The Bulge Radial Velocity Assay for RR Lyrae Stars (BRAVA-RR) DR2: A Bimodal Bulge?

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Kunder, Andrea ^[1] ; Perez-Villegas, Angeles ^[2] ; Rich, R. Michael ^[3] ; Ogata, Jonathan ^[1] ; Murari, Emma ^[1] ; Boren, Emilie ^[1] ; Johnson, I, Christian ; Nataf, David ^{[4, 5]} ; Walker, Alistair ^[6] ; Bono, Giuseppe ^{[7, 8]} ; Koch, Andreas ^[9] ; De Propris, Roberto ^[10] ; Storm, Jesper ^[11] ; Wojno, Jennifer ^{[4, 5]}

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^[1] St Martins Univ, 5000 Abbey Way SE, Lacey, WA 98503 - USA

^[2] Univ Sao Paulo, IAG, Rua Matao 1226, Cidade Univ, BR-05508900 Sao Paulo - Brazil

^[3] Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 - USA

^[4] Johns Hopkins Univ, Dept Phys & Astron, Baltimore, MD 21218 - USA

^[5] Johns Hopkins Univ, Ctr Astrophys Sci, Baltimore, MD 21218 - USA

^[6] Cerro Tololo Interamer Observ, NSFs Natl Opt Infrared Astron Res Lab, Casilla 603, La Serena - Chile

^[7] Univ Roma Tor Vergata, Dipartimento Fis, Via Ric Sci 1, I-00133 Rome - Italy

^[8] INAF, Rome Astron Observ, Via Frascati 33, I-00040 Monte Porzio Catone - Italy

^[9] Heidelberg Univ, Zentrum Astron, Astron Rechen Inst, Monchhofstr 12-14, D-69120 Heidelberg - Germany

^[10] Univ Turku, FINCA, Vesilinnantie 5, Turku 20014 - Finland

^[11] Leibniz Inst Astrophys AIP, Sternwarte 16, D-14482 Potsdam - Germany

• Tipo de documento: Artigo Científico
• Fonte: ASTRONOMICAL JOURNAL; v. 159, n. 6 JUN 2020.
• Citações Web of Science: 0

Resumo

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. (AU)

• Processo FAPESP: 17/15893-1 - Órbitas de aglomerados globulares do bojo: formação e evolução da Via Láctea
• Beneficiário: Maria de Los Angeles Perez Villegas
• Linha de fomento: Bolsas no Brasil - Pós-Doutorado