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arXiv · 1711.06728

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

Ling Zhu·Glenn van de Ven·Remco van den Bosch·Hans-Walter Rix·Mariya Lyubenova·Jesús Falcón-Barroso·Marie Martig·Shude Mao·Dandan Xu·Yunpeng Jin·Aura Obreja·Robert J. J. Grand·Aaron A. Dutton·Andrea V. Maccio·Facundo A. Gómez·Jakob C. Walcher·Rubén García-Benito·Stefano Zibetti·Sebastian F. Sánchez
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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 $λ_z \simeq1$ and the random-motion dominated orbits with low circularity $λ_z \simeq0$ 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, $p(λ_z~|~M_\star)$, and its volume-averaged total distribution, $p(λ_z)$. We find that across most of the considered mass range and across morphological types, there are more stars on `warm' orbits defined as $0.25\le λ_z \le 0.8$ than on either `cold' or `hot' orbits. This orbit-based "Hubble diagram" provides a benchmark for galaxy formation simulations in a cosmological context.

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Ling Zhu, Glenn van de Ven, Remco van den Bosch, Hans-Walter Rix, Mariya Lyubenova, Jesús Falcón-Barroso, Marie Martig, Shude Mao, Dandan Xu, Yunpeng Jin, Aura Obreja, Robert J. J. Grand, Aaron A. Dutton, Andrea V. Maccio, Facundo A. Gómez, Jakob C. Walcher, Rubén García-Benito, Stefano Zibetti, Sebastian F. Sánchez. 2018-01-08. The stellar orbit distribution in present-day galaxies inferred from the CALIFA survey. https://arxiv.org/abs/1711.06728

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