124 research outputs found
Constraints on the Star Formation Efficiency of Galaxies During the Epoch of Reionization
Reionization is thought to have occurred in the redshift range of , which is now being probed by both deep galaxy surveys and CMB observations.
Using halo abundance matching over the redshift range and assuming
smooth, continuous gas accretion, we develop a model for the star formation
efficiency of dark matter halos at that matches the measured
galaxy luminosity functions at these redshifts. We find that peaks
at at halo masses --~M, in
qualitative agreement with its behavior at lower redshifts. We then investigate
the cosmic star formation histories and the corresponding models of
reionization for a range of extrapolations to small halo masses. We use a
variety of observations to further constrain the characteristics of the galaxy
populations, including the escape fraction of UV photons. Our approach provides
an empirically-calibrated, physically-motivated model for the properties of
star-forming galaxies sourcing the epoch of reionization. In the case where
star formation in low-mass halos is maximally efficient, an average escape
fraction can reproduce the optical depth reported by Planck, whereas
inefficient star formation in these halos requires either about twice as many
UV photons to escape, or an escape fraction that increases towards higher
redshifts. Our models also predict how future observations with JWST can
improve our understanding of these galaxy populations.Comment: 19 pages, 12 figures, accepted for publication in MNRAS, minor
modification
A minimalist feedback-regulated model for galaxy formation during the epoch of reionization
Near-infrared surveys have now determined the luminosity functions of galaxies at 6 ≲ z ≲ 8 to impressive precision and identified a number of candidates at even earlier times. Here, we develop a simple analytic model to describe these populations that allows physically motivated extrapolation to earlier times and fainter luminosities. We assume that galaxies grow through accretion on to dark matter haloes, which we model by matching haloes at fixed number density across redshift, and that stellar feedback limits the star formation rate. We allow for a variety of feedback mechanisms, including regulation through supernova energy and momentum from radiation pressure. We show that reasonable choices for the feedback parameters can fit the available galaxy data, which in turn substantially limits the range of plausible extrapolations of the luminosity function to earlier times and fainter luminosities: for example, the global star formation rate declines rapidly (by a factor of ∼20 from z = 6 to 15 in our fiducial model), but the bright galaxies accessible to observations decline even faster (by a factor ≳ 400 over the same range). Our framework helps us develop intuition for the range of expectations permitted by simple models of high-z galaxies that build on our understanding of ‘normal’ galaxy evolution. We also provide predictions for galaxy measurements by future facilities, including James Webb Space Telescope and Wide-Field Infrared Survey Telescope
Seen and unseen: bursty star formation and its implications for observations of high-redshift galaxies with JWST
Both observations and simulations have shown strong evidence for highly
time-variable star formation in low-mass and/or high-redshift galaxies, which
has important observational implications because high-redshift galaxy samples
are rest-UV selected and therefore particularly sensitive to the recent star
formation. Using a suite of cosmological "zoom-in" simulations at from
the Feedback in Realistic Environments (FIRE) project, we examine the
implications of bursty star formation histories for observations of
high-redshift galaxies with JWST. We characterize how the galaxy observability
depends on the star formation history. We also investigate selection effects
due to bursty star formation on the physical properties measured, such as the
gas fraction, specific star formation rate, and metallicity. We find the
observability to be highly time-dependent for galaxies near the survey's
limiting flux due to the SFR variability: as the star formation rate
fluctuates, the same galaxy oscillates in and out of the observable sample. The
observable fraction at and to for a JWST/NIRCam survey reaching a limiting
magnitude of -, representative of
surveys such as JADES and CEERS. JWST-detectable galaxies near the survey limit
tend to have properties characteristic of galaxies in the bursty phase: on
average, they show approximately 2.5 times higher cold, dense gas fractions and
20 times higher specific star formation rates at a given stellar mass than
galaxies below the rest-UV detection threshold. Our study represents a first
step in quantifying selection effects and the associated biases due to bursty
star formation in studying high-redshift galaxy properties.Comment: 8 pages, 4 figures, resubmitted after incorporating referee's
comments; analysis expanded to include more galaxies and some quantitative
results correcte
A Self-consistent Framework for Multiline Modeling in Line Intensity Mapping Experiments
Line intensity mapping (LIM) is a promising approach to study star formation and the interstellar medium (ISM) in galaxies by measuring the aggregate line emission from the entire galaxy population. In this work, we develop a simple yet physically motivated framework for modeling the line emission as would be observed in LIM experiments. It is done by building on analytic models of the cosmic infrared background that connect total infrared luminosity of galaxies to their host dark matter halos. We present models of the H I 21 cm, CO (1−0), [C II] 158 μm, and [N II] 122 and 205 μm lines consistent with current observational constraints. With four case studies of various combinations of these lines that probe different ISM phases, we demonstrate the potential for reliably extracting physical properties of the ISM, and the evolution of these properties with cosmic time, from auto- and cross-correlation analysis of these lines as measured by future LIM experiments
Probing bursty star formation by cross-correlating extragalactic background light and galaxy surveys
Understanding the star formation rate (SFR) variability and how it depends on
physical properties of galaxies is important for developing and testing the
theory of galaxy formation. We investigate how statistical measurements of the
extragalactic background light (EBL) can shed light on this topic and
complement traditional methods based on observations of individual galaxies.
