Carbon star survey in the Local Group. VII. NGC 3109 a galaxy without a stellar halo

TL;DR

This study surveys carbon stars in NGC 3109, showing they are confined to the disk with no extensive halo, confirming the universality of their mean magnitude and providing insights into the galaxy's structure and stellar populations.

Contribution

It provides the first wide-field survey of carbon stars in NGC 3109, demonstrating the absence of an extensive stellar halo and confirming the uniformity of carbon star magnitudes in the Local Group.

Findings

Carbon stars are confined to the disk of NGC 3109.

No extensive stellar halo is detected around NGC 3109.

The global C/M ratio is 1.75 +/- 0.20.

Abstract

We present a CFH12K wide field survey of the carbon star population in and around NGC 3109. Carbon stars, the brightest members of the intermediate-age population, were found nearly exclusively in and near the disk of NGC 3109, ruling out the existence of an extensive intermediate-age halo like the one found in NGC 6822. Over 400 carbon stars identified have < M_I > = -4.71, confirming the nearly universality of mean magnitude of C star populations in Local Group galaxies. Star counts over the field reveal that NGC 3109 is a truncated disk shaped galaxy without an extensive stellar halo. The minor axis star counts reach the foreground density between 4' and 5', a distance that can be explained by an inclined disk rather than a spheroidal halo. We calculate a global C/M ratio of 1.75 +/- 0.20, a value expected for such a metal poor galaxy.