Wilkinson, Aaron K.R.
(2017)
From starburst to quiescence: the rapid evolution of galaxies within the large-scale structure.
PhD thesis, University of Nottingham.
Abstract
Submillimetre galaxies (SMGs) and post-starburst (PSB) galaxies are among the most rare and interesting classes of objects in extragalactic study. SMGs are extremely active dust-obscured galaxies in the early Universe, forming stars with an immense rate of up to 1000 solar masses per year. PSB galaxies are characterised by strong Balmer absorption lines in their spectra, consistent with a recent burst of star formation before being rapidly quenched. The origin of both of these objects and how they relate to the more common populations of red-sequence and blue-cloud galaxies remain elusive. My thesis involves weighing the dark matter halos inhabited by these rare galaxies, by investigating their clustering at 0.5<z<3.5. To achieve this, I use data from two deep large-scale near-infrared surveys: the UKIDSS Ultra Deep Survey (UDS) and the Cosmic Evolution Survey (COSMOS). The former survey is complemented by 850 micron maps from the SCUBA-2 Cosmology Legacy Survey, from which SMGs are identified. Both UDS and COSMOS fields also benefit from a wide range of multi-wavelength imaging, vital for the photometric selection of PSB galaxies.
I begin this thesis with a review of a novel Principal Component Analysis (PCA) technique used to select PSB galaxies with broad-band photometry. I implement this technique to identify ~4000 PSB candidates in the COSMOS field up to z=2.5, making this the largest high-redshift sample of its kind. The photometric selection of PSB candidates is confronted with spectroscopy, revealing that the PCA is robust.
In Chapter 3, I set out to investigate the clustering of 610 SMG counterparts identified in the UDS field. Using angular cross-correlation techniques, I found that the SMGs, on average, occupy high-mass dark matter halos (M_halo>10^13 solar masses) at redshifts z>2.5, consistent with being the progenitors of massive quiescent galaxies in present day clusters. I also find evidence of halo downsizing, in which SMG activity shifts to lower mass haloes at lower redshifts. In terms of their clustering and halo masses, SMGs appear to be consistent with normal star-forming galaxies at any given redshift.
In Chapter 4, I obtain clustering measurements for the PCA-selected populations in the UDS and COSMOS fields, using the same methodology as Chapter 3. Low-mass, low-redshift (0.5<z<1.0) PSB galaxies preferentially reside in very high-mass dark matter halos (M_halo>10^14 solar masses) and are likely to be infalling satellite galaxies in cluster-like environments. Conversely, high-mass PSB galaxies are not as clustered. These key results indicate two main channels are responsible for the rapid quenching of galaxies. High-redshift (z>1) galaxies tend to be quenched by feedback mechanisms related to the stellar mass of the galaxy (`mass-quenching'). Processes associated with dense environments (`environmental-quenching') are likely to be the key driver of rapid quenching of galaxies in the low-redshift Universe (z<1). Finally, we present tentative evidence that SMGs pass through a PSB phase before migrating to the red-sequence, over timescales of ~500 Myr.
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