The Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) is a survey of 660 deg 2 with the PACS and SPIRE cameras in five photometric bands: 100, 160, 250, 350, and 500 μm. This is the second of three papers describing the data release for the large fields at the south and north Galactic poles (NGP and SGP). In this paper we describe the catalogs of far-infrared and submillimeter sources for the NGP and SGP, which cover 177.1 deg 2 and 303.4 deg 2 , respectively. The catalogs contain 118,908 sources for the NGP field and 193,527 sources for the SGP field detected at more than 4σ significance in any of the 250, 350, or 500 μmbands. The source detection is based on the 250 μm map, and we present photometry in all five bands for each source, including aperture photometry for sources known to be extended. The rms positional accuracy for the faintest sources is about 2.4 arcsec in both R.A. and decl. We present a statistical analysis of the catalogs and discuss the practical issuescompleteness, reliability, flux boosting, accuracy of positions, accuracy of flux measurements-necessary to use the catalogs for astronomical projects.

We investigate the evolution of the gas mass fraction for galaxies in the COSMOS field using submillimetre emission from dust at 850µm. We use stacking methodologies on the 850 µm 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 < M * (M ) < 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.

We investigate the evolution in galactic dust mass over cosmic time through i) empirically derived dust masses using stacked submillimetre fluxes at 850μm in the COSMOS field, and ii) dust masses derived using a robust post-processing method on the results from the cosmological hydrodynamical simulation IllustrisTNG. We effectively perform a ‘self-calibration’ of the dust mass absorption coefficient by forcing the model and observations to agree at low redshift and then compare the evolution shown by the observations with that predicted by the model. We create dust mass functions (DMFs) based on the IllustrisTNG simulations from 0 &lt;z &lt; 0.5 and compare these with previously observed DMFs. We find a lack of evolution in the DMFs derived from the simulations, in conflict with the rapid evolution seen in empirically derived estimates of the low redshift DMF. Furthermore, we observe a strong evolution in the observed mean ratio of dust mass to stellar mass of galaxies over the redshift range 0 &lt;z &lt; 5, whereas the corresponding dust masses from IllustrisTNG show relatively little evolution, even after splitting the sample into satellites and centrals. The large discrepancy between the strong observed evolution and the weak evolution predicted by IllustrisTNG plus post-processing may be explained by either strong cosmic evolution in the properties of the dust grains or limitations in the model. In the latter case, the limitation may be connected to previous claims that the neutral gas content of galaxies does not evolve fast enough in IllustrisTNG.

The Herschel-ATLAS unbiased survey of cold dust in the local Universe is dominated by a surprising population of very blue (F U V − K < 3.5), dust-rich galaxies with high gas fractions (f HI = M HI /( M * + M HI ) > 0.5). Dubbed 'Blue and Dusty Gas Rich Sources' (BADGRS) they have cold diffuse dust temperatures, and the highest dustto-stellar mass ratios of any galaxies in the local Universe. Here, we explore the molecular ISM in a representative sample of BADGRS, using very deep CO(J up = 1, 2, 3) observations across the central and outer disk regions. We find very low CO brightnesses (T p = 5 − 30 mK), despite the bright far-infrared emission and metallicities in the range 0.5 < Z/Z < 1.0. The CO line ratios indicate a range of conditions with R 21 = T 21 b /T 10 b = 0.6 − 2.1 and R 31 = T 32 b /T 10 b = 0.2 − 1.2. Using a metallicity dependent conversion from CO luminosity to molecular gas mass we find M H2 / M d ∼ 7 − 27 and Σ H2 = 0.5 − 6 M pc −2 , around an order of magnitude lower than expected. The BADGRS have lower molecular gas depletion timescales (τ d ∼ 0.5 Gyr) than other local spirals, lying offset from the Kennicutt-Schmidt relation by a similar factor to Blue Compact Dwarf galaxies. The cold diffuse dust temperature in BADGRS (13-16 K) requires an interstellar radiation field 10-20 times lower than that inferred from their observed surface brightness. We speculate that the dust in these sources has either a very clumpy geometry or a very different opacity in order to explain the cold temperatures and lack of CO emission. BADGRS also have low UV attenuation for their UV colour suggestive of an SMC-type dust attenuation curve, different star formation histories or different dust/star geometry. They lie in a similar part of the IRX-β space as z ∼ 5 galaxies and may be useful as local analogues for high gas fraction galaxies in the early Universe.