Stellar kinematics in the remote Leo II dwarf spheroidal galaxy -- Another brick in the wall

摘要

We present the projected velocity dispersion profile for the remote(d=233kpc) Galactic dwarf spheroidal (dSph) galaxy Leo II, based on 171discrete stellar radial velocities that were obtained from medium-resolutionspectroscopy using the FLAMES/GIRAFFE spectrograph at the European SouthernObservatory, Chile. The dispersion profile of those stars with good membershipprobabilities is essentially flat with an amplitude of 6.6+-0.7 km/s over thefull radial extent of our data, which probe to the stellar boundary of thisgalaxy. We find no evidence of any significant apparent rotation or velocityasymmetry which suggests that tidal effects cannot be invoked to explain LeoII's properties. From basic mass modeling, employing Jeans' equation, we derivea mass out to the limiting radius of (2.7+-0.5) 10^7 Msun and a global mass tolight ratio of 27-45 in solar units, depending on the adopted total luminosity.A cored halo profile and a mild amount of tangential velocity anisotropy isfound to account well for Leo II's observed kinematics, although we cannotexclude the possibility of a cusped halo with radially varying velocityanisotropy. All in all, this galaxy exhibits dark matter properties whichappear to be concordant with the other dSph satellites of the Milky Way, namelya halo mass profile which is consistent with a central core and a total masswhich is similar to the common mass scale seen in other dSphs.