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

• Published in: The Astrophysical Journal
• Main Authors: 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.
• Format: Article in Journal/Newspaper
• Language: English
• Published: IOP Publishing
• Subjects: Galaxy evolution; Galaxy dynamics; Galaxy structure; Galaxy kinematics; sami
• Online Access: http://hdl.handle.net/1885/316467; https://doi.org/10.3847/1538-4357/ac5bd5; https://openresearch-repository.anu.edu.au/bitstream/1885/316467/3/Santucci_2022_ApJ_930_153.pdf.jpg

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 109.5-1012 M ⊙. We find that the changes in internal structures within 1R e 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 logM⋆/M⊙>10.50 are more likely to be non-oblate. We find a mean dark matter fraction of f DM = 0.28 ± 0.20, within 1R e. Galaxies with higher intrinsic ellipticity (flatter) are found to have more negative velocity anisotropy β r (tangential anisotropy). β r also shows an anticorrelation with the edge-on spin parameter λRe,EO , so that β r decreases with increasing λRe,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 - h 3) 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. The SAMI Galaxy Survey is based on observations made at the Anglo-Australian Telescope. SAMI was developed jointly by the University of Sydney and the Australian Astronomical Observatory. The SAMI input catalog is based on data taken from SDSS, the GAMA Survey, and the VST ATLAS Survey. The SAMI Galaxy Survey is supported by the Australian Research Council center of Excellence for All Sky Astro- physics in 3 ...