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We study the evolution of the radio spectral index and far-infrared/radio correlation (FRC) across the star-formation rate - stellarmasse (i.e. SFR-M*) plane up to z ~ 2.We start from a stellar-mass-selected sample of galaxies with reliable SFR and redshift estimates. We then grid the SFR-M* plane in several redshift ranges and measure the infrared luminosity, radio luminosity, radio spectral index, and ultimately the FRC index (i.e. qFIR) of each SFR-M*- z bin. The infrared luminosities of our SFR-M*- z bins are estimated using their stacked far-infrared flux densities inferred from observations obtained with the Herschel Space Observatory. Their radio luminosities and radio spectral indices (i.e. α, where Sv α v-α) are estimated using their stacked 1.4 GHz and 610MHz flux densities from the Very Large Array and Giant Metre-wave Radio Telescope, respectively. Our far-infrared and radio observations include the most widely studied blank extragalactic fields - GOODS-N, GOODS-S, ECDFS, and COSMOS - covering a total sky area of ~2.0 deg². Using this methodology, we constrain the radio spectral index and FRC index of star-forming galaxies with M* > 1010 M⊙ and 0 < z < 2.3. We find that α1.4 GHz610MHz does not evolve significantly with redshift or with the distance of a galaxy with respect to the main sequence (MS) of the SFR-M* plane (i.e. △log(SSFR)MS = log[SSFR(galaxy)/SSFRMS(M*, z)]). Instead, star-forming galaxies have a radio spectral index consistent with a canonical value of 0.8, which suggests that their radio spectra are dominated by non-thermal optically thin synchrotron emission. We find that the FRC index, qFIR, displays a moderate but statistically significant redshift evolution as qFIR(z) = (2.35±0.08)×(1+z)-0.12 ± 0.04, consistent with some previous literature. Finally, we find no significant correlation between qFIR and ?log(SSFR)MS, though a weak positive trend, as observed in one of our redshift bins (i.e. △[qFIR]/△[△log(SSFR)MS] = 0.22 ± 0.07 at 0.5 < z < 0.8), cannot be firmly ruled out using our dataset. [ABSTRACT FROM AUTHOR]

ABSTRACT We report new, sensitive observations of two z ∼ 3-3.5 far-infrared-luminous radio galaxies, 6C 1909+72 and B3 J2330+3927, in the 12CO J = 1−0 transition with the Karl Jansky Very Large Array and at 100-500 m using Herschel, alongside new and archival 12CO J = 4−3 observations from the Plateau de Bure Interferometer. We introduce a new colour-colour diagnostic plot to constrain the redshifts of several distant, dusty galaxies in our target fields. A bright SMG near 6C 1909+72 likely shares the same node or filament as the signpost active galactic nuclei (AGN), but it is not detected in 12CO despite ∼20 000 km s−1 of velocity coverage. Also in the 6C 1909+72 field, a large, red dust feature spanning ≈500 kpc is aligned with the radio jet. We suggest several processes by which metal-rich material may have been transported, favouring a collimated outflow reminiscent of the jet-oriented metal enrichment seen in local cluster environments. Our interferometric imaging reveals a gas-rich companion to B3 J2330+3927; indeed, all bar one of the eight z ≳ 2 radio galaxies (or companions) detected in 12CO provide some evidence that starburst activity in radio-loud AGN at high redshift is driven by the interaction of two or more gas-rich systems in which a significant mass of stars has already formed, rather than via steady accretion of cold gas from the cosmic web. We find that the 12CO brightness temperature ratios in radio-loud AGN host galaxies are significantly higher than those seen in similarly intense starbursts where AGN activity is less pronounced. Our most extreme example, where [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate the potential of submm-mm and submm-mm-radio photometric redshifts using a sample of mm-selected sources as seen at 250, 350 and 500μm by the SPIRE instrument on Herschel. From a sample of 63 previously identified mm sources with reliable radio identifications in the Great Observatories Origins Deep Survey North and Lockman Hole North fields, 46 (73 per cent) are found to have detections in at least one SPIRE band. We explore the observed submm/mm colour evolution with redshift, finding that the colours of mm sources are adequately described by a modified blackbody with constant optical depth τ= (ν/ nu0)β, where β=+1.8 and ν0= c/100 μm. We find a tight correlation between dust temperature and IR luminosity. Using a single model of the dust temperature and IR luminosity relation, we derive photometric redshift estimates for the 46 SPIRE-detected mm sources. Testing against the 22 sources with known spectroscopic or good quality optical/near-IR photometric redshifts, we find submm/mm photometric redshifts offer a redshift accuracy of |Δ z|/(1 + z) = 0.16 (〈|Δ z|〉= 0.51). Including constraints from the radio-far-IR correlation, the accuracy is improved to |Δ z|/(1 + z) = 0.15 (〈|Δ z|〉= 0.45). We estimate the redshift distribution of mm-selected sources finding a significant excess at z > 3 when compared to ∼ 850 μm selected samples. [ABSTRACT FROM AUTHOR]

We report the results of a pilot study with the Expanded Very Large Array (EVLA) of CO emission from four submillimetre-selected galaxies at -2.5, each with an existing detection of CO , one of which comprises two distinct spatial components. Using the EVLA's most compact configuration, we detect strong, broad [medians: 990 km s full width at zero intensity; 540 km s full width at half-maximum (FWHM)] line emission from all of our targets - coincident in position and velocity with their emission. The median linewidth ratio, , suggests that the is more spatially extended than the 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 () ratio is , consistent with local galaxies with L, noting that our value may be biased high because of the based sample selection. Naively, this suggests gas masses roughly two times higher than estimates made using higher transitions of CO, with the discrepancy due entirely to the difference in assumed ratio. We also estimate molecular gas masses using the CO line and the observed global ratios, assuming standard underlying 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 (). Using this new method, we find a median molecular gas mass of 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 kpc for our sample is 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 or 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 mass estimates, the possibilities for breaking them, and the future prospects for imaging and studying cold, quiescent molecular gas at high redshifts. [ABSTRACT FROM AUTHOR]

We present the first study of the far-infrared (FIR) properties of high-redshift, radio-selected ultraluminous infrared galaxies (ULIRGs) using deep observations obtained with the Spectral and Photometric Imaging Receiver (SPIRE) from the Herschel Multi-tiered Extragalactic Survey (HerMES). These galaxies span a large range of 850-m fluxes from submillimetre-luminous 10 mJy sources (SCUBA galaxies) to 1.5 mJy from stacked SCUBA non-detections, thus likely representing a complete distribution of ULIRG spectral energy distributions (SEDs). From Keck spectroscopic surveys in the Lockman-North field we identified a sample of 31 submillimetre galaxies (SMGs) and 37 submillimetre-faint, optically faint radio galaxies (OFRGs), all with radio-inferred IR luminosities L. These galaxies were cross-identified with SPIRE 250-, 350- and 500-m catalogues based on fluxes extracted at 24-m positions in the SWIRE survey, yielding a sample of more than half of the galaxies well detected in at least two of the SPIRE bandpasses. By fitting greybody dust models to the SPIRE photometry together with SCUBA 850-m measurements (for OFRGs, only 850- upper limits), we infer dust temperatures and FIR luminosities. The OFRGs detected by SPIRE have median K and the SMGs have K, both in reasonable agreement with previous (pre- Herschel) estimates, reaffirming that the local FIR/radio correlation holds (at least for this subset of high- ULIRGs) at high redshift (we measure using derived from greybody fit coupled with a power-law extrapolation to the 24 m). Our observations first confirm that a substantial fraction of OFRGs exhibits large infrared luminosities corresponding to SFRs of 400 M yr. The SPIRE observations secondly confirm the higher dust temperatures for these OFRGs than similarly selected SMGs, consistent with early predictions of the submillimetre-faint radio populations. Our observations also clearly confirm the large infrared luminosities of most SMGs selected with mJy and radio and strong 24-m detections, corresponding to SFRs of 700 M yr. [ABSTRACT FROM AUTHOR]

We present new multiwavelength observations of the first submillimetre-selected galaxy (SMG) SMM J 0136 at . These observations include mapping of the CO J= 0 emission using elements of the Expanded Very Large Array, as well as high-resolution 1.4-GHz imaging and optical/infrared (IR) data from the Very Large Array, Hubble Space Telescope, Spitzer and Keck-I. Together, these new data provide fundamental insights into the mass and distribution of stars, gas and dust within this archetypal SMG. The CO J= 0 emission, with its minimal excitation and density requirements, traces the bulk of the metal-rich molecular gas, and reveals a molecular gas mass of , extending over approximately 5 arcsec (∼25 kpc in the source plane), although there is tentative evidence that it may be significantly larger. Our data suggest that three or more distinct structures are encompassed by this molecular gas reservoir, including the broad absorption line (BAL) quasar from which the redshift of the SMG was initially determined. In particular, the new rest-frame near-IR observations identify a massive, obscured, starburst which is coincident with a previously known Lyα cloud. This starburst dominates the far-IR emission from the system and requires a re-assessment of previous claims that the gas reservoir resides in a massive, extended disc around the BAL quasi-stellar object (QSO). Instead, it appears that SMM J 0136 comprises a merger between a far-IR-luminous, but highly obscured starburst, the BAL QSO host and a faint third component. Our findings suggest that this archetypal SMG and its immediate environment mark a vast and complex galactic nursery and that detailed studies of other SMGs are likely to uncover a similarly rich diversity of properties. [ABSTRACT FROM AUTHOR]

