arXiv subjects

K. E. K. Coppin

Publications and source records attributed to K. E. K. Coppin.

At least 55 records · Page 3Linked to original sources

arXiv2013

A submillimetre-bright z~3 overdensity behind a z~1 supercluster revealed by SCUBA-2 and Herschel

We present a wide-field (30' diameter) 850um SCUBA-2 map of the spectacular three-component merging supercluster, RCS 231953+00, at z=0.9. The brightest submillimetre galaxy (SMG) in the field (S_850=12mJy) is within 30" of one of the cluster cores (RCS 2319-C), and is likely to be a more distant, lensed galaxy. Interestingly, the wider field around RCS 2319-C reveals a local overdensity of SMGs, exceeding the average source density by a factor of 4.5, with a <1 per cent chance of being found in a random field. Utilizing Herschel-SPIRE observations, we find three of these SMGs have similar submillimetre colours. We fit their observed 250-850um spectral energy distributions to estimate their redshift, yielding 2.5<z<3.5, and calculate prodigious star formation rates (SFRs) ranging from 500-2500 solar masses per year. We speculate that these galaxies are either lensed SMGs, or signpost a physical structure at z~3: a 'protocluster' inhabited by young galaxies in a rapid phase of growth, destined to form the core of a massive galaxy cluster by z=0.

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arXiv2013

An ALMA survey of submillimeter galaxies in the Extended Chandra Deep Field South: Source catalog and multiplicity

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 micron survey with ALMA (ALESS) has produced maps ~3X deeper and with a beam area ~200X 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 X 5 kpc for the rest-frame ~300 um emission region in one resolved SMG, implying a star formation rate surface density of 80 M_sol yr^-1 kpc^-2, and we constrain the emission regions in the remaining SMGs to be <10 kpc. As the first statistically reliable survey of SMGs, this will provide the basis for an unbiased multiwavelength study of SMG properties.

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arXiv2013

Physical Conditions of the Gas in an ALMA [CII]-identified Submillimetre Galaxy at z = 4.44

We present CO(2-1) observations of the submillimetre galaxy ALESS65.1 performed with the Australia Telescope Compact Array at 42.3 GHz. A previous ALMA study of submillimetre galaxies in the Extended Chandra Deep Field South detected [CII] 157.74 micron emission from this galaxy at a redshift of z = 4.44. No CO(2-1) emission was detected but we derive a firm upper limit to the cold gas mass in ALESS65.1 of M_gas < 1.7 x 10^10 M_odot. The estimated gas depletion timescale is <50 Myr, which is similar to other high redshift SMGs, and consistent with z > 4 SMGs being the likely progenitors of massive red-and-dead galaxies at z > 2. The ratio of the [CII], CO and far-infrared luminosities implies a strong far-ultraviolet field of G_0 > 10^3, as seen in Galactic star forming regions or local ULIRGs. The observed L_[CII]/L_FIR = 2.3 x 10^{-3} is high compared to local ULIRGs and, combined with L_[CII]/L_CO > 2700, it is consistent with ALESS65.1 either having an extended (several kpc) [CII] emitting region or lower than solar metallicity.

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arXiv2012

The SCUBA-2 Cosmology Legacy Survey: blank-field number counts of 450um-selected galaxies and their contribution to the cosmic infrared background

The first deep blank-field 450um map (1-sigma~1.3mJy) from the SCUBA-2 Cosmology Legacy Survey (S2CLS), conducted with the James Clerk Maxwell Telescope (JCMT) is presented. Our map covers 140 arcmin^2 of the COSMOS field, in the footprint of the HST CANDELS area. Using 60 submillimetre galaxies (SMGs) detected at >3.75-sigma, we evaluate the number counts of 450um-selected galaxies with flux densities S_450>5mJy. The 8-arcsec JCMT beam and high sensitivity of SCUBA-2 now make it possible to directly resolve a larger fraction of the cosmic infrared background (CIB, peaking at ~200um) into the individual galaxies responsible for its emission than has previously been possible at this wavelength. At S_450>5mJy we resolve (7.4[+/-]0.7)x10^-2 MJy/sr of the CIB at 450um (equivalent to 16[+/-]7% of the absolute brightness measured by COBE at this wavelength) into point sources. A further ~40% of the CIB can be recovered through a statistical stack of 24um emitters in this field, indicating that the majority (~60%) of the CIB at 450um is emitted by galaxies with S_450>2mJy. The average redshift of 450um emitters identified with an optical/near-infrared counterpart is estimated to be =1.3, implying that the galaxies in the sample are in the ultraluminous class (L_IR~1.1x10^12 L_sun). If the galaxies contributing to the statistical stack lie at similar redshifts, then the majority of the CIB at 450um is emitted by galaxies in the LIRG class with L_IR>3.6x10^11 L_sun.

