Title: Detection of the Circumgalactic Medium of Nearby Galaxies via Emission Lines

Speaker: Huanian Zhang, Steward Observatory, University of Arizona

Host: Taotao Fang

Time: 16:30-18:30, Thursday, Jan 9, 2020

Location: Physics Building 552

Abstract: Galaxies are surrounded by diffuse and extended gas, which is often called the circumgalactic medium (CGM) and is the least understood part of galactic ecosystems. The CGM harbors more than 60% of the total baryons in a galaxy, is both the reservoir of gas for subsequent star formation and the depository of chemically processed gas, energy, and angular momentum from feedback. Observations and simulations of the CGM suggest that it is a multi-phase medium characterized by rich dynamics and complex ionization states. The study of the CGM has so far generally come from absorption line studies of the spectra of distant objects, typically QSOs, whose lines of sight intersect lower redshift galaxy halos. However, such study is limited by statistics. Instead, I will describe a novel approach to study the CGM via emission lines, which allows for direct mapping of individual galaxies and a variety of results obtained. In this talk, I will introduce our novel method to study the CGM, the simple theoretical model to reconstruct the emission signal and the estimation of cool gas fraction, the different ionization states of the cool gas inferred from the line ratio presented in the BPT diagram, and the dependence of the emission flux from the CGM on the local and global environment.

Bio: Huanian Zhang is a postdoc at Steward Observatory, University of Arizona. He obtained his PhD on phenomenology of Particle Physics in August 2016. Afther that, He moved from the physics building to the astronomy building just a few blocks away. His main focus now is on probing the Circumgalactic Medium (CGM). He had the first dection of CGM of nearby galaxies up to 100 kpc via Halpha and [NII] emission lines. He is also working on the all-sky search for globular clusters in the Local Volume using combined datasets of Decals, WISE and Galex and on studing the Milky Way halo structure using halo stars up to 100 kpc.