We have studied the μJy radio properties of K-selected galaxy populations detected in the Ultra-Deep Survey (UDS) portion of the United Kingdom Infrared Telescope (UKIRT) Deep Sky Survey using 610- and 1400-MHz images from the Very Large Array and the Giant Metre-wave Telescope. These deep radio mosaics, combined with the largest and deepest K-band image currently available, allow high signal-to-noise ratio (S/N) detections of many K-selected subpopulations, including sBzK and pBzK star-forming and passive galaxies. We find a strong correlation between the radio and K-band fluxes and a linear relationship between star formation rate (SFR) and K-band luminosity. We find no evidence, either from radio spectral indices or a comparison with submm-derived SFRs, that the full sample is strongly contaminated by active galactic nuclei (AGN) at these low flux densities, though this is very difficult to determine from this data set. The photometric redshift distributions for the BzK galaxies place 37 (29) per cent of pBzK (sBzK) galaxies at , implying that location on the BzK diagram alone is not sufficient to select samples at . The sBzK and pBzK galaxies have similar levels of radio flux density, SFR and specific SFR (SSFR – SFR per unit stellar mass) at , suggesting there is strong contamination of the pBzK sample by star-forming galaxies. At , the pBzK galaxies become difficult to detect in the radio stack, though the implied SFRs are still much higher than expected for passively evolving galaxies. It may be that their radio emission comes from low-luminosity AGN. Extremely red objects (EROs) straddle the passive and star-forming regions of the BzK diagram and also straddle the two groups in terms of their radio properties. We find that K-bright ERO samples are dominated by passive galaxies and faint ERO samples contain more star-forming galaxies. The star formation history (SFH) from stacking all K-band sources in the UDS agrees well with that derived for other wavebands and other radio surveys, at least out to . The radio-derived SFH then appears to fall more steeply than that measured at other wavelengths. The SSFR for K-selected sources rises strongly with redshift at all stellar masses, and shows a weak dependence on stellar mass. High- and low-mass galaxies show a similar decline in SSFR since . [ABSTRACT FROM AUTHOR]

High-resolution submillimetre (submm) imaging of the high-redshift radio galaxy (HzRG), 4C 60.07, at , has revealed two dusty components of roughly equal integrated flux. Spitzer imaging shows that one of these components (‘B’) is coincident with an extremely red active galactic nucleus (AGN), offset by ∼4 arcsec (∼30 kpc) from the HzRG core. The other submm component (‘A’) – resolved by our synthesized beam and devoid of emission at 3.6–8.0μm – lies between ‘B’ and the HzRG core. Since the radio galaxy was discovered via its extremely young, steep-spectrum radio lobes and the creation of these lobes was likely triggered by the interaction, we argue that we are witnessing an early-stage merger, prior to its eventual equilibrium state. The interaction is between the host galaxy of an actively fuelled black hole (BH) and a gas-rich starburst/AGN (‘B’) marked by the compact submm component and coincident with broad CO(4–3) emission. The second submm component (‘A’) is a plume of cold, dusty gas, associated with a narrow (∼150 km s−1) CO feature, and may represent a short-lived tidal structure. It has been claimed that HzRGs and submillimetre-selected galaxies (SMGs) differ only in the activity of their AGNs, but such complex submm morphologies are seen only rarely amongst SMGs, which are usually older, more relaxed systems. Our study has important implications: where a galaxy's gas reservoir is not aligned with its central BH, CO may be an unreliable probe of dynamical mass, affecting work on the co-assembly of BHs and host spheroids. Our data support the picture wherein close binary AGN are induced by mergers. They also raise the possibility that some supposedly jet-induced starbursts may have formed co-evally (yet independently of) the radio jets, both triggered by the same interaction. Finally, we note that the HzRG host would have gone unnoticed without its jets and its companion, so there may be many other unseen BHs at high redshift, lost in the sea of similarly bright Infrared Array Camera (IRAC) sources – sufficiently massive to drive a -W radio source, yet practically invisible unless actively fuelled. [ABSTRACT FROM AUTHOR]

Bolometer arrays on large antennas at high, dry sites have unveiled a dusty population of massive, luminous galaxies – submillimetre galaxies, or SMGs – which make a significant contribution to the star formation rate density at . The most crucial piece of information required to derive the history of obscured star formation is the redshift distribution of this galaxy population, N( z), which breaks degeneracies in the models and allows the mass and dynamics of the galaxies to be explored via high-resolution three-dimensional imaging in CO and by determining their level of clustering. Many SMGs are extremely faint, optically; some have no plausible counterparts, even in the infrared (IR), making the determination of an unbiased N( z) very difficult. The arrival of the Herschel Space Observatory and next-generation ground-based submm cameras will likely exacerbate this so-called redshift deadlock. Here, we report the first test of a new method for determining redshifts, based on the observed dependence of maser and IR luminosities. We have searched the dusty, lensed, hyperluminous quasar, APM 08279+5255, for the 1612-, 1665- and 1667-MHz hydroxyl lines as well as the 22-GHz water line. At , these are shifted to 329, 340 and 4538 MHz. Our relatively shallow test data reveal no convincing maser activity, but we set a meaningful constraint on the OH maser luminosity and we approach the expected thermal noise levels, meaning progress is possible. As an aside, we present deep new submm and radio imaging of this field. Using a simple shift-and-add technique, we uncover a new submm galaxy, conceivably at the redshift of APM 08279+5255. [ABSTRACT FROM AUTHOR]

The modest significance of most sources detected in current (sub)millimetre [(sub)mm] surveys can potentially compromise some analyses due to the inclusion of spurious sources in catalogues typically selected at ≥3.0–3.5σ. Here, we develop and apply a dual-survey extraction technique to Submillimetre Common-User Bolometer Array (SCUBA) and Max-Planck Millimetre Bolometer (MAMBO) images of the Lockman Hole. Cut above 5σ, our catalogue of submillimetre galaxies (SMGs) is more robust than previous samples, with a reduced likelihood of real, but faint SMGs (beneath and around the confusion limit) entering via superposition with noise. Our selection technique yields 19 SMGs in an effective area of 165 arcmin2, of which we expect at most two to be due to chance superposition of SCUBA and MAMBO noise peaks. The effective flux limit of the survey (∼4 mJy at ∼1 mm) is well matched to our deep 1.4-GHz image . The former is sensitive to luminous, dusty galaxies at extreme redshifts whilst the latter probes the regime. A high fraction of our robust SMGs (∼80 per cent) have radio counterparts which, given the ∼10 per cent contamination by spurious sources, suggests that very distant SMGs are unlikely to make up more than ∼10 per cent of the bright SMG population. This implies that almost all of the SMG population is amenable to study via the deepest current radio imaging. We use these radio counterparts to provide an empirical calibration of the positional uncertainty in SMG catalogues. We then go on to outline the acquisition of redshifts for radio-identified SMGs, from sample selection in the submm, to counterpart selection in the radio and optical/infrared, to slit placement on spectrograph masks. We determine a median of from a sample of six secure redshifts for unambiguous radio-identified submm sources and when we include submm sources with multiple radio counterparts and/or less reliable redshifts. These figures are consistent with previous estimates, suggesting that our knowledge of the median redshift of bright SMG population has not been biased by the low significance of the source catalogues employed. [ABSTRACT FROM AUTHOR]

ABSTRACT The Astronomical Thermal Emission Camera (AzTEC) 1.1 mm survey of the two SCUBA HAlf Degree Extragalactic Survey (SHADES) fields is the largest (0.7 deg2) blank-field millimetre-wavelength (mm-wavelength) survey undertaken to date at a resolution of ≃18 arcsec and a depth of ≃1 mJy. We have used the deep optical to radio multiwavelength data in the SHADES Lockman Hole East and SXDF/UDS fields to obtain galaxy identifications for ≃64 per cent (≃80 per cent including tentative identifications) of the 148 AzTEC-SHADES 1.1 mm sources reported by Austermann et al., exploiting deep radio and 24 μm data complemented by methods based on 8 μm flux density and red optical-infrared ( i − K) colour. This unusually high identification rate can be attributed to the relatively bright mm-wavelength flux density threshold, combined with the relatively deep supporting multifrequency data now available in these two well-studied fields. We have further exploited the optical-mid-infrared-radio data to derive an ≃60 per cent (≃75 per cent including 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/submm 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/submm sources are massive ( M > 1011 M⊙) star-forming galaxies tracing large-scale structures over scales of 10-20 Mpc. This confirms the importance of surveys covering several deg2 (as now underway with SCUBA2) to obtain representative samples of bright (sub)mm-selected galaxies. This work provides a foundation for the further exploitation of the Spitzer and Herschel data in the SHADES fields in the study of the stellar masses and specific star formation rates of the most active star-forming galaxies in cosmic history. [ABSTRACT FROM AUTHOR]

