Stellar 3D kinematics in the Draco dwarf spheroidal galaxy

被引:39
|
作者
Massari, D. [1 ,2 ,3 ]
Helmi, A. [1 ]
Mucciarelli, A. [2 ,3 ]
Sales, L., V [4 ]
Spina, L. [5 ]
Tolstoy, E. [1 ]
机构
[1] Univ Groningen, Kapteyn Astron Inst, NL-9747 AD Groningen, Netherlands
[2] Univ Bologna, Dipartimento Fis & Astron, Via Gobetti 93-2, I-40129 Bologna, Italy
[3] INAF Osservatorio Astrofis & Sci Spazio Bologna, Via Gobetti 93-3, I-40129 Bologna, Italy
[4] Univ Calif Riverside, Dept Phys & Astron, 900 Univ Ave, Riverside, CA 92507 USA
[5] Monash Univ, Sch Phys & Astron, Monash Ctr Astrophys, Clayton, Vic 3800, Australia
基金
澳大利亚研究理事会;
关键词
galaxies; dwarf; Local Group; kinematics and dynamics; proper motions; techniques; radial velocities; MILKY-WAY SATELLITES; DARK-MATTER; STRUCTURAL-PROPERTIES; INTERNAL KINEMATICS; VELOCITY DISPERSION; EVOLUTION; PROFILES; CORES;
D O I
10.1051/0004-6361/201935613
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Aims. We present the first three-dimensional internal motions for individual stars in the Draco dwarf spheroidal galaxy. Methods. By combining first-epoch Hubble Space Telescope observations and second-epoch Gaia Data Release 2 positions, we measured the proper motions of 149 sources in the direction of Draco. We determined the line-of-sight velocities for a sub-sample of 81 red giant branch stars using medium resolution spectra acquired with the DEIMOS spectrograph at the Keck II telescope. Altogether, this resulted in a final sample of 45 Draco members with high-precision and accurate 3D motions, which we present as a table in this paper. Results. Based on this high-quality dataset, we determined the velocity dispersions at a projected distance of similar to 120 pc from the centre of Draco to be sigma(R) = 11.0(1.5)(+2.1) km s(-1), sigma(T) = 9.9(3.1)(+2.3) km s(-1) and sigma(LOS) = 9.0(1.1)(+1.1) km s(-1) in the projected radial, tangential, and line-of-sight directions. This results in a velocity anisotropy beta = 0.25(-1.38)(+0.47) at r greater than or similar to 120 pc. Tighter constraints may be obtained using the spherical Jeans equations and assuming constant anisotropy and Navarro-Frenk-White (NFW) mass profiles, also based on the assumption that the 3D velocity dispersion should be lower than approximate to 1/3 of the escape velocity of the system. In this case, we constrain the maximum circular velocity V-max of Draco to be in the range of 10.2-17.0 km s(-1). The corresponding mass range is in good agreement with previous estimates based on line-of-sight velocities only. Conclusions. Our Jeans modelling supports the case for a cuspy dark matter profile in this galaxy. Firmer conclusions may be drawn by applying more sophisticated models to this dataset and with new datasets from upcoming Gaia releases.
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页数:11
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