Recovering the intrinsic shape of early-type galaxies

Abstract

We investigate how well the intrinsic shape of early-type galaxies can be recovered when both photometric and two-dimensional stellar kinematic observations are available. We simulate these observations with galaxy models that are representative of observed oblate fast-rotator to triaxial slow-rotator early-type galaxies. By fitting realistic triaxial dynamical models to these simulated observations, we recover the intrinsic shape (and mass-to-light ratio), without making additional (ad-hoc) assumptions on the orientation. For (near) axisymmetric galaxies the dynamical modelling can strongly exclude triaxiality, but the regular kinematics do not further tighten the constraint on the intrinsic flattening significantly, so that the inclination is nearly unconstrained above the photometric lower limit even with two-dimensional stellar kinematics. Triaxial galaxies can have additional complexity in both the observed photometry and kinematics, such as twists and (central) kinematically decoupled components, which allows the intrinsic shape to be accurately recovered. For galaxies that are very round or show no significant rotation, recovery of the shape is degenerate, unless additional constraints such as from a thin disk are available.

12 pages, 7 figures, PDFLaTeX, accepted to MNRAS, minor revisions

References in corpus (6)

• The SAURON project -- IX. A kinematic classification for early-type galaxies
• Measuring the inclination and mass-to-light ratio of axisymmetric galaxies via anisotropic Jeans models of stellar kinematics
• Triaxial orbit based galaxy models with an application to the (apparent) decoupled core galaxy NGC 4365
• The SAURON project - XII. Kinematic substructures in early-type galaxies: evidence for disks in fast rotators
• Recovery of the internal orbital structure of galaxies
• Axisymmetric orbit models of N-body merger remnants: a dependency of reconstructed mass on viewing angle

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