Investigating the Impact of Environment on the Galaxy Luminosity Function.

Abstract

In this thesis, we present the DESI Y1 Bright Galaxy Survey (BGS) Luminosity Functions (LFs) in the , , and -bands from . To do this, we describe a method for finding k-corrections based on the FastSpecFit (FSF) k-corrections; an evolutionary model for finding e-corrections; and a series of weights to account for target and redshift incompleteness of the BGS Y1 survey. We construct LFs that are extremely faint, reaching magnitudes of in the -band. Moreover, we observe the existence of an upturn in the LFs at . These LFs are in agreement with those presented in the literature. We further validate our results by using a range of methodologies (, , ) to construct the LFs, which broadly agree with each other. We note some areas where further investigation is needed. This includes a disparity between the North and South LFs at the bright end, a potential need for a more complex evolutionary model, and the issue of imaging systematics at the faint end of the LF. Nevertheless, the small jackknife errorbars on our global LFs demonstrate that our results are well-constrained, and these errors will only become smaller with the release of the Y3 and Y5 BGS datasets. Moreover, we confirm that our methodology of dealing with the differing photometry in North and South is broadly successful.

We extend this analysis by using the luminosity function to investigate the environmental dependencies of galaxies. In particular, we investigate how luminosity and colour depend on local density, and present our results here. These results agree well with prior results in the literature from GAMA, indicating that we have developed a successful methodology for dealing with boundary corrections and holes in the survey. Although the effective volume of the BGS survey is similar to the GAMA results due to boundary corrections, this will yield promising results on the Y3 and Y5 results which will be more complete and will have a much larger effective volume.

Finally, we then use our methodology to generate Stellar Mass Functions (SMFs). With these SMFs, we help to test and validate a new methodology called Photometric Objects Around Cosmic Webs (PAC). PAC was developed to estimate the excess projected density distribution of a spectroscopic catalogue by utilising the signal in the cross-correlation of faint galaxies from the Legacy photometric surveys with the brighter DESI BGS galaxies with known spectroscopic redshift. In doing so, PAC can estimate the SMF in a novel way, and yields results that agree with our SMF above but currently differs at the low-mass end. Both our LF and SMF results serve as useful results that can act to better constrain and distinguish between different galaxy formation models.