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Register a new userAn ALMA survey of the SCUBA-2 CLS UDS field: Physical properties of 707 Sub-millimetre Galaxies
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We analyse the physical properties of a large, homogeneously selected sample of ALMA-located sub-mm galaxies (SMGs). This survey, AS2UDS, identified 707 SMGs across the ~1 sq.deg. field, including ~17 per cent, which are undetected at $K$>~25.7 mag. We interpret their ultraviolet-to-radio data using MAGPHYS and determine a median redshift of z=2.61+-0.08 (1$sigma$ range of z=1.8-3.4) with just ~6 per cent at z>4. Our survey provides a sample of massive dusty galaxies at z>~1, with median dust and stellar masses of $M_d$=(6.8+-0.3)x10$^{8}$M$_odot$ (thus, gas masses of ~10$^{11}$M$_odot$) and $M_ast=$(1.26+-0.05)x10$^{11}$M$_odot$. We find no evolution in dust temperature at a constant far-infrared luminosity across z~1.5-4. The gas mass function of our sample increases to z~2-3 and then declines at z>3. The space density and masses of SMGs suggest that almost all galaxies with $M_ast$>~3x10$^{11}$M$_odot$ have passed through an SMG-like phase. The redshift distribution is well fit by a model combining evolution of the gas fraction in halos with the growth of halo mass past a threshold of $M_h$~6x10$^{12}$M$_odot$, thus SMGs may represent the highly efficient collapse of gas-rich massive halos. We show that SMGs are broadly consistent with simple homologous systems in the far-infrared, consistent with a centrally illuminated starburst. Our study provides strong support for an evolutionary link between the active, gas-rich SMG population at z>1 and the formation of massive, bulge-dominated galaxies across the history of the Universe.
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We present an ALMA study of the ~180 brightest sources in the SCUBA-2 map of the COSMOS field from the S2COSMOS survey, as a pilot study for AS2COSMOS - a full survey of the ~1,000 sources in this field. In this pilot we have obtained 870-um continuum maps of an essentially complete sample of the brightest 182 sub-millimetre sources (S_850um=6.2mJy) in COSMOS. Our ALMA maps detect 260 sub-millimetre galaxies (SMGs) spanning a range in flux density of S_870um=0.7-19.2mJy. We detect more than one SMG counterpart in 34+/-2 per cent of sub-millimetre sources, increasing to 53+/-8 per cent for SCUBA-2 sources brighter than S_850um>12mJy. We estimate that approximately one-third of these SMG-SMG pairs are physically associated (with a higher rate for the brighter secondary SMGs, S_870um>3mJy), and illustrate this with the serendipitous detection of bright [CII] 157.74um line emission in two SMGs, AS2COS0001.1 & 0001.2 at z=4.63, associated with the highest significance single-dish source. Using our source catalogue we construct the interferometric 870um number counts at S_870um>6.2mJy. We use the extensive archival data of this field to construct the multiwavelength spectral energy distribution of each AS2COSMOS SMG, and subsequently model this emission with MAGPHYS to estimate their photometric redshifts. We find a median photometric redshift for the S_870um>6.2mJy AS2COSMOS sample of z=2.87+/-0.08, and clear evidence for an increase in the median redshift with 870-um flux density suggesting strong evolution in the bright-end of the 870um luminosity function.
We present the catalogue and properties of sources in AS2UDS, an 870-$mu$m continuum survey with the Atacama Large Millimetre/sub-millimetre Array (ALMA) of 716 single-dish sub-millimetre sources detected in the UKIDSS/UDS field by the SCUBA-2 Cosmology Legacy Survey. In our sensitive ALMA follow-up observations we detect 708 sub-millimetre galaxies (SMGs) at $>$,4.3$sigma$ significance across the $sim$,1-degree diameter field. We combine our precise ALMA positions with the extensive multi-wavelength coverage in the UDS field to fit the spectral energy distributions of our SMGs to derive a median redshift of $z_{rm phot}=$,2.61$pm$0.09. This large sample reveals a statistically significant trend of increasing sub-millimetre flux with redshift suggestive of galaxy downsizing. 101 ALMA maps do not show a $>$,4.3$sigma$ SMG, but we demonstrate from stacking {it Herschel} SPIRE observations at these positions, that the vast majority of these blank maps correspond to real single-dish sub-millimetre sources. We further show that these blank maps contain an excess of galaxies at $z_{rm phot}=$,1.5--4 compared to random fields, similar to the redshift range of the ALMA-detected SMGs. In addition, we combine X-ray and mid-infrared active galaxy nuclei activity (AGN) indicators to yield a likely range for the AGN fraction of 8--28,% in our sample. Finally, we compare the redshifts of this population of high-redshift, strongly star-forming galaxies with the inferred formation redshifts of massive, passive galaxies being found out to $zsim$,2, finding reasonable agreement -- in support of an evolutionary connection between these two classes of massive galaxy.