ABSTRACT We present Herschel-Spectral and Photometric Imaging Receiver (SPIRE) Fourier transform spectrometer (FTS) and radio follow-up observations of two Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS)-detected strongly lensed distant galaxies. In one of the targeted galaxies H-ATLAS J090311.6+003906 (SDP.81), we detect [O iii] 88 μm and [C ii] 158 μm lines at a signal-to-noise ratio of ∼5. We do not have any positive line identification in the other fainter target H-ATLAS J091305.0−005343 (SDP.130). Currently, SDP.81 is the faintest submillimetre galaxy with positive line detections with the FTS, with continuum flux just below 200 mJy in the 200-600 μm wavelength range. The derived redshift of SDP.81 from the two detections is z = 3.043 ± 0.012, in agreement with ground-based CO measurements. This is the first detection by Herschel of the [O iii] 88 μm line in a galaxy at redshift higher than 0.05. Comparing the observed lines and line ratios with a grid of photodissociation region (PDR) models with different physical conditions, we derive the PDR cloud density n ≈ 2000 cm−3 and the far-ultraviolet ionizing radiation field G0≈ 200 (in units of the Habing field - the local Galactic interstellar radiation field of 1.6 × 10−6 W m−2). Using the CO-derived molecular mass and the PDR properties, we estimate the effective radius of the emitting region to be 500-700 pc. These characteristics are typical for star-forming, high-redshift galaxies. The radio observations indicate that SDP.81 deviates significantly from the local far-infrared/radio (FIR/radio) correlation, which hints that some fraction of the radio emission is coming from an active galactic nucleus (AGN). The constraints on the source size from millimetre-wave observations put a very conservative upper limit of the possible AGN contribution to less than 33 per cent. These indications, together with the high [O iii]/FIR ratio and the upper limit of [O i] 63 μm/[C ii] 158 μm, suggest that some fraction of the ionizing radiation is likely to originate from the AGN. [ABSTRACT FROM AUTHOR]

We investigate whether strong molecular and atomic emission lines at far-infrared wavelengths can influence the identification and derived properties of galaxies selected from broad-band, far-infrared or submillimetre observations. Several of these lines, for example, [C ] 158 m, have been found to be very bright in some galaxies, with fluxes of ≳0.1-1 per cent of the total far-infrared luminosity, and may be even brighter in certain populations at high redshifts. At redshifts where these lines fall in instrument passbands, they can significantly increase the broad-band flux measurements. We estimate that the contributions from line emission could boost the apparent broad-band flux by ≳20-40 per cent in the Herschel and SCUBA-2 bands. Combined with the steep source counts in the submillimetre and far-infrared bands, line contamination has potentially significant consequences for the properties of sources detected in flux-limited continuum surveys, biasing the derived redshift distributions and bolometric luminosities. Indeed, it is possible that some z > 4 sources found in 850-m surveys are being identified in part due to the line contamination from strong [C ] emission. These biases may be even stronger for less-luminous and lower metallicity populations at high redshifts, which are observable with the ALMA and which may have even stronger line-to-continuum ratios. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate the far-infrared-radio correlation (FRC) of stellar-mass-selected galaxies in the Extended Chandra Deep Field-South using far-infrared (FIR) imaging from Spitzer and radio imaging from the Very Large Array and Giant Metre-Wave Radio Telescope. We stack in redshift bins to probe galaxies below the noise and confusion limits. Radio fluxes are K-corrected using observed flux ratios, leading to tentative evidence for an evolution in spectral index. We compare spectral energy distribution (SED) templates of local galaxies for K-correcting FIR fluxes and show that the data are best fitted by a quiescent spiral template (M51) rather than a warm starburst (M82) or ultra-luminous infrared galaxy (Arp 220), implying a predominance of cold dust in massive galaxies at high redshift. In contrast, we measure total infrared luminosities that are consistent with high star-formation rates. We observe that the FRC index ( q) does not evolve significantly over z= 0-2 when computed from K-corrected 24- or 160-μm photometry, but that using 70-μm fluxes leads to an apparent decline in q beyond z∼ 1. This suggests some change in the SED at high redshift, either a steepening of the spectrum at rest-frame ∼25-35 μm or a deficiency at ∼70 μm leading to a drop in the total infrared-radio ratios. We compare our results to other work in the literature and find synergies with recent findings on the high-redshift FRC, high specific star formation rates of massive galaxies and the cold dust temperatures in these galaxies. [ABSTRACT FROM AUTHOR]

We present first results of a study of the submillimetre (submm) (rest-frame far-infrared) properties of Lyman break galaxies (LBGs) and their lower redshift counterparts BX/BM galaxies, based on Herschel-SPIRE observations of the Northern field of the Great Observatories Origins Deep Survey (GOODS-N). We use stacking analysis to determine the properties of LBGs well below the current limit of the survey. Although LBGs are not detected individually, stacking the infrared luminous LBGs (those detected with Spitzer at 24 m) yields a statistically significant submm detection with mean flux mJy confirming the power of SPIRE in detecting UV-selected high-redshift galaxies at submm wavelengths. In comparison, the Spitzer 24 m detected BX/BM galaxies appear fainter with a stacked value of mJy. By fitting the spectral energy distributions (SEDs) we derive median infrared luminosities, , of 2.8 × 10 L and 1.5 × 10 L for LBGs and BX/BMs, respectively. We find that estimates derived from present measurements are in good agreement with those based on UV data for BX/BM galaxies, unlike the case for infrared luminous LBGs where the UV underestimates the true . Although sample selection effects may influence this result we suggest that differences in physical properties (such as morphologies, dust distribution and extent of star-forming regions) between LBGs and BX/BMs may also play a significant role. [ABSTRACT FROM AUTHOR]

A significant fraction of the energy emitted in the early Universe came from very luminous galaxies that are largely hidden at optical wavelengths (because of interstellar dust grains); this energy now forms part of the cosmic background radiation at wavelengths near 1?mm (ref. 1). Some submillimetre (submm) galaxies have been resolved from the background radiation, but they have been difficult to study because of instrumental limitations. This has impeded the determination of their redshifts (z), which is a crucial element in understanding their nature and evolution. Here we report spectroscopic redshifts for ten submm galaxies that were identified using high-resolution radio observations. The median redshift for our sample is 2.4, with a quartile range of 1.9-2.8. This population therefore coexists with the peak activity of quasars, suggesting a close relationship between the growth of massive black holes and luminous dusty galaxies. The space density of submm galaxies at redshifts over 2 is about 1,000 times greater than that of similarly luminous galaxies in the present-day Universe, so they represent an important component of star formation at high redshifts. [ABSTRACT FROM AUTHOR]

We present new empirical constraints on the evolution of , the cosmological mass density of molecular hydrogen, back to z ≈ 2.5. We employ a statistical approach measuring the average observed 850 μm flux density of near-infrared selected galaxies as a function of redshift. The redshift range considered corresponds to a span where the 850 μm band probes the Rayleigh–Jeans tail of thermal dust emission in the rest frame, and can therefore be used as an estimate of the mass of the interstellar medium. Our sample comprises of ≈150,000 galaxies in the UK InfraRed Telescope Infrared Deep Sky Survey Ultra-Deep Survey field with near-infrared magnitudes KAB ≤ 25 mag and photometric redshifts with corresponding probability distribution functions derived from deep 12-band photometry. With a sample approximately 2 orders of magnitude larger than in previous works we significantly reduce statistical uncertainties on to z ≈ 2.5. Our measurements are in broad agreement with recent direct estimates from blank field molecular gas surveys, finding that the epoch of molecular gas coincides with the peak epoch of star formation with at z ≈ 2. We demonstrate that can be broadly modeled by inverting the star formation rate (SFR) density with a fixed or weakly evolving star formation efficiency. This "constant efficiency" model shows a similar evolution to our statistically derived , indicating that the dominant factor driving the peak star formation history at z ≈ 2 is a larger supply of molecular gas in galaxies rather than a significant evolution of the SFR efficiency within individual galaxies. [ABSTRACT FROM AUTHOR]

