J/MNRAS/514/1706 Spectroscopy of Tri II LOS and member stars (Buttry+, 2022)
Stellar kinematics of dwarf galaxies from multi-epoch spectroscopy
application to Triangulum II.
Buttry R., Pace A.B., Koposov S.E., Walker M.G., Caldwell N., Kirby E.N.,
Martin N.F., Mateo M., Olszewski E.W., Starkenburg E., Badenes C.,
Daher C.M.
<Mon. Not. R. Astron. Soc. 514, 1706-1719 (2022)>
=2022MNRAS.514.1706B 2022MNRAS.514.1706B (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, dwarf ; Stars, double and multiple ; Spectroscopy ;
Optical ; Positional data ; Radial velocities ;
Effective temperatures ; Abundances, [Fe/H]
Keywords: binaries: spectroscopic - galaxies: kinematics and dynamics
Abstract:
We present new MMT/Hectochelle spectroscopic measurements for 257
stars observed along the line of sight to the ultrafaint dwarf galaxy
Triangulum II (Tri II). Combining results from previous Keck/DEIMOS
spectroscopy, we obtain a sample that includes 16 likely members of
Tri II, with up to 10 independent redshift measurements per star. To
this multi-epoch kinematic data set, we apply methodology that we
develop in order to infer binary orbital parameters from sparsely
sampled radial velocity curves with as few as two epochs. For a
previously identified (spatially unresolved) binary system in Tri II,
we infer an orbital solution with period 296.0+3.8-3.3 d,
semimajor axis 1.12+0.41-0.24 au, and systemic velocity
-380.0 ± 1.7 km/s that we then use in the analysis of Tri II's
internal kinematics. Despite this improvement in the modelling of
binary star systems, the current data remain insufficient to resolve
the velocity dispersion of Tri II. We instead find a 95 per cent
confidence upper limit of σv ≲ 3.4 km/s.
Description:
Dwarf galaxies are of great importance for astrophysics. From a galaxy
formation perspective, dwarf galaxies are among the oldest and least
chemically evolved objects From a dark matter perspective, they
include the most dark matter dominated systems known, with published
dynamical mass-to-light ratios reaching as high as 104 in solar
unitsIn this vein, dwarf galaxies are believed to be key components in
unpacking the mystery of dark matter, as they probe the small-scale
structure (< 1 Mpc) regime of ΛCDM cosmology. The Triangulum II
(Tri II) ultrafaint dwarf galaxy provides an interesting case study.
As explained in the section 2, we consider new spectroscopic
observational data acquired with Hectochelle spectroscop at the 6.5-m
MMT Observatory on Mt. Hopkins, Arizona. We observed using the 'RV31'
filter, isolating the wavelength range of 5150-5300 Å at resolution
R ≃ 34000. We processed all raw Hectochelle spectra using the CfA
pipeline, we then analysed each individual spectrum by fitting a model
based on a library of synthetic template spectra that span a regular
grid in effective temperature, surface gravity, and [Fe/H]
metallicity. In addition to the stellar-atmospheric parameters, we fit
for line-of-sight velocity, as well as several free parameters that
specify the continuum shape and correct for wavelength-dependent
velocity shifts. As recorded sample is then composed of 295 individual
observations on 257 stars on which 13 are Tri II members. Results are
available in tabled1.dat.
Next, we matched our previous MMT Hectochelle sample with spectroscopy
obtained with Keck DEIMOS spectrographs (i.e see section 2.2 and 2.3).
