arXiv subjects

K. E. K. Coppin

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

At least 37 records · Page 2Linked to original sources

arXiv2017

The SCUBA-2 Cosmology Legacy Survey: Multi-wavelength Properties of ALMA-identified Submillimeter Galaxies in UKIDSS-UDS

We present a multi-wavelength analysis of 52 sub-millimeter galaxies (SMGs), identified using ALMA 870$μ$m continuum imaging in a pilot program to precisely locate bright SCUBA2-selected sub-mm sources in the UKIDSS Ultra Deep Survey (UDS) field. Using the available deep (especially near-infrared), panoramic imaging of the UDS field at optical-to-radio wavelengths we characterize key properties of the SMG population. The median photometric redshift of the bright ALMA/SCUBA-2 UDS (AS2UDS) SMGs that are detected in a sufficient number of wavebands to derive a robust photometric redshift is $z$=2.65$\pm$0.13. However, similar to previous studies, 27% of the SMGs are too faint at optical-to-near-infrared wavelengths to derive a reliable photometric redshift. Assuming that these SMGs lie at z$\gtrsim$3 raises the median redshift of the full sample to $z$=2.9$\pm$0.2. A subset of 23, unlensed, bright AS2UDS SMGs have sizes measured from resolved imaging of their rest-frame far-infrared emission. We show that the extent and luminosity of the far-infrared emission are consistent with the dust emission arising from regions that are optically thick, on average, at a wavelength of $λ_0$$\ge$75$μ$m (1-$σ$ dispersion of 55-90$μ$m). Using the dust masses derived from our optically-thick spectral energy distribution models we determine that these galaxies have a median hydrogen column density of $N_{H}$=9.8$_{-0.7}^{+1.4}$$\times$10$^{23}$cm$^{-2}$, or a corresponding median $V$-band obscuration of $A_\mathrm{v}$=540$^{+80}_{-40}$mag, averaged along the line of sight to the source of their restframe $\sim$200$μ$m emission. We discuss the implications of this extreme attenuation by dust for the multiwavelength study of dusty starbursts and reddening-sensitive tracers of star formation.

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arXiv2017

Evolution of cosmic star formation in the SCUBA-2 Cosmology Legacy Survey

We present a new exploration of the cosmic star-formation history and dust obscuration in massive galaxies at redshifts $0.5< z<6$. We utilize the deepest 450 and 850$μ$m imaging from SCUBA-2 CLS, covering 230arcmin$^2$ in the AEGIS, COSMOS and UDS fields, together with 100-250$μ$m imaging from Herschel. We demonstrate the capability of the T-PHOT deconfusion code to reach below the confusion limit, using multi-wavelength prior catalogues from CANDELS/3D-HST. By combining IR and UV data, we measure the relationship between total star-formation rate (SFR) and stellar mass up to $z\sim5$, indicating that UV-derived dust corrections underestimate the SFR in massive galaxies. We investigate the relationship between obscuration and the UV slope (the IRX-$β$ relation) in our sample, which is similar to that of low-redshift starburst galaxies, although it deviates at high stellar masses. Our data provide new measurements of the total SFR density (SFRD) in $M_\ast>10^{10}M_\odot$ galaxies at $0.5 10$. One third of this is accounted for by 450$μ$m-detected sources, while one fifth is attributed to UV-luminous sources (brighter than $L^\ast_{UV}$), although even these are largely obscured. By extrapolating our results to include all stellar masses, we estimate a total SFRD that is in good agreement with previous results from IR and UV data at $z\lesssim3$, and from UV-only data at $z\sim5$. The cosmic star-formation history undergoes a transition at $z\sim3-4$, as predominantly unobscured growth in the early Universe is overtaken by obscured star formation, driven by the build-up of the most massive galaxies during the peak of cosmic assembly.