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arXiv2012

Observational limits on the gas mass of a z=4.9 galaxy

We present the results of a search for molecular gas emission from a star-forming galaxy at z = 4.9. The galaxy benefits from magnification of 22 +/- 5x due to strong gravitational lensing by the foreground cluster MS1358+62. We target the CO(5-4) emission at a known position and redshift from existing Hubble Space Telescope/ACS imaging and Gemini/NIFS [OII]3727 imaging spectroscopy, and obtain a tentative detection at the 4.3sigma level with a flux of 0.104 +/- 0.024Jkm/s. From the CO line luminosity and assuming a CO-to-H2 conversion factor alpha=2, we derive a gas mass M_gas ~ 1^{+1}_{-0.6} x 10^9 M_sun. Combined with the existing data, we derive a gas fraction Mgas/(Mgas + M*) = 0.59^{+0.11}_{-0.06}. The faint line flux of this galaxy highlights the difficulty of observing molecular gas in representative galaxies at this epoch, and suggests that routine detections of similar galaxies in the absence of gravitational lensing will remain challenging even with ALMA in full science operations.

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arXiv2012

AzTEC half square degree survey of the SHADES fields - II. Identifications, redshifts, and evidence for large-scale structure

The AzTEC 1.1 mm survey of the SCUBA HAlf Degree Extragalactic Survey (SHADES) fields is the largest (0.7 deg2) blank-field millimetre-wavelength survey undertaken to date at a resolution of ~18" and a depth of ~1 mJy. We have used the deep optical-to-radio multi-wavelength data in the SHADES Lockman Hole East and SXDF/UDS fields to obtain galaxy identifications for ~64% (~80% with tentative identifications) of the 148 AzTEC-SHADES 1.1 mm sources, exploiting deep radio and 24 um data complemented by methods based on 8 um flux-density and red optical-infrared (i-K) colour. This unusually high identification rate can be attributed to the relatively bright millimetre-wavelength flux-density threshold, combined with the relatively deep supporting multi-frequency data. We have further exploited the optical-mid-infrared-radio data to derive a ~60% (~75% with tentative identifications) complete redshift distribution for the AzTEC-SHADES sources, yielding a median redshift of z~2.2, with a high-redshift tail extending to at least z~4. Despite the larger area probed by the AzTEC survey relative to the original SCUBA SHADES imaging, the redshift distribution of the AzTEC sources is consistent with that displayed by the SCUBA sources, and reinforces tentative evidence that the redshift distribution of mm/sub-mm sources in the Lockman Hole field is significantly different from that found in the SXDF/UDS field. Comparison with simulated surveys of similar scale extracted from semi-analytic models based on the Millennium simulation indicates that this is as expected if the mm/sub-mm sources are massive (M>10^11 Mo) star-forming galaxies tracing large-scale structures over scales of 10-20 Mpc. This confirms the importance of surveys covering several square degrees (as now underway with SCUBA2) to obtain representative samples of bright (sub)mm-selected galaxies.

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arXiv2012

The evolutionary connection between QSOs and SMGs: molecular gas in far-infrared luminous QSOs at z ~ 2.5

We present IRAM Plateau de Bure Interferometer observations of the 12CO(3-2) emission from two far-infrared luminous QSOs at z ~ 2.5 selected from the Herschel-ATLAS survey. These far-infrared bright QSOs were selected to have supermassive black holes (SMBHs) with masses similar to those thought to reside in sub-millimetre galaxies (SMGs) at z ~ 2.5; making them ideal candidates as systems in transition from an ultraluminous infrared galaxy phase to a sub-mm faint, unobscured, QSO. We detect 12CO(3-2) emission from both QSOs and we compare their baryonic, dynamical and SMBH masses to those of SMGs at the same epoch. We find that these far-infrared bright QSOs have similar dynamical but lower gas masses than SMGs. In particular we find that far-infrared bright QSOs have ~50+-23% less warm/dense gas than SMGs, which combined with previous results showing the QSOs lack the extended, cool reservoir of gas seen in SMGs, suggests that they are at a different evolutionary stage. This is consistent with the hypothesis that far-infrared bright QSOs represent a short (~1Myr) but ubiquitous phase in the transformation of dust obscured, gas-rich, starburst-dominated SMGs into unobscured, gas-poor, QSOs.

