Farhanul Hasan Dissertation Proposal

February 11, 2022

01:00 PM - 03:00 PM



Unveiling Galaxy Evolution In Gaseous Ecosystems With Statistical And Visual Analysis
The evolution of galaxies is profoundly influenced by the physical processes at play in their surrounding gaseous ecosystems, consisting of the circumgalactic Medium (CGM) and the intergalactic medium (IGM). Central to this picture is the baryon cycle, wherein matter flows into galaxies from the surroundings and out of galaxies due to internal processes such as star formation and central black hole activity. The gaseous halos which encode the history of galaxy formation are most commonly studied via absorption in the spectra of background quasars. The projects in this thesis proposal are aimed towards understanding the evolution of metal-enriched gas, the connection between galaxy evolution and the nearby and large-scale environment, and scrutinizing the likely incomplete picture of the CGM from quasar absorption line observations. I will utilize a combination of statistical and visual analytical methods, leveraging both observations and cosmological simulations. This will include analysis with CosmoVis, an interactive software for the visualization of simulation data.
Project 1: We study the evolution of >1200 CIV absorption systems down to an Equivalent Width of Wr=0.05 Angstrom detected in hundreds of high-resolution quasar spectra from Keck/HIRES and VLT/UVES. Across ~12.5 Gyr, the cosmic incidence of CIV rises with time, with the rise more rapid for stronger (higher Wr) absorbers. These trends result from star formation-driven metal enrichment and evolving ionization conditions. Assuming each CIV absorber is associated with a galaxy, we use observed galaxy statistics to infer the characteristic size of CIV absorbing halos. We find that weak CIV absorbers typically reside in the outer CGM or IGM, while stronger absorbers live further inside the CGM. Our results indicate different origin scenarios for weak and strong CIV absorbers and more extended CIV halos for higher mass galaxies than for lower mass galaxies.
Project 2: I will investigate the connection between the cooling and accretion of gas on to galaxies and the environment of the galaxies. Using CosmoVis, I will characterize the cooling timescales and kinematics of simulated galaxies from EAGLE and IllustrisTNG to identify how cooling and accretion differ for central and satellite galaxies and for galaxies with differing densities of nearby galaxies and halos. I will also assess the assumption of a statistically "average" CGM in most quasar absorption line observations by simulating such observations in CosmoVis, which will enable us to understand the intra-halo and halo-to-halo variations in the CGM, especially in its small-scale structure. 
Project 3: I will investigate how gas and galaxies are distributed inside the large-scale structure of the universe, the "cosmic web". Through both visual analysis and algorithmic cosmic web reconstruction techniques,  I will assemble a hierarchical network catalog of the knots, filaments, and voids of the cosmic web inside EAGLE and TNG. I will study how the gas and galaxy distribution and the geometry and connectivity of the cosmic web affect the mass, star formation activity and spin of galaxies. Finally, I will investigate how the density, temperature, and entropy structure of the cosmic web manifest in absorption signals from various ions such as HI and OVI.