Outer-Disk Populations in NGC 7793: Evidence for Stellar Radial Migration

TL;DR

This study uses HST imaging to analyze stellar populations in NGC 7793, revealing evidence of stellar radial migration through the analysis of disk breaks and stellar distribution beyond the HI disk.

Contribution

It provides observational evidence for stellar radial migration in a late-type galaxy, linking stellar population profiles with galaxy evolution models.

Findings

Disk breaks at 5.1 kpc for all populations

Younger stars have steeper outer profiles

Older stars extend beyond the HI disk

Abstract

We analyzed the radial surface brightness profile of the spiral galaxy NGC 7793 using HST/ACS images from the GHOSTS survey and a new HST/WFC3 image across the disk break. We used the photometry of resolved stars to select distinct populations covering a wide range of stellar ages. We found breaks in the radial profiles of all stellar populations at 280" (~5.1 kpc). Beyond this disk break, the profiles become steeper for younger populations. This same trend is seen in numerical simulations where the outer disk is formed almost entirely by radial migration. We also found that the older stars of NGC 7793 extend significantly farther than the underlying HI disk. They are thus unlikely to have formed entirely at their current radii, unless the gas disk was substantially larger in the past. These observations thus provide evidence for substantial stellar radial migration in late-type disks.