Kinematics and metallicities of globular clusters in M104

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Abstract
We have obtained spectra for globular cluster candidates in M104 with the Low Dispersion Survey Spectrograph (LDSS-2) on the William Herschel Telescope, confirming 34 objects as M104 globular clusters. We find a cluster velocity dispersion of ∼260 km s −1, and the projected mass estimator gives a mass of 5.0 (3.5,6.7) × 1011 M⊙ for M104 within a projected radius of ∼ 330 arcsec (14 kpc for D = 8.55 Mpc). Our best estimate for the mass-to-light ratio is M/LVt = 16 −5.0+5.5 within the same radius. Considering all of the possible sources of uncertainty, we find a lower limit of M/Lv=5.3, which is larger than the M/Lv ratio found from rotation curve analyses inside 180 arcsec. We thus conclude that the mass-to-light ratio increases with radius, or in other words that M104 possesses a dark matter halo. There is a marginal detection of rotation in the M104 cluster system at the 92.5 per cent confidence level; larger samples will be needed to investigate this possibility. Interestingly, the M104 globular cluster and planetary nebulae (PNe) kinematics are roughly consistent inside ∼ 100 arcsec. Finally, we find a mean cluster metallicity of [Fe/H] = − 0.70 ± 0.3, which is more typical of clusters in giant elliptical (gE)/cD galaxies than it is of clusters in other spirals.

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