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arXiv2011

The LABOCA Survey of the Extended Chandra Deep Field South: Clustering of submillimetre galaxies

We present a measurement of the spatial clustering of submillimetre galaxies (SMGs) at z = 1-3. Using data from the 870 micron LESS survey, we employ a novel technique to measure the cross-correlation between SMGs and galaxies, accounting for the full probability distributions for photometric redshifts of the galaxies. From the observed projected two-point cross-correlation function we derive the linear bias and characteristic dark matter (DM) halo masses for the SMGs. We detect clustering in the cross-correlation between SMGs and galaxies at the > 4 sigma level. For the SMG autocorrelation we obtain r_0 = 7.7 (+1.8,-2.3) h^-1 Mpc, and derive a corresponding DM halo mass of log(M_halo [h^-1 M_sun]) = 12.8 (+0.3,-0.5). Based on the evolution of DM haloes derived from simulations, we show that that the z = 0 descendants of SMGs are typically massive (~2-3 L*) elliptical galaxies residing in moderate- to high-mass groups (log(M_halo [h^-1 M_sun]) = 13.3 (+0.3,-0.5). From the observed clustering we estimate an SMG lifetime of ~100 Myr, consistent with lifetimes derived from gas consumption times and star-formation timescales, although with considerable uncertainties. The clustering of SMGs at z ~ 2 is consistent with measurements for optically-selected quasi-stellar objects (QSOs), supporting evolutionary scenarios linking starbursts and QSOs. Given that SMGs reside in haloes of characteristic mass ~ 6 x 10^12 h^-1 M_sun, we demonstrate that the redshift distribution of SMGs can be described remarkably well by the combination of two effects: the cosmological growth of structure and the evolution of the molecular gas fraction in galaxies. We conclude that the powerful starbursts in SMGs likely represent a short-lived but universal phase in massive galaxy evolution, associated with the transition between cold gas-rich, star-forming galaxies and passively evolving systems. [Abridged]

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arXiv2011

Herschel-ATLAS: detection of a far-infrared population around galaxy clusters

We report the detection of a significant excess in the surface density of far-infrared sources from the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS) within ~1 Mpc of the centres of 66 optically-selected clusters of galaxies in the SDSS with ~0.25. From the analysis of the multiwavelength properties of their counterparts we conclude that the far-infrared emission is associated with dust-obscured star formation and/or active galactic nuclei within galaxies in the clusters themselves. The excess reaches a maximum at a radius of ~0.8 Mpc, where we find 1.0\pm0.3 S_250um>34 mJy sources on average per cluster above what would be expected for random field locations. If the far-infrared emission is dominated by star formation (as opposed to AGN) then this corresponds to an average star formation rate of ~7 M_sun/yr per cluster in sources with L_IR>5d10 L_sun. Although lensed sources make a negligible contribution to the excess signal, a fraction of the sources around the clusters could be gravitationally lensed, and we have identified a sample of potential cases of cluster-lensed Herschel sources that could be targeted in follow-up studies.

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arXiv2011

CO observations of high-z radio galaxies MRC 2104-242 and MRC 0943-242: spectral-line performance of the Compact Array Broadband Backend

We present the first 7-millimetre observations of two high-redshift, Lya-bright radio galaxies (MRC 2104-242 and MRC 0943-242) performed with the 2 x 2 GHz instantaneous bandwidth of the Compact Array Broadband Backend (CABB) at the Australia Telescope Compact Array (ATCA). The aim was to search for 12CO(1-0) emission in these systems and test the millimetre capabilities of CABB for performing spectral line observations at high redshifts. We show that the stable band and enhanced velocity coverage of CABB, combined with hybrid array configurations, provide the ATCA with excellent 7-mm capabilities that allow reliable searches for the ground transition of CO at high redshifts. In this paper we explicitly discuss the calibration procedures used to reach our results. We set a firm upper limit to the mass of molecular gas in MRC 2104-242 (z = 2.5) of M(H2) < 2 x 10^10 (alpha_x/0.8) M_sun. For MRC 0943-242 (z=2.9) we derive an upper limit of M(H2) < 6 x 10^10 (alpha_x/0.8) M_sun. We also find a tentative 3-sigma CO detection in the outer part of the giant Lya halo that surrounds MRC 0943-242. The 30-33 GHz radio continuum of MRC 2104-242 and MRC 0943-242 is reliably detected. Both radio sources show a spectral index of alpha ~ -1.5 between 1.4 and 30 GHz, with no evidence for spectral curvature within this range of frequencies.

