Farthest Neighbor: The Distant Milky Way Satellite Eridanus II

T. S. Li; J. D. Simon; A. Drlica-Wagner; K. Bechtol; M. Y. Wang; J. García-Bellido; J. Frieman; J. L. Marshall; D. J. James; L. Strigari; A. B. Pace; E. Balbinot; Y. Zhang; T. M.C. Abbott; S. Allam; A. Benoit-Lévy; G. M. Bernstein; E. Bertin; D. Brooks; D. L. Burke; A. Carnero Rosell; M. Carrasco Kind; J. Carretero; C. E. Cunha; C. B. D'Andrea; L. N.Da Costa; D. L. Depoy; S. Desai; H. T. Diehl; T. F. Eifler; B. Flaugher; D. A. Goldstein; D. Gruen; R. A. Gruendl; J. Gschwend; G. Gutierrez; E. Krause; K. Kuehn; H. Lin; M. A.G. Maia; M. March; F. Menanteau; R. Miquel; A. A. Plazas; A. K. Romer; E. Sanchez; B. Santiago; M. Schubnell; I. Sevilla-Noarbe; R. C. Smith; F. Sobreira; E. Suchyta; G. Tarle; D. Thomas; D. L. Tucker; A. R. Walker; R. H. Wechsler; W. Wester; B. Yanny

doi:10.3847/1538-4357/aa6113

Farthest Neighbor: The Distant Milky Way Satellite Eridanus II

T. S. Li, J. D. Simon, A. Drlica-Wagner, K. Bechtol, M. Y. Wang, J. García-Bellido, J. Frieman, J. L. Marshall, D. J. James, L. Strigari, A. B. Pace, E. Balbinot, Y. Zhang, T. M.C. Abbott, S. Allam, A. Benoit-Lévy, G. M. Bernstein, E. Bertin, D. Brooks, D. L. BurkeA. Carnero Rosell, M. Carrasco Kind, J. Carretero, C. E. Cunha, C. B. D'Andrea, L. N.Da Costa, D. L. Depoy, S. Desai, H. T. Diehl, T. F. Eifler, B. Flaugher, D. A. Goldstein, D. Gruen, R. A. Gruendl, J. Gschwend, G. Gutierrez, E. Krause, K. Kuehn, H. Lin, M. A.G. Maia, M. March, F. Menanteau, R. Miquel, A. A. Plazas, A. K. Romer, E. Sanchez, B. Santiago, M. Schubnell, I. Sevilla-Noarbe, R. C. Smith, F. Sobreira, E. Suchyta, G. Tarle, D. Thomas, D. L. Tucker, A. R. Walker, R. H. Wechsler, W. Wester, B. Yanny

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Abstract

© 2017. The American Astronomical Society. All rights reserved. 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 Vhel 75.6 ± 1.3(stat.) ± 2.0 (sys.) Km s1 and a velocity dispersion of 6.9+1.2-0.9 Km s1. Assuming that Eri II is a dispersion-supported system in dynamical equilibrium, we derive a mass within the half-light radius of 1.2+0.4-0.3 × 107 M⊙, indicating a mass-to-light ratio of 420+140-210 M⊙/L⊙ 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 ω(Fe/H)=0.47+0.12-0.09.The velocity of Eri II in the Galactic standard of rest frame is v 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 ∼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 M⊙.

Original language	English
Article number	8
Journal	Astrophysical Journal
Volume	838
Issue number	1
DOIs	https://doi.org/10.3847/1538-4357/aa6113
Publication status	Published - 20 Mar 2017

Keywords

dark matter
galaxies: dwarf
galaxies: individual (Eridanus II)
galaxies: stellar content
Local Group
stars: abundances

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10.3847/1538-4357/aa6113

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Li, T. S., Simon, J. D., Drlica-Wagner, A., Bechtol, K., Wang, M. Y., García-Bellido, J., Frieman, J., Marshall, J. L., James, D. J., Strigari, L., Pace, A. B., Balbinot, E., Zhang, Y., Abbott, T. M. C., Allam, S., Benoit-Lévy, A., Bernstein, G. M., Bertin, E., Brooks, D., ... Yanny, B. (2017). Farthest Neighbor: The Distant Milky Way Satellite Eridanus II. Astrophysical Journal, 838(1), Article 8. https://doi.org/10.3847/1538-4357/aa6113

