Avinash Ck | Searcharxiv

arXiv2026

Mass-Metallicity Relation of the Fossil Disk in Six Nearby Galaxies using JWST RGB Stars

We here present the first ever mass-metallicity relation (MZR) of fossil disk populations using the resolved stellar populations in the James Webb Space Telescope Near-Infrared Camera (JWST/NIRCam) images of six nearby galaxies. Both the mass and metallicity were determined using the Red Giant Branch (RGB) stars, employing methods that have been well established to study the halo populations of nearby galaxies using the Hubble Space Telescope images. Specifically, we obtained the mass and metallicity by comparing the color, magnitude and number density near the tip of the RGB (TRGB) stars in the F115W$-$F200W vs F200W color-magnitude diagrams (CMDs) with that of the PARSEC isochrones of 4 and 13~Gyr. The RGB metallicities of the disks of nearby galaxies closely match those found in galaxies at redshifts $z>8$, with the metallicity range following a power-law relation with the fossil disk mass. The power-law index of the fossil disk MZR, $γ\approx0.26$, compares well with the typical value found in MZRs obtained using gas metallicities across redshifts. Through this work, we illustrate the utility of JWST/NIRCam images for obtaining the mass and metallicity of the fossil disks of nearby galaxies at precisions that were not possible earlier, which opens up a new method to carry out the near-field cosmological studies.

astro-ph.GA↗

arXiv2026

Ages of the resolved stellar populations inside the JWST/MIRI bubbles in NGC 628

JWST images in the MIRI filters are characterized by prominent interstellar bubbles, most of which are expected to be created by mechanical energy injected into the interstellar medium by dying massive stars. In this work, we use resolved stellar populations (RSPs) in JWST/NIRCam images of NGC 628 from the JWST-FEAST dataset to determine the demography of stellar populations within these bubbles by comparing them with PARSEC+COLIBRI isochrones using a Bayesian framework. Our analysis reveals the presence of multiple stellar populations younger than 100 Myr within the bubbles, suggesting secondary star formation following the first generation of stars that formed the bubble. We find a clear preference for the most recently formed stars to lie closer to the bubble shell. In contrast, relatively older stars are distributed throughout the bubble interior, consistent with a scenario in which stars formed in dense shells are left behind as the shell expands. We also examine PHANGS-HST cluster candidates within large bubbles and find no convincing progenitor clusters responsible for the initial trigger, indicating that low-mass clusters or OB associations may be sufficient to drive the initial expansion. However, the cluster may dissolve as it co-evolves with the bubble, producing the dispersed stellar distributions observed in larger bubbles. We establish a fundamental plane relation for stellar feedback-driven bubbles that involves the stellar population mass, age, bubble size, gas density, and feedback efficiency, highlighting the ability of JWST/NIRCam CMDs to characterize stellar populations driving interstellar bubble expansion in nearby galaxies

astro-ph.GA↗