ar X iv : 0 90 5 . 28 33 v 1 [ as tr o - ph . C O ] 1 8 M ay 2 00 9 A Search for Dust Emission in the Leo Intergalactic Cloud ∗

We present a search for infrared dust emission associated with the Leo cloud, a large intergalactic cloud in the M96 group. Mid-infrared and far-infrared images were obtained with IRAC and MIPS on the Spitzer Space Telescope. Our analysis of these maps is done at each wavelength relative to the Hi spatial distribution. We observe a probable detection at 8 μm and a marginal detection at 24μm associated with the highest Hi column densities in the cloud. At 70 and 160μm, upper limits on the dust emission are deduced. The level of the detection is low so that the possibility of a fortuitous cirrus clump or of an overdensity of extragalactic sources along the line of sight can not be excluded. If this detection is confirmed, the quantities of dust inferred imply a dust to gas ratio in the intergalactic cloud up to a few times solar but no less than 1/20 solar. A confirmed detection would therefore exclude the possibility that the intergalactic cloud has a primordial origin. Instead, this large intergalactic cloud could therefore have been formed through interactions between galaxies in the group. Subject headings: ISM: clouds – ISM: individual (Leo cloud) – galaxies: intergalactic medium – infrared: ISM This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. California Institute of Technology, Pasadena CA 91125, USA UMR7550, Centre de données Astronomiques de Strasbourg (CDS), 67000 Strasbourg, France NASA Herschel Science Center, California Institute of Technology, Pasadena CA 91125, USA Department of Astronomy, Universtiy of Massachusetts, Amherst, MA 01003, USA Department of Astronomy/NAIC, Cornell University, Ithaca, NY 14853, USA