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Stellar Kinematics and Metallicities in the Ultra-Faint Dwarf Galaxy Reticulum II

Simon, JD, Drlica-Wagner, A, Li, TS, Nord, B, Geha, M, Bechtol, K, Balbinot, E, Buckley-Geer, E, Lin, H, Marshall, J , Santiago, B, Strigari, L, Wang, M, Wechsler, RH, Yanny, B, Abbott, T, Bauer, AH, Bernstein, GM, Bertin, E, Brooks, D, Burke, DL, Capozzi, D, Rosell, AC, Kind, MC, D'Andrea, CB, Costa, LND, DePoy, DL, Desai, S, Diehl, HT, Dodelson, S, Cunha, CE, Estrada, J, Evrard, AE, Neto, AF, Fernandez, E, Finley, DA, Flaugher, B, Frieman, J, Gaztanaga, E, Gerdes, D, Gruen, D, Gruendl, RA, Honscheid, K, James, D, Kent, S, Kuehn, K, Kuropatkin, N, Lahav, O, Maia, MAG, March, M, Martini, P, Miller, CJ, Miquel, R, Ogando, R, Romer, AK, Roodman, A, Rykoff, ES, Sako, M, Sanchez, E, Schubnell, M, Sevilla, I, Smith, RC, Soares-Santos, M, Sobreira, F, Suchyta, E, Swanson, MEC, Tarle, G, Thaler, J, Tucker, D, Vikram, V, Walker, AR and Wester, W (2015) Stellar Kinematics and Metallicities in the Ultra-Faint Dwarf Galaxy Reticulum II Letters of the Astrophysical Journal.

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Abstract

We present Magellan/M2FS, VLT/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 +/- 0.5 km/s and a velocity dispersion of 3.3 +/- 0.7 km/s. The mass-to-light ratio of Ret II within its half-light radius is 470 +/- 210 Msun/Lsun, 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 83 km/s, respectively, suggesting that it is not gravitationally bound to the Magellanic system. The likely member stars of Ret II span 1.3 dex in metallicity, with a dispersion of 0.28 +/- 0.09 dex, 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 log J = 18.8 +/- 0.6 Gev^2/cm^5 within 0.2 degrees, indicating that the predicted gamma-ray flux from dark matter annihilation in Ret II is lower than that of several other dwarf galaxies.

Item Type: Article
Authors :
NameEmailORCID
Simon, JD
Drlica-Wagner, A
Li, TS
Nord, B
Geha, M
Bechtol, K
Balbinot, Ee.balbinot@surrey.ac.uk
Buckley-Geer, E
Lin, H
Marshall, J
Santiago, B
Strigari, L
Wang, M
Wechsler, RH
Yanny, B
Abbott, T
Bauer, AH
Bernstein, GM
Bertin, E
Brooks, D
Burke, DL
Capozzi, D
Rosell, AC
Kind, MC
D'Andrea, CB
Costa, LND
DePoy, DL
Desai, S
Diehl, HT
Dodelson, S
Cunha, CE
Estrada, J
Evrard, AE
Neto, AF
Fernandez, E
Finley, DA
Flaugher, B
Frieman, J
Gaztanaga, E
Gerdes, D
Gruen, D
Gruendl, RA
Honscheid, K
James, D
Kent, S
Kuehn, K
Kuropatkin, N
Lahav, O
Maia, MAG
March, M
Martini, P
Miller, CJ
Miquel, R
Ogando, R
Romer, AK
Roodman, A
Rykoff, ES
Sako, M
Sanchez, E
Schubnell, M
Sevilla, I
Smith, RC
Soares-Santos, M
Sobreira, F
Suchyta, E
Swanson, MEC
Tarle, G
Thaler, J
Tucker, D
Vikram, V
Walker, AR
Wester, W
Date : 11 April 2015
Identification Number : 10.1088/0004-637X/808/1/95
Uncontrolled Keywords : astro-ph.GA, astro-ph.GA, astro-ph.CO
Related URLs :
Depositing User : Symplectic Elements
Date Deposited : 17 May 2017 13:36
Last Modified : 17 May 2017 15:11
URI: http://epubs.surrey.ac.uk/id/eprint/839831

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