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Session 10 - Spiral Galaxies.
Display session, Monday, June 10
As a class, Sa galaxies have broader distributions of HI and FIR surface densities and bulge to disk ratios compared to later type spirals, typically occupy higher density environments and require little to no dark matter beyond their optical disks. In order to uncover the reason for the diversity of the Sa class, we have been conducting a study of the dynamics and kinematics of a sample of 23 nearby, non-interacting RSA Sa's with a range of HI content and bulge-to-disk ratio. Over the past 3 years we have obtained major and minor axis long slit spectra at the Palomar 200'' telescope using both the red and blue cameras of the Double Spectrograph. Thirty to 80 minute integrations used a 120''x2'' slit with a 1200 lines/mm grating and a dichroic at 5500 ÅThe red camera produced a spectral resolution of 0.82 Åpixel over a range of 6190-6850 Å\ including the H\alpha, [NII], and [SII] lines. The blue camera gave a spectral resolution of 0.56 Åpixel over a range of 4950-5400 Å\ covering the [OIII] and MgI b lines. Rotation curves and velocity dispersion profiles have been extracted for both the emission and absorption line components. The gas rotation curves and velocity dispersion profiles were measured by fitting gaussians to the emission line profiles. In many cases, the [NII] \lambda 6563Å\ line provides a better measurement of the rotation curve because the H\alpha line appears both in absoption and emission. The stellar line of sight velocity distributions (LOSVD) which were derived using the cross correlation technique provide rotational velocities and velocity dispersion profiles into the disk of the galaxy. Here, we will present the gas and stellar rotation curves and velocity dispersion profiles, and preliminary conclusions.
Program listing for Monday