Using semi-empirical models of galaxy evolution and SFR indicators sensitive to
different star formation timescales (e.g., H and UV continuum
luminosities), we show that the SFR variability, quantified by the joint
probability distribution of the SFR indicators (i.e., the bivariate conditional
luminosity function), can be characterized as a function of galaxy mass and
redshift through the cross-correlation between deep, near-infrared maps of the
EBL and galaxy distributions. As an example, we consider combining upcoming
SPHEREx maps of the EBL with galaxy samples from Rubin/LSST. We demonstrate
that their cross-correlation over a sky fraction of can
constrain the joint SFR indicator distribution at high significance up to
for mass-complete samples of galaxies down to
. These constraints not only allow models of
different SFR variability to be distinguished, but also provide unique
opportunities to investigate physical mechanisms that require large number
statistics such as environmental effects. The cross-correlations investigated
illustrate the power of combining cosmological surveys to extract information
inaccessible from each data set alone, while the large galaxy populations
probed capture ensemble-averaged properties beyond the reach of targeted
observations towards individual galaxies.Comment: 12 pages, 7 figures, MNRAS accepte
The Early Universe was Dust-Rich and Extremely Hot
We investigate the dust properties and star-formation signature of galaxies
in the early universe by stacking 111,227 objects in the recently released
COSMOS catalogue on maps at wavelengths bracketing the peak of warmed dust
emission. We find an elevated far-infrared luminosity density to redshift 10,
indicating abundant dust in the early universe. We further find an increase of
dust temperature with redshift, reaching ~ 119 +- 7 K at z ~ 9, suggesting
either the presence of silicate rich dust originating from Population II stars,
or sources of heating beyond simply young hot stars. Lastly, we try to
understand how these objects have been missed in previous surveys, and how to
design observations to target them. All code, links to the data, and
instructions to reproduce this research in full is located at
https://github.com/marcoviero/simstack3/
Bursty Star Formation Naturally Explains the Abundance of Bright Galaxies at Cosmic Dawn
Recent discoveries of a significant population of bright galaxies at cosmic
dawn have enabled critical tests of cosmological
galaxy formation models. In particular, the bright end of the galaxy UV
luminosity function (UVLF) appears higher than predicted by many models. Using
approximately 25,000 galaxy snapshots at in a suite of
FIRE-2 cosmological "zoom-in'' simulations from the Feedback in Realistic
Environments (FIRE) project, we show that the observed abundance of UV-bright
galaxies at cosmic dawn is reproduced in these simulations with a multi-channel
implementation of standard stellar feedback processes, without any fine-tuning.
Notably, we find no need to invoke previously suggested modifications such as a
non-standard cosmology, a top-heavy stellar initial mass function, or a
strongly enhanced star formation efficiency. We contrast the UVLFs predicted by
bursty star formation in these original simulations to those derived from star
formation histories (SFHs) smoothed over prescribed timescales (e.g., 100 Myr).
The comparison demonstrates that the strongly time-variable SFHs predicted by
the FIRE simulations play a key role in correctly reproducing the observed,
bright-end UVLFs at cosmic dawn: the bursty SFHs induce order-or-magnitude
changes in the abundance of UV-bright () galaxies
at . The predicted bright-end UVLFs are consistent with both the
spectroscopically confirmed population and the photometrically selected
candidates. We also find good agreement between the predicted and
observationally inferred integrated UV luminosity densities, which evolve more
weakly with redshift in FIRE than suggested by some other models.Comment: 12 pages, 4 figures + 1 table, submitted to ApJ
A minimalist feedback-regulated model for galaxy formation during the epoch of reionization
Near-infrared surveys have now determined the luminosity functions of galaxies at 6 ≲ z ≲ 8 to impressive precision and identified a number of candidates at even earlier times. Here, we develop a simple analytic model to describe these populations that allows physically motivated extrapolation to earlier times and fainter luminosities. We assume that galaxies grow through accretion on to dark matter haloes, which we model by matching haloes at fixed number density across redshift, and that stellar feedback limits the star formation rate. We allow for a variety of feedback mechanisms, including regulation through supernova energy and momentum from radiation pressure. We show that reasonable choices for the feedback parameters can fit the available galaxy data, which in turn substantially limits the range of plausible extrapolations of the luminosity function to earlier times and fainter luminosities: for example, the global star formation rate declines rapidly (by a factor of ∼20 from z = 6 to 15 in our fiducial model), but the bright galaxies accessible to observations decline even faster (by a factor ≳ 400 over the same range). Our framework helps us develop intuition for the range of expectations permitted by simple models of high-z galaxies that build on our understanding of ‘normal’ galaxy evolution. We also provide predictions for galaxy measurements by future facilities, including James Webb Space Telescope and Wide-Field Infrared Survey Telescope
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