79 research outputs found
The Herschel Stripe 82 Survey (HerS): maps and early catalog
We present the first set of maps and band-merged catalog from the Herschel Stripe 82 Survey (HerS). Observations at 250, 350, and 500ÎŒm were taken with the Spectral and Photometric Imaging Receiver instrument aboard the Herschel Space Observatory. HerS covers 79deg 2 along the SDSS Stripe 82 to an average depth of 13.0, 12.9, and 14.8mJybeam â1 (including confusion) at 250, 350, and 500ÎŒm, respectively. HerS was designed to measure correlations with external tracers of the dark matter density fieldâeither point-like (i.e., galaxies selected from radio to X-ray) or extended (i.e., clusters and gravitational lensing)âin order to measure the bias and redshift distribution of intensities of infrared-emitting dusty star-forming galaxies and active galactic nuclei. By locating HerS in Stripe 82, we maximize the overlap with available and upcoming cosmological surveys. The band-merged catalog contains 3.3 Ă 10 4 sources detected at a significance of ?3Ï (including confusion noise). The maps and catalog are available at http://www.astro.caltech.edu/hers/
UVUDF: Ultraviolet Imaging of the Hubble Ultradeep Field with Wide-field Camera 3
We present an overview of a 90-orbit Hubble Space Telescope treasury program
to obtain near ultraviolet imaging of the Hubble Ultra Deep Field using the
Wide Field Camera 3 UVIS detector with the F225W, F275W, and F336W filters.
This survey is designed to: (i) Investigate the episode of peak star formation
activity in galaxies at 1<z<2.5; (ii) Probe the evolution of massive galaxies
by resolving sub-galactic units (clumps); (iii) Examine the escape fraction of
ionizing radiation from galaxies at z~2-3; (iv) Greatly improve the reliability
of photometric redshift estimates; and (v) Measure the star formation rate
efficiency of neutral atomic-dominated hydrogen gas at z~1-3. In this overview
paper, we describe the survey details and data reduction challenges, including
both the necessity of specialized calibrations and the effects of charge
transfer inefficiency. We provide a stark demonstration of the effects of
charge transfer inefficiency on resultant data products, which when
uncorrected, result in uncertain photometry, elongation of morphology in the
readout direction, and loss of faint sources far from the readout. We agree
with the STScI recommendation that future UVIS observations that require very
sensitive measurements use the instrument's capability to add background light
through a "post-flash". Preliminary results on number counts of UV-selected
galaxies and morphology of galaxies at z~1 are presented. We find that the
number density of UV dropouts at redshifts 1.7, 2.1, and 2.7 is largely
consistent with the number predicted by published luminosity functions. We also
confirm that the image mosaics have sufficient sensitivity and resolution to
support the analysis of the evolution of star-forming clumps, reaching 28-29th
magnitude depth at 5 sigma in a 0.2 arcsecond radius aperture depending on
filter and observing epoch.Comment: Accepted A
GOODS-Herschel: star formation, dust attenuation, and the FIR-radio correlation on the main sequence of star-forming galaxies up to z=4
We use deep panchromatic data sets in the GOODS-N field, from GALEX to the deepest Herschel far-infrared (FIR) and VLA radio continuum imaging, to explore the evolution of star-formation activity and dust attenuation properties of star-forming galaxies to z sime 4, using mass-complete samples. Our main results can be summarized as follows: (i) the slope of the star-formation rateâM* correlation is consistent with being constant sime0.8 up to z sime 1.5, while its normalization keeps increasing with redshift; (ii) for the first time we are able to explore the FIRâradio correlation for a mass-selected sample of star-forming galaxies: the correlation does not evolve up to z sime 4; (iii) we confirm that galaxy stellar mass is a robust proxy for UV dust attenuation in star-forming galaxies, with more massive galaxies being more dust attenuated. Strikingly, we find that this attenuation relation evolves very weakly with redshift, with the amount of dust attenuation increasing by less than 0.3 mag over the redshift range [0.5â4] for a fixed stellar mass; (iv) the correlation between dust attenuation and the UV spectral slope evolves with redshift, with the median UV slope becoming bluer with redshift. By z sime 3, typical UV slopes are inconsistent, given the measured dust attenuations, with the predictions of commonly used empirical laws. (v) Finally, building on existing results, we show that gas reddening is marginally larger (by a factor of around 1.3) than the stellar reddening at all redshifts probed. Our results support a scenario where the ISM conditions of typical star-forming galaxies evolve with redshift, such that at z â„ 1.5 Main Sequence galaxies have ISM conditions moving closer to those of local starbursts
