The extended disc and halo of the Andromeda galaxy observed with Spitzer-IRAC

TL;DR

This study uses extensive Spitzer-IRAC observations to map the extended disc and halo of the Andromeda galaxy, providing detailed surface brightness profiles and a large catalog of sources to analyze its stellar content.

Contribution

First comprehensive infrared survey of M31's outer regions combining surface brightness profiles with a new stellar catalog and statistical object classification.

Findings

Extended surface brightness profiles of M31's outer disc and halo.

Catalog of over 426,000 sources with probabilistic classification.

Insights into the stellar mass and point source populations in the galaxy's outskirts.

Abstract

We present the first results from an extended survey of the Andromeda galaxy (M31) using 41.1 h of observations by Spitzer-IRAC at 3.6 and 4.5$\,\mu$m. This survey extends previous observations to the outer disc and halo, covering total lengths of 4$.\!\!^\circ$4 and 6$.\!\!^\circ$6 along the minor and major axes, respectively. We have produced surface brightness profiles by combining the integrated light from background-corrected maps with stellar counts from a new catalogue of point sources. Using auxiliary catalogues we have carried out a statistical analysis in colour-magnitude space to discriminate M31 objects from foreground Milky Way stars and background galaxies. The catalogue includes 426,529 sources, of which 66 per cent have been assigned probability values to identify M31 objects with magnitude depths of [3.6]$\,=\,$19.0$\,\pm\,$0.2, [4.5]$\,=\,$18.7$\,\pm\,$0.2. We discuss applications of our data for constraining the stellar mass and characterising point sources in the outer radii.