In addition to the topics covered above, the ISO archive will soon offer a wealth of data on a wide variety of extragalactic subjects affecting our understanding of normal galaxies. Studies in galaxy clusters and groups for instance have targeted the population of medium-distant clusters at z = 0.1-0.3 (Lémonon et al. 1999, Fadda & Elbaz 1999; Metcalfe et al. 1999). Stickel et al. (1998) have reported the detection of intracluster dust in Coma at 200 µm, and related it to the cooling flows revealed by X-ray observations, while Xu, Sulentic & Tuffs (1999) have studied intergalactic star formation in Stefan's Quintet using mid-infrared data. Charmandaris et al. (1999) and Gallais et al. (1999) have taken a detailed look at some of the nearest interacting galaxy systems in order to study collisionally induced star formation.
Beichman et al. (1999) and Gilmore & Unavane (1998) report on deep searches for mid-infrared haloes around edge-on galaxies, and place upper limits on the contribution to the missing mass by low-mass stars. Jarrett et al. (1999) report on mid-infrared detection of a bridge of interstellar gas and magnetized plasma created between two galaxies after a collision which caused the two disks to pass through each other and entangle the interstellar media.
Observations of Local Group members allow detailed analysis of the ISM and star formation on the few parsec scale, and are a crucial stepping stone to understanding the integrated emission in more distant objects. Such detailed studies of HII and star formation regions, or of the stellar population in the Magellanic Clouds are reported by Comerón & Claes (1999), Henning et al. (1999), Loup et al. (1999), Missoulis et al. (1999), and Vermeij, van der Hulst & Baluteau (1999).