MAGELLAN/M2FS SPECTROSCOPY of the RETICULUM 2 DWARF SPHEROIDAL GALAXY

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

Research output: Contribution to journalArticle

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Abstract

We present results from spectroscopic observations with the Michigan/Magellan Fiber System (M2FS) of 182 stellar targets along the line of sight (LOS) to the newly discovered "ultrafaint" object Reticulum 2 (Ret 2). For 37 of these targets, the spectra are sufficient to provide simultaneous estimates of LOS velocity (ν<inf>los</inf>, median random error δ<inf>νlos</inf>= 1.4 km s<sup>-1</sup>), effective temperature (T<inf>eff</inf>, Δ <inf>Teff</inf> K), surface gravity (loh g, δ<inf>log g</inf> = 0.63 dex), and iron abundance ([Fe/H], <sup>δ</sup>[Fe/H] = 0.47 dex). We use these results to confirm 17 stars as members of Ret 2. From the member sample we estimate a velocity dispersion of σ<inf>νlos</inf> = 3.6<inf>0.7</inf><sup>+1.0</sup>km s<sup>-1</sup> about a mean of 〈ν<inf>los</inf>〉 = 64.3<inf>-1.2</inf><sup>+1.2</sup> km s<sup>-1</sup> in the solar rest frame ( ∼ -90.9 km s<sup>-1</sup> in the Galactic rest frame), and a metallicity dispersion of <sup>σ</sup> [Fe/H] = 0.49<inf>-0.14</inf><sup>0.19</sup> dex about a mean of 〈 [Fe/H]〉= -2.58<inf>-0.33</inf><sup>+0.34</sup>. These estimates marginalize over possible velocity and metallicity gradients, which are consistent with zero. Our results place Ret 2 on chemodynamical scaling relations followed by the Milky Way's dwarf-galactic satellites. Under assumptions of dynamic equilibrium and negligible contamination from binary stars - both of which must be checked with deeper imaging and repeat spectroscopic observations - the estimated velocity dispersion suggests a dynamical mass of M(R<inf>h</inf>)≈5R<inf>hσνlos;</inf><sup>2</sup>/(2G) = 2.4<inf>-0.8</inf><sup>+1.4</sup> × 10<sup>5</sup> M<inf>⊙</inf>enclosed within projected halflight radius R<inf>h</inf> ∼32 pc, with mass-to-light ratio ≈2M (R<inf>h</inf>)/L<inf>V</inf> = 467<inf>-168</inf><sup>+286</sup>in solar units.

Original languageEnglish (US)
Article number108
JournalAstrophysical Journal
Volume808
Issue number2
DOIs
StatePublished - Aug 1 2015

Fingerprint

dwarf galaxies
line of sight
metallicity
estimates
mass to light ratios
random errors
binary stars
contamination
gravity
gravitation
scaling
iron
stars
gradients
radii
fibers
temperature

Keywords

  • galaxies: dwarf
  • galaxies: individual (Reticulum 2)
  • galaxies: kinematics and dynamics
  • Local Group
  • methods: data analysis
  • techniques: spectroscopic

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Walker, M. G., Mateo, M., Olszewski, E. W., Iii, J. I. B., Koposov, S. E., Belokurov, V., & Evans, N. W. (2015). MAGELLAN/M2FS SPECTROSCOPY of the RETICULUM 2 DWARF SPHEROIDAL GALAXY. Astrophysical Journal, 808(2), [108]. https://doi.org/10.1088/0004-637X/808/2/108

MAGELLAN/M2FS SPECTROSCOPY of the RETICULUM 2 DWARF SPHEROIDAL GALAXY. / Walker, Matthew G.; Mateo, Mario; Olszewski, Edward W; Iii, John I Bailey; Koposov, Sergey E.; Belokurov, Vasily; Evans, N. Wyn.

In: Astrophysical Journal, Vol. 808, No. 2, 108, 01.08.2015.