We have used ALMA and NOEMA to study the molecular gas reservoirs in 61 ALMA-identified submillimetre galaxies (SMGs) in the COSMOS, UDS, and ECDFS fields. We detect 12CO (⁠|$J_{\rm up} =$| 2–5) emission lines in 50 sources, and [C  i ](3P1 − 3P0) emission in eight, at |$z =$| 1.2–4.8 and with a median redshift of 2.9 ± 0.2. By supplementing our data with literature sources, we construct a statistical CO spectral line energy distribution and find that the 12CO line luminosities in SMGs peak at J up ∼ 6, consistent with similar studies. We also test the correlations of the CO, [C  i ], and dust as tracers of the gas mass, finding the three to correlate well, although the CO and dust mass as estimated from the 3-mm continuum are preferable. We estimate that SMGs lie mostly on or just above the star-forming main sequence, with a median gas depletion timescale, t dep = M gas/SFR, of 210 ± 40 Myr for our sample. Additionally, t dep declines with redshift across z  ∼ 1–5, while the molecular gas fraction, μgas = M gas/ M *, increases across the same redshift range. Finally, we demonstrate that the distribution of total baryonic mass and dynamical line width, M baryon–σ, for our SMGs is consistent with that followed by early-type galaxies in the Coma cluster, providing strong support to the suggestion that SMGs are progenitors of massive local spheroidal galaxies. On the basis of this, we suggest that the SMG populations above and below an 870- μ m flux limit of S 870 ∼ 5 mJy may correspond to the division between slow and fast rotators seen in local early-type galaxies. [ABSTRACT FROM AUTHOR]

Using the Eight MIxer Receiver (EMIR) instrument on the Institut de RadioAstronomie Millimétrique (IRAM) 30-m telescope, we conducted a spectroscopic redshift search of seven z phot ∼ 4 submillimetre bright galaxies selected from the Herschel Bright Sources sample with fluxes at 500 μm greater than 80 mJy. For four sources, we obtained spectroscopic redshifts between 3.4 < z < 4.1 through the detection of multiple CO-spectral lines with J  ≥ 3. Later, we detected low- J transitions for two of these sources with the Green Bank Telescope including the CO(1–0) transition. For the remaining three sources, more data are needed to determine the spectroscopic redshift unambiguously. The measured CO luminosities and line widths suggest that all these sources are gravitationally lensed. These observations demonstrate that the 2 mm window is indispensable to confirm robust spectroscopic redshifts for z < 4 sources. Finally, we present an efficient graphical method to correctly identify spectroscopic redshifts. [ABSTRACT FROM AUTHOR]

Historically, GHz radio emission has been used extensively to characterize the star-formation activity in galaxies. In this work, we look for empirical relationships amongst the radio luminosity, the infrared luminosity, and the CO-based molecular gas mass. We assemble a sample of 278 nearby galaxies with measurements of radio continuum and total infrared emission, and the 12CO J = 1–0 emission line. We find a correlation between the radio continuum and the CO emission line (with a scatter of 0.36 dex), in a large sample of different kinds of galaxies. Making use of this correlation, we explore the evolution of the molecular gas mass function and the cosmological molecular gas mass density in six redshift bins up to z = 1.5. These results agree with previous semi-analytic predictions and direct measurements: the cosmic molecular gas density increases up to z = 1.5. In addition, we find a single plane across five orders of magnitude for the explored luminosities, with a scatter of 0.27 dex. These correlations are sufficiently robust to be used for samples where no CO measurements exist. [ABSTRACT FROM AUTHOR]

We analyse 870  |$\mu$| m Atacama Large Millimetre Array (ALMA) dust continuum detections of 41 canonically selected |$z$| ≃ 3 Lyman-break galaxies (LBGs), as well as 209 ALMA-undetected LBGs, in follow-up of SCUBA-2 mapping of the UKIDSS Ultra Deep Survey (UDS) field. We find that our ALMA-bright LBGs lie significantly off the local IRX-beta relation and have relatively bluer rest-frame UV slopes (as parametrized by β), given their high values of the 'infrared excess' (IRX ≡ L IR/ L UV), relative to the average 'local' IRX-β relation. We attribute this finding in part to the young ages of the underlying stellar populations but we find that the main reason behind the unusually blue UV slopes are the relatively shallow slopes of the corresponding dust attenuation curves. We show that, when stellar masses, M *, are being established via SED fitting, it is absolutely crucial to allow the attenuation curves to vary (rather than fixing it on Calzetti-like law), where we find that the inappropriate curves may underestimate the resulting stellar masses by a factor of ≃2–3× on average. In addition, we find these LBGs to have relatively high specific star-formation rates (sSFRs), dominated by the dust component, as quantified via the fraction of obscured star formation |$(f_{\rm obs}\equiv {\rm SFR_{\rm IR}/{\rm SFR}_{\rm UV+IR}})$|⁠. We conclude that the ALMA-bright LBGs are, by selection, massive galaxies undergoing a burst of a star formation (large sSFRs, driven, for example, by secular or merger processes), with a likely geometrical disconnection of the dust and stars, responsible for producing shallow dust attenuation curves. [ABSTRACT FROM AUTHOR]

We identify multi-wavelength counterparts to 1147 submillimeter sources from the S2COSMOS SCUBA-2 survey of the COSMOS field by employing a recently developed radio+machine-learning method trained on a large sample of Atacama Large Millimeter/submillimeter Array (ALMA)–identified submillimeter galaxies (SMGs), including 260 SMGs identified in the AS2COSMOS pilot survey. In total, we identify 1222 optical/near-infrared (NIR)/radio counterparts to the 897 S2COSMOS submillimeter sources with S850 > 1.6 mJy, yielding an overall identification rate of (78 ± 9)%. We find that (22 ± 5)% of S2COSMOS sources have multiple identified counterparts. We estimate that roughly 27% of these multiple counterparts within the same SCUBA-2 error circles very likely arise from physically associated galaxies rather than line-of-sight projections by chance. The photometric redshift of our radio+machine-learning-identified SMGs ranges from z = 0.2 to 5.7 and peaks at z = 2.3 ± 0.1. The AGN fraction of our sample is (19 ± 4)%, which is consistent with that of ALMA SMGs in the literature. Comparing with radio/NIR-detected field galaxy population in the COSMOS field, our radio+machine-learning-identified counterparts of SMGs have the highest star formation rates and stellar masses. These characteristics suggest that our identified counterparts of S2COSMOS sources are a representative sample of SMGs at z ≲ 3. We employ our machine-learning technique to the whole COSMOS field and identified 6877 potential SMGs, most of which are expected to have submillimeter emission fainter than the confusion limit of our S2COSMOS surveys (mJy). We study the clustering properties of SMGs based on this statistically large sample, finding that they reside in high-mass dark matter halos ((1.2 ± 0.3) × 1013h−1), which suggests that SMGs may be the progenitors of massive ellipticals we see in the local universe. [ABSTRACT FROM AUTHOR]

We have observed 104 gravitationally lensed quasars at z ~ 1-4 with Herschel/SPIRE, the largest such sample ever studied. By targeting gravitational lenses, we probe intrinsic farinfrared (FIR) luminosities and star formation rates (SFRs) more typical of the population than the extremely luminous sources that are otherwise accessible. We detect 72 objects with Herschel/SPIRE and find 66 per cent (69 sources) of the sample have spectral energy distributions (SEDs) characteristic of dust emission. For 53 objects with sufficiently constrained SEDs, we find a median effective dust temperature of 38+12-5 K. By applying the radio--infrared correlation, we find no evidence for an FIR excess that is consistent with starformation- heated dust. We derive a median magnification-corrected FIR luminosity of 3.6+4.8-2.4 x 1011 Lʘ and median SFR of 120+160-80 Mʘ yr-1 for 94 quasars with redshifts. We find ***10 per cent of our sample have FIR properties similar to typical dusty star-forming galaxies at z *** 2-3 and a range of SFRs <20-10 000Mʘ yr-1 for our sample as a whole. These results are in line with current models of quasar evolution and suggests a coexistence of dust-obscured star formation and AGN activity is typical of most quasars. We do not find a statistically significant difference in the FIR luminosities of quasars in our sample with a radio excess relative to the radio--infrared correlation. Synchrotron emission is found to dominate at FIR wavelengths for <15 per cent of those sources classified as powerful radio galaxies. [ABSTRACT FROM AUTHOR]

With the advent of wide-area submillimetre surveys, a large number of high-redshift gravitationally lensed dusty star-forming galaxies have been revealed. Because of the simplicity of the selection criteria for candidate lensed sources in such surveys, identified as those with S500 µm > 100 mJy, uncertainties associated with the modelling of the selection function are expunged. The combination of these attributes makes submillimetre surveys ideal for the study of strong lens statistics. We carried out a pilot study of the lensing statistics of submillimetreselected sources by making observations with the Atacama Large Millimeter Array (ALMA) of a sample of strongly lensed sources selected from surveys carried out with the Herschel Space Observatory. We attempted to reproduce the distribution of image separations for the lensed sources using a halo mass function taken from a numerical simulation that contains both dark matter and baryons. We used three different density distributions, one based on analytical fits to the haloes formed in the EAGLE simulation and two density distributions [Singular Isothermal Sphere (SIS) and SISSA] that have been used before in lensing studies. We found that we could reproduce the observed distribution with all three density distributions, as long as we imposed an upper mass transition of ~1013M⊙ for the SIS and SISSA models, above which we assumed that the density distribution could be represented by a Navarro-Frenk-White profile. We show that we would need a sample of ~500 lensed sources to distinguish between the density distributions, which is practical given the predicted number of lensed sources in the Herschel surveys. [ABSTRACT FROM AUTHOR]

