J/A+A/698/A53 Sextans dwarf spheroidal members (Tolstoy+, 2025)
A 3D view of dwarf galaxies with Gaia and VLT FLAMES.
II. The Sextans dwarf spheroidal.
Tolstoy E., Battaglia G., Arroyo-Polonio J.M., Brown A.G.A., van Essen T.,
Massari D., Skuladottir A., Irwin M.J., Taibi S., Pritchard J.
<Astron. Astrophys. 698, A53 (2025)>
=2025A&A...698A..53T 2025A&A...698A..53T (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Stars, giant ; Radial velocities ;
Spectroscopy ; Optical
Keywords: stars: abundances - galaxies: dwarf - galaxies: evolution -
galaxies: individual: Sextans dwarf spheroidal
Abstract:
The Sextans dwarf spheroidal galaxy has been challenging to study in a
comprehensive way as it is highly extended on the sky, with an
uncertain but large tidal radius of between 80-160 arcminutes (or
3-4kpc), and an extremely low central surface brightness of
SigmaV∼26.2mag/arcsec2.
Here, we present a new homogeneous survey of 41 VLT/FLAMES multi-fibre
spectroscopic pointings that contain 2108 individual spectra, and
combined with Gaia DR3 photometry and astrometry we present vlos
measurements for 333 individual red giant branch stars that are
consistent with membership in the Sextans dwarf spheroidal galaxy. In
addition, we provide the metallicity, [Fe/H], determined from the two
strongest CaII triplet lines, for 312 of these stars.
We look again at the global characteristics of Sextans, deriving a
mean line-of-sight velocity of =+227.1km/s and a mean
metallicity of <[Fe/H]≥-2.37. The metallicity distribution is clearly
double-peaked, with the highest peak at [Fe/H]=-2.81 and another
broader peak at [Fe/H]~=-2.09. Thus, it appears that Sextans hosts two
populations and the superposition leads to a radial variation in the
mean metallicity, with the more metal-rich population being centrally
concentrated.
In addition, there is an intriguing group of nine probable members in
the outer region of Sextans at higher [Fe/H] than the mean in this
region. If these stars were confirmed as members, they would eliminate
the metallicity gradient. We also look again at the colour-magnitude
diagram of the resolved stellar population in Sextans, and at the
relation between Sextans and the intriguingly nearby globular cluster,
Pal 3.
The global properties of Sextans have not changed significantly
compared to previous studies, but they are now more precise, and the
sample of known members in the outer regions is now more complete.
Description:
We present our new measurements of vlos and [Fe/H] for new and
archival data for individual stars in the Sextans dSph from the ESO
(European Southern Observatory) Very Large Telescope (VLT)
FLAMES/GIRAFFE spectra of RGB stars. These data were collected between
2003 and 2019 in two main observing campaigns
From a combination of new and old re-processed archival VLT/FLAMES LR8
data, we have obtained a uniform sample of [Fe/H], vlos and Gaia DR3
astrometric parameters for 312 individual member RGB stars, extending
to (and beyond) the nominal tidal radius.
The full sample of measurements of the 604 likely members of the
Sextans dSph are presented online (Table D.1). Table D.1 includes,
where it is available, FLAMES spectroscopic information, and for those
stars not in the FLAMES sample but with a reliable Walker vlos
measurement (Walker et al. 2023ApJS..268...19W 2023ApJS..268...19W, Cat. J/ApJS/268/19),
these are also included in Table D.1. In addition, the FLAMES
spectroscopic and Gaia DR3 properties of the 9 probable members that
are vlos members but have uncertain Sextans membership based on Gaia
DR3 are included in Table D.1. In Table D.2 we also provide the Gaia
DR3 and spectroscopic information for the stars for which we have
FLAMES observations but either are very clear non-members on the basis
of their spectroscopic vlos or their spectroscopic measurements were
not found to be reliable enough. If the unreliable spectroscopic
members are likely Gaia members then this also noted in Table D.1 and
D.2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tabled1.dat 225 612 *Full sample of measurements of the 604 likely
members of the Sextans dSph
tabled2.dat 178 1713 Gaia DR3 and spectroscopic information for the stars
for which we have FLAMES observations but either
are very clear non-members on the basis of their
spectroscopic vlos or their spectroscopic
measurements were not found to be reliable enough
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Note on tabled1.dat: We have included here all the Gaia DR3 likely members in
this table even those without FLAMES spectra.
