Extended Chandra Deep Field South Research Articles

Compact radio cores in radio-quiet active galactic nuclei

The mechanism of radio emission in radio-quiet (RQ) active galactic nuclei (AGN) is still debated and might arise from the central AGN, from star formation activity in the host, or from either of these sources. A direct detection of compact and bright radio cores embedded in sources that are classified as RQ can unambiguously determine whether a central AGN significantly contributes to the radio emission. We search for compact, high-surface-brightness radio cores in RQ AGNs that are caused unambiguously by AGN activity. We used the Australian Long Baseline Array to search for compact radio cores in four RQ AGNs located in the Extended Chandra Deep Field South (ECDFS). We also targeted four radio-loud (RL) AGNs as a control sample. We detected compact and bright radio cores in two AGNs that are classified as RQ and in one that is classified as RL. Two RL AGNs were not imaged because the quality of the observations was too poor. We report on a first direct evidence of radio cores in RQ AGNs at cosmological redshifts. Our detections show that some of the sources that are classified as RQ contain an active AGN that can contribute significantly (about 50% or more) to the total radio emission.

EDDINGTON RATIO DISTRIBUTION OF X-RAY-SELECTED BROAD-LINE AGNs AT 1.0 < z < 2.2

We investigate the Eddington ratio distribution of X-ray selected broad-line active galactic nuclei (AGN) in the redshift range 1.0<z<2.2, where the number density of AGNs peaks. Combining the optical and Subaru/FMOS near-infrared spectroscopy, we estimate black hole masses for broad-line AGNs in the Chandra Deep Field-South (CDF-S), Extended Chandra Deep Field-South (E-CDF-S), and the XMM-Newton Lockman Hole (XMM-LH) surveys. AGNs with similar black hole masses show a broad range of AGN bolometric luminosities, which are calculated from X-ray luminosities, indicating that the accretion rate of black holes is widely distributed. We find that a substantial fraction of massive black holes accreting significantly below the Eddington limit at z~2, in contrast to what is generally found for luminous AGNs at high redshift. Our analysis of observational selection biases indicates that the "AGN cosmic downsizing" phenomenon can be simply explained by the strong evolution of the co-moving number density at the bright end of the AGN luminosity function, together with the corresponding selection effects. However, it might need to consider a correlation between the AGN luminosity and the accretion rate of black holes that luminous AGNs have higher Eddington ratios than low-luminosity AGNs in order to understand the relatively small fraction of low-luminosity AGNs with high accretion rates in this epoch. Therefore, the observed downsizing trend could be interpreted as massive black holes with low accretion rates, which are relatively fainter than less massive black holes with efficient accretion.

The ATLAS 5.5 GHz survey of the extendedChandraDeep Field South: the second data release

We present a new image of the 5.5 GHz radio emission from the extended Chandra Deep Field South. Deep radio observations at 5.5 GHz were obtained in 2010 and presented in the first data release. A further 76 hours of integration has since been obtained, nearly doubling the integration time. This paper presents a new analysis of all the data. The new image reaches 8.6 microJy rms, an improvement of about 40% in sensitivity. We present a new catalogue of 5.5 GHz sources, identifying 212 source components, roughly 50% more than were detected in the first data release. Source counts derived from this sample are consistent with those reported in the literature for S_{5.5GHz} > 0.1 mJy but significantly lower than published values in the lowest flux density bins (S_{5.5GHz} < 0.1 mJy), where we have more detected sources and improved statistical reliability. The 5.5 GHz radio sources were matched to 1.4 GHz sources in the literature and we find a mean spectral index of -0.35 +- 0.10 for S_{5.5GHz} > 0.5 mJy, consistent with the flattening of the spectral index observed in 5 GHz sub-mJy samples. The median spectral index of the whole sample is \alpha_{med} = -0.58, indicating that these observations may be starting to probe the star forming population. However, even at the faintest levels (0.05 < S_{5.5GHz} < 0.1 mJy), 39% of the 5.5 GHz sources have flat or inverted radio spectra. Four flux density measurements from our data, across the full 4.5 to 6.5 GHz bandwidth, are combined with those from literature and we find 10% of sources (S_{5.5GHz} >~ 0.1 mJy) show significant curvature in their radio spectral energy distribution spanning 1.4 to 9 GHz.

