Abstract:
This thesis presents a comprehensive study of HI absorption within the ISM of galaxies, focusing on the detection and analysis of absorption signatures using radio spectral data. Initially, we sought to identify absorption features by examining likely candidates, such as galaxy mergers. Subsequently, through a "blind search" approach, we aimed to detect HI absorption without prior selection of galaxies or objects of interest. These methodologies offers insights into the interactions between galaxies and their surrounding environments. Our study leveraged data from two major sources: the Galaxy Zoo DESI catalog and the MeerKAT Absorption Line Survey. Using a machine learning model from the literature trained on Galaxy Zoo morphology classifications, we identified potential galaxy mergers, narrowing down to a handful of galaxy-source pairs based on criteria such as proximity to strong radio sources and peak flux densities of those sources. No significant HI absorption was detected in our initial sample of 17000 objects. We calculated upper limits on optical depth and column density for non-detections, which provide valuable constraints on the neutral gas content of these systems. We present a detailed case study of the galaxy NGC5363, which was identified through a blind search of spectra. The spectral data exhibited notable signs of HI absorption, highlighting the potential of this technique to reveal cold gas systems in galaxies. This thesis contributes to the field by demonstrating the effectiveness of blind spectral searches for detecting cold gas and offers new insights into the ISM of galaxies. Our findings contribute to ongoing studies aimed at probing the connection between galaxy evolution, ISM content, and star formation activity across cosmic epoch.
