Mathematics – Probability
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...208.1413h&link_type=abstract
American Astronomical Society Meeting 208, #14.13; Bulletin of the American Astronomical Society, Vol. 38, p.95
Mathematics
Probability
Scientific paper
We aim to quantify the kinematics of the stellar populations (thin disk and thick disk and/or 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 potentially 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 approximately 1000 individual red giant stars throughout M33. We derived radial velocities for 320 stars to date from five fields along the major and minor axes of the galaxy, with typical 1σ random errors of 18 km/s. The observed stars range in magnitude from 20.8 mag≤I≤22.5 mag, with a median signal-to-noise ratio of S/N=5. Of these stars, 185 have a >95% probability of being M33 red giants rather than foreground Milky Way dwarfs based solely on photometric observations made in the V, I and DDO51 filters, using the separation between giants and dwarfs in the (V-I, 51-V) color-color diagram. These M33 red giants show a significant component with a large velocity dispersion of 30 km/s around the HI disk rotation and an additional component with an even larger velocity dispersion. 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 et al. 1973), suggesting the existence of a stellar halo and/or thick disk. Chandar et al. (2002) saw a similar large velocity dispersion component for 18 old (ages >1Gyr) star clusters in M33.We gratefully acknowledge financial support from grant NSF AST-0307863 to Tammy Smecker-Hane.
Ferguson Annette M.
Hood Michael A.
Irwin Mary Jane
Smecker-Hane Tammy
Teig Matthew
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