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In this paper, we present the third data release (DR3) of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). We identify likely near-infrared counterparts to submillimetre sources in the South Galactic Pole (SGP) field using the VISTA VIKING survey. We search for the most probable counterparts within 15 arcsec of each Herschel source using a probability measure based on the ratio between the likelihood the true counterpart is found close to the submillimetre source and the likelihood that an unrelated object is found in the same location. For 110 374 (57.0 per cent) sources, we find galaxies on the near-infrared images where the probability that the galaxy is associated to the source is greater than 0.8. We estimate the false identification rate to be 4.8 per cent, with a probability that the source has an associated counterpart on the VIKING images of 0.835 ± 0.009. We investigate the effects of gravitational lensing and present 41 (0.14 deg−2) candidate lensed systems with observed flux densities >100 mJy at 500 μm. We include in the data release a probability that each source is gravitationally lensed and discover an additional 5923 sources below 100 mJy that have a probability greater than 0.94 of being gravitationally lensed. We estimate that ∼400–1 000 sources have multiple true identifications in VIKING based on the similarity of redshift estimates for multiple counterparts close to a Herschel source. The data described in this paper can be found at the H-ATLAS website. [ABSTRACT FROM AUTHOR]

We present the Herschel Extragalactic Legacy Project (HELP). This project collates, curates, homogenizes, and creates derived data products for most of the premium multiwavelength extragalactic data sets. The sky boundaries for the first data release cover 1270 deg2 defined by the Herschel SPIRE extragalactic survey fields; notably the Herschel Multi-tiered Extragalactic Survey (HerMES) and the Herschel Atlas survey (H-ATLAS). Here, we describe the motivation and principal elements in the design of the project. Guiding principles are transparent or 'open' methodologies with care for reproducibility and identification of provenance. A key element of the design focuses around the homogenization of calibration, meta data, and the provision of information required to define the selection of the data for statistical analysis. We apply probabilistic methods that extract information directly from the images at long wavelengths, exploiting the prior information available at shorter wavelengths and providing full posterior distributions rather than maximum-likelihood estimates and associated uncertainties as in traditional catalogues. With this project definition paper, we provide full access to the first data release of HELP; Data Release 1 (DR1), including a monolithic map of the largest SPIRE extragalactic field at 385 deg2 and 18 million measurements of PACS and SPIRE fluxes. We also provide tools to access and analyse the full HELP data base. This new data set includes far-infrared photometry, photometric redshifts, and derived physical properties estimated from modelling the spectral energy distributions over the full HELP sky. All the software and data presented is publicly available. [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]

We investigate the evolution of the gas mass fraction for galaxies in the COSMOS field using submillimetre emission from dust at 850  μ m. We use stacking methodologies on the 850   μ m S2COSMOS map to derive the gas mass fraction of galaxies out to high redshifts, 0 ≤ z ≤ 5, for galaxies with stellar masses of |$10^{9.5} \lt M_* (\rm M_{\odot }) \lt 10^{11.75}$|⁠. In comparison to previous literature studies we extend to higher redshifts, include more normal star-forming galaxies (on the main sequence), and also investigate the evolution of the gas mass fraction split by star-forming and passive galaxy populations. We find our stacking results broadly agree with scaling relations in the literature. We find tentative evidence for a peak in the gas mass fraction of galaxies at around z ∼ 2.5–3, just before the peak of the star formation history of the Universe. We find that passive galaxies are particularly devoid of gas, compared to the star-forming population. We find that even at high redshifts, high stellar mass galaxies still contain significant amounts of gas. [ABSTRACT FROM AUTHOR]

