Galaxy Structure, Stellar Populations, and Star Formation Quenching at 0.6 $\lesssim$ $z$ $\lesssim$ 1.2

TL;DR

This study investigates the relationship between galaxy morphology, stellar populations, and star formation activity at redshifts 0.6 to 1.2 using Hubble data, revealing that bulge presence correlates with quenching but is not the sole factor.

Contribution

It provides a detailed spectroscopic and morphological analysis of quiescent galaxies at intermediate redshifts, highlighting the complex interplay between bulge development and star formation cessation.

Findings

Most quiescent galaxies have prominent bulges.

Bulge-dominated galaxies show positive correlations among D4000, mass, and Sersic index.

Presence of a bulge is necessary but not sufficient for quenching.

Abstract

We use both photometric and spectroscopic data from the {\it Hubble Space Telescope} to explore the relationships among 4000 \AA\ break (D4000) strength, colors, stellar masses, and morphology, in a sample of 352 galaxies with log$(M_{*}/M_{\odot}) > 9.44$ at 0.6 $\lesssim z \lesssim$ 1.2. We have identified authentically quiescent galaxies in the $UVJ$ diagram based on their D4000 strengths. This spectroscopic identification is in good agreement with their photometrically-derived specific star formation rates (sSFR). Morphologically, most (that is, 66 out of 68 galaxies, $\sim$ 97 \%) of these newly identified quiescent galaxies have a prominent bulge component. However, not all of the bulge-dominated galaxies are quenched. We found that bulge-dominated galaxies show positive correlations among the D4000 strength, stellar mass, and the S\'ersic index, while late-type disks do not show such strong positive correlations. Also, bulge-dominated galaxies are clearly separated into two main groups in the parameter space of sSFR vs. stellar mass and stellar surface density within the effective radius, $\Sigma_{\rm e}$, while late-type disks and irregulars only show high sSFR. This split is directly linked to the `blue cloud' and the `red sequence' populations, and correlates with the associated central compactness indicated by $\Sigma_{\rm e}$. While star-forming massive late-type disks and irregulars (with D4000 $<$ 1.5 and log$(M_{*}/M_{\odot}) \gtrsim 10.5$) span a stellar mass range comparable to bulge-dominated galaxies, most have systematically lower $\Sigma_{\rm e}$ $\lesssim$ $10^{9}M_{\odot}\rm{kpc^{-2}}$. This suggests that the presence of a bulge is a necessary but not sufficient requirement for quenching at intermediate redshifts.