| Description |
Being the end-product of the hierarchical merging scenario, early-type (elliptical and lenticular) galaxies (ETGs) are the "live" fossil records that permit compelling tests of galaxy formation theories within a cosmological context. Also, ETGs can be extremely luminous and serve as the ideal cosmological tracers in the Universe. Additionally, the mysterious dark matter (DM), which is believed to constitute almost 85% of the observed mass portion, acts as the host of galaxies and hence plays a pivotal role in shaping the observed Universe. A thorough understanding of DM, including its nature, properties, and structures provides crucial insights into the fundamental laws of physics and cosmology. On the luminous side, a hierarchical Bayesian determination o f the velocity-dispersion function of approximately 430000 massive luminous red galaxies observed by the Baryon Oscillation Spectroscopic Survey (BOSS) is performed. We use the full velocity-dispersion likelihood function for each galaxy to make a self-consistent determination of the velocitydispersion distribution parameters as a function of absolute magnitude and redshift. Parameterizing the distribution at each point in the luminosity-redshift plane with a log-normal form, we detect significant evolution in the width of the distribution toward higher intrinsic scatter at higher redshifts, which indicates a more diverse heterogeneity in ETGs at earlier cosmic time. On the dark side, I report the discovery of 40 strong gravitational lenses in the SLACS for the Masses (S4TM) Survey and 33 additional systems with single-lensed images in S4TM and SLACS Surveys, for which upper limits of the Einstein radii are determined. A hierarchical Bayesian analysis reveals strong evidence (4a) of variations of the total mass-density structure toward shallower profiles at larger velocity dispersion when upper limits are incorporated. Estimating the stellar masses based on the HST I-band photometry, we find a significant trend of higher dark-matter fraction at higher velocity dispersion. A Salpeter initial mass function is substantially disfavored for all but the most massive lens galaxies by predicting stellar masses in excess of the total lensing-measured mass. An approach of constraining mass structure via a joint analysis of lensing and stellar kinematics is also outlined, the application of which on a sample of strong lenses shows a 4a evolution trend in the sense of steeper mass profiles at later cosmic times. |
