207 research outputs found
An Analysis of ALMA Deep Fields and the Perceived Dearth of High-z Galaxies
Deep, pencil-beam surveys from ALMA at 1.1-1.3mm have uncovered an apparent
absence of high-redshift dusty galaxies, with existing redshift distributions
peaking around . This has led to a perceived dearth of dusty
systems at , and the conclusion, according to some models, that the early
Universe was relatively dust-poor. In this paper, we extend the backward
evolution galaxy model described by Casey et al. (2018) to the ALMA regime (in
depth and area) and determine that the measured number counts and redshift
distributions from ALMA deep field surveys are fully consistent with
constraints of the infrared luminosity function (IRLF) at determined by
single-dish submillimeter and millimeter surveys conducted on much larger
angular scales (deg). We find that measured 1.1-1.3mm number
counts are most constraining for the measurement of the faint-end slope of the
IRLF at . Recent
studies have suggested that UV-selected galaxies at may be particularly
dust-poor, but we find their millimeter-wave emission cannot rule out
consistency with the Calzetti dust attenuation law even by assuming relatively
typical, cold-dust (K) SEDs. Our models suggest that
the design of ALMA deep fields requires substantial revision to constrain the
prevalence of early Universe obscured starbursts. The most promising
avenue for detection and characterization of such early dusty galaxies will
come from future ALMA 2mm blank field surveys covering a few hundred
arcmin and the combination of existing and future dual-purpose 3mm
datasets.Comment: 21 pages, 12 figures, accepted for publication in Ap
Kinematic classifications of local interacting galaxies: implications for the merger/disk classifications at high-z
The classification of galaxy mergers and isolated disks is key for
understanding the relative importance of galaxy interactions and secular
evolution during the assembly of galaxies. The kinematic properties of galaxies
as traced by emission lines have been used to suggest the existence of a
significant population of high-z star-forming galaxies consistent with isolated
rotating disks. However, recent studies have cautioned that post-coalescence
mergers may also display disk-like kinematics. To further investigate the
robustness of merger/disk classifications based on kinematic properties, we
carry out a systematic classification of 24 local (U)LIRGs spanning a range of
galaxy morphologies: from isolated spiral galaxies, ongoing interacting
systems, to fully merged remnants. We artificially redshift the WiFeS
observations of these local (U)LIRGs to z=1.5 to make a realistic comparison
with observations at high-z, and also to ensure that all galaxies have the same
spatial sampling of ~900 pc. Using both kinemetry-based and visual
classifications, we find that the reliability of kinematic classification shows
a strong trend with the interaction stage of galaxies. Mergers with two nuclei
and tidal tails have the most distinct kinematic properties compared to
isolated disks, whereas a significant population of the interacting disks and
merger remnants are indistinguishable from isolated disks. The high fraction of
late-stage mergers showing disk-like kinematics reflects the complexity of the
dynamics during galaxy interactions. However, the exact fractions of
misidentified disks and mergers depend on the definition of kinematic
asymmetries and the classification threshold when using kinemetry-based
classifications. Our results suggest that additional indicators such as
morphologies traced by stars or molecular gas are required to further constrain
the merger/disk classifications at high-z.Comment: 16 pages, 5 figures, ApJ accepte
The Molecular Gas Reservoirs of Galaxies: A comparison of CO(1-0) and dust-based molecular gas masses
We test the use of long-wavelength dust continuum emission as a molecular gas
tracer at high redshift, via a unique sample of 12, z~2 galaxies with
observations of both the dust continuum and CO(1-0) line emission (obtained
with the Atacama Large Millimeter Array and Karl G. Jansky Very Large Array,
respectively). Our work is motivated by recent, high redshift studies that
measure molecular gas masses (\ensuremath{\rm{M}_{\rm{mol}}}) via a calibration
of the rest-frame m luminosity () against the
CO(1-0)-derived \ensuremath{\rm{M}_{\rm{mol}}}\ of star-forming galaxies. We
hereby test whether this method is valid for the types of high-redshift,
star-forming galaxies to which it has been applied. We recover a clear
correlation between the rest-frame m luminosity, inferred from the
single-band, long-wavelength flux, and the CO(1-0) line luminosity, consistent
with the samples used to perform the m calibration. The molecular gas
masses, derived from , agree to within a factor of
two with those derived from CO(1-0). We show that this factor of two
uncertainty can arise from the values of the dust emissivity index and
temperature that need to be assumed in order to extrapolate from the observed
frequency to the rest-frame at 850. The extrapolation to
850 therefore has a smaller effect on the accuracy of \Mmol\
derived via single-band dust-continuum observations than the assumed
CO(1-0)-to-\ensuremath{\rm{M}_{\rm{mol}}}\ conversion factor. We therefore
