The SAURON project – X. The orbital anisotropy of elliptical and lenticular galaxies: revisiting the (V/σ, ɛ) diagram with integral‐field stellar kinematics

By M. Cappellari, Eric Emsellem, R. Bacon, M. Bureau, Roger Davies, P. de Zeeuw, J. Falc'on-Barroso, D. Krajnovi'c, H. Kuntschner, R. McDermid and 4 more. 2007

433 citations recorded by the source corpus.

We analyse the orbital distribution of elliptical (E) and lenticular (S0) galaxies using SAURON integral-field stellar kinematics within about one effective (half-light) radius. We construct the anisotropy diagram, which relates the ratio of the ordered and random motion in a galaxy (V/sigma) to its observed ellipticity (epsilon), for the 48 E/S0 galaxies from the SAURON survey. For a subsample of 24 galaxies consistent with axisymmetry, we use three-integral axisymmetric Schwarzschild dynamical models to recover the detailed orbital distribution, and we find good agreement with the anisotropy derived from the (V/sigma, epsilon) diagram. In a companion paper (Paper IX), we show that the early-type galaxies can be subdivided into two classes of systems with or without a significant amount of specific stellar angular momentum. Here, we show that the two classes have different distributions on the (V/sigma, epsilon) diagram. The slow rotators are more common among the most massive systems and are generally classified as E from photometry alone. Those in our sample tend to be fairly round(epsilon less than or similar to 0.3), but can have significant kinematical misalignments, indicating that as a class they are moderately triaxial, and span a range of anisotropies (delta less than or similar to 0.3). The fast rotators are generally fainter and are classified as either E or S0. They can appear quite flattened (epsilon less than or similar to 0.7), do not show significant kinematical misalignments (unless barred or interacting), indicating they are nearly axisymmetric and span an even larger range of anisotropies (delta less than or similar to 0.5). These results are confirmed when we extend our analysis to 18 additional E/S0 galaxies observed with SAURON. The dynamical models indicate that the anisotropy inferred from the (V/sigma, epsilon) diagram is due to a flattening of the velocity ellipsoid in the meridional plane (sigma(R) > sigma(z)), which we quantify with the beta anisotropy parameter. We find a trend of increasing beta for intrinsically flatter galaxies. A number of the fast rotators show evidence for containing a flattened, kinematically distinct component, which in some cases counter-rotates relative to the main galaxy body. These components are generally more metal rich than the galaxy body. All these results support the idea that fast rotators are nearly oblate and contain disc-like components. The role of gas must have been important for their formation. The slow rotators are weakly triaxial. Current collisionless merger models seem unable to explain their detailed observed properties.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/3b0c1bd263041a195e40407930deef9474464aed

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In Astronomy and Astrophysics