Reionization after Planck: the derived growth of the cosmic ionizing emissivity now matches the growth of the galaxy UV luminosity density
Thomson optical depth tau measurements from Planck provide new insights into
the reionization of the universe. In pursuit of model-independent constraints
on the properties of the ionising sources, we determine the empirical evolution
of the cosmic ionizing emissivity. We use a simple two-parameter model to map
out the evolution in the emissivity at z>~6 from the new Planck optical depth
tau measurements, from the constraints provided by quasar absorption spectra
and from the prevalence of Ly-alpha emission in z~7-8 galaxies. We find the
redshift evolution in the emissivity dot{N}_{ion}(z) required by the
observations to be d(log Nion)/dz=-0.15(-0.11)(+0.08), largely independent of
the assumed clumping factor C_{HII} and entirely independent of the nature of
the ionising sources. The trend in dot{N}_{ion}(z) is well-matched by the
evolution of the galaxy UV-luminosity density (dlog_{10}
rho_UV/dz=-0.11+/-0.04) to a magnitude limit >~-13 mag, suggesting that
galaxies are the sources that drive the reionization of the universe. The role
of galaxies is further strengthened by the conversion from the UV luminosity
density rho_UV to dot(N)_{ion}(z) being possible for physically-plausible
values of the escape fraction f_{esc}, the Lyman-continuum photon production
efficiency xi_{ion}, and faint-end cut-off to the luminosity
function. Quasars/AGN appear to match neither the redshift evolution nor
normalization of the ionizing emissivity. Based on the inferred evolution in
the ionizing emissivity, we estimate that the z~10 UV-luminosity density is
8(-4)(+15)x lower than at $z~6, consistent with the observations. The present
approach of contrasting the inferred evolution of the ionizing emissivity with
that of the galaxy UV luminosity density adds to the growing observational
evidence that faint, star-forming galaxies drive the reionization of the
universe.Comment: 20 pages, 12 figures, 5 tables, Astrophysical Journal, updated to
match version in press, Figure 6 shows the main result of the pape
Constraining the Lyα escape fraction with far-infrared observations of Lyα emitters
We study the far-infrared properties of 498 Lyα emitters (LAEs) at z = 2.8, 3.1, and 4.5 in the Extended Chandra Deep Field-South, using 250, 350, and 500ÎŒm data from the Herschel Multi-tiered Extragalactic Survey and 870ÎŒm data from the LABOCA ECDFS Submillimeter Survey. None of the 126, 280, or 92 LAEs at z = 2.8, 3.1, and 4.5, respectively, are individually detected in the far-infrared data. We use stacking to probe the average emission to deeper flux limits, reaching 1Ï depths of âŒ0.1 to 0.4 mJy. The LAEs are also undetected at ?3Ï in the stacks, although a 2.5Ï signal is observed at 870ÎŒm for the z = 2.8 sources. We consider a wide range of far-infrared spectral energy distributions (SEDs), including an M82 and an Sd galaxy template, to determine upper limits on the far-infrared luminosities and far-infrared-derived star formation rates of the LAEs. These star formation rates are then combined with those inferred from the Lyα and UV emission to determine lower limits on the LAEsâ Lyα escape fraction (f esc (Lyα)). For the Sd SED template, the inferred LAEs f esc (Lyα) are ?30% (1Ï) at z = 2.8, 3.1, and 4.5, which are all significantly higher than the global f esc (Lyα) at these redshifts. Thus, if the LAEs f esc (Lyα) follows the global evolution, then they have warmer far-infrared SEDs than the Sd galaxy template. The average and M82 SEDs produce lower limits on the LAE f esc (Lyα) of âŒ10%â20% (1Ï), all of which are slightly higher than the global evolution of f esc (Lyα), but consistent with it at the 2Ïâ3Ï level
ZFOURGE/CANDELS: On the Evolution of \u3cem\u3eM\u3c/em\u3e* Galaxy Progenitors from \u3cem\u3ez\u3c/em\u3e=3 to 0.5*
