Ordered versus random motions, the morphology dependence of the Tully-Fisher relation and the Fundamental Manifold of spiral galaxies.
Chiara Tonini (Swinburne University of Technology, Melbourne)
We investigate the morphology dependence of the Tully-Fisher (TF) relation, and the expansion of the relation into a higher-dimensional manifold akin to the ellipticals Fundamental Plane, to account for such a feature.
In this work, we take advantage of a full semi-analytic hierarchical model (based from Croton et al. 2006), built on cosmological simulations of structure formation, to model galaxy evolution and build the theoretical TF relation. With this tool, we analyse a unique dataset of galaxies (Catinella et al. 2010) for which luminosity and both the total circular velocity and the central velocity dispersion are provided. We provide a theoretical framework to calculate such measurable quantities from hierarchical semi-analytic models.
We establish the morphology dependence of the TF relation in both model and data. We analyse the dynamical properties of the model galaxies and determine that the parameter $\sigma_A/V_C$, i.e. the ratio between random and total motions characterised by velocity dispersion and circular velocity profiles, is an accurate proxy for galaxy morphology. We apply such dynamical cuts to the observed galaxies and find indeed that such selection produces a differential slope of the TF relation. We conclude that the $\sigma_A/V_C$ is a valid parameter to expand the TF relation into a three-dimensional manifold, and that it successfully characterises the hierarchical assembly history that determines the disk-to-bulge ratio and therefore the galaxy morphology.