We study cosmic variance in deep high-redshift surveys and its influence on the determination of the luminosity function for high-redshift galaxies. For several survey geometries relevant for Hubble ...Space Telescope (HST) and James Webb Space Telescope (JWST) instruments, we characterize the distribution of the galaxy number counts. This is obtained by means of analytic estimates via the two-point correlation function in extended Press-Schechter theory, as well as by using synthetic catalogs extracted from N-body cosmological simulations of structure formation. We adopt a simple luminosity-dark halo mass relation to investigate the effects of environment on the fitting of the luminosity function. We show that in addition to variations of the normalization of the luminosity function, a steepening of its slope is also expected in underdense fields, similar to what is observed within voids in the local universe. Therefore, to avoid introducing artificial biases, caution must be taken when attempting to correct for field underdensity, such as in the case of the HST UDF i- dropout sample, which exhibits a deficit of bright counts with respect to the average counts in GOODS. A public version of the cosmic variance calculator based on the two-point correlation function integration is available on the Web at STScI.
Abstract
This paper highlights initial photometric analyses of JWST NIRCam imaging data in the sightline of SMACS0723, aiming to identify galaxies at redshift
z
> 7. By applying a conservative ...Lyman-break selection followed by photometric-redshift analysis and visual inspection, we identify four F090W-dropout and two F150W-dropout sources, three of which were recently confirmed in an independent spectroscopic analysis to
z
= 7.663, 7.665, and 8.499. We then supplement our sample with a photometric-redshift selection, and identify five additional candidates at 7 <
z
phot
< 13. The NIRCam images clearly resolve all sources and reveal their subgalactic components that were not resolved/detected in the previous imaging by Hubble Space Telescope. Our spectral energy distribution analysis reveals that the selected galaxies are characterized by young stellar populations (median age of ∼50 Myr) of subsolar metallicity (∼0.2
Z
⊙
) and little dust attenuation (
A
V
∼ 0.5). In several cases, we observe extreme H
β
+O
iii
lines being captured in the F444W band and seen as color excess, which is consistent with their observed high star formation rate surface density. Eight of the 11 sources identified in this study appear in at least one of the recent studies (Adams et al.; Atek et al.; Donnan et al.; Harikane et al.; Yan et al.) of the same fields, implying the high fidelity of our selection. We crossmatch all high-
z
galaxy candidates presented in the five studies with our catalog and discuss the possible causes of discrepancy in the final lists.
We present a full data analysis of the pure-parallel Hubble Space Telescope (HST) imaging observations in the Brightest of Reionizing Galaxies Survey (BoRGz9) in Cycle 22. The medium-deep exposures ...with five HST/WFC3IR+UVIS filter bands from 79 independent sightlines (∼370 arcmin2) provide the least biased determination of number density for z 9 bright galaxies against cosmic variance. After a strict two-step selection for candidate galaxies, including dropout color and photometric redshift analyses, and revision of previous BoRG candidates, we identify one source at z ∼ 10 and two sources at z ∼ 9. The z ∼ 10 candidate shows evidence of line-of-sight lens magnification ( ∼ 1.5), yet it appears surprisingly luminous ( mag), making it one of the brightest candidates at known (∼0.3 mag brighter than the z = 8.68 galaxy EGSY8p7, spectroscopically confirmed by Zitrin and collaborators). For z ∼ 9 candidates, we include previous data points at fainter magnitudes and find that the data are well fitted by a Schechter luminosity function with , mag, and Mpc−3 mag−1, for the first time without fixing any parameters. The inferred cosmic star formation rate density is consistent with unaccelerated evolution from lower redshift.
The IRAC ultradeep field and IRAC Legacy over GOODS programs are two ultradeep imaging surveys at 3.6 and 4.5 mum with the Spitzer Infrared Array Camera (IRAC). The primary aim is to directly detect ...the infrared light of reionization epoch galaxies at z > 7 and to constrain their stellar populations. The observations cover the Hubble Ultra Deep Field (HUDF), including the two HUDF parallel fields, and the CANDELS/GOODS-South, and are combined with archival data from all previous deep programs into one ultradeep data set. The resulting imaging reaches unprecedented coverage in IRAC 3.6 and 4.5 mum ranging from >50 hr over 150 arcmin super(2), >100 hr over 60 sq arcmin super(2), to ~200 hr over 5-10 arcmin super(2). This paper presents the survey description, data reduction, and public release of reduced mosaics on the same astrometric system as the CANDELS/GOODS-South Wide Field Camera 3 (WFC3) data. To facilitate prior-based WFC3+IRAC photometry, we introduce a new method to create high signal-to-noise PSFs from the IRAC data and reconstruct the complex spatial variation due to survey geometry. The PSF maps are included in the release, as are registered maps of subsets of the data to enable reliability and variability studies. Simulations show that the noise in the ultradeep IRAC images decreases approximately as the square root of integration time over the range 20-200 hr, well below the classical confusion limit, reaching 1sigma point-source sensitivities as faint as 15 nJy (28.5 AB) at 3.6 mum and 18 nJy (28.3 AB) at 4.5 mum. The value of such ultradeep IRAC data is illustrated by direct detections of z = 7-8 galaxies as faint as H sub(AB) = 28.