conclude that single-band observations of long-wavelength dust emission can be
used to reliably constrain the molecular gas masses of massive, star-forming
galaxies at
The Brightest Galaxies in the Dark Ages: Galaxies' Dust Continuum Emission During the Reionization Era
Though half of cosmic starlight is absorbed by dust and reradiated at long
wavelengths (3m-3mm), constraints on the infrared through millimeter
galaxy luminosity function (the `IRLF') are poor in comparison to the
rest-frame ultraviolet and optical galaxy luminosity function, particularly at
z>2.5. Here we present a backward evolution model for interpreting number
counts, redshift distributions, and cross-band flux density correlations in the
infrared and submillimeter sky, from 70m-2mm, using a model for the IRLF
out to the epoch of reionization. Mock submillimeter maps are generated by
injecting sources according to the prescribed IRLF and flux densities drawn
from model spectral energy distributions that mirror the distribution of SEDs
observed in dusty star-forming galaxies (DSFGs). We explore two extreme
hypothetical case-studies: a dust-poor early Universe model, where DSFGs
contribute negligibly (10%) to the integrated star-formation rate density at
, and an alternate dust-rich early Universe model, where DSFGs dominate
90% of star-formation. We find that current submm/mm datasets do
not clearly rule out either of these extreme models. We suggest that future
surveys at 2mm will be crucial to measuring the IRLF beyond . The model
framework developed in this paper serves as a unique tool for the
interpretation of multiwavelength IR/submm extragalactic datasets and will
enable more refined constraints on the IRLF than can be made from direct
measurements of individual galaxies' integrated dust emission.Comment: 34 pages, 16 figures, accepted for publication in Ap
Searching Far and Long I: Pilot ALMA 2mm Follow-up of Bright Dusty Galaxies as a Redshift Filter
A complete census of dusty star-forming galaxies (DSFGs) at early epochs is
necessary to constrain the obscured contribution to the cosmic star formation
rate density (CSFRD), however DSFGs beyond are both rare and hard to
identify from photometric data alone due to degeneracies in submillimeter
photometry with redshift. Here, we present a pilot study obtaining follow-up
Atacama Large Millimeter Array (ALMA) mm observations of a complete sample
of 39 -bright dusty galaxies in the SSA22 field. Empirical
modeling suggests mm imaging of existing samples of DSFGs selected at
mm can quickly and easily isolate the "needle in a
haystack" DSFGs that sit at or beyond. Combining archival submillimeter
imaging with our measured ALMA mm photometry (mJybeam rms), we characterize the galaxies' IR SEDs and use
them to constrain redshifts. With available redshift constraints fit via the
combination of six submillimeter bands, we identify 6/39 high- candidates
each with likelihood to sit at , and find a positive correlation
between redshift and mm flux density. Specifically, our models suggest the
addition of mm to a moderately constrained IR SED will improve the
accuracy of a millimeter-derived redshift from to
. Our IR SED characterizations provide evidence for
relatively high emissivity spectral indices () in the sample. We measure that especially bright (mJy) DSFGs contribute % to the cosmic-averaged CSFRD from
, confirming findings from previous work with similar samples.Comment: 22 pages, 7 figures, accepted for publication in Ap
Missing Giants: Predictions on Dust-Obscured Galaxy Stellar Mass Assembly Throughout Cosmic Time
Due to their extremely dust-obscured nature, much uncertainty still exists
surrounding the stellar mass growth and content in dusty, star-forming galaxies
(DSFGs) at . In this work, we present a numerical model built using
empirical data on DSFGs to estimate their stellar mass contributions across the
first 10 Gyr of cosmic time. We generate a dust-obscured stellar mass
function that extends beyond the mass limit of star-forming stellar mass
functions in the literature, and predict that massive DSFGs constitute as much
as of all star-forming galaxies with M M at
. We predict the number density of massive DSFGs and find general
agreement with observations, although more data is needed to narrow wide
observational uncertainties. We forward model mock massive DSFGs to their
quiescent descendants and find remarkable agreement with observations from the
literature demonstrating that, to first order, massive DSFGs are a sufficient
ancestral population to describe the prevalence of massive quiescent galaxies
at . We predict that massive DSFGs and their descendants contribute as
much as to the cosmic stellar mass density during the peak of cosmic
star formation, and predict an intense epoch of population growth during the
Gyr from to 3 during which the majority of the most massive
galaxies at high- grow and then quench. Future studies seeking to understand
massive galaxy growth and evolution in the early Universe should strategize
synergies with data from the latest observatories (e.g. JWST and ALMA) to
better include the heavily dust-obscured galaxy population.Comment: 22 pages, 9 figures, submitted to Ap
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