Galaxies with stellar masses near M* contain the majority of stellar mass in the universe, and are therefore of special interest in the study of galaxy evolution. The Milky Way (MW) and Andromeda (M31) have present-day stellar masses near M*, at 5 Ă 1010 M â (defined here to be MW-mass) and 1011 M â (defined to be M31-mass). We study the typical progenitors of these galaxies using the FOURSTAR Galaxy Evolution Survey (ZFOURGE). ZFOURGE is a deep medium-band near-IR imaging survey, which is sensitive to the progenitors of these galaxies out to z ~ 3. We use abundance-matching techniques to identify the main progenitors of these galaxies at higher redshifts. We measure the evolution in the stellar mass, rest-frame colors, morphologies, far-IR luminosities, and star formation rates, combining our deep multiwavelength imaging with near-IR Hubble Space Telescope imaging from Cosmic Near-IR Deep Extragalactic Legacy Survey (CANDELS), and Spitzer and Herschel far-IR imaging from Great Observatories Origins Deep Survey-Herschel and CANDELS-Herschel. The typical MW-mass and M31-mass progenitors passed through the same evolution stages, evolving from blue, star-forming disk galaxies at the earliest stages to redder dust-obscured IR-luminous galaxies in intermediate stages and to red, more quiescent galaxies at their latest stages. The progenitors of the MW-mass galaxies reached each evolutionary stage at later times (lower redshifts) and with stellar masses that are a factor of two to three lower than the progenitors of the M31-mass galaxies. The process driving this evolution, including the suppression of star formation in present-day M* galaxies, requires an evolving stellar-mass/halo-mass ratio and/or evolving halo-mass threshold for quiescent galaxies. The effective size and SFRs imply that the baryonic cold-gas fractions drop as galaxies evolve from high redshift to z ~ 0 and are strongly anticorrelated with an increase in the SĂ©rsic index. Therefore, the growth of galaxy bulges in M* galaxies corresponds to a rapid decline in the galaxy gas fractions and/or a decrease in the star formation efficiency
CEERS Key Paper VII: Emission Line Ratios from NIRSpec and NIRCam Wide-Field Slitless Spectroscopy at z>2
We use James Webb Space Telescope Near-Infrared Camera Wide Field Slitless
Spectroscopy (NIRCam WFSS) and Near-Infrared spectrograph (NIRSpec) in the
Cosmic Evolution Early Release survey (CEERS) to measure rest-frame optical
emission-line of 155 galaxies at z>2. The blind NIRCam grism observations
include a sample of galaxies with bright emission lines that were not observed
on the NIRSpec masks. We study the changes of the Ha, [OIII]/Hb, and
[NeIII]/[OII] emission lines in terms of redshift by comparing to lower
redshift SDSS and CLEAR samples. We find a significant (>3) correlation
between [OIII]/Hb with redshift, while [NeIII]/[OII] has a marginal (2)
correlation with redshift. We compare [OIII]/Hb and [NeIII]/[OII] to stellar
mass and Hb SFR. We find that both emission-line ratios have a correlation with
Hb SFR and an anti-correlation with stellar mass across the redshifts 0<z<9.
Comparison with MAPPINGS~V models indicates that these trends are consistent
with lower metallicity and higher ionization in low-mass and high-SFR galaxies.
We additionally compare to IllustriousTNG predictions and find that they
effectively describe the highest [OIII]/Hb ratios observed in our sample,
without the need to invoke MAPPINGS models with significant shock ionizionation
components.Comment: 16 pages, 11 figure
A spatially resolved analysis of star-formation burstiness by comparing UV and H in galaxies at z1 with UVCANDELS
The UltraViolet imaging of the Cosmic Assembly Near-infrared Deep
Extragalactic Legacy Survey Fields (UVCANDELS) program provides HST/UVIS F275W
imaging for four CANDELS fields. We combine this UV imaging with existing
HST/near-IR grism spectroscopy from 3D-HST+AGHAST to directly compare the
resolved rest-frame UV and H emission for a sample of 979 galaxies at
spanning a range in stellar mass of . Since
both rest-UV and H are sensitive to on-going star-formation but over
different timescales, their resolved comparison allows us to infer the
burstiness in star-formation as a function of galaxy structural parameters. We
generate homogenized maps of rest-UV and H emission for all galaxies in
our sample and stack them to compute the average UV-to-H luminosity
ratio as a function of galactocentric radius. We find that galaxies below
stellar mass of , at all radii, have a UV-to-H
ratio higher than the equilibrium value expected from constant star-formation,
indicating a significant contribution from bursty star-formation. Even for
galaxies with stellar mass , the UV-to-H ratio
is elevated towards in their outskirts (), suggesting that
bursty star-formation is likely prevalent in the outskirts of even the most
massive galaxies but is likely over-shadowed by their brighter cores.
Furthermore, we present the UV-to-H ratio as a function of galaxy
surface brightness, a proxy for stellar mass surface density, and find that
regions below are consistent with bursty
star-formation, regardless of their galaxy stellar mass, potentially suggesting
that local star-formation is independent of global galaxy properties at the
smallest scales.Comment: 19 pages, 8 figures; submitted to Ap
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