ABSTRACT We present the first results and design from the redshift z ∼ 9-10 Brightest of the Reionizing Galaxies Hubble Space Telescope survey BoRGz9-10, aimed at searching for intrinsically luminous ...unlensed galaxies during the first 700 Myr after the Big Bang. BoRGz9-10 is the continuation of a multi-year pure-parallel near-IR and optical imaging campaign with the Wide Field Camera 3. The ongoing survey uses five filters, optimized for detecting the most distant objects and offering continuous wavelength coverage from λ = 0.35 m to λ = 1.7 m. We analyze the initial ∼130 arcmin2 of area over 28 independent lines of sight (∼25% of the total planned) to search for galaxies using a combination of Lyman-break and photometric redshift selections. From an effective comoving volume of (5-25) × 105 Mpc3 for magnitudes brighter than in the -band respectively, we find five galaxy candidates at 8.3-10 detected at high confidence ( ), including a source at 8.4 with ( ), which, if confirmed, would be the brightest galaxy identified at such early times ( ). In addition, BoRGz9-10 data yield four galaxies with . These new Lyman-break galaxies with are ideal targets for follow-up observations from ground and space-based observatories to help investigate the complex interplay between dark matter growth, galaxy assembly, and reionization.
The extreme Deep Field (XDF) combines data from 10 years of observations with the Hubble Space Telescope Advanced Camera for Surveys (ACS) and the Wide-Field Camera 3 Infra-Red (WFC3/IR) into the ...deepest image of the sky ever in the optical/near-IR. Since the initial observations of the Hubble Ultra-Deep Field (HUDF) in 2003, numerous surveys and programs, including supernovae follow-up, HUDF09, CANDELS, and HUDF12, have contributed additional imaging data across this region. However, these images have never been combined and made available as one complete ultra-deep image dataset. We combine them now with the XDF program. Our new and improved processing techniques provide higher quality reductions of the total dataset. All WFC3/IR and optical ACS data sets have been fully combined and accurately matched, resulting in the deepest imaging ever taken at these wavelengths, ranging from 29.1 to 30.3 AB mag (5sigma in a 0".35 diameter aperture) in 9 filters. The combined image therefore reaches to 31.2 AB mag 5sigma (32.9 at 1sigma) for a flat functionof sub(nu) source. The gains in the optical for the four filters done in the original ACS HUDF correspond to a typical improvement of 0.15 mag, with gains of 0.25 mag in the deepest areas. Such gains are equivalent to adding ~130 to ~240 orbits of ACS data to the HUDF. Improved processing alone results in a typical gain of ~0.1 mag. Our 5sigma (optical+near-IR) SExtractor catalogs reveal about 14,140 sources in the full field and about 7121 galaxies in the deepest part of the XDF.
We present a comprehensive analysis of z > 8 galaxies based on ultra-deep WFC3/IR data. We exploit all the WFC3/IR imaging over the Hubble Ultra-Deep Field from the HUDF09 and the new HUDF12 program, ...in addition to the HUDF09 parallel field data, as well as wider area imaging over GOODS-South. Galaxies are selected based on the Lyman break technique in three samples centered around z ~ 9, z ~ 10, and z ~ 11, with seven z ~ 9 galaxy candidates, and one each at z ~ 10 and z ~ 11. We confirm a new z ~ 10 candidate (with z = 9.8 + or - 0.6) that was not convincingly identified in our first z ~ 10 sample. Using these candidates, we perform one of the first estimates of the z ~ 9 UV luminosity function (LF) and improve our previous constraints at z ~ 10. Extrapolating the lower redshift UV LF evolution should have revealed 17 z ~ 9 and 9 z ~ 10 sources, i.e., a factor ~3x and 9 x larger than observed. The inferred star formation rate density (SFRD) in galaxies above 0.7 M sub(middot in circle) yr super(-1) decreases by 0.6 + or - 0.2 dex from z ~ 8 to z ~ 9, in excellent agreement with previous estimates. From a combination of all current measurements, we find a best estimate of a factor 10x decrease in the SFRD from z ~ 8 to z ~ 10, following (1 + z) super(-11.4+ or -3.1). Our measurements thus confirm our previous finding of an accelerated evolution beyond z ~ 8, and signify a very rapid build-up of galaxies with M sub(UV) < -17.7 mag within only ~200 Myr from z ~ 10 to z ~ 8, in the heart of cosmic reionization.
