| Abstract: |
One of the central puzzles in galaxy evolution is how and why galaxies abruptly shut down their star formation. Massive galaxies with little or no star formation have been identified as early as z ~ 4–5, yet it remains unclear how they evolve. The James Webb Space Telescope (JWST) now enables us to investigate such quiescent galaxies at high redshift in unprecedented detail. While many studies have focused on individual objects, a systematic understanding of the overall population is still limited. To address this, we are conducting both our own JWST GO program, "DeepDive", which targets 10 massive quiescent galaxies at z~3-4, and a comprehensive compilation of publicly available JWST/NIRSpec spectra of quiescent galaxies. So far, we have constructed a homogeneous sample of 150 NIRSpec grating spectra of quiescent galaxies at z ~ 1–5, which represents the most comprehensive spectral dataset of quiescent galaxies at this redshift to date, allowing us to explore their population properties in a statistically robust way. Using this sample, we have investigated their dynamical properties, based on the stellar velocity dispersion from NIRSpec spectra, and AGN properties of some of the sources with broad Halpha line. Beyond statistical trends, such activities of archival compilation have led to several serendipitous discoveries, including two low-mass (logMstar ~ 9) quiescent galaxies at z ~ 5 — the second and third most distant quiescent galaxies known so far — as well as a very deep NIRSpec observation of a logMstar = 9.7 quiescent galaxy at z~2. |