@article{2cefa58495d34ec287798d01d4616d50,

title = "Farthest Neighbor: The Distant Milky Way Satellite Eridanus II",

abstract = "{\textcopyright} 2017. The American Astronomical Society. All rights reserved. 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 Vhel 75.6 ± 1.3(stat.) ± 2.0 (sys.) Km s1 and a velocity dispersion of 6.9+1.2-0.9 Km s1. Assuming that Eri II is a dispersion-supported system in dynamical equilibrium, we derive a mass within the half-light radius of 1.2+0.4-0.3 × 107 M⊙, indicating a mass-to-light ratio of 420+140-210 M⊙/L⊙ 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 ω(Fe/H)=0.47+0.12-0.09.The velocity of Eri II in the Galactic standard of rest frame is v 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 ∼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 M⊙.",

keywords = "dark matter, galaxies: dwarf, galaxies: individual (Eridanus II), galaxies: stellar content, Local Group, stars: abundances",

author = "Li, {T. S.} and Simon, {J. D.} and A. Drlica-Wagner and K. Bechtol and Wang, {M. Y.} and J. Garc{\'i}a-Bellido and J. Frieman and Marshall, {J. L.} and James, {D. J.} and L. Strigari and Pace, {A. B.} and E. Balbinot and Y. Zhang and Abbott, {T. M.C.} and S. Allam and A. Benoit-L{\'e}vy and Bernstein, {G. M.} and E. Bertin and D. Brooks and Burke, {D. L.} and Rosell, {A. Carnero} and Kind, {M. Carrasco} and J. Carretero and Cunha, {C. E.} and D'Andrea, {C. B.} and Costa, {L. N.Da} and Depoy, {D. L.} and S. Desai and Diehl, {H. T.} and Eifler, {T. F.} and B. Flaugher and Goldstein, {D. A.} and D. Gruen and Gruendl, {R. A.} and J. Gschwend and G. Gutierrez and E. Krause and K. Kuehn and H. Lin and Maia, {M. A.G.} and M. March and F. Menanteau and R. Miquel and Plazas, {A. A.} and Romer, {A. K.} and E. Sanchez and B. Santiago and M. Schubnell and I. Sevilla-Noarbe and Smith, {R. C.} and F. Sobreira and E. Suchyta and G. Tarle and D. Thomas and Tucker, {D. L.} and Walker, {A. R.} and Wechsler, {R. H.} and W. Wester and B. Yanny",

year = "2017",

month = mar,

day = "20",

doi = "10.3847/1538-4357/aa6113",

language = "English",

volume = "838",

journal = "Astrophysical Journal",

issn = "0004-637X",

number = "1",

}

Li, TS, Simon, JD, Drlica-Wagner, A, Bechtol, K, Wang, MY, García-Bellido, J, Frieman, J, Marshall, JL, James, DJ, Strigari, L, Pace, AB, Balbinot, E, Zhang, Y, Abbott, TMC, Allam, S, Benoit-Lévy, A, Bernstein, GM, Bertin, E, Brooks, D, Burke, DL, Rosell, AC, Kind, MC, Carretero, J, Cunha, CE, D'Andrea, CB, Costa, LND, Depoy, DL, Desai, S, Diehl, HT, Eifler, TF, Flaugher, B, Goldstein, DA, Gruen, D, Gruendl, RA, Gschwend, J, Gutierrez, G, Krause, E, Kuehn, K, Lin, H, Maia, MAG, March, M, Menanteau, F, Miquel, R, Plazas, AA, Romer, AK, Sanchez, E, Santiago, B, Schubnell, M, Sevilla-Noarbe, I, Smith, RC, Sobreira, F, Suchyta, E, Tarle, G, Thomas, D, Tucker, DL, Walker, AR, Wechsler, RH, Wester, W & Yanny, B 2017, 'Farthest Neighbor: The Distant Milky Way Satellite Eridanus II', Astrophysical Journal, vol. 838, no. 1, 8. https://doi.org/10.3847/1538-4357/aa6113

TY - JOUR

T1 - Farthest Neighbor: The Distant Milky Way Satellite Eridanus II

AU - Li, T. S.

