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Paper: Kinematics of the Stellar Populations of M33
Volume: 374, From Stars to Galaxies: Building the Pieces to Build Up the Universe
Page: 281
Authors: Hood, M.; Smecker-Hane, T.; Teig, M.; Ferguson, A.M.N.; Irwin, M.J.
Abstract: We are quantifying the kinematics of the stellar populations (thin disk, thick disk and halo) of the nearby spiral galaxy M33. Photometry from Ferguson et al. (2006) shows M33’s inner region is well–fit by a single exponential disk with a scale length of 0.1° (1.4 kpc) out to a radius of 0.6°, although individual stars observed well outside a radius of 1.0° are potential members of a thick disk or halo. We are using the DEIMOS spectrograph at the Keck II 10–meter telescope to obtain spectra surrounding the CaII near–infrared triplet lines for ~1000 individual red giant stars throughout M33. We derived radial velocities for 331 stars to date from five fields along the major and minor axes of the galaxy, with typical 1-σ random errors of 10 km/s. Of these stars, 234 are probable M33 red giants rather than foreground Milky Way dwarfs based on our photometric observations made in the narrow–band DDO51 filter. In addition to a thin disk with a velocity dispersion of 15 km/s around the HI disk, we also see a component with a large velocity dispersion of 47 km/s. This dispersion is much larger than the 17 km/s dispersion seen in young disk clusters (Chandar et al. 2002) and the 9 km/s dispersion found in the HI disk (Warner, Wright & Baldwin 1973), suggesting the existence of a thick disk and stellar halo that make up 30% and 4% of the total number of stars in these fields, respectively.
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