J/ApJ/808/95 Spectroscopy of Reticulum II (Simon+, 2015)
Stellar kinematics and metallicities in the ultra-faint dwarf galaxy
Reticulum II.
Simon J.D., Drlica-Wagner A., Li T.S., Nord B., Geha M., Bechtol K.,
Balbinot E., Buckley-Geer E., Lin H., Marshall J., Santiago B.,
Strigari L., Wang M., Wechsler R.H., Yanny B., Abbott T., Bauer A.H.,
Bernstein G.M., Bertin E., Brooks D., Burke D.L., Capozzi D.,
Carnero Rosell A., Carrasco Kind M., D'Andrea C.B., da Costa L.N.,
Depoy D.L., Desai S., Diehl H.T., Dodelson S., Cunha C.E., Estrada J.,
Evrard A.E., Neto A.F., Fernandez E., Finley D.A., Flaugher B., Frieman J.,
Gaztanaga E., Gerdes D., Gruen D., Gruendl R.A., Honscheid K., James D.,
Kent S., Kuehn K., Kuropatkin N., Lahav O., Maia M.A.G., March M.,
Martini P., Miller C.J., Miquel R., Ogando R., Romer A.K., Roodman A.,
Rykoff E.S., Sako M., Sanchez E., Schubnell M., Sevilla I., Smith R.C.,
Soares-Santos M., Sobreira F., Suchyta E., Swanson M.E.C., Tarle G.,
Thaler J., Tucker D., Vikram V., Walker A.R., Wester W.,
(the DES Collaboration)
<Astrophys. J., 808, 95 (2015)>
=2015ApJ...808...95S 2015ApJ...808...95S (SIMBAD/NED BibCode)
ADC_Keywords: Abundances, [Fe/H] ; Radial velocities ; Galaxies, nearby ;
Spectroscopy
Keywords: dark matter; galaxies: dwarf; galaxies: individual: Reticulum II;
galaxies: stellar content; Local Group; stars: abundances
Abstract:
We present Magellan/M2FS, Very Large Telescope/GIRAFFE, and Gemini
South/GMOS spectroscopy of the newly discovered Milky Way satellite
Reticulum II. Based on the spectra of 25 Ret II member stars selected
from Dark Energy Survey imaging, we measure a mean heliocentric
velocity of 62.8±0.5km/s and a velocity dispersion of 3.3±0.7km/s.
The mass-to-light ratio of Ret II within its half-light radius is
470±210M☉/L☉, demonstrating that it is a strongly dark
matter-dominated system. Despite its spatial proximity to the
Magellanic Clouds, the radial velocity of Ret II differs from that of
the LMC and SMC by 199 and 83km/s, respectively, suggesting that it is
not gravitationally bound to the Magellanic system. The likely member
stars of Ret II span 1.3dex in metallicity, with a dispersion of
0.28±0.09dex, and we identify several extremely metal-poor stars
with [Fe/H]←3. In combination with its luminosity, size, and
ellipticity, these results confirm that Ret II is an ultra-faint dwarf
galaxy. With a mean metallicity of [Fe/H]=-2.65±0.07, Ret II matches
Segue 1 as the most metal-poor galaxy known. Although Ret II is the
third-closest dwarf galaxy to the Milky Way, the line-of-sight
integral of the dark matter density squared is
log10(J)=18.8±0.6GeV2/cm5 within 0.2°, indicating that the
predicted gamma-ray flux from dark matter annihilation in Ret II is
lower than that of several other dwarf galaxies.
Description:
Spectroscopic targets were selected from the object catalog derived
from the coadded images of the first internal annual release of DES
data (Y1A1; Sevilla et al. 2011arXiv1109.6741S 2011arXiv1109.6741S; Desai et al. 2012,
J/ApJ/757/83; Mohr et al. 2012SPIE.8451E..0DM; Balbinot et al.
2015MNRAS.449.1129B 2015MNRAS.449.1129B; R. A. Gruendl et al., 2015 in preparation).
