Final published version
Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Stellar kinematics and metallicities in the Leo I dwarf spheroidal galaxy
T2 - wide-field implications for galactic evolution
AU - Koch, Andreas
AU - Wilkinson, Mark I.
AU - Kleyna, Jan
AU - Gilmore, Gerard
AU - Grebel, Eva K.
AU - Mackey, A. Dougal
AU - Wyn Evans, N.
AU - Wyse, Rosemary F. G.
PY - 2007/3/1
Y1 - 2007/3/1
N2 - We present low-resolution spectroscopy of 120 red giants in the Galactic satellite dwarf spheroidal (dSph) Leo I, obtained with GeminiN GMOS and Keck DEIMOS. We find stars with velocities consistent with membership of Leo I out to 1.3 King tidal radii. By measuring accurate radial velocities with a median measurement error of 4.6 km s-1, we find a mean systemic velocity of 284.2 km s-1 with a global velocity dispersion of 9.9 km s-1. The dispersion profile is consistent with being flat out to the last data point. We show that a marginally significant rise in the radial dispersion profile at a radius of 3' is not associated with any real localized kinematical substructure. Given its large distance from the Galaxy, tides are not likely to have affected the velocity dispersion, a statement we support from a quantitative kinematical analysis, as we observationally reject the occurrence of a significant apparent rotational signal or an asymmetric velocity distribution. Mass determinations adopting both isotropic stellar velocity dispersions and more general models yield an M/L of 24, which is consistent with the presence of a significant dark halo with a mass of about 3 × 107 M☉, in which the luminous component is embedded. This suggests that Leo I exhibits dark matter properties similar to those of other dSphs in the Local Group. Our data allowed us also to determine metallicities for 58 of the targets. We find a mildly metal-poor mean of -1.31 dex and a full spread covering 1 dex. In contrast to the majority of dSphs, Leo I appears to show no radial gradient in its metallicities, which points to a negligible role of external influences in this galaxy's evolution.
AB - We present low-resolution spectroscopy of 120 red giants in the Galactic satellite dwarf spheroidal (dSph) Leo I, obtained with GeminiN GMOS and Keck DEIMOS. We find stars with velocities consistent with membership of Leo I out to 1.3 King tidal radii. By measuring accurate radial velocities with a median measurement error of 4.6 km s-1, we find a mean systemic velocity of 284.2 km s-1 with a global velocity dispersion of 9.9 km s-1. The dispersion profile is consistent with being flat out to the last data point. We show that a marginally significant rise in the radial dispersion profile at a radius of 3' is not associated with any real localized kinematical substructure. Given its large distance from the Galaxy, tides are not likely to have affected the velocity dispersion, a statement we support from a quantitative kinematical analysis, as we observationally reject the occurrence of a significant apparent rotational signal or an asymmetric velocity distribution. Mass determinations adopting both isotropic stellar velocity dispersions and more general models yield an M/L of 24, which is consistent with the presence of a significant dark halo with a mass of about 3 × 107 M☉, in which the luminous component is embedded. This suggests that Leo I exhibits dark matter properties similar to those of other dSphs in the Local Group. Our data allowed us also to determine metallicities for 58 of the targets. We find a mildly metal-poor mean of -1.31 dex and a full spread covering 1 dex. In contrast to the majority of dSphs, Leo I appears to show no radial gradient in its metallicities, which points to a negligible role of external influences in this galaxy's evolution.
U2 - 10.1086/510879
DO - 10.1086/510879
M3 - Journal article
VL - 657
SP - 241
EP - 261
JO - The Astrophysical Journal
JF - The Astrophysical Journal
SN - 0004-637X
IS - 1
ER -