We present results from a {ap}100 ks Chandra observation of the 2QZ Cluster 1004+00 structure at z = 2.23 (hereafter 2QZ Clus). 2QZ Clus was originally identified as an overdensity of four... Show moreWe present results from a {ap}100 ks Chandra observation of the 2QZ Cluster 1004+00 structure at z = 2.23 (hereafter 2QZ Clus). 2QZ Clus was originally identified as an overdensity of four optically-selected QSOs at z = 2.23 within a 15 { imes} 15 arcmin$^{2}$ region. Narrow-band imaging in the near-IR (within the K band) revealed that the structure contains an additional overdensity of 22 z = 2.23 H{$α$}-emitting galaxies (HAEs), resulting in 23 unique z = 2.23 HAEs/QSOs (22 within the Chandra field of view). Our Chandra observations reveal that three HAEs in addition to the four QSOs harbor powerfully accreting supermassive black holes (SMBHs), with 2-10 keV luminosities of {ap}(8-60) { imes} 10$^{43}$ erg s$^{-1}$ and X-ray spectral slopes consistent with unobscured active galactic nucleus (AGN). Using a large comparison sample of 210 z = 2.23 HAEs in the Chandra-COSMOS field (C-COSMOS), we find suggestive evidence that the AGN fraction increases with local HAE galaxy density. The 2QZ Clus HAEs reside in a moderately overdense environment (a factor of {ap}2 times over the field), and after excluding optically-selected QSOs, we find that the AGN fraction is a factor of {ap}3.5$^{+3.8}$ $_{-2.2}$ times higher than C-COSMOS HAEs in similar environments. Using stacking analyses of the Chandra data and Herschel SPIRE observations at 250 {$μ$}m, we respectively estimate mean SMBH accretion rates ($ackslash$dot${$M$}$_BH) and star formation rates (SFRs) for the 2QZ Clus and C-COSMOS samples. We find that the mean 2QZ Clus HAE stacked X-ray luminosity is QSO-like (L $_{2-10 keV}$ {ap} [6-10] { imes} 10$^{43}$ erg s$^{-1}$), and the implied $ackslash$dot${$M$}$_BH/SFR {ap} (1.6-3.2) { imes} 10$^{-3}$ is broadly consistent with the local M $_{BH}$/M $_{sstarf}$ relation and z {ap} 2 X-ray selected AGN. In contrast, the C-COSMOS HAEs are on average an order of magnitude less X-ray luminous and have $ackslash$dot${$M$}$_BH/SFR {ap} (0.2-0.4) { imes} 10$^{-3}$, somewhat lower than the local M $_{BH}$/M $_{sstarf}$ relation, but comparable to that found for z {ap} 1-2 star-forming galaxies with similar mean X-ray luminosities. We estimate that a periodic QSO phase with duty cycle {ap}2%-8% would be sufficient to bring star-forming galaxies onto the local M $_{BH}$/M $_{sstarf}$ relation. This duty cycle is broadly consistent with the observed C-COSMOS HAE AGN fraction ({ap}0.4%-2.3%) for powerful AGN with L $_X$ {gt}~{} 10$^{44}$ erg s$^{-1}$. Future observations of 2QZ Clus will be needed to identify key factors responsible for driving the mutual growth of the SMBHs and galaxies. Show less
Del Moro, A.; Alexander, D.; Mullaney, J.; Daddi, E.; Pannella, M.; Bauer, F.; ... ; Xue, Y. 2013
Context. A tight correlation exists between far-infrared and radio emission for star-forming galaxies (SFGs), which seems to hold out to high redshifts (z {ap} 2). Any excess of radio emission... Show moreContext. A tight correlation exists between far-infrared and radio emission for star-forming galaxies (SFGs), which seems to hold out to high redshifts (z {ap} 2). Any excess of radio emission over that expected from star formation processes is most likely produced by an active galactic nucleus (AGN), often hidden by large amounts of dust and gas. Identifying these radio-excess sources will allow us to study a population of AGN unbiased by obscuration and thus find some of the most obscured, Compton-thick AGN, which are in large part unidentified even in the deepest X-ray and infrared (IR) surveys. Aims: We present here a new spectral energy distribution (SED) fitting approach that we adopt to select radio-excess sources amongst distant star-forming galaxies in the GOODS-Herschel (North) field and to reveal the presence of hidden, highly obscured AGN. Methods: Through extensive SED analysis of 458 galaxies with radio 1.4 GHz and mid-IR 24 {$μ$}m detections