Undergraduate Honors Theses

Thesis Defended

Fall 2014

Document Type

Thesis

Type of Thesis

Departmental Honors

Department

Astronomy

First Advisor

Erica Ellingson

Abstract

Here we present an investigation into galaxy evolution in the cluster and intercluster filamentary environments, and follow the evolution of the large scale structure of the universe over 4 billion years. After designing and applying a new “filament finding algorithm” to galaxy survey data from the Sloan Digital Sky Survey and the Red Sequence Cluster Survey, we identify galaxies belonging to the intercluster filamentary environment, along with three other cluster populations. By carrying out a detailed photometric and spectroscopic investigation into the star formation rates of galaxies in different environments, we are able to shed light on the processes responsible for the cessation of star formation in cluster galaxies. In particular, we find that the quenching mechanisms of harassment and mergers are quite effective at pre‐processing galaxy groups outside of the cluster, contingent upon the local density being large enough. Next, we find that the filamentary environment at low redshift does have a considerable effect on the evolution of a galaxy. Specifically, we see evidence that the intrafilamentary medium has the potential to ram pressure strip the gaseous halos of infalling galaxies, and that infalling galaxies are subject to significant filament tidal forces at a few virial radii, enough to dismantle infalling groups within filaments. We see evidence for the filamentary environment inducing starbursts in infalling dwarf galaxies within groups, which we attribute to the exponentiation of the harassment mechanism by filament tidal forces. However, we conclude that this starburst population is relatively small, and thus starbursts are not a main contributor to the population of passive galaxies within clusters. Lastly, we compare the cluster composition between the two data sets, which provides insight into the assembly of galaxy clusters and the evolution of large scale structure over 4 billion years. From this comparison study, we see direct observational evidence for hierarchical clustering, and find that the dominant mechanism responsible for the population of “red and dead” galaxies in cluster cores is ram pressure stripping in the intracluster medium.

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