We present ~0.6" resolution IRAM PdBI interferometry of eight submillimeter galaxies at z~2 to 3.4, where we detect continuum at 1mm and/or CO lines at 3 and 1 mm. The CO 3-2/4-3 line profiles in five of the sources are double-peaked, indicative of orbital motion either in a single rotating disk or of a merger of two galaxies. The millimeter line and continuum emission is compact; we marginally resolve the sources or obtain tight upper limits to their intrinsic sizes in all cases. The median FWHM diameter for these sources and the previously resolved sources, SMMJ023952-0136 and SMMJ140104+0252 is ≤0.5" (4 kpc). The compactness of the sources does not support a scenario where the far-IR/submm emission comes from 1 Based on observations obtained at the IRAM Plateau de Bure Interferometer (PdBI). IRAM is funded by the Centre National de la Recherche Scientifique (France), the Max-Planck Gesellschaft (Germany), and the Instituto Geografico Nacional (Spain). a cold (T<30 K), very extended dust distribution. These measurements clearly show that the submillimeter galaxies we have observed resemble scaled-up and more gas rich versions of the local Universe, ultra-luminous galaxy (ULIRG) population. Their central densities and potential well depths are much greater than in other z~2-3 galaxy samples studied so far. They are comparable to those of elliptical galaxies or massive bulges. The SMG properties fulfill the criteria of 'maximal' starbursts, in which most of the available initial gas reservoir of 10 10 -10 11 M is converted to stars on a time scale ~3-10 t dyn~a few 10 7 years.

In this paper, we present results from an Institut de Radio Astronomie Millimétrique (IRAM) Plateau de Bure millimetre‐wave Interferometer (PdBI) survey for carbon monoxide (CO) emission towards radio‐detected submillimetre galaxies (SMGs) with known optical and near‐infrared spectroscopic redshifts. Five sources in the redshift range z∼ 1–3.5 were detected, nearly doubling the number of SMGs detected in CO. We summarize the properties of all 12 CO‐detected SMGs, as well as six sources not detected in CO by our survey, and use this sample to explore the bulk physical properties of the submillimetre galaxy (SMG) population as a whole. The median CO line luminosity of the SMGs is 〈L′CO〉= (3.8 ± 2.0) × 1010 K km s‐1 pc2. Using a CO‐to‐H2 conversion factor appropriate for starburst galaxies, this corresponds to a molecular gas mass 〈M(H2)〉= (3.0 ± 1.6) × 1010 M⊙ within an ∼ 2 kpc radius, approximately 4 times greater than the most luminous local ultraluminous infrared galaxies (ULIRGs) but comparable to that of the most extreme high‐redshift radio galaxies (HzRGs) and quasi‐sellar objects (QSOs). The median CO FWHM linewidth is broad, 〈FWHM〉= 780 ± 320 km s−1, and the SMGs often have double‐peaked line profiles, indicative of either a merger or a disc. From their median gas reservoirs (∼ 3 × 1010 M⊙) and star formation rates (≳ 700 M⊙ yr−1), we estimate a lower limit on the typical gas‐depletion time‐scale of ≳ 40 Myr in SMGs. This is marginally below the typical age expected for the starbursts in SMGs and suggests that negative feedback processes may play an important role in prolonging the gas consumption time‐scale. We find a statistically significant correlation between the far‐infrared and CO luminosities of the SMGs, which extends the observed correlation for local ULIRGs to higher luminosities and higher redshifts. The non‐linear nature of the correlation implies that SMGs have higher far‐infrared to CO luminosity ratios and possibly higher star formation efficiencies (SFEs), than local ULIRGs. Assuming a typical CO source diameter of θ∼ 0.5 arcsec (D∼ 4 kpc), we estimate a median dynamical mass of 〈Mdyn〉≃ (1.2 ± 1.5) × 1011 M⊙ for the SMG sample. Both the total gas and stellar masses imply that SMGs are very massive systems, dominated by baryons in their central regions. The baryonic and dynamical properties of these systems mirror those of local giant ellipticals and are consistent with numerical simulations of the formation of the most massive galaxies. We have been able to impose a lower limit of ≳ 5 × 10−6 Mpc−3 to the comoving number density of massive galaxies in the redshift range z∼ 2–3.5, which is in agreement with results from recent spectroscopic surveys and the most recent model predictions.

