generally insensitive to the SFR variability in the FIRE simulations and remains ~5 Myr at all times. These time-scales are shorter than the 100 Myr and 10 Myr time-scales sometimes assumed in the literature for FUV and H$α$, respectively, because while the FUV emission persists for stellar populations older than 100 Myr, the time-dependent luminosities are strongly dominated by younger stars. Our results confirm that the ratio of SFRs inferred using H$α$ vs. FUV can be used to probe the burstiness of star formation in galaxies.
NIRSpec View of the Appearance and Evolution of Balmer Breaks and the Transition from Bursty to Smooth Star Formation Histories from Deep Within the Epoch of Reionization to Cosmic Noon
JADES: Differing assembly histories of galaxies -- Observational evidence for bursty SFHs and (mini-)quenching in the first billion years of the Universe
Metallicity Gradients in Modern Cosmological Simulations II: The Role of Bursty Versus Smooth Feedback at High-Redshift
University of Virginia（弗吉尼亚大学）；Virginia Institute for Theoretical Astronomy, University of Virginia（弗吉尼亚大学理论天体物理研究所）；Max Planck Institut für Astrophysik（马克斯·普朗克天体物理学研究所）；Massachusetts Institute of Technology（麻省理工学院）；Philipps Universität Marburg（马尔堡菲利普斯大学）；Kavli Institute for Cosmology, University of Cambridge（剑桥大学卡弗里宇宙学研究所）；Cavendish Laboratory, University of Cambridge（剑桥大学卡文迪许实验室）
Stellar feedback in dwarf galaxies plays a critical role in regulating star formation via galaxy-scale winds. Recent hydrodynamical zoom simulations of dwarf galaxies predict that the periodic outward flow of gas can change the gravitational potential sufficiently to cause radial migration of stars. To test the effect of bursty star formation on stellar migration, we examine star formation observables and sizes of 86 local dwarf galaxies. We find a correlation between the R-band half-light radius (R$_e$) and far-UV luminosity (L$_{FUV}$) for stellar masses below 10$^8 $ M$_{\odot}$ and a weak …
The orbits of satellite galaxies encode rich information about their histories. We investigate the orbital dynamics and histories of satellite galaxies around Milky Way (MW)-mass host galaxies using the FIRE-2 cosmological simulations, which, as previous works have shown, produce satellite mass functions and spatial distributions that broadly agree with observations. We first examine trends in orbital dynamics at z = 0, including total velocity, specific angular momentum, and specific total energy: the time of infall into the MW-mass halo primarily determines these orbital properties. We then …
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_…
We investigate a large sample of massive galaxies at $z\sim1$ with combined $HST$ broad-band and grism observations to constrain the star-formation histories of these systems as they transition from a star-forming state to quiescence. Among our sample of massive $(M_*>10^{10}~{\rm M_\odot})$ galaxies at $0.7<z<1.2$, dust-corrected H$α$ and UV star-formation indicators agree with a small dispersion ($\sim0.2$~dex) for galaxies on the main sequence, but diverge and exhibit substantial scatter ($\sim0.7$~dex) once they drop significantly below the star-forming main sequence. Significant H$α$ emis…
We derive the recent star formation histories of 23 active dwarf galaxies using HST observations from the Legacy Extragalactic UV Survey (LEGUS). We apply a color-magnitude diagram fitting technique using two independent sets of stellar models, PARSEC-COLIBRI and MIST. Despite the non-negligible recent activity, none of the 23 star forming dwarfs show enhancements in the last 100 Myr larger than three times the 100-Myr-average. The unweighted mean of the individual SFHs in the last 100 Myr is also consistent with a rather constant activity, irrespective of the atomic gas fraction. We confirm p…