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arXiv2011

The BLAST 250-micron selected galaxy population in GOODS-South

We identify and investigate the nature of the 20 brightest 250-micron sources detected by the BLAST within the central 150 sq. arcmin of the GOODS-South field. Aided by the available deep VLA radio imaging, reaching S_1.4 = 30 micro-Jy, we have identified radio counterparts for 17/20 of the 250-micron sources. The resulting enhanced positional accuracy of ~1 arcsec has then allowed us to exploit the deep multi-frequency imaging of GOODS-South to establish secure galaxy counterparts for the 17 radio-identified sources, and plausible galaxy candidates for the 3 radio-unidentified sources. Confusion is a serious issue for this deep BLAST 250-micron survey, due to the large size of the beam. Nevertheless, we argue that our chosen counterparts are significant, and often dominant contributors to the measured BLAST flux densities. For all of these 20 galaxies we have been able to determine spectroscopic (8) or photometric (12) redshifts. The result is the first `complete' redshift distribution for a deep 250-micron selected galaxy sample. This reveals that 250-micron surveys reaching detection limits of ~30 mJy contain not only low-redshift spirals/LIRGs, but also the extreme z~2 dust-enshrouded starburst galaxies previously discovered at sub-millimetre wavelengths. Based on their IRAC colours, we find that virtually all of the BLAST galaxy identifications appear better described as analogues of the M82 starburst galaxy, or Sc star-forming discs rather than highly obscured ULIRGs. Inspection of the LABOCA 870-micron imaging of the GOODS-South field yields detections of 7/11 of the z>1 BLAST sources, and reveals 250/870 flux-density ratios consistent with a standard 40K modified black-body fit with a dust emissivity index beta=1.5.

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arXiv2010

The LABOCA survey of the Extended Chandra Deep Field South - radio and mid-infrared counterparts to submillimetre galaxies

We present radio and infrared (3.6-24um) counterparts to submillimetre galaxies (SMGs) detected in the Extended Chandra Deep Field South with the LABOCA 870-um bolometer camera on the 12-m Atacama Pathfinder Experiment. Using the Very Large Array at 1.4GHz and Spitzer we have identified secure counterparts to 79 of the 126 SMGs (SNR>3.7, S_870>4.4mJy) in the field, 62 via their radio and/or 24-um emission, the remainder using a colour-flux cut on IRAC 3.6- and 5.8-um sources chosen to maximise the number of secure, coincident radio and 24-um counterparts. In constructing our radio catalogue, we have corrected for the effects of `flux boosting', then used the corrected flux densities to estimate the redshifts of the SMGs based on the radio/submm spectral indices. The effect of the boosting correction is to increase the median redshift by 0.2 resulting in a value of z=2.2 (+0.7-0.8) (1-sigma errors) for the secure radio counterparts, in agreement with other studies, both spectroscopic and photometric.

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arXiv2010

The LABOCA survey of the Extended Chandra Deep Field South: A photometric redshift survey of submillimetre galaxies

[abridged] We derive photometric redshifts from 17-band optical to mid-IR photometry of 74 robust counterparts to 68 of the 126 submillimetre galaxies (SMGs) selected at 870um by LABOCA observations in the ECDFS. The median photometric redshift of identified SMGs is z=2.2\pm0.1, the interquartile range is z=1.8-2.7 and we identify 10 (~15%) high-redshift (z>3) SMGs. We derive a simple redshift estimator for SMGs based on the 3.6 and 8um fluxes, which is accurate to Delta_z~0.4 for SMGs at z<4. A statistical analysis of sources around unidentified SMGs identifies a population of likely counterparts with a redshift distribution peaking at z=2.5\pm0.3, which likely comprises ~60% of the unidentified SMGs. This confirms that the bulk of the undetected SMGs are coeval with those detected in the radio/mid-IR. We conclude that ~15% of all the SMGs are below the flux limits of our survey and lie at z>3 and hence ~30% of all SMGs have z>3. We estimate that the full S_870um>4mJy SMG population has a median redshift of 2.5\pm0.6. In contrast to previous suggestions we find no significant correlation between S_870um and redshift. The median stellar mass of the SMGs derived from SED fitting is (9.2\pm0.9)x10^10Msun and the interquartile range is (4.7-14)x10^10Msun, although we caution that uncertainty in the star-formation histories results in a factor of ~5 uncertainty in these stellar masses. The median characteristic dust temperature of SMGs is 35.9\pm1.4K and the interquartile range is 28.5-43.3K. The infrared luminosity function shows that SMGs at z=2-3 typically have higher far-IR luminosities and luminosity density than those at z=1-2. This is mirrored in the evolution of the star-formation rate density (SFRD) for SMGs which peaks at z~2. The maximum contribution of bright SMGs to the global SFRD (~5% for SMGs with S_870um>4mJy; ~50% for SMGs with S_870um>1mJy) also occurs at z~2.