HerMES: disentangling active galactic nuclei and star formation in the radio source population

We separate the extragalactic radio source population above ~50 uJy into active galactic nuclei (AGN) and star-forming sources. The primary method of our approach is to fit the infrared spectral energy distributions (SEDs), constructed using Spitzer/IRAC and MIPS and Herschel/SPIRE photometry, of 380 radio sources in the Extended Chandra Deep Field-South. From the fitted SEDs, we determine the relative AGN and star-forming contributions to their infrared emission. With the inclusion of other AGN diagnostics such as X-ray luminosity, Spitzer/IRAC colours, radio spectral index and the ratio of star-forming total infrared flux to k-corrected 1.4 GHz flux density, qIR, we determine whether the radio emission in these sources is powered by star formation or by an AGN. The majority of these radio sources (60 per cent) show the signature of an AGN at some wavelength. Of the sources with AGN signatures, 58 per cent are hybrid systems for which the radio emission is being powered by star formation. This implies that radio sources which have likely been selected on their star formation have a high AGN fraction. Below a 1.4 GHz flux density of 1 mJy, along with finding a strong contribution to the source counts from pure star-forming sources, we find that hybrid sources constitute 20-65 per cent of the sources. This result suggests that hybrid sources have a significant contribution, along with sources that do not host a detectable AGN, to the observed flattening of the source counts at ~1mJy for the extragalactic radio source population.

THENuSTAREXTRAGALACTIC SURVEYS: INITIAL RESULTS AND CATALOG FROM THE EXTENDEDCHANDRADEEP FIELD SOUTH

We present initial results and the source catalog from the NuSTAR survey of the Extended Chandra Deep Field South (hereafter, ECDFS) - currently the deepest contiguous component of the NuSTAR extragalactic survey program. The survey covers the full ~30 arcmin x 30 arcmin area of this field to a maximum depth of ~360 ks (~220 ks when corrected for vignetting at 3-24 keV), reaching sensitivity limits of ~1.3 x 10^-14 erg/cm2/s (3-8 keV), ~3.4 x 10^-14 erg/cm2/s (8-24 keV) and ~3.0 x 10^-14 erg/cm2/s (3-24 keV). Fifty four (54) sources are detected over the full field, although five of these are found to lie below our significance threshold once contaminating flux from neighboring (i.e., blended) sources is taken into account. Of the remaining 49 that are significant, 19 are detected in the 8-24 keV band. The 8-24 keV to 3-8 keV band ratios of the twelve sources that are detected in both bands span the range 0.39-1.7, corresponding to a photon index range of Gamma ~ 0.5-2.3, with a median photon index of 1.70 +/- 0.52. The redshifts of the 49 sources in our main sample span the range z = 0.21-2.7, and their rest-frame 10-40 keV luminosities (derived from the observed 8-24 keV fluxes) span the range L(10-40 keV) ~ (0.7-300) x 10^43 erg/s, sampling below the "knee" of the X-ray luminosity function out to z ~ 0.8-1. Finally, we identify one NuSTAR source that has neither a Chandra nor an XMM-Newton counterpart, but that shows evidence of nuclear activity at infrared wavelengths, and thus may represent a genuine, new X-ray source detected by NuSTAR in the ECDFS.

