The Distribution of Stellar Orbits in the Giant Elliptical Galaxy NGC 2320

Abstract

We present direct observational constraints on the orbital distribution of the stars in the giant elliptical NGC 2320. Long-slit spectra along multiple position angles are used to derive the stellar line-of-sight velocity distribution within one effective radius. In addition, the rotation curve and dispersion profile of an ionized gas disk are measured from the [OIII] emission lines. After correcting for the asymmetric drift, we derive the circular velocity of the gas, which provides an independent constraint on the gravitational potential.To interpret the stellar motions, we build axisymmetric three-integral dynamical models based on an extension of the Schwarzschild orbit-superposition technique. We consider two families of gravitational potential, one in which the mass follows the light (i.e., no dark matter) and one with a logarithmic gravitational potential.Using χ 2 -statistics, we compare our models to both the stellar and gas data to constrain the value of the V-band mass-to-light ratio Υ V . We find Υ V = 15.0 ± 0.6 h 75 for the mass-follows-light models and Υ V = 17.0 ± 0.7 h 75 for the logarithmic models. For the latter, Υ V is defined within a sphere of 15 ′′ radius.Models with radially constant Υ V and logarithmic models with dark matter provide comparably good fits to the data and possess similar dynamical structure. Across the full range of Υ V permitted by the observational constraints, the models are radially anisotropic in the equatorial plane over the radial range of our kinematical data (1 ′′ ∼ < r ∼ < 40 ′′ ). Along the true minor axis, they are more nearly isotropic. The best fitting model has σ r /σ total ≃ 0.7, σ φ /σ total ≃ 0.5 − 0.6 and σ θ /σ total ≃ 0.5 in the equatorial plane.

Dynamics of Stars and Globular Clusters in M87

“…We used similar techniques to examine the uncertainty in a high-redshift galaxy's mass as implied by a measurement of its central velocity dispersion -an important step in determining H 0 from certain gravitational lens systems (Romanowsky & Kochanek 1999, hereafter Paper I). Other recent orbit modeling efforts have concentrated on applying the method to three-integral axisymmetric systems (e.g., van der Marel et al 1998;Cretton & van den Bosch 1999;Gebhardt et al 2000;Cretton, Rix, & de Zeeuw 2000). Here we extend our spherical method to include the discrete velocities of GCs.…”

Solar System Tests of Some Models of Modified Gravity Proposed to Explain Galactic Rotation Curves without Dark Matter

“…Logarithmic corrections to the Newtonian gravitational potential have been recently used to phenomenologically tackle the problem of dark matter in galaxies [18][19][20][21][22][23]. For example, Fabris and Campos [22] used…”

“…Since we are interested in taking the ratios of the perihelia, there is no need to exactly compute (19); the eccentricities of the Solar System planets are small and similar for all of them, so that we will reasonably assume that G(e A;β )/G(e B ; β) ≈ 1. Note that β = 0 would yield a vanishing apsidal precession because G(e; 0) = 0 (the case β = 1 is not relevant because it would yield a constant additional potential and no extra force).…”

Evidence for a Supermassive Black Hole in the S0 Galaxy NGC 3245

“…For IC 1459, where the nuclear disk becomes rounder at small radii and the innermost velocities appear to depart from a Keplerian curve, Verdoes Kleijn et al (2000) suggest that asymmetric drift may be important. Similarly, Cretton, Rix, & de Zeeuw (2000) describe an application of an asymmetric drift correction to the gas velocities in the elliptical galaxy NGC 2320, in order to derive the true circular velocity from the observed rotation velocity of the gas. On the other hand, most previous gasdynamical BH measurements have assumed that the gas velocity dispersion results from a local "" microturbulence ÏÏ and that the gas still rotates at the circular velocity.…”