We identify 73 z ~ 7 and 59 z ~ 8 candidate galaxies in the reionization epoch, and use this large 26-29.4 AB mag sample of galaxies to derive very deep luminosity functions to < -- 18 AB mag and the ...star formation rate (SFR) density at z ~ 7 and z ~ 8 (just 800 Myr and 650 Myr after recombination, respectively). The galaxy sample is derived using a sophisticated Lyman-break technique on the full two-year Wide Field Camera 3/infrared (WFC3/IR) and Advanced Camera for Surveys (ACS) data available over the HUDF09 (~29.4 AB mag, 5 Delta *s), two nearby HUDF09 fields (~29 AB mag, 5 Delta *s, 14 arcmin2), and the wider area Early Release Science (~27.5 AB mag, 5 Delta *s, ~40 arcmin2). The application of strict optical non-detection criteria ensures the contamination fraction is kept low (just ~7% in the HUDF). This very low value includes a full assessment of the contamination from lower redshift sources, photometric scatter, active galactic nuclei, spurious sources, low-mass stars, and transients (e.g., supernovae). From careful modeling of the selection volumes for each of our search fields, we derive luminosity functions for galaxies at z ~ 7 and z ~ 8 to < -- 18 AB mag. The faint-end slopes Delta *a at z ~ 7 and z ~ 8 are uncertain but very steep at Delta *a = --2.01 ? 0.21 and Delta *a = --1.91 ? 0.32, respectively. Such steep slopes contrast to the local Delta *a --1.4 and may even be steeper than that at z ~ 4 where Delta *a = --1.73 ? 0.05. With such steep slopes ( Delta *a --1.7) lower luminosity galaxies dominate the galaxy luminosity density during the epoch of reionization. The SFR densities derived from these new z ~ 7 and z ~ 8 luminosity functions are consistent with the trends found at later times (lower redshifts). We find reasonable consistency with the SFR densities implied from reported stellar mass densities being only ~40% higher at z < 7. This suggests that (1) the stellar mass densities inferred from the Spitzer Infrared Array Camera (IRAC) photometry are reasonably accurate and (2) that the initial mass function at very high redshift may not be very different from that at later times.
Abstract
To extend the search for quasars in the epoch of reionization beyond the tip of the luminosity function, we explore point-source candidates at redshift
z
∼ 8 in SuperBoRG, a compilation of ...∼0.4 deg
2
archival medium-deep (
m
F160
W
∼ 26.5 ABmag, 5
σ
) parallel infrared (IR) images taken with the Hubble Space Telescope (HST). Initial candidates are selected by using the Lyman-break technique. We then carefully analyze source morphology, and robustly identify three point sources at
z
∼ 8. Photometric redshift analysis reveals that they are preferentially fit by extragalactic templates, and we conclude that they are unlikely to be low-
z
interlopers, including brown dwarfs. A clear IRAC ch2 flux excess is seen in one of the point sources, which is expected if the source has strong H
β
+O
iii
emission with a rest-frame equivalent width of ∼3000 Å. Deep spectroscopic data taken with Keck/MOSFIRE, however, do not reveal Ly
α
emission from the object. In combination with the estimated H
β
+O
iii
equivalent width, we place an upper limit on its Ly
α
escape fraction of
. We estimate the number density of these point sources as ∼1 × 10
−6
Mpc
−3
mag
−1
at
M
UV
∼ −23 mag. The final interpretation of our results remains inconclusive: extrapolation from low-
z
studies of
faint
quasars suggests that ≳100× survey volume may be required to find one of this luminosity. The James Webb Space Telescope will be able to conclusively determine the nature of our luminous point-source candidates, while the Roman Space Telescope will probe ∼200 times the area of the sky with the same observing time considered in this HST study.
We present the first results on the search for very bright (M AB --21) galaxies at redshift z ~ 8 from the Brightest of Reionizing Galaxies (BoRG) survey. BoRG is a Hubble Space Telescope Wide Field ...Camera 3 (WFC3) pure-parallel survey that is obtaining images on random lines of sight at high Galactic latitudes in four filters (F606W, F098M, F125W, and F160W), with integration times optimized to identify galaxies at z 7.5 as F098M dropouts. We discuss here results from a search area of approximately 130 arcmin2 over 23 BoRG fields, complemented by six other pure-parallel WFC3 fields with similar filters. This new search area is more than two times wider than previous WFC3 observations at z ~ 8. We identify four F098M-dropout candidates with high statistical confidence (detected at greater than 8 Delta *s confidence in F125W). These sources are among the brightest candidates currently known at z ~ 8 and approximately 10 times brighter than the z = 8.56 galaxy UDFy-38135539. They thus represent ideal targets for spectroscopic follow-up observations and could potentially lead to a redshift record, as our color selection includes objects up to z ~ 9. However, the expected contamination rate of our sample is about 30% higher than typical searches for dropout galaxies in legacy fields, such as the GOODS and HUDF, where deeper data and additional optical filters are available to reject contaminants.
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