1. M. Cappellari
2. L. Hernquist
3. P. Hopkins
4. T. Naab
5. Volker Springel
6. C. Conroy
7. T. Treu
8. Thomas J. Cox

In Instrumentation

1. M. Cappellari
2. L. Hernquist
3. P. Hopkins
4. T. Naab
5. Volker Springel
6. T. Treu
7. J. Kormendy
8. C. Conroy

Citations in the corpus

• The SAURON project – XVII. Stellar population analysis of the absorption line strength maps of 48 early-type galaxies (2010, background): “This new library provides better fits to our spectra, therefore minimizing template mismatch (see also Cappellari et al. 2007).”
• THE DENSITY PROFILES OF MASSIVE, RELAXED GALAXY CLUSTERS. II. SEPARATING LUMINOUS AND DARK MATTER IN CLUSTER CORES (2012, background): “As discussed in Paper I (Section 9.3), this is a good approximation for luminous, nonrotating giant ellipticals in their central regions (e.g., Gerhard et al. 2001; Cappellari et al. 2007).”
• Triaxial orbit based galaxy models with an application to the (apparent) decoupled core galaxy NGC 4365 (2007, background): “They both consist of two counter-rotating discs, similar to the two main components in NGC 4365: the prograde and retrograde short-axis orbits (Rix et al. 1992; Cappellari et al. 2007).”
• Physical properties and environments of nearby galaxies (2009, background): “Using SAURON data, Cappellari et al. (2007) argue for a different estimator λR = 〈R|V |〉/〈R √ V 2 + σ2〉, where the averages are weighted by flux.”
• THE BARYON CONTENT OF COSMIC STRUCTURES (2009, background): “Elliptical Galaxies Observations of giant elliptical galaxies typically do not extend far enough radially to identify the equivalent of Vc (Cappellari et al. 2007).”
• Two-dimensional kinematics of SLACS lenses – III. Mass structure and dynamics of early-type lens galaxies beyond z ≃ 0.1 (2011, background): “As a comparison to the SLACS systems, Figure 8 also displays the location on the diagram of a sub-sample of 24 SAURON early-type galaxies, whose observables have also been corrected for inclination, analyzed by Cappellari et al. (2007).”
• Galaxy morphology and star formation in the Illustris Simulation at z = 0 (2015, background): “…7, the low-redshift Illustris galaxies occupy a sequence very similar to the one put forth by observational studies (e.g., Emsellem et al. 2007; Cappellari et al. 2007, 2011b): quenched bulge-dominated galaxies with very little rotation are rare and occupy the bottom left tip of the locus of…”
• Photometric scaling relations of lenticular and spiral galaxies (2010, background): “Two examples of such low mass bulges in S0s were discussed by Erwin et al. (2003), and more recently, similar cases were found for a sample of early-type galaxies based on integral-field spectroscopy by Cappellari et al. (2007).”
• 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 (2012, methodology): “In Cappellari et al. (2006), it was shown that, when the surface brightness distribution is accurately reproduced and good quality integral-field data are available, simple two-integral Jeans models measure masses nearly as accurate as those of Schwarzschild’s models, with errors of 6 per cent.”
• The ATLAS3D project - II. Morphologies, kinemetric features and alignment between photometric and kinematic axes of early-type galaxies (2011, background): “…momentum, the early-type galaxies separate into slow and fast rotators (Emsellem et al. 2007), where slow rotators are weakly triaxial, but not far from isotropic, while fast rotators are nearly axisymmetric, intrinsically flatter and span a large range of anisotropies (Cappellari et al. 2007).”
• Measuring the inclination and mass-to-light ratio of axisymmetric galaxies via anisotropic Jeans models of stellar kinematics (2008, methodology): “It was motivated by our modeling results on the orbital distribu ion of a sample of real galaxies (Cappellari et al. 2007).”
• Dynamical modelling of luminous and dark matter in 17 Coma early-type galaxies (2007, background): “A suppression of vertical energy (corresponding to βϑ > 0) has recently been reported for SAURON ellipticals (Cappellari et al. 2007).”
• Structure and Kinematics of Early-Type Galaxies from Integral Field Spectroscopy (2016, methodology): “However they were found to be only weakly triaxial and actually close to spherical and isotropic within 1Re (Cappellari et al. 2007).”
• THE DENSITY PROFILES OF MASSIVE, RELAXED GALAXY CLUSTERS. I. THE TOTAL DENSITY OVER THREE DECADES IN RADIUS (2012, methodology): “Prior studies (e.g., Carter et al. 1999; Gerhard et al. 2001; Cappellari et al. 2007, and see references in Section 6.3) have shown this to be a good approximation for luminous, non-rotating ellipticals in their central regions, with a possible tendency toward slightly radial orbits.”
• VLT/VIMOS integral field spectroscopy of luminous and ultraluminous infrared galaxies: 2D kinematic properties (2013, neutral): “For E/S0, v andσ are luminosityweighted square quantities derived, respectively, from the velocity field and velocity dispersion maps (see details in Cappellari et al. 2007).”
• The ATLAS3D project – I. A volume-limited sample of 260 nearby early-type galaxies: science goals and selection criteria (2010, background): “…classify these galaxies in a way that is more r bust than the(V/σ, ε) diagram, is nearly insensitive to projection effects (Emsellem et al. 2007; Cappellari et al. 2007).λR relates directly to their formation, and is precisely reproducible in current cosmological simulations (Jesseit et al.…”
• Galaxy Masses: A Review (2013, background): “In fact, these suggest that both fast-rotator ETGs (Cappellari et al. 2007; Thomas et al. 2009) and disk galaxies have a dynamical structure roughly characterized by a flattening of the velocity ellipsoid in the z direction parallel to the galaxy symmetry axis (Gerssen et al.”