Ionized Gas in Elliptical Galaxies

Abstract

We report observations of H alpha nebulosities in the X-ray bright elliptical galaxies which are members of nearby groups of galaxies or clusters. Our sample includes NGC 1399, NGC 1600, NGC 2563, NGC 3607, NGC 4203, NGC 4636, NGC 4753 and NGC 5044. Some of these galaxies have X-ray cooling flows. The results are based on CCD surface photometry carried out using the broad band filters V and R. and a narrow band filter appropriate for the red-shifted Ha + [N II] emission. We present the integrated Ha luminosities in these galaxies and examine various emission mechanisms. Photoionization by young stars is a viable mechanism. New features like dust and shells with blue colours have been discovered in some galaxies. The presence of the 10*K gas is asso- ciated with the presence of such features indicative of galaxy-galaxy interac- tions. In NGC 3607, rings or a disk of dust surrounds the ionized gas. In NGC 4753, a very complex system of dust lanes is observed. We suggest that the dust and associated gas in NGC 3607 is acquired from an interacting neighbour NGC 3608. Accretion events or mergers may be common in these galaxies.