Details

Autor(en) / Beteiligte

• Ho, Nhung
• Geha, M
• Munoz, R R
• Guhathakurta, P
• Kalirai, J
• Gilbert, K M
• Tollerud, E
• Bullock, J
• Beaton, R L
• Majewski, S R

Titel

STELLAR KINEMATICS OF THE ANDROMEDA II DWARF SPHEROIDAL GALAXY

Ist Teil von

• The Astrophysical journal, 2012-10, Vol.758 (2), p.1-12

Ort / Verlag

United States

Erscheinungsjahr

2012

Link zum Volltext

Quelle

Free E-Journal (出版社公開部分のみ）

Beschreibungen/Notizen

• We present kinematical profiles and metallicity for the M31 dwarf spheroidal (dSph) satellite galaxy Andromeda II (And II) based on Keck DEIMOS spectroscopy of 531 red giant branch stars. Our kinematical sample is among the largest for any M31 satellite and extends out to two effective radii (r sub(eff) = 5'.3 = 1.1 kpc). We find a mean systemic velocity of -192.4 + or - 0.5 km s super(-1) and an average velocity dispersion of [sigma] sub([upsilon]) = 7.8 + or - 1.1 km s super(-1). While the rotation velocity along the major axis of And II is nearly zero (<1 km s super(-1)), the rotation along the minor axis is significant with a maximum rotational velocity of [upsilon] sub(max) = 8.6 + or - 1.8 km s super(-1). We find a kinematical major axis, with a maximum rotational velocity of [upsilon] sub(max) = 10.9 + or - 2.4 km s super(-1), misaligned by 67[degrees] to the isophotal major axis. And II is thus the first dwarf galaxy with evidence for nearly prolate rotation with a [upsilon] sub(max)/[sigma] sub([upsilon]) = 1.1, although given its ellipticity of [epsilon] = 0.10, this object may be triaxial. We measured metallicities for a subsample of our data, finding a mean metallicity of [Fe/H] = -1.39 + or - 0.03 dex and an internal metallicity dispersion of 0.72 + or - 0.03 dex. We find a radial metallicity gradient with metal-rich stars more centrally concentrated, but do not observe a significant difference in the dynamics of the two metallicity populations. And II is the only known dwarf galaxy to show minor axis rotation, making it a unique system whose existence offers important clues on the processes responsible for the formation of dSphs.