The Herschel Space Observatory has revealed a very different galaxyscape from that shown by optical surveys which presents a challenge for galaxy-evolution models. The Herschel surveys reveal (1) that there was rapid galaxy evolution in the very recent past and (2) that galaxies lie on a single Galaxy Sequence (GS) rather than a star-forming 'main sequence' and a separate region of 'passive' or 'red-and-dead' galaxies. The form of the GS is now clearer because far-infrared surveys such as the Herschel ATLAS pick up a population of optically red starforming galaxies that would have been classified as passive using most optical criteria. The space-density of this population is at least as high as the traditional star-forming population. By stacking spectra of H-ATLAS galaxies over the redshift range 0.001 < z < 0.4, we show that the galaxies responsible for the rapid low-redshift evolution have high stellar masses, high star-formation rates but, even several billion years in the past, old stellar populations - they are thus likely to be relatively recent ancestors of early-type galaxies in the Universe today. The form of the GS is inconsistent with rapid quenching models and neither the analytic bathtub model nor the hydrodynamical EAGLE simulation can reproduce the rapid cosmic evolution. We propose a new gentler model of galaxy evolution that can explain the new Herschel results and other key properties of the galaxy population. [ABSTRACT FROM AUTHOR]

We present an extragalactic survey using observations from the Atacama Large Millimeter/ submillimeter Array (ALMA) to characterize galaxy populations up to z = 0.35: the ValparaÍso ALMA Line Emission Survey (VALES). We use ALMA Band-3 CO(1-0) observations to study themolecular gas content in a sample of 67 dusty normal star-forming galaxies selected from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). We have spectrally detected 49 galaxies at >5σ significance and 12 others are seen at low significance in stacked spectra. CO luminosities are in the range of (0.03-1.31) × 1010 K km s-1 pc2, equivalent to log(Mgas/M☉) = 8.9-10.9 assuming an αCO = 4.6 (K km s-1 pc2)-1, which perfectly complements the parameter space previously explored with local and high-z normal galaxies. We compute the optical to CO size ratio for 21 galaxies resolved by ALMA at ~3.5 arcsec resolution (6.5 kpc), finding that the molecular gas is on average ~0.6 times more compact than the stellar component. We obtain a global Schmidt-Kennicutt relation, given by log[∑SFR/(M☉ yr-1 kpc-2)] = (1.26 ± 0.02) × log[∑MH2/(M☉ pc-2)] - (3.6 ± 0.2). We find a significant fraction of galaxies lying at 'intermediate efficiencies' between a longstanding mode of star formation activity and a starburst, specially at LIR = 1011-12 L☉. Combining our observations with data taken from the literature, we propose that star formation efficiencies can be parametrized by log [SFR/MH2 ] = 0.19 × (log LIR - 11.45) - 8.26 - 0.41 × arctan[-4.84 (logLIR - 11.45)]. Within the redshift range we explore (z < 0.35), we identify a rapid increase of the gas content as a function of redshift. [ABSTRACT FROM AUTHOR]

We use new Band 3 CO(1-0) observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA) to study the physical conditions in the interstellar gas of a sample of 27 dusty main-sequence star-forming galaxies at 0:03 < z < 0:2 present in the Valparaíso ALMA Line Emission Survey (VALES). The sample is drawn from far-IR bright galaxies over ~160 deg2 in the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS), which is covered by high-quality ancillary data including Herschel [Cπ] 158 μm spectroscopy and far-infrared (FIR) photometry. The [Cπ] and CO(1-0) lines are both detected at >5σ in 26 sources. We find an average [Cπ] to CO(1-0) luminosity ratio of 3500 ± 1200 for our sample that is consistent with previous studies. Using the [Cπ], CO(1-0) and FIR measurements as diagnostics of the physical conditions of the interstellar medium, we compare these observations to the predictions of a photodissociation region (PDR) model to determine the gas density, surface temperature, pressure, and the strength of the incident far-ultraviolet (FUV) radiation field, G0, normalised to the Habing Field. The majority of our sample exhibit hydrogen densities of 4 < log n=cm³ < 5:5 and experience an incident FUV radiation field with strengths of 2 < logG0 < 3 when adopting standard adjustments. A comparison to galaxy samples at different redshifts indicates that the average strength of the FUV radiation field appears constant up to redshift z ~ 6:4, yet the neutral gas density increases as a function of redshift by a factor of ~100 from z = 0 to z = 0:2 that persists regardless of various adjustments to our observable quantities. Whilst this evolution could provide an explanation for the observed evolution of the star formation rate density with cosmic time, the result most likely arises from a combination of observational biases when using different suites of emission lines as diagnostic tracers of PDR gas. [ABSTRACT FROM AUTHOR]

This paper is the second in a pair of papers presenting data release 1 (DR1) of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS), the largest single open-time key project carried out with the Herschel Space Observatory. The H-ATLAS is a wide-area imaging survey carried out in five photometric bands at 100, 160, 250, 350 and 500 µm covering a total area of 600 deg². In this paper, we describe the identification of optical counterparts to submillimetre sources in DR1, comprising an area of 161 deg² over three equatorial fields of roughly 12 × 4.5 deg centred at 9h, 12h and 14. h 5, respectively. Of all the H-ATLAS fields, the equatorial regions benefit from the greatest overlap with current multiwavelength surveys spanning ultraviolet (UV) to mid-infrared regimes, as well as extensive spectroscopic coverage. We use a likelihood ratio technique to identify Sloan Digital Sky Survey counterparts at r < 22.4 for 250-μm-selected sources detected at ≥4σ (28 mJy). We find 'reliable' counterparts (reliability R ≥ 0.8) for 44 835 sources (39 per cent), with an estimated completeness of 73.0 per cent and contamination rate of 4.7 per cent. Using redshifts and multi-wavelength photometry from GAMA and other public catalogues, we show that H-ATLAS-selected galaxies at z < 0.5 span a wide range of optical colours, total infrared (IR) luminosities and IR/UV ratios, with no strong disposition towards mid-IR-classified active galactic nuclei in comparison with optical selection. The data described herein, together with all maps and catalogues described in the companion paper, are available from the H-ATLAS website at www.h-atlas.org. [ABSTRACT FROM AUTHOR]

We report the redshift of an unlensed, highly obscured submillimetre galaxy (SMG), HS1100.850.1, the brightest SMG (S850 μm = 19.1 mJy) detected in the James Clerk Maxwell Telescope/Submillimetre Common-user Bolomete12r Array-2 (JCMT/SCUBA-2) Baryonic Structure Survey, based on the detection of its CO line emission. Using the Institute Radio Astronomie Millimetrique Plateau de Bure Interferometer with 3.6 GHz band width, we serendipitously detect an emission line at 150.6 GHz. From a search over 14.5 GHz in the 3- and 2-mm atmospheric windows, we confirm the identification of this line as 12CO(5-4) at z = 2.816, meaning that it does not reside in the z ~ 2.30 proto-cluster in this field. Mea- surement of the 810 μm source size (<0.85 arcsec) from the Sub-Millimetre Array (SMA) confirms a compact emission in a S870 μm = 14.5 mJy, LIR ~ 1013 L⊙ component, suggesting an Eddington-limited starburst. We use the double-peaked 12CO line profile measurements along with the SMA size constraints to study the gas dynamics of a HyLIRG, estimating the gas and dynamical masses of HS1100.850.1. While HS1100.850.1 is one of the most extreme galaxies known in the Universe, we find that it occupies a relative void in the Lyman-Break Galaxy distribution in this field. Comparison with other extreme objects at similar epochs (HyLIRG Quasars), and cosmological simulations, suggests such an anti-bias of bright SMGs could be relatively common, with the brightest SMGs rarely occupying the most overdense regions at z = 2-4. [ABSTRACT FROM AUTHOR]

We report the redshift of an unlensed, highly obscured submillimetre galaxy (SMG), HS1700.850.1, the brightest SMG (S850µm = 19.1 mJy) detected in the James Clerk Maxwell Telescope/Submillimetre Common-user Bolometer Array-2 (JCMT/SCUBA-2) Baryonic Structure Survey, based on the detection of its 12CO line emission. Using the Institute Radio Astronomie Millimetrique Plateau de Bure Interferometer with 3.6 GHz band width, we serendipitously detect an emission line at 150.6 GHz. From a search over 14.5 GHz in the 3- and 2-mm atmospheric windows, we confirm the identification of this line as 12CO(5-4) at z = 2.816, meaning that it does not reside in the z ~ 2.30 proto-cluster in this field. Measurement of the 870 µm source size (<0.85 arcsec) from the Sub-Millimetre Array (SMA) confirms a compact emission in a S870µm = 14.5 mJy, LIR ~ 1013 L⊙ component, suggesting an Eddington-limited starburst. We use the double-peaked 12CO line profile measurements along with the SMA size constraints to study the gas dynamics of a HyLIRG, estimating the gas and dynamical masses of HS1700.850.1. While HS1700.850.1 is one of the most extreme galaxies known in the Universe, we find that it occupies a relative void in the Lyman-Break Galaxy distribution in this field. Comparison with other extreme objects at similar epochs (HyLIRG Quasars), and cosmological simulations, suggests such an anti-bias of bright SMGs could be relatively common, with the brightest SMGs rarely occupying the most overdense regions at z = 2-4. [ABSTRACT FROM AUTHOR]

