The stellar velocity dispersion in nearby spirals: radial profiles and correlations

The stellar velocity dispersion, σ, is a quantity of crucial importance for spiral galaxies, where it enters fundamental dynamical processes such as gravitational instability and disc heating. Here we analyse a sample of 34 nearby spirals from the Calar Alto Legacy Integral Field Area (CALIFA) spectroscopic survey, deproject the line-of-sight σ to σ_R, and present reliable radial profiles of σ_R as well as accurate measurements of <σ_R>, the radial average of σ_R over one effective (half-light) radius. We show that there is a trend for σ_R to increase with decreasing R, that <σ_R> correlates with stellar mass (M_⋆), and tested correlations with other galaxy properties. The most significant and strongest correlation is the one with M_⋆: < σ _R> ∝ M_{\star }^{0.5}. This tight scaling relation is applicable to spiral galaxies of type Sa-Sd and stellar mass M_⋆ ≈ 10^9.5-10^11.5 M_⊙. Simple models that relate σ_R to the stellar surface density and disc scale length roughly reproduce that scaling, but overestimate <σ_R> significantly.