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/ApJS/268/19 : M2FS + Hectochelle spectra of dSph in MW halo (Walker+, 2023)
J/A+A/675/A49 : vlos of Sculptor dSph red giants (Tolstoy+, 2023)
Byte-by-byte Description of file: tabled1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaDR3 Gaia DR3 identification number
21- 29 F9.5 deg RAdeg Gaia right ascension (ICRS) at Ep=2016.0
31- 38 F8.5 deg DEdeg Gaia declination (ICRS) at Ep=2016.0
40- 45 F6.3 mag Gmag Gaia G magnitude
47- 52 F6.3 mag BPmag Gaia BP magnitude
54- 59 F6.3 mag RPmag Gaia RP magnitude
61- 67 F7.4 mas plx Gaia parallax
69- 74 F6.4 mas e_plx Gaia parallax error
76- 81 F6.3 mas/yr pmRA Gaia proper motion along RA
83- 87 F5.3 mas/yr e_pmRA Gaia proper motion along RA error
89- 94 F6.3 mas/yr pmDE Gaia proper motion along DE
96-100 F5.3 mas/yr e_pmDE Gaia proper motion along DE error
102-119 A18 --- FLAMESfield Name of the VLT/FLAMES pointing
121-128 A8 --- SpecName Name of object in VLT/FLAMES pointing
130 I1 --- Nspec ? Number of individual VLT/FLAMES spectra
combined
132-137 F6.2 --- CombSN ? Combined signal to noise for the
FLAMES spectra (1)
139-144 F6.2 km/s Vel ? Average radial velocity for the
FLAMES spectra (2)
146-150 F5.3 km/s e_Vel ? Average radial velocity error for the
FLAMES spectra (2)
152-156 F5.3 km/s varVel ? Variance of radial velocity
measurements, if Nspec>1 (2)
158-162 F5.2 [-] [Fe/H] ? Average [Fe/H] for FLAMES spectra (3)
164-168 F5.3 [-] e_[Fe/H] ? Error on average [Fe/H] for
FLAMES spectra (3)
170-174 F5.3 [-] var[Fe/H] ? Variance of [Fe/H] measurements,
if Nspec>1 (3)
176-180 F5.3 --- Pmem [0/1] Probability of membership from
Battaglia et al. (2022A&A...657A..54B 2022A&A...657A..54B,
Cat. J/A+A/657/A54) analysis (4)
182-225 A44 --- Notes Previous observations (5)
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Note (1): the signal-to-noise of the single (for Nspec=1) or combined
VLT/FLAMES spectra.
Note (2): The vlos for this star measured from VLT/FLAMES spectra, averaged if
Nspec>1.
The velocities in this table can be reliable if the stars are members,
but are advised to be used with caution, if at all. They are not used in this
paper. Some stars have other better FLAMES spectra as part of this survey and
are thus listed in Table.D.1 with those values (which may differ from what is
here).
Note (3): [Fe/H] for the star determined from the CaT measurement from
VLT/FLAMES spectra, averaged if Nspec>1.
Note (4): Stars with Pmem=0 are stars with VLT/FLAMES spectroscopic vlos
compatible with membership in Sextans but the Gaia proper motions and/or
parallaxes are just on the wrong side of the membership cuts. They are
borderline members.
Note (5): Notes refer to previous measurements of these stars:
Walker et al. (2023ApJS..268...19W 2023ApJS..268...19W, Cat. J/ApJS/268/19) (W23) with the radial
velocity, Theler et al. (2020A&A...642A.176T 2020A&A...642A.176T, Cat. J/A+A/642/A176);
Shetrone et al. (2001ApJ...548..592S 2001ApJ...548..592S); Aoki et al. (2009A&A...502..569A 2009A&A...502..569A).
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Byte-by-byte Description of file: tabled2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaDR3 ? Gaia DR3 identifier
21- 31 F11.7 deg RAdeg Gaia right ascension (ICRS) at Ep=2016.0
33- 43 E11.3 deg DEdeg Gaia declination (ICRS) at Ep=2016.0
45- 62 A18 --- FLAMESfield FLAMES field name
64- 71 A8 --- Specname FLAMES target name
73- 81 F9.6 mag Gmag ? Gaia DR3 G magnitude
83- 93 F11.7 --- S/N Signal-to-noise ratio
95-101 F7.2 km/s Vel Helioenctric radial velocity
103-106 F4.2 --- Pmem [0/1]? Probability of membership
108-111 A4 --- Cmem Membership class (1)
113-178 A66 --- Notes Why rejected
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Note (1): Membership class code as follows:
LM = likely member
LMp = likely member, the star maybe a member but it is peculiar
(a C-star or a double star, for example)
M = member
Mp = member, the star is a member but it is peculiar
(a C-star or a double star, for example)
NM = not member
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Acknowledgements:
Eline Tolstoy, etolstoy(at)astro.rug.nl
References:
Tolstoy et al., Paper I 2023A&A...675A..49T 2023A&A...675A..49T, Cat. J/A+A/675/A49
(End) Patricia Vannier [CDS] 22-Apr-2025