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arXiv2016

A deep ALMA image of the Hubble Ultra Deep Field

We present the results of the first, deep ALMA imaging covering the full 4.5 sq arcmin of the Hubble Ultra Deep Field (HUDF) as previously imaged with WFC3/IR on HST. Using a mosaic of 45 pointings, we have obtained a homogeneous 1.3mm image of the HUDF, achieving an rms sensitivity of 35 microJy, at a resolution of 0.7 arcsec. From an initial list of ~50 >3.5sigma peaks, a rigorous analysis confirms 16 sources with flux densities S(1.3) > 120 microJy. All of these have secure galaxy counterparts with robust redshifts ( = 2.15), and 12 are also detected at 6GHz in new deep JVLA imaging. Due to the wealth of supporting data in this unique field, the physical properties of the ALMA sources are well constrained, including their stellar masses (M*) and UV+FIR star-formation rates (SFR). Our results show that stellar mass is the best predictor of SFR in the high-z Universe; indeed at z > 2 our ALMA sample contains 7 of the 9 galaxies in the HUDF with M* > 2 x 10^10 Msun and we detect only one galaxy at z > 3.5, reflecting the rapid drop-off of high-mass galaxies with increasing redshift. The detections, coupled with stacking, allow us to probe the redshift/mass distribution of the 1.3-mm background down to S(1.3) ~ 10 micro-Jy. We find strong evidence for a steep `main sequence' for star-forming galaxies at z ~ 2, with SFR \propto M* and a mean specific SFR = 2.2 /Gyr. Moreover, we find that ~85% of total star formation at z ~ 2 is enshrouded in dust, with ~65% of all star formation at this epoch occurring in high-mass galaxies (M* > 2 x 10^10 Msun), for which the average obscured:unobscured SF ratio is ~200. Finally, we combine our new ALMA results with the existing HST data to revisit the cosmic evolution of star-formation rate density; we find that this peaks at z ~ 2.5, and that the star-forming Universe transits from primarily unobscured to primarily obscured thereafter at z ~ 4.

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arXiv2016

Kiloparsec-scale dust disks in high-redshift luminous submillimeter galaxies

We present high-resolution (0.16$"$) 870um Atacama Large Millimeter/submillimeter Array (ALMA) imaging of 16 luminous (L_IR ~ 4 x 10^12 L_sun) submillimeter galaxies (SMGs) from the ALESS survey of the Extended Chandra Deep Field South. This dust imaging traces the dust-obscured star formation in these z~2.5 galaxies on ~1.3 kpc scales. The emission has a median effective radius of $R_e=0.24" \pm 0.02"$, corresponding to a typical physical size of $R_{e}=1.8\pm$0.2 kpc. We derive a median Sérsic index of $n=0.9\pm0.2$, implying that the dust emission is remarkably disk-like at the current resolution and sensitivity. We use different weighting schemes with the visibilities to search for clumps on 0.12$"$ (~1.0 kpc) scales, but we find no significant evidence for clumping in the majority of cases. Indeed, we demonstrate using simulations that the observed morphologies are generally consistent with smooth exponential disks, suggesting that caution should be exercised when identifying candidate clumps in even moderate S/N interferometric data. We compare our maps to comparable-resolution HST H$_{160}$-band images, finding that the stellar morphologies appear significantly more extended and disturbed, and suggesting that major mergers may be responsible for driving the formation of the compact dust disks we observe. The stark contrast between the obscured and unobscured morphologies may also have implications for SED fitting routines that assume the dust is co-located with the optical/near-IR continuum emission. Finally, we discuss the potential of the current bursts of star formation to transform the observed galaxy sizes and light profiles, showing that the $z\sim0$ descendants of these SMGs are expected to have stellar masses, effective radii, and gas surface densities consistent with the most compact massive (M_* ~ 1-2 x 10^11 M_sun) early-type galaxies observed locally.

