37 research outputs found
Ultra-Diffuse Galaxies as Extreme Star-forming Environments I: Mapping Star Formation in HI-Rich UDGs
Ultra-Diffuse Galaxies are both extreme products of galaxy evolution and
extreme environments in which to test our understanding of star formation. In
this work, we contrast the spatially resolved star formation activity of a
sample of 22 HI-selected UDGs and 35 low-mass galaxies from the NASA Sloan
Atlas (NSA) within 120 Mpc. We employ a new joint SED fitting method to compute
star formation rate and stellar mass surface density maps that leverage the
high spatial resolution optical imaging data of the Hyper Suprime-Cam Subaru
Strategic Program (HSC-SSP) and the UV coverage of GALEX, along with HI radial
profiles estimated from a subset of galaxies that have spatially resolved HI
maps. We find that the UDGs have low star formation efficiencies as a function
of their atomic gas down to scales of 500 pc. We additionally find that the
stellar mass-weighted sizes of our UDG sample are unremarkable when considered
as a function of their HI mass -- their stellar sizes are comparable to the NSA
dwarfs at fixed HI mass. This is a natural result in the picture where UDGs are
forming stars normally, but at low efficiencies. We compare our results to
predictions from contemporary models of galaxy formation, and find in
particular that our observations are difficult to reproduce in models where
UDGs undergo stellar expansion due to vigorous star formation feedback should
bursty star formation be required down to .Comment: Accepted to ApJ, 27 pages, 18 figure
Diffuse Ionized Gas in Simulations of Multiphase, Star-Forming Galactic Disks
It has been hypothesized that photons from young, massive star clusters are
responsible for maintaining the ionization of diffuse warm ionized gas seen in
both the Milky Way and other disk galaxies. For a theoretical investigation of
the warm ionized medium (WIM), it is crucial to solve radiation transfer
equations where the ISM and clusters are modeled self-consistently. To this
end, we employ a Solar neighborhood model of TIGRESS, a magnetohydrodynamic
simulation of the multiphase, star-forming ISM, and post-process the simulation
with an adaptive ray tracing method to transfer UV radiation from star
clusters. We find that the WIM volume filling factor is highly variable, and
sensitive to the rate of ionizing photon production and ISM structure. The mean
WIM volume filling factor rises to ~0.15 at |z|~1 kpc. Approximately half of
ionizing photons are absorbed by gas and half by dust; the cumulative ionizing
photon escape fraction is 1.1%. Our time-averaged synthetic H line
profile matches WHAM observations on the redshifted (outflowing) side, but has
insufficient intensity on the blueshifted side. Our simulation matches the
Dickey-Lockman neutral density profile well, but only a small fraction of
snapshots have high-altitude WIM density consistent with Reynolds Layer
estimates. We compute a clumping correction factor C = /sqrt~0.2
that is remarkably constant with distance from the midplane and time; this can
be used to improve estimates of ionized gas mass and mean electron density from
observed H surface brightness profiles in edge-on galaxies.Comment: Accepted to ApJ; 31 pages, 17 figure
HFF-DeepSpace photometric catalogs of the 12 Hubble frontier fields, clusters, and parallels : photometry, photometric redshifts, and stellar masses
We present Hubble multi-wavelength photometric catalogs, including (up to) 17 filters with the Advanced Camera for Surveys and Wide Field Camera 3 from the ultra-violet to near-infrared for the Hubble Frontier Fields and associated parallels. We have constructed homogeneous photometric catalogs for all six clusters and their parallels. To further expand these data catalogs, we have added ultra-deep KS-band imaging at 2.2. mu m from the Very Large Telescope HAWK-I and Keck-I MOSFIRE instruments. We also add post-cryogenic Spitzer imaging at 3.6 and 4.5. mu m with the Infrared Array Camera (IRAC), as well as archival IRAC 5.8 and 8.0. mu m imaging when available. We introduce the public release of the multi-wavelength (0.2-8 mu m) photometric catalogs, and we describe the unique steps applied for the construction of these catalogs. Particular emphasis is given to the source detection band, the contamination of light from the bright cluster galaxies (bCGs), and intra-cluster light (ICL). In addition to the photometric catalogs, we provide catalogs of photometric redshifts and stellar population properties. Furthermore, this includes all the images used in the construction of the catalogs, including the combined models of bCGs and ICL, the residual images, segmentation maps, and more. These catalogs are a robust data set of the Hubble Frontier Fields and will be an important aid in designing future surveys, as well as planning follow-up programs with current and future observatories to answer key questions remaining about first light, reionization, the assembly of galaxies, and many more topics, most notably by identifying high-redshift sources to target
