Everything Every Band All at Once II: The Relationship Between Optical Size and Stellar Mass Over Eight Billion Years of Cosmic History

TL;DR

This study analyzes the evolution of galaxy sizes relative to their stellar mass over eight billion years using JWST data, revealing distinct growth phases and differences between star-forming and quiescent galaxies.

Contribution

It introduces a comprehensive size-mass relation across cosmic time using flexible modeling and symbolic regression, expanding understanding of galaxy structural evolution.

Findings

Star-forming galaxies show three growth phases: rapid, halo-mimicking, and plateau.

Quiescent galaxies' size-mass relation flattens at low masses and inverts at high redshift.

Sizes of star-forming and quiescent galaxies are similar at low and high masses, differing mainly around log M*/M_sun=10.

Abstract

While the size-mass relation provides insight into the structural evolution of galaxies, the data available and methods employed have hindered our ability to study a detailed and comprehensive description of this key relation across cosmic history. The first paper in this series presents a morphology catalog based on 20 band JWST data in the field of Abell 2744. In this paper we utilize this catalog to measure the size-mass relation from $0.5<z<8$ and $0.5<z<3$ for star-forming and quiescent galaxies respectively. We perform a global fit to our sample using B-splines to flexibly model the redshift evolution which enforces smooth evolution and can account for all observational uncertainties. Symbolic regression is used to derive simple and portable expressions that describe the redshift evolution of the size-mass relation. Analyzing the size evolution of star-forming galaxies in the context of previous work at $z\sim0$ and $z>10$, we discuss three distinct phases: Rapid growth at $z>5$, growth that mimics dark matter halos at $5< z <1$ and a late plateau at $0.5<z<1$. For quiescent galaxies we confirm previous findings that the size-mass relation flattens at $\log\ M_*/M_\odot < 10$, which inverts at $z>1$. Our results imply that quiescent galaxies are smaller than their star-forming counterparts only at around $\log M_*/M_\odot = 10$; the two populations have similar sizes at lower and higher masses.