Globular cluster kinematics and X-ray emission in the early-type galaxy NGC 1399

¹ Dipartimento di Astronomia, Università di Trieste, via Tiepolo 11, 34131 Trieste, Italy e-mail: srdjan@ts.astro.it
² INAF, Osservatorio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy e-mail: danziger@ts.astro.it
³ Astronomical Observatory, Volgina 7, 11160 Belgrade, Serbia and Montenegro

Received: 13 February 2006
Accepted: 7 July 2006

Abstract

Context.Of the various observational methods used to address the question of dark matter in early-type galaxies there is the possibility of spatial overlap in using kinematics of stars, clusters and X-ray halos.

Aims.To investigate methods for the determination of velocity distribution profiles and deviations from a Gaussian distribution using globular clusters in early-type galaxies, and the implications for dark matter.

Methods.The maximum likelihood method together with standard statistical procedures were used to calculate the velocity dispersion. A new “tracer mass estimator” was applied to obtain a mass estimate based on the globular clusters, which is then compared to the mass obtained using X-rays.

Results.In NGC 1399 the departures from a Gaussian distribution of the velocities at all radial distances are small. Our conclusion is that in spite of the observations that show that the velocity dispersion decreases between 4 and 10 R_e there is evidence that dark matter exists beyond .