The Intrinsic Shapes of Low Surface Brightness Galaxies (LSBGs):A Discriminant of LSBG Galaxy Formation Mechanisms
We use the low surface brightness galaxy (LSBG) samples created from the Hyper Suprime-Cam Subaru Strategic Program (781 galaxies), the Dark Energy Survey (20977 galaxies), and the Legacy Survey (selected via H I detection in the Arecibo Legacy Fast ALFA Survey, 188 galaxies) to infer the intrinsic shape distribution of the LSBG population. To take into account the effect of the surface brightness cuts employed when constructing LSBG samples, we simultaneously model both the projected ellipticity and the apparent surface brightness in our shape inference. We find that the LSBG samples are well characterized by oblate spheroids, with no significant difference between red and blue LSBGs. This inferred shape distribution is in good agreement with similar inferences made for ultra-diffuse cluster galaxy samples, indicating that environment does not play a key role in determining the intrinsic shape of LSBGs. We also find some evidence that LSBGs are more thickened than similarly massive high surface brightness dwarfs. We compare our results to intrinsic shape measures from contemporary cosmological simulations, and find that the observed LSBG intrinsic shapes place considerable constraints on the formation path of such galaxies. In particular, LSBG production via the migration of star formation to large radii produces intrinsic shapes in good agreement with our observational findings
Beyond Ultra-Diffuse Galaxies I: Mass-Size Outliers Among the Satellites of Milky Way Analogs
Large diffuse galaxies are hard to find, but understanding the environments
where they live, their numbers, and ultimately their origins, is of intense
interest and importance for galaxy formation and evolution. Using Subaru's
Hyper Suprime-Cam Strategic Survey Program, we perform a systematic search for
low surface brightness galaxies and present novel and effective methods for
detecting and modeling them. As a case study, we surveyed 922 Milky Way analogs
in the nearby Universe () and build a large sample of
satellite galaxies that are outliers in the mass-size relation. These
``ultra-puffy'' galaxies (UPGs), defined to be above the average
mass-size relation, represent the tail of the satellite size distribution. We
find that each MW analog hosts ultra-puffy
galaxies on average, which is consistent with but slightly lower than the
observed abundance at this halo mass in the Local Volume. We also construct a
sample of ultra-diffuse galaxies (UDGs) in MW analogs and find an abundance of
per host. With literature results, we confirm that
the UDG abundance scales with the host halo mass following a sublinear power
law. We argue that our definition for ultra-puffy galaxies, which is based on
the mass-size relation, is more physically-motivated than the common definition
of ultra-diffuse galaxies, which depends on surface brightness and size cuts
and thus yields different surface mass density cuts for quenched and
star-forming galaxies.Comment: 19 pages, 7 figures, submitted to Ap
The Compact Structures of Massive z ∼ 0.7 Post-starburst Galaxies in the SQuIGGL⃗E Sample
We present structural measurements of 145 spectroscopically selected intermediate-redshift (z ∼ 0.7), massive (M⋆ ∼ 1011 M⊙) post-starburst galaxies from the sample measured using wide-depth Hyper Suprime-Cam i-band imaging. This deep imaging allows us to probe the sizes and structures of these galaxies, which we compare to a control sample of star-forming and quiescent galaxies drawn from the LEGA-C Survey. We find that post-starburst galaxies systematically lie ∼0.1 dex below the quiescent mass–size (half-light radius) relation, with a scatter of ∼0.2 dex. This finding is bolstered by nonparametric measures, such as the Gini coefficient and the concentration, which also reveal these galaxies to have more compact light profiles than both quiescent and star-forming populations at similar mass and redshift. The sizes of post-starburst galaxies show either negative or no correlation with the time since quenching, such that more recently quenched galaxies are larger or similarly sized. This empirical finding disfavors the formation of post-starburst galaxies via a purely central burst of star formation that simultaneously shrinks the galaxy and shuts off star formation. We show that the central densities of post-starburst and quiescent galaxies at this epoch are very similar, in contrast with their effective radii. The structural properties of z ∼ 0.7 post-starburst galaxies match those of quiescent galaxies that formed in the early universe, suggesting that rapid quenching in the present epoch is driven by a similar mechanism to the one at high redshift
Complete IRAC mapping of the CFHTLS-DEEP, MUSYC AND NMBS-II FIELDS
The IRAC mapping of the NMBS-II fields program is an imaging survey at 3.6
and 4.5m with the Spitzer Infrared Array Camera (IRAC). The observations
cover three Canada-France-Hawaii Telescope Legacy Survey Deep (CFHTLS-D)
fields, including one also imaged by AEGIS, and two MUSYC fields. These are
then combined with archival data from all previous programs into deep mosaics.
