Abundant Dust Found in Intergalactic Space

Galactic dust constitutes approximately half of the elements more massivethan helium produced in stellar nucleosynthesis. Notwithstanding the formationof dust grains in the dense, cool atmospheres of late-type stars, there stillremain huge uncertainties concerning the origin and fate of galactic stardust.In this paper, we identify the intergalactic medium (i.e. the region betweengravitationally-bound galaxies) as a major sink for galactic dust. We discovera systematic shift in the colour of background galaxies viewed through theintergalactic medium of the nearby M81 group. This reddening coincides withatomic, neutral gas previously detected between the group members. Thedust-to-HI mass ratio is high (1/20) compared to that of the solar neighborhood(1/120) suggesting that the dust originates from the centre of one or more ofthe galaxies in the group. Indeed, M82, which is known to be ejecting dust andgas in a starburst-driven superwind, is cited as the probable main source.Comment: 5 pages, 3 figures, 1 table. ApJ Letters in pres