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Durham University

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Publication details for Dr Alis Deason

Deason, Alis J, Belokurov, Vasily & Sanders, Jason L (2019). The total stellar halo mass of the Milky Way. Monthly Notices of the Royal Astronomical Society 490(3): 3426-3439.

Author(s) from Durham


We measure the total stellar halo luminosity using red giant branch (RGB) stars selected
from Gaia data release 2. Using slices in magnitude, colour, and location on the sky, we
decompose RGB stars belonging to the disc and halo by fitting two-dimensional Gaussians
to the Galactic proper motion distributions. The number counts of RGB stars are converted
to total stellar halo luminosity using a suite of isochrones weighted by age and metallicity,
and by applying a volume correction based on the stellar halo density profile. Our method
is tested and calibrated using Galaxia and N-body models. We find a total luminosity (out
to 100 kpc) of Lhalo = 7.9 ± 2.0 × 108 L excluding Sgr, and Lhalo = 9.4 ± 2.4 × 108 L
including Sgr. These values are appropriate for our adopted stellar halo density profile and
metallicity distribution, but additional systematics related to these assumptions are quantified
and discussed. Assuming a stellar mass-to-light ratio appropriate for a Kroupa initial mass
function (M/L = 1.5), we estimate a stellar halo mass of M
halo = 1.4 ± 0.4 × 109 M. This
mass is larger than previous estimates in the literature, but is in good agreement with the
emerging picture that the (inner) stellar halo is dominated by one massive dwarf progenitor.
Finally, we argue that the combination of a ∼109 M mass and an average metallicity of
[Fe/H]∼−1.5 for the Galactic halo points to an ancient (∼10 Gyr) merger event.