J/ApJ/866/22 Spectroscopic analysis of Tuc III stream (Li+, 2018)
The first tidally disrupted ultra-faint dwarf galaxy: a spectroscopic analysis
of the Tucana III stream.
Li T.S., Simon J.D., Kuehn K., Pace A.B., Erkal D., Bechtol K., Yanny B.,
Drlica-Wagner A., Marshall J.L., Lidman C., Balbinot E., Carollo D.,
Jenkins S., Martinez-Vazquez C.E., Shipp N., Stringer K.M., Vivas A.K.,
Walker A.R., Wechsler R.H., Abdalla F.B., Allam S., Annis J., Avila S.,
Bertin E., Brooks D., Buckley-Geer E., Burke D.L., Carnero Rosell A.,
Carrasco Kind M., Carretero J., Cunha C.E., D'Andrea C.B., da Costa L.N.,
Davis C., De Vicente J., Doel P., Eifler T.F., Evrard A.E., Flaugher B.,
Frieman J., Garcia-Bellido J., Gaztanaga E., Gerdes D.W., Gruen D.,
Gruendl R.A., Gschwend J., Gutierrez G., Hartley W.G., Hollowood D.L.,
Honscheid K., James D.J., Krause E., Maia M.A.G., March M., Menanteau F.,
Miquel R., Plazas A.A., Sanchez E., Santiago B., Scarpine V., Schindler R.,
Schubnell M., Sevilla-Noarbe I., Smith M., Smith R.C., Soares-Santos M.,
Sobreira F., Suchyta E., Swanson M.E.C., Tarle G., Tucker D.L.
<Astrophys. J., 866, 22 (2018)>
=2018ApJ...866...22L 2018ApJ...866...22L
ADC_Keywords: Galaxies, spectra; Radial velocities; Equivalent widths;
Abundances, [Fe/H]; Photometry; Optical
Keywords: dark matter ; galaxies: dwarf ; galaxies: individual (Tucana III) ;
Local Group ; stars: abundances
Abstract:
We present a spectroscopic study of the tidal tails and core of the
Milky Way satellite Tucana III, collectively referred to as the
Tucana III stream, using the 2dF+AAOmega spectrograph on the
Anglo-Australian Telescope and the IMACS spectrograph on the Magellan
Baade Telescope. In addition to recovering the brightest nine
previously known member stars in the Tucana III core, we identify 22
members in the tidal tails. We observe strong evidence for a velocity
gradient of 8.0±0.4km/s/deg over at least 3° on the sky. Based
on the continuity in velocity, we confirm that the Tucana III tails
are real tidal extensions of Tucana III. The large velocity gradient
of the stream implies that Tucana III is likely on a radial orbit. We
successfully obtain metallicities for four members in the core and 12
members in the tails. We find that members close to the ends of the
stream tend to be more metal-poor than members in the core, indicating
a possible metallicity gradient between the center of the progenitor
halo and its edge. The spread in metallicity suggests that the
progenitor of the Tucana III stream is likely a dwarf galaxy rather
than a star cluster. Furthermore, we find that with the precise
photometry of the Dark Energy Survey data, there is a discernible
color offset between metal-rich disk stars and metal-poor stream
members. This metallicity-dependent color offers a more efficient
method to recognize metal-poor targets and will increase the selection
efficiency of stream members for future spectroscopic follow-up
programs on stellar streams.
Description:
We observed candidate member stars in the Tuc III stream with the
2dF+AAOmega spectrograph on the 3.9m Anglo-Australian Telescope (AAT).
We focus on the spectra obtained with the red arm using the 1700D
grating, which has a spectral resolution of R=10000 and a wavelength
coverage of 8400-8810Å. Observations were conducted on 2016 June 30,
July 9-13, and July 25-27 and 2017 August 22.
In order to better probe the transition region (0.3°≲r≲0.5°)
between the (presumably) bound core of Tuc III and the tidal tails, we
also obtained additional spectroscopy of Tuc III with the IMACS
spectrograph on the Magellan Baade telescope. We observed three slit
masks on the nights of 2017 June 19 and 21. The spectrograph
configuration provided a spectral resolution of R=11000 over the
wavelength range ∼7500-8800Å.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 124 609 Velocity and metallicity measurements of
the observed stars
table3.dat 78 51 Potential members in the Tuc III stream
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See also:
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
J/AJ/135/2177 : High proper motion stars in the DSS. IV. (Lepine, 2008)
J/MNRAS/397/1748 : Spectroscopic study of Segue 2 (Belokurov+, 2009)
J/ApJ/704/898 : Photometry of the Hercules dwarf galaxy (Sand+, 2009)
J/ApJ/694/L144 : Spectroscopic study of Leo V dSph (Walker+, 2009)
J/ApJ/710/1664 : BV photometry in Leo IV and Leo V dSphs (de Jong+, 2010)
J/ApJ/756/121 : Variable stars in Her dwarf galaxy (Musella+, 2012)
J/ApJ/756/79 : Opt. photom. in 3 Local Group dwarf galaxies (Sand+, 2012)
J/MNRAS/434/1681 : Extremely metal-poor stars CaII triplet (Carrera+, 2013)
J/ApJ/770/16 : Spectroscopic members of Segue 2 galaxy (Kirby+, 2013)
J/AJ/145/102 : Sp. of bright M dwarfs in northern sky (Lepine+, 2013)
J/A+A/570/A61 : PM-selected stars of Hercules galaxy (Fabrizio+, 2014)
J/ApJ/808/95 : Spectroscopy of Reticulum II (Simon+, 2015)
J/ApJ/819/1 : Wide-field photometry of the GC Palomar 5 (Ibata+, 2016)
J/ApJ/838/44 : Abundances of the Tuc III brightest members (Hansen+, 2017)
J/ApJ/842/120 : Large sp. survey of Palomar 5 stellar stream (Ibata+, 2017)
J/ApJ/838/11 : Member stars in the MW satellite Tucana III (Simon+, 2017)
J/ApJ/857/145 : MagLiteS Carina II and Carina III spectroscopy (Li+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 1 I1 --- Set [0/3]? Subset (1)
3- 5 A3 --- --- [DES]
6- 24 A19 --- DES Identifier, Jhhmmss.ss-ddmmss.s (G1)
26- 34 F9.5 deg RAdeg Right Ascension (J2000)
36- 44 F9.5 deg DEdeg [-60.4/-58.8] Declination (J2000)
46- 51 F6.3 mag gmag [15.9/21.1] Dereddened g band PSF magnitude (G2)
53- 58 F6.3 mag rmag [15/20.5] Dereddened r band PSF magnitude (G2)
60- 62 A3 --- Cat Either DES DR1 or Y2Q catalog (G2)
64- 68 A5 --- Inst Telescope/instrument (G3)
70- 74 F5.1 --- SNR [4.1/237.3] Average spectra
signal-to-noise ratio
76- 82 F7.2 km/s HRV [-326/430] Heliocentric Radial Velocity
84- 87 F4.2 km/s e_HRV [0.5/6.5] Uncertainty in HRV
89- 92 F4.2 0.1nm EW [1.2/8.4]? Equivalent Width, Angstroms
94- 97 F4.2 0.1nm e_EW [0.2/1.6]? Uncertainty in EW
99-103 F5.2 [-] [Fe/H] [-3/-2.2]? Metallicity
105-108 F4.2 [-] e_[Fe/H] [0.1/0.6]? Uncertainty in [Fe/H]
110-110 I1 --- Mm [0/1]? Subjective membership
(1:member; 0:non-member) (2)
112-115 F4.2 % Prob ? Membership probability,
objective mixture model (3)
117-124 A8 --- Comm Comment
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Note (1): Subset of stars in catalog as follows:
1 = Tucana III Leading/West Tail with -140 < HRV < -70km/s;
2 = Tucana III Core with -140 < HRV < -70km/s. Also observed by
Simon+ (2017, J/ApJ/838/11);
3 = Tucana III Trailing/East Tail with -140 < HRV < -70km/s;
0 = Other observed stars; HRV < -140 or HRV > -70km/s.
Note (2): We identified a total of 31 members in the AAT and IMACS combined
data set, nine of which are members of the Tuc III core and were
previously confirmed in Simon+ (2017, J/ApJ/838/11). The other
22 members are in the Tuc III tails and are identified for the first
time in this work.
We note that the membership identification of Tuc III stream members
is a subjective selection process using the following parameters:
velocity, metallicity, color, magnitude, and the spectrum itself.
See section 3.1 for further details.
Note (3): Only stars observed with AAT has membership probability.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [DES]
4- 22 A19 --- DES Identifier, Jhhmmss.ss-ddmmss.s (G1)
24- 32 F9.5 deg RAdeg Right Ascension, decimal degrees (J2000)
34- 42 F9.5 deg DEdeg [-60.3/-59] Declination, decimal degrees (J2000)
44- 49 F6.3 mag gmag [18.7/21.6] Dereddened g band PSF magnitude (G2)
51- 56 F6.3 mag rmag [18.3/21.3] Dereddened r band PSF magnitude (G2)
58- 60 A3 --- Cat Either DR1 or Y2Q catalog (G2)
62- 66 A5 --- Inst Telescope/instrument (G3)
68- 70 F3.1 --- SNR [1.6/6.7] Spectra Signal-to-noise ratio at
72- 78 F7.2 km/s HRV [-137.1/-71] Heliocentric Radial Velocity (1)
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Note (1): Stars that are observed with AAT or IMACS and have measured RVs in
the range of -140km/s < HRV < -70km/s, but the S/N of the spectra
are too low to obtain robust velocity measurements, and therefore these
stars are not included in the analysis. RVs should be used with caution.
See details in Appendix C.
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Global notes:
Note (G1): The star IDs are computed based on the Right Ascension and
Declination from either DES DR1 (Abbott+, 2018ApJS..239...18A 2018ApJS..239...18A) or
Y2Q (Drlica-Wagner+, 2015ApJ...813..109D 2015ApJ...813..109D) catalog in the format of
Jhhmmss.ss-ddmmss.s. Due to the small difference in the astrometry
between the two catalogs, the star ID in DR1 catalog could be slightly
different (in the last decimal point) from the Y2Q catalog; the latter
one was used to produce the star IDs in the previous literatures for
Tuc III (e.g., Simon+ 2017, J/ApJ/838/11 and Hansen+ 2017, J/ApJ/838/44).
Note (G2): Quoted magnitudes represent the dereddened PSF magnitude in either
DES DR1 (Abbott+, 2018ApJS..239...18A 2018ApJS..239...18A) or
Y2Q catalog (Drlica-Wagner+, 2015ApJ...813..109D 2015ApJ...813..109D) as given
by the 'Cat' column.
Note (G3): Telescopes and instruments used for obtaining the spectra of the
targets as follows:
AAT = AAT/2df+AAOmega;
IMACS = Magellan/IMACS.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 27-Sep-2019