Radio-faint AGN: a tale of two populations

We study the Extended Chandra Deep Field South (E-CDFS) Very Large Array sample, which reaches a flux density limit at 1.4 GHz of 32.5 microJy at the field centre and redshift ~ 4, and covers ~ 0.3 deg^2. Number counts are presented for the whole sample while the evolutionary properties and luminosity functions are derived for active galactic nuclei (AGN). The faint radio sky contains two totally distinct AGN populations, characterised by very different evolutions, luminosity functions, and Eddington ratios: radio-quiet (RQ)/radiative-mode, and radio-loud/jet-mode AGN. The radio power of RQ AGN evolves ~ (1+z)^2.5, similarly to star-forming galaxies, while the number density of radio-loud ones has a peak at ~ 0.5 and then declines at higher redshifts. The number density of radio-selected RQ AGN is consistent with that of X-ray selected AGN, which shows that we are sampling the same population. The unbiased fraction of radiative-mode RL AGN, derived from our own and previously published data, is a strong function of radio power, decreasing from ~ 0.5 at P_1.4GHz ~ 10^24 W/Hz to ~ 0.04$ at P_1.4GHz ~ 10^22 W/Hz. Thanks to our enlarged sample, which now includes ~ 700 radio sources, we also confirm and strengthen our previous results on the source population of the faint radio sky: star-forming galaxies start to dominate the radio sky only below ~ 0.1 mJy, which is also where radio-quiet AGN overtake radio-loud ones.

S-CANDELS: THE SPITZER -COSMIC ASSEMBLY NEAR-INFRARED DEEP EXTRAGALACTIC SURVEY. SURVEY DESIGN, PHOTOMETRY, AND DEEP IRAC SOURCE COUNTS

The Spitzer-Cosmic Assembly Deep Near-infrared Extragalactic Legacy Survey (S-CANDELS; PI G.Fazio) is a Cycle 8 Exploration Program designed to detect galaxies at very high redshifts (). To mitigate the effects of cosmic variance and also to take advantage of deep coextensive coverage in multiple bands by the Hubble Space Telescope (HST) Multi-cycle Treasury Program CANDELS, S-CANDELS was carried out within five widely separated extragalactic fields: the UKIDSS Ultra-deep Survey, the Extended Chandra Deep Field South, COSMOS, the HST Deep Field North, and the Extended Groth Strip. S-CANDELS builds upon the existing coverage of these fields from the Spitzer Extended Deep Survey (SEDS), a Cycle 6 Exploration Program, by increasing the integration time from SEDS' 12 hr to a total of 50 hr but within a smaller area, 0.16 deg2. The additional depth significantly increases the survey completeness at faint magnitudes. This paper describes the S-CANDELS survey design, processing, and publicly available data products. We present Infrared Array Camera (IRAC) dual-band catalogs reaching to a depth of 26.5 AB mag. Deep IRAC counts for the roughly 135,000 galaxies detected by S-CANDELS are consistent with models based on known galaxy populations. The increase in depth beyond earlier Spitzer/IRAC surveys does not reveal a significant additional contribution from discrete sources to the diffuse Cosmic Infrared Background (CIB). Thus it remains true that only roughly half of the estimated CIB flux from COBE/DIRBE is resolved.

AN ALMA SURVEY OF SUB-MILLIMETER GALAXIES IN THE EXTENDEDCHANDRADEEP FIELD SOUTH: PHYSICAL PROPERTIES DERIVED FROM ULTRAVIOLET-TO-RADIO MODELING

[abridged] The ALESS survey has followed-up a sample of 122 sub-millimeter sources in the Extended Chandra Deep Field South at 870um with ALMA, allowing to pinpoint the positions of sub-millimeter galaxies (SMGs) to 0.3'' and to find their precise counterparts at different wavelengths. This enabled the first compilation of the multi-wavelength spectral energy distributions (SEDs) of a statistically reliable survey of SMGs. In this paper, we present a new calibration of the MAGPHYS modelling code that is optimized to fit these UV-to-radio SEDs of z>1 star-forming galaxies using an energy balance technique to connect the emission from stellar populations, dust attenuation and dust emission in a physically consistent way. We derive statistically and physically robust estimates of the photometric redshifts and physical parameters for the ALESS SMGs. We find that they have a median stellar mass $M_\ast=(8.9\pm0.1)\times10^{10} M_\odot$, SFR$=280\pm70 M_\odot$/yr, overall V-band dust attenuation $A_V=1.9\pm0.2$ mag, dust mass $M_\rm{dust}=(5.6\pm1.0)\times10^8 M_\odot$, and average dust temperature Tdust~40 K. The average intrinsic SED of the ALESS SMGs resembles that of local ULIRGs in the IR range, but the stellar emission of our average SMG is brighter and bluer, indicating lower dust attenuation, possibly because they are more extended. We explore how the average SEDs vary with different parameters, and we provide a new set of SMG templates. To put the ALESS SMGs into context, we compare their stellar masses and SFRs with those of less actively star-forming galaxies at the same redshifts. At z~2, about half of the SMGs lie above the star-forming main sequence, while half are at the high-mass end of the sequence. At higher redshifts (z~3.5), the SMGs tend to have higher SFR and Mstar, but the fraction of SMGs that lie significantly above the main sequence decreases to less than a third.

