Physical Explanation for the Galaxy Distribution on the $({\lambda }_{\mathrm{R}},\epsilon )$ and $(V/\sigma ,\epsilon )$ Diagrams or for the Limit on Orbital Anisotropy

Abstract

In the $({\lambda }_{\mathrm{R}},\epsilon )$ and $(V/\sigma ,\epsilon )$ diagrams for characterizing dynamical states, the fast-rotator galaxies (both early-type and spirals) are distributed within a well-defined leaf-shaped envelope. This was explained as due to an upper limit to the orbital anisotropy increasing with galaxy intrinsic flattening. However, a physical explanation for this empirical trend was missing. Here we construct Jeans Anisotropic Models (JAM), with either cylindrically or spherically aligned velocity ellipsoid (two extreme assumptions), and each with either spatially-constant or -variable anisotropy. We use JAM to build mock samples of axisymmetric galaxies, assuming on average an oblate shape for the velocity ellipsoid (as required to reproduce the rotation of real galaxies), and limiting the radial anisotropy $\beta$ to the range allowed by physical solutions. We find that all four mock samples naturally predict the observed galaxy distribution on the $({\lambda }_{\mathrm{R}},\epsilon )$ and $(V/\sigma ,\epsilon )$ diagrams, without further assumptions. Given the similarity of the results from quite different models, we conclude that the empirical anisotropy upper limit in real galaxies, and the corresponding observed distributions in the $({\lambda }_{\mathrm{R}},\epsilon )$ and $(V/\sigma ,\epsilon )$ diagrams, are due to the lack of physical axisymmetric equilibrium solutions at high $\beta$ anisotropy when the velocity ellipsoid is close to oblate.

arXiv comment5 pages, 4 figures, accepted for publication on MNRAS Letters

References in corpus (21)

• Adaptive spatial binning of integral-field spectroscopic data using Voronoi tessellations
• The SAURON project -- IX. A kinematic classification for early-type galaxies
• The ATLAS3D project - III. A census of the stellar angular momentum within the effective radius of early-type galaxies: unveiling the distribution of Fast and Slow Rotators
• The Atlas3D project - XV. Benchmark for early-type galaxies scaling relations from 260 dynamical models: mass-to-light ratio, dark matter, Fundamental Plane and Mass Plane
• The SAURON project -- X. The orbital anisotropy of elliptical and lenticular galaxies: revisiting the (V/sigma,epsilon) diagram with integral-field stellar kinematics
• Measuring the inclination and mass-to-light ratio of axisymmetric galaxies via anisotropic Jeans models of stellar kinematics
• Efficient Multi-Gaussian Expansion of galaxies
• Structure and Kinematics of Early-Type Galaxies from Integral-Field Spectroscopy
• The SAMI Galaxy Survey: Revisiting Galaxy Classification Through High-Order Stellar Kinematics
• SDSS-IV MaNGA: Stellar angular momentum of about 2300 galaxies: unveiling the bimodality of massive galaxy properties
• Rotation and anisotropy of galaxies revisited
• Heating of Galactic Disks by Infalling Satellites
• Observational Constraints on Disk Heating as a Function of Hubble Type
• Efficient solution of the anisotropic spherically-aligned axisymmetric Jeans equations of stellar hydrodynamics for galactic dynamics
• The ATLAS3D Project - XXI. Correlations between gradients of local escape velocity and stellar populations in early-type galaxies
• The relationship between the morphology and kinematics of galaxies and its dependence on dark matter halo structure in EAGLE
• Systematic trends in total-mass profiles from dynamical models of early-type galaxies
• The flattening and the orbital structure of early-type galaxies and collisionless N-body binary disk mergers
• SDSS-IV MaNGA: The kinematic-morphology of galaxies on the mass vs star-formation relation in different environments
• A quartet of black holes and a missing duo: probing the low-end of the Mbh - sigma relation with the adaptive optics assisted integral-field spectroscopy
• Supermassive black holes from OASIS and SAURON integral-field kinematics

Cited by in corpus (7)

• MaNGA DynPop -- I. Quality-assessed stellar dynamical modelling from integral-field spectroscopy of 10K nearby galaxies: a catalogue of masses, mass-to-light ratios, density profiles and dark matter
• SDSS-IV MaNGA: Integral-field kinematics and stellar population of a sample of galaxies with counter-rotating stellar disks selected from about 4000 galaxies
• Early-Type Galaxies: Elliptical and S0 Galaxies, or Fast and Slow Rotators
• The kinematic bimodality: Efficient feedback and cold gas deficiency in slow-rotating galaxies
• Universal bimodality in kinematic morphology and the divergent pathways to galaxy quenching
• On the kinematic nature of apparent discs at high redshifts: Local counterparts are not dominated by ordered rotation but by tangentially anisotropic random motion
• A stellar dynamical mass measurement of an inactive black hole at redshift 2