We present detections at 850 μm of the Lyman-break galaxy (LBG) population at z ≈ 3, 4, and 5 using data from the Submillimetre Common User Bolometer Array 2 Cosmology Legacy Survey in the United Kingdom Infrared Deep Sky Survey 'Ultra Deep Survey' field. We employ stacking to probe beneath the survey limit, measuring the average 850 μm flux density of LBGs at z ≈ 3, 4, and 5 with typical ultraviolet luminosities of L1700 ≈ 1029 erg s-1 Hz-1. We measure 850 μm flux densities of (0.25 ± 0.03), (0.41 ± 0.06), and (0.88 ± 0.23) mJy, respectively, finding that they contribute at most 20 per cent to the cosmic far-infrared (IR) background at 850 μm. Fitting an appropriate range of spectral energy distributions to the z∼3, 4, and 5 LBG stacked 24-850 μm fluxes, we derive IR luminosities of L8-1000μm ≈ 3.2, 5.5, and 11.0 × 1011 L☉[and star formation rates (SFRs) of ≈50-200M☉yr-1], 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-to-ultraluminous IR galaxies at these epochs. We observe a positive correlation between stellar mass and IR luminosity and confirm that, for a fixed mass, the reddest LBGs (UV slope β →0) are redder due to dust extinction, with SFR(IR)/SFR(UV) increasing by about an order of magnitude over -2 < β < 0 with SFR(IR)/SFR(UV) ∼ 20 for the reddest LBGs. Furthermore, the most massive LBGs tend to have higher obscured-to-unobscured ratios, hinting at a variation in the obscuration properties across the mass range. [ABSTRACT FROM AUTHOR]

We present the results from a 1.1-mm imaging survey of the SSA22 field, known for having an overdensity of z =3.1 Lyman α emitting galaxies (LAEs), taken with the astronomical thermal emission camera (AzTEC) on the Atacama Submillimeter Telescope Experiment (ASTE).We imaged a 950-arcmin2 field down to a 1σ sensitivity of 0.7–1.3 mJy beam−1 to find 125 submillimetre galaxies (SMGs) with a signal-to-noise ratio ≥3.5. Counterpart identification using radio and near/mid-infrared data was performed and one or more counterpart candidates were found for 59 SMGs. Photometric redshifts based on optical to near-infrared images were evaluated for 45 of these SMGs with Spitzer/IRAC data and the median value is found to be z =2.4. By combining these estimations with estimates from the literature, we determined that 10 SMGs might lie within the large-scale structure at z = 3.1. The two-point angular cross-correlation function between LAEs and SMGs indicates that the positions of the SMGs are correlated with the z = 3.1 protocluster. These results suggest that the SMGs were formed and evolved selectively in the high dense environment of the high-redshift Universe. This picture is consistent with the predictions of the standard model of hierarchical structure formation. [ABSTRACT FROM AUTHOR]

We present Submillimeter Array [C II] 158 μm and Karl G. Jansky Very Large Array 12CO(1-0) line emission maps for the bright, lensed, submillimeter source at z = 5.2430 behind A 773: HLSJ091828.6+514223 (HLS0918). We combine these measurements with previously reported line profiles, including multiple 12CO rotational transitions, [C I], water, and [N II], providing some of the best constraints on the properties of the interstellar medium in a galaxy at z > 5. HLS0918 has a total far-infrared (FIR) luminosity LFIR(8–1000 μm) = (1.6 ± 0.1) × 1014L☼ μ–1, where the total magnification μtotal = 8.9 ± 1.9, via a new lens model from the [C II] and continuum maps. Despite a HyLIRG luminosity, the FIR continuum shape resembles that of a local LIRG. We simultaneously fit all of the observed spectral line profiles, finding four components that correspond cleanly to discrete spatial structures identified in the maps. The two most redshifted spectral components occupy the nucleus of a massive galaxy, with a source-plane separation <1 kpc. The reddest dominates the continuum map (demagnified LFIR, component = (1.1 ± 0.2) × 1013L☼) and excites strong water emission in both nuclear components via a powerful FIR radiation field from the intense star formation. A third star-forming component is most likely a region of a merging companion (ΔV ∼ 500 km s–1) exhibiting generally similar gas properties. The bluest component originates from a spatially distinct region and photodissociation region analysis suggests that it is lower density, cooler, and forming stars less vigorously than the other components. Strikingly, it has very strong [N II] emission, which may suggest an ionized, molecular outflow. This comprehensive view of gas properties and morphology in HLS0918 previews the science possible for a large sample of high-redshift galaxies once ALMA attains full sensitivity. [ABSTRACT FROM AUTHOR]

We study the evolution of the dust temperature of galaxies in the SFR-M• plane up to z ~ 2 using far-infrared and submillimetre observations from the Herschel Space Observatory taken as part of the PACS Evolutionary Probe (PEP) and Herschel Multi-tiered Extragalactic Survey (HerMES) guaranteed time key programmes. Starting from a sample of galaxies with reliable star-formation rates (SFRs), stellar masses (M•) and redshift estimates, we grid the SFR-M• parameter space in several redshift ranges and estimate the mean dust temperature (Tdust) of each SFR-M•-z bin. Dust temperatures are inferred using the stacked far-infrared flux densities (100-500 µm) of our SFR-M•-z bins. At all redshifts, the dust temperature of galaxies smoothly increases with rest-frame infrared luminosities (LIR), specific SFRs (SSFR; i.e., SFR/M•), and distances with respect to the main sequence (MS) of the SFR-M• plane (i.e., ? log (SSFR)MS = log [SSFR(galaxy)/SSFRMS(M•, z)]). The Tdust-SSFR and Tdust - ?log (SSFR)MS correlations are statistically much more significant than the Tdust-LIR one. While the slopes of these three correlations are redshiftindependent, their normalisations evolve smoothly from z = 0 and z ~ 2. We convert these results into a recipe to derive Tdust from SFR, M• and z, valid out to z ~ 2 and for the stellar mass and SFR range covered by our stacking analysis. The existence of a strong Tdust-?log (SSFR)MS correlation provides us with several pieces of information on the dust and gas content of galaxies. Firstly, the slope of the Tdust-?log (SSFR)MS correlation can be explained by the increase in the star-formation efficiency (SFE; SFR/Mgas) with ? log (SSFR)MS as found locally by molecular gas studies. Secondly, at fixed ? log (SSFR)MS, the constant dust temperature observed in galaxies probing wide ranges in SFR and M• can be explained by an increase or decrease in the number of star-forming regions with comparable SFE enclosed in them. And thirdly, at high redshift, the normalisation towards hotter dust temperature of the Tdust-? log (SSFR)MS correlation can be explained by the decrease in the metallicities of galaxies or by the increase in the SFE of MS galaxies. All these results support the hypothesis that the conditions prevailing in the star-forming regions of MS and far-above-MS galaxies are different. MS galaxies have star-forming regions with low SFEs and thus cold dust, while galaxies situated far above the MS seem to be in a starbursting phase characterised by star-forming regions with high SFEs and thus hot dust. [ABSTRACT FROM AUTHOR]

We quantify the fraction of the cosmic infrared background (CIB) that originates from galaxies identified in the UV/optical/near-infrared by stacking 81,250 (∼35.7 arcmin–2) K-selected sources (KAB < 24.0) split according to their rest-frame U – V versus V – J colors into 72,216 star-forming and 9034 quiescent galaxies, on maps from Spitzer/MIPS (24 μm), Herschel/PACS (100, 160 μm), Herschel/SPIRE (250, 350, 500 μm), and AzTEC (1100 μm). The fraction of the CIB resolved by our catalog is (69% ± 15%) at 24 μm, (78% ± 17%) at 70 μm, (58% ± 13%) at 100 μm, (78% ± 18%) at 160 μm, (80% ± 17%) at 250 μm, (69% ± 14%) at 350 μm, (65% ± 12%) at 500 μm, and (45% ± 8%) at 1100 μm. Of that total, about 95% originates from star-forming galaxies, while the remaining 5% is from apparently quiescent galaxies. The CIB at λ ≲ 200 μm appears to be sourced predominantly from galaxies at z ≲ 1, while at λ ≳ 200 μm the bulk originates from 1 ≲ z ≲ 2. Galaxies with stellar masses log(M/M☼) = 9.5-11 are responsible for the majority of the CIB, with those in the log(M/M☼) = 9.5-10 bin contributing mostly at λ < 250 μm, and those in the log(M/M☼) = 10-11 bin dominating at λ > 350 μm. The contribution from galaxies in the log(M/M☼) = 9.0-9.5 (lowest) and log(M/M☼) = 11.0-12.0 (highest) stellar-mass bins contribute the least—both of order 5%—although the highest stellar-mass bin is a significant contributor to the luminosity density at z ≳ 2. The luminosities of the galaxies responsible for the CIB shifts from combinations of “normal” and luminous infrared galaxies (LIRGs) at λ ≲ 160 μm, to LIRGs at 160 ≲ λ ≲ 500 μm, to finally LIRGs and ultra-luminous infrared galaxies at λ ≳ 500 μm. Stacking analyses were performed using SIMSTACK, a novel algorithm designed to account for possible biases in the stacked flux density due to clustering. It is made available to the public at www.astro.caltech.edu/∼viero/viero_homepage/toolbox.html. [ABSTRACT FROM AUTHOR]

