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Published May 20, 2018 | Published + Submitted
Journal Article Open

The Profile of the Galactic Halo from Pan-STARRS1 3π RR Lyrae


We characterize the spatial density of the Pan-STARRS1 (PS1) sample of Rrab stars to study the properties of the old Galactic stellar halo. This sample, containing 44,403 sources, spans galactocentric radii of 0.55 kpc ≤ R_(gc) ≤ 141 kpc with a distance precision of 3% and thus is able to trace the halo out to larger distances than most previous studies. After excising stars that are attributed to dense regions such as stellar streams, the Galactic disk and bulge, and halo globular clusters, the sample contains ~11,000 sources within 20 kpc ≤ R-(gc) ≤ 131 kpc. We then apply forward modeling using Galactic halo profile models with a sample selection function. Specifically, we use ellipsoidal stellar density models ρ(l, b, R gc) with a constant and a radius-dependent halo flattening q(R gc). Assuming constant flattening q, the distribution of the sources is reasonably well fit by a single power law with n = 4.40^(+0.05)_(-0.04) and q = 0.918^(+0.016)_(-0.014) and comparably well fit by an Einasto profile with n = 9.53^(+0.27)_(_-0.28), an effective radius r_(eff) = 1.07 ± 0.10 kpc, and a halo flattening of q = 0.923 ± 0.007. If we allow for a radius-dependent flattening q(R_(gc)), we find evidence for a distinct flattening of q ~ 0.8 of the inner halo at ~25 kpc. Additionally, we find that the south Galactic hemisphere is more flattened than the north Galactic hemisphere. The results of our work are largely consistent with many earlier results (e.g., Watkins et al.; Iorio et al.). We find that the stellar halo, as traced in RR Lyrae stars, exhibits a substantial number of further significant over- and underdensities, even after masking all known overdensities.

Additional Information

© 2018 The American Astronomical Society. Received 2017 November 1; revised 2018 March 28; accepted 2018 April 18; published 2018 May 21. H.-W.R. acknowledges funding from the European Research Council under the European Unions Seventh Framework Programme (FP 7) ERC grant agreement no. 321035. The Pan-STARRS1 Surveys (PS1) have been made possible through contributions of the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg, and the Max Planck Institute for Extraterrestrial Physics, Garching, Johns Hopkins University, Durham University, the University of Edinburgh, Queen's University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under grant no. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation under grant no. AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), and the Los Alamos National Laboratory.

Attached Files

Published - Hernitschek_2018_ApJ_859_31.pdf

Submitted - 1801.10260.pdf


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August 19, 2023
October 18, 2023