The SAMI Galaxy Survey: The Internal Orbital Structure and Mass Distribution of Passive Galaxies from Triaxial Orbit-superposition Schwarzschild Models

Santucci, Giulia; Brough, Sarah; van de Sande, Jesse; McDermid, Richard M.; van de Ven, Glenn; Zhu, Ling; D’Eugenio, Francesco; Bland-Hawthorn, Joss; Barsanti, Stefania; Bryant, Julia J.; M. Croom, Scott; Davies, Roger L.; Green, Andrew W.; Lawrence, Jon S.; Lorente, Nuria P.F.; Owers, Matt S.; Poci, Adriano; Richards, Samuel N.; Thater, Sabine; Yi, Sukyoung

Abstract

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. Here, we build triaxial Schwarzschild orbit-superposition models of galaxies taken from the SAMI Galaxy Survey, in order to reconstruct their inner orbital structure and mass distribution. The sample consists of 161 passive galaxies with total stellar masses in the range 109.5–1012M⊙. We find that the changes in internal structures within 1Re are correlated with the total stellar mass of the individual galaxies. The majority of the galaxies in the sample (73% ± 3%) are oblate, while 19% ± 3% are mildly triaxial and 8% ± 2% have triaxial/prolate shape. Galaxies with $\mathrm{log}{M}_{\star }/{M}_{\odot }\gt 10.50$ are more likely to be non-oblate. We find a mean dark matter fraction of fDM = 0.28 ± 0.20, within 1Re. Galaxies with higher intrinsic ellipticity (flatter) are found to have more negative velocity anisotropy βr (tangential anisotropy). βr also shows an anticorrelation with the edge-on spin parameter ${\lambda }_{\mathrm{Re},\mathrm{EO}}$, so that βr decreases with increasing ${\lambda }_{\mathrm{Re},\mathrm{EO}}$, reflecting the contribution from disk-like orbits in flat, fast-rotating galaxies. We see evidence of an increasing fraction of hot orbits with increasing stellar mass, while warm and cold orbits show a decreasing trend. We also find that galaxies with different (V/σ – h3) kinematic signatures have distinct combinations of orbits. These results are in agreement with a formation scenario in which slow- and fast-rotating galaxies form through two main channels.

Citation

Santucci, G., Brough, S., van de Sande, J., McDermid, R. M., van de Ven, G., Zhu, L., D’Eugenio, F., Bland-Hawthorn, J., Barsanti, S., Bryant, J. J., M. Croom, S., Davies, R. L., Green, A. W., Lawrence, J. S., Lorente, N. P., Owers, M. S., Poci, A., Richards, S. N., Thater, S., & Yi, S. (2022). The SAMI Galaxy Survey: The Internal Orbital Structure and Mass Distribution of Passive Galaxies from Triaxial Orbit-superposition Schwarzschild Models. Astrophysical Journal, 930(2), Article 153. https://doi.org/10.3847/1538-4357/ac5bd5

• Journal Article Type: Article
• Acceptance Date: Mar 6, 2022
• Online Publication Date: May 13, 2022
• Publication Date: May 10, 2022
• Deposit Date: Jul 14, 2022
• Publicly Available Date: Jul 14, 2022
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 930
• Issue: 2
• Article Number: 153
• DOI: https://doi.org/10.3847/1538-4357/ac5bd5
• Public URL: https://durham-repository.worktribe.com/output/1197707