J/ApJ/838/83 Radial velocities, abundances & membership in TriII (Kirby+, 2017)
Triangulum II. Not especially dense after all.
Kirby E.N., Cohen J.G., Simon J.D., Guhathakurta P., Thygesen A.O.,
Duggan G.E.
<Astrophys. J., 838, 83-83 (2017)>
=2017ApJ...838...83K 2017ApJ...838...83K (SIMBAD/NED BibCode)
ADC_Keywords: Abundances ; Radial velocities ; Velocity dispersion ;
Equivalent widths ; Photometry, SDSS ; Galaxies, nearby
Keywords: galaxies: abundances; galaxies: dwarf; Local Group
Abstract:
Among the Milky Way satellites discovered in the past three years,
Triangulum II has presented the most difficulty in revealing its
dynamical status. Kirby+ (2015ApJ...814L...7K 2015ApJ...814L...7K) identified it as the
most dark-matter-dominated galaxy known, with a mass-to-light ratio
within the half-light radius of 3600-2100+3500M☉/L☉.
On the other hand, Martin+ (2016ApJ...818...40M 2016ApJ...818...40M) measured an outer
velocity dispersion that is 3.5±2.1 times larger than the central
velocity dispersion, suggesting that the system might not be in
equilibrium. From new multi-epoch Keck/DEIMOS measurements of 13
member stars in Triangulum II, we constrain the velocity dispersion to
be σv<3.4km/s (90%C.L.). Our previous measurement of
σv, based on six stars, was inflated by the presence of a
binary star with variable radial velocity. We find no evidence that
the velocity dispersion increases with radius. The stars display a
wide range of metallicities, indicating that Triangulum II retained
supernova ejecta and therefore possesses, or once possessed, a massive
dark matter halo. However, the detection of a metallicity dispersion
hinges on the membership of the two most metal-rich stars. The stellar
mass is lower than galaxies of similar mean stellar metallicity, which
might indicate that Triangulum II is either a star cluster or a
tidally stripped dwarf galaxy. Detailed abundances of one star show
heavily depressed neutron-capture abundances, similar to stars in most
other ultra-faint dwarf galaxies but unlike stars in globular
clusters.
Description:
Observations were obtained with the Deep Extragalactic Imaging
Multi-Object Spectrograph (DEIMOS) medium-resolution spectrograph at
the Nasmyth focus of the Keck II telescope on five different dates
spanning 2015 Oct to 2016 Sep. This 1200G grating provided a spectral
resolving power of R=7000 at 8500Å.
We obtained Keck/HIRES spectra of star 40, the brightest known member
of Tri II, on 2016 August 25 (spectral resolving power of R=49000 over
the spectral range of 3933-8374Å).
Objects:
----------------------------------------------------------------------------
RA (ICRS) DE Designation(s) (HRV)
----------------------------------------------------------------------------
02 13 17.40 +36 10 42.4 Triangulum II = NAME Triangulum II (-382km/s)
02 13 16.54 +36 10 45.7 TriII 40 = [MIC2016] 40 (-382km/s)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 93 34 Radial velocities
table4.dat 93 6 Chemical abundances
table5.dat 41 167 *Line list with equivalent widths of [MIC2016] 40;
from erratum published in 2017, ApJ, 839, 135
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Note on table5.dat: These summary data are provided for the reader's
information, but the abundances were actually computed with
Cohen et al.'s (2004ApJ...612.1107C 2004ApJ...612.1107C) longer hyperfine line lists.
