We present the X-UDS survey, a set of wide and deep Chandra observations of the Subaru-XMM Deep/UKIDSS Ultra Deep Survey (SXDS/UDS) field. The survey consists of 25 observations that cover a total ...area of 0.33 deg2. The observations are combined to provide a nominal depth of ∼600 ks in the central 100 arcmin2 region of the field that has been imaged with Hubble/WFC3 by the CANDELS survey and ∼200 ks in the remainder of the field. In this paper, we outline the survey's scientific goals, describe our observing strategy, and detail our data reduction and point source detection algorithms. Our analysis has resulted in a total of 868 band-merged point sources detected with a false-positive Poisson probability of <1 × 10−4. In addition, we present the results of an X-ray spectral analysis and provide best-fitting neutral hydrogen column densities, NH, as well as a sample of 51 Compton-thick active galactic nucleus candidates. Using this sample, we find the intrinsic Compton-thick fraction to be 30%-35% over a wide range in redshift (z = 0.1-3), suggesting the obscured fraction does not evolve very strongly with epoch. However, if we assume that the Compton-thick fraction is dependent on luminosity, as is seen for Compton-thin sources, then our results are consistent with a rise in the obscured fraction out to z ∼ 3. Finally, an examination of the host morphologies of our Compton-thick candidates shows a high fraction of morphological disturbances, in agreement with our previous results. All data products described in this paper are made available via a public website.
We present Keck/MOSFIRE H-band spectroscopy targeting C iii λ1907, 1909 in a z = 7.5056 galaxy previously identified via Ly emission. We detect strong line emission at with a line flux of (2.63 0.52) ...× 10−18 erg s−1 cm−2. We tentatively identify this line as C iii λ1907, but we are unable to detect C iii λ1909 owing to sky emission at the expected location. This gives a galaxy systemic redshift, , with a velocity offset to Ly of = 88 27 km s−1. The ratio of combined C iii/Ly is 0.30-0.45, one of the highest values measured for any z > 2 galaxy. We do not detect Si iii λλ1883, 1892, and place an upper limit on Si iii/C iii < 0.35 (2 ). Comparing our results to photoionization models, the C iii equivalent width (WC iii = 16.23 2.32 ), low Si iii/C iii ratio, and high implied O iii equivalent width (from the Spitzer/IRAC 3.6-4.5 0.8 mag color) require subsolar metallicities (Z 0.1-0.2 Z ) and a high ionization parameter, log U −1.5. These results favor models that produce higher ionization, such as the bpass models for the photospheres of high-mass stars, and that include both binary stellar populations and/or an IMF that extends to 300 M . The combined C iii equivalent width and 3.6-4.5 color are more consistent with ionization from young stars than active galactic nuclei (AGNs); however, we cannot rule out ionization from a combination of an AGN and young stars. We make predictions for James Webb Space Telescope spectroscopy using these different models, which will ultimately test the nature of the ionizing radiation in this source.
Using the CANDELS photometric catalogs for the Hubble Space Telescope/ACS and WFC3, we identified massive evolved galaxies at 3 < z < 4.5 employing three different selection methods. We find the ...comoving number density of these objects to be ∼2 × 10−5 and 8 × 10−6 Mpc−3 after correction for completeness for two redshift bins centered at z = 3.4, 4.7. We quantify a measure of how much confidence we should have for each candidate galaxy from different selections and what the conservative error estimates propagated into our selection are. Then we compare the evolution of the corresponding number densities and their stellar mass density with numerical simulations, semianalytical models, and previous observational estimates, which shows slight tension at higher redshifts as the models tend to underestimate the number and mass densities. By estimating the average halo masses of the candidates (Mh 4.2, 1.9, and 1.3 × 1012 M for redshift bins centered at z = 3.4, 4.1, and 4.7), we find them to be consistent with halos that were efficient in turning baryons to stars, relatively immune to the feedback effects, and on the verge of transition into hot-mode accretion. This can suggest the relative cosmological starvation of the cold gas followed by an overconsumption phase in which the galaxy rapidly consumes the available cold gas as one of the possible drivers for the quenching of the massive evolved population at high redshift.
