A Study of multiple probes of the circumgalactic medium

Abstract

The circumgalactic medium (CGM) is, arguably, the next frontier of studying the physics of galactic halo gas and holds key information about galactic evolution, energetics and cosmology. Observation and physical interpretation of the CGM, which is the gaseous medium lying between the interstellar medium (ISM) and the intergalactic medium (IGM), is poised to be one of the thrust areas of extragalactic astrophysics in coming years. During my Ph.D., I have focused on multiple potential probes of the CGMand on the prospects of constraining its properties by combining these probes. Additionally, I have studied X-ray emission from the active galactic nuclei (AGN), which plays a crucial role in extracting the X-ray signal from the CGM. I have also explored the impact of the CGM on infalling IGM as well as the outflowing gas. Standard cosmology (L-CDM) predicts that when a galaxy is formed, the baryons comprise approximately 16% of the total galactic mass. However, more than half of these baryons are observationally missing, thus giving rise to the missing baryon problem. Recent detections of X-ray emission from nearby massive spiral galaxies out to large galactocentric radii and the stripping of satellites of the Milky-way suggest the presence of a significant amount of gas occupying much larger volume than the central, optically visible part of the galaxy. This gaseous medium is called the CGM or the halo gas. Additionally, simulations suggest that the feedback processes taking place near the central part of the galaxy considerably change the density and temperature profiles of the CGM. Therefore, constraining the amount, distribution and energetics of the CGM has the potential to play an important role in the missing baryon problem and in constraining the feedback processes.