Panchromatic observations of the best candidate HyLIRG from the widest Herschel extragalactic imaging survey have led to the discovery of at least four intrinsically luminous z = 2.41 galaxies across a ≈100-kpc region -a cluster of starbursting proto-ellipticals. Via sub-arcsecond interferometric imaging we have measured accurate gas and star-formation surface densities. The two brightest galaxies span ∼3 kpc FWHM in submm/radio continuum and CO J = 4−3, and double that in CO J = 1−0. The broad CO line is due partly to the multitude of constituent galaxies and partly to large rotational velocities in two counter-rotating gas disks -a scenario predicted to lead to the most intense starbursts, which will therefore come in pairs. The disks have M dyn of several ×10 11 M ⊙ , and gas fractions of ∼ 40%. Velocity dispersions are modest so the disks are unstable, potentially on scales commensurate with their radii: these galaxies are undergoing extreme bursts of star formation, not confined to their nuclei, at close to the Eddington limit. Their specific star-formation rates place them > ∼ 5× above the main sequence, which supposedly comprises large gas disks like these. Their high star-formation efficiencies are difficult to reconcile with a simple volumetric star-formation law. N-body and dark matter simulations suggest this system is the progenitor of a B(inary)-type ≈ 10 14.6 -M ⊙ cluster.

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.

We present the dust properties and star formation histories of local submillimetre‐selected galaxies, classified by optical morphology. Most of the galaxies are late types and very few are early types. The early‐type galaxies (ETGs) that are detected contain as much dust as typical spirals, and form a unique sample that has been blindly selected at submillimetre wavelengths. Additionally, we investigate the properties of the most passive, dusty spirals. We morphologically classify 1087 galaxies detected in the Herschel‐Astrophysical Terahertz Large Area Survey (H‐ATLAS) Science Demonstration Phase data. Comparing to a control sample of optically selected galaxies, we find 5.5 per cent of luminous ETGs are detected in H‐ATLAS. The H‐ATLAS ETGs contain a significant mass of cold dust: the mean dust mass is 5.5 × 107 M⊙, with individual galaxies ranging from 9 × 105 to 4 × 108 M⊙. This is comparable to that of spiral galaxies in our sample, and is an order of magnitude more dust than that found for the control early‐types, which have a median dust mass inferred from stacking of (0.8–4.0) × 106 M⊙ for a cold dust temperature of 25–15 K. The early‐types detected in H‐ATLAS tend to have bluer NUV − r colours, higher specific star formation rates and younger stellar populations than early‐types which are optically selected, and may be transitioning from the blue cloud to the red sequence. We also find that H‐ATLAS and control early‐types inhabit similar low‐density environments. We investigate whether the observed dust in H‐ATLAS early‐types is from evolved stars, or has been acquired from external sources through interactions and mergers. We conclude that the dust in H‐ATLAS and control ETGs cannot be solely from stellar sources, and a large contribution from dust formed in the interstellar medium or external sources is required. Alternatively, dust destruction may not be as efficient as predicted. We also explore the properties of the most passive spiral galaxies in our sample with specific star formation rate (SSFR) < 10−11 yr−1. We find these passive spirals have lower dust‐to‐stellar mass ratios, higher stellar masses and older stellar population ages than normal spirals. The passive spirals inhabit low‐density environments similar to those of the normal spiral galaxies in our sample. This shows that the processes which turn spirals passive do not occur solely in the intermediate‐density environments of group and cluster outskirts.

We use the Herschel‐ATLAS survey to conduct the first large‐scale statistical study of the submillimetre properties of optically selected galaxies. Using ∼80 000 r‐band selected galaxies from 126  deg2 of the GAMA survey, we stack into submillimetre imaging at 250, 350 and 500 μ m to gain unprecedented statistics on the dust emission from galaxies at z < 0.35. We find that low‐redshift galaxies account for 5 per cent of the cosmic 250‐μm background (4 per cent at 350 μ m; 3 per cent at 500 μ m), of which approximately 60 per cent comes from ‘blue’ and 20 per cent from ‘red’ galaxies (rest‐frame g−r). We compare the dust properties of different galaxy populations by dividing the sample into bins of optical luminosity, stellar mass, colour and redshift. In blue galaxies we find that dust temperature and luminosity correlate strongly with stellar mass at a fixed redshift, but red galaxies do not follow these correlations and overall have lower luminosities and temperatures. We make reasonable assumptions to account for the contaminating flux from lensing by red‐sequence galaxies and conclude that galaxies with different optical colours have fundamentally different dust emission properties. Results indicate that while blue galaxies are more luminous than red galaxies due to higher temperatures, the dust masses of the two samples are relatively similar. Dust mass is shown to correlate with stellar mass, although the dust‐to‐stellar mass ratio is much higher for low stellar mass galaxies, consistent with the lowest mass galaxies having the highest specific star formation rates. We stack the 250 μ m‐to‐NUV luminosity ratio, finding results consistent with greater obscuration of star formation at lower stellar mass and higher redshift. Submillimetre luminosities and dust masses of all galaxies are shown to evolve strongly with redshift, indicating a fall in the amount of obscured star formation in ordinary galaxies over the last four billion years.

We report the discovery of a well-defined correlation between B-band face-on central optical depth due to dust, τ f B , and the stellar mass surface density, µ * , of nearby (z ≤ 0.13) spiral galaxies: log(τ f B ) = 1.12(±0.11) · log µ * M⊙kpc −2 − 8.6(±0.8). This relation was derived from a sample of spiral galaxies taken from the Galaxy and Mass Assembly (GAMA) survey, which were detected in the FIR/submm in the Herschel -ATLAS science demonstration phase field. Using a quantitative analysis of the NUV attenuation-inclination relation for complete samples of GAMA spirals categorized according to stellar mass surface density we demonstrate that this correlation can be used to statistically correct for dust attenuation purely on the basis of optical photometry and Sérsic-profile morphological fits. Considered together with previously established empirical relationships of stellar mass to metallicity and gas mass, the near linearity and high constant of proportionality of the τ f B − µ * relation disfavors a stellar origin for the bulk of refractory grains in spiral galaxies, instead being consistent with the existence of a ubiquitous and very rapid mechanism for the growth of dust in the ISM. We use the τ f B − µ * relation in conjunction with the radiation transfer model for spiral galaxies of Popescu & Tuffs (2011) to derive intrinsic scaling relations between specific star formation rate, stellar mass, and stellar surface density, in which attenuation of the UV light used for the measurement of star-formation rate is corrected on an object-to-object basis. A marked reduction in scatter in these relations is achieved which we demonstrate is due to correction of both the inclination-dependent and face-on components of attenuation. Our results are consistent with a general picture of spiral galaxies in which most of the submm emission originates from grains residing in translucent structures, exposed to UV in the diffuse interstellar radiation field.