The SAMI Galaxy Survey: Revisiting Galaxy Classification through High-order Stellar Kinematics
Abstract
Recent cosmological hydrodynamical simulations suggest that integral field spectroscopy can connect the high-order stellar kinematic moments h3 (∼skewness) and h4 (∼kurtosis) in galaxies to their cosmological assembly history. Here, we assess these results by measuring the stellar kinematics on a sample of 315 galaxies, without a morphological selection, using two-dimensional integral field data from the SAMI Galaxy Survey. Proxies for the spin parameter ({λ }{R{{e}}}) and ellipticity ({ɛ }{{e}}) are used to separate fast and slow rotators; there exists a good correspondence to regular and non-regular rotators, respectively, as also seen in earlier studies. We confirm that regular rotators show a strong h3 versus V/σ anti-correlation, whereas quasi-regular and non-regular rotators show a more vertical relation in h3 and V/σ . Motivated by recent cosmological simulations, we develop an alternative approach to kinematically classify galaxies from their individual h3 versus V/σ signatures. Within the SAMI Galaxy Survey, we identify five classes of high-order stellar kinematic signatures using Gaussian mixture models. Class 1 corresponds to slow rotators, whereas Classes 2-5 correspond to fast rotators. We find that galaxies with similar {λ }{R{{e}}}{--}{ɛ }{{e}} values can show distinctly different {h}3{--}V/σ signatures. Class 5 objects are previously unidentified fast rotators that show a weak h3 versus V/σ anti-correlation. From simulations, these objects are predicted to be disk-less galaxies formed by gas-poor mergers. From morphological examination, however, there is evidence for large stellar disks. Instead, Class 5 objects are more likely disturbed galaxies, have counter-rotating bulges, or bars in edge-on galaxies. Finally, we interpret the strong anti-correlation in h3 versus V/σ as evidence for disks in most fast rotators, suggesting a dearth of gas-poor mergers among fast rotators.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2017
- DOI:
- 10.3847/1538-4357/835/1/104
- arXiv:
- arXiv:1611.07039
- Bibcode:
- 2017ApJ...835..104V
- Keywords:
-
- cosmology: observations;
- galaxies: evolution;
- galaxies: formation;
- galaxies: kinematics and dynamics;
- galaxies: stellar content;
- galaxies: structure;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted for Publication in The Astrophysical Journal. 35 pages and 30 figures, abstract abridged for arXiv submission. The key figures of the paper are: 7, 11, 12 , and 14