Context. Level population inversion of hydrogen atoms in ionized gas may lead to stimulated emission recombination lines, and the level populations can turn be affected by powerful emissions. Aims. In this work interaction radiation fields is studied. The effect emissions on line profiles also investigated. Methods. Our previous nl-model for calculating lines improved. effects continuum are con...

Sub-arcsecond images, taken in B, R, and Hα filters, and area spectroscopy obtained with the WIYN 3.5-m telescope provide the basis for an investigation of the unusual structures in the stellar body and ionized gas in and around the Perseus cluster central galaxy, NGC 1275. Our Hα filter is tuned to gas at the velocity of NGC 1275, revealing complex, probably unresolved, small-scale features in...

We report the detection of ionized intracluster gas in the globular cluster 47 Tucanae. Pulsars in this cluster with a negative period derivative, which must lie in the distant half of the cluster, have significantly higher measured integrated electron column densities than the pulsars with a positive period derivative. We derive the plasma density within the central few pc of the cluster using...

We present a multiwavelength analysis of a compact group of galaxies infalling at high speed into the dynamically young cluster Abell 1367. Peculiar morphologies and unusually high Hα emission are associated with two giant galaxies and at least ten dwarfs/extragalactic HII regions, making this group the region with the highest density of star formation activity ever observed in the local cluste...

Echo mapping exploits light travel time delays, revealed by multi-wavelength variability studies, to map the geometry, kinematics, and physical conditions of reprocessing sites in photo-ionized gas flows. In AGNs, the ultra-violet to near infra-red light arises in part from reprocessing of EUV and X-ray light from a compact and erratically variable source in the nucleus. The observed time delay...