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arXiv2016

A resolved map of the infrared excess in a Lyman Break Galaxy at z=3

We have observed the dust continuum of ten z=3.1 Lyman Break Galaxies with the Atacama Large Millimeter/Submillimeter Array at ~450 mas resolution in Band 7. We detect and resolve the 870um emission in one of the targets with an integrated flux density of S(870)=(192+/-57) uJy, and measure a stacked 3-sigma signal of S(870)=(67+/-23) uJy for the remaining nine. The total infrared luminosities estimated from full spectral energy distribution fits are L(8-1000um)=(8.4+/-2.3)x10^10 Lsun for the detection and L(8-1000um)=(2.9+/-0.9)x10^10 Lsun for the stack. With HST ACS I-band imaging we map the rest-frame UV emission on the same scale as the dust, effectively resolving the 'infrared excess' (IRX=L_FIR/L_UV) in a normal galaxy at z=3. Integrated over the galaxy we measure IRX=0.56+/-0.15, and the galaxy-averaged UV slope is beta=-1.25+/-0.03. This puts the galaxy a factor of ~10 below the IRX-beta relation for local starburst nuclei of Meurer et al. (1999). However, IRX varies by more than a factor of 3 across the galaxy, and we conclude that the complex relative morphology of the dust relative to UV emission is largely responsible for the scatter in the IRX-beta relation at high-z. A naive application of a Meurer-like dust correction based on the UV slope would dramatically over-estimate the total star formation rate, and our results support growing evidence that when integrated over the galaxy, the typical conditions in high-z star-forming galaxies are not analogous to those in the local starburst nuclei used to establish the Meurer relation.

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arXiv2016

The SCUBA-2 Cosmology Legacy Survey: galaxies in the deep 850-micron survey, and the star-forming `main sequence'

We investigate the properties of the galaxies selected from the deepest 850-micron survey undertaken to date with SCUBA-2 on the JCMT. This deep 850-micron imaging was taken in parallel with deep 450-micron imaging in the very best observing conditions as part of the SCUBA-2 Cosmology Legacy Survey. A total of 106 sources were uncovered at 850 microns from ~150, sq. arcmin in the centre of the COSMOS/UltraVISTA/CANDELS field, imaged to a typical rms depth of ~0.25 mJy. We utilise the wealth of available deep multi-frequency data to establish the complete redshift distribution for this sample, yielding = 2.38 +- 0.09, a mean redshift comparable with that derived for all but the brightest previous sub-mm samples. We have also been able to establish the stellar masses of the majority of the galaxy identifications, enabling us to explore their location on the star-formation-rate:stellar-mass (SFR:M*) plane. Crucially, our new deep sample reaches flux densities equivalent to SFR ~ 100 Msun/yr, enabling us to confirm that sub-mm galaxies form the high-mass end of the `main sequence' (MS) of star-forming galaxies at z > 1.5 (with a mean specific SFR of sSFR = 2.25 +- 0.19 /Gyr at z ~ 2.5). Our results are consistent with no significant flattening of the MS towards high masses at these redshifts, suggesting that reports of such flattening possibly arise from under-estimates of dust-enshrouded star-formation activity in massive star-forming galaxies. However, our findings add to the growing evidence that average sSFR rises only slowly at high redshift, resulting in log(sSFR) being an apparently simple linear function of the age of the Universe.

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arXiv2016

The SCUBA-2 Cosmology Legacy Survey: 850um maps, catalogues and number counts

We present a catalogue of nearly 3,000 submillimetre sources detected at 850um over ~5 square degrees surveyed as part of the James Clerk Maxwell Telescope (JCMT) SCUBA-2 Cosmology Legacy Survey (S2CLS). This is the largest survey of its kind at 850um, probing a meaningful cosmic volume at the peak of star formation activity and increasing the sample size of submillimetre galaxies selected at 850um by an order of magnitude. We describe the wide 850um survey component of S2CLS, which covers the key extragalactic survey fields: UKIDSS-UDS, COSMOS, Akari-NEP, Extended Groth Strip, Lockman Hole North, SSA22 and GOODS-North. The average 1-sigma depth of S2CLS is 1.2 mJy/beam, approaching the SCUBA-2 850um confusion limit, which we determine to be ~0.8 mJy/beam. We measure the single dish 850um number counts to unprecedented accuracy, reducing the Poisson errors on the differential counts to approximately 4% at S_850~3mJy. With several independent fields, we investigate field-to-field variance, finding that the number counts on 0.5-1 degree scales are generally within 50% of the S2CLS mean for S_850>3mJy, with scatter consistent with the Poisson and estimated cosmic variance uncertainties, although there is a marginal (2-sigma) density enhancement in the GOODS-North field. The observed number counts are in reasonable agreement with recent phenomenological and semi-analytic models. Finally, the large solid angle of S2CLS allows us to measure the bright-end counts: at S_850>10mJy there are approximately ten sources per square degree, and we detect the distinctive up-turn in the number counts indicative of the detection of local sources of 850um emission and strongly lensed high-redshift galaxies. Here we describe the data collection and reduction procedures and present calibrated maps and a catalogue of sources; these are made publicly available.

