Structural evolution of quiescent galaxies at intermediate redshifts at UV and red rest-frame wavelengths

TL;DR

This study investigates how the structural parameters of quiescent galaxies at intermediate redshifts vary with wavelength, revealing inside-out quenching and size evolution driven by minor mergers, based on extensive multi-band photometry and spectroscopy.

Contribution

It provides the first detailed analysis of wavelength-dependent structural evolution of quiescent galaxies at intermediate redshifts, highlighting the role of inside-out quenching and minor mergers.

Findings

Quiescent galaxies show size decline and increased concentration at shorter wavelengths.

Newcomers are larger and have different profiles compared to aging populations.

Size increases by ~30% from z~0.6 to z~0.2 in red wavelengths, constant in UV.

Abstract

We model the wavelength dependence of structural parameters for a mass-limited sample ($M_\star>10^{10}M_\odot$) of $\sim27,000$ quiescent galaxies with $0.2 < z < 0.6$ using $grizy$ photometry from Subaru/Hyper Suprime-Cam and dense spectroscopy from the HectoMAP survey. Based on S\'ersic profile fits in all five bands, we estimate the circularized half-light radius $R_{e,c}$ and S\'ersic index $n$ in two rest-frames: UV (3500 \r{A}) and red (7000 \r{A}). Combined with $M_\star$, $z$, and D$_n4000$, $R_{e,c}$ and $n$ enable exploration of the evolution in the structural properties - stellar mass correlations for quiescent galaxies with different stellar population ages. At intermediate redshift, quiescent galaxies at all stellar masses show a systematic decline in $R_{e,c}$ and rise in $n$ with rest-frame wavelength. These structural variations are stronger for galaxies that recently joined the quiescent population (newcomers) than for the descendants of galaxies that are already quiescent at the survey limit, $z \sim 0.6$ (aging population). The combined evidence supports inside-out quenching as the dominant mechanism halting star formation during this epoch. The typical size of a $M_\star\sim10^{11}M_\odot$ quiescent galaxy increases by $\sim30\%$ between $z \sim 0.6$ and $z \sim 0.2$ in the red and remains constant in the UV; newcomers are $\sim20\%$ larger than the aging population. In the UV, quiescent galaxies maintain a constant $n\sim4$ for the aging population and $n\sim2$ for newcomers; in the red, both subpopulations have de Vaucouleurs profiles. Our findings link newcomers to their direct progenitors in the star-forming population. For the aging population, we suggest minor mergers with progressively redder satellites at lower redshifts as the primary driver of quiescent galaxy evolution. Forthcoming sensitive large-area imaging surveys will allow testing this prediction.