A search for variable and transient radio sources in the extended Chandra Deep Field South at 5.5 GHz

We present a three epoch survey for transient and variables in the extended Chandra Deep Field South at 5.5 GHz with the Australia Telescope Compact Array. A region covering $\sim$0.3 deg$^{2}$ was observed on timescales of 2.5 months and 2.5 years and typical sensitivities 12.1 $-$ 17.1 $\mu$Jy beam$^{-1}$ (1$\sigma$) were achieved. This survey represents the deepest search for transient and variable radio sources at 5.5 GHz. In total 124 sources were detected above the 5.5$\sigma$ level. One highly variable radio source was found with $\Delta S > 50%$ implying a surface density of $\sim$3 deg$^{-2}$. A further three radio sources were found with lower levels of variability equating to a surface density of $\sim$13 deg$^{-2}$ above a detection threshold of 82.3 $\mu$Jy. All of the variable sources have inverted radio spectra (between 1.4 and 5.5 GHz) and are associated with active galactic nuclei. We conclude that these variables are young gigahertz peaked-spectrum sources with active and self-absorbed radio jets. We explore the variability completeness of this sample and conclude that the fairly low levels of variability would only be detectable in 3$-$25% of all sources within the field. No radio transients were detected in this survey and we place an upper limit on the surface density of transient events $ < 7.5$ deg$^{-2}$ above a detection threshold of 68.8~$\mu$Jy.

The evolution of galaxy star formation activity in massive haloes

There is now a large consensus that the current epoch of the Cosmic Star Formation History (CSFH) is dominated by low mass galaxies while the most active phase at 1<z<2 is dominated by more massive galaxies, which undergo a faster evolution. Massive galaxies tend to inhabit very massive halos such as galaxy groups and clusters. We aim to understand whether the observed "galaxy downsizing" could be interpreted as a "halo downsizing", whereas the most massive halos, and their galaxy populations, evolve more rapidly than the halos of lower mass. Thus, we study the contribution to the CSFH of galaxies inhabiting group-sized halos. This is done through the study of the evolution of the Infra-Red (IR) luminosity function of group galaxies from redshift 0 to ~1.6. We use a sample of 39 X-ray selected groups in the Extended Chandra Deep Field South (ECDFS), the Chandra Deep Field North (CDFN), and the COSMOS field, where the deepest available mid- and far-IR surveys have been conducted with Spitzer MIPS and Hersche PACS. Groups at low redshift lack the brightest, rarest, and most star forming IR-emitting galaxies observed in the field. Their IR-emitting galaxies contribute <10% of the comoving volume density of the whole IR galaxy population in the local Universe. At redshift >~1, the most IR-luminous galaxies (LIRGs and ULIRGs) are preferentially located in groups, and this is consistent with a reversal of the star-formation rate vs .density anti-correlation observed in the nearby Universe. At these redshifts, group galaxies contribute 60-80% of the CSFH, i.e. much more than at lower redshifts. Below z~1, the comoving number and SFR densities of IR-emitting galaxies in groups decline significantly faster than those of all IR-emitting galaxies. Our results are consistent with a "halo downsizing" scenario and highlight the significant role of "environment" quenching in shaping the CSFH.

