Star Formation in Galaxies: From the Epoch of Reionisation to the Present Day
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.