Abstract
We present a new method based on information theory to find the optimal number of bands required to measure the physical properties of galaxies with desired accuracy. As a proof of concept, ...using the recently updated COSMOS catalog (COSMOS2020), we identify the most relevant wave bands for measuring the physical properties of galaxies in a Hawaii Two-0- (H20) and UVISTA-like survey for a sample of
i
< 25 AB mag galaxies. We find that with the available
i
-band fluxes,
r
,
u
, IRAC/
ch
2, and
z
bands provide most of the information regarding the redshift with importance decreasing from
r
band to
z
band. We also find that for the same sample, IRAC/
ch
2,
Y
,
r
, and
u
bands are the most relevant bands in stellar-mass measurements with decreasing order of importance. Investigating the intercorrelation between the bands, we train a model to predict UVISTA observations in near-IR from H20-like observations. We find that magnitudes in the
YJH
bands can be simulated/predicted with an accuracy of 1
σ
mag scatter ≲0.2 for galaxies brighter than 24 AB mag in near-IR bands. One should note that these conclusions depend on the selection criteria of the sample. For any new sample of galaxies with a different selection, these results should be remeasured. Our results suggest that in the presence of a limited number of bands, a machine-learning model trained over the population of observed galaxies with extensive spectral coverage outperforms template fitting. Such a machine-learning model maximally comprises the information acquired over available extensive surveys and breaks degeneracies in the parameter space of template fitting inevitable in the presence of a few bands.
We present deep mid-IR spectroscopy with Spitzer of 13 SMGs in the GOODS-N field. We find strong PAH emission in all of our targets, which allows us to measure mid-IR spectroscopic redshifts and ...place constraints on the contribution from star formation and AGN activity to the mid-IR emission. In the high-S/N composite spectrum, we find that the hot dust continuum from an AGN contributes at most 30% of the mid-IR luminosity. Individually, only 2/13 SMGs have continuum emission dominating the mid-IR luminosity; one of these SMGs, C1, remains undetected in the deep X-ray images but shows a steeply rising continuum in the mid-IR indicative of a Compton-thick AGN. We find that the mid-IR properties of SMGs are distinct from those of 24 mum- selected ULIRGs at image ; the former are predominantly dominated by star formation, while the latter are a more heterogeneous sample with many showing significant AGN activity. We fit the IRS spectrum and the mid-IR to radio photometry of SMGs with template SEDs to determine the best estimate of the total IR luminosity from star formation. While many SMGs contain an AGN as evinced by their X-ray properties, our multiwavelength analysis shows that the total IR luminosity, L sub(IR), in SMGs is dominated by star formation. We find that high-redshift SMGs lie on the relation between L sub(IR) and image (or image or image) that has been established for local starburst galaxies. This suggests that PAH luminosity can be used as a proxy for the SFR in SMGs. SMGs are consistent with being a short-lived cool phase in a massive merger where the AGN does not appear to have become strong enough to heat the dust and dominate the mid- or far-IR emission.
Observations of very distant galaxies probe both the formation and evolution of galaxies, and also the nature of the sources responsible for reionizing the intergalactic medium (IGM). Here, we study ...the physical characteristics of galaxies at 6.3 < z {<=} 8.6, selected from deep near-infrared imaging with the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope. We investigate the rest-frame ultraviolet (UV) colors, stellar masses, ages, metallicities, and dust extinction of this galaxy sample. Accounting for the photometric scatter using simulations, galaxies at z{approx} 7 have bluer UV colors compared to typical local starburst galaxies at >4{sigma} confidence. Although the blue colors of galaxies at these redshifts necessitate young ages (<100 Myr), low or zero dust attenuation, and low metallicities, these are explicable by normal (albeit unreddened) stellar populations, with no evidence for near-zero metallicities and/or top-heavy initial mass functions. Most of these galaxies are undetected in deep Spitzer Infrared Array Camera imaging. However, the age of the universe at these redshifts limits the amount of stellar mass in late-type populations, and the WFC3 photometry implies galaxy stellar masses {approx}10{sup 8}-10{sup 9} M{sub sun} for Salpeter initial mass functions to a limiting magnitude of M{sub 1500} {approx} -18. The masses of 'characteristic' (L*) z > 7 galaxies are smaller than those of L* Lyman break galaxies at lower redshifts, and are comparable to less evolved galaxies selected on the basis of their Ly{alpha} emission at 3 < z < 6, implying that the 6.3 < z {<=} 8.6 galaxies are the progenitors of more evolved galaxies at lower redshifts. We estimate that Ly{alpha} emission is able to contribute to the observed WFC3 colors of galaxies at these redshifts, with an estimated typical line flux of {approx} 10{sup -18} erg s{sup -1} cm{sup -2}, roughly a factor of 4 below currently planned surveys. The integrated UV specific luminosity for the detected galaxies at z {approx} 7 and z {approx} 8 is within factors of a few of that required to reionize the IGM assuming low clumping factors, even with no correction for luminosity incompleteness. This implies that in order to reionize the universe, galaxies at these redshifts have a high ({approx}50%) escape fraction of Lyman continuum photons, possibly substantiated by the very blue colors of this population.
