The distribution of dark matter in the halo of the early-type galaxy NGC 4636

We present the density structure of dark matter in the outer parts ( to about seven effective radii) of the elliptical galaxy NGC 4636, from the radial velocities of 174 globular clusters (GCs), using the non-parametric, inverse algorithm CHASSIS. We find the galaxy to be rich in dark matter, with R-band mass-to-light ratios (M/L) rising to about 30, at nearly 4R(e); the K-band M/L at about 3R(e) is found to be nearly 10. The result does not depend on applying the method to the red and blue GCs separately. This estimate of M/L is higher than the previous analysis from the same kinematic data. We also find that the dark-matter distribution is highly concentrated toward the inner halo.