1999A&A...343..420S

We draw a quantitative comparison of the distribution of the galaxies and the intra-cluster gas in the Virgo cluster by extending the morphological analysis by Binggeli et al. (1987) to the intra-cluster gas. We use the Virgo Cluster Catalog in combination with data from the ROSAT All-Sky Survey. The galaxy distribution and the gas distribution are relatively similar. The steep density gradient southwest of M87 previously observed in the optical is also seen in the X-ray emission. In both wavebands the irregular structure of Virgo can be decomposed into three major subclusters centred on M87, M49, and M86. A new statistical method of subcluster decomposition is applied. Radial galaxy and X-ray density profiles of the three subclusters are fitted with β-models, allowing analytic deprojection. Comparison of these profiles reveals no significant difference between the galaxy number density and the smoothed galaxy luminosity density if the inner part is excluded (r<60', dominated by the central giant galaxy), i.e. there is no general luminosity segregation in the cluster. The gas density profile is steeper than the galaxy density profile in the inner part (again excluding the central galaxy), while this trend is reversed in the outer part. The turning point is around 300kpc. A comparison among the subclusters shows the poorer the subcluster the steeper its radial profile, i.e. the more compact it is, both in the optical and the X-rays. This is in general agreement with recent N-body simulations by Navarro et al. (1997ApJ...490..493N). The subcluster profiles for different Hubble types confirm the well-known result that the distribution of the late-type galaxies is more extended than the early types. Differential and integrated mass density profiles of the different components in the M87 and M49 subclusters are presented. The total, gravitating mass (dominated by dark matter) is inferred from the distribution of the X-ray gas assuming hydrostatic equilibrium. In the M87 subcluster the gas mass is about three times the mass in galaxies (assuming a constant M/L=20 for the single galaxies), while it accounts only for 8% to 14% of the total mass at 0.4 and 1Mpc, respectively. In the M49 subcluster there is more mass in the galaxies than in the gas and the gas-to-total mass fraction is only 1%, which is unusually low for a cluster. The profiles of the projected mass-to-light ratio show relatively constant values around 500M_☉/L_☉,B.