THE PHOTOMETRIC AND KINEMATIC STRUCTURE AND ASYMMETRY OF DISK GALAXIES

Open Access
Author:
Andersen, David Roger
Graduate Program:
Astronomy and Astrophysics
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
October 08, 2001
Committee Members:
  • Steinn Sigurdsson, Committee Member
  • James J Beatty, Committee Member
  • Matthew A Bershady, Committee Chair
  • Robin Bruce Ciardullo, Committee Member
  • Lawrence William Ramsey, Committee Chair
Keywords:
  • galaxy kinematics
  • galaxy structure
Abstract:
We establish a sample of 39 nearby, nearly face-on disk galaxies for a detailed study of their photometric and kinematic structure and asymmetries. For this sample we collected two-dimensional H-alpha velocity-fields at echelle resolutions with the DensePak integral field unit on the WIYN 3.5m telescope, HI line widths taken with the Nancay radio telescope, and deep R and I-band imaging from the WIYN telescope, the 2.1m telescope at KPNO, and the Harlan J. Smith 2.7m telescope at McDonald Observatory. We use these data to put constraints on the shape of disk galaxies and their halos and to study the fundamental disk galaxy scaling relationship between rotation speed and luminosity, i.e., the Tully-Fisher relation. To study the shapes of galaxy disks, we measured both photometric and kinematic asymmetries. From studies of the asymmetry, we were able to show that the now commonly used photometric rotational asymmetry index does not measure disk flocculence as previously suggested; instead it is shown to be equivalent to low order, odd Fourier amplitudes, i.e., lopsidedness. In addition to studying disk lopsidedness, we establish a set of kinematic and photometric indices which we use to present the first measurements of disk ellipticity for galaxies outside the Milky Way. These measurements are decoupled from a phase angle (between the line of nodes and major axis of the un-inclined, elliptical galaxy) which plagues previous estimates of disk ellipticity. Nonetheless, our disk ellipticity measurement of 0.083+-0.054 is consistent with these previous estimates. This measurement allows us to put a limit of 0.15 mag on Tully-Fisher scatter due to the intrinsic ellipticity of disk galaxies. Kinematic inclination angles, one of the primary kinematic indices used to measure disk ellipticity, were derived from model velocity-field fits to our H-alpha velocity fields. These inclinations are shown to be both accurate and precise and allowed us to create the first Tully-Fisher relation for nearly face-on disk galaxies. We demonstrate that our face-on Tully-Fisher sample is well fit by a published Tully-Fisher relation. In fact, the Tully-Fisher scatter for our data was smaller that of the parent Tully-Fisher survey. The future of integral field units like SparsePak, newly commissioned on the WIYN telescope, promises more advances in the study of galaxy kinematics. Programs are under way to measure disk masses from stellar absorption line velocity fields; disk masses which will constrain bulge-disk mass decomposition models.