Structural Parameters of the M87 Globular Clusters

TL;DR

This study measures the sizes, shapes, and color distributions of approximately 2000 globular clusters in M87 using deep Hubble images, revealing size differences based on metallicity and location, and a bimodal color distribution.

Contribution

It provides detailed structural parameters for M87's globular clusters, including size, ellipticity, and color bimodality, using advanced PSF-convolved profile fitting techniques.

Findings

Cluster sizes peak at ~2.5 pc, similar to Milky Way clusters.

Metal-poor clusters are on average 24% larger than metal-rich ones.

Cluster size increases with galactocentric distance.

Abstract

We derive structural parameters for ~2000 globular clusters in the giant Virgo elliptical M87 using extremely deep Hubble Space Telescope images in F606W (V) and F814W (I) taken with the ACS/WFC. The cluster scale sizes (half-light radii r_h) and ellipticities are determined from PSF-convolved King-model profile fitting. We find that the r_h distribution closely resembles the inner Milky Way clusters, peaking at r_h~2.5 pc and with virtually no clusters more compact than r_h ~ 1 pc. The metal-poor clusters have on average an r_h 24% larger than the metal-rich ones. The cluster scale size shows a gradual and noticeable increase with galactocentric distance. Clusters are very slightly larger in the bluer waveband V a possible hint that we may be beginning to see the effects of mass segregation within the clusters. We also derived a color magnitude diagram for the M87 globular cluster system which show a striking bimodal distribution.