We present an Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 0 survey of 126 submillimeter sources from the LABOCA ECDFS Submillimeter Survey (LESS). Our 870μm 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 ~300μm emission region in one resolved SMG, implying a star formation rate surface density of 80M☉ 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. [ABSTRACT FROM AUTHOR]

Massive present-day early-type (elliptical and lenticular) galaxies probably gained the bulk of their stellar mass and heavy elements through intense, dust-enshrouded starbursts-that is, increased rates of star formation-in the most massive dark-matter haloes at early epochs. However, it remains unknown how soon after the Big Bang massive starburst progenitors exist. The measured redshift (z) distribution of dusty, massive starbursts has long been suspected to be biased low in z owing to selection effects, as confirmed by recent findings of systems with redshifts as high as ∼5 (refs 2-4). Here we report the identification of a massive starburst galaxy at z = 6.34 through a submillimetre colour-selection technique. We unambiguously determined the redshift from a suite of molecular and atomic fine-structure cooling lines. These measurements reveal a hundred billion solar masses of highly excited, chemically evolved interstellar medium in this galaxy, which constitutes at least 40 per cent of the baryonic mass. A 'maximum starburst' converts the gas into stars at a rate more than 2,000 times that of the Milky Way, a rate among the highest observed at any epoch. Despite the overall downturn in cosmic star formation towards the highest redshifts, it seems that environments mature enough to form the most massive, intense starbursts existed at least as early as 880 million years after the Big Bang. [ABSTRACT FROM AUTHOR]

Dust emission at submillimetre wavelengths allows us to trace the early phases of star formation in the Universe. In order to understand the physical processes involved in this mode of star formation, it is essential to gain knowledge about the dark matter structures – most importantly their masses – that submillimetre galaxies live in. Here we use the magnification effect of gravitational lensing to determine the average mass and dust content of submillimetre galaxies with 250 μm flux densities of S250 > 15 mJy selected using data from the Herschel Multi-tiered Extragalactic Survey. The positions of hundreds of submillimetre foreground lenses are cross-correlated with the positions of background Lyman-break galaxies at z ∼ 3–5 selected using optical data from the Canada–France–Hawaii Telescope Legacy Survey. We detect a cross-correlation signal at the 7σ level over a sky area of 1 deg2, with ∼80 per cent of this signal being due to magnification, whereas the remaining ∼20 per cent comes from dust extinction. Adopting some simple assumptions for the dark matter and dust profiles and the redshift distribution enables us to estimate the average mass of the haloes hosting the submillimetre galaxies to be log 10[M200/M⊙] = 13.17+ 0.05− 0.08(stat.) and their average dust mass fraction (at radii of >10 kpc) to be Mdust/M200 ≈ 6 × 10−5. This supports the picture that submillimetre galaxies are dusty, forming stars at a high rate, reside in massive group-sized haloes and are a crucial phase in the assembly and evolution of structure in the Universe. [ABSTRACT FROM AUTHOR]

ABSTRACT We present Atacama Large Millimeter Array (ALMA) 870-μm (345-GHz) observations of two submillimetre galaxies (SMGs) drawn from an ALMA study of the 126 submillimetre sources from the LABOCA Extended Chandra Deep Field-South Survey (LESS). The ALMA data identify the counterparts to these previously unidentified submillimetre sources and serendipitously detect bright emission lines in their spectra which we show are most likely to be [C ii] 157.74 μm emission yielding redshifts of z = 4.42 and 4.44. This blind detection rate within the 7.5-GHz bandpass of ALMA is consistent with the previously derived photometric redshift distribution of SMGs and suggests a modest, but not dominant (≲25 per cent), tail of 870-μm selected SMGs at z ≳ 4. We find that the ratio of L[C II]/ LFIR in these SMGs is much higher than seen for similarly far-infrared-luminous galaxies at z ∼ 0, which is attributed to the more extended gas reservoirs in these high-redshift ultraluminous infrared galaxies (ULIRGs). Indeed, in one system we show that the [C ii] emission shows hints of extended emission on ≳ 3 kpc scales. Finally, we use the volume probed by our ALMA survey to show that the bright end of the [C ii] luminosity function evolves strongly between z = 0 and ∼4.4, reflecting the increased interstellar medium cooling in galaxies as a result of their higher star formation rates. These observations demonstrate that even with short integrations, ALMA is able to detect the dominant fine-structure cooling lines from high-redshift ULIRGs, measure their energetics and spatially resolved properties and trace their evolution with redshift. [ABSTRACT FROM AUTHOR]

ABSTRACT We present integral field spectroscopy observations, covering the [O iii] λλ4959, 5007 emission-line doublet of eight high-redshift ( z = 1.4-3.4) ultraluminous infrared galaxies (ULIRGs) that host active galactic nucleus (AGN) activity, including known submillimetre luminous galaxies. The targets have moderate radio luminosities that are typical of high-redshift ULIRGs ( L1.4 GHz = 1024-1025 W Hz−1) and therefore are not radio-loud AGNs. We decouple kinematic components due to the galaxy dynamics and mergers from those due to outflows. We find evidence in the four most luminous systems ( [ABSTRACT FROM AUTHOR]

Herschel images in six photometric bands show the thermal emission of the debris disk surrounding β Pic. In the three PACS bands at 70 μm, 100 μm and 160 μm and in the 250 μm SPIRE band, the disk is well-resolved, and additional photometry is available in the SPIRE bands at 350 μm and 500 μm, where the disk is only marginally resolved. The SPIRE maps reveal a blob to the southwest of β Pic, coinciding with submillimetre detection of excess emission in the disk. We investigated the nature of this blob. Our comparison of the colours, spectral energy distribution and size of the blob, the disk and the background sources shows that the blob is most likely a background source with a redshift between z = 1.0 and z = 1.6. [ABSTRACT FROM AUTHOR]

During our Herschel Lensing Survey (HLS) of massive galaxy clusters, we have discovered an exceptionally bright source behind the z = 0.22 cluster Abell 773, which appears to be a strongly lensed submillimeter galaxy (SMG) at z = 5.2429. This source is unusual compared to most other lensed sources discovered by Herschel so far, because of its higher submm flux (∼200 mJy at 500 μm) and its high redshift. The dominant lens is a foreground z = 0.63 galaxy, not the cluster itself. The source has a far-infrared (FIR) luminosity of LFIR = 1.1 × 1014/μ L☉, where μ is the magnification factor, likely ∼11. We report here the redshift identification through CO lines with the IRAM-30 m, and the analysis of the gas excitation, based on CO(7-6), CO(6-5), CO(5-4) detected at IRAM and the CO(2-1) at the EVLA. All lines decompose into a wide and strong red component, and a narrower and weaker blue component, 540 km s-1 apart. Assuming the ultraluminous galaxy (ULIRG) CO-to-H2 conversion ratio, the H2 mass is 5.8×1011/μ M☉, of which one third is in a cool component. From the CI(3P2-3 P1) line we derive a CI/H2 number abundance of 6 × 10-5 similar to that in other ULIRGs. The H2Op(2, 0, 2-1, 1, 1) line is strong only in the red velocity component, with an intensity ratio I(H2O)/I(CO) ∼ 0.5, suggesting a strong local FIR radiation field, possibly from an active nucleus (AGN) component. We detect the [NII]205 μm line for the first time at high-z. It shows comparable blue and red components, with a strikingly broad blue one, suggesting strong ionized gas flows. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a submillimetre survey of seven high-redshift galaxy clusters (0.64 < z < 1.0) using the Submillimetre Common-User Bolometer Array (SCUBA) at 850 and 450 m. The targets, of similar richness and redshift, are selected from the Red-sequence Cluster Survey (RCS). We use this sample to investigate the apparent excess of submillimetre source counts in the direction of cluster fields compared to blank fields, as seen in the literature. The sample consists of three galaxy clusters that exhibit multiple optical arcs due to strong gravitational lensing, and a control group of four clusters with no apparent strong lensing. A tentative excess of 2.7σ is seen in the number density of submillimetre sources within the lensing cluster fields compared to that in the control group. Ancillary observations at radio, mid-infrared, optical and X-ray wavelengths allow for the identification of counterparts to many of the submillimetre luminous galaxies (SMGs), and provide improved astrometry and redshift constraints. Utilizing photometric redshifts, we conclude that at least three of the galaxies within the lensing fields have redshifts consistent with the clusters and implied infrared luminosities of ∼1012 L⊙. The existence of submillimetre cluster members may therefore be boosting source counts in the lensing cluster fields, which might be an effect of the dynamical state of those clusters. However, we find that the removal of potential cluster members from the counts analysis does not entirely eliminate the difference between the cluster samples. We also investigate possible occurrences of lensing between background submillimetre sources and lower redshift optical galaxies, though further observations are required to make any conclusive claims. Although the excess counts between the two cluster samples have not been unambiguously accounted for, these results warrant caution for interpreting submillimetre source counts in cluster fields and point source contamination for Sunyaev-Zel'dovich surveys. [ABSTRACT FROM AUTHOR]

