J/A+A/635/A152 Tucana dSph galaxy spectroscopic dataset (Taibi+, 2020)
The Tucana dwarf spheroidal galaxy: not such a massive failure after all.
Taibi S., Battaglia G., Rejkuba M., Leaman R., Kacharov N., Iorio G.,
Jablonka P., Zoccali M.
<Astron. Astrophys., 635, A152 (2020)>
=2020A&A...635A.152T 2020A&A...635A.152T (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Photometry ; Radial velocities ; Abundances
Keywords: galaxies: dwarf - Local Group - galaxies: stellar content -
galaxies: kinematics and dynamics - galaxies: abundances -
techniques: spectroscopic
Abstract:
Isolated local group (LG) dwarf galaxies have evolved most or all of
their life unaffected by interactions with the large LG spirals and
therefore offer the opportunity to learn about the intrinsic
characteristics of this class of objects.
Our aim is to explore the internal kinematic and metallicity
properties of one of the three isolated LG early-type dwarf galaxies,
the Tucana dwarf spheroidal. This is an intriguing system, as it has
been found in the literature to have an internal rotation of up to
16km/s, a much higher velocity dispersion than dwarf spheroidals of
similar luminosity, and a possible exception to the too-big-too-fail
problem.
We present the results of a new spectroscopic dataset that we procured
from the Very Large Telescope (VLT) taken with the FORS2 instrument in
the region of the Ca II triplet for 50 candidate red giant branch
stars in the direction of the Tucana dwarf spheroidal. These yielded
line-of-sight (l.o.s.) velocity and metallicity ([Fe/H]) measurements
of 39 effective members that double the number of Tucana's stars with
such measurements. In addition, we re-reduce and include in our
analysis the other two spectroscopic datasets presented in the
literature, the VLT/FORS2 sample by Fraternali et al.
(2009A&A...499..121F 2009A&A...499..121F), and the VLT/FLAMES one from Gregory et al.
(2019MNRAS.485.2010G 2019MNRAS.485.2010G).
Across the various datasets analyzed, we consistently measure a l.o.s.
systemic velocity of 180±1.3km/s and find that a dispersion-only
model is moderately favored over models that also account for internal
rotation. Our best estimate of the internal l.o.s. velocity dispersion
is 6.2-1.3+1.6km/s, much smaller than the values reported in the
literature and in line with similarly luminous dwarf spheroidals; this
is consistent with NFW halos of circular velocities <30km/s.
Therefore, Tucana does not appear to be an exception to the
too-big-to-fail problem, nor does it appear to reside in a dark matter
halo much more massive than those of its siblings. As for the
metallicity properties, we do not find anything unusual; there are
hints of the presence of a metallicity gradient, but more data are
needed to pinpoint its presence.
Description:
The primary dataset (P91 FORS2 dataset) analyzed in this work was
obtained with the FORS2 instrument mounted at the UT1 (Antu) of the
Very Large Telescope (VLT) at the ESO Paranal observatory.
Observations were taken in service mode over several nights between
July 2013 and July 2014 as part of the ESO program 091.B-0251, PI: M.
Zoccali.
The instrumental set-up of the P69 program (Fraternali et al.,
2009A&A...499..121F 2009A&A...499..121F) was similar to the one we adopted for our
observations, with the difference being that the size of each slit was
of 1.2"x8", which translates into a slightly lower spectral resolution
(∼30km/s/pix). A total of 45 initial targets were assigned to an
equivalent number of slits packed into a single pointing centered on
Tucana. For the sake of homogeneity, we therefore reduced the F09
dataset again following the same procedure as adopted for the P91
sample. Hereinafter, we refer to this additional sample as the P69
FORS2 dataset.
Gregory et al. (2019MNRAS.485.2010G 2019MNRAS.485.2010G) recently presented an additional
sample of l.o.s. velocities (not metallicities) for individual stars
in the direction of Tucana, taken with the FLAMES/GIRAFFE instrument
at the VLT, as part of the ESO program 095.B-0133(A), PI: M. Collins.
