2000A&A...363...41H

We report on high angular resolution near-infrared (NIR) observations of three galaxy clusters at different redshifts using adaptive optics (AO). In the case of the barred spiral UGC 1347 in Abell 262 we presented the first AO results obtained using a laser guide star. The observations have been carried out with the MPE/MPIA adaptive optics laser guide star system ALFA and the ESO AO system ADONIS combined with the SHARP II+ camera built at MPE. The three clusters are well suited for high resolution investigations since bright field stars for tip-tilt or wavefront sensing are located close to the line of sight to cluster galaxies. In summary our high angular resolution NIR data combined with other information clearly indicates star formation activity or interaction between cluster members at all three redshifts. The results and implications for future high angular resolution adaptive optics observations are discussed in the framework of current galaxy and cluster evolution models. For two barred galaxies in the Abell 262 cluster, UGC 1344 and UGC 1347, we interpret our NIR imaging results in combination with published radio, far-infrared, and Hα data in the framework of a star formation model. In addition to the star-forming resolved NIR nucleus in UGC 1347 we found a bright and compact region of recent and enhanced star formation at one tip of the bar. The L_K/L_Lyc ratio as well as the V - K color of that region imply a starburst that happened about 10⁷ years ago. For UGC 1344 we find that the overall star formation activity is low and that the system is deficient in fuel for star formation. The importance of star formation in galaxy clusters is also supported by a comparison of seeing corrected nuclear bulge sizes of a sample of spiral galaxies within and outside the central HI deficient zone of the Abell 262 and Abell 1367 clusters. We find that the galaxies inside the Abell radii of both clusters show a tendency for more compact bulges than those outside. This phenomenon could be due to increased star formation activity triggered by interactions of cluster members inside the Abell radius. The star formation activity in the two higher redshift clusters J1836.3CR and PKS 0743-006 is investigated via comparison to GISSEL stellar population models in JHK two-color-diagrams. While J1836.3CR is consistent with an evolved cluster, the objects in the field of PKS 0743-006 show indications of more recent star formation activity. The central object in J1836.3CR shows a radial intensity profile that is indicative for cD galaxies in a rich cluster environment. Extended wings in its light distribution may be consistent with recent or ongoing galaxy-galaxy interaction in this cluster.