Witnessing the rapid growth of disk galaxies over cosmic time using JWST and HST

TL;DR

This study uses JWST and HST data to analyze galaxy edges at redshift 1, revealing inside-out growth and stellar migration effects through detailed age and metallicity profiles.

Contribution

It introduces a physically motivated galaxy size definition based on the galaxy edge and applies it to high-resolution data at z=1.

Findings

Galaxies at z=1 grow inside-out with significant outer region mass increase.

Age profiles show a U-shape with a turnover near the galaxy edge.

Metallicity profiles decrease steadily with radius.

Abstract

Measuring galaxy sizes is fundamental to understanding how galaxies grow and evolve. Traditional methods to measure sizes either trace the concentration of light (i.e., effective radius) or are limited by the depth of the survey (isophotal methods). With the advent of deep, wide surveys, a new physically motivated definition of size has emerged: the edge of the galaxy, defined as the most distant location where star formation has occurred or is still occurring. In this work, we take advantage of the extraordinary depth and spatial resolution of the Hubble and James Webb Space Telescopes to perform an accurate study of galaxy edges at $z=1$. Using 22 photometric bands, we derive radial age and metallicity profiles for two disk galaxies in the GOODS-South field with stellar masses of around $4\times10^{10}\ M_\odot$. The age profiles display a characteristic U-shape, while the metallicity profiles steadily decrease with galactocentric distance. The turnover in the age profile occurs near the galaxy edge, suggesting that stellar migration is responsible for the stars beyond the edge of these galaxies. Comparison with $z=0$ disk galaxies suggests that galaxies at $z=1$ grow inside-out, with little or no increase in mass within the inner 8 kpc, but a significant increase (approximately 300\%) in the outer regions.