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arXiv2015

Cold Dust Emission from X-ray AGN in the SCUBA-2 Cosmology Legacy Survey: Dependence on Luminosity, Obscuration & AGN Activity

We study the 850um emission in X-ray selected AGN in the 2 sq-deg COSMOS field using new data from the SCUBA-2 Cosmology Legacy Survey. We find 19 850um bright X-ray AGN in a high-sensitivity region covering 0.89 sq-deg with flux densities of S850=4-10 mJy. The 19 AGN span the full range in redshift and hard X-ray luminosity covered by the sample - 0.7 1 X-ray AGN - S850=0.71+/-0.08mJy. We explore trends in the stacked 850um flux densities with redshift, finding no evolution in the average cold dust emission over the redshift range probed. For Type 1 AGN, there is no significant correlation between the stacked 850um flux and hard X-ray luminosity. However, in Type 2 AGN the stacked submm flux is a factor of 2 higher at high luminosities. When averaging over all X-ray luminosities, no significant differences are found in the stacked submm fluxes of Type 1 and Type 2 AGN as well as AGN separated on the basis of X-ray hardness ratios and optical-to-infrared colours. However, at log10(LX) >44.4, dependences in average submm flux on the optical-to-infrared colours become more pronounced. We argue that these high luminosity AGN represent a transition from a secular to a merger-driven evolutionary phase where the star formation rates and accretion luminosities are more tightly coupled. Stacked AGN 850um fluxes are compared to the stacked fluxes of a mass-matched sample of K-band selected non-AGN galaxies. We find that at 10.5<log10(M*/M0)<11.5, the non-AGN 850um fluxes are 1.5-2x higher than in Type 2 AGN of equivalent mass. We suggest these differences are due to the presence of massive dusty, red starburst galaxies in the K-band selected non-AGN sample, which are not present in optically selected catalogues covering a smaller area.

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arXiv2015

Early Science with the Large Millimeter Telescope: Observations of dust continuum and CO emission lines of cluster-lensed submillimetre galaxies at z=2.0-4.7

We present Early Science observations with the Large Millimeter Telescope, AzTEC 1.1 mm continuum images and wide bandwidth spectra (73-111 GHz) acquired with the Redshift Search Receiver, towards four bright lensed submillimetre galaxies identified through the Herschel Lensing Survey-snapshot and the SCUBA-2 Cluster Snapshot Survey. This pilot project studies the star formation history and the physical properties of the molecular gas and dust content of the highest redshift galaxies identified through the benefits of gravitational magnification. We robustly detect dust continuum emission for the full sample and CO emission lines for three of the targets. We find that one source shows spectroscopic multiplicity and is a blend of three galaxies at different redshifts (z=2.040, 3.252 and 4.680), reminiscent of previous high-resolution imaging follow-up of unlensed submillimetre galaxies, but with a completely different search method, that confirm recent theoretical predictions of physically unassociated blended galaxies. Identifying the detected lines as 12CO (J_up=2-5) we derive spectroscopic redshifts, molecular gas masses, and dust masses from the continuum emission. The mean H_2 gas mass of the full sample is (2.0 +- 0.2) x 10^11 M_sun/μ, and the mean dust mass is (2.0+-0.2) x 10^9 M_sun/μ, where μ=2-5 is the expected lens amplification. Using these independent estimations we infer a gas-to-dust ratio of δ_GDR=55-75, in agreement with other measurements of submillimetre galaxies. Our magnified high-luminosity galaxies fall on the same locus as other high-redshift submillimetre galaxies, extending the L'_CO - L_FIR correlation observed for local luminous and ultraluminous infrared galaxies to higher FIR and CO luminosities.

