Revealing the formation of massive quiescent galaxies using various techniques

Abstract

Understanding why and how galaxies stop forming stars (``quenched'') and become quiescent has been a key question in galaxy evolution. This thesis aims to understand the formation of massive quiescent galaxies at various epochs by combining three different approaches: 1) Galaxy formation simulations, 2) Ground- & space-based spectroscopic observations, and 3) Stellar population synthesis models. In the local Universe (z~0), star-forming activity/quiescence is closely linked to galaxy morphology. To understand how galaxy quenching and morphological transformation are related, I use a high-resolution cosmological galaxy simulation (Illustris-TNG50). I track the evolution of massive quiescent galaxies down to z=0 and show how quenching histories/timescales and mechanisms differ for quiescent galaxies with different morphology. Cosmic noon (z~2) is the epoch when galaxy growth and feedback are the most active. I focus on young quiescent galaxies at z~2, as they likely still hold the evidence of powerful rapid quenching they underwent recently. I perform Magellan/FIRE spectroscopic observations of young quiescent galaxies at z~2, infer their star formation histories from spectral energy distribution fitting, and analyze their ionized emission lines and their sizes. JWST has enabled us to obtain a larger spectroscopic sample of massive quiescent galaxies at cosmic noon. I study the quenching histories and mechanisms of 14 massive quiescent galaxies at z~2 from deep JWST/NIRSpec observations (JWST Cycle-1 program: the Blue Jay survey). I reconstruct their star formation histories and investigate their neutral and ionized gas properties to understand the physical mechanism behind rapid quenching. Finally, I develop new self-consistent alpha-enhanced stellar population models, which will be essential in deriving accurate physical properties of high-z galaxies where alpha-enhancement is expected to be common. For future work, I will apply these new alpha-enhanced models to early massive quiescent galaxies (z>3) to reveal their true formation histories. Since these galaxies are likely descendants of the first galaxies and progenitors of the massive quiescent galaxies in the local universe, revealing their accurate formation histories will shed light on how the first galaxies grow into the most massive galaxies we see today.