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Title: Spectroscopic analysis of primeval galaxy candidates
Author: Caruana, Joseph
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2013
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This thesis presents spectroscopic observations of z ≥ 7 galaxy candidates in the Hubble Ultra Deep Field, which were selected with HST WFC3 imaging, using the Lyman-Break technique. Four z-band (z ≈ 7) dropout galaxies were targeted with Gemini/GNIRS, one z-band dropout galaxy and three Y -band (z ≈ 8 − 9) dropout galaxies with VLT/XSHOOTER, and 22 z-band dropouts with VLT/FORS2, where 15 of the latter are strong candidates. No evidence of Lyman-α emission is found, and the upper limits on the Lyman-α flux and the broad-band magnitudes are used to constrain the rest-frame equivalent widths for this line emission. Amongst the targeted objects, observations were made of HUDF.YD3, a relatively bright Y -band dropout galaxy likely to be at z ≈ 8 − 9 on the basis of its colours in the HST ACS and WFC3 images. Lehnert et al. (2010) observed this galaxy using the VLT/SINFONI integral field spectrograph and claim that it exhibits Lyman-α emission at z = 8.55. In observations of this object described in this thesis, which were made with VLT/XSHOOTER and Subaru/MOIRCS, this line was not reproduced despite the expected signal in the combined MOIRCS & XSHOOTER data being 5σ. Hence it appears unlikely that the reported Lyman-α line emission at z > 8 is real. Accounting for incomplete spectral coverage, in total (across all spectro- graphs) 9.63 z-band dropouts and 1.15 Y -band dropouts are surveyed to a Lyman-α rest-frame Equivalent Width better than 75 ̊A. A model where the fraction of high rest-frame equivalent width emitters follows the trend seen at z = 3−6.5 is inconsistent with these non-detections at z = 7−9 at a confidence level of ∼ 91%, which may indicate that a significant neutral HI fraction (χHI) in the intergalactic medium suppresses the Lyman-α line at z > 7. In particular, the lack of detection of Lyman-α emission in this spectroscopy is compared with results at lower redshift by Stark et al. (2010), who derive a mapping between Lyman-α fractions and χHI based on radiative transfer simulations by McQuinn et al. (2007). These results suggest a lower limit of χHI ~ 0.5.
Supervisor: Bunker, Andrew Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: galaxies ; galaxy formation ; galaxy evolution ; starburst galaxies ; Lyman-alpha emission ; high-redshift galaxies ; high-redshift universe ; reionisation ; astrophysics ; observational cosmology ; physics