[Paper Review] Morphology of the Virgo Cluster: Gas versus Galaxies

S. Schindler, B. Binggeli+1 more|arXiv (Cornell University)|Nov 30, 1998

Galaxies: Formation, Evolution, Phenomena10 citations

TL;DR

This study compares the spatial distribution of galaxies and intra-cluster gas in the Virgo Cluster using ROSAT X-ray data and the Virgo Cluster Catalog. It identifies three main subclusters (M87, M49, M86) via a new statistical decomposition method, finds steeper gas density profiles than galaxy profiles in cluster centers, and reveals that gas contributes ~3× more mass than galaxies in M87 but only 1–14% in M49, with mass-to-light ratios near 500 M☉/L☉.

ABSTRACT

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. 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 beta-models, allowing analytic deprojection. Comparison of these profiles reveals, that there is no general luminosity segregation. The gas density profile is steeper than the galaxy density profile in the inner part, while this trend is reversed in the outer part. 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. 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 is inferred from the distribution of the X-ray gas. In the M87 subcluster the gas mass is about three times the mass in galaxies, while it accounts only for 8% to 14% of the total mass at 0.4 and 1 Mpc, 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 mass-to-light ratios show relatively constant values around 500Msol/Lsol.

Motivation & Objective

• To quantitatively compare the spatial morphology of galaxies and intra-cluster gas in the Virgo Cluster.
• To identify and characterize substructures within the Virgo Cluster using statistical decomposition of galaxy and X-ray distributions.
• To analyze radial density profiles of galaxies and X-ray gas in subclusters using beta-models for deprojection.
• To determine mass distributions and mass-to-light ratios in the M87 and M49 subclusters based on X-ray gas deprojection.
• To investigate luminosity segregation and Hubble type-dependent spatial distributions in the cluster.

Proposed method

• Utilized the Virgo Cluster Catalog for optical galaxy positions and magnitudes.
• Combined with ROSAT All-Sky Survey X-ray data to map intra-cluster gas distribution.
• Applied a new statistical method for subcluster decomposition based on spatial clustering of galaxies and X-ray emission.
• Fitted radial galaxy and X-ray density profiles with beta-models to enable analytic deprojection of 3D density profiles.
• Calculated differential and integrated mass density profiles from X-ray gas temperature and density via hydrostatic equilibrium.
• Computed mass-to-light ratios using total gravitating mass and total V-band luminosity of galaxies.

Experimental results

Research questions

• RQ1 How do the spatial distributions of galaxies and intra-cluster gas compare in the Virgo Cluster?
• RQ2 What is the substructure composition of the Virgo Cluster in terms of galaxy and X-ray gas distributions?
• RQ3 Are there differences in radial density profiles between galaxies and X-ray gas in the cluster subcomponents?
• RQ4 What is the relative contribution of gas and galaxies to the total mass in the M87 and M49 subclusters?
• RQ5 How do mass-to-light ratios and mass fractions vary across different subclusters and Hubble types?

Key findings

• The galaxy and gas distributions in the Virgo Cluster show significant structural similarity, both exhibiting three dominant subclusters centered on M87, M49, and M86.
• The gas density profile is steeper than the galaxy profile in the inner regions of subclusters, but the trend reverses in the outer parts.
• Poorer subclusters (lower mass) have steeper radial profiles, indicating greater compactness in both optical and X-ray emissions.
• Late-type galaxies are more extended than early-type galaxies, confirming known morphological segregation.
• In the M87 subcluster, the gas mass is approximately three times the stellar mass, while in M49, gas contributes only 1% of the total mass, an unusually low value.
• Mass-to-light ratios are relatively constant at around 500 M☉/L☉ across the subclusters, indicating consistent gravitational mass relative to luminous matter.