| dc.description.abstract | In this thesis, I explore both obscured and unobscured star formation over a
large fraction of cosmic time. I use the HAWK-I Y -band science verification
data over GOODS-South, in conjunction with optical and infrared data to
search for Lyman-break galaxies at z >∼
6.5 (i.e. within the first billion
years of the Universe). I find four possible (two robust) z′-drop candidates
(z >∼
6.5) and four possible (but no robust) Y -drop candidates (z >∼
7). I
use my results to place constraints on the luminosity function at z ∼ 6.5 and
find significant evolution in the population of Lyman-break galaxies between
3 < z <∼
6.5.
I also explore obscured star formation with a population of 70μm selected
galaxies over the COSMOS field. I use AAT spectroscopy in conjunction with
other available spectroscopic redshifts for my sample, and photometric redshifts
otherwise, to calculate the total infrared luminosity of each galaxy.
Two libraries of spectral energy distributions are considered; Siebenmorgen
& Kr¨ugel (2007) templates and Chary & Elbaz (2001) models. We have
supplemented our data with that of Huynh et al. (2007) collected over the
GOODS-North field and adapted it to directly compare with the results of
this work. The far-infrared luminosity function is then determined using the
1/Vmax technique. A double power law parameterisation is found to provide
the best fit to the data. The far-infrared luminosity function was fitted for
all parameters and the evolution was measured out to z ∼ 1. Three different
types of evolution were allowed, pure luminosity, pure density and luminosity
dependent density evolution. In all cases strong positive evolution was evident
with the best-fit case being pure luminosity evolution where p = 2.4+0.6
−0.7.
Due to the larger volume surveyed compared to previous studies, this work
provides better constraints on the bright end of the far-infrared luminosity
function displaying a shallower bright end slope (α2 ∼ −1.6) than previously
determined, implying a higher number density of the most luminous objects
and thereby a greater contribution from these objects to the total infrared
energy density. However the shallower slope determined here can be reconciled
with other work if the Chary & Elbaz (2001) models are used instead of
the Siebenmorgen & Kr¨ugel templates; demonstrating that spectral energy
distribution model selection is a key component in determining luminosity
functions at far-infrared wavelengths.
The far-infrared–radio correlation (FIRC; qIR) was determined for the
sample of 70μm selected star-forming galaxies using 1.4GHz radio data over
the COSMOS field, and no evolution was found out to z ∼ 2. The 70μm
monochromatic evolution in the FIRC was also examined (q70) and no evolution
was found in this parameter with redshift. | en_US |
