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

¹ Leiden Observatory, Leiden University, Oort Building, Niels Bohrweg 2, 2333 CA Leiden, The Netherland
e-mail: piladiez@strw.leidenuniv.nl; kuijken@strw.leidenuniv.nl; jelte@strw.leidenuniv.nl; hoekstra@strw.leidenuniv.nl
² Laboratoire AIM, IRFU/Service d’Astrophysique – CEA/DSM – CNRS, Université Paris Diderot, Bât. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
e-mail: remco.van-der-burg@cea.fr

Received: 3 December 2014
Accepted: 2 February 2015

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 point spread function homogenization techniques we obtain catalogues of F stars (near-main sequence turnoff stars) out to Galactocentric distances up to 60 kpc. 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 0.79 ± 0.02. Furthermore, we cannot rule out a mild triaxiality (w ≥ 0.88 ± 0.07). 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.