Kinematics of Globular Clusters in M49 and M87

Abstract

We present recent multi-object spectroscopy of globular clusters in the Virgo gEs M49 and M87. In M49, we have a total of 144 confirmed clusters out to 8 arcmin radius (∼ 6 Reff or 35 kpc). We find that the blue (metal-poor) clusters have both a higher velocity dispersion and rotation than the red (metal-poor) clusters. For the metal-rich population we place an upper limit of (v/σ)proj < 0.34 at 99% confidence. We calculate the velocity dispersion as a function of radius, and show that this is consistent with isotropic cluster orbits and the M49 mass distribution determined from X-ray data. For M87, we combine new CFHT data with previous data to obtain a total sample of 278 clusters out to 10 arcmin radius (∼ 45 kpc). We find a similar global rotation for the metal-poor and metal-rich clusters of 160–170 km/sec. Beyond ⋍ 2 Reff (15 kpc), both the metal-poor and metal-rich clusters appear to rotate about the photometric minor axis. The combined cluster sample is consistent with isotropic orbits, but when considered separately, the metal-poor clusters show significant tangential bias of βcl ⋍ −0.4, while the metal-rich clusters show a radial bias with βcl ⋍ +0.4. In both galaxies, the metal-rich and metal-poor clusters share different kinematics, but there is no clear preference for any one formation scenario.