Participation in the Herschel-ATLAS survey

(Stevens, Hardcastle, Bonfield, Brassington, Smith)

The Herschel ATLAS survey is the biggest of the sky conducted at far-infrared wavelengths, covering approximately 550 square degrees (Eales et al. 2010, PASP, 122, 499). Within this survey we are leading science in a number of areas:

• A study of Broad Absorption Line (BAL) QSOs. Using early data we have shown that BAL QSOs have far-infrared properties (and hence star-formation rates) indistinguishable from those of ordinary QSOs (Orjales, Stevens et al. 2012, MNARS, submitted). This result supports a simple orientation hypothesis for the BAL phenomena, i.e. BALs are just ordinary QSOs viewed at an angle that intercepts outflowing material from the central AGN. We are currently seeking to extend this work using ATLAS and/or SCUBA-2 to observe a subset of BALs called LoBALs which were largely absent from our sample but might not fit within this simple unified scheme.
• Studies of the far-infrared output of radio-selected galaxies as a function of luminosity, redshift and other source properties (Hardcastle et al. 2010, MNRAS, 409, 122; Virdee et al in prep; Hardcastle et a.l, in prep.). This work aims to determine the relationship between star formation and radio-loud AGN activity; are radio galaxies always, or even sometimes, associated with star-formation activity resulting from a gas-rich merger? We have shown that typical radio galaxies have no more star-formation activity than colour- and magnitude-matched radio-quiet galaxies. However, radio galaxies with strong AGN-related emission lines appear to be associated with higher dust temperatures, implying on-going star formation.
• The link between accretion luminosity and star-formation in quasar host galaxies (Bonfield et al. 2011, MNRAS, 416, 13). Dave to add.
• Though the sensitivity and field-of-view of Herschel is unprecedented, the angular resolution is limited due to the long wavelength at which it operates. Consequently, in contrast to shorter-wavelength surveys, it is non-trivial to identify the dusty far-infrared sources in optical data, which we must if we are to study the multi-wavelength properties of Herschel sources. In Smith et al. (2011, MNRAS, 416, 857) we used a likelihood ratio analysis to achieve this for the 16 deg2 of Science Demonstration phase data of the Herschel-ATLAS survey, comprising 6621 galaxies. We showed that the 250um galaxy population is bimodal in redshift, broadly comprising both local (z < 0.5) and distant (z > 1) components. This study has already been expanded on for the next ~100 deg2 of H-ATLAS, and also to explore the impact of cross-matching to ancillary data on studies with Square Kilometer Array (SKA) precursors (McAlpine, et al., 2012, MNRAS, in press).In Smith et al. (submitted), we built upon the cross-matched Herschel - optical catalogue to derive full multiwavelength spectral energy distributions of 1400 far-infrared selected galaxies at z < 0.5. In doing so, we derived their physical properties, including showing that these galaxies contained larger dust masses than had previously been realised. We also used the large sample of galaxies to determine a new set of empirical panchromatic SED templates, which are inconsistent with those derived in previous studies. These Smith et al. SED templates, which may be more appropriate for studies of local star-forming galaxies, and are the only SED templates of which the authors are aware to include uncertainties as a function of wavelength, are available here.
• Star-Formation Rates in Pair Galaxies: Through observations of merging galaxies in the local Universe it is clear that galaxy interactions can lead to enhanced star-formation. However, we also know that not all interactions result in increased activity. From the galaxy group catalogue of the Galaxy And Mass Assembly (GAMA) survey (Robotham et al., 2011, MNRAS, 416, 2640) we have selected a sample of close galaxy pairs to investigate the dependence of star-formation rate on environment, out to redshift 0.85. By cross-correlating this sample with the H-ATLAS survey we are able to determine the star-forming properties of these systems and probe its dependence on pair separation over redshift bins.