A1 Refereed original research article in a scientific journal
The Bulge Radial Velocity Assay for RR Lyrae Stars (BRAVA-RR) DR2: A Bimodal Bulge?
Authors: Andrea Kunder, Angeles Perez-Villegas, R. Michael Rich, Jonathan Ogata, Enna Murari, Emilie Boren, Christian I. Johnson, David Nataf, Alistair Walker, Giuseppe Bono, Andreas Koch, Roberto De Propris, Jesper Storm, Jennifer Wojno
Publisher: IOP PUBLISHING LTD
Publication year: 2020
Journal: The Astronomical Journal
Journal name in source: ASTRONOMICAL JOURNAL
Journal acronym: ASTRON J
Article number: ARTN 270
Volume: 159
Issue: 6
Number of pages: 13
ISSN: 0004-6256
eISSN: 1538-3881
DOI: https://doi.org/10.3847/1538-3881/ab8d35
Web address : https://iopscience.iop.org/article/10.3847/1538-3881/ab8d35
Abstract
The radial velocities of 2768 fundamental-mode RR Lyrae stars (RRLs) toward the southern Galactic bulge are presented, spanning the southern bulge from -8 degrees < l b < -6 degrees. Distances derived from the pulsation properties of the RRLs are combined with Gaia proper motions to give constraints on the orbital motions of 1389 RRLs. The majority (similar to 75%) of the bulge RRLs have orbits consistent with these stars being permanently bound to <3.5 kpc from the Galactic Center, similar to the bar. However, unlike the bulge giants, the RRLs exhibit slower rotation and a higher velocity dispersion. The higher velocity dispersion arises almost exclusively from halo interlopers passing through the inner Galaxy. We present 82 stars with space velocities greater than or similar to 500 km s(-1) and find that the majority of these high-velocity stars are halo interlopers; it is unclear if a subsample of these stars with similar space velocities has a common origin. Once the 25% of the sample represented by halo interlopers is cleaned, we can clearly discern two populations of bulge RRLs in the inner Galaxy. The first population of RRLs is not as tightly bound to the Galaxy (but is still confined to the inner similar to 3.5 kpc) and is both spatially and kinematically consistent with the barred bulge. The second population is more centrally concentrated and does not trace the bar. One possible interpretation is that this population was born prior to bar formation, as their spatial location, kinematics, and pulsation properties suggest, possibly from an accretion event at high redshift.
The radial velocities of 2768 fundamental-mode RR Lyrae stars (RRLs) toward the southern Galactic bulge are presented, spanning the southern bulge from -8 degrees < l b < -6 degrees. Distances derived from the pulsation properties of the RRLs are combined with Gaia proper motions to give constraints on the orbital motions of 1389 RRLs. The majority (similar to 75%) of the bulge RRLs have orbits consistent with these stars being permanently bound to <3.5 kpc from the Galactic Center, similar to the bar. However, unlike the bulge giants, the RRLs exhibit slower rotation and a higher velocity dispersion. The higher velocity dispersion arises almost exclusively from halo interlopers passing through the inner Galaxy. We present 82 stars with space velocities greater than or similar to 500 km s(-1) and find that the majority of these high-velocity stars are halo interlopers; it is unclear if a subsample of these stars with similar space velocities has a common origin. Once the 25% of the sample represented by halo interlopers is cleaned, we can clearly discern two populations of bulge RRLs in the inner Galaxy. The first population of RRLs is not as tightly bound to the Galaxy (but is still confined to the inner similar to 3.5 kpc) and is both spatially and kinematically consistent with the barred bulge. The second population is more centrally concentrated and does not trace the bar. One possible interpretation is that this population was born prior to bar formation, as their spatial location, kinematics, and pulsation properties suggest, possibly from an accretion event at high redshift.
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