Ultra steep spectrum (USS) radio sources have been successfully used to select powerful radio sources at high redshifts (z ≳ 2). Typically restricted to large-sky surveys and relatively bright radio flux densities, it has gradually become possible to extend the USS search to sub-mJy levels, thanks to the recent appearance of sensitive low-frequency radio facilities. Here a first detailed analysis of the nature of the faintest USS sources is presented. By using Giant Metrewave Radio Telescope and Very Large Array radio observations of the Lockman Hole at 610 MHz and 1.4 GHz, a sample of 58 USS sources, with 610 MHz integrated fluxes above 100 µJy, is assembled. Deep infrared data at 3.6 and 4.5 µm from the Spitzer Extragalactic Representative Volunte Survey (SERVS) are used to reliably identify counterparts for 48 (83%) of these sources, showing an average total magnitude of [3.6]AB = 19.8 mag. Spectroscopic redshifts for 14 USS sources, together with photometric redshift estimates, improved by the use of the deep SERVS data, for a further 19 objects, show redshifts ranging from z = 0.1 to z = 2.8, peaking at z ~ 0.6 and tailing off at high redshifts. The remaining 25 USS sources, with no redshift estimate, include the faintest 13.61 magnitudes, with 10 sources undetected at 3.6 and 4.5 µm (typically [3.6] ≳ 22-23 mag from local measurements), which suggests the likely existence of higher redshifts among the sub-mJy USS population. The comparison with the Square Kilometre Array Design Studies Simulated Skies models indicates that Fanaroff-Riley type I radio sources and radio-quiet active galactic nuclei may constitute the bulk of the faintest USS population, and raises the possibility that the high efficiency of the USS technique for the selection of high-redshift sources remains even at the sub-mJy level. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a spectroscopic catalogue of 40 luminous starburst galaxies at z= 0.7-1.7 (median z= 1.3). 19 of these are submillimetre galaxies (SMGs) and 21 are submillimetre-faint radio galaxies (SFRGs). This sample helps us to fill in the redshift desert at z= 1.2-1.7 in previous studies as well as to probe a lower luminosity population of galaxies. Radio fluxes are used to determine star formation rates for our sample which range from around 50-500 M⊙ yr−1 and are generally lower than those in z∼ 2 SMGs. We identify nebular [O ii] 3727 emission in the rest-UV spectra and use the linewidths to show that SMGs and SFRGs in our sample have larger linewidths and therefore dynamical masses than optically selected star-forming galaxies at similar redshifts. The linewidths are indistinguishable from those measured in the z∼ 2 SMG populations suggesting little evolution in the dynamical masses of the galaxies between redshift 1 and 2. [Ne v] and [Ne iii] emission lines are identified in a subset of the spectra indicating the presence of an active galactic nucleus (AGN). In addition, a host of interstellar absorption lines corresponding to transitions of Mg ii and Fe ii ions are also detected. These features show up prominently in composite spectra and we use these composites to demonstrate that the absorption lines are present at an average blueshift of −240 ± 50 km s−1 relative to the systemic velocities of the galaxies derived from [O ii]. This indicates the presence of large-scale outflowing interstellar gas in these systems. We do not find any evidence for differences in outflow velocities between SMGs and SFRGs of similar infrared luminosities. We find that the outflow velocities of z∼ 1.3 SMGs and SFRGs are consistent with the V∝ SFR0.3 local envelope seen in lower redshift ultraluminous infrared galaxies (ULIRGs). These observations are well explained by a momentum-driven wind model. [ABSTRACT FROM AUTHOR]

ABSTRACT For the first time, we investigate the X-ray/infrared (IR) correlation for star-forming galaxies (SFGs) at z∼ 1, using SPIRE submm data from the recently launched Herschel Space Observatory and deep X-ray data from the 2-Ms Chandra Deep Field-North survey. We examine the X-ray/IR correlation in the soft X-ray (SX; 0.5-2 keV) and hard X-ray (HX; 2-10 keV) bands by comparing our z∼ 1 SPIRE-detected SFGs to equivalently IR-luminous ( LIR > 1010 L⊙) samples in the local/low-redshift Universe. Our results suggest that the X-ray/IR properties of the SPIRE SFGs are on average similar to those of their local counterparts, as we find no evidence for evolution in the LSX/ LIR and LHX/ LIR ratios with redshift. We note, however, that at all redshifts, both LSX/ LIR and LHX/ LIR are strongly dependent on IR luminosity, with luminous and ultraluminous IR galaxies (LIRGs and ULIRGs; LIR > 1011 L⊙) having up to an order of magnitude lower values than normal IR galaxies ( LIR < 1011 L⊙). We derive a LSX- LIR relation and confirm the applicability of an existing LHX- LIR relation for both local and distant LIRGs and ULIRGs, consistent with a scenario where X-ray luminosity is correlated with the star formation rate. [ABSTRACT FROM AUTHOR]

We present a new study of stellar mass in a sample of ∼70 submillimeter-selected galaxies (SMGs) with accurate spectroscopic redshifts. We fit combinations of stellar population synthesis models and power laws to the galaxies' observed-frame optical through mid-IR spectral energy distributions (SEDs) to separate stellar emission from non-stellar near-IR continuum. The availability of spectroscopic redshifts significantly enhances our ability to determine unambiguously not only the mass and luminosity of SMGs, but also the presence and contribution of non-stellar emission to their SEDs. By separating the stellar emission from the non-stellar near-IR continuum, we find that ∼50% of our sample have non-stellar contributions of less than 10% in rest-frame H band and ∼10% of our sample have non-stellar contributions greater than 50%. We find that the K-band luminosity of the non-stellar continuum emission is correlated with hard X-ray luminosity, indicating an active galactic nucleus (AGN) origin of the emission. Upon subtracting this AGN-contributed continuum component from all of the galaxies in our sample, we determine a lower median stellar mass for SMGs than previous studies, ∼7 x 1010 Mʘ. We use constraints of the starburst timescale from molecular gas studies to estimate the amount of fading our sample would undergo if they passively evolve after the starburst terminates. The results suggest that typical SMGs, while among the most massive galaxies at ɀ ∼ 2, are likely to produce descendants of similar mass and luminosity to L* galaxies in the local universe. [ABSTRACT FROM AUTHOR]

ABSTRACT We present the results of a narrow-band (H2S1, λc= 2.121 μm, δλ= 0.021 μm) imaging search with Wide Field Camera/United Kingdom Infrared Telescope for Hα emitters (HAEs) around several potential signposts of rare (∼10−7-10−8 comoving Mpc−3) overdense regions at z = 2.23: an overdensity of quasi-stellar objects [QSOs; 2dF QSO Redshift Survey (2QZ) cluster], a powerful, high-redshift radio galaxy (HzRG) and a concentration of submillimetre galaxies (SMGs) and optically faint radio galaxies (OFRGs). In total, we detect 137 narrow-band emitter candidates down to emission-line fluxes of 0.5-1 × 10−16 erg s−1 cm−2, across a total area of 0.56 deg2 (2.1 × 105 comoving Mpc3 at z = 2.23) in these fields. The BzK colours of the emitters suggest that at least 80 per cent of our sample are likely to be HAEs at z = 2.23. This is one of the largest HAE samples known at z ≳ 2. Although there is no evidence for large-scale (20 comoving Mpc) overdensities of the emitters around the targets, we find modest (∼3σ) local overdensities associated with all three targets on smaller scales (5-10 comoving Mpc). In the 2QZ cluster field, the structure appears to be connecting the QSOs, while in the HzRG and SMG/OFRG fields, the structures are seen only in the vicinities of the targets. Our results suggest that these rare targets are located in local overdensities of galaxies, rather than average density regions, although it is not clear whether these structures are likely to evolve into rare, rich clusters. The K-band magnitudes and the Hα equivalent widths of the emitters are weakly correlated with the overdensities of the emitters: emitters in overdense regions are more evolved systems compared to those in underdense regions at z = 2.23. We find several examples of extended HAEs near to the targets, including a striking example with a spatial extent of 7.5 arcsec (60 kpc at z = 2.23) in the 2QZ cluster field, suggesting that these are relatively common in overdense regions. We conclude that narrow-band Hα surveys are efficient routes to map overdense regions at high redshifts and thus to understand the relation between the growth of galaxies and their surrounding large-scale structures. [ABSTRACT FROM AUTHOR]