The COSMOS Spitzer survey (S-COSMOS) is a Legacy program (Cycles 2+3) designed to carry out a uniform deep survey of the full 2 deg(2) COSMOS field in all seven Spitzer bands (3.6, 4.5, 5.6, 8.0, ...24.0, 70.0, and 160.0 km). This paper describes the survey parameters, mapping strategy, data reduction procedures, achieved sensitivities to date, and the complete data set for future reference. We show that the observed infrared backgrounds in the S-COSMOS field are within 10% of the predicted background levels. The fluctuations in the background at 24 urn have been measured and do not show any significant contribution from cirrus, as expected. In addition, we report on the number of asteroid detections in the low Galactic latitude COSMOS field. We use the Cycle 2 S-COSMOS data to determine preliminary number counts, and compare our results with those from previous Spitzer Legacy surveys (e.g., SWIRE, GOODS). The results from this "first analysis" confirm that the S-COSMOS survey will have sufficient sensitivity with IRAC to detect 6L* disks and spheroids out to z unk 3, and with MIPS to detect ultraluminous starbursts and AGNs out to z 6 3 at 24 km and out to z 6 1.5-2 at 70 and 160 km.
Context. The James Webb Space Telescope’s (JWST’s) unprecedented combination of sensitivity, spatial resolution, and infrared coverage has enabled a new era of galaxy morphology exploration across ...most of cosmic history. Aims. We analyze the near-infrared (NIR ∼ 0.8 − 1 μm) rest-frame morphologies of galaxies with log M * / M ⊙ > 9 in the redshift range of 0 < z < 6, compare with previous HST-based results and release the first JWST-based morphological catalog of ∼20 000 galaxies in the CEERS survey. Methods. We classified the galaxies in our sample into four main broad classes: spheroid, disk+spheroid, disk, and disturbed, based on imaging with four filters: F 150 W , F 200 W , F 356 W , and F 444 W . We used convolutional neural networks (CNNs) trained on HST/WFC3 labeled images and domain-adapted to JWST/NIRCam. Results. We find that ∼90% and ∼75% of galaxies at z < 3 have the same early and late and regular and irregular classification, respectively, in JWST and HST imaging when considering similar wavelengths. For small (large) and faint objects, JWST-based classifications tend to systematically present less bulge-dominated systems (peculiar galaxies) than HST-based ones, but the impact on the reported evolution of morphological fractions is less than ∼10%. Using JWST-based morphologies at the same rest-frame wavelength (∼0.8 − 1 μm), we confirm an increase in peculiar galaxies and a decrease in bulge-dominated galaxies with redshift, as reported in previous HST-based works, suggesting that the stellar mass distribution, in addition to light distribution, is more disturbed in the early Universe. However, we find that undisturbed disk-like systems already dominate the high-mass end of the late-type galaxy population (log M * / M ⊙ > 10.5) at z ∼ 5, and bulge-dominated galaxies also exist at these early epochs, confirming a rich and evolved morphological diversity of galaxies ∼1 Gyr after the Big Bang. Finally, we find that the morphology-quenching relation is already in place for massive galaxies at z > 3, with massive quiescent galaxies (log M * / M ⊙ > 10.5) being predominantly bulge-dominated.
We present a new near-infrared survey covering the 2 deg2 COSMOS field conducted using WIRCam at the Canada-France-Hawaii Telescope. By combining our near-infrared data with Subaru B and z images, we ...construct a deep, wide-field optical-infrared catalog. At K s < 23 (AB magnitudes), our survey completeness is greater than 90% and 70% for stars and galaxies, respectively, and contains 143,466 galaxies and 13,254 stars. Using the BzK diagram, we divide our galaxy catalog into quiescent and star-forming galaxy candidates. At z ~ 2, our catalogs contain 3931 quiescent and 25,757 star-forming galaxies representing the largest and most secure sample at these depths and redshifts to date. Our counts of quiescent galaxies turns over at K s ~ 22, an effect that we demonstrate cannot be due to sample incompleteness. Both the number of faint and bright quiescent objects in our catalogs exceed the predictions of a recent semi-analytic model of galaxy formation, indicating potentially the need for further refinements in the amount of merging and active galactic nucleus feedback at z ~ 2 in these models. We measure the angular correlation function for each sample and find that the slope of the field galaxy correlation function flattens to 1.5 by K s ~ 23. At small angular scales, the angular correlation function for passive BzK galaxies is considerably in excess of the clustering of dark matter. We use precise 30-band photometric redshifts to derive the spatial correlation length and the redshift distributions for each object class. At K s < 22, we find r Delta *g/1.8 0 = 7.0 +/- 0.5h -1 Mpc for the passive BzK candidates and 4.7 +/- 0.8 h -1 Mpc for the star-forming BzK galaxies. Our pBzK galaxies have an average photometric redshift of zp ~ 1.4, in approximate agreement with the limited spectroscopic information currently available. The stacked K s image will be made publicly available from IRSA.
