Complex extended line emission in the cD galaxy in Abell 2390

Abstract

This paper reports maps of the cD galaxy in the rich z=0.23 cluster Abell 2390 at UV, [OII], L alpha and H alpha wavelengths. Spatially resolved UV and optical spectra were obtained with STIS on the Hubble Space Telescope; the 2 arcsec wide slit was aligned close to the long axis and blue lane of the galaxy and includes all the inner bright features seen in WFPC2 images. The L alpha is seen in emission from several bright knots and over an extended region from 4 arcsec NW to 2 arcsec SE of the nucleus. Three of these knots have detected UV continuum as well. H alpha images were obtained with OSIS at CFHT; both H alpha and [O II] show extended emission that roughly trace L alpha, primarily to the NW. Notable differences between the spatial distributions of H alpha, L alpha and [O II] emission and the blue knots in the galaxy may be the result of inhomogeneous dust extinction, or variations in ionisation. The L alpha emission velocities depend the uncertain identification with features in the undispersed images; there is strong evidence for resolved emission knots to have large velocities, >~1000 km/s, indicative of infall. The L alpha spectrum shows a sharp cutoff which may be due to absorption; we entertain the possibility that this edge is due to an shell of absorbing gas, outflowing at several thousand km/s.