Kinematics and metallicities of globular clusters in M104

Abstract

We have obtained spectra for globular cluster candidates in M104 with LDSS-2 on the William Herschel Telescope, confirming 34 objects as M104 globular clusters. We find a cluster velocity dispersion of ∼ 260 km/sec, and the Projected Mass Estimator gives a mass of 5.0 (3.5,6.7) × 10 11 M ⊙ for M104 within a projected radius of ∼ 330 ′′ (14 kpc for D=8.55 Mpc). Our best estimate for the mass-to-light ratio is M/L VT = 16 +5.5 −5.0 within the same radius. Considering all of the possible sources of uncertainty, we find a lower limit of M/L V = 5.3, which is larger than the M/L V found from rotation curve analyses inside 180 ′′ . 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% 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 ′′ . Finally, we find a mean cluster metallicity of [Fe/H] = −0.70 ± 0.3, which is more typical of clusters in gE/cD galaxies than it is of clusters in other spirals.

Spectra of globular clusters in the Sombrero galaxy: evidence for spectroscopic metallicity bimodality★

“…Hence, within the uncertainties, the spectroscopic metallicities we derive here are in good agreement with the photometric ones. For example, the mean spectroscopic metallicity of [Fe/H]∼−1.2 agrees well with that estimated previously by Bridges et al (1997, 2007) and Larsen et al (2002). Furthermore, the mean difference in [Fe/H] for the four GCs in common with those studied in Larsen et al (2002) is only −0.14 ± 0.07 dex (our–theirs), which is small within the uncertainties.…”

“…4, in which the different studies are coded by symbol type. Nearly all of the repeats are from the 2dF and William Herschel Telescope (WHT) studies of Bridges et al (1997, 2007). There is no evidence for a zero‐point offset in the velocity scales, with median differences (in the stated sense of new–old) of −3 and −17 km s −1 for the two studies, respectively.…”

Hubble Space Telescope photometry of globular clusters in the Sombrero galaxy

“…A similar number of GCs was found by Bridges & Hanes (1992) who also estimated a mean metallicity of based on colours. This mean metallicity was confirmed spectroscopically by Bridges et al (1997) who obtained a mean for a sample of 34 GCs. Ground‐based Charge‐coupled device (CCD) imaging of the GCS by Forbes et al (1997a) found some tentative evidence for two populations of GCs.…”

Chandra and XMM-Newton detection of large-scale diffuse X-ray emission from the Sombrero galaxy

“…Given the K ‐band magnitude of Sombrero, the total stellar mass is estimated to be 1.6 × 10 11 M ⊙ , according to the K ‐band mass‐to‐light relation of Bell & de Jong (2001). However, Bridges et al (1997) found a kinematic mass about three times of this value within a projected radius of ∼15 kpc. Therefore, a second gravitational component, i.e.…”