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See also:
J/A+A/287/927 : Abundances for lines of n-capture in 19 stars (Gratton+ 1994)
J/AJ/120/1841 : Abundances & Kinematics of Halo & Disk Stars (Fulbright 2000)
J/A+A/416/1117 : Abundances in the early Galaxy (Cayrel+, 2004)
J/AJ/131/2114 : Radial velocities in Fornax dSph (Walker+, 2006)
J/ApJ/663/960 : Radial velocities of Leo I stars (Sohn+, 2007)
J/ApJ/682/1217 : Abundances in red giants in 7 globular clusters (Kirby+, 2008)
J/ApJ/692/1464 : Spectroscopy of Segue 1 (Geha+, 2009)
J/ApJ/705/328 : Abundance measurements in Sculptor dSph (Kirby+, 2009)
J/ApJ/708/560 : Spectroscopy of UMa II and Coma Ber (Frebel+, 2010)
J/ApJS/191/352 : Abundances in stars of MW dwarf satellites (Kirby+, 2010)
J/ApJ/740/60 : EWs for NGC2419 and NGC7099 RGB stars (Cohen+, 2011)
J/ApJ/736/146 : Radial velocities of stars in Bootes I (Koposov+, 2011)
J/ApJ/733/46 : Velocity measurements in Segue 1 (Simon+, 2011)
J/ApJ/760/86 : Equivalent widths for 13 NGC2419 RGB stars (Cohen+, 2012)
J/AJ/144/168 : Spectroscopy of Scl 1019417 and UMi 20103 (Kirby+, 2012)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/ApJ/750/99 : The Pan-STARRS1 photometric system (Tonry+, 2012)
J/ApJ/769/57 : Equivalent widths of metal-poor stars (Frebel+, 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/767/134 : Abundances of red giant stars in UFD galaxies (Vargas+, 2013)
J/ApJ/786/74 : EW measurements of 6 Segue 1 red giants (Frebel+, 2014)
J/ApJ/801/125 : Carbon in red giants in GCs and dSph galaxies (Kirby+, 2015)
J/ApJ/808/95 : Spectroscopy of Reticulum II (Simon+, 2015)
J/ApJ/830/93 : Ret II brightest red giant members abundances (Ji+, 2016)
J/ApJ/817/41 : Abundances of 4 metal-poor red giants in BooII (Ji+, 2016)
J/ApJ/819/135 : Lithium-rich giants in globular clusters (Kirby+, 2016)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- [KCS2015] [45/177]? Identifier from
Kirby+ (2015ApJ...814L...7K 2015ApJ...814L...7K)
5- 6 I2 --- [MIC2016] [1/50]? Identifier from
Martin+ (2016ApJ...818...40M 2016ApJ...818...40M)
8- 10 A3 --- f_[MIC2016] [a,h ] Flag(s) on Star (1)
12- 13 I2 h RAh [2] Hour of Right Ascension (J2000)
15- 16 I2 min RAm [12/13] Minute of Right Ascension (J2000)
18- 22 F5.2 s RAs Second of Right Ascension (J2000)
24 A1 --- DE- [+] Sign of the Declination (J2000)
25- 26 I2 deg DEd [36] Degree of Declination (J2000)
28- 29 I2 arcmin DEm [5/16] Arcminute of Declination (J2000)
31- 34 F4.1 arcsec DEs Arcsecond of Declination (J2000)
36- 39 F4.2 arcmin Rad [0.1/8.3] Radius
41- 45 F5.2 mag gP1mag [17/22] Pan-STARRS-1 g mag photometry (2)
47- 50 F4.2 mag e_gP1mag [0/0.2] Uncertainty for gP1mag
52- 56 F5.2 mag iP1mag [16.3/21.7] Pan-STARRS-1 i mag photometry (2)
58- 61 F4.2 mag e_iP1mag [0/0.2] Uncertainty for iP1mag
63- 67 A5 --- Masks [ b-g] Slit Mask identifier(s) (3)
69- 73 F5.1 --- S/N [14/220] Signal-to-noise ratio in Å-1 (4)
75- 80 F6.1 km/s HRV [-388/11]? Heliocentric radial velocity
82- 85 F4.1 km/s e_HRV [1.5/18]? Uncertainty in HRV
87- 89 F3.1 km/s sigma [0.1/3]? Velocity dispersion σ(ν)
91 A1 --- Mm Member status (Y: 13 sources; N: 20 sources)
93 A1 --- f_Mm [b] Flag on M16 25 (5)
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Note (1): Flag as follows:
a = one of the six stars for which it was possible to measure abundances
h = Star 40 was also observed with Keck/HIRES; see text and
the "Description" section above.
