Stellar Populations and Assembly Histories of Galaxies in Nearby Massive Clusters

Abstract

Understanding how massive galaxies form and grow is of profound importance to modern theories of galaxy evolution and cosmology. In this thesis, I investigate the stellar population and assembly histories of massive galaxies and their surrounding satellite galaxies in nearby galaxy clusters, with particular focus on how they maintain the remarkable scaling relations among their stellar mass, their stellar population properties, and the mass of their host dark matter halos regardless of the stochastic mergers and the complex baryonic processes they experienced. I begin by introducing the “coordinated assembly” picture for massive galaxies using an ongoing brightest cluster (BCG) assembly case at z ∼ 0.1. With detailed stellar population analysis, we look into both the scaling relations between stellar mass and galaxy central stellar population properties, as well as the radial profiles where their stellar population bear the imprint of the assembly history. We found that the cluster center shapes the [α/Fe]–σ⋆ and [α/Fe]–M⋆ relations differently than other environments, suggesting the assembly of massive galaxies is coordinated in a way that their building blocks are not just random draws from the general low mass galaxy population, but featuring early truncated star formation histories, making them a special sample among the general population. Next, I present a deep and comprehensive optical spectroscopic survey of galaxies in the Coma cluster–the Deep Coma project. This is part of the SDSS IV/MaNGA Survey. Taking advantage of the deep integral field spectroscopy and the powerful full spectral modeling method, we investigated the stellar population in various types of targets, in addition to central and outskirts of BCGs and massive early type galaxies. In particular, our results show that the stellar populations of intracluster light (ICL) are old and metal poor, indicating the build-up of ICL in Coma is likely to be through the accretion of low mass galaxies or the tidal stripping of the outskirts of massive galaxies that have ended their star formation early on. The old and shallow radial profiles of stellar age from the BCG centers to ICL are also consistent with the “coordinated assembly” picture. Mean- while, we find that the ultra-diffuse galaxies (UDGs) in Coma have as old or older stellar age than galaxies at similar stellar mass or velocity dispersion. Despite their diffuse structures and their un- usual large size, they in general follow the well-established M⋆–stellar metallicity relation, with one exception lies below the σ⋆-metallicity relation, suggesting that stellar mass plays a more important role in setting stellar population properties for these galaxies than either size or surface brightness. In Chapter 5, I look into the stellar mass-halo mass relation, and investigate the origins of its scatter, by combining N-body simulations with observational constraints. We find that at the group and cluster scale, the scatter is mostly due to hierarchical assembly. At lower masses, in situ buildup of stellar mass plays an important role. Our results indicate that the scatter in the SMHM relation can provide unique insight into the regularity of the galaxy formation process. surface brightness. In the last chapter, I briefly demonstrate the “coordinated assembly” picture in the IllustrisTNG simulations.