The Nature of a Dusty Ring in Virgo

Abstract

We detected a ring-like distribution of far-infrared emission in the direction of the center of the Virgo cluster. We studied this feature in the FIR, radio, and optical domains, and deduced that the dust within the feature reddens the galaxies in the direction of the Virgo cluster but does not affect stars within the Milky Way. This is likely to be a dusty feature in the foreground of the Virgo cluster, presumably in the galactic halo. The HI distribution follows the morphology of the FIR emission and shows peculiar kinematicbehavior. We propose that a highly supersonic past collision between an HI cloud and the Galactic HI formed a shock that heated the interface gas to soft X-ray temperatures. HI remnants from the projectile and from the shocked Galactic HI rain down onto the disk as intermediate velocity gas. Our finding emphasizes that extragalactic astronomy must consider the possibility ofextinction by dust at high Galactic latitude and far from the Galactic plane, which may show structure on one-degree and smaller scales. This is particularly important for studies of the Virgo cluster, for example in the determination of the Hubble constant from Cepheids in cluster galaxies.