We study the relationship between the structure and star formation rate (SFR) of X-ray selected low and moderate luminosity active galactic nuclei (AGNs) in the two Chandra Deep Fields, using Hubble ...Space Telescope imaging from the Cosmic Assembly Near Infrared Extragalactic Legacy Survey (CANDELS) and deep far-infrared maps from the PEP+GOODS-Herschel survey. We derive detailed distributions of structural parameters and FIR luminosities from carefully constructed control samples of galaxies, which we then compare to those of the AGNs. At z ~ 1, AGNs show slightly diskier light profiles than massive inactive (non-AGN) galaxies, as well as modestly higher levels of gross galaxy disturbance (as measured by visual signatures of interactions and clumpy structure). In contrast, at z ~ 2, AGNs show similar levels of galaxy disturbance as inactive galaxies, but display a red central light enhancement, which may arise from a more pronounced bulge in AGN hosts or extinguished nuclear light. We undertake a number of tests of both these alternatives, but our results do not strongly favor one interpretation over the other. The mean SFR and its distribution among AGNs and inactive galaxies are similar at z> 1.5. At z< 1, however, clear and significant enhancements are seen in the SFRs of AGNs with bulge-dominated light profiles. These trends suggest an evolution in the relation between nuclear activity and host properties with redshift, towards a minor role for mergers and interactions at z> 1.5.
Models of galaxy evolution assume some connection between the AGN and star formation activity in galaxies. We use the multi-wavelength information of the CDFS to assess this issue. We select the AGNs ...from the 3 Ms XMM-Newton survey and measure the star-formation rates of their hosts using data that probe rest-frame wavelengths longward of 20 μm, predominantly from deep 100 μm and 160 μm Herschel observations, but also from Spitzer-MIPS-70 μm. Star-formation rates are obtained from spectral energy distribution fits, identifying and subtracting an AGN component. Our sample consists of sources in the z ≈ 0.5−4 redshift range, with star-formation rates SFR ≈ 101−103 M⊙ yr-1 and stellar masses M⋆ ≈ 1010−1011.5 M⊙. We divide the star-formation rates by the stellar masses of the hosts to derive specific star-formation rates (sSFR) and find evidence for a positive correlation between the AGN activity (proxied by the X-ray luminosity) and the sSFR for themost active systems with X-ray luminosities exceeding Lx ≃ 1043 erg s-1 and redshifts z ≳ 1. We do not find evidence for such a correlation for lower luminosity systems or those at lower redshifts, consistent with previous studies. We do not find any correlation between the SFR (or the sSFR) and the X-ray absorption derived from high-quality XMM-Newton spectra either, showing that the absorption is likely to be linked to the nuclear region rather than the host, while the star-formation is not nuclear. Comparing the sSFR of the hosts to the characteristic sSFR of star-forming galaxies at the same redshift (the so-called “main sequence”) we find that the AGNs reside mostly in main-sequence and starburst hosts, reflecting the AGN-sSFR connection; however the infrared selection might bias this result. Limiting our analysis to the highest X-ray luminosity AGNs (X-ray QSOs with Lx > 1044 erg s-1), we find that the highest-redshift QSOs (with z ≳ 2) reside predominantly in starburst hosts, with an average sSFR more than double that of the “main sequence”, and we find a few cases of QSOs at z ≈ 1.5 with specific star-formation rates compatible with the main-sequence, or even in the “quiescent” region. Finally, we test the reliability of the colour–magnitude diagram (plotting the rest-frame optical colours against the stellar mass) in assessing host properties, and find a significant correlation between rest-frame colour (without any correction for AGN contribution or dust extinction) and sSFR excess relative to the “main sequence” at a given redshift. This means that the most “starbursty” objects have the bluest rest-frame colours.
The Epoch of Reionization (EoR) began when galaxies grew in abundance and luminosity, so their escaping Lyman continuum (LyC) radiation started ionizing the surrounding neutral intergalactic medium ...(IGM). Despite significant recent progress, the nature and role of cosmic reionizers are still unclear: in order to define them, it would be necessary to directly measure their LyC escape fraction ( f esc ). However, this is impossible during the EoR due to the opacity of the IGM. Consequently, many efforts at low and intermediate redshift have been made to determine measurable indirect indicators in high-redshift galaxies so that their f esc can be predicted. This work presents the analysis of the indirect indicators of 62 spectroscopically confirmed star-forming galaxies at 6 ≤ z ≤ 9 from the Cosmic Evolution Early Release Science (CEERS) survey, combined with 12 sources with public data from other JWST-ERS campaigns. From the NIRCam and NIRSpec observations, we measured their physical and spectroscopic properties. We discovered that on average 6 < z < 9 star-forming galaxies are compact in the rest-frame UV ( r e ∼ 0.4 kpc), are blue sources (UV- β slope ∼ − 2.17), and have a predicted f esc of about 0.13. A comparison of our results to models and predictions as well as an estimation of the ionizing budget suggests that low-mass galaxies with UV magnitudes fainter than M 1500 = −18 that we currently do not characterize with JWST observations probably played a key role in the process of reionization.
