NGC 6822 as a Probe of Dwarf Galactic Evolution
Abstract
NGC 6822 is the closest isolated dwarf irregular galaxy to the Milky Way. Its proximity and stellar mass ( ${10}^{8}{M}_{\odot }$ , large for a dwarf galaxy) allow for a detailed study of its kinematic properties. The red giant branch (RGB) stars at the galaxy's center are particularly interesting because they are aligned on an axis perpendicular to the galaxy's more extended H I disk. We detected a velocity gradient among the RGB population using spectra from Keck/Deep Imaging Multi-Object Spectrograph (DEIMOS). This rotation is aligned with the H I disk, but the sense of rotation is about the major axis of the central RGB population. We measured the rotation velocity (v) and velocity dispersion (σ) of the RGB population in five metallicity bins. We found an increase of rotation support (v/σ) with increasing metallicity, driven primarily by decreasing dispersion. We also deduced an increasing radial distance for lower metallicity stars at -0.5 kpc dex-1 by relating the observed stellar kinematics to position via NGC 6822's H I velocity curve. While the inverted metallicity gradient-like distribution could be interpreted as evidence for an outside-in formation scenario, it may instead indicate that stellar feedback disturbed a centrally star-forming galaxy over time. * The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2020
- DOI:
- 10.3847/1538-4357/abb5f4
- arXiv:
- arXiv:2009.04555
- Bibcode:
- 2020ApJ...903...10B
- Keywords:
-
- Dwarf irregular galaxies;
- Stellar kinematics;
- 417;
- 1608;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 10 pages, 8 figures. Accepted to ApJ