We targeted Ret II for follow-up spectroscopy with both Magellan/M2FS
and Gemini/GMOS, and we have also made use of publicly available Very
Large Telescope (VLT)/GIRAFFE spectra of Ret II stars in the ESO
Archive.
We observed Ret II with the multi-fiber M2FS spectrograph on the
Magellan/Clay Telescope on 2015 February 19 (see section 2.2).
We also observed Ret II with the GMOS-S spectrograph on the Gemini
South Telescope in queue mode on several nights beginning on 2015
February 15 through program GS-2014B-DD-8 (see section 2.3).
Ret II was observed with the FLAMES/GIRAFFE spectrograph on the
VLT/UT2 telescope as part of the Gaia/ESO survey (Gilmore et al.
2012Msngr.147...25G 2012Msngr.147...25G); see section 2.4.
Objects:
------------------------------------------------------------------
RA (ICRS) DE Designation(s) (Distance)
------------------------------------------------------------------
03 35 41 -54 03 00 Reticulum II = NAME Reticulum II (D=32kpc)
------------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 120 59 Velocity and metallicity measurements
--------------------------------------------------------------------------------
See also:
B/eso : ESO Science Archive Catalog (ESO, 1991-2015)
I/324 : The Initial Gaia Source List (IGSL) (Smart, 2013)
J/ApJ/801/74 : Dark matter profiles in dwarf gal. (Geringer-Sameth+, 2015)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/MNRAS/434/1681 : Extremely metal-poor stars CaII triplet (Carrera+, 2013)
J/ApJ/767/134 : Abundances of red giant stars in UFD gal. (Vargas+, 2013)
J/ApJ/757/83 : The Blanco Cosmology Survey (BCS) (Desai+, 2012)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/MNRAS/418/1526 : Dark matter in dSph galaxies (Charbonnier+, 2011)
J/ApJ/733/46 : Velocity measurements in Segue 1 (Simon+, 2011)
J/MNRAS/380/281 : Faint galactic satellites spectrosc. survey (Martin+, 2007)
J/MNRAS/326/959 : Empirical calibration of the NIR Ca triplet (Cenarro+ 2001)
http://archive.eso.org/cms/eso-data.html : ESO data archive
http://www.darkenergysurvey.org/ : Dark Energy Survey home page
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Inst Instrument ("MF2S", "GIRAFFE" or "GMOS")
9- 11 A3 --- --- [DES]
12- 31 A20 --- DES Star identifier (JHHMMSS.ss+DDMMSS.s)
33- 40 F8.5 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 [16.4/21.3] g-band magnitude (1)
58- 62 F5.2 mag rmag [15.6/21] r-band magnitude (1)
64- 69 F6.2 km/s Vel [-25.2/311.1] Velocity
71- 74 F4.2 km/s e_Vel [0.9/8.3]? Velocity uncertainty
76- 79 F4.2 --- EW1 [0.9/7]? Giraffe equivalent width
81- 84 F4.2 --- e_EW1 [0.1/0.6]? EW1 uncertainty
86- 90 F5.2 --- [Fe/H]1 [-3.4/-2]? Giraffe metallicity
92- 95 F4.2 --- e_[Fe/H]1 [0.1/0.6]? [Fe/H]1 uncertainty
97-100 F4.2 --- EW2 [1.1/4.7]? GMOS equivalent width
102-105 F4.2 --- e_EW2 [0.2/0.6]? EW2 uncertainty
107-111 F5.2 --- [Fe/H]2 [-3.2/-2.8]? GMOS metallicity
113-116 F4.2 --- e_[Fe/H]2 [0.1/0.4]? [Fe/H]2 uncertainty
118-120 A3 --- Mm Code membership
--------------------------------------------------------------------------------
Note (1): Quoted magnitudes represent the PSF magnitude derived from the DES
(Dark Energy Survey; Diehl+, 2014SPIE.9149E..0VD) coadded images
by SExtractor. The one exception is DES J033523.85-540407.5 which
uses the median AUTO magnitude derived from the individual DES single
epoch images.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 20-Nov-2015