AN ALMA SURVEY OF SUBMILLIMETER GALAXIES IN THE EXTENDED CHANDRA DEEP FIELD SOUTH: NEAR-INFRARED MORPHOLOGIES AND STELLAR SIZES

We analyse HST WFC3/$H_{160}$-band observations of a sample of 48 ALMA-detected submillimeter galaxies (SMGs) in the Extended Chandra Deep Field South field, to study their stellar morphologies and sizes. We detect 79$\pm$17% of the SMGs in the $H_{160}$-band imaging with a median sensitivity of 27.8 mag, and most (80%) of the non-detections are SMGs with 870$\mu$m fluxes of $S_{870} < $3 mJy. With a surface brightness limit of $\mu_H \sim $26 mag arcsec$^{-2}$, we find that 82$\pm$9% of the $H_{160}$-band detected SMGs at $z =$ 1-3 appear to have disturbed morphologies, meaning they are visually classified as either irregulars or interacting systems, or both. By determining a S\'ersic fit to the $H_{160}$ surface-brightness profiles we derive a median S\'ersic index of $n = $1.2$\pm$0.3 and a median half-light radius of $r_e = $4.4$^{+1.1}_{-0.5}$ kpc for our SMGs at $z = $1-3. We also find significant displacements between the positions of the $H_{160}$-component and 870$\mu$m emission in these systems, suggesting that the dusty star-burst regions and less-obscured stellar distribution are not co-located. We find significant differences in the sizes and the S\'ersic index between our $z = $2-3 SMGs and $z \sim $2 quiescent galaxies, suggesting a major transformation of the stellar light profile is needed in the quenching processes if SMGs are progenitors of the red-and-dead $z\sim$2 galaxies. Given the short-lived nature of SMGs, we postulate that the majority of the $z = $2-3 SMGs with $S_{870} \gtrsim $2 mJy are early/mid-stage major mergers.

RECENT STELLAR MASS ASSEMBLY OF LOW-MASS STAR-FORMING GALAXIES AT REDSHIFTS 0.3 &lt;z&lt; 0.9

The epoch when low-mass star forming galaxies (LMSFGs) form the bulk of their stellar mass is uncertain. While some models predict an early formation, others favor a delayed scenario until later ages of the universe. We present constraints on the star formation histories (SFHs) of a sample of LMSFGs obtained through the analysis of their spectral energy distributions using a novel approach that (1) consistently combines photometric (broadband) and spectroscopic (equivalent widths of emission lines) data, and (2) uses physically motivated SFHs with non-uniform variations of the star formation rate (SFR) as a function of time. The sample includes 31 spectroscopically confirmed LMSFGs (7.3 < log M*/Msun < 8.0) at 0.3 < z_spec < 0.9 in the Extended-Chandra Deep Field-South field (E-CDF-S). Among them, 24 were selected with photometric stellar mass log M*/Msun < 8.0, 0.3 < z_phot < 1.0, and NB816 < 26 AB mag; the remaining 7 were selected as blue compact dwarfs (BCDs) within the same photometric redshift and magnitude ranges. We also study a secondary sample of 43 more massive spectroscopically confirmed galaxies (8.0 < log M*/Msun < 9.1), selected with the same criteria. The SFRs and stellar masses derived for both samples place our targets on the standard main sequence of star forming galaxies. The median SFH of LMSFGs at intermediate redshifts appears to form 90% of the median stellar mass inferred for the sample in the 0.5-1.8 Gyr immediately preceding the observation. These results suggest a recent stellar mass assembly for LMSFGs, consistent with the cosmological downsizing trends. We find similar median SFH timescales for the more massive secondary sample.

Properties of submillimetre galaxies in a semi-analytic model using the ‘Count Matching’ approach: application to the ECDF-S

We present a new technique for modeling submillimeter galaxies (SMGs): the "Count Matching" approach. Using lightcones drawn from a semi-analytic model of galaxy formation, we choose physical galaxy properties given by the model as proxies for their submillimeter luminosities, assuming a monotonic relationship. As recent interferometric observations of the Extended Chandra Deep Field South show that the brightest sources detected by single-dish telescopes are comprised by emission from multiple fainter sources, we assign the submillimeter fluxes so that the combined LABOCA plus bright-end ALMA observed number counts for this field are reproduced. After turning the model catalogs given by the proxies into submillimeter maps, we perform a source extraction to include the effects of the observational process on the recovered counts and galaxy properties. We find that for all proxies, there are lines of sight giving counts consistent with those derived from LABOCA observations, even for input sources with randomized positions in the simulated map. Comparing the recovered redshift, stellar mass and host halo mass distributions for model SMGs with observational data, we find that the best among the proposed proxies is that in which the submillimeter luminosity increases monotonically with the product between dust mass and SFR. This proxy naturally reproduces a positive trend between SFR and bolometric IR luminosity. The majority of components of blended sources are spatially unassociated.

