J/A+A/620/A155 Gaia proper motions of 7 UFD galaxies (Massari+, 2018)
With and without spectroscopy: Gaia DR2 proper motions of seven ultra-faint
dwarf galaxies.
Massari D., Helmi A.
<Astron. Astrophys. 620, A155 (2018)>
=2018A&A...620A.155M 2018A&A...620A.155M (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Proper motions
Keywords: Galaxy: kinematics and dynamics - galaxies: dwarf - Local Group -
astrometry - proper motions
Abstract:
We present mean absolute proper motion measurements for seven ultra-
faint dwarf galaxies orbiting the Milky Way, namely Bootes III,
Carina II, Grus II, Reticulum II, Sagittarius II, Segue 2 and
Tucana IV. For four of these dwarfs our proper motion estimate is the
first ever provided.
The adopted astrometric data come from the second data release of the
Gaia mission. We determine the mean proper motion for each galaxy
starting from an initial guess of likely members, based either on
radial velocity measurements or using stars on the Horizontal Branch
identified in the Gaia (GBP-GRP, G) colour-magnitude diagram in
the field of view towards the UFD. We then refine their membership
iteratively using both astrometry and photometry. We take into account
the full covariance matrix among the astrometric parameters when
deriving the mean proper motions for these systems.
Our procedure provides mean proper motions with typical uncertainties
of ∼0.1mas/yr, even for galaxies without prior spectroscopic
information. In the case of Segue 2 we find that using radial velocity
members only leads to biased results, presumably because of the small
number of stars with measured radial velocities. Conclusions: our
procedure allows to maximize the number of member stars per galaxy
regardless of the existence of prior spectroscopic information, and
can therefore be applied on any faint or distant stellar system within
reach of Gaia.
Description:
List of stellar members for the seven ultra-faint dwarf galaxies.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 55 7 *Results for the seven UFDs analysed in this paper
members.dat 66 282 Stellar IDs and positions (table 2)
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Note on table1.dat: We remark that an additional systematic error of 0.035mas/yr
should be added to the quoted uncertainties, as explained in Gaia
Collaboration et al. (2018A&A...616A..12G 2018A&A...616A..12G).
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Name Ultra-faint dwarf galaxy (UFD) name
16- 17 A2 --- IG [RV HB] Initial guess (1)
19- 23 F5.2 mas/yr <pmRAcosDE> Mean proper motion along RA, pmRA*cosDE
25- 28 F4.2 mas/yr e_<pmRAcosDE> rms uncertainty on <pmRAcosDE>
30- 34 F5.2 mas/yr <pmDE> Mean proper motion along DE
36- 39 F4.2 mas/yr e_<pmDE> rms uncertainty on <pmDE>
41- 45 F5.2 --- cov Covariance, cov(pmRAcosDE,pmDE)
47- 48 I2 --- Nmemb Number of members
50- 55 A6 --- SName Short name of UDF galaxy
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Note (1): Initial guess of likely members, based either on radial velocity
measurements (RV) or using stars on the Horizontal Branch (HB) identified in
the Gaia (GBP-GRP, G) colour-magnitude diagram in the field of view
towards the UFD.
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Byte-by-byte Description of file: members.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Name Ultra-faint dwarf galaxy (UFD) short name
8- 26 I19 --- ID Gaia source_id
28- 46 F19.15 deg RAdeg Right ascension (ICRS, epoch J2015.5)
48- 66 F19.15 deg DEdeg Declination (ICRS, epoch J2015.5)
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Acknowledgements:
Davide Massari, massari(at)astro.rug.nl
(End) D. Massari [Univ. Groningen, The Netherlands] P. Vannier [CDS] 17-Oct-2018