Farthest Neighbor: The Distant Milky Way Satellite Eridanus II

By Tian Li, J. Simon, Alex Drlica-Wagner, K. Bechtol, Mei-Yu Wang, Juan García-Bellido, Joshua A. Frieman, J. Marshall, David J. James, L. Strigari and 49 more. 2016

138 citations recorded by the source corpus.

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 and a velocity dispersion of . Assuming that Eri II is a dispersion-supported system in dynamical equilibrium, we derive a mass within the half-light radius of , indicating a mass-to-light ratio of / 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 . The velocity of Eri II in the Galactic standard of rest frame is vGSR = −66.6 , 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 ∼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 ≳10 .

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/052326edfabb709bc3b0c257efe1ad00bb1fb8e9

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Citations in the corpus

Gaia DR2 proper motions of dwarf galaxies within 420 kpc (2018, methodology): “We use the catalog by Li et al. (2017) with binary probabilities, 12 of which are bright enough to have Gaia DR2 kinematic measurements.”
Massive Primordial Black Holes as Dark Matter and their detection with Gravitational Waves (2017, background): “Long lived star clusters at the centers of dwarf galaxies therefore can be used to detect massive PBH, although the constraints weaken if there is an intermediate mass BH at the center of the dwarf galaxy, which provides stability and increases the velocity dispersion [79].”
A MegaCam Survey of Outer Halo Satellites. III. Photometric and Structural Parameters (2018, unknown): “…Washington Yearb., 58, 60 Notes for Secondary Sample: (26) – Kirby et al. (2017, 95% confidence limit for kinematic data); (27) – Koposov et al. (2015b); (28) – Kim & Jerjen (2015a); (29) – Li et al. (2017); (30) – Kirby et al. (2015); (31) – Balbinot et al. (2013); (32) – Kim & Jerjen (2015c).”