We present an analysis of the morphology and profiles of the dust continuum emission in 153 bright sub-millimetre galaxies (SMGs) detected with ALMA at S/N ratios of $>8$ in high-resolution $0.18$ ($sim1$kpc) 870$mu$m maps. We measure sizes, shapes and light profiles for the rest-frame far-infrared emission from these luminous star-forming systems and derive a median effective radius ($R_e$) of $0.10pm0.04$ for our sample with a median flux of $S_{870}=5.6pm0.2$mJy. We find that the apparent axial ratio ($b/a$) distribution of the SMGs peaks at $b/asim0.63pm0.24$ and is best described by triaxial morphologies, while their emission profiles are best fit by a Sersic model with $nsimeq1.0pm0.1$, similar to exponential discs. This combination of triaxiality and $nsim1$ Sersic index are characteristic of bars and we suggest that the bulk of the 870$mu$m dust continuum emission in the central $sim2$kpc of these galaxies arises from bar-like structures. By stacking our 870$mu$m maps we recover faint extended dust continuum emission on $sim4$kpc scales which contributes $13pm1$% of the total 870$mu$m emission. The scale of this extended emission is similar to that seen for the molecular gas and rest-frame optical light in these systems, suggesting that it represents an extended dust and gas disc at radii larger than the more active bar component. Including this component in our estimated size of the sources we derive a typical effective radius of $simeq0.15pm0.05$ or $1.2pm0.4$kpc. Our results suggest that kpc-scale bars are ubiquitous features of high star-formation rate systems at $zgg1$, while these systems also contain fainter and more extended gas and stellar envelopes. We suggest that these features, seen some $10-12$Gyrs ago, represent the formation phase of the earliest galactic-scale components: stellar bulges.
We report the first results of AS2UDS: an 870 $mu$m continuum survey with the Atacama Large Millimeter/Submillimeter Array (ALMA) of a total area of $sim$ 50 arcmin$^2$ comprising a complete sample of 716 submillimeter sources drawn from the SCUBA-2 Cosmology Legacy Survey (S2CLS) map of the UKIDSS/UDS field. The S2CLS parent sample covers a 0.96 degree$^2$ field at $sigma_{850}=0.90pm0.05$ mJy beam$^{-1}$. Our deep, high-resolution ALMA observations with $sigma_{rm 870}sim$ 0.25 mJy and a 0.15--0.30 FWHM synthesized beam, provide precise locations for 695 submillimetre galaxies (SMGs) responsible for the submillimeter emission corresponding to 606 sources in the low resolution, single-dish map. We measure the number counts of SMGs brighter than $S_{rm 870}geq$ 4 mJy, free from the effects of blending and show that the normalisation of the counts falls by 28 $pm$ 2% in comparison to the SCUBA-2 parent sample, but that the shape remains unchanged. We determine that 44$^{+16}_{-14}$% of the brighter single-dish sources with $S_{850}geq$ 9 mJy consist of a blend of two or more ALMA-detectable SMGs brighter than $S_{870}sim$ 1 mJy (corresponding to a galaxy with a total-infrared luminosity of $L_{IR}geq$ 10$^{12}$ L$_odot$), in comparison to 28 $pm$ 2% for the single-dish sources at $S_{rm 850}geq$ 5 mJy. Using the 46 single-dish submillimeter sources that contain two or more ALMA-detected SMGs with photometric redshifts, we show that there is a significant statistical excess of pairs of SMGs with similar redshifts ($<$1% probability of occurring by chance), suggesting that at least 30% of these blends arise from physically associated pairs of SMGs.
We present an analysis of the spatial clustering of a large sample of high-resolution, interferometically identified, submillimetre galaxies (SMGs). We measure the projected cross-correlation function of ~350 SMGs in the UKIDSS Ultra Deep-Survey Field across a redshift range of $z=1.5-3$ utilising a method that incorporates the uncertainties in the redshift measurements for both the SMGs and cross-correlated galaxies through sampling their full probability distribution functions. By measuring the absolute linear bias of the SMGs we derive halo masses of $log_{10}(M_{rm halo}[{h^{-1},rm M_{odot}}])sim12.8$ with no evidence of evolution in the halo masses with redshift, contrary to some previous work. From considering models of halo mass growth rates we predict that the SMGs will reside in haloes of mass $log_{10}(M_{rm halo}[{h^{-1},rm M_{odot}}])sim13.2$ at $z=0$, consistent with the expectation that the majority of $z=1.5-3$ SMGs will evolve into present-day spheroidal galaxies. Finally, comparing to models of stellar-to-halo mass ratios, we show that SMGs may correspond to systems that are maximally efficient at converting their gas reservoirs into stars. We compare them to a simple model for gas cooling in halos that suggests that the unique properties of the SMG population, including their high levels of star-formation and their redshift distribution, are a result of the SMGs being the most massive galaxies that are still able to accrete cool gas from their surrounding intragalactic medium.
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