using some of the deepest Chandra X-ray, Spitzer and Herschel infrared, and VLA radio data available to date, we have robustly identified a sample of 51 radio-excess AGN (~{}1300 deg$^{-2}$) out to redshift z {ap} 3. These radio-excess AGN have a significantly lower far-IR/radio ratio (q {lt} 1.68, 3{$σ$}) than the typical relation observed for star-forming galaxies (q {ap} 2.2). Results: We find that {ap}45% of these radio-excess sources have a dominant AGN component in the mid-IR band, while for the remainders the excess radio emission is the only indicator of AGN activity. The presence of an AGN is also confirmed by the detection of a compact radio core in deep VLBI 1.4 GHz observations for eight of our radio-excess sources ({ap}16%; {ap}66% of the VLBI detected sources in this field), with the excess radio flux measured from our SED analysis agreeing, to within a factor of two, with the radio core emission measured by VLBI. We find that the fraction of radio-excess AGN increases with X-ray luminosity reaching ~{}60% at L$_X$ {ap} 10$^{44}$ - 10$^{45}$ erg s$^{-1}$, making these sources an important part of the total AGN population. However, almost half (24/51) of these radio-excess AGN are not detected in the deep Chandra X-ray data, suggesting that some of these sources might be heavily obscured. Amongst the radio-excess AGN we can distinguish three groups of objects: i) AGN clearly identified in infrared (and often in X-rays), a fraction of which are likely to be distant Compton-thick AGN; ii) moderate luminosity AGN (L$_X$ {lsim} 10$^{43}$ erg s$^{-1}$) hosted in strong star-forming galaxies; and iii) a small fraction of low accretion-rate AGN hosted in passive (i.e. weak or no star-forming) galaxies. We also find that the specific star formation rates (sSFRs) of the radio-excess AGN are on average lower that those observed for X-ray selected AGN hosts, indicating that our sources are forming stars more slowly than typical AGN hosts, and possibly their star formation is progressively quenching. Tables 1, 3 and Appendices are available in electronic form at http://www.aanda.orgShow less
Hodge, J.; Karim, A.; Smail, I.; Swinbank, A.; Walter, F.; Biggs, A.; ... ; Werf, P.P. van der 2013
We present an Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 0 survey of 126 submillimeter sources from the LABOCA ECDFS Submillimeter Survey (LESS). Our 870 {$μ$}m survey with ALMA ... Show moreWe present an Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 0 survey of 126 submillimeter sources from the LABOCA ECDFS Submillimeter Survey (LESS). Our 870 {$μ$}m survey with ALMA (ALESS) has produced maps ~{}3{ imes} deeper and with a beam area ~{}200{ imes} smaller than the original LESS observations, doubling the current number of interferometrically-observed submillimeter sources. The high resolution of these maps allows us to resolve sources that were previously blended and accurately identify the origin of the submillimeter emission. We discuss the creation of the ALESS submillimeter galaxy (SMG) catalog, including the main sample of 99 SMGs and a supplementary sample of 32 SMGs. We find that at least 35% (possibly up to 50%) of the detected LABOCA sources have been resolved into multiple SMGs, and that the average number of SMGs per LESS source increases with LESS flux density. Using the (now precisely known) SMG positions, we empirically test the theoretical expectation for the uncertainty in the single-dish source positions. We also compare our catalog to the previously predicted radio/mid-infrared counterparts, finding that 45% of the ALESS SMGs were missed by this method. Our ~{}1.''6 resolution allows us to measure a size of ~{}9 kpc { imes} 5 kpc for the rest-frame ~{}300 {$μ$}m emission region in one resolved SMG, implying a star formation rate surface density of 80 M $_{⊙}$ yr$^{-1}$ kpc$^{-2}$, and we constrain the emission regions in the remaining SMGs to be {lt}10 kpc. As the first statistically reliable survey of SMGs, this will provide the basis for an unbiased multiwavelength study of SMG properties. Show less
