Herschel-ATLAS: Extragalactic number counts from 250 to 500 microns

Abstract

Aims. The Herschel-ATLAS survey (H-ATLAS) will be the largest area survey to be undertaken by the Herschel Space Observatory. It will cover 550 sq. deg. of extragalactic sky at wavelengths of 100, 160, 250, 350 and 500µm when completed, reaching flux limits (5σ) from 32 to 145mJy. We here present galaxy number counts obtained for SPIRE observations of the first ∼14 sq. deg. observed at 250, 350 and 500µm. Methods. Number counts are a fundamental tool in constraining models of galaxy evolution. We use source catalogs extracted from the H-ATLAS maps as the basis for such an analysis. Correction factors for completeness and flux boosting are derived by applying our extraction method to model catalogs and then applied to the raw observational counts. Results. We find a steep rise in the number counts at flux levels of 100-200mJy in all three SPIRE bands, consistent with results from BLAST. The counts are compared to a range of galaxy evolution models. None of the current models is an ideal fit to the data but all ascribe the steep rise to a population of luminous, rapidly evolving dusty galaxies at moderate to high redshift.

Dusty star-forming galaxies at high redshift

“…The work of Blain et al (1999), Smail et al (2002), Cowie et al (2002), Knudsen et al (2008) and Chen et al (2013a) used gravitational lensing in cluster fields to survey flux densities <1 mJy. Oliver et al, 2010;Clements et al, 2010;Béthermin et al, 2010bBéthermin et al, , 2012b, and 1.1 mm Austermann et al, 2010;Scott et al, 2010;Hatsukade et al, 2011;Aretxaga et al, 2011;Scott et al, 2012). Figure 14 gathers all of these results together and plots all submillimeter number counts together in Euclideannormalized units, allowing for a more clear view of how the slope, normalization, and intrinsic variance vary between selection wavelengths and what relative dynamic range is probed at each wavelength.…”

“…Figure 12 illustrates both 850-870µm number counts (from Scuba, Laboca, Scuba-2, and ALMA Blain et al, 1999;Scott et al, 2002;Chapman et al, 2002;Cowie et al, 2002;Borys et al, 2003;Webb et al, 2003;Barnard et al, 2004;Coppin et al, 2006;Scott et al, 2006;Knudsen et al, 2008;Beelen et al, 2008;Weiß et al, 2009a;Karim et al, 2013;Casey et al, 2013;Chen et al, 2013a) and 450-500µm (from Scuba, Herschel and Scuba-2 Smail et al, 2002;Oliver et al, 2010;Clements et al, 2010;Béthermin et al, 2012b;Geach et al, 2013;Casey et al, 2013;Chen et al, 2013a). Figure 13 illustrates other infrared and submillimeter number counts in the literature in direct units, from 70µm Béthermin et al, 2010a;Berta et al, 2011), 100µm (Héraudeau et al, 2004;Rodighiero & Franceschini, 2004;Kawara et al, 2004;Berta et al, 2011;Magnelli et al, 2013b), 160µm Kawara et al, 2004;Béthermin et al, 2010a;Berta et al, 2011;Magnelli et al, 2013b), 250µm and 350µm Chen+13 (850) Casey+13 (850 Figure 12: Differential submillimeter number counts at 850µm/870µm (left) and 450-500 µm (right).…”

“…At 160µm-170µm, data are from Spitzer MIPS Béthermin et al, 2010a), ISO ISOPHOT (Kawara et al, 2004), and Herschel PACS Magnelli et al, 2013b). At both 250µm and 350µm, data come from BLAST Béthermin et al, 2010b) and Herschel SPIRE Clements et al, 2010;Béthermin et al, 2012b). All 1.1 mm number counts studies have been undertaken with the AzTEC instrument on JCMT and ASTE and summarized in Scott et al (2012), including prior datasets described in Perera et al (2008), Austermann et al (2010), Scott et al (2010), Hatsukade et al (2011), andAretxaga et al (2011).…”

“…While the integrated intensity is known, albeit highly uncertain, we still do not have a complete understanding of the sources responsible for the background, the key reason being that existing surveys are limited by large beamsizes and confusion noise. For example, recent deep surveys with Herschel and ground-based sub-mm and mm-wave instruments have only managed to directly resolve about 5% to 15% of the background to individual galaxies at wavelengths longer than 250µm (Coppin et al, 2006;Scott et al, 2010;Oliver et al, 2010;Clements et al, 2010). At far-infrared wavelengths of 100 and 160µm, deep surveys with Herschel/PACS have now resolved ∼60% and 75% of the COBE/DIRBE CIB intensity .…”

Herschel Observations in the Akari Nep Field: Initial Source Counts

“…In Figure 3 (a-c) the SPIRE source counts (down to the 50% completeness level) at the NEP are compared to the results from the H-ATLAS Herschel Open Time Key Programme (Clements et al, 2010) and the HerMES Herschel Guaranteed Time programme (Oliver et al, 2010). The NEP source counts in the SPIRE bands reach interesting cosmological depths where the counts peak and turn over.…”