We report subarcsecond resolution IRAM PdBI millimeter CO interferometry of four z $ 2 submillimeter galaxies (SMGs), and sensitive CO(3Y2) flux limits toward three z $ 2 UV/optically selected star-forming galaxies. The new data reveal for the first time spatially resolved CO gas kinematics in the observed SMGs. Two of the SMGs show double or multiple morphologies, with complex, disturbed gas motions. The other two SMGs exhibit CO velocity gradients of $500 km s À1 across 0.2 00 (1.6 kpc) diameter regions, suggesting that the star-forming gas is in compact, rotating disks. Our data provide compelling evidence that these SMGs represent extreme, short-lived ''maximum'' star-forming events in highly dissipative mergers of gas-rich galaxies. The resulting high-mass surface and volume densities of SMGs are similar to those of compact quiescent galaxies in the same redshift range and much higher than those in local spheroids. From the ratio of the comoving volume densities of SMGs and quiescent galaxies in the same mass and redshift ranges, and from the comparison of gas exhaustion timescales and stellar ages, we estimate that the SMG phase duration is about 100 Myr. Our analysis of SMGs and optically/ UV selected high-redshift starforming galaxies supports a ''universal'' Chabrier IMF as being valid over the star-forming history of these galaxies. We find that the 12 CO luminosity to total gas mass conversion factors at z $ 2Y3 are probably similar to those assumed at z $ 0. The implied gas fractions in our sample galaxies range from 20% to 50%.

We present the results from a survey for 12 CO emission in 40 luminous sub-millimetre galaxies (SMGs), with 850-µm fluxes of S 850µm = 4 − 20 mJy, conducted with the Plateau de Bure Interferometer. We detect 12 CO emission in 32 SMGs at z ∼ 1.2 -4.1, including 16 SMGs not previously published. Using multiple 12 CO line (J up = 2-7) observations, we derive a median spectral line energy distribution for luminous SMGs and use this to estimate a mean gas mass of (5.3 ± 1.0) × 10 10 M . We report the discovery of a fundamental relationship between 12 CO FWHM and 12 CO line luminosity in high-redshift starbursts, which we interpret as a natural consequence of the baryon-dominated dynamics within the regions probed by our observations. We use far-infrared luminosities to assess the star-formation efficiency in our SMGs, finding a steepening of the L CO -L FIR relation as a function of increasing 12 CO J up transition. We derive dynamical masses and molecular gas masses, and use these to determine the redshift evolution of the gas content of SMGs, finding that they do not appear to be significantly more gas rich than less vigorously star-forming galaxies at high redshifts. Finally, we collate X-ray observations, and study the interdependence of gas and dynamical properties of SMGs with their AGN activity and supermassive black hole masses (M BH ), finding that SMGs lie significantly below the local M BH -σ relation. We conclude that SMGs represent a class of massive, gas-rich ultraluminous galaxies with somewhat heterogeneous properties, ranging from starbursting disc-like systems with L∼ 10 12 L , to the most highly star-forming mergers in the Universe.

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 μm survey with ALMA (ALESS) has produced maps ∼3× deeper and with a beam area ∼200× 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 × 5 kpc for the rest-frame ∼300 μm 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 <10 kpc. As the first statistically reliable survey of SMGs, this will provide the basis for an unbiased multiwavelength study of SMG properties.

The ALESS survey has followed-up a sample of 122 sub-millimeter sources in the Extended Chandra Deep Field South at 870µm with ALMA, allowing to pinpoint the positions of sub-millimeter galaxies (SMGs) to ∼ 0.3 arcsec 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 SED modelling code that is optimized to fit these ultraviolet-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 (such as stellar masses, dust attenuation, star formation rates, dust masses) for the ALESS SMGs. We find that the ALESS SMGs have a median stellar mass M * = (8.9 ± 0.1) × 10 10 M ⊙ , median star formation rate SFR = 280 ± 70 M ⊙ yr −1 , median overall V -band dust attenuation A V = 1.9 ± 0.2 mag, median dust mass M dust = (5.6 ± 1.0) × 10 8 M ⊙ , and median average dust temperature T dust ≃ 40 K. We find that the average intrinsic spectral energy distribution of the ALESS SMGs resembles that of local ultra-luminous infrared galaxies in the infrared 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 (redshift, sub-millimeter flux, dust attenuation and total infrared luminosity), and we provide a new set of SMG templates that can be used to interpret other SMG observations. To put the ALESS SMGs into context, we compare their stellar masses and star formation rates with those of less actively star-forming galaxies at the same redshifts. We find that, at z ≃ 2, about half of the SMGs lie above the star-forming main sequence (with star formation rates three times larger than normal galaxies of the same stellar mass), while half are consistent with being at the high-mass end of the main sequence. At higher redshifts (z ≃ 3.5), the SMGs tend to have higher star formation rates and stellar masses, but the fraction of SMGs that lie significantly above the main sequence decreases to less than a third.

