Intergalactic cold dust in the NGC 4631 group

We have detected extraplanar cold dust at distances out to >10 kiloparsecs, situated in the halo of the interacting galaxy NGC 4631, The dust emission disk is much thinner than the warped Ht disk, and new structures emerge, I n particular, a giant are has been found that is linked to anomalies in the kinematical structure of the atomic gas. Most of the extraplanar dust is c losely associated with Hr spurs that have been found earlier [Weliachew, L, , Sancisi, R, & Guelin, M. (1978) Astron. Astrophys. 65, 37-45; Rand, R, J, (1994) Astron.;Astrophys. 285, 833-856]. These spurs obviously are traces of the interaction [Combes, F. (1978) Astron. Astrophys. 65, 47-55], The du st emission within the plane reaches the border of the optical disk The act ivity of the disk of NGC 4631 is moderately enhanced by the interaction, bu t no gas moving in the z-direction could be found [Rand, R, J., Kulkarni, S , R & Hester, J, J, (1992) Astrophys. J. 396, 97-103; Golla, G., Dettmar, R .-J, & Domgorgen, H, (1996) Astron. Astrophys. 313, 439-447], Hence, it see ms unlikely that strong winds have deposited the high-z dust. Instead, the coincidence with the Hr features suggests that we see a track left behind b y the interaction. In addition, the Hr shows a supershell formed by an impa ct [Rand, R, J, & Stone, J, M, (1996) Astron. J. 111, 190-196] in the zone where the dust trail crosses the disk. This region is also characterized by disturbances in the distribution of the H alpha light. The masses associat ed with the dust can be estimated only very roughly on the basis of the exi sting data; they are of the order of a few 10(9) M-. of gas.