Farthest Neighbor: The Distant Milky Way Satellite Eridanus II*

  title={Farthest Neighbor: The Distant Milky Way Satellite Eridanus II*},
  author={T. S. Li and Joshua D. Simon and Alex Drlica-Wagner and Keith C. Bechtol and M. Y. Wang and Juan Garc'ia-Bellido and Joshua A. Frieman and Jennifer L. Marshall and David J. James and Louis E. Strigari and Andrew B. Pace and Eduardo Balbinot and Y. Zhang and Timothy M. C. Abbott and Sahar Allam and Aur{\'e}lien Benoit-L{\'e}vy and Gary M. Bernstein and Emmanuel Bertin and David Brooks and David L. Burke and Aurelio Carnero Rosell and Matias Carrasco Kind and Jorge Carretero and Carlos E. Cunha and Chris D'Andrea and Luiz Nicolaci da Costa and Darren Lee Depoy and Shantanu Desai and H. Thomas Diehl and T. F. Eifler and Brenna L. Flaugher and Daniel A. Goldstein and Daniel Gruen and Robert A. Gruendl and Julia Gschwend and Gaston R. Guti{\'e}rrez and E. Krause and Kyler W. Kuehn and H. Lin and Marcio A. G. Maia and M March and Felipe Menanteau and Ramon Miquel and Andreas Alejandro Plazas and A. K. Romer and Eusebio S{\'a}nchez and Bas{\'i}lio Xavier Santiago and Michael S. Schubnell and Ignacio Sevilla-Noarbe and R. C. Smith and Flavia Sobreira and Eric Suchyta and Gregory G. Tarl{\'e} and D. Thomas and Douglas L. Tucker and Alistair R. Walker and Risa H. Wechsler and William C. Wester and Brian Yanny},
  journal={The Astrophysical Journal},
We present Magellan/IMACS spectroscopy of the recently discovered Milky Way satellite Eridanus II (Eri II). We identify 28 member stars in Eri II, from which we measure a systemic radial velocity of nu(hel)= 75.6 +/- 1.3(stat.) +/- 2.0 (sys.) km s(-1) and a velocity dispersion of 6.9(-0.9)(+1.2) km s(-1). Assuming that Eri. II is a dispersion-supported system in dynamical equilibrium, we derive a mass within the half-light radius of 1.2(-0.3)(+0.4) x 10(7) M-circle dot, indicating a mass… 
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