107 research outputs found
Ceers key paper. I. An early look into the first 500myr of galaxy formation with jwst
We present an investigation into the first 500 Myr of galaxy evolution from the Cosmic Evolution Early Release
Science (CEERS) survey. CEERS, one of 13 JWST ERS programs, targets galaxy formation from z ∼ 0.5 to >10
using several imaging and spectroscopic modes. We make use of the first epoch of CEERS NIRCam imaging,
spanning 35.5 arcmin2
, to search for candidate galaxies at z > 9. Following a detailed data reduction process
implementing several custom steps to produce high-quality reduced images, we perform multiband photometry
across seven NIRCam broad- and medium-band (and six Hubble broadband) filters focusing on robust colors and
accurate total fluxes. We measure photometric redshifts and devise a robust set of selection criteria to identify a
sample of 26 galaxy candidates at z ∼ 9–16. These objects are compact with a median half-light radius of ∼0.5 kpc.
We present an early estimate of the z ∼ 11 rest-frame ultraviolet (UV) luminosity function, finding that the number
density of galaxies at MUV ∼ −20 appears to evolve very little from z ∼ 9 to 11. We also find that the abundance
(surface density [arcmin−2
]) of our candidates exceeds nearly all theoretical predictions. We explore potential
implications, including that at z > 10, star formation may be dominated by top-heavy initial mass functions, which
would result in an increased ratio of UV light per unit halo mass, though a complete lack of dust attenuation and/or
changing star formation physics may also play a role
A Mixture of LBG Overdensities in the Fields of Three Quasars: Implications for the Robustness of Photometric Selection
The most luminous quasars at are suspected to be both highly
clustered and reside in the most massive dark matter halos in the early
Universe, making them prime targets to search for galaxy overdensities and/or
protoclusters. We search for Lyman-break dropout-selected galaxies using HST
WFC3/ACS broadband imaging in the fields of three quasars, as well
as their simultaneously observed coordinated-parallel fields, and constrain
their photometric redshifts using EAZY. One field, J0305-3150, shows a volume
density 10 higher than the blank-field UV luminosity function (UVLF) at
M, with tentative evidence of a 3 overdensity in its
parallel field located 15 cMpc away. Another field, J2054-0005, shows an
angular overdensity within 500 ckpc from the quasar but still consistent with
UVLF predictions within 3, while the last field, J2348-3054, shows no
enhancement. We discuss methods for reducing uncertainty in overdensity
measurements when using photometric selection and show that we can robustly
select LBGs consistent with being physically associated with the quasar,
corroborated by existing JWST/NIRCam WFSS data in the J0305 field. Even
accounting for incompleteness, the overdensities in J0305 and J2054 are higher
for brighter galaxies at short angular separations, suggesting preferential
enhancement of more massive galaxies in the immediate vicinity of the quasar.
