Magellan/M2FS Spectroscopy of the Reticulum 2 Dwarf Spheroidal Galaxy

Matthew G. Walker, Mario Mateo, Edward W. Olszewski, I. Bailey III John, Sergey E. Koposov, Vasily Belokurov, N. Wyn Evans

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

We present results from spectroscopic observations with the Michigan/MagellanFiber System(M2FS)of 182 stellartargets along the line of sight(LOS)to the newly discovered“ultrafaint”object Reticulum 2(Ret 2). For 37 of thesetargets, the spectra are sufficient to provide simultaneous estimates of LOS velocity(vlos, median random error1.4vlosd=km s−1), effective temperature(Teff,478Teffd=K), surface gravity(glog,0.63glogd=dex), and ironabundance([Fe H],0.47[Fe H]d=dex). We use these results to confirm 17 stars as members of Ret 2. From themember sample we estimate a velocity dispersion ofvloss=3.60.71.0-+km s−1about a mean ofvlosáñ=64.31.21.2-+km s−1in the solar rest frame(90.9~-km s−1in the Galactic rest frame), and a metallicity dispersion of[Fe H]s=0.490.140.19-+dex about a mean of[Fe H]áñ=2.580.330.34--+. These estimates marginalize over possible velocity and metallicitygradients, which are consistent with zero. Our results place Ret 2 on chemodynamical scaling relations followed bythe Milky Way’s dwarf-galactic satellites. Under assumptions of dynamic equilibrium and negligible contaminationfrom binary stars—both of which must be checked with deeper imaging and repeat spectroscopic observations—theestimated velocity dispersion suggests a dynamical mass ofMRRG() 5(2)vhh2loss»=2.4100.81.45 ́-+Menclosedwithin projected halflight radiusR32h~pc, with mass-to-light ratioMR L2()Vh»=467168286-+in solar units.
Original languageEnglish
JournalAstrophysical Journal
DOIs
Publication statusPublished - 27 Jul 2015

Keywords / Materials (for Non-textual outputs)

  • astro-ph.GA

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