J/ApJ/892/137 Spectroscopy of Grus II, Tuc IV and Tuc V (Simon+, 2020)
Birds of a feather? Magellan/IMACS spectroscopy of the ultra-faint satellites
Grus II, Tucana IV, and Tucana V.
Simon J.D., Li T.S., Erkal D., Pace A.B., Drlica-Wagner A., James D.J.,
Marshall J.L., Bechtol K., Hansen T., Kuehn K., Lidman C., Allam S.,
Annis J., Avila S., Bertin E., Brooks D., Burke D.L., Carnero Rosell A.,
Carrasco Kind M., Carretero J., da Costa L.N., De Vicente J., Desai S.,
Doel P., Eifler T.F., Everett S., Fosalba P., Frieman J., Garcia-Bellido J.,
Gaztanaga E., Gerdes D.W., Gruen D., Gruendl R.A., Gschwend J.,
Gutierrez G., Hollowood D.L., Honscheid K., Krause E., Kuropatkin N.,
MacCrann N., Maia M.A.G., March M., Miquel R., Palmese A., Paz-Chinchon F.,
Plazas A.A., Reil K., Roodman A., Sanchez E., Santiago B., Scarpine V.,
Schubnell M., Serrano S., Smith M., Suchyta E., Tarle G., Walker A.R.
(The DES Collaboration)
<Astrophys. J., 892, 137 (2020)>
=2020ApJ...892..137S 2020ApJ...892..137S
ADC_Keywords: Galaxies, spectra; Radial velocities; Equivalent widths;
Abundances, [Fe/H]; Photometry, VRI
Keywords: Local Group ; Dwarf galaxies ; Magellanic Clouds ; Milky Way Galaxy ;
Dark matter
Abstract:
We present Magellan/IMACS spectroscopy of three recently discovered
ultra-faint Milky Way satellites, Grus II, Tucana IV, and Tucana V. We
measure systemic velocities of vhel=-110.0±0.5km/s,
vhel=15.9-1.7+1.8km/s, and vhel=-36.2-2.2+2.5km/s for the
three objects, respectively. Their large relative velocities
demonstrate that the satellites are unrelated despite their close
physical proximity. We determine a velocity dispersion for Tuc IV of
σ=4.3-1.0+1.7km/s, but we cannot resolve the velocity
dispersions of the other two systems. For Gru II, we place an upper
limit (90% confidence) on the dispersion of σ<1.9km/s, and for
Tuc V, we do not obtain any useful limits. All three satellites have
metallicities below [Fe/H]=-2.1, but none has a detectable metallicity
spread. We determine proper motions for each satellite based on Gaia
astrometry and compute their orbits around the Milky Way. Gru II is on
a tightly bound orbit with a pericenter of 25-7+6kpc and orbital
eccentricity of 0.45-0.05+0.08. Tuc V likely has an apocenter
beyond 100kpc and could be approaching the Milky Way for the first
time. The current orbit of Tuc IV is similar to that of Gru II, with a
pericenter of 25-8+11kpc and an eccentricity of
0.36-0.06+0.13. However, a backward integration of the position of
Tuc IV demonstrates that it collided with the Large Magellanic Cloud
at an impact parameter of 4kpc ∼120Myr ago, deflecting its trajectory
and possibly altering its internal kinematics. Based on their sizes,
masses, and metallicities, we classify Gru II and Tuc IV as likely
dwarf galaxies, but the nature of Tuc V remains uncertain.
Description:
We observed Gru II, Tuc IV, and Tuc V with the IMACS spectrograph
on the Magellan/Baade telescope during a number of observing runs
spanning from 2015 August to 2018 September. As in previous studies
(Simon+ 2017, J/ApJ/838/11 ; Li+ 2017ApJ...838....8L 2017ApJ...838....8L and
2018, J/ApJ/857/145), we used the f/4 camera and the 1200l/mm
grating blazed at 9000Å to produce R∼11000 spectra from ∼7500
to 8900Å.
In 2016 July, we obtained some shallow spectroscopy of wide fields
surrounding Gru II and Tuc IV with the AAOmega spectrograph on the
Anglo-Australian Telescope (AAT). Although the AAT velocity
measurements are not used in our analysis, we provide the data in
Table 2. See Section 2.2.
Spectroscopic targets were selected from the Dark Energy Survey (DES)
Year 2 quick release (Y2Q1) catalog (Drlica-Wagner+ 2015ApJ...813..109D 2015ApJ...813..109D)
photometric catalog.
Objects:
-----------------------------------------------------------------
RA (ICRS) DE Designation(s) (Dist)
-----------------------------------------------------------------
22 04 06 -46 26.5 Grus II = NAME Gru II (D=55kpc)
00 02 52 -60 49.8 Tucana IV = NAME Tuc IV (D=47kpc)
23 37 23 -63 16.0 Tucana V = NAME Tuc V (D=55kpc)
-----------------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 79 210 *Anglo-Australian Telescope (AAT) velocity
measurements for Gru II and Tuc IV
table3.dat 108 515 Magellan/Baade IMACS velocity and metallicity
measurements for Gru II, Tuc IV, and Tuc V
--------------------------------------------------------------------------------
Note on table2.dat: Although the AAT velocity measurements are not used in
our analysis, we provide the data here. See Section 2.2.
