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Abstract
The structure and dynamics of spiral galaxies are used to test both canonical Cold Dark Matter (CDM) paradigm predictions on galactic scales and the standard disk galaxy formation scenario within this framework. Three distinct projects are undertaken, that span the observed range of disk galaxy properties in the local Universe.
First, to understand the nature of the discrepancy between theoretical CDM profiles and those inferred for dark matter dominated galaxies, inner halo shapes for 165 low-mass systems are derived from optical rotation curves assuming minimum disks and spherical symmetry. While the inner slopes obtained are substantially shallower than predicted by the ΛCDM paradigm, simulations demonstrate that this apparent cusp/core problem may be reconciled by considering the impact of observing and data processing techniques on rotation curves derived from long-slit spectra.
In the second test, the anticipated relationships between the structure and kinematics of disks formed in the standard monolithic collapse scenario are compared to the measured properties of over 3700 normal spirals. The scaling laws self-consistently recover parameter correlations in the data provided that disks formed at low redshift conserving specific angular momentum, the average halo baryon fraction is ∼ 5%, and the average mass-to-light ratio is 80% solar in the I-band. The theoretical predictions are therefore powerful tools in constraining the details of disk assembly within the ΛCDM framework.
Finally, to evaluate the role of the standard disk stability criterion in setting the observed upper bound to spiral galaxy rotational velocities, the dynamics of 8 of the fastest known rotators are examined using aperture synthesis neutral hydrogen maps and optical long-slit spectra. Halo shapes derived from their rotation curves are combined with archived photometry to estimate the angular momentum of their parent halos. In contrast to the extreme values expected for massive systems, the measured spin parameters lie near the peak of the theoretical probability distribution. Given the baryon contributions assumed in the mass models, it is clear that if CDM halos do stabilize dynamically cold disks and limit their rotational velocities, then the galaxies in the fast rotator sample harbor substantially sub-maximal disks.