ABSTRACT
We present the Arizona CDFS Environment Survey (ACES), a recently completed spectroscopic redshift survey of the Chandra Deep Field-South (CDFS) conducted using the Inamori-Magellan Areal ...Camera and Spectrograph on the Magellan-Baade telescope. In total, the survey targeted 7277 unique sources down to a limiting magnitude of R
AB = 24.1, yielding 5080 secure redshifts across the ∼30 arcmin × 30 arcmin extended CDFS region. The ACES data set delivers a significant increase to both the spatial coverage and the sampling density of the spectroscopic observations in the field. Combined with previously published spectroscopic redshifts, ACES now creates a highly complete survey of the galaxy population at R < 23, enabling the local galaxy density (or environment) on relatively small scales (∼1 Mpc) to be measured at z < 1 in one of the most heavily studied and data-rich fields in the sky. Here, we describe the motivation, design and implementation of the survey and present a preliminary redshift and environment catalogue. In addition, we utilize the ACES spectroscopic redshift catalogue to assess the quality of photometric redshifts from both the COMBO-17 and Multiwavelength Survey by Yale-Chile imaging surveys of the CDFS.
Abstract We combine deep imaging data from the CEERS early release JWST survey and Hubble Space Telescope imaging from CANDELS to examine the size–mass relation of star-forming galaxies and the ...morphology–quenching relation at stellar masses M ⋆ ≥ 10 9.5 M ⊙ over the redshift range 0.5 < z < 5.5. In this study with a sample of 2450 galaxies, we separate star-forming and quiescent galaxies based on their star formation activity and confirm that star-forming and quiescent galaxies have different morphologies out to z = 5.5, extending the results of earlier studies out to higher redshifts. We find that star-forming and quiescent galaxies have typical Sérsic indices of n ∼ 1.3 and n ∼ 4.3, respectively. Focusing on star-forming galaxies, we find that the slope of the size–mass relation is nearly constant with redshift, as was found previously, but shows a modest increase at z ∼ 4.2. The intercept in the size–mass relation declines out to z = 5.5 at rates that are similar to what earlier studies found. The intrinsic scatter in the size–mass relation is relatively constant out to z = 5.5.
We present a WFC3 F160W (H-band) selected catalog in the CANDELS/GOODS-N field containing photometry from the ultraviolet (UV) to the far-infrared (IR), photometric redshifts, and stellar parameters ...derived from the analysis of the multiwavelength data. The catalog contains 35,445 sources over the 171 arcmin2 of the CANDELS F160W mosaic. The 5 detection limits (within an aperture of radius 0 17) of the mosaic range between H = 27.8, 28.2, and 28.7 in the wide, intermediate, and deep regions, which span approximately 50%, 15%, and 35% of the total area. The multiwavelength photometry includes broadband data from the UV (U band from KPNO and LBC), optical (HST/ACS F435W, F606W, F775W, F814W, and F850LP), near-to-mid IR (HST/WFC3 F105W, F125W, F140W, and F160W; Subaru/MOIRCS Ks; CFHT/Megacam K; and Spitzer/IRAC 3.6, 4.5, 5.8, and 8.0 m), and far-IR (Spitzer/MIPS 24 m, HERSCHEL/PACS 100 and 160 m, SPIRE 250, 350 and 500 m) observations. In addition, the catalog also includes optical medium-band data (R ∼ 50) in 25 consecutive bands, λ = 500-950 nm, from the SHARDS survey and WFC3 IR spectroscopic observations with the G102 and G141 grisms (R ∼ 210 and 130). The use of higher spectral resolution data to estimate photometric redshifts provides very high, and nearly uniform, precision from z = 0-2.5. The comparison to 1485 good-quality spectroscopic redshifts up to z ∼ 3 yields Δz/(1 + zspec) = 0.0032 and an outlier fraction of = 4.3%. In addition to the multiband photometry, we release value-added catalogs with emission-line fluxes, stellar masses, dust attenuations, UV- and IR-based star formation rates, and rest-frame colors.
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