We investigate thin and thick stellar disc formation in Milky-Way-mass galaxies using twelve FIRE-2 cosmological zoom-in simulations. All simulated galaxies experience an early period of bursty star formation that transitions to a late-time steady phase of near-constant star formation. Stars formed during the late-time steady phase have more circular orbits and thin-disc-like morphology at $z=0$, whilst stars born during the bursty phase have more radial orbits and thick-disc structure. The median age of thick-disc stars at $z=0$ correlates strongly with this transition time. We also find that…
We study star formation histories (SFHs) of $\simeq500$ dwarf galaxies (stellar mass $M_\ast = 10^5 - 10^9\,M_\odot$) from FIRE-2 cosmological zoom-in simulations. We compare dwarfs around individual Milky Way (MW)-mass galaxies, dwarfs in Local Group (LG)-like environments, and true field (i.e. isolated) dwarf galaxies. We reproduce observed trends wherein higher-mass dwarfs quench later (if at all), regardless of environment. We also identify differences between the environments, both in terms of "satellite vs. central" and "LG vs. individual MWvs. isolated dwarf central." Around the individ…
Milky Way-mass galaxies in the FIRE-2 simulations demonstrate two main modes of star formation. At high redshifts star formation occurs in a series of short and intense bursts, while at low redshifts star formation proceeds at a steady rate with a transition from one mode to another at times ranging from 3 to 7 Gyr ago for different galaxies. We analyse how the mode of star formation affects iron and alpha-element abundance. We find that the early bursty regime imprints a measurable pattern in stellar elemental abundances in the form of a "sideways chevron" shape on the [Fe/H] - [O/Fe] plane a…
We use FIRE-2 simulations to examine 3-D variations of gas-phase elemental abundances of [O/H], [Fe/H], and [N/H] in 11 Milky Way (MW) and M31-mass galaxies across their formation histories at $z \leq 1.5$ ($t_{\rm lookback} \leq 9.4$ Gyr), motivated by characterizing the initial conditions of stars for chemical tagging. Gas within $1$ kpc of the disk midplane is vertically homogeneous to $\lesssim 0.008$ dex at all $z \leq 1.5$. We find negative radial gradients (metallicity decreases with galactocentric radius) at all times, which steepen over time from $\approx -0.01$ dex kpc$^{-1}$ at $z =…
Recent observations and simulations indicate substantial evolution in the properties of galaxies with time, wherein rotationally-supported and steady thin discs (like those frequently observed in the local universe) emerge from galaxies that are clumpy, irregular, and have bursty star formation rates (SFRs). To better understand the progenitors of local disc galaxies we carry out an analysis of three FIRE-2 simulated galaxies with a mass similar to the Milky Way at redshift z=0. We show that all three galaxies transition from bursty to steady SFRs at a redshift between z=0.5 and z=0.8, and tha…
The Star-forming Main Sequence and Bursty Star-formation Histories at $z>1.4$ in JADES and AURORA
University of California, Los Angeles（加州大学洛杉矶分校）；Steward Observatory, University of Arizona（亚利桑那大学斯图尔德天文台）；Cosmic Dawn Center (DAWN)（宇宙黎明中心）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯玻尔研究所）；University of Kentucky（肯塔基大学）；Department of Physics & Astronomy, University of California, Riverside（加州大学河滨分校物理与天文学系）
We characterize the 3-D spatial variations of [Fe/H], [Mg/H], and [Mg/Fe] in stars at the time of their formation, across 11 simulated Milky Way (MW)- and M31-mass galaxies in the FIRE-2 simulations, to inform initial conditions for chemical tagging. The overall scatter in [Fe/H] within a galaxy decreased with time until $\approx 7$ Gyr ago, after which it increased to today: this arises from a competition between a reduction of azimuthal scatter and a steepening of the radial gradient in abundance over time. The radial gradient is generally negative, and it steepened over time from an initial…
Caught Napping by JWST UNCOVER+MegaScience: Constraining bursty star formation histories and number densities of mini-quenched galaxies at redshifts 4-7
University of Washington（华盛顿大学）；University of Pittsburgh（匹兹堡大学）；University of Colorado, Boulder（科罗拉多大学博尔德分校）；University of California, Santa Cruz（加州大学圣克鲁兹分校）；Princeton University（普林斯顿大学）
