We present evidence for very high gas fractions and extended molecular gas reservoirs in normal, near-infrared selected (BzK) galaxies at z∼1.5. Our results are based on multi-configuration CO[2-1] observations obtained at the IRAM Plateau de Bure Interferometer. All six star forming galaxies observed were detected at high significance. High spatial resolution observations resolve the CO emission in four of them, implying sizes of the gas reservoirs of order of 6-11 kpc and suggesting the presence of ordered rotation. The galaxies have UV morphologies consistent with clumpy, unstable disks, and UV sizes that are consistent with those measured in CO. The star formation efficiencies are homogeneously low within the sample and similar to those of local spirals -the resulting gas depletion times are ∼ 0.5 Gyr, much higher than what is seen in high-z submm galaxies and quasars. The CO luminosities can be predicted to within 0.15 dex from the observed star formation rates and stellar masses, implying a tight correlation of the gas mass with these quantities. We use new dynamical models of clumpy disk galaxies to derive dynamical masses for our sample. These models are able to reproduce the peculiar spectral line shapes of the CO emission. After accounting for the stellar and dark matter masses we derive molecular gas reservoirs with masses of 0.4-1.2×10 11 M ⊙ . The implied conversion (CO luminosity-to-gas mass) factor is very high: α CO = 3.6 ± 0.8, consistent with a Galactic conversion factor but four times higher than that of local ultra-luminous IR galaxies that is typically used for high-redshift objects. The gas mass in these galaxies is comparable to or larger than the stellar mass, and the gas accounts for an impressive 50-65% of the baryons within the galaxies' half light radii. We are thus witnessing truly gasdominated galaxies at z ∼ 1.5, a finding that explains the high specific SFRs observed for z > 1 galaxies. The BzK galaxies can be viewed as scaled-up versions of local disk galaxies, with low efficiency star formation taking place inside extended, low excitation gas disks. These galaxies are markedly different than local ULIRGs and high-z submm galaxies and quasars, where higher excitation and more compact gas is found.

We present evidence that bona fide disks and starburst systems occupy distinct regions in the gas mass versus star formation (SF) rate plane, both for the integrated quantities and for the respective surface densities. This result is based on CO observations of galaxy populations at low and high redshifts, and on the current consensus for the CO luminosity to gas mass conversion factors. The data suggest the existence of two different star formation regimes: a long-lasting mode for disks and a more rapid mode for starbursts, the latter probably occurring during major mergers or in dense nuclear SF regions. Both modes are observable over a large range of SF rates. The detection of CO emission from distant near-IR selected galaxies reveals such bimodal behavior for the first time, as they allow us to probe gas in disk galaxies with much higher SF rates than are seen locally. The different regimes can potentially be interpreted as the effect of a top-heavy IMF in starbursts. However, we favor a different physical origin related to the fraction of molecular gas in dense clouds. The IR luminosity to gas mass ratio (i.e., the SF efficiency) appears to be inversely proportional to the dynamical (rotation) timescale. Only when accounting for the dynamical timescale, a universal SF law is obtained, suggesting a direct link between global galaxy properties and the local SF rate.

Using data from the mid-infrared to millimeter wavelengths for individual galaxies and for stacked ensembles at 0.5 < z < 2, we derive robust estimates of dust masses (M dust ) for main-sequence (MS) galaxies, which obey a tight correlation between star formation rate (SFR) and stellar mass (M * ), and for starbursting galaxies that fall outside that relation. Exploiting the correlation of gas-to-dust mass with metallicity (M gas /M dust -Z), we use our measurements to constrain the gas content, CO-to-H 2 conversion factors (α CO ), and star formation efficiencies (SFE) of these distant galaxies. Using large statistical samples, we confirm that α CO and SFE are an order of magnitude higher and lower, respectively, in MS galaxies at high redshifts compared to the values of local galaxies with equivalently high infrared luminosities (L IR > 10 12 L ). For galaxies within the MS, we show that the variations of specific star formation rates (sSFRs = SFR/M * ) are driven by varying gas fractions. For relatively massive galaxies like those in our samples, we show that the hardness of the radiation field, U , which is proportional to the dust-mass-weighted luminosity (L IR /M dust ) and the primary parameter defining the shape of the IR spectral energy distribution (SED), is equivalent to SFE/Z. For MS galaxies with stellar mass log(M * /M ) 9.7 we measure this quantity, U , showing that it does not depend significantly on either the stellar mass or the sSFR. This is explained as a simple consequence of the existing correlations between SFR-M * , M * -Z, and M gas -SFR. Instead, we show that U (or equally L IR /M dust ) does evolve, with MS galaxies having harder radiation fields and thus warmer temperatures as redshift increases from z = 0 to 2, a trend that can also be understood based on the redshift evolution of the M * -Z and SFR-M * relations. These results motivate the construction of a universal set of SED templates for MS galaxies that are independent of their sSFR or M * but vary as a function of redshift with only one parameter, U .