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arXiv2010

An excess of star-forming galaxies in the fields of high-redshift QSOs

We present submillimetre and mid-infrared imaging observations of five fields centred on quasi-stellar objects (QSOs) at 1.7<z<2.8. All 5 QSOs were detected previously at submillimetre wavelengths. At 850 (450) um we detect 17 (11) submillimetre galaxies (SMGs) in addition to the QSOs. The total area mapped at 850 um is ~28 arcmin^2 down to RMS noise levels of 1-2 mJy/beam, depending on the field. Integral number counts are computed from the 850 um data using the same analytical techniques adopted by `blank-field' submillimetre surveys. We find that the `QSO-field' counts show a clear excess over the blank-field counts at deboosted flux densities of 2-4 mJy; at higher flux densities the counts are consistent with the blank-field counts. Robust mid-infrared counterparts are identified for all four submillimetre detected QSOs and ~60 per cent of the SMGs. The mid-infrared colours of the QSOs are similar to those of the local ULIRG/AGN Mrk 231 if placed at 1<z<3 whilst most of the SMGs have colours very similar to those of the local ULIRG Arp 220 at 1<z<3. Mid-infrared diagnostics therefore find no strong evidence that the SMGs host buried AGN although we cannot rule out such a possibility. Taken together our results suggest that the QSOs sit in regions of the early universe which are undergoing an enhanced level of major star-formation activity, and should evolve to become similarly dense regions containing massive galaxies at the present epoch. Finally, we find evidence that the level of star-formation activity in individual galaxies appears to be lower around the QSOs than it is around more powerful radio-loud AGN at higher redshifts.

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arXiv2009

An AzTEC 1.1-mm Survey for ULIRGs in the field of the Galaxy Cluster MS 0451.6-0305

We have undertaken a deep (sigma~1.1 mJy) 1.1-mm survey of the z=0.54 cluster MS 0451.6-0305 using the AzTEC camera on the James Clerk Maxwell Telescope. We detect 36 sources with S/N>3.5 in the central 0.10 deg^2 and present the AzTEC map, catalogue and number counts. We identify counterparts to 18 sources (50%) using radio, mid-infrared, Spitzer IRAC and Submillimeter Array data. Optical, near- and mid-infrared spectral energy distributions are compiled for the 14 of these galaxies with detectable counterparts, which are expected to contain all likely cluster members. We then use photometric redshifts and colour selection to separate background galaxies from potential cluster members and test the reliability of this technique using archival observations of submillimetre galaxies. We find two potential MS 0451-03 members, which, if they are both cluster galaxies have a total star-formation rate (SFR) of ~100 solar masses per year -- a significant fraction of the combined SFR of all the other galaxies in MS 0451-03. We also examine the stacked rest-frame mid-infrared, millimetre and radio emission of cluster members below our AzTEC detection limit and find that the SFRs of mid-IR selected galaxies in the cluster and redshift-matched field populations are comparable. In contrast, the average SFR of the morphologically classified late-type cluster population is ~3 times less than the corresponding redshift-matched field galaxies. This suggests that these galaxies may be in the process of being transformed on the red-sequence by the cluster environment. Our survey demonstrates that although the environment of MS 0451-03 appears to suppress star-formation in late-type galaxies, it can support active, dust-obscured mid-IR galaxies and potentially millimetre-detected LIRGs.