We present an analysis of the $R\lesssim 1.5$ kpc core regions of seven simulated Milky Way mass galaxies, from the FIRE-2 (Feedback in Realistic Environments) cosmological zoom-in simulation suite, for a finely sampled period ($Δt = 2.2$ Myr) of 22 Myr at $z \approx 0$, and compare them with star formation rate (SFR) and gas surface density observations of the Milky Way's Central Molecular Zone (CMZ). Despite not being tuned to reproduce the detailed structure of the CMZ, we find that four of these galaxies are consistent with CMZ observations at some point during this 22 Myr period. The gala…
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…
We investigate the bursty star formation histories (SFHs) of dwarf galaxies using the distribution of log($L_{Hα}/L_{UV}$) of 185 local galaxies. We expand on the work of Weisz et al. 2012 to consider a wider range of SFHs and stellar metallicities, and show that there are large degeneracies in a periodic, top-hat burst model. We argue that all galaxies of a given mass have similar SFHs and we can therefore include the $L_{Hα}$ distributions (subtracting the median trend with stellar mass, referred to as $Δ\text{log}(L_{Hα})$) in our analyses. $Δ\text{log}(L_{Hα})$ traces the amplitude of the …
Emission line galaxies provide a crucial tool for the study of galaxy formation and evolution, providing a means to trace a galaxy's star formation history or metal enrichment, and to identify galaxies at a range of stellar masses. In this paper we present a study of emission line galaxies in the SHARDS Frontier Fields medium-band survey. Through detailed flux calibrations we combine the first results of the SHARDS-FF survey with existing Hubble Frontier Field data to select 1,098 candidate emission line galaxies from the Hubble Frontier Filed clusters Abell 370 and MACS J1149.5+2223. Furtherm…
Widespread Extended [CII] Emission in High-Redshift Galaxies: Insights from the FIRE-2 Cosmological Zoom-in Simulations
California Institute of Technology（加州理工学院）；CIERA and Department of Physics and Astronomy, Northwestern University（西北大学 CIERA 与物理和天文系）；IPAC, California Institute of Technology（加州理工学院 IPAC）；Department of Physics and Astronomy, University of Pennsylvania（宾夕法尼亚大学物理和天文系）
It's More Complicated Than You Think: A Forward Model to Infer the Recent Star Formation History, Bursty or Not, of Galaxy Populations
The Pennsylvania State University（宾夕法尼亚州立大学）；Princeton University（普林斯顿大学）；Wesleyan University（卫斯理安大学）；Columbia University（哥伦比亚大学）；Flatiron Institute（平井研究所）
We use the FIRE-2 cosmological simulations to study the formation of a quasi-static, virial-temperature gas phase in the circumgalactic medium (CGM) at redshifts 0<z<5, and how the formation of this virialized phase affects the evolution of galactic discs. We demonstrate that when the halo mass crosses ~10^12 M_sun, the cooling time of shocked gas in the inner CGM (~0.1 R_vir, where R_vir is the virial radius) exceeds the local free-fall time. The inner CGM then experiences a transition from on average sub-virial temperatures (T<<T_vir), large pressure fluctuations and supersonic inflow/outflo…
Extended, old, and round stellar halos appear to be ubiquitous around high-mass dwarf galaxies ($10^{8.5}<M_\star/M_\odot<10^{9.6}$) in the observed universe. However, it is unlikely that these dwarfs have undergone a sufficient number of minor mergers to form stellar halos that are composed of predominantly accreted stars. Here, we demonstrate that FIRE-2 (Feedback in Realistic Environments) cosmological zoom-in simulations are capable of producing dwarf galaxies with realistic structure, including both a thick disk and round stellar halo. Crucially, these stellar halos are formed in-situ, la…
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…
The Impact of Star Formation Histories on the Inner Dark Matter Density Slopes of Galaxies
Instituto de Astrofísica de Canarias (IAC)（加那利天体物理研究所）；Universidad de La Laguna（拉古纳大学）；Department of Physics & Astronomy, University of Southern California（南加州大学物理与天文系）；New York University Abu Dhabi（阿布扎比纽约大学）；Center for Astrophysics and Space Science, New York University Abu Dhabi（阿布扎比纽约大学天体物理学与空间科学中心）
