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Title: A wide-area search for high redshift Lyman alpha haloes
Author: Smith, Daniel J. B.
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2007
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Abstract:
In this thesis I present our wide-field narrow-band survey, designed to locate the brightest and rarest Lyman 0: haloes at redshifts around 3. I describe the technical aspects of our survey, such as the observing strategy and sensitivity, and calculate our ability to measure Equivalent ·Widths, which are considered a key tool in separating Lyman 0: emitters from objects exhibiting other species of emission lines. I present the first results from this survey which comprises observations of three extragalactic survey fields; the XMM-Large Scale Structure Field, the Lockman Hole, and the Spitzer First Look Survey region. These observations are spread among three narrow-band filters centred on the wavelengths of the Hell, H,B, [Om] emission lines at 4686A, 4861A and 5008A respectively. Our survey also includes additional broad-band observations in the Sloan g', r' & i' photometric bands. Using the First Look Survey portion of this new data set, I present a new sample of 65 highly luminous (L > 1043 erg s-I), and extended high redshift Lyman 0: haloes. Spectroscopic follow-up of 26 galaxies from this sample produces 17 confirmed Ly-o: haloes, varying in size from 7kpc to ~ 95 kpc. A comparison of these haloes and the Lyman 0: emitter luminosity function suggests that these bright objects belong to a different population of galaxies than Lyman 0: emitters in general. A set of crude SED-fitting analyses using our multi-wavelength data set suggests that at least one of these galaxies contains an obscured active galactic nucleus component. The most extended of these haloes - a Ly-o: Blob, so-called on account of its amoebic appearance and almost monochromatic emission - was thought in our preliminary findings to be ionized by a 'cold accretion' process, in which the apparent power source for the profuse Lyman 0: emission is collisional excitation followed by radiative cooling. We expand on these results which were published in Smith & Jarvis (2007), and present independent tests of the cold accretion hypothesis using the IRAC & MIPS cameras on the Spitzer Space Telescope at mid-infrared wavelengths, and using the 8 metre Gemini North Telescope with high resolution 2-dimensional GMOS-N optical spectroscopy. These very deep observations in the mid-infrared include a non-detection in the 24Jlm band down to a 30' flux limit of 16.4JlJy, while the high resolution spectroscopy indicates a velocity structure which is readily explained by inflowing neutral gas. These findings reinforce our view that cold accretion is the most likely source of power. Having observed the region around the 100 kpc Lyman 0: Blob using Lyman Break techniques, we find no evidence for a local over-density of Lyman Break Galaxies. The actual halo itself is positioned away from the peak in local Lyman Break Galaxy surface number density, reminiscent of the environment of at least one other known Lyman 0: halo (LAB2 from Steidel, 2000). It is unclear to what extent these results are typical since there are currently only three Lyman 0: Blobs that have been subject to this kind of study. The full sample of Ly-o: haloes, and thumbnail images of our coverage of the Spitzer First Look Survey region are included as appendices.
Supervisor: Not available Sponsor: Not available
Qualification Name: University of Oxford, 2007 Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.491965  DOI: Not available
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