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Title: Dust-enshrouded star formation at high redshift
Author: Scott, Susan
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2003
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Since the advent of SCUBA, deep submillimetre surveys have succeeded in resolving the bulk of the far-infrared extragalactic background into discrete sources, revealing a population of high-redshift (z > 1) heavily dust-enshrouded massive-starforming galaxies. Here, the nature of the most luminous 850μm sources (S850 > 5 mJy) are considered, in particular their link with the formation and evolution of the most massive elliptical galaxies visible in the present-day Universe. The “SCUBA 8 mJy Survey” is the largest of the blank field submillimetre surveys completed to date, designed specifically with the aim of identifying the brightest 850μm sources. It covers ~ 260 square arcminutes of sky to a depth of σrms ~ 2.5mJy/beam, evenly split between two areas of low galactic cirrus emission; the Lockman Hole East and ELAIS N2. The data have in part been reduced by the standard JCMT SURF procedures, but the primary reduction method was an alternative IDL-based pipeline which has the advantage of producing uncorrelated noise images. This later approach has enabled me to develop a maximum-likelihood source extraction algorithm which simultaneously measures the statistical significance of every peak in a SCUBA map, leading to properly quantified errors on the flux densities of all potential sources. Applying the source extraction algorithm to these two fields has revealed 19 sources with S/N > 4.00, 40 sources with S/N > 3.50, and 85 sources with S/N > 3.00. Completeness, mean output vs. input flux density, and contamination from spurious/confused sources were quantified using extensive Monte Carlo simulations. Using deep 1.4 GHz imaging of the survey fields to determine the radio-to-submillimetre spectral indices for every 850μm detection, all sources were constrained to lie at z > 1, with a median redshift zmed ~  2.4. This being the case, the inferred star formation rates are ~ 1000 M? yr-1, sufficient to form the most massive elliptical galaxies on timescales of ~ 1 Gyr, but heavily obscured by 108 – 109 M? of dust. The commoving number density of high redshift galaxies forming stars at > 1000 M? yr-1 is ~ 10-5 Mpc-3, with only a weak dependence on the precise redshift distribution, also corresponding to the number density of massive ellipticals with L > 3 – 4L* in the present-day Universe, as well as the co-moving number density of comparably massive, passively-evolving objects in the redshift band 1 < z < 2 inferred from recent surveys of extremely red objects. This suggests that the bright submillimetre sources uncovered by this survey can plausibly account for the formation of all present-day massive spheroids.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available