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arXiv2009

AzTEC Half Square Degree Survey of the SHADES Fields -- I. Maps, Catalogues, and Source Counts

We present the first results from the largest deep extragalactic millimetre-wavelength survey undertaken to date. These results are derived from maps covering over 0.7 deg^2, made at 1.1mm, using the AzTEC continuum camera mounted on the James Clerk Maxwell Telescope. The maps were made in the two fields originally targeted at 0.85mm with SCUBA in the SHADES project, namely the Lockman Hole East (mapped to a depth of 0.9-1.3 mJy rms) and the Subaru XMM Deep Field (1.0-1.7 mJy rms). The wealth of existing and forthcoming deep multi-frequency data in these two fields will allow the bright mm source population revealed by these images to be explored in detail in subsequent papers. Here we present the maps themselves, a catalogue of 114 high-significance sub-millimetre galaxy detections, and a thorough statistical analysis leading to the most robust determination to date of the 1.1mm source number counts. Through careful comparison, we find that both the COSMOS and GOODS North fields, also imaged with AzTEC, contain an excess of mm sources over the new 1.1mm source-count baseline established here. In particular, our new AzTEC/SHADES results indicate that very luminous high-redshift dust enshrouded starbursts (S_{1.1} > 3 mJy) are 25-50% less common than would have been inferred from these smaller surveys, thus highlighting the potential roles of cosmic variance and clustering in such measurements. We compare number count predictions from recent models of the evolving mm/sub-mm source population to these SMG surveys, which provide important constraints for the ongoing refinement of semi-analytic and hydrodynamical models of galaxy formation, and find that all recent models over-predict the number of bright sub-millimetre galaxies found in this survey.

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arXiv2009

A 100-kpc inverse Compton X-ray halo around 4C60.07 at z=3.79

We analyse a 100-ks Chandra observation of the powerful radio galaxy, 4C60.07 at z=3.79. We identify extended X-ray emission with Lx~10^45 erg/s across a ~90-kpc region around the radio galaxy. The energetics of this X-ray halo and its morphological similarity to the radio emission from the galaxy suggest that it arises from inverse Compton (IC) scattering, by relativistic electrons in the radio jets, of Cosmic Microwave Background photons and potentially far-infrared photons from the dusty starbursts around this galaxy. The X-ray emission has a similar extent and morphology to the Ly-alpha halo around the galaxy, suggesting that it may be ionising this halo. Indeed we find that the GHz-radio and X-ray and Ly-alpha luminosities of the halo around 4C60.07 are identical to those of 4C41.17 (also at z=3.8) implying that these three components are linked by a single physical process. This is only the second example of highly-extended IC emission known at z>3, but it underlines the potential importance of IC emission in the formation of the most massive galaxies at high redshifts. In addition, we detect two X-ray luminous active galactic nuclei (AGN) within ~30kpc of the radio galaxy. These two companion AGN imply that the radio and starburst activity in the radio galaxy is triggered through multiple mergers of massive progenitors on a short timescale, ~100Myrs. These discoveries demonstrate the wealth of information which sensitive X-ray observations can yield into the formation of massive galaxies at high redshifts.

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arXiv2009

A LABOCA survey of the Extended Chandra Deep Field South - submillimeter properties of near-IR selected galaxies

Using the 330hr ESO-MPG 870-micron survey of the Extended Chandra Deep Field South (ECDF-S) obtained with the Large Apex BOlometer CAmera (LABOCA) on the Atacama Pathfinder EXperiment (APEX), we have carried out a stacking analysis at submillimeter (submm) wavelengths of a sample of 8266 near-infra-red (near-IR) selected (K_vega <= 20) galaxies, including 893 BzK galaxies, 1253 extremely red objects (EROs) and 737 distant red galaxies (DRGs), selected from the Multi-wavelength Survey by Yale-Chile (MUSYC). We measure average 870-micron fluxes of 0.20+-0.01mJy (20.0sigma), 0.45+-0.04mJy (11.3sigma), 0.42+-0.03mJy (14.0sigma), and 0.41+-0.04mJy (10.3sigma) for the K_vega <= 20, BzK, ERO and DRG samples, respectively. For the BzK, ERO and DRG subsamples, which overlap to some degree and are like to be at z ~ 1-2, this implies an average far-IR luminosity of ~2-6x10^{11} Lsolar and star formation rate of ~40-100Msolar. Splitting the BzK galaxies up into star-forming (sBzK) and passive (pBzK) galaxies, the former is significantly detected (0.48+-0.04mJy, 12.0sigma) while the latter is only marginally detected (0.27+-0.10mJy, 2.7sigma), thus confirming that the sBzK/pBzK criteria do isolate obscured, star forming and truly passive galaxies. The K_vega <= 20 galaxies are found to contribute with 6.6+-0.3Jy deg^{-2} (~15%) to the 870-micron extragalactic background light (EBL). sBzK and pBzK galaxies contribute 1.7+-0.2Jy deg^{-2} (~4%) and 0.2+-0.1 Jy deg^{-2} (< 0.5%) to the EBL. [Abridged]

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