In these studies, they used the 1200G grating, which achieves a
spectral resolution of R ∼ 7000 at 8500 Å, in the spectral vicinity
of the Ca II infrared triplet. We found 50 observations on 14 Tri II
stars member and resumed these line-of-sight velocities from spectral
fits in tabled2.dat.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tabled1.dat 458 295 Individual observations of Tri II members taken
with MMT Hectochelle spectrograph
tabled2.dat 51 50 Individual observations of Tri II members from
Keck DEIMOS used in this analysis after a fixed
amount of 1.33 ± 0.33 km/s zero-point offset
correction from each velocity measurement
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See also:
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
II/349 : The Pan-STARRS release 1 (PS1) Survey - DR1 (Chambers+,2016)
J/A+A/657/A54 : Local Group Gaia eDR3 systemic motions (Battaglia+, 2022)
J/AJ/156/257 : Spectroscopy of RGB stars in Draco & Ursa Minor
(Spencer+, 2018)
J/ApJ/870/83 : Abundances in the ultra-faint dwarf gal. GruI & TriII
(Ji+, 2019)
J/ApJ/838/83 : Radial velocities, abundances & membership in TriII
(Kirby+, 2017)
J/MNRAS/490/3508 : The Southern Stellar Stream Sp. Survey (S5) (Li+, 2019)
J/MNRAS/495/3022 : Stellar populations of the Ursa Minor dSph galaxy
(Pace+, 2020)
J/MNRAS/448/2717 : Bayesian analysis of resolved stellar spectra (Walker+,2015)
https://zenodo.org/records/6561483 : data of this work in zenodo
Byte-by-byte Description of file: tabled1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 I18 --- GaiaEDR3 Unique source identifier from GaiaEDR3
(source_id)
20- 22 I3 --- KCS2015 ? Identifier number [KCS2015] NNN from
Kirby et al. 2015ApJ...814L...7K 2015ApJ...814L...7K (KCS2015)
24- 25 I2 --- MIC2016 ? Identifier number [MIC2016] NN from
Martin et al. 2016ApJ...818...40M 2016ApJ...818...40M
(MIC2016)
27 I1 --- Memb [0/1] Tri II membership flag 1 for true
with 13 objects and 0 for false with 282
objects, refer to section 2.4 (member)
29- 46 F18.15 deg RAdeg Right ascension (ICRS) at Ep=2016.0
(ra_deg)
48- 65 F18.15 deg DEdeg Declination (ICRS) at Ep=2016.0 (dec_deg)
67- 84 F18.10 d HJD Heliocentric Julian Day (hjd)
86-104 F19.16 --- SNR Signal to noise ratio from MMT
Hectochelle observations see section 2.1
(sn_ratio)
106-127 F22.17 km/s vLOS Heliocentric line-of-sight velocity (vlos)
129-147 F19.17 km/s e_vLOS Mean error of vLOS (vlos_error)
149-170 F22.19 --- vSkew Statistical skewness value of the vLOS
velocity (vlos_skew)
172-193 F22.19 --- vKurt Statistical Kurtosis value for vLOS
velocity (vlos_kurtosis)
195-212 F18.13 K Teff Effective temperature (teff)
214-233 F20.15 K e_Teff Mean uncertainty of Teff (teff_error)
235-256 F22.19 --- TSkew Statistical skewness value of the Teff
temeprature (teff_skew)
258-279 E22.20 --- TKurt Statistical Kurtosis value for Teff
temeprature (teff_kurtosis)
281-298 F18.16 [cm/s2] logg Surface gravity (logg)
300-319 F20.18 [cm/s2] e_logg Mean uncertainty of logg (logg_error)
321-343 E23.20 --- gSkew Statistical skewness value of the logg
surface gravity (logg_skew)
345-366 F22.19 --- gKurt Statistical Kurtosis value for logg
surface gravity (logg_kurtosis)
368-389 F22.19 [Sun] [Fe/H] Iron to hydrogen abundance ratio (feh)
391-410 F20.18 [Sun] e_[Fe/H] Mean uncertainty of [Fe/H] (feh_error)
412-433 E22.20 --- [Fe/H]Skew Statistical skewness value of the [Fe/H]
abundance ratio (feh_skew)
435-456 F22.19 --- [Fe/H]Kurt Statistical Kurtosis value for [Fe/H]
abundance ratio (feh_kurtosis)
458 I1 --- q_[Fe/H] [0/1] The [Fe/H] observation data
quality, 1 for yes with 207 cases on 295
(feh_qual) (1)
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Note (1): As explicited in section Appendix C, only measurements with an
e_[Fe/H] < 0.4 dex are considerated as being good-quality.
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Byte-by-byte Description of file: tabled2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- KCS2015 ? Identifier number [KCS2015] NNN from
Kirby et al. 2015ApJ...814L...7K 2015ApJ...814L...7K (KCS2015)
5- 6 I2 --- MIC2016 ? Identifier number [MIC2016] NN from
Martin et al. 2016ApJ...818...40M 2016ApJ...818...40M (MIC2016)
8- 17 F10.7 deg RAdeg Right ascension (ICRS) at Ep=2016.0 (RAICRS)
19- 28 F10.7 deg DEdeg Declination (ICRS) at Ep=2016.0 (DecICRS)
30- 39 F10.2 d HJD Heliocentric Julian Day (HJD)
41- 46 F6.1 km/s vLOS Heliocentric line-of-sight velocity (vlos)
48- 51 F4.1 km/s e_vLOS Mean error of vLOS (vlos_error)
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 03-Apr-2025