A skewer survey of the Galactic halo from deep CFHT and INT images

TL;DR

This study analyzes the structure of the Galactic halo using deep multicolour imaging, revealing a steepening density profile, flattening towards the poles, and the presence of substructures, contributing to our understanding of the halo's shape and composition.

Contribution

It provides detailed measurements of the Galactic halo's density profile and shape using deep multicolour data, including evidence for steepening and flattening, and identifies substructures.

Findings

Density profile steepens beyond 20 kpc

Halo is flattened with an axis ratio of 0.63

Substructures and streams are detected

Abstract

We study the density profile and shape of the Galactic halo using deep multicolour images from the MENeaCS and CCCP projects, over 33 fields selected to avoid overlap with the Galactic plane. Using multicolour selection and PSF homogenization techniques we obtain catalogues of F stars (near-main sequence turnoff stars) out to Galactocentric distances up to 60kpc. Grouping nearby lines of sight, we construct the stellar density profiles through the halo in eight different directions by means of photometric parallaxes. Smooth halo models are then fitted to these profiles. We find clear evidence for a steepening of the density profile power law index around R=20 kpc, from -2.50 +- 0.04 to -4.85 +- 0.04, and for a flattening of the halo towards the poles with best-fit axis ratio 0.63 +- 0.02. Furthermore, we cannot rule out a mild triaxiality (w>=0.8). We recover the signatures of well-known substructure and streams that intersect our lines of sight. These results are consistent with those derived from wider but shallower surveys, and augur well for upcoming, wide-field surveys of comparable depth to our pencil beam surveys.