Galaxy formation and evolution

Abstract:

Aims. We aim to demonstrate that the Herschel-ATLAS (H-ATLAS) is suitable for a blind and unbiased survey for debris disks by identifying candidate debris disks associated with main sequence stars in the initial science demonstration field of the survey. We show that H-ATLAS reveals a population of far-infrared/sub-mm sources that are associated with stars or star-like objects on the SDSS main-sequence locus. We validate our approach by comparing the properties of the most likely candidate disks to those of the known population. Methods. We use a photometric selection technique to identify main sequence stars in the SDSS DR7 catalogue and a Bayesian Likelihood Ratio method to identify H-ATLAS catalogue sources associated with these main sequence stars. Following this photometric selection we apply distance cuts to identify the most likely candidate debris disks and rule out the presence of contaminating galaxies using UKIDSS LAS K-band images. Results. We identify 78 H-ATLAS sources associated with SDSS point sources on the main-sequence locus, of which two are the most likely debris disk candidates: H-ATLAS J090315.8 and H-ATLAS J090240.2. We show that they are plausible candidates by comparing their properties to the known population of debris disks. Our initial results indicate that bright debris disks are rare, with only 2 candidates identified in a search sample of 851 stars. We also show that H-ATLAS can derive useful upper limits for debris disks associated with Hipparcos stars in the field and outline the future prospects for our debris disk search programme. © 2010 ESO.

Abstract:

We have carried out two extremely deep surveys with SPIRE, one of the two cameras on Herschel, at 250 μm, close to the peak of the far-infrared background. We have used the results to investigate the evolution of the rest-frame 250-μm luminosity function out to z = 2. We find evidence for strong evolution out to z $\simeq$ 1 but evidence for at most weak evolution beyond this redshift. Our results suggest that a significant part of the stars and metals in the universe today were formed at z 1.4 in spiral galaxies. © 2010 ESO.

Abstract:

Nuclear and starburst activity are known to often occur concomitantly. Herschel-SPIRE provides sampling of the far-infrared (FIR) spectral energy distributions (SEDs) of type 1 and type 2 AGN, allowing for the separation between the hot dust (torus) and cold dust (starburst) emission. We study large samples of spectroscopically confirmed type 1 and type 2 AGN lying within the Herschel Multi-tiered Extragalactic Survey (HerMES) fields observed during the science demonstration phase, aiming to understand their FIR colour distributions and constrain their starburst contributions. We find that one third of the spectroscopically confirmed AGN in the HerMES fields have 5σ detections at 250 μm, in agreement with previous (sub)mm AGN studies. Their combined Spitzer-MIPS and Herschel-SPIRE colours (specifically S250/S 70 vs S70/S24) quite clearly separate them from the non-AGN, star forming galaxy population, as their 24 μm flux is dominated by the hot torus emission. However, their SPIRE colours alone do not differ from those of non-AGN galaxies. SED fitting shows that all those AGN need a starburst component to fully account for their FIR emission. For objects at z > 2 we find a correlation between the infrared luminosity attributed to the starburst component, LSB, and the AGN accretion luminosity, L acc, with LSB proptoLacc0.35. Type 2 AGN detected at 250 μm show on average higher LSB than type 1 objects but their number is still too low to establish whether this trend indicates stronger star formation activity. © 2010 ESO.

Abstract:

We measure the angular correlation function, w(θ), from 0.5 to 30 arcmin of detected sources in two wide fields of the Herschel Multi-tiered Extragalactic Survey (HerMES). Our measurements are consistent with the expected clustering shape from a population of sources that trace the dark matter density field, including non-linear clustering at arcminute angular scales arising from multiple sources that occupy the same dark matter halos. By making use of the halo model to connect the spatial clustering of sources to the dark matter halo distribution, we estimate source bias and halo occupation number for dusty sub-mm galaxies at z ∼ 2. We find that sub-mm galaxies with 250 μm flux densities above 30 mJy reside in dark matter halos with mass above (5±4)×1012 M⊙, while (14±8)% of such sources appear as satellites in more massive halos. © 2010 ESO.

Abstract:

Emission at far-infrared wavelengths makes up a significant fraction of the total light detected from galaxies over the age of Universe. Herschel provides an opportunity for studying galaxies at the peak wavelength of their emission. Our aim is to provide a benchmark for models of galaxy population evolution and to test pre-existing models of galaxies. With the Herschel Multi-tiered Extra-galactic survey, HerMES, we have observed a number of fields of different areas and sensitivity using the SPIRE instrument on Herschel. We have determined the number counts of galaxies down to ~20 mJy. Our constraints from directly counting galaxies are consistent with, though more precise than, estimates from the BLAST fluctuation analysis. We have found a steep rise in the Euclidean normalised counts <100 mJy. We have directly resolved ~15% of the infrared extra-galactic background at the wavelength near where it peaks. © 2010 ESO.