Galaxy formation and evolution

Abstract:

We describe the reduction of data taken with the PACS instrument on board the Herschel Space Observatory in the Science Demonstration Phase of the Herschel-ATLAS (H-ATLAS) survey, specifically data obtained for a 4 × 4 deg2 region using Herschel's fast-scan (60 arcsec s-1) parallel mode. We describe in detail a pipeline for data reduction using customized procedures within hipe from data retrieval to the production of science-quality images. We found that the standard procedure for removing cosmic ray glitches also removed parts of bright sources and so implemented an effective two-stage process to minimize these problems. The pronounced 1/f noise is removed from the timelines using 3.4- and 2.5-arcmin boxcar high-pass filters at 100 and 160 μm. Empirical measurements of the point spread function (PSF) are used to determine the encircled energy fraction as a function of aperture size. For the 100- and 160-μm bands, the effective PSFs are ~9 and ~13 arcsec (FWHM), and the 90-per cent encircled energy radii are 13 and 18 arcsec. Astrometric accuracy is good to ≤2 arcsec. The noise in the final maps is correlated between neighbouring pixels and rather higher than advertised prior to launch. For a pair of cross-scans, the 5σ point-source sensitivities are 125-165 mJy for 9-13 arcsec radius apertures at 100 μm and 150-240 mJy for 13-18 arcsec radius apertures at 160 μm. © 2010 The Authors. Journal compilation © 2010 RAS.

Abstract:

Dusty, star-forming galaxies contribute to a bright, currently unresolved cosmic far-infrared background. Deep Herschel-Spectral and Photometric Imaging Receiver (SPIRE) images designed to detect and characterize the galaxies that comprise this background are highly confused, such that the bulk lies below the classical confusion limit. We analyse three fields from the Herschel Multi-tiered Extragalactic Survey (HerMES) programme in all three SPIRE bands (250, 350 and 500 μm); parametrized galaxy number count models are derived to a depth of ~2 mJy beam-1, approximately four times the depth of previous analyses at these wavelengths, using a probability of deflection [P(D)] approach for comparison to theoretical number count models. Our fits account for 64, 60 and 43 per cent of the far-infrared background in the three bands. The number counts are consistent with those based on individually detected SPIRE sources, but generally inconsistent with most galaxy number count models, which generically overpredict the number of bright galaxies and are not as steep as the P(D)-derived number counts. Clear evidence is found for a break in the slope of the differential number counts at low flux densities. Systematic effects in the P(D) analysis are explored. We find that the effects of clustering have a small impact on the data, and the largest identified systematic error arises from uncertainties in the SPIRE beam. © 2010 The Authors. Journal compilation © 2010 RAS.

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. © ESO 2010.

Abstract:

We present first results of a study of the submillimetre (submm) (rest-frame far-infrared) properties of z ~ 3 Lyman break galaxies (LBGs) and their lower redshift counterparts BX/BM galaxies, based on Herschel-SPIRE observations of the Northern field of the Great Observatories Origins Deep Survey (GOODS-N). We use stacking analysis to determine the properties of LBGs well below the current limit of the survey. Although LBGs are not detected individually, stacking the infrared luminous LBGs (those detected with Spitzer at 24 |xm) yields a statistically significant submm detection with mean flux 〈S250〉 = 5.9 ±1.4 mJy confirming the power of SPIRE in detecting UV-selected high-redshift galaxies at submm wavelengths. In comparison, the Spitzer 24 |j.m detected BX/BM galaxies appear fainter with a stacked value of 〈S250〉 = 2.7 ± 0.8 mJy. By fitting the spectral energy distributions (SEDs) we derive median infrared luminosities, LIR, of 2.8 × 1012 L⊙ and 1.5 × 1011 L. for z ~ 3 LBGs and BX/BMs, respectively. We find that LIR estimates derived from present measurements are in good agreement with those based on UV data for z ~ 2 BX/BM galaxies, unlike the case for z ~ 3 infrared luminous LBGs where the UV underestimates the true LIR. Although sample selection effects may influence this result we suggest that differences in physical properties (such as morphologies, dust distribution and extent of star-forming regions) between z ~ 3 LBGs and z ~ 2 BX/BMs may also play a significant role. © 2010 The Authors. Journal compilation © 2010 RAS.

Abstract:

Wehave analysed the rest-frame far-infrared properties ofa sample of massive (M* > 1011 M⊙) galaxies at 2 ≲ z ≲ 3 in the Great Observatories Origins Deep Survey-North (GOODS-N) field using the Spectral and Photometric Imaging Receiver (SPIRE) instrument aboard the Herschel Space Observatory. To conduct this analysis we take advantage of the data from the Herschel Multi-tiered Extragalactic Survey (HerMES) key programme. The sample comprises 45 massive galaxies with structural parameters characterized with HST NICMOS-3. We study detections at submm Herschel bands, together with Spitzer 24-μm data, as a function of the morphological type, mass and size. We find that 26/45 sources are detected at MIPS 24 μm and 15/45 (all MIPS 24-μm detections) are detected at SPIRE 250 μ with disc-like galaxies more easily detected. We derive star formation rates (SFRs) and specific star formation rates (sSFRs) by fitting the spectral energy distribution of our sources, taking into account non-detections for SPIRE and systematic effects for MIPS derived quantities. We find that the mean SFR for the spheroidal galaxies (~50-100M⊙ yr-1) is substantially (a factor ~3) lower than the mean value presented by disc-like galaxies (~250-300M⊙ yr-1). © 2010 The Authors. Journal compilation © 2010 RAS.