Mass distribution and orbital anisotropy of early-type galaxies: constraints from the Mass Plane

Details Mass distribution and orbital anisotropy of early-type galaxies: constraints from the Mass Plane Mass distribution and orbital anisotropy of early-type galaxies: constraints from the Mass Plane

2008-06-03

arxiv.org/abs/0806.0570v2

Astronomy and Astrophysics

Astrophysics

MNRAS in press, 15 pages, 9 figures. Revised Section 4, Fig. 9 and discussion. Added references

Scientific paper

10.1111/j.1365-2966.2008.13745.x

Massive early-type galaxies are observed to lie on the Mass Plane (MP), a two-dimensional manifold in the space of effective radius R_e, projected mass M_p (measured via strong gravitational lensing) and projected velocity dispersion sigma within R_e/2. The MP is less `tilted' than the Fundamental Plane, and the two have comparable associated scatter. This means that c_e2=2*G*M_p/(R_e*sigma^2) is a nearly universal constant in the range sigma=175-400 km/s. This finding can be used to constrain the mass distribution and internal dynamics of early-type galaxies. We find that a relatively wide class of spherical galaxy models has values of c_e2 in the observed range, because c_e2 is not very strongly sensitive to the mass distribution and orbital anisotropy. If the total mass distribution is isothermal, a broad range of stellar luminosity profile and anisotropy is consistent with the observations, while NFW dark-matter halos require more fine tuning of the stellar mass fraction, luminosity profile and anisotropy. If future data can cover a broader range of masses, the MP could be seen to be tilted and the value of any such tilt would provide a discriminant between models for the total mass-density profile of the galaxies. [Abridged]

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