J/A+A/633/A36 3D kinematics in the Draco dwarf spheroidal (Massari+, 2020)
Stellar 3D kinematics in the Draco dwarf spheroidal galaxy.
Massari D., Helmi A., Mucciarelli A., Sales L.V., Spina L., Tolstoy E.
<Astron. Astrophys. 633, A36 (2020)>
=2020A&A...633A..36M 2020A&A...633A..36M (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, optical ; Radial velocities ; Proper motions
Keywords: galaxies: dwarf - Local Group - galaxies: kinematics and dynamics -
proper motions - techniques: radial velocities
Abstract:
We present the first three-dimensional internal motions for individual
stars in the Draco dwarf spheroidal galaxy. 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 of 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 members of
Draco with high-precision and accurate 3D motions, which we publish as
a table in this paper. With this high-quality dataset we determined
the velocity dispersions at a projected distance of ∼120pc from the
centre of Draco to be sigmaR=11.0+2.1-1.5km/s,
sigmaT=9.9+2.3-3.1km/s and sigmaLOS=9.0+1.1-1.1 km/s in
the projected radial, tangential and line-of-sight directions. This
results in a velocity anisotropy beta=0.25+0.47-1.38 at r>120pc.
Tighter constraints can be obtained using the spherical Jeans
equations and assuming constant anisotropy and NFW mass profiles, as
well as that the 3D velocity dispersion should be lower than ∼1/3 of
the escape velocity of the system. In this case, we constrain the
maximum circular velocity Vmax of Draco to be in the range of
10.2-17.0km/s. The corresponding mass range is in good agreement with
previous estimates based on line-of-sight velocities only. 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 on this dataset and with upcoming data releases.
Description:
Positions, magnitudes, radial velocities, proper motions and related
uncertainties for stars in the Draco dwarf spheroidal galaxy, obtained
combining first epoch Hubble Space Telescope observations and second
epoch Gaia Data Release and observations from the DEIMOS spectrograph
at the Keck II telescope.
The first table (Table 2) includes 81 stars, of which 51 targeted for
the first time (flag=1), 18 in common with Walker et al. (2015, Cat.
J/MNRAS/448/2717) (flag=2) and 12 coming from Walker et al. (2015,
Cat. J/MNRAS/448/2717) only (flag=0). The second table (Table 3)
includes the 45 stars with precise 3D kinematics, used to determine
the velocity dispersions.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 43 81 Parameters for the radial velocity sample
table3.dat 72 45 Measurements for the sample with 3D kinematics
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/MNRAS/448/2717 : Bayesian analysis of resolved stellar spectra (Walker+ 2015)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 11 F11.7 deg RAdeg Right ascension (ICRS) at Ep=2015.5
13- 22 F10.7 deg DEdeg Declination (ICRS) at Ep=2015.5
24- 29 F6.3 mag Gmag Gaia G magnitude
31- 36 F6.1 km/s vlos Radial velocity
38- 40 F3.1 km/s e_vlos Radial velocity uncertainty
43 I1 --- Flag [0/2]? Flag (1)
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Note (1): Flag as follows:
1 = stars targeted for the first time (51 stars)
2 = stars in common with Walker et al. (2015, Cat. J/MNRAS/448/2717)
(18 stars)
0 = stars coming from Walker et al. (2015, Cat. J/MNRAS/448/2717) only
(12 stars)
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 14 F14.10 deg RAdeg Right ascension (ICRS) at Ep=2015.5
16- 28 F13.10 deg DEdeg Declination (ICRS) at Ep=2015.5
30- 35 F6.3 mag Gmag Gaia G magnitude
37- 42 F6.3 mas/yr pmRA* Proper motion along RA, mualpha*cos(delta)
44- 48 F5.3 mas/yr e_pmRA* mualpha*cos(delta) uncertainty
50- 55 F6.3 mas/yr pmDE Proper motion alongDE, mudelta
57- 61 F5.3 mas/yr e_pmDE mudelta uncertainty
63- 68 F6.1 km/s vlos Radial velocity
70- 72 F3.1 km/s e_vlos Radial velocity uncertainty
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Acknowledgements:
Davide Massari, davide.massari(at)unibo.it
(End) D. Massari [Univ. di Bologna, Italy], P. Vannier [CDS] 13-Nov-2019