The Mass and Age Distribution of Halo White Dwarfs in the Canada-France Imaging Survey

TL;DR

This study analyzes the mass and age distribution of 18 halo white dwarfs using spectroscopic and photometric data, revealing a wide age spread and suggesting an extended star formation history in the Galactic halo.

Contribution

First detailed spectroscopic analysis of halo white dwarfs combining multiple surveys, deriving their ages and masses to understand halo formation history.

Findings

Mean age of 9.03 Gyr with significant dispersion

Wide age spread inconsistent with simple formation models

Evidence for extended star formation in the local halo

Abstract

We present optical spectroscopy for 18 halo white dwarfs identified using photometry from the Canada-France Imaging Survey and Pan-STARRS1 DR1 3$\pi$ survey combined with astrometry from Gaia DR2. The sample contains 13 DA, 1 DZ, 2 DC, and two potentially exotic types of white dwarf. We fit both the spectrum and the spectral energy distribution in order to obtain the temperature and surface gravity, which we then convert into a mass, and then an age, using stellar isochrones and the initial-to-final mass relation. We find a large spread in ages that is not consistent with expected formation scenarios for the Galactic halo. We find a mean age of 9.03$^{+2.13}_{-2.03}$ Gyr and a dispersion of 4.21$^{+2.33}_{-1.58}$ Gyr for the inner halo using a maximum likelihood method. This result suggests an extended star formation history within the local halo population.