Also, we detected CO in four galaxies in which HI has not been seen, allowing us to obtain their distances for the first time. This indicates that CO linewidths can be used at least as reliably as HI for distance determinations, which becomes important for those galaxies where reliable HI data is not available, due to environmental effects. Our preliminary findings are that the CO line-centers agree with those of HI to within 2sigma and the linewidths agree to within 1sigma. As these are very weak sources, our integration times went as high as 128 minutes. Our detections have a lower gas-mass limit of 0.5 K-km/s or about 4x10(8) Msun the strongest detections indicate masses of approximately 2x10(9) Msun. ![]() Using data obtained with the IRAM-Granada 30-m dish, we detected CO in 13 out of the 32 galaxies searched in the Hercules cluster (z = 0.03). molecular gas is more tightly bound to the center of the disk, and so CO does not suffer these effects. In rich cluster environments, however, the HI disks of spirals are disrupted or even stripped due to interactions with the intergalactic medium. Previous Tully-Fisher calculations have depended on lambda 21 cm linewidths. We are studying the feasibility of using the CO lambda 1.3 mm and lambda 2.6 mm lines for performing Tully-Fisher calculations on galaxies in distant rich clusters. The temperature structure of A1750 and the lack of gas distorsion in the region of interaction give support for an early phase of merger, before core passage. Moreover, optical observations suggest a possible 3 body interaction. The comparison between simulations and X-ray data suggests that the subcluster in A3921 is at the distance of closest core passage. In both clusters we detect a complex temperature structure indicating interaction in the merging direction. We present two targets from our XMM-Newton guaranteed time programme: A3921, an off-set merger between a main cluster and a smaller subcluster, and the bimodal cluster A1750. X-ray spectro-imaging observations are well suited to deeper investigation of the dynamical processes behind this substructure. Hydrodynamical simulations show that a merging event strongly changes the physical characteristics of the intracluster medium, and in particular that the temperature structure is a good indicator of cluster formation history through merger events. ![]() The new X-ray satellites, XMM-Newton and Chandra, have begun to give us a new vision of clusters of galaxies and their dynamical status.
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