A-type stars in the Canada-France Imaging Survey I. The stellar halo of the 
Milky Way traced to large radius by blue horizontal branch stars

Thomas, Guillaume F.; McConnachie, Alan W.; Ibata, Rodrigo A.; Côté, Patrick; Martin, Nicolas; Starkenburg, Else; Carlberg, Raymond; Chapman, Scott; Fabbro, Sébastien; Famaey, Benoit; Fantin, Nicholas; Gwyn, Stephen; Hénault-Brunet, Vincent; Malhan, Khyati; Navarro, Julio; Robin, Annie C.; Scott, Douglas

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A-type stars in the Canada-France Imaging Survey I. The stellar halo of the Milky Way traced to large radius by blue horizontal branch stars

MPS-Authors

Thomas, Guillaume F.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

McConnachie, Alan W.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Ibata, Rodrigo A.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Côté, Patrick
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Martin, Nicolas
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Starkenburg, Else
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Carlberg, Raymond
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Chapman, Scott
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Fabbro, Sébastien
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Famaey, Benoit
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Fantin, Nicholas
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Gwyn, Stephen
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Hénault-Brunet, Vincent
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Malhan, Khyati
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Navarro, Julio
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Robin, Annie C.
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

Scott, Douglas
Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners;

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https://ui.adsabs.harvard.edu/abs/2018MNRAS.481.5223T
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Citation

Thomas, G. F., McConnachie, A. W., Ibata, R. A., Côté, P., Martin, N., Starkenburg, E., et al. (2018). A-type stars in the Canada-France Imaging Survey I. The stellar halo of the Milky Way traced to large radius by blue horizontal branch stars. Monthly Notices of the Royal Astronomical Society, 481, 5223-5235.

Cite as: https://hdl.handle.net/21.11116/0000-0005-CAB8-8

Abstract

We present the stellar density profile of the outer halo of the Galaxy traced over a range of Galactocentric radii in the range 15 < R_GC < 220 kpc by blue horizontal branch (BHB) stars. These stars are identified photometrically using deep u-band imaging from the new Canada-France Imaging Survey (CFIS) that reaches 24.5 mag. This is combined with griz bands from Pan-STARRS 1 and covers a total of ̃4000 deg² of the northern sky. We present a new method to select BHB stars that has low contamination from blue stragglers and high completeness. We use this sample to measure and parametrize the three- dimensional density profile of the outer stellar halo. We fit the profile using (i) a simple power law with a constant flattening (ii) a flattening that varies as a function of Galactocentric radius (iii) a broken power-law profile. We find that outer stellar halo traced by the BHB is well modelled by a broken power law with a constant flattening of q = 0.86 ± 0.02, with an inner slope of γ = 4.24 ± 0.08. This is much steeper than the preferred outer profile that has a slope of β = 3.21 ± 0.07 after a break radius of r_ b=41.4^{+2.5}_{-2.4} kpc. The outer profile of the stellar halo trace by BHB stars is shallower than that recently measured using RR Lyrae, a surprising result given the broad similarity of the ages of these stellar populations.