ABSTRACT
We present 10 main-sequence ALPINE galaxies (log (M/M⊙) = 9.2−11.1 and ${\rm SFR}=23-190\, {\rm M_{\odot }\, yr^{-1}}$) at z ∼ 4.5 with optical O ii measurements from Keck/MOSFIRE ...spectroscopy and Subaru/MOIRCS narrow-band imaging. This is the largest such multiwavelength sample at these redshifts, combining various measurements in the ultraviolet, optical, and far-infrared including C ii158 $\mu$m line emission and dust continuum from ALMA and H α emission from Spitzer photometry. For the first time, this unique sample allows us to analyse the relation between O ii and total star-formation rate (SFR) and the interstellar medium (ISM) properties via O ii/C ii and O ii/H α luminosity ratios at z ∼ 4.5. The O ii−SFR relation at z ∼ 4.5 cannot be described using standard local descriptions, but is consistent with a metal-dependent relation assuming metallicities around $50{{\ \rm per\ cent}}$ solar. To explain the measured dust-corrected luminosity ratios of $\log (L_{\rm OII}/L_{\rm CII}) \sim 0.98^{+0.21}_{-0.22}$ and $\log (L_{\rm OII}/L_{\rm H\alpha }) \sim -0.22^{+0.13}_{-0.15}$ for our sample, ionization parameters log (U) < −2 and electron densities $\log (\rm n_e / {\rm cm^{-3}}) \sim 2.5-3$ are required. The former is consistent with galaxies at z ∼ 2−3, however lower than at z > 6. The latter may be slightly higher than expected given the galaxies’ specific SFR. The analysis of this pilot sample suggests that typical log (M/M⊙) > 9 galaxies at z ∼ 4.5 to have broadly similar ISM properties as their descendants at z ∼ 2 and suggest a strong evolution of ISM properties since the epoch of reionization at z > 6.
We study the impact of the environment on the evolution of galaxies in the zCOSMOS 10 k sample in the redshift range 0.1 ≤ z ≤ 1.0 over an area of ~1.5 deg2. The considered sample of secure ...spectroscopic redshifts contains about 8500 galaxies, with their stellar masses estimated by SED fitting of the multiwavelength optical to near-infrared (NIR) photometry. The evolution of the galaxy stellar mass function (GSMF) in high and low density regions provides a tool to study the mass assembly evolution in different environments; moreover, the contributions to the GSMF from different galaxy types, as defined by their SEDs and their morphologies, can be quantified. At redshift z ~ 1, the GSMF is only slightly dependent on environment, but at lower redshifts the shapes of the GSMFs in high- and low-density environments become extremely different, with high density regions exhibiting a marked bimodality, not reproducible by a single Schechter function. As a result of this analysis, we infer that galaxy evolution depends on both the stellar mass and the environment, the latter setting the probability of a galaxy to have a given mass: all the galaxy properties related to the stellar mass show a dependence on environment, reflecting the difference observed in the mass functions. The shapes of the GSMFs of early- and late-type galaxies are almost identical for the extremes of the density contrast we consider, ranging from isolated galaxies to rich group members. The evolution toward z = 0 of the transition mass ℳcross, i.e., the mass at which the early- and late-type GSMFs match each other, is more rapid in high density environments, because of a difference in the evolution of the normalisation of GSMFs compared to the total one in the considered environment. The same result is found by studying the relative contributions of different galaxy types, implying that there is a more rapid evolution in overdense regions, in particular for intermediate stellar masses. The rate of evolution is different for sets of galaxy types divided on the basis of their SEDs or their morphologies, tentatively suggesting that the migration from the blue cloud to the red sequence occurs on a shorter timescale than the transformation from disc-like morphologies to ellipticals. Our analysis suggests that environmental mechanisms of galaxy transformation start to be more effective at z < 1. The comparison of the observed GSMFs to the same quantities derived from a set of mock catalogues based on semi-analytical models shows disagreement, in both low and high density environments: in particular, blue galaxies in sparse environments are overproduced in the semi-analytical models at intermediate and high masses, because of a deficit of star formation suppression, while at z < 0.5 an excess of red galaxies is present in dense environments at intermediate and low masses, because of the overquenching of satellites.
