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

TL;DR

This study uses combined photometric data from CFHT, SDSS, and Pan-STARRS to map the Milky Way's chemical composition and develop a non-parametric method for decomposing stellar populations by metallicity and distance.

Contribution

It introduces a novel non-parametric algorithm for metallicity-distance decomposition and applies it to extensive survey data to analyze the Milky Way's stellar populations.

Findings

Metallicity of stars can be reliably measured to ~0.2 dex.

The Milky Way's stellar halo has an exponential vertical density profile.

Three main stellar populations are identified with consistent metallicity distributions.

Abstract

We present the chemical distribution of the Milky Way, based on 2,900$\, {\rm deg^2}$ of $u$-band photometry taken as part of the Canada-France Imaging Survey. When complete, this survey will cover 10,000$\, {\rm deg^2}$ of the Northern sky. By combing the CFHT $u$-band photometry together with SDSS and Pan-STARRS $g,r,$ and $i$, we demonstrate that we are able to measure reliably the metallicities of individual stars to $\sim 0.2$ dex, and hence additionally obtain good photometric distance estimates. This survey thus permits the measurement of metallicities and distances of the dominant main-sequence population out to approximately 30 kpc, and provides 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 $30\deg < |b| < 70\deg$ 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 main-sequence stars, the stellar halo component shows a vertical density profile that is close to exponential, with a scale height of around 3 kpc. This may indicate that the inner halo was formed partly from disk stars ejected in an ancient minor merger.