Dissertation Defense
Mohammad Akhshik
Physics Department, University of Connecticut
Advisor: Katherine Whitaker
Event Details:
Date and Time: February 4th, 2022 at 9:30AM
Meeting Link: Zoom Link Here
“The Lensed Perspective: Searching for the Signatures and the Mechanisms of Quenching”
By the time the Universe is merely 3 billion years old (z~2), roughly half of massive galaxies have already ceased forming new stars. Explaining the formation of these massive ``quiescent'' compact objects turns out to be one of the major challenges of observational extragalactic astronomy. Simulations suggest two possible evolutionary pathways for quiescent galaxies, and these two different classes of scenarios leave unique fingerprints on the spatially resolved ages and star-formation histories. In this dissertation, we use the natural magnification of strong gravitational lensing as a powerful observational tool to analyze spatially resolved stellar populations and study the proposed potential formation pathways. We have identified 8 targets for such an analysis that span redshifts of z = 1.6-2.9 and stellar-masses of log M*/M_odot = 10.6-12, defining the REQUIEM-2D galaxy survey (REsolving QUIEscent Magnified galaxies using 2D grism spectroscopy). We observe the REQUIEM-2D galaxies with Hubble and Spitzer Space Telescopes and also use the existing archival data in our analysis. A probabilistic programming code, texttt{requiem2d}, is developed as a part of this dissertation, fitting all spectrophotometric observations of the REQUIEM-2D sample within a Bayesian framework. Our prior for the star-formation histories is justified using those of the similar galaxies in the Illustris cosmological simulations. After demonstrating the feasibility of our approach by presenting our analysis of the REQUIEM-2D pilot target, MRG-S0851, we show that quiescent galaxies in the REQUIEM-2D survey have diverse formation histories manifesting at different physical distances. Combined together and accounting for the different physical radial distances and formation time-scales, we find that the REQUIEM-2D galaxies that are formed earlier in the universe exhibit slow and uniform growth in their inner cores, whereas the galaxies that are formed later have rapid inner core growth with younger ages relative to the outskirts. While this may suggest a shift in the major formation pathway for quiescent galaxies that form early versus late, significantly larger samples with similar data quality are required to validate this finding.
For more information, contact: Jack / Physics at Jack.potter@uconn.edu