Date of Award

4-30-2025

Document Type

Open Access Thesis

First Advisor

Varsha Kulkarni

Second Advisor

Yuriy Pershyn

Abstract

Understanding the gas in and around galaxies is crucial for understanding galaxy evolution. Absorption lines detected in the spectra of background quasars offer a powerful tool to study the gas in and around the intervening galaxies. As a part of an effort to understand how the gas interacts with the stellar component of galaxies, our team previously obtained imaging and spectroscopic observations for a large sample of galaxies using the Hubble Space Telescope (HST), the Very Large Telescope (VLT), and the Atacama Large Millimeter Array (ALMA). This sample includes thousands of galaxies, including many without spectroscopic data. The overall goal of this work is to estimate the redshifts of as many of the galaxies without spectroscopic redshifts as possible. Redshift is a fundamental parameter in observing any galaxy. In this work, we make use of photometric data to estimate the redshifts of the galaxies. This is done using a technique called spectral energy distribution (SED) fitting. The base sample of galaxies is from the MUSE-ALMA-HST study, from which we chose 720 galaxies that had photometric measurements in at least one Hubble Space Telescope (HST) band and also had photometric data from the SDSS and/or in DELVE surveys and within an angular separation of 1 arc-second from the galaxy coordinates known from the HST imaging. We performed SED fitting for these 720 galaxies using these photometric measurements. Out of 720 galaxies, 146 galaxies have a spectroscopic redshift to compare with, which we used to test our SED fitting methodology. Having thus confirmed the methodology, we determined the photometric redshifts of the remaining 574 galaxies. We present our results on the photometric redshifts for the galaxies with and without the spectroscopic redshifts. We also report the distribution of the photometric redshifts for galaxies without the spectroscopic redshifts. Our results suggest that most absorbers in our sample are associated with multiple galaxies or galaxy groups. Finally, we discuss possibilities for future improvements.

Rights

© 2025, Ananthavishnu Santhigiri Unni

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