We refer to this sample as FLAMES dataset.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablec1.dat 92 58 Properties of observed P91-FORS2 dataset in
the Tucana dSph
tablec2.dat 93 28 Properties of observed P69-FORS2 dataset in the
Tucana dSph
tablec3.dat 77 164 Properties of observed FLAMES/GIRAFFE dataset
in the Tucana dSph
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Byte-by-byte Description of file: tablec1.dat
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Bytes Format Units Label Explanations
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1 I1 --- Field [0/1]? Field, 0 for Tuc0 and 1 for Tuc1
3- 4 I2 --- Slit Slit number within the field (1)
6 A1 --- n_Slit [R] R for repeated measurements (2)
8- 15 F8.4 deg RAdeg Right ascension (J2000)
17- 25 F9.5 deg DEdeg Declination (J2000)
27- 31 F5.2 mag Vmag V magnitude from VLT/FORS2 photometric catalog
33- 36 F4.2 mag e_Vmag rms uncertainty on V magnitude
38- 42 F5.2 mag Imag I magnitude from VLT/FORS2 photometric catalog
44- 47 F4.2 mag e_Imag rms uncertainty on I magnitude
49- 53 F5.1 km/s HV ? LOS heliocentric velocity
55- 58 F4.1 km/s e_HV ? rms uncertainty on heliocentric velocity
60- 64 F5.2 [-] [Fe/H] ? Metallicity
66- 69 F4.2 [-] e_[Fe/H] ? rms uncertainty on metallicity
71- 74 F4.1 pix-1 S/N Signal-to-noise ratio
(the conversion factor to Å-1 is 1.09)
76- 77 A2 --- nP [Ph ] Ph for non-members (G1)
79- 82 F4.2 --- P1 ? Probability of membership obtained using
the P91 dataset alone
84- 87 F4.2 --- P2 ? Probability of membership obtained using
the P91 dataset combining with the P69
89- 92 F4.2 --- P3 ? Probability of membership obtained using
the P91 dataset combining with the P69 and
further adding the FLAMES data
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Note (1): Slit aperture: numbers <30 indicate observed targets from chip-1,
otherwise from chip-2 - numbers counted from bottom to top of the CCD.
Note (2): Four stars had repeated measurements: targets 31, 32, 33, and 35 from
Tuc0 field corresponding to targets 31, 32, 33, and 36 from Tuc1 field,
respectively.
We report the single measurements as well as the averaged values used during
the analysis process (with R in n_Slit).
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Byte-by-byte Description of file: tablec2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Slit Slit number (1)
4- 6 A3 --- n_Slit [a,b ] Note on Slit (2)
8- 15 F8.4 deg RAdeg Right ascension (J2000)
17- 25 F9.5 deg DEdeg Declination (J2000)
27- 31 F5.2 mag Vmag ?=0 V magnitude from VLT/FORS2 photometric
catalog
33- 36 F4.2 mag e_Vmag ?=0 rms uncertainty on Vmag
38- 42 F5.2 mag Imag ?=0 I magnitude from VLT/FORS2 photometric
catalog
44- 47 F4.2 mag e_Imag ?=0 rms uncertainty on Imag
49- 54 F6.1 km/s HV LOS heliocentric velocity
56- 59 F4.1 km/s e_HV rms uncertainty on HV
61- 65 F5.2 [-] [Fe/H] ? Metallicity
67- 70 F4.2 [-] e_[Fe/H] ? rms uncertainty on [Fe/H]
72- 75 F4.1 pix-1 S/N Signal-to-noise ratio
(the conversion factor to Å-1 is 1.08)
77- 78 A2 --- nP [Ph ] Ph for non-members (G1)
80- 83 F4.2 --- P1 ? Probability of membership obtained using
the P91 dataset alone
85- 88 F4.2 --- P2 ? Probability of membership obtained using
the P91 dataset combining with the P69
90- 93 F4.2 --- P3 ? Probability of membership obtained using
the P91 dataset combining with the P69 and
further adding the FLAMES data
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Note (1): slit aperture: numbers <30 indicate observed targets from chip-1,
otherwise from chip-2 - numbers counted from bottom to top of the CCD;
Note (2): Notes as follows:
a = New with respect to Fraternali et al. (2009A&A...499..121F 2009A&A...499..121F)
b = In common with the P91-FORS2 dataset
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Byte-by-byte Description of file: tablec3.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- Object Object-ID from fits header
8- 10 I3 --- Fiber Fiber-ID used through text
12- 20 F9.5 deg RAdeg Right ascension (J2000)
22- 31 F10.6 deg DEdeg Declination (J2000)
33- 38 F6.3 mag Vmag V magnitude transformed from
DES photometric catalog
40- 45 F6.3 mag Imag I magnitude transformed from
DES photometric catalog
47- 52 F6.1 km/s HV ? LOS heliocentric velocity
54- 57 F4.1 km/s e_HV ? rms uncertainty on HV
59- 63 F5.1 pix-1 S/N Signal-to-noise ratio
(the conversion factor to Å-1 is 2.24)
65- 66 A2 --- nP [Ph ] Ph for non-members (G1)
68- 71 F4.2 --- P1 ? Probability of membership obtained using the
FLAMES dataset alone
73- 76 F4.2 --- P2 ? Probability of membership obtained using the
FLAMES dataset combining with the FORS2 data
77 A1 --- Note [a] a: in common with the FORS2 dataset
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Global notes:
Note (G1): nonmembers, excluded according to their magnitudes and colors, or
because they lack reliable measurements (see Sect. 4 for full description).
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 05-Jun-2020