Distribution of ionized gas in X-ray bright early-type galaxies

Abstract

We report imaging observations of Hα+[N II] nebulosities in seven early type galaxies viz., NGC 1399, NGC 1600, NGC 2563, NGC 4203, NGC 4636, NGC 4753 and NGC 5044. These are primarily X-ray bright galaxies which are the dominant members of nearby groups. Many of these galaxies have X-ray cooling flows. The results are based on CCD surface photometry carried out using a broad-band filter R, and a narrow band filter appropriate for the red-shifted Hα+[N II] emission. We present the integrated Hα luminosities in these galaxies and examine various emission mechanisms. The observed Hα luminosity implies a mass of ~