Prof. Matt Jarvis

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 present the results of our search for high-redshift Lyman-break galaxies over the GOODS-South field. We use Hubble Space Telescope (HST)-ACS data in B, V, i′ & z′, Very Large Telescope (VLT)-ISAAC J and Ks, Spitzer-Infrared Array Camera (IRAC) 3.6, 4.5, 5.8 and 8.0 μm data in conjunction with the new HAWK-I Y-band science verification data to search for dropout galaxies in the redshift range 6 < z < 9. We survey ≈119 arcmin² to YAB = 25.7 (5σ), of which 37.5 arcmin² reaches YAB = 25.9. Candidate z′ and Y dropouts were selected on the basis of a colour cut of (Y - J)AB > 0.75 mag and (z′ - Y)AB > 1.0 mag, respectively. We find no robust Y-drops (z ≈ 9) brighter than JAB < 25.4. In our search for z′-band dropouts (z ≈ 6.5-7.5), we identify four possible candidates, two with z′-drop colours and clear Spitzer-IRAC detections and two less likely candidates. We also identify two previously known Galactic T-dwarf stellar contaminants with these colours, and two likely transient objects seen in the Y-band data. The implications if all or none of our candidates is real on the ultraviolet galaxy luminosity functions at z > 6.5 are explored. We find our number of z′-drop candidates to be insufficient based on the expected number of z′ drops in a simple no-evolution scenario from the z = 3 Lyman-break galaxy luminosity function but we are consistent with the observed luminosity function at z ≈ 6 (if all our candidates are real). However, if one or both of our best z′-drop candidates are not z > 6.5 galaxies, this would demand evolution of the luminosity function at early epochs, in the sense that the number density of ultraviolet luminous star- forming galaxies at z > 7 is less than at z ~ 6. We show that the future surveys to be conducted with the European Southern Observatory VISTA telescope over the next 5 yr will be able to measure the bulk of the luminosity function for both z′ and Y dropouts and thus provide the strongest constraints on the level of star-formation within the epoch of reionization. © 2010 The Authors. Journal compilation. © 2010 RAS.

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.