We have analysed Herschel observations of M31, using the ppmap  procedure. The resolution of ppmap  images is sufficient (⁠|$\sim 31\, {\rm pc}$| on M31) that we can analyse far-IR dust emission on the scale of giant molecular clouds. By comparing ppmap  estimates of the far-IR emission optical depth at |$300\, \mu {\rm m}\, (\tau _{{300}})$|⁠ , and the near-IR extinction optical depth at |$1.1\, \mu {\rm m}\, (\tau _{{1.1}})$| obtained from the reddening of Red Giant Branch (RGB) stars, we show that the ratio |${\cal R}^{\mathrm{ obs.}}_\tau \equiv \tau _{{1.1}}/\tau _{{300}}$| falls in the range |$500\lesssim {\cal R}^{\mathrm{ obs.}}_\tau \lesssim 1500$|⁠. Such low values are incompatible with many commonly used theoretical dust models, which predict values of |${\cal R}^{\mathrm{ model}}_\kappa \equiv \kappa _{{1.1}}/\kappa _{{300}}$| (where κ is the dust opacity coefficient) in the range |$2500\lesssim {\cal R}^{\mathrm{ model}}_\kappa \lesssim 4000$|⁠. That is, unless a large fraction, |$\gtrsim 60{{\ \rm per\ cent}}$|⁠ , of the dust emitting at |$300\, \mu {\rm m}$| is in such compact sources that they are unlikely to intercept the lines of sight to a distributed population like RGB stars. This is not a new result: variants obtained using different observations and/or different wavelengths have already been reported by other studies. We present two analytic arguments for why it is unlikely that |$\gtrsim 60{{\ \rm per\ cent}}$| of the emitting dust is in sufficiently compact sources. Therefore it may be necessary to explore the possibility that the discrepancy between observed values of |${\cal R}^{\mathrm{ obs.}}_\tau$| and theoretical values of |${\cal R}^{\mathrm{ model}}_\kappa$| is due to limitations in existing dust models. ppmap  also allows us to derive optical-depth weighted mean values for the emissivity index, β ≡ −dln (κλ)/dln (λ), and the dust temperature, T , denoted |${\bar{\beta }}$| and |${\bar{T}}$|⁠. We show that, in M31, |${\cal R}^{\mathrm{ obs.}}_\tau$| is anticorrelated with |${\bar{\beta }}$| according to |${\cal R}^{\mathrm{ obs.}}_\tau \simeq 2042(\pm 24)-557(\pm 10){\bar{\beta }}$|⁠. If confirmed, this provides a challenging constraint on the nature of interstellar dust in M31. [ABSTRACT FROM AUTHOR]

We present measurements of the angular correlation function of sub-millimetre (sub-mm) galaxies (SMGs) identified in four out of the five fields of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) – GAMA-9h, GAMA-12h, GAMA-15h, and NGP – with flux densities |$S_{250 \, \mu {\rm m}} \gt 30$| mJy at 250 μm. We show that galaxies selected at this wavelength trace the underlying matter distribution differently at low and high redshifts. We study the evolution of the clustering finding that at low redshifts sub-mm galaxies exhibit clustering strengths of r 0 ∼ 2–3 h −1 Mpc, below |$z$| < 0.3. At high redshifts, on the other hand, we find that sub-mm galaxies are more strongly clustered with correlation lengths r 0 = 8.1 ± 0.5, 8.8 ± 0.8, and 13.9 ± 3.9 h −1 Mpc at |$z$|  = 1–2, 2–3. and 3–5, respectively. We show that sub-mm galaxies across the redshift range 1 < |$z$| < 5, typically reside in dark-matter halos of mass of the order of |${\sim } 10^{12.5}\hbox{--}10^{13.0} \, h^{-1}\, \mathrm{M}_{\odot}$| and are consistent with being the progenitors of local massive elliptical galaxies that we see in the local Universe. [ABSTRACT FROM AUTHOR]