Note (2): gi photometry is from the Pan-STARRS-1 observations by
Martin+ (2016ApJ...818...40M 2016ApJ...818...40M).
Note (3): Slit Mask identifier from table 1 (DEIMOS observations):
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Slitmask Targets UT date Airmass Seeing Exposures Exp. Time
(arcsec) (s)
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TriIIb* 29 2015 Oct 8 1.4 0.9 3 3120
TriIIc 25 2015 Dec 14 1.1 0.9 4 7200
TriIId 28 2016 Jan 29 1.1 0.9 4 5100
TriIIe 25 2016 Jan 29 1.3 1.1 3 4803
TriIIf 21 2016 Jun 29 1.6 1.0 2 2700
TriIIg 27 2016 Sep 7 1.1 0.7 3 3060
---------------------------------------------------------------------
*: Observations by Kirby+, 2015ApJ...814L...7K 2015ApJ...814L...7K
Note (4): To convert to S/N per pixel, multiply by 0.57.
Note (5):
b = M16 25 is a double-lined spectroscopic binary. The velocities of
the individual components straddle the mean radial velocity of Tri II,
but the two epochs were not sufficient to measure the center-of-mass
velocity reliably.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- [KCS2015] [65/128]? Identification number from
Kirby+ (2015ApJ...814L...7K 2015ApJ...814L...7K)
5- 6 I2 --- [MIC2016] [20/46]? Identification number from
Martin+ (2016ApJ...818...40M 2016ApJ...818...40M)
8- 11 I4 K Teff [4917/5635] Effective temperature
13- 16 F4.2 [cm/s2] logg [1.8/3.5] Log surface gravity
18- 22 F5.2 [-] [Fe/H]CaT [-3.2/-0.9] Metallicity from the Ca triplet
24- 27 F4.2 [-] e_[Fe/H]CaT [0.02/0.2] [Fe/H]CaT uncertainty
29- 33 F5.2 [-] [Fe/H] [-3/-1.4] [Fe/H] abundance
35- 38 F4.2 [-] e_[Fe/H] [0.1/0.3] [Fe/H] uncertainty
40- 44 F5.2 [-] [Mg/Fe] [0.2/1.1]? [Mg/Fe] abundance
46- 49 F4.2 [-] e_[Mg/Fe] [0.2/0.9]? [Mg/Fe] uncertainty
51- 55 F5.2 [-] [Si/Fe] [-0.09/0.6]? [Si/Fe] abundance
57- 60 F4.2 [-] e_[Si/Fe] [0.1/0.5]? [Si/Fe] uncertainty
62- 66 F5.2 [-] [Ca/Fe] [-0.4/0.5] [Ca/Fe] abundance
68- 71 F4.2 [-] e_[Ca/Fe] [0.1/0.9] [Ca/Fe] uncertainty
73- 77 F5.2 [-] [Ti/Fe] [-0.8/1]? [Ti/Fe] abundance
79- 82 F4.2 [-] e_[Ti/Fe] [0.1/0.8]? [Ti/Fe] uncertainty
84- 88 F5.2 [-] [a/Fe] [-0.5/0.5] [α/Fe] abundance
90- 93 F4.2 [-] e_[a/Fe] [0.1/0.36] [a/Fe] uncertainty
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Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Ion Ion
7- 14 F8.3 0.1nm lamAir [3949.9/7699] Wavelength in air,
in Å units (1)
16- 20 F5.3 eV ExPot [0/5.7] Excitation potential
22- 27 F6.3 [-] loggf [-9.8/0.7] Logarithm of oscillator strength (2)
29 A1 --- l_EW Upper limit flag on EW
30- 34 F5.1 0.1pm EW [4/287] Equivalent width
36 A1 --- l_eps Upper limit flag on eps
37- 41 F5.2 [Sun] eps [-3.2/6.8] Abundance derived from this line,
unitless relative to Sun
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Note (1): The average wavelengths of the absorption lines in each hyperfine
complex.
Note (2): The oscillator strengths are the sum of the individual hyperfine
oscillator strengths.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 31-Oct-2017