CANDELS/GOODS-S, CDFS, AND ECDFS: PHOTOMETRIC REDSHIFTS FOR NORMAL AND X-RAY-DETECTED GALAXIES

We present photometric redshifts and associated probability distributions for all detected sources in the Extended Chandra Deep Field South (ECDFS). This work makes use of the most up-to-date data from the Cosmic Assembly Near-IR Deep Legacy Survey (CANDELS) and the Taiwan ECDFS Near-Infrared Survey (TENIS) in addition to other data. We also revisit multi-wavelength counterparts for published X-ray sources from the 4 Ms CDFS and 250 ks ECDFS surveys, finding reliable counterparts for 1207 out of 1259 sources (∼96%). Data used for photometric redshifts include intermediate-band photometry deblended using the TFIT method, which is used for the first time in this work. Photometric redshifts for X-ray source counterparts are based on a new library of active galactic nuclei/galaxy hybrid templates appropriate for the faint X-ray population in the CDFS. Photometric redshift accuracy for normal galaxies is 0.010 and for X-ray sources is 0.014 and outlier fractions are 4% and 5.2%, respectively. The results within the CANDELS coverage area are even better, as demonstrated both by spectroscopic comparison and by galaxy-pair statistics. Intermediate-band photometry, even if shallow, is valuable when combined with deep broadband photometry. For best accuracy, templates must include emission lines.

Detection of molecular gas in an ALMA [C ii]-identified submillimetre galaxy at z = 4.44

Abstract We present the detection of 12CO(2–1) in the z = 4.44 submillimetre galaxy ALESS65.1 using the Australia Telescope Compact Array. A previous Atacama Large Millimeter/submillimeter Array study of submillimetre galaxies (SMGs) in the Extended Chandra Deep Field South determined the redshift of this optically and near-infrared undetected source through the measurement of [C ii] 157.74 μm emission. Using the luminosity of the 12CO(2–1) emission, we estimate the gas mass to be Mgas ∼ 1.7 × 1010 M⊙. The gas depletion time-scale of ALESS65.1 is ∼ 25 Myr, similar to other high-redshift SMGs and consistent with z &amp;gt; 4 SMGs being the progenitors of massive ‘red-and-dead’ galaxies at z &amp;gt; 2. The ratio of the [C ii], 12CO and far-infrared luminosities implies a strong far-ultraviolet field of G0 ∼ 103.25, which is at the high end of the far-ultraviolet fields seen in local starbursts, but weaker than the far-ultraviolet fields of most nearby ultraluminous infrared galaxies (ULIRGs). The high ratio of $L_{\rm [{\rm C\,\small {II}}]}/L_{\rm FIR} = 1.0 \times 10^{-3}$ observed in ALESS65.1, combined with $L_{\rm [{\rm C\,\small {II}}]}/L_{\rm CO} \sim 2300$, is consistent with ALESS65.1 having more extended regions of intense star formation than local ULIRGs.

An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South: radio properties and the far-infrared/radio correlation

We present a study of the radio properties of 870$\mu$m-selected submillimetre galaxies (SMGs), observed at high resolution with ALMA in the Extended Chandra Deep Field South. From our initial sample of 76 ALMA SMGs, we detect 52 SMGs at $>3\sigma$ significance in VLA 1400MHz imaging, of which 35 are also detected at $>3\sigma$ in new 610MHz GMRT imaging. Within this sample of radio-detected SMGs, we measure a median radio spectral index $\alpha_{610}^{1400} = -0.79 \pm 0.06$, (with inter-quartile range $\alpha=[-1.16,-0.56]$) and investigate the far-infrared/radio correlation via the parameter $q_{\rm IR}$, the logarithmic ratio of the rest-frame 8-1000$\mu$m flux and monochromatic radio flux. Our median $q_{\rm IR} = 2.56 \pm 0.05$ (inter-quartile range $q_{\rm IR}=[2.42,2.78]$) is higher than that typically seen in single-dish 870$\mu$m-selected sources ($q_{\rm IR} \sim 2.4$), which may reflect the fact that our ALMA-based study is not biased to radio-bright counterparts, as previous samples were. Finally, we search for evidence that $q_{\rm IR}$ and $\alpha$ evolve with age in a co-dependent manner, as predicted by starburst models: the data populate the predicted region of parameter space, with the stellar mass tending to increase along tracks of $q_{\rm IR}$ versus $\alpha$ in the direction expected, providing the first observational evidence in support of these models.