This paper forms part of the second major public data release of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). In this work, we describe the identification of optical and near-infrared counterparts to the submillimetre detected sources in the 177 deg2 North Galactic Plane (NGP) field. We used the likelihood ratio method to identify counterparts in the Sloan Digital Sky Survey and in the United Kingdom InfraRed Telescope Imaging Deep Sky Survey within a search radius of 10 arcsec of the H-ATLAS sources with a 4s detection at 250 µm. We obtained reliable (R ≥ 0.8) optical counterparts with r < 22.4 for 42 429 H-ATLAS sources (37.8 per cent), with an estimated completeness of 71.7 per cent and a false identification rate of 4.7 per cent. We also identified counterparts in the nearinfrared using deeper K-band data which covers a smaller ~25 deg2. We found reliable nearinfrared counterparts to 61.8 per cent of the 250-µm-selected sources within that area. We assessed the performance of the likelihood ratio method to identify optical and near-infrared counterparts taking into account the depth and area of both input catalogues. Using catalogues with the same surface density of objects in the overlapping ~25 deg² area, we obtained that the reliable fraction in the near-infrared (54.8 per cent) is significantly higher than in the optical (36.4 per cent). Finally, using deep radio data which covers a small region of the NGP field, we found that 80-90 per cent of our reliable identifications are correct. [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]

We present the first major data release of the largest single key-project in area carried out in open time with the Herschel Space Observatory. The Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) is a survey of 600 deg² in five photometric bands - 100, 160, 250, 350 and 500 µm - with the Photoconductor Array Camera and Spectrometer and Spectral and Photometric Imaging Receiver (SPIRE) cameras. In this paper and the companion Paper II, we present the survey of three fields on the celestial equator, covering a total area of 161.6 deg² and previously observed in the Galaxy and Mass Assembly (GAMA) spectroscopic survey. This paper describes the Herschel images and catalogues of the sources detected on the SPIRE 250 µm images. The 1σ noise for source detection, including both confusion and instrumental noise, is 7.4, 9.4 and 10.2 mJy at 250, 350 and 500 µm. Our catalogue includes 120 230 sources in total, with 113 995, 46 209 and 11 011 sources detected at >4σ at 250, 350 and 500 µm. The catalogue contains detections at >3σ at 100 and 160 µm for 4650 and 5685 sources, and the typical noise at these wavelengths is 44 and 49 mJy.We include estimates of the completeness of the survey and of the effects of flux bias and also describe a novel method for determining the true source counts. The H-ATLAS source counts are very similar to the source counts from the deeper HerMES survey at 250 and 350 µm, with a small difference at 500 µm. Appendix A provides a quick start in using the released data sets, including instructions and cautions on how to use them. [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 present the properties of the first 250 μm blind sample of nearby galaxies (15 < D < 46 Mpc) containing 42 objects from the Herschel Astrophysical Terahertz Large Area Survey. Herschel's sensitivity probes the faint end of the dust luminosity function for the first time, spanning a range of stellar mass (7.4 < M⋆ < 11.3 log10 M⊙), star formation activity (-11.8 < SSFR < -8.9 log10 yr-1), gas fraction (3-96 per cent), and colour (0.6 < FUV-KS < 7.0 mag). The median cold dust temperature is 14.6 K, colder than in the Herschel Reference Survey (18.5 K) and Planck Early Release Compact Source Catalogue (17.7 K). The mean dust-to-stellar mass ratio in our sample is higher than these surveys by factors of 3.7 and 1.8, with a dust mass volume density of (3.7 ± 0.7) × 105 M⊙ Mpc-3. Counter-intuitively, we find that the more dust rich a galaxy, the lower its UV attenuation. Over half of our dust-selected sample are very blue in FUV-KS colour, with irregular and/or highly flocculent morphology; these galaxies account for only 6 per cent of the sample's stellar mass but contain over 35 per cent of the dust mass. They are the most actively star-forming galaxies in the sample, with the highest gas fractions and lowest UV attenuation. They also appear to be in an early stage of converting their gas into stars, providing valuable insights into the chemical evolution of young galaxies. [ABSTRACT FROM AUTHOR]