We present the deepest 100 to 500 μm far-infrared observations obtained with the Herschel Space Observatory as part of the GOODS-Herschel key program, and examine the infrared (IR) 3-500 μm spectral energy distributions (SEDs) of galaxies at 0 < z < 2.5, supplemented by a local reference sample from IRAS, ISO, Spitzer, and AKARI data. We determine the projected star formation densities of local galaxies from their radio and mid-IR continuum sizes. We find that the ratio of total IR luminosity to rest-frame 8 μm luminosity, IR8 (≡L tot IR /L 8 ), follows a Gaussian distribution centered on IR8 = 4 (σ = 1.6) and defines an IR main sequence for star-forming galaxies independent of redshift and luminosity. Outliers from this main sequence produce a tail skewed toward higher values of IR8. This minority population (<20%) is shown to consist of starbursts with compact projected star formation densities. IR8 can be used to separate galaxies with normal and extended modes of star formation from compact starbursts with high-IR8, high projected IR surface brightness (Σ IR > 3 × 10 10 L kpc −2 ) and a high specific star formation rate (i.e., starbursts). The rest-frame, UV-2700 Å size of these distant starbursts is typically half that of main sequence galaxies, supporting the correlation between star formation density and starburst activity that is measured for the local sample. Locally, luminous and ultraluminous IR galaxies, (U)LIRGs (L tot IR ≥ 10 11 L ), are systematically in the starburst mode, whereas most distant (U)LIRGs form stars in the "normal" main sequence mode. This confusion between two modes of star formation is the cause of the so-called "mid-IR excess" population of galaxies found at z > 1.5 by previous studies. Main sequence galaxies have strong polycyclic aromatic hydrocarbon (PAH) emission line features, a broad far-IR bump resulting from a combination of dust temperatures (T dust ∼ 15-50 K), and an effective T dust ∼ 31 K, as derived from the peak wavelength of their infrared SED. Galaxies in the starburst regime instead exhibit weak PAH equivalent widths and a sharper far-IR bump with an effective T dust ∼ 40 K. Finally, we present evidence that the mid-to-far IR emission of X-ray active galactic nuclei (AGN) is predominantly produced by star formation and that candidate dusty AGNs with a power-law emission in the mid-IR systematically occur in compact, dusty starbursts. After correcting for the effect of starbursts on IR8, we identify new candidates for extremely obscured AGNs.

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 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.

We present the first photometric redshift distribution for a large sample of 870 µm SMGs with robust identifications based on observations with ALMA. In our analysis we consider 96 SMGs in the ECDFS, 77 of which have 4-19 band photometry. We model the SEDs for these 77 SMGs, deriving a median photometric redshift of z phot = 2.3 ± 0.1. The remaining 19 SMGs have insufficient photometry to derive photometric redshifts, but a stacking analysis of Herschel observations confirms they are not spurious. Assuming that these SMGs have an absolute H-band magnitude distribution comparable to that of a complete sample of z ∼ 1-2 SMGs, we demonstrate that they lie at slightly higher redshifts, raising the median redshift for SMGs to z phot = 2.5 ± 0.2. Critically we show that the proportion of galaxies undergoing an SMG-like phase at z ≥ 3 is at most 35 ± 5 per cent of the total population. We derive a median stellar mass of M ⋆ = (8 ± 1) × 10 10 M ⊙ , although there are systematic uncertainties of up to 5 × for individual sources. Assuming that the star formation activity in SMGs has a timescale of ∼ 100 Myr we show that their descendants at z ∼ 0 would have a space density and M H distribution which are in good agreement with those of local ellipticals. In addition the inferred mass-weighted ages of the local ellipticals broadly agree with the look-back times of the SMG events. Taken together, these results are consistent with a simple model that identifies SMGs as events which form most of the stars seen in the majority of luminous elliptical galaxies at the present day.