--------------------------------------------------------------------------------
See also:
II/357 : The Dark Energy Survey (DES): Data Release 1 (Abbott+, 2018)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/AJ/131/2514 : Radial velocities of red giants in the SMC (Harris+, 2006)
J/AJ/141/175 : Abundances in M15 RGB/RHB stars (Sobeck+, 2011)
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/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/ApJ/780/59 : The Araucaria project: EBs in SMC (Graczyk+, 2014)
J/ApJ/808/95 : Spectroscopy of Reticulum II (Simon+, 2015)
J/MNRAS/458/L59 : Draco II stars gi mag & radial velocities (Martin+, 2016)
J/ApJ/819/53 : Magellan/M2FS spec. of Tucana 2 & Grus 1 (Walker+, 2016)
J/ApJ/838/83 : Rvel, abundances & membership in TriII (Kirby+, 2017)
J/ApJ/838/11 : Member stars in the MW satellite Tucana III (Simon+, 2017)
J/ApJ/866/22 : Spectroscopic analysis of Tuc III stream (Li+, 2018)
J/ApJ/857/145 : MagLiteS Carina II and Carina III spectroscopy (Li+, 2018)
J/A+A/620/A155 : Gaia proper motions of 7 UFD galaxies (Massari+, 2018)
J/ApJ/863/89 : Gaia PMs of stars in ultra-faint MW satellites (Simon, 2018)
J/AJ/156/257 : Spec. of RGB stars in Draco & Ursa Minor (Spencer+, 2018)
J/MNRAS/482/5138 : Galactic GC mean PMs & velocities (Baumgardt+, 2019)
J/ApJ/883/11 : Magellan/IMACS spectra of Crater II & Hercules (Fu+, 2019)
J/ApJ/870/83 : Abund. in ultra-faint dwarf gal. GruI & TriII (Ji+, 2019)
J/ApJ/885/53 : Spectrosc. & HST phot. of galaxy Leo V (Mutlu-Pakdil+, 2019)
J/ApJ/875/77 : PMs of MW satellites with Gaia & DES (Pace+, 2019)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [DES]
4- 22 A19 --- DES Identifier (JHHMMSS.ss+DDMMSS.s)
24- 30 F7.1 d MJD [57596.1/57596.6] Modified Julian Date
32- 40 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000)
42- 50 F9.5 deg DEdeg Declination in decimal degrees (J2000)
52- 56 F5.2 mag gmag [16.2/19.25] DES dereddened g band (AB)
magnitude (G1)
58- 62 F5.2 mag rmag [15.25/18.7] DES dereddened r band (AB)
magnitude (G1)
64- 67 F4.1 --- S/N [6/42] Signal to noise ratio
69- 74 F6.1 km/s HRV [-164/258] Heliocentric radial velocity
76- 79 F4.1 km/s e_HRV [0.7/24.2] Uncertainty in HRV
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Gal Galaxy satellite ("GruII", "TucIV" or "TucV");
column added by CDS
7- 9 A3 --- --- [DES]
10- 28 A19 --- DES Identifier (JHHMMSS.ss+DDMMSS.s)
30- 38 F9.5 deg RAdeg Right Ascension (J2000)
40- 48 F9.5 deg DEdeg [-63.34/-46.2] Declination (J2000)
50- 54 F5.2 mag gmag [16.7/22] DES dereddened g band (AB)
magnitude (G1)
56- 60 F5.2 mag rmag [15.78/21.3] DES dereddened r band (Ab)
magnitude (G1)
62- 68 F7.1 d MJD [57247.4/58363.8] Modified Julian Date
70- 74 F5.1 --- S/N [4/162] Signal to noise ratio
76- 81 F6.1 km/s HRV [-227/349] Heliocentric radial velocity
83- 85 F3.1 km/s e_HRV [1/9.6] Uncertainty in HRV
87- 90 F4.2 0.1nm EW [0.4/8.3]? Ca triplet equivalent width
92- 95 F4.2 0.1nm e_EW [0.3/2]? Uncertainty in EW
97-101 F5.2 [Sun] [Fe/H] [-3.4/-1.5]? Metallicity
103-106 F4.2 [Sun] e_[Fe/H] [0.16/0.9]? Uncertainty in [Fe/H]
108 I1 --- Mm [0/1] Membership code (1)
--------------------------------------------------------------------------------
Note (1): A value of 1 indicates that the star is a member of the relevant
satellite (94 members), while 0 indicates a non-member.
--------------------------------------------------------------------------------
Global notes:
Note (G1): Quoted magnitudes represent the weighted-average dereddened PSF
magnitude derived from the DES images using SourceExtractor.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 17-Aug-2021