Finally, we compare the LBG population with previously-identified [CII] and
mm-continuum companions; the LBG overdensities are not accompanied by an
enhanced number of dusty galaxies, suggesting that the overdense quasar fields
are not in the bursty star-forming phase sometimes seen in high-redshift
protoclusters.Comment: 22 pages (main text), 12 figures, 10 tables, 2 appendices. Final
version after addressing referee report, accepted to ApJ May 202
HST Grism-derived Forecasts for Future Galaxy Redshift Surveys
The mutually complementary Euclid and Roman galaxy redshift surveys will use Hα- and [O III]-selected emission-line galaxies (ELGs) as tracers of the large-scale structure at 0.9 ≾ z ≾ 1.9 (Hα) and 1.5 ≾ z ≾ 2.7 ([O III]). It is essential to have a reliable and sufficiently precise knowledge of the expected numbers of Hα-emitting galaxies in the survey volume in order to optimize these redshift surveys for the study of dark energy. Additionally, these future samples of ELGs will, like all slitless spectroscopy surveys, be affected by a complex selection function that depends on galaxy size and luminosity, line equivalent width (EW), and redshift errors arising from the misidentification of single ELGs. Focusing on the specifics of the Euclid survey, we combine two slitless spectroscopic WFC3-IR data sets—3D-HST+AGHAST and the WFC3 Infrared Spectroscopic Parallel survey—to construct a Euclid-like sample that covers an area of 0.56 deg² and includes 1277 ELGs. We detect 1091 (~3270 deg⁻²) Hα+[N II]-emitting galaxies in the range 0.9 ≤ z ≤ 1.6 and 162 (~440 deg⁻²) [O III] λ5007 emitters over 1.5 ≤ z ≤ 2.3 with line fluxes ≥2 × 10⁻¹⁶ erg s⁻¹ cm⁻². The median of the Hα+[N II] EW distribution is ~250 Å, and the effective radii of the continuum and Hα+[N II] emission are correlated with a median of ~0.”38 and significant scatter (σ ~ 0.”2–0.”35). Finally, we explore the prevalence of redshift misidentification in future Euclid samples, finding potential contamination rates of ~14%–20% and ~6% down to 2 × 10⁻¹⁶ erg s⁻¹ cm−2 and 6 × 10⁻¹⁷ erg s⁻¹ cm⁻², respectively, although with increased wavelength coverage these percentages drop to nearly zero
Semi-analytic forecasts for Roman -- the beginning of a new era of deep-wide galaxy surveys
The Nancy Grace Roman Space Telescope, NASA's next flagship observatory, will
redefine deep-field galaxy survey with a field of view two orders of magnitude
larger than Hubble and an angular resolution of matching quality. These future
deep-wide galaxy surveys necessitate new simulations to forecast their
scientific output and to optimise survey strategies. In this work, we present
five realizations of 2-deg^2 lightcones, containing a total of >25 million
simulated galaxies with -16 < MUV < -25 spanning z ~ 0 to 10. This dataset
enables a new set of experiments with the impacts of survey size on the derived
galaxy formation and cosmological constraints. The intrinsic and observable
galaxy properties are predicted using a well-established, physics-based
semi-analytic modelling approach. We provide forecasts for number density,
cosmic SFR, field-to-field variance, and angular two-point correlation
functions, and demonstrate how the future wide-field surveys will be able to
improve these measurements relative to current generation surveys. We also
present a comparison between these lightcones and others that have been
constructed with empirical models. The mock lightcones are designed to
facilitate the exploration of multi-instrument synergies and connecting with
current generation instruments and legacy surveys. In addition to Roman, we
also provide photometry for a number of other instruments on upcoming
facilities, including Euclid and Rubin, as well as the instruments that are
part of many legacy surveys. Full object catalogues and data tables for the
results presented in this work are made available through a web-based,
interactive portal https://www.simonsfoundation.org/semi-analytic-forecasts.Comment: 25 pages, 16 figures. Accepted for publication in MNRA
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A High Space Density of Luminous Lyα Emitters at z ~ 6.5
We present the results of a systematic search for Lyα emitters (LAEs) at 6 ≾ z ≾ 7.6 using the HST WFC3 Infrared Spectroscopic Parallel (WISP) Survey. Our total volume over this redshift range is ~ 8 x 10^5 Mpc^3, comparable to many of the narrowband surveys despite their larger area coverage. We find two LAEs at z = 6.38 and 6.44 with line luminosities of L_(Lyα) ~ 4.7 x 10^(43) erg s^(−1), putting them among the brightest LAEs discovered at these redshifts. Taking advantage of the broad spectral coverage of WISP, we are able to rule out almost all lower-redshift contaminants. The WISP LAEs have a high number density of 7.7 x 10(-6) Mpc^(−3). We argue that the LAEs reside in megaparsec-scale ionized bubbles that allow the Lyα photons to redshift out of resonance before encountering the neutral intergalactic medium. We discuss possible ionizing sources and conclude that the observed LAEs alone are not sufficient to ionize the bubbles
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