AN ALMA SURVEY OF SUBMILLIMETER GALAXIES IN THE EXTENDED CHANDRA DEEP FIELD SOUTH: THE REDSHIFT DISTRIBUTION AND EVOLUTION OF SUBMILLIMETER GALAXIES

We present the first photometric redshift distribution for a large unbiased sample of 870um selected submillimeter galaxies (SMGs) with robust identifications based on observations with the Atacama Large Millimeter Array (ALMA). In our analysis we consider 96 SMGs in the Extended Chandra Deep Field South, 77 of which have 4-19 band, optical-near-infrared, photometry. We model the Spectral Energy Distributions (SEDs) for these 77 SMGs, deriving a median photometric redshift of z=2.3+/-0.1. The remaining 19 SMGs have insufficient optical or near-infrared photometry to derive photometric redshifts, but a stacking analysis of IRAC and Herschel observations confirms they are not spurious. Assuming these sources have an absolute H-band magnitude distribution comparable to that of a complete sample of z~1-2 SMGs, we demonstrate that the undetected SMGs lie at higher redshifts, raising the median redshift for SMGs to z=2.5+/-0.2. More critically we show that the proportion of galaxies undergoing an SMG phase at z>3 is 35+/-5% of the total population. We derive a median stellar mass for SMGs of Mstar=(8+/-1)x10^10Mo, but caution that there are significant systematic uncertainties in our stellar mass estimate, up to x5 for individual sources. We compare our sample of SMGs to a volume-limited, morphologically classified sample of ellipticals in the local Universe. Assuming the star formation activity in SMGs has a timescale of ~100Myr we show that their descendants at z~0 would have a space density and M_H distribution which are in good agreement with those of local ellipticals. In addition the inferred mass-weighted ages of the local ellipticals broadly agree with the look-back times of the SMG events. Taken together, these results are consistent with a simple model that identifies SMGs as events that form most of the stars seen in the majority of luminous elliptical galaxies at the present day.

CONSTRAINING THE Lyα ESCAPE FRACTION WITH FAR-INFRARED OBSERVATIONS OF Lyα EMITTERS

We study the far-infrared properties of 498 Lyman Alpha Emitters (LAEs) at z=2.8, 3.1 and 4.5 in the Extended Chandra Deep Field-South, using 250, 350 and 500 micron data from the Herschel Multi-tiered Extragalactic Survey (HerMES) and 870 micron data from the LABOCA ECDFS Submillimeter Survey (LESS). 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 $1\sigma$ depths of ~0.1 to 0.4 mJy. The LAEs are also undetected at $\ge3\sigma$ in the stacks, although a $2.5\sigma$ signal is observed at 870 micron for the z=2.8 sources. We consider a wide range of far-infrared spectral energy distributions (SEDs), including a 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 Ly$\alpha$ and UV emission to determine lower limits on the LAEs Ly$\alpha$ escape fraction ($f_{\rm esc}($Ly$\alpha$)). For the Sd SED template, the inferred LAEs $f_{\rm esc}($Ly$\alpha$) are $\gtrsim30%$ ($1\sigma$) at z=2.8, 3.1 and 4.5, which are all significantly higher than the global $f_{\rm esc}($Ly$\alpha$) at these redshifts. Thus, if the LAEs $f_{\rm esc}($Ly$\alpha$) 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 $f_{\rm esc}($Ly$\alpha$) of ~10 to 20% ($1\sigma$), all of which are slightly higher than the global evolution of $f_{\rm esc}($Ly$\alpha$) but consistent with it at the 2 to 3$\sigma$ level.