We report the results of a pilot study with the Expanded Very Large Array (EVLA) of 12 CO J = 1-0 emission from four submillimetre-selected galaxies at z = 2.2-2.5, each with an existing detection of 12 CO J = 3-2, one of which comprises two distinct spatial components. Using the EVLA's most compact configuration, we detect strong, broad [medians: 990 km s −1 full width at zero intensity; 540 km s −1 full width at half-maximum (FWHM)] J = 1-0 line emission from all of our targets -coincident in position and velocity with their J = 3-2 emission. The median linewidth ratio, σ 1-0 /σ 3-2 = 1.15 ± 0.06, suggests that the J = 1-0 is more spatially extended than the J = 3-2 emission, a situation confirmed by our maps which reveal velocity structure in several cases and typical sizes of ∼16 kpc FWHM. The median brightness temperature (T b ) ratio is r 3−2/1−0 = 0.55 ± 0.05, consistent with local galaxies with L IR > 10 11 L , noting that our value may be biased high because of the J = 3-2 based sample selection. Naively, this suggests gas masses roughly two times higher than estimates made using higher J transitions of CO, with the discrepancy due entirely to the difference in assumed T b ratio. We also estimate molecular gas masses using the 12 CO J = 1-0 line and the observed global T b ratios, assuming standard underlying T b ratios for the non-star-forming and star-forming gas phases as well as a limiting star formation efficiency for the latter in all systems, i.e. without calling upon X CO (≡ α). Using this new method, we find a median molecular gas mass of (2.5 ± 0.8) × 10 10 M , with a plausible range stretching up to three times higher. Even larger masses cannot be ruled out, but are not favoured by dynamical constraints: the median dynamical mass within R ∼ 7 kpc for our sample is (2.3 ± 1.4) × 10 11 M or ∼6 times more massive than UV-selected galaxies at this epoch. We examine the Schmidt-Kennicutt (S-K) relation for all the distant galaxy populations for which CO J = 1-0 or J = 2-1 data are available, finding small systematic differences between galaxy populations. These have previously been interpreted as evidence for different modes of star formation, but we argue that these differences are to be expected, given the still considerable uncertainties, certainly when considering the probable excitation biases due to the molecular lines used, and the possibility of sustained S-K offsets during the evolution of individual gas-rich systems. Finally, we discuss the morass of degeneracies surrounding molecular gas E-mail: rji@roe.ac.uk C 2011 The Authors Monthly Notices of the Royal Astronomical Society C 2011 RAS R. J. Ivison et al. mass estimates, the possibilities for breaking them, and the future prospects for imaging and studying cold, quiescent molecular gas at high redshifts.

We present a sensitive 870 μm survey of the Extended Chandra Deep Field South (ECDFS) combining 310 hr of observing time with the Large Apex BOlometer Camera (LABOCA) on the APEX telescope. The LABOCA ECDFS Submillimetre Survey (LESS) covers the full 30 × 30 field size of the ECDFS and has a uniform noise level of σ 870 μm ≈ 1.2 mJy beam −1. LESS is thus the largest contiguous deep submillimeter survey undertaken to date. The noise properties of our map show clear evidence that we are beginning to be affected by confusion noise. We present a catalog of 126 submillimeter galaxies (SMGs) detected with a significance level above 3.7σ , at which level we expect five false detections given our map area of 1260 arcmin 2. The ECDFS exhibits a deficit of bright SMGs relative to previously studied blank fields but not of normal star-forming galaxies that dominate the extragalactic background light (EBL). This is in line with the underdensities observed for optically defined high redshift source populations in the ECDFS (BzKs, DRGs, optically bright active galactic nucleus, and massive K-band-selected galaxies). The differential source counts in the full field are well described by a power law with a slope of α = −3.2, comparable to the results from other fields. We show that the shape of the source counts is not uniform across the field. Instead, it steepens in regions with low SMG density. Towards the highest overdensities we measure a source-count shape consistent with previous surveys. The integrated 870 μm flux densities of our source-count models down to S 870 μm = 0.5 mJy account for >65% of the estimated EBL from COBE measurements. We have investigated the clustering of SMGs in the ECDFS by means of a two-point correlation function and find evidence for strong clustering on angular scales <1 with a significance of 3.4σ. Assuming a power-law dependence for the correlation function and a typical redshift distribution for the SMGs we derive a characteristic angular clustering scale of θ 0 = 14 ± 7 and a spatial correlation length of r 0 = 13 ± 6 h −1 Mpc.