Spatially Resolved Spectroscopic Star Formation Histories of Nearby Disks: Hints of Stellar Migration

TL;DR

This study uses spatially resolved spectroscopy of nearby disk galaxies to investigate stellar populations and surface brightness profile breaks, providing evidence for stellar migration and other mechanisms influencing galaxy disk evolution.

Contribution

It presents new observational evidence linking surface brightness profile breaks with stellar population changes, supporting the role of stellar migration in galaxy disk evolution.

Findings

Outer disks with profile breaks show older stellar populations, consistent with stellar migration.

Some galaxies show no change in stellar populations across the break, indicating multiple mechanisms.

Radial migration alone cannot explain all observed profile breaks.

Abstract

We use the Mitchell Spectrograph (formerly VIRUS-P) to observe 12 nearby disk galaxies. We successfully measure ages in the outer disk in six systems. In three cases (NGC 2684, NGC 6155, and NGC 7437), we find that a downward break in the disk surface brightness profile corresponds with a change in the dominant stellar population with the interior being dominated by active star formation and the exterior having older stellar populations that are best-fit with star formation histories that decline with time. The observed increase in average stellar ages beyond a profile break is similar to theoretical models that predict surface brightness breaks are caused by stellar migration, with the outer disk being populated from scattered old interior stars. In three more cases (IC 1132, NGC 4904, and NGC 6691), we find no significant change in the stellar population as one crosses the break radius. In these galaxies, both the inner and outer disks are dominated by active star formation and younger stellar populations. While radial migration can contribute to the stellar populations beyond the break, it appears more than one mechanism is required to explain all of our observed stellar profile breaks.