NuSTAR J033202–2746.8: DIRECT CONSTRAINTS ON THE COMPTON REFLECTION IN A HEAVILY OBSCURED QUASAR AT z ≈ 2

We report NuSTAR observations of NuSTAR J033202-2746.8, a heavily obscured, radio-loud quasar detected in the Extended Chandra Deep Field-South, the deepest layer of the NuSTAR extragalactic survey (~400 ks, at its deepest). NuSTAR J033202-2746.8 is reliably detected by NuSTAR only at E>8 keV and has a very flat spectral slope in the NuSTAR energy band (Gamma=0.55^{+0.62}_{-0.64}; 3-30 keV). Combining the NuSTAR data with extremely deep observations by Chandra and XMM-Newton (4 Ms and 3 Ms, respectively), we constrain the broad-band X-ray spectrum of NuSTAR J033202-2746.8, indicating that this source is a heavily obscured quasar (N_H=5.6^{+0.9}_{-0.8}x10^23 cm^-2) with luminosity L_{10-40 keV}~6.4x10^44 erg s^-1. Although existing optical and near-infrared (near-IR) data, as well as follow-up spectroscopy with the Keck and VLT telescopes, failed to provide a secure redshift identification for NuSTAR J033202-2746.8, we reliably constrain the redshift z=2.00+/-0.04 from the X-ray spectral features (primarily from the iron K edge). The NuSTAR spectrum shows a significant reflection component (R=0.55^{+0.44}_{-0.37}), which was not constrained by previous analyses of Chandra and XMM-Newton data alone. The measured reflection fraction is higher than the R~0 typically observed in bright radio-loud quasars such as NuSTAR J033202-2746.8, which has L_{1.4 GHz}~10^27 W Hz^-1. Constraining the spectral shape of AGN, including bright quasars, is very important for understanding the AGN population, and can have a strong impact on the modeling of the X-ray background. Our results show the importance of NuSTAR in investigating the broad-band spectral properties of quasars out to high redshift.

An ALMA survey of sub-millimetre Galaxies in the Extended Chandra Deep Field South: the far-infrared properties of SMGs

We exploit ALMA 870um (345GHz) observations of submillimetre sources in the Extended Chandra Deep Field South to investigate the far-infrared properties of high-redshift submillimetre galaxies (SMGs). Using the precisely located 870um ALMA positions of 99 SMGs, together with 24um and radio imaging of this field, we deblend the Herschel/SPIRE imaging of this region to extract their far-infrared fluxes and colours. The median photometric redshifts for ALMA LESS (ALESS) SMGs which are detected in at least two SPIRE bands increases with wavelength of the peak in their SEDs, with z=2.3+/-0.2, 2.5+/-0.3 and 3.5+/-0.5 for the 250, 350 and 500-um peakers respectively. We find that 34 ALESS SMGs do not have a >3-sigma counterpart at 250, 350 or 500-um. These galaxies have a median photometric redshift of z=3.3+/-0.5, which is higher than the full ALESS SMG sample; z=2.5+/-0.2. Using the photometric redshifts together with the 250-870um photometry, we estimate the far-infrared luminosities and characteristic dust temperature of each SMG. The median infrared luminosity of the S_870um>2mJy SMGs is L_IR=(3.0+/-0.3)x10^{12}Lo(SFR=300+/-30Mo/yr). At a fixed luminosity, the characteristic dust temperature of these high-redshift SMGs is 2-3K lower than comparably luminous galaxies at z=0, reflecting the more extended star formation occurring in these systems. By extrapolating the 870um number counts to S_ 870um=1mJy, we show that the contribution of S_870um>1mJy SMGs to the cosmic star formation budget is 20% of the total over the redshift range z~1-4. We derive a median dust mass for these SMGs of M_d=(3.6+/-0.3)x10^8Mo and by adopting an appropriate gas-to-dust ratio, we estimate an average molecular mass of M_H2=(4.2+/-0.4)x10^{10}Mo. Finally, we use our estimates of the H2 masses to show that SMGs with S_870um>1mJy contain ~10% of the z~2 volume-averaged H2 mass density at this epoch.