The resulting imaging covers a combined area of about 3 , with at least
2 hr integration time for each field. In this work, we present our data
reduction techniques and document the resulting coverage maps at 3.6 and
4.5m. All of the images are W-registered to the reference image, which is
either the z-band stack image of the 25\% best seeing images from the CFHTLS-D
for CFHTLS-D1, CFHTLS-D3, and CFHTLS-D4, or the K-band images obtained at the
Blanco 4-m telescope at CTIO for MUSYC1030 and MUSYC1255. We make all images
and coverage maps described herein publicly available via the Spitzer Science
Center.Comment: Accepted in PASP; released IRAC mosaics available upon publication of
the pape
Tidal Features at 0.05<z<0.45 in the Hyper Suprime-Cam Subaru Strategic Program: Properties and Formation Channels
We present 1,201 galaxies at that host tidal features, detected
from the first deg of imaging from the Hyper Suprime-Cam
Subaru Strategic Program (HSC-SSP). All galaxies in the present sample have
spectroscopic observations from the Sloan Digital Sky Survey (SDSS)
spectroscopic campaigns, generating a sample of 21208 galaxies. Of these
galaxies, we identify 214 shell systems and 987 stream systems. For 575 of
these systems, we are additionally able to measure the colors of the
tidal features. We find evidence for star formation in a subset of the streams,
with the exception of streams around massive ellipticals, and find that stream
host galaxies span the full range of stellar masses in our sample. Galaxies
which host shells are predominantly red and massive: we find that observable
shells form more frequently around ellipticals than around disc galaxies of the
same stellar mass. Although the majority of the shells in our sample are
consistent with being formed by minor mergers, of shell host
galaxies have colors as red as their host galaxy, consistent with being
formed by major mergers. These "red shells" are additionally preferentially
aligned with the major axis of the host galaxy, as previously predicted from
simulations. We suggest that although the bulk of the observable shell
population originates from fairly minor mergers, which preferentially form
shells that are not aligned with the major axis of the galaxy, major mergers
produce a significant number of observable shells.Comment: 24 pages, 14 figures. Submitted to Ap
Early Science with the Large Millimeter Telescope: Detection of Dust Emission in Multiple Images of a Normal Galaxy at z \u3e 4 Lensed by a Frontier Fields Cluster
We directly detect dust emission in an optically detected, multiply imaged galaxy lensed by the Frontier Fields cluster MACSJ0717.5+3745. We detect two images of the same galaxy at 1.1 mm with the AzTEC camera on the Large Millimeter Telescope leaving no ambiguity in the counterpart identification. This galaxy, MACS0717_Az9, is at z \u3e 4 and the strong lensing model (μ=7.5) allows us to calculate an intrinsic IR luminosity of 9.7 × 1010 Le and an obscured star formation rate of 14.6 ± 4.5 Me yr−1. The unobscured star formation rate from the UV is only 4.1 ± 0.3 Me yr−1, which means the total star formation rate (18.7 ± 4.5 Me yr−1) is dominated (75%–80%) by the obscured component. With an intrinsic stellar mass of only 6.9 × 109 Me, MACS0717_Az9 is one of only a handful of z \u3e 4 galaxies at these lower masses that is detected in dust emission. This galaxy lies close to the estimated star formation sequence at this epoch. However, it does not lie on the dust obscuration relation (IRX-β) for local starburst galaxies and is instead consistent with the Small Magellanic Cloud attenuation law. This remarkable lower mass galaxy, showing signs of both low metallicity and high dust content, may challenge our picture of dust production in the early universe