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arXiv2015

Resolved spectroscopy of gravitationally lensed galaxies: global dynamics and star-forming clumps on ~100pc scales

We present adaptive optics-assisted integral field spectroscopy around the Ha or Hb lines of 12 gravitationally lensed galaxies obtained with VLT/SINFONI, Keck/OSIRIS and Gemini/NIFS. We combine these data with previous observations and investigate the dynamics and star formation properties of 17 lensed galaxies at z = 1-4. Thanks to gravitational magnification of 1.4 - 90x by foreground clusters, effective spatial resolutions of 40 - 700 pc are achieved. The magnification also allows us to probe lower star formation rates and stellar masses than unlensed samples; our target galaxies feature dust-corrected SFRs derived from Ha or Hb emission of 0.8 - 40Msol/yr, and stellar masses M* ~ 4e8 - 6e10 Msol. All of the galaxies have velocity gradients, with 59% consistent with being rotating discs and a likely merger fraction of 29%, with the remaining 12% classed as 'undetermined.' We extract 50 star-forming clumps with sizes in the range 60pc - 1kpc from the Ha (or Hb) maps, and find that their surface brightnesses and their characteristic luminosities evolve to higher luminosities with redshift. We show that this evolution can be described by fragmentation on larger scales in gas-rich discs, and is likely to be driven by evolving gas fractions.

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arXiv2014

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$μ$m fluxes of $S_{870} < $3 mJy. With a surface brightness limit of $μ_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 Sérsic fit to the $H_{160}$ surface-brightness profiles we derive a median Sérsic 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$μ$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 Sérsic 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.

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arXiv2014

The SCUBA-2 Cosmology Legacy Survey: ALMA resolves the rest-frame far-infrared emission of sub-millimeter galaxies

We present high-resolution (0.3'') ALMA 870um imaging of 52 sub-millimeter galaxies (SMGs) in the Ultra Deep Survey (UDS) field and investigate the size and morphology of the sub-millimeter (sub-mm) emission on 2-10kpc scales. We derive a median intrinsic angular size of FWHM=0.30$\pm$0.04'' for the 23 SMGs in the sample detected at a signal-to-noise ratio (SNR) >10. Using the photometric redshifts of the SMGs we show that this corresponds to a median physical half-light diameter of 2.4$\pm$0.2kpc. A stacking analysis of the SMGs detected at an SNR <10 shows they have sizes consistent with the 870um-bright SMGs in the sample. We compare our results to the sizes of SMGs derived from other multi-wavelength studies, and show that the rest-frame ~250um sizes of SMGs are consistent with studies of resolved 12CO (J=3-2 to 7-6) emission lines, but that sizes derived from 1.4GHz imaging appear to be approximately two times larger on average, which we attribute to cosmic ray diffusion. The rest-frame optical sizes of SMGs are around four times larger than the sub-millimeter sizes, indicating that the star formation in these galaxies is compact relative to the pre-existing stellar distribution. The size of the starburst region in SMGs is consistent with the majority of the star formation occurring in a central region, a few kpc in extent, with a median star formation rate surface density of 90$\pm$30Msol/yr/kpc$^2$, which may suggest that we are witnessing an intense period of bulge growth in these galaxies.

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arXiv2014

The SCUBA-2 Cosmology Legacy Survey: the submillimetre properties of Lyman break galaxies at z=3-5

We present statistically significant detections at 850um of the Lyman Break Galaxy (LBG) population at z=3, 4, and 5 using data from the Submillimetre Common User Bolometer Array 2 (SCUBA-2) Cosmology Legacy Survey (S2CLS) in the United Kingdom Infrared Deep Sky Survey Ultra Deep Survey (UKIDSS-UDS) field. We employ a stacking technique to probe beneath the survey limit to measure the average 850um flux density of LBGs at z=3, 4, and 5 with typical ultraviolet luminosities of L(1700A)~10^29 erg/s/Hz. We measure 850um flux densities of (0.25 +/- 0.03, (0.41 +/- 0.06), and (0.88 +/- 0.23) mJy respectively, and find that they contribute at most 20 per cent to the cosmic far-infrared background at 850um. Fitting an appropriate range of spectral energy distributions to the z=3, 4, and 5 LBG stacked 24-850um fluxes, we derive infrared (IR) luminosities of L(8-1000um)~3.2, 5.5, and 11.0x10^11 Lsun (corresponding to star formation rates of ~50-200 Msun/yr) respectively. We find that the evolution in the IR luminosity density of LBGs is broadly consistent with model predictions for the expected contribution of luminous IR galaxy (LIRG) to ultraluminous IR galaxy (ULIRG) type systems at these epochs. We also see a strong positive correlation between stellar mass and IR luminosity. Our data are consistent with the main sequence of star formation showing little or no evolution from z=3 to 5. We have also confirmed that, for a fixed mass, the reddest LBGs (UV slope Beta -> 0) are indeed redder due to dust extinction, with SFR(IR)/SFR(UV) increasing by approximately an order of magnitude over -2<Beta<0 such that SFR(IR)/SFR(UV)~20 for the reddest LBGs. Furthermore, the most massive LBGs also tend to have higher obscured-to-unobscured ratio, hinting at a variation in the obscuration properties across the mass range.

