The SAMI Galaxy Survey: Environmental analysis of the orbital structures of passive galaxies

Dynamical models are crucial for uncovering the internal dynamics of galaxies. However, most of the results to date assume axisymmetry, which is not representative of a significant fraction of massive galaxies. We have built triaxial orbit-superposition Schwarzschild models of galaxies observed by the SAMI Galaxy Survey, in order to reconstruct their inner orbital structure and mass distribution. The sample consists of 153 passive galaxies with total stellar masses in the range $10^{9.5}$ to $10^{12} M_{\odot}$. We present an analysis of the internal structures and intrinsic properties of these galaxies as a function of their environment. We measure their environment using three proxies: central or satellite designation, halo mass and local $5^{th}$ nearest neighbour galaxy density. We find that although these intrinsic properties correlate strongly with stellar mass, environment does play a secondary role: at fixed stellar mass, galaxies in the densest regions are more radially anisotropic. In addition, central galaxies, and galaxies in high local densities, show lower values of $\lambda_{Re, EO}$. We also find hints of a possible trend of the fractions of orbits with environment for lower-mass galaxies (between $10^{9.5}$ and $10^{11} M_{\odot}$). Our results demonstrate that after stellar mass, environment does play a role in shaping present-day galaxies.

For this analysis, we use orbital structures and intrinsic parameters (such as intrinsic shape and velocity anisotropy) derived in Santucci et al. 2022 using Schwarzschild models.

This project could potentially overlap with other SAMI projects that are comparing kinematics and environment. However, although the main goal is the same, the techniques used are very different and this is one of the very first analyses of how the properties derived by Schwarzschild models change with environment (and the very first for SAMI galaxies).

Paper is ready for team review and it can be downloaded through overleaf here:

Publication Date: 
August 2022