We present the results of a program to acquire high-quality optical spectra of X-ray sources detected in the Extended-Chandra Deep Field-South (E-CDF-S) and its central 2 Ms area. New spectroscopic ...redshifts, up to z = 4, are measured for 283 counterparts to Chandra sources with deep exposures (t ~ 2-9 hr per pointing) using multi-slit facilities on both VLT (VIMOS) and Keck (DEIMOS), thus bringing the total number of spectroscopically identified X-ray sources to over 500 in this survey field. Since our new spectroscopic identifications are mainly associated with X-ray sources in the shallower 250 ks coverage, we provide a comprehensive catalog of X-ray sources detected in the E-CDF-S including the optical and near-infrared counterparts, determined by a likelihood routine, and redshifts (both spectroscopic and photometric), that incorporate published spectroscopic catalogs, thus resulting in a final sample with a high fraction (80%) of X-ray sources having secure identifications. We demonstrate the remarkable coverage of the luminosity-redshift plane now accessible from our data while emphasizing the detection of active galactic nuclei (AGNs) that contribute to the faint end of the luminosity function (L 0.5-8 keV ~ 1043-1044 erg s--1) at 1.5 z 3 including those with and without broad emission lines. Our redshift catalog includes 17 type-2 QSOs at 1 z 3.5 that significantly increases such samples (2X). Based on our deepest (9 hr) VLT/VIMOS observation, we identify 'elusive' optically faint galaxies (R mag ~ 25) at z ~ 2-3 based upon the detection of interstellar absorption lines (e.g., O II+Si IV, C II, C IV); we highlight one such case, an absorption-line galaxy at z = 3.208 having no obvious signs of an AGN in its optical spectrum. In addition, we determine accurate distances to eight galaxy groups with extended X-ray emission detected both by Chandra and XMM-Newton. Finally, we measure the physical extent of known large-scale structures (z ~ 0.7) evident in the CDF-S. While a thick sheet (a radial size of 67.7 Mpc) at z ~ 0.67 extends over the full field, the z ~ 0.73 structure is thin (18.8 Mpc) and filamentary as traced by both AGNs and galaxy groups. In the Appendix, we provide spectroscopic redshifts for 49 counterparts to fainter X-ray sources detected only in the 1 and 2 Ms catalogs, and 48 Very Large Array radio sources not detected in X-rays.
Context. Dust attenuation curves in external galaxies are useful for studying their dust properties as well as interpreting their intrinsic spectral energy distributions. These functions are not very ...well known in the UV range whether at low or high redshift. In particular, the presence or absence of a UV bump at 2175 Å remains an open issue that has consequences on the interpretation of broad band colours of galaxies involving the UV range. Aims. We want to study the dust attenuation curve in the UV range at z > 1 where the UV is redshifted into the visible and with Herschel data to constrain dust emission and a global dust attenuation. In particular, we search for a UV bump and related implications for dust attenuation determinations. Methods. We use deep photometric data of the Chandra Deep Field South obtained with intermediate and broad band filters by the MUSYC project to sample the UV rest frame of galaxies with 1 < z < 2. Herschel/PACS and Spitzer/MIPS data are used to measure the dust emission. We select 30 galaxies with high S/N in all bands. Their SEDs from the UV to the far-IR are fitted using the CIGALE code and the characteristics of the dust attenuation curves obtained as Bayesian outputs of the SED fitting process. Results. The mean dust attenuation curve we derive exhibits a significant UV bump at 2175 Å whose amplitude corresponds to 35% (76%) that of the Milky Way (Large Magellanic Cloud: LMC2 supershell) extinction curve. An analytical expression of the average attenuation curve (A(λ)/AV) is given and found to be slightly steeper than the Calzetti et al. one, although at a 1σ level. Our galaxy sample is used to study the derivation of the slopes of the UV continuum from broad band colours, including the rest frame GALEX FUV − NUV colour. Systematic errors induced by the presence of the bump are quantified. We compare dust attenuation factors measured with CIGALE to the slope of the UV continuum and find that there is a large scatter around the relation valid for local starbursts (~0.7 mag). The uncertainties on the determination of the UV slope lead to an extra systematic error in a range of 0.3 to 0.7 mag on dust attenuation when a filter overlaps the UV bump.
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![The ALPINE-ALMA [C ii ] su...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0035-8711/small "The ALPINE-ALMA [C ii ] survey: Investigation of 10 galaxies at z ∼ 4.5 with [O ii ] and [C ii ] line emission − ISM properties and [O ii ]−SFR relation")