The Structure and Metallicity Gradient in the Extreme Outer Disk of NGC 7793

TL;DR

This study investigates the structure and metallicity distribution in the outer disk of NGC 7793, revealing an extended exponential disk with a flat or non-negative metallicity gradient, enhancing understanding of galaxy outskirts.

Contribution

It provides detailed star count analysis of NGC 7793's outer disk, extending previous work and showing no disk break and a flat metallicity gradient at large radii.

Findings

Outer disk extends to ~9 scale lengths (~11.5 kpc).

No evidence of a break in the light profile down to very faint surface brightness.

Metallicity gradient remains flat or non-negative in the outer regions.

Abstract

Studies of outer regions of spirals disks are fundamental to our understanding of both the process of galaxy assembly and the subsequent secular evolution of galaxies. In an earlier series of papers we explored the extent and abundance gradient in the outer disk of NGC 300 and found an extended purely exponential disk with a metallicity gradient which flattens off in the outermost regions. We now continue the study of outskirts of pure disk spirals with another Sculptor Group spiral, NGC 7793. Using Gemini Multi Object Spectrograph camera at Gemini South, we trace the disk of NGC 7793 with star counts out to ~9 scale lengths, corresponding to 11.5 kpc at our calibrated distance of 3.61+/-0.53 Mpc. The outer disk of NGC 7793 shows no evidence of a break in its light profile down to an effective surface brightness of ~30 mag/arcsec^2 (~3 mag/arcsec^2 deeper than what has been achieved with surface photometry) and exhibits a non-negative abundance gradient within the radial extent of our data.