The Nuclear Disk of M31
Session 32 -- Local Group Galaxies
Display presentation, Tuesday, 9:30-6:30, Heller Lounge Room

[32.08] The Nuclear Disk of M31

M. A. Pahre, J. R. Mould, K. Matthews (Caltech), K. Mighell, R. M. Rich (Columbia)

We present near infrared (0.87, 1.04, 2.2, and 3.6 $\mu$m) images of the nucleus of M31 obtained with Hubble Space Telescope and the Hale 5-m telescope at Palomar. The images show a central disk with axis ratio $b/a\simeq$0.7 (at 2.2 and 3.6 $\mu$m) and position angle $\sim$55$\deg$, which is inclined at $\sim$17$\deg$ with respect to the galaxy's major axis. Deconvolution of the 0.87 $\mu$m image by the HST PSF and reconvolution with the Palomar PSF indicates similar morphological structure in both the optical and the infrared. At all wavelengths there is a pronounced asymmetric elongation of $\sim$20\% to the SW of the peak emission of the nucleus. The FWHM of the disk along the major axis is 1.9$''$ in the K and L bands and is similar in the convolved optical image. We examine the properties of the disk as a function of wavelength, and discuss various models which might be invoked to explain the observations, such as a star cluster orbiting the kinematic center of the galaxy, a partially obscured disk or a flattened spheroid of stars.