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arXiv2014

A submillimeter galaxy illuminating its circumgalactic medium: Ly-alpha scattering in a cold, clumpy outflow

We report the detection at 850um of the central source in SSA22-LAB1, the archetypal Lyman-alpha Blob (LAB), a 100kpc-scale radio-quiet emission-line nebula at z=3.1. The flux density of the source, $S_{850}=4.6\pm1.1$mJy implies the presence of a galaxy, or group of galaxies, with a total luminosity of $L_{\rm IR}\approx10^{12}L_\odot$. The position of an active source at the center of a ~50kpc-radius ring of linearly polarized Ly-alpha emission detected by Hayes et al. (2011) suggests that the central source is leaking Ly-alpha photons preferentially in the plane of the sky, which undergo scattering in HI clouds at large galactocentric radius. The Ly-alpha morphology around the submillimeter detection is reminiscent of biconical outflow, and the average Ly-alpha line profiles of the two `lobes' are dominated by a red peak, expected for a resonant line emerging from a medium with a bulk velocity gradient that is outflowing relative to the line center. Taken together, these observations provide compelling evidence that the central active galaxy (or galaxies) is responsible for a large fraction of the extended Ly-alpha emission and morphology. Less clear is the history of the cold gas in the circumgalactic medium being traced by Ly-alpha: is it mainly pristine material accreting into the halo that has not yet been processed through an interstellar medium (ISM), now being blown back as it encounters an outflow, or does it mainly comprise gas that has been swept-up within the ISM and expelled from the galaxy?

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arXiv2014

Detection of molecular gas in an ALMA [CII]-identified Submillimetre Galaxy at z = 4.44

We present the detection of $^{12}$CO(2-1) in the $z = 4.44$ submillimetre galaxy ALESS65.1 using the Australia Telescope Compact Array. A previous ALMA study of submillimetre galaxies in the Extended Chandra Deep Field South determined the redshift of this optically and near-infrared undetected source through the measurement of [CII] 157.74 $μ$m emission. Using the luminosity of the $^{12}$CO(2-1) emission we estimate the gas mass to be $M_{\rm gas} \sim 1.7 \times 10^{10}$ ${\rm M}_\odot$. The gas depletion timescale of ALESS65.1 is $\sim$ 25 Myr, similar to other high redshift submillimetre galaxies and consistent with $z > 4$ SMGs being the progenitors of massive "red-and-dead" galaxies at $z > 2$. The ratio of the [CII], $^{12}$CO and far-infrared luminosities implies a strong far-ultraviolet field of $G_0 \sim 10^{3.25}$, 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 ULIRGs. The high ratio of $L_{\rm [CII]}/L_{\rm FIR} = 1.0 \times 10^{-3}$ observed in ALESS65.1, combined with $L_{\rm [CII]}/L_{\rm CO} \sim 2300$, is consistent with ALESS65.1 having more extended regions of intense star formation than local ULIRGs.