Research output: Contribution to journalArticle

Walker, MG, Mateo, M, Olszewski, EW, Iii, JIB, Koposov, SE, Belokurov, V & Evans, NW 2015, 'MAGELLAN/M2FS SPECTROSCOPY of the RETICULUM 2 DWARF SPHEROIDAL GALAXY', Astrophysical Journal, vol. 808, no. 2, 108. https://doi.org/10.1088/0004-637X/808/2/108
Walker, Matthew G. ; Mateo, Mario ; Olszewski, Edward W ; Iii, John I Bailey ; Koposov, Sergey E. ; Belokurov, Vasily ; Evans, N. Wyn. / MAGELLAN/M2FS SPECTROSCOPY of the RETICULUM 2 DWARF SPHEROIDAL GALAXY. In: Astrophysical Journal. 2015 ; Vol. 808, No. 2.
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title = "MAGELLAN/M2FS SPECTROSCOPY of the RETICULUM 2 DWARF SPHEROIDAL GALAXY",
abstract = "We present results from spectroscopic observations with the Michigan/Magellan Fiber System (M2FS) of 182 stellar targets along the line of sight (LOS) to the newly discovered {"}ultrafaint{"} object Reticulum 2 (Ret 2). For 37 of these targets, the spectra are sufficient to provide simultaneous estimates of LOS velocity (νlos, median random error δνlos= 1.4 km s-1), effective temperature (Teff, Δ Teff K), surface gravity (loh g, δlog g = 0.63 dex), and iron abundance ([Fe/H], δ[Fe/H] = 0.47 dex). We use these results to confirm 17 stars as members of Ret 2. From the member sample we estimate a velocity dispersion of σνlos = 3.60.7+1.0km s-1 about a mean of 〈νlos〉 = 64.3-1.2+1.2 km s-1 in the solar rest frame ( ∼ -90.9 km s-1 in the Galactic rest frame), and a metallicity dispersion of σ [Fe/H] = 0.49-0.140.19 dex about a mean of 〈 [Fe/H]〉= -2.58-0.33+0.34. These estimates marginalize over possible velocity and metallicity gradients, which are consistent with zero. Our results place Ret 2 on chemodynamical scaling relations followed by the Milky Way's dwarf-galactic satellites. Under assumptions of dynamic equilibrium and negligible contamination from binary stars - both of which must be checked with deeper imaging and repeat spectroscopic observations - the estimated velocity dispersion suggests a dynamical mass of M(Rh)≈5Rhσνlos;2/(2G) = 2.4-0.8+1.4 × 105 M⊙enclosed within projected halflight radius Rh ∼32 pc, with mass-to-light ratio ≈2M (Rh)/LV = 467-168+286in solar units.",
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AU - Mateo, Mario

AU - Olszewski, Edward W

AU - Iii, John I Bailey

AU - Koposov, Sergey E.

AU - Belokurov, Vasily

AU - Evans, N. Wyn

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N2 - We present results from spectroscopic observations with the Michigan/Magellan Fiber System (M2FS) of 182 stellar targets along the line of sight (LOS) to the newly discovered "ultrafaint" object Reticulum 2 (Ret 2). For 37 of these targets, the spectra are sufficient to provide simultaneous estimates of LOS velocity (νlos, median random error δνlos= 1.4 km s-1), effective temperature (Teff, Δ Teff K), surface gravity (loh g, δlog g = 0.63 dex), and iron abundance ([Fe/H], δ[Fe/H] = 0.47 dex). We use these results to confirm 17 stars as members of Ret 2. From the member sample we estimate a velocity dispersion of σνlos = 3.60.7+1.0km s-1 about a mean of 〈νlos〉 = 64.3-1.2+1.2 km s-1 in the solar rest frame ( ∼ -90.9 km s-1 in the Galactic rest frame), and a metallicity dispersion of σ [Fe/H] = 0.49-0.140.19 dex about a mean of 〈 [Fe/H]〉= -2.58-0.33+0.34. These estimates marginalize over possible velocity and metallicity gradients, which are consistent with zero. Our results place Ret 2 on chemodynamical scaling relations followed by the Milky Way's dwarf-galactic satellites. Under assumptions of dynamic equilibrium and negligible contamination from binary stars - both of which must be checked with deeper imaging and repeat spectroscopic observations - the estimated velocity dispersion suggests a dynamical mass of M(Rh)≈5Rhσνlos;2/(2G) = 2.4-0.8+1.4 × 105 M⊙enclosed within projected halflight radius Rh ∼32 pc, with mass-to-light ratio ≈2M (Rh)/LV = 467-168+286in solar units.

AB - We present results from spectroscopic observations with the Michigan/Magellan Fiber System (M2FS) of 182 stellar targets along the line of sight (LOS) to the newly discovered "ultrafaint" object Reticulum 2 (Ret 2). For 37 of these targets, the spectra are sufficient to provide simultaneous estimates of LOS velocity (νlos, median random error δνlos= 1.4 km s-1), effective temperature (Teff, Δ Teff K), surface gravity (loh g, δlog g = 0.63 dex), and iron abundance ([Fe/H], δ[Fe/H] = 0.47 dex). We use these results to confirm 17 stars as members of Ret 2. From the member sample we estimate a velocity dispersion of σνlos = 3.60.7+1.0km s-1 about a mean of 〈νlos〉 = 64.3-1.2+1.2 km s-1 in the solar rest frame ( ∼ -90.9 km s-1 in the Galactic rest frame), and a metallicity dispersion of σ [Fe/H] = 0.49-0.140.19 dex about a mean of 〈 [Fe/H]〉= -2.58-0.33+0.34. These estimates marginalize over possible velocity and metallicity gradients, which are consistent with zero. Our results place Ret 2 on chemodynamical scaling relations followed by the Milky Way's dwarf-galactic satellites. Under assumptions of dynamic equilibrium and negligible contamination from binary stars - both of which must be checked with deeper imaging and repeat spectroscopic observations - the estimated velocity dispersion suggests a dynamical mass of M(Rh)≈5Rhσνlos;2/(2G) = 2.4-0.8+1.4 × 105 M⊙enclosed within projected halflight radius Rh ∼32 pc, with mass-to-light ratio ≈2M (Rh)/LV = 467-168+286in solar units.

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KW - galaxies: individual (Reticulum 2)

KW - galaxies: kinematics and dynamics

KW - Local Group

KW - methods: data analysis

KW - techniques: spectroscopic

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