• DOI:10.3847/1538-4357/aa6113
• Corpus ID: 45137837

Farthest Neighbor: The Distant Milky Way Satellite Eridanus II*

@article{Li2016FarthestNT,
  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},
  year={2016},
  volume={838},
  pages={8}
}

• T. Li, J. Simon, +56 authors B. Yanny
• Published 15 November 2016
• Physics
• 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-tolight ratio of 420(-140)(+210) M-circle dot/L-circle dot and confirming that it is a dark matter-dominated dwarf galaxy. From the equivalent width measurements of the Ca triplet lines of 16 red giant member stars, we derive a mean metallicity of [ Fe/H] = -2.38 +/- 0.13 and a metallicity dispersion of sigma[Fe/H]= 0.47(-0.09)(+0.12). The velocity of Eri. II in the Galactic standard of rest frame is nu(GSR) = -66.6 km s(-1), indicating that either Eri. II is falling into the Milky Way potential for the first time or that it has passed the apocenter of its orbit on a subsequent passage. At a Galactocentric distance of similar to 370 kpc, Eri II is one of the Milky Way's most distant satellites known. Additionally, we show that the bright blue stars previously suggested to be a young stellar population are not associated with Eri. II. The lack of gas and recent star formation in Eri II is surprising given its mass and distance from the Milky Way, and may place constraints on models of quenching in dwarf galaxies and on the distribution of hot gas in the Milky Way halo. Furthermore, the large velocity dispersion of Eri II can be combined with the existence of a central star cluster to constrain massive compact halo object dark matter with mass greater than or similar to 10 M-circle dot.