AU - Simon, J. D.

AU - Drlica-Wagner, A.

AU - Bechtol, K.

AU - Wang, M. Y.

AU - García-Bellido, J.

AU - Frieman, J.

AU - Marshall, J. L.

AU - James, D. J.

AU - Strigari, L.

AU - Pace, A. B.

AU - Balbinot, E.

AU - Zhang, Y.

AU - Abbott, T. M.C.

AU - Allam, S.

AU - Benoit-Lévy, A.

AU - Bernstein, G. M.

AU - Bertin, E.

AU - Brooks, D.

AU - Burke, D. L.

AU - Rosell, A. Carnero

AU - Kind, M. Carrasco

AU - Carretero, J.

AU - Cunha, C. E.

AU - D'Andrea, C. B.

AU - Costa, L. N.Da

AU - Depoy, D. L.

AU - Desai, S.

AU - Diehl, H. T.

AU - Eifler, T. F.

AU - Flaugher, B.

AU - Goldstein, D. A.

AU - Gruen, D.

AU - Gruendl, R. A.

AU - Gschwend, J.

AU - Gutierrez, G.

AU - Krause, E.

AU - Kuehn, K.

AU - Lin, H.

AU - Maia, M. A.G.

AU - March, M.

AU - Menanteau, F.

AU - Miquel, R.

AU - Plazas, A. A.

AU - Romer, A. K.

AU - Sanchez, E.

AU - Santiago, B.

AU - Schubnell, M.

AU - Sevilla-Noarbe, I.

AU - Smith, R. C.

AU - Sobreira, F.

AU - Suchyta, E.

AU - Tarle, G.

AU - Thomas, D.

AU - Tucker, D. L.

AU - Walker, A. R.

AU - Wechsler, R. H.

AU - Wester, W.

AU - Yanny, B.

PY - 2017/3/20

Y1 - 2017/3/20

N2 - © 2017. The American Astronomical Society. All rights reserved. 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 Vhel 75.6 ± 1.3(stat.) ± 2.0 (sys.) Km s1 and a velocity dispersion of 6.9+1.2-0.9 Km s1. Assuming that Eri II is a dispersion-supported system in dynamical equilibrium, we derive a mass within the half-light radius of 1.2+0.4-0.3 × 107 M⊙, indicating a mass-to-light ratio of 420+140-210 M⊙/L⊙ 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 ω(Fe/H)=0.47+0.12-0.09.The velocity of Eri II in the Galactic standard of rest frame is v 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 ∼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 M⊙.

AB - © 2017. The American Astronomical Society. All rights reserved. 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 Vhel 75.6 ± 1.3(stat.) ± 2.0 (sys.) Km s1 and a velocity dispersion of 6.9+1.2-0.9 Km s1. Assuming that Eri II is a dispersion-supported system in dynamical equilibrium, we derive a mass within the half-light radius of 1.2+0.4-0.3 × 107 M⊙, indicating a mass-to-light ratio of 420+140-210 M⊙/L⊙ 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 ω(Fe/H)=0.47+0.12-0.09.The velocity of Eri II in the Galactic standard of rest frame is v 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 ∼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 M⊙.

KW - dark matter

KW - galaxies: dwarf

KW - galaxies: individual (Eridanus II)

KW - galaxies: stellar content

KW - Local Group

KW - stars: abundances

U2 - 10.3847/1538-4357/aa6113

DO - 10.3847/1538-4357/aa6113

M3 - Article

SN - 0004-637X

VL - 838

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 1

M1 - 8

ER -

Farthest Neighbor: The Distant Milky Way Satellite Eridanus II

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