Chemical Mapping of the Milky Way with The Canada–France Imaging Survey: A Non-parametric Metallicity–Distance Decomposition of the Galaxy

Abstract

Abstract We present the chemical distribution of the Milky Way, based on 2900 of u-band photometry taken as part of the Canada–France Imaging Survey. When complete, this survey will cover 10,000 of the northern sky. By combing the CFHT u-band photometry together with Sloan Digital Sky Survey and Pan-STARRS and i, we demonstrate that we are able to reliably measure the metallicities of individual stars to ∼0.2 dex, and hence additionally obtain good photometric distance estimates. This survey thus permits the measurement of metallicities and distances of the dominant main-sequence (MS) population out to approximately , and provides a much higher number of stars at large extraplanar distances than have been available from previous surveys. We develop a non-parametric distance–metallicity decomposition algorithm and apply it to the sky at and to the North Galactic Cap. We find that the metallicity–distance distribution is well-represented by three populations whose metallicity distributions do not vary significantly with vertical height above the disk. As traced in MS stars, the stellar halo component shows a vertical density profile that is close to exponential, with a scale height of around . This may indicate that the inner halo was formed partly from disk stars ejected in an ancient minor merger.