The inner mass distribution of late-type spiral galaxies from SAURON stellar kinematic maps

TL;DR

This study compares two dynamical models to infer the central mass distribution of late-type spiral galaxies using stellar kinematic maps, revealing model agreement depends on the ratio of ordered to random motions.

Contribution

It provides a comparative analysis of ADC and JAM models applied to SAURON data, highlighting the conditions under which they agree or diverge in mass distribution estimates.

Findings

ADC and JAM are consistent within 5% when ordered motions dominate.

Discrepancies increase when the ratio of ordered to random motions drops below 1.5.

Results suggest stellar mass contributions from bulges and thick disks are significant.

Abstract

We infer the central mass distributions within 0.4-1.2 disc scale lengths of 18 late-type spiral galaxies using two different dynamical modelling approaches - the Asymmetric Drift Correction (ADC) and axisymmetric Jeans Anisotropic Multi-gaussian expansion (JAM) model. ADC adopts a thin disc assumption, whereas JAM does a full line-of-sight velocity integration. We use stellar kinematics maps obtained with the integral-field spectrograph SAURON to derive the corresponding circular velocity curves from the two models. To find their best-fit values, we apply Markov Chain Monte Carlo (MCMC) method. ADC and JAM modelling approaches are consistent within 5% uncertainty when the ordered motions are significant comparable to the random motions, i.e, $\overline{v_{\phi}}/\sigma_R$ is locally greater than 1.5. Below this value, the ratio $v_\mathrm{c,JAM}/v_\mathrm{c,ADC}$ gradually increases with decreasing $\overline{v_{\phi}}/\sigma_R$, reaching $v_\mathrm{c,JAM}\approx 2 \times v_\mathrm{c,ADC}$. Such conditions indicate that the stellar masses of the galaxies in our sample are not confined to their disk planes and likely have a non-negligible contribution from their bulges and thick disks.