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The stellar orbit distribution in present-day galaxies inferred from the CALIFA survey

Zhu, L, Ven, GVD, Bosch, RVD, Rix, H-W, Lyubenova, M, Falcón-Barroso, J, Martig, M, Mao, S, Xu, D, Jin, Y, Obreja, A, Grand, RJJ, Dutton, AA, Maccio, AV, Gómez, FA, Walcher, JC, García-Benito, R, Zibetti, S and Sánchez, SF (2018) The stellar orbit distribution in present-day galaxies inferred from the CALIFA survey. Nature Astronomy. ISSN 2397-3366

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Abstract

Galaxy formation entails the hierarchical assembly of mass, along with the condensation of baryons and the ensuing, self-regulating star formation. The stars form a collisionless system whose orbit distribution retains dynamical memory that can constrain a galaxy's formation history. The ordered-rotation dominated orbits with near maximum circularity $\lambda_z \simeq1$ and the random-motion dominated orbits with low circularity $\lambda_z \simeq0$ are called kinematically cold and kinematically hot, respectively. The fraction of stars on `cold' orbits, compared to the fraction of stars on `hot' orbits, speaks directly to the quiescence or violence of the galaxies' formation histories. Here we present such orbit distributions, derived from stellar kinematic maps via orbit-based modelling for a well defined, large sample of 300 nearby galaxies. The sample, drawn from the CALIFA survey, includes the main morphological galaxy types and spans the total stellar mass range from $10^{8.7}$ to $10^{11.9}$ solar masses. Our analysis derives the orbit-circularity distribution as a function of galaxy mass, $p(\lambda_z~|~M_\star)$, and its volume-averaged total distribution, $p(\lambda_z)$. We find that across most of the considered mass range and across morphological types, there are more stars on `warm' orbits defined as $0.25\le \lambda_z \le 0.8$ than on either `cold' or `hot' orbits. This orbit-based "Hubble diagram" provides a benchmark for galaxy formation simulations in a cosmological context.

Item Type: Article
Uncontrolled Keywords: astro-ph.GA; astro-ph.GA
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Nature Publishing Group
Related URLs:
Date Deposited: 25 Jan 2018 09:28
Last Modified: 25 Jan 2018 09:28
DOI or Identification number: 10.1038/s41550-017-0348-1
URI: http://researchonline.ljmu.ac.uk/id/eprint/7891

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