The globular cluster systems of the three Virgo ellipticals

Abstract

An analysis of the systems of globular clusters around three of the brightest elliptical galaxies in the Virgo cluster (NGC 4406, NGC 4472, and NGC 4486) has been carried out with a digital detector whose field is 9 arcmin on a side. The point-source detections reach to g = 25 mag, and nearly all galaxies brighter than g ≈ 22.5 mag can be eliminated. The author finds that the colors of the globular clusters show no detectable spatial gradient, and that the median color and the distribution in color are independent of cluster luminosity and spatial position within the halo of the underlying elliptical galaxy. The median color of the Virgo globular systems is slightly redder than that of the set of globulars in the Milky Way, implying a mean metallicity difference of about a factor of 3. The magnitude distribution is not a power law, having a definite turnover at g ≈ 24.2 mag, which constrains the distance to the Virgo cluster if one believes in a universal globular cluster luminosity function. In each of the three cases, the globular cluster system has the same ellipticity and position angle as the light of the halo of the underlying galaxy, but is more extended spatially in the case of NGC 4472 and NGC 4486.