The Spheroid of M33: Bulge or Halo?
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Session 23 -- Galaxies I
Oral presentation, Wednesday, January 12, 10:15-11:45, Salon IV Room (Crystal Gateway)

[23.04] The Spheroid of M33: Bulge or Halo?

Michael W. Regan, Stuart N. Vogel (UMd)

Because of its proximity, M33 provides a unique opportunity to investigate a spiral galaxy with a very small bulge. However, the existence of a bulge in M33 remains controversial (van den Bergh 1991). For example, Kent (1987) suggested that the excess light seen near the nucleus is due to spiral structure, while Bothun (1992) stated that the central surface brightness of M33 could not be fit by a single r$^{1/4}$ law and may not be a bulge but a large scale diffuse halo. Recently, Minniti, Olszewski, and Rieke (1993) used H-band photometry of individual stars near the center of M33 and concluded that there is a bulge, and that it has undergone recent ($<1$ Gyr) star formation. We present J, H, and K-band observations of M33 obtained with the SQIID camera on the KPNO 1.3 meter telescope that show that the inner spheriodal light distribution of M33 is better characterized by a halo than a bulge. The total light in the halo is larger than previous estimates for the bulge of M33, leading to an estimate of the ratio of globular clusters to total spheriodal luminosity closer to that measured for other spiral galaxies.

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