Orbital decomposition of CALIFA spiral galaxies

TL;DR

This paper introduces Schwarzschild dynamical models for CALIFA survey's late-type galaxies, revealing detailed internal mass distributions, orbital structures, and dark matter fractions, validated through mock data tests.

Contribution

First application of Schwarzschild models to late-type galaxies, providing detailed orbital and mass distribution insights.

Findings

Mass profiles within 2 R_e are constrained with ~10% error.

Dark matter fraction increases from 14% to 18% in NGC 4210 and 15% to 30% in NGC 6278 from R_e to 2 R_e.

Galactic orbits are classified into cold, warm, and hot components, correlating with photometric structures.

Abstract

Schwarzschild orbit-based dynamical models are widely used to uncover the internal dynamics of early-type galaxies and globular clusters. Here we present for the first time the Schwarzschild models of late-type galaxies: an SBb galaxy NGC 4210 and an S0 galaxy NGC 6278 from the CALIFA survey. The mass profiles within $2\,R_e$ are constrained well with $1\sigma$ statistical error of $\sim 10\%$. The luminous and dark mass can be disentangled with uncertainties of $\sim 20\%$ and $\sim 50\%$ respectively. From $R_e$ to $2\,R_e$, the dark matter fraction increases from $14\pm10\%$ to $18\pm10\%$ for NGC 4210 and from $15\pm10\%$ to $30\pm20\%$ for NGC 6278. The velocity anisotropy profiles of both $\sigma_r/\sigma_t$ and $\sigma_z/\sigma_R$ are well constrained. The inferred internal orbital distributions reveal clear substructures. The orbits are naturally separated into three components: a cold component with near circular orbits, a hot component with near radial orbits, and a warm component in between. The photometrically-identified exponential disks are predominantly made up of cold orbits only beyond $\sim 1\,R_e$, while they are constructed mainly with the warm orbits inside. Our dynamical hot components are concentrated in the inner regions, similar to the photometrically-identified bulges. The reliability of the results, especially the orbit distribution, are verified by applying the model to mock data.