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arXiv2013

An ALMA survey of sub-millimeter galaxies in the Extended Chandra Deep Field South: Sub-millimeter properties of color-selected galaxies

We study the sub-mm properties of color-selected galaxies via a stacking analysis applied for the first time to interferometric data at sub-mm wavelengths. We base our study on 344 GHz ALMA continuum observations of ~20''-wide fields centered on 86 sub-mm sources detected in the LABOCA Extended Chandra Deep Field South Sub-mm Survey (LESS). We select various classes of galaxies (K-selected, star-forming sBzK galaxies, extremely red objects and distant red galaxies) according to their optical/NIR fluxes. We find clear, >10-sigma detections in the stacked images of all these galaxy classes. We include in our stacking analysis Herschel/SPIRE data to constrain the dust SED of these galaxies. We find that their dust emission is well described by a modified black body with Tdust~30 K and beta=1.6 and IR luminosities of (5-11)x10^{11} Lsun, or implied star formation rates of 75-140 Msun/yr. We compare our results with those of previous studies based on single-dish observations at 870 micron and find that our flux densities are a factor 2-3 higher than previous estimates. The discrepancy is observed also after removing sources individually detected in ALESS maps. We report a similar discrepancy by repeating our analysis on 1.4\,GHz observations of the whole ECDFS. Hence we find tentative evidence that galaxies that are associated in projected and redshift space with sub-mm bright sources are brighter than the average population. Finally, we put our findings in the context of the cosmic star formation rate density as a function of redshift.

astro-ph.CO↗

arXiv2013

An ALMA Survey of Submillimeter Galaxies in the Extended Chandra Deep Field South: The AGN Fraction and X-ray Properties of Submillimeter Galaxies

The large gas and dust reservoirs of submm galaxies (SMGs) could potentially provide ample fuel to trigger an Active Galactic Nucleus (AGN), but previous studies of the AGN fraction in SMGs have been controversial largely due to the inhomogeneity and limited angular resolution of the available submillimeter surveys. Here we set improved constraints on the AGN fraction and X-ray properties of the SMGs with ALMA and Chandra observations in the Extended Chandra Deep Field-South (E-CDF-S). This study is the first among similar works to have unambiguously identified the X-ray counterparts of SMGs; this is accomplished using the fully submm-identified, statistically reliable SMG catalog with 99 SMGs from the ALMA LABOCA E-CDF-S Submillimeter Survey (ALESS). We found 10 X-ray sources associated with SMGs (median redshift z = 2.3), of which 8 were identified as AGNs using several techniques that enable cross-checking. The other 2 X-ray detected SMGs have levels of X-ray emission that can be plausibly explained by their star-formation activity. 6 of the 8 SMG-AGNs are moderately/highly absorbed, with N_H > 10e23 cm-2. An analysis of the AGN fraction, taking into account the spatial variation of X-ray sensitivity, yields an AGN fraction of 17+16-6% for AGNs with rest-frame 0.5-8 keV absorption-corrected luminosity >7.8x10e42 erg s-1; we provide estimated AGN fractions as a function of X-ray flux and luminosity. ALMA's high angular resolution also enables direct X-ray stacking at the precise positions of SMGs for the first time, and we found 4 potential SMG-AGNs in our stacking sample.

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arXiv2013

The SCUBA-2 Cosmology Legacy Survey: demographics of the 450 μm-population

We investigate the multi-wavelength properties of a sample of 450-μm selected sources from the SCUBA-2 Cosmology Legacy Survey (S2CLS). A total of 69 sources were identified above 4σ in deep SCUBA-2 450-μm observations overlapping the UDS and COSMOS fields and covering 210 sq. arcmin to a typical depth of σ450=1.5 mJy. Reliable cross identification are found for 58 sources (84 per cent) in Spitzer and Hubble Space Telescope WFC3/IR data. The photometric redshift distribution (dN/dz) of 450μm-selected sources is presented, showing a broad peak in the redshift range 1 =10^12 +/- 0.8 L_sol, =42 +/- 11 K and <β_D>=1.6 +/- 0.5, respectively. The relationship between these SED parameters and the physical properties of galaxies is investigated, revealing correlations between T_D and LIR and between β_D and both stellar mass and effective radius. The connection between star formation rate and stellar mass is explored, with 24 per cent of 450 μm sources found to be ``star-bursts'', i.e. displaying anomalously high specific SFRs. However, both the number density and observed properties of these ``star-burst'' galaxies are found consistent with the population of normal star-forming galaxies.

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