Work

Resolved Ages and Stellar Metallicities in Progenitors of Milky Way Analogs: A Closer Look at Their Star Formation Histories Since z = 5

Year: 2026

Type: article

Abstract: We present the evolution of the resolved mass-weighted age, stellar metallicity, and specific star formation rate (sSFR) of 872 Milky Way analog (MWA) progenitors up to redshift z = 5 from the Canadian Unbiased Cluster Survey. The metallicity and mass-weighted ages were obtained via spatially resolved spectral energy distribution fitting with the nonparametric code Dense Basis . We split the sample into mergers versus nonmergers using the merger parameter from the Gini– M 20 plane obtained through Gini– M 20 analysis of the morphology of the stellar mass maps with Statmorph . Across our redshift range, nonmergers have negative or flat average age gradients from −0.022 to 0.005 dex kpc −1 , and positive or flat sSFR gradients from −0.089 to 0.092 dex kpc −1 , consistent with inside-out assembly. The average log ( Z / Z ⊙ ) gradients for nonmergers range from −0.029 to 0.044 dex kpc −1 ; however, positive gradients only appear between 2 < z < 3. At every redshift epoch, mergers typically have flatter age gradients, more negative sSFR gradients, and similar metallicity gradients compared to nonmergers. We divide the property maps of ongoing mergers into separate regions based on their component galaxies, and find little to no difference between the components’ average ages or metallicities, but the less massive of the merging system is on average 0.1−0.4 dex higher in sSFR. Our results point to major mergers contributing some momentary disruption to the general trend of inside-out mass assembly, but this does not upend the overall picture of MWA disks growing inside-out over cosmic time.

Source: The Astrophysical Journal

DOI: 10.3847/1538-4357/aea6dc