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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, JDUNSPECIFIEDUNSPECIFIED
Drlica-Wagner, AUNSPECIFIEDUNSPECIFIED
Li, TSUNSPECIFIEDUNSPECIFIED
Nord, BUNSPECIFIEDUNSPECIFIED
Geha, MUNSPECIFIEDUNSPECIFIED
Bechtol, KUNSPECIFIEDUNSPECIFIED
Balbinot, Ee.balbinot@surrey.ac.ukUNSPECIFIED
Buckley-Geer, EUNSPECIFIEDUNSPECIFIED
Lin, HUNSPECIFIEDUNSPECIFIED
Marshall, JUNSPECIFIEDUNSPECIFIED
Santiago, BUNSPECIFIEDUNSPECIFIED
Strigari, LUNSPECIFIEDUNSPECIFIED
Wang, MUNSPECIFIEDUNSPECIFIED
Wechsler, RHUNSPECIFIEDUNSPECIFIED
Yanny, BUNSPECIFIEDUNSPECIFIED
Abbott, TUNSPECIFIEDUNSPECIFIED
Bauer, AHUNSPECIFIEDUNSPECIFIED
Bernstein, GMUNSPECIFIEDUNSPECIFIED
Bertin, EUNSPECIFIEDUNSPECIFIED
Brooks, DUNSPECIFIEDUNSPECIFIED
Burke, DLUNSPECIFIEDUNSPECIFIED
Capozzi, DUNSPECIFIEDUNSPECIFIED
Rosell, ACUNSPECIFIEDUNSPECIFIED
Kind, MCUNSPECIFIEDUNSPECIFIED
D'Andrea, CBUNSPECIFIEDUNSPECIFIED
Costa, LNDUNSPECIFIEDUNSPECIFIED
DePoy, DLUNSPECIFIEDUNSPECIFIED
Desai, SUNSPECIFIEDUNSPECIFIED
Diehl, HTUNSPECIFIEDUNSPECIFIED
Dodelson, SUNSPECIFIEDUNSPECIFIED
Cunha, CEUNSPECIFIEDUNSPECIFIED
Estrada, JUNSPECIFIEDUNSPECIFIED
Evrard, AEUNSPECIFIEDUNSPECIFIED
Neto, AFUNSPECIFIEDUNSPECIFIED
Fernandez, EUNSPECIFIEDUNSPECIFIED
Finley, DAUNSPECIFIEDUNSPECIFIED
Flaugher, BUNSPECIFIEDUNSPECIFIED
Frieman, JUNSPECIFIEDUNSPECIFIED
Gaztanaga, EUNSPECIFIEDUNSPECIFIED
Gerdes, DUNSPECIFIEDUNSPECIFIED
Gruen, DUNSPECIFIEDUNSPECIFIED
Gruendl, RAUNSPECIFIEDUNSPECIFIED
Honscheid, KUNSPECIFIEDUNSPECIFIED
James, DUNSPECIFIEDUNSPECIFIED
Kent, SUNSPECIFIEDUNSPECIFIED
Kuehn, KUNSPECIFIEDUNSPECIFIED
Kuropatkin, NUNSPECIFIEDUNSPECIFIED
Lahav, OUNSPECIFIEDUNSPECIFIED
Maia, MAGUNSPECIFIEDUNSPECIFIED
March, MUNSPECIFIEDUNSPECIFIED
Martini, PUNSPECIFIEDUNSPECIFIED
Miller, CJUNSPECIFIEDUNSPECIFIED
Miquel, RUNSPECIFIEDUNSPECIFIED
Ogando, RUNSPECIFIEDUNSPECIFIED
Romer, AKUNSPECIFIEDUNSPECIFIED
Roodman, AUNSPECIFIEDUNSPECIFIED
Rykoff, ESUNSPECIFIEDUNSPECIFIED
Sako, MUNSPECIFIEDUNSPECIFIED
Sanchez, EUNSPECIFIEDUNSPECIFIED
Schubnell, MUNSPECIFIEDUNSPECIFIED
Sevilla, IUNSPECIFIEDUNSPECIFIED
Smith, RCUNSPECIFIEDUNSPECIFIED
Soares-Santos, MUNSPECIFIEDUNSPECIFIED
Sobreira, FUNSPECIFIEDUNSPECIFIED
Suchyta, EUNSPECIFIEDUNSPECIFIED
Swanson, MECUNSPECIFIEDUNSPECIFIED
Tarle, GUNSPECIFIEDUNSPECIFIED
Thaler, JUNSPECIFIEDUNSPECIFIED
Tucker, DUNSPECIFIEDUNSPECIFIED
Vikram, VUNSPECIFIEDUNSPECIFIED
Walker, ARUNSPECIFIEDUNSPECIFIED
Wester, WUNSPECIFIEDUNSPECIFIED
Date : 11 April 2015
Identification Number : https://doi.org/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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