J/ApJ/819/53 Magellan/M2FS spectroscopy of Tucana 2 and Grus 1 (Walker+, 2016)
Magellan/M2FS spectroscopy of Tucana 2 and Grus 1.
Walker M.G., Mateo M., Olszewski E.W., Koposov S., Belokurov V., Jethwa P.,
Nidever D.L., Bonnivard V., Bailey III J.I., Bell E.F., Loebman S.R.
<Astrophys. J., 819, 53 (2016)>
=2016ApJ...819...53W 2016ApJ...819...53W (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Spectroscopy ; Abundances, [Fe/H] ;
Photometry, ugriz
Keywords: galaxies: dwarf; galaxies: individual: (Tucana 2, Gru 1);
galaxies: kinematics and dynamics; Local Group;
techniques: spectroscopic
Abstract:
We present results from spectroscopic observations with the
Michigan/Magellan Fiber System (M2FS) of 147 stellar targets along the
line of sight to the newly discovered "ultrafaint" stellar systems
Tucana 2 (Tuc 2) and Grus 1 (Gru 1). Based on simultaneous estimates
of line of sight velocity and stellar-atmospheric parameters, we
identify 8 and 7 stars as probable members of Tuc 2 and and Gru 1,
respectively. Our sample for Tuc 2 is sufficient to resolve an
internal velocity dispersion of 8.6+4.4-2.7km/s about a mean of
-129.1±3.5km/s (solar rest frame), and to estimate a mean
metallicity of [Fe/H]=-2.23+0.18-0.12. These results place Tuc 2
on chemodynamical scaling relations followed by dwarf galaxies,
suggesting a dominant dark matter component with dynamical mass
2.7+3.1-1.3x106M☉ enclosed within the central ∼160pc, and
dynamical mass-to-light ratio 1913+2234-950M☉/Lν,☉.
For Gru 1 we estimate a mean velocity of -140.5+2.4-1.6km/s and a
mean metallicity of [Fe/H]=-1.42+0.55-0.42 but our sample does not
resolve Gru 1's velocity dispersion. The radial coordinates of Tuc 2
and Gru 1 in Galactic phase space suggest that their orbits are among
the most energetic within a distance of ≲300pc. Moreover, their
proximity to each other in this space arises naturally if both objects
are trailing the Large Magellanic Cloud.
Description:
We observed Tuc 2 and Gru 1 with the Michigan/Magellan Fiber System
(M2FS) at the 6.5m Magellan/Clay telescope at Las Campanas
Observatory, Chile, on the nights of July 17 (Tuc 2) and July 18 (Gru
1) 2015. We obtained repeat observations of the Tuc 2 field on 2015
September 12.
We selected spectroscopic targets from the photometric catalogs that
K15 (Koposov+ 2015ApJ...805..130K 2015ApJ...805..130K) generated from public images taken
as part of the Dark Energy Survey (DES; Bechtol+, 2015ApJ...807...50B 2015ApJ...807...50B).
DES is a wide-field optical imaging survey in the grizY bands
performed with the Dark Energy Camera (DECam) installed at the prime
focus of the 4m Blanco telescope at Cerro Tololo Inter-American
Observatory. The full DES survey is scheduled for 525 nights
distributed over 5 years. Uncertainties in the offsets between the DES
photometric system and the AB system are estimated to be ∼1%.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 168 330 Michigan/Magellan Fiber System (M2FS) stellar
spectroscopy of Tucana 2 and Grus 1
--------------------------------------------------------------------------------
See also:
J/ApJ/808/108 : M2FS stellar spectroscopy of Reticulum 2 (Walker+, 2015)
J/MNRAS/448/2717 : Bayesian analysis of resolved spectra (Walker+, 2015)
J/ApJ/801/74 : Dark matter profiles in dwarf galaxies (Geringer-Sameth+, 2015)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/AJ/136/2050 : SEGUE stellar parameter pipeline. II. (Lee+, 2008)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Gal Dwarf galaxy ("Gru1" or "Tuc2")
5 A1 --- --- [-]
6- 8 I03 --- Seq [1/137] Target Identifier (1)
10- 11 I2 h RAh [22] Hour of Right Ascension (J2000)
13- 14 I2 min RAm [50/58] Minute of Right Ascension (J2000)
16- 20 F5.2 s RAs Second of Right Ascension (J2000)
22 A1 --- DE- [-] Sign of the Declination (J2000)
23- 24 I2 deg DEd [49/58] Degree of Declination (J2000)
26- 27 I2 arcmin DEm Arcminute of Declination (J2000)
29- 32 F4.1 arcsec DEs Arcsecond of Declination (J2000)
34- 38 F5.2 mag gmag [17/22.5] g band AB magnitude (1)
40- 44 F5.2 mag rmag [15.8/22.3] r band AB magnitude (1)
46- 53 F8.3 d HJD Heliocentric Julian date; HJD-2450000
55- 59 F5.1 --- S/N [-0.4/32] Median Signal/Noise Ratio
per pixel
61- 66 F6.1 km/s Vlos [-264/469] Line-of-Sight velocity,
solar rest frame
68- 72 F5.1 km/s e_Vlos [0.3/328] Uncertainty in Vlos
74- 79 F6.1 --- SVlos [-109/33] Skewness in Vlos
81- 87 F7.1 --- KVlos [1.6/13935] Kurtosis in Vlos
89- 92 I4 K Teff [4025/7921] Effective Temperature
94- 97 I4 K e_Teff [21/991] Uncertainty in Teff
99-103 F5.1 --- STeff [-1.7/1.6] Skewness in Teff
105-109 F5.1 --- KTeff [2/7] Kurtosis in Teff
111-114 F4.2 [cm/s2] logg [0.7/5.2] Log surface gravity, cgs units
116-119 F4.2 [cm/s2] e_logg [0.1/1.5] Uncertainty in logg
121-125 F5.1 --- Slogg [-3/3] Skewness in logg
127-131 F5.1 --- Klogg [1.8/15] Kurtosis in logg
133-137 F5.2 [Sun] [Fe/H] [-3.9/0.9] Metallicity
139-142 F4.2 [Sun] e_[Fe/H] [0.05/1.9] Uncertainty in [Fe/H]
144-148 F5.1 --- S[Fe/H] [-3.8/0.6] Skewness in [Fe/H]
150-154 F5.1 --- K[Fe/H] [1.6/20.4] Kurtosis in [Fe/H]
156-159 F4.2 --- PMm [0/1] Probability of membership (2)
161-164 F4.2 --- e_PMm [0/0.3] Uncertainty in PMm
166 A1 --- Ch Spectrograph channel (B:Blue, R:Red)
168 A1 --- Md Spectrograph mode (H:HiRes, M:MedRes)
--------------------------------------------------------------------------------
Note (1): From K15's catalogs: Koposov et al. 2015ApJ...805..130K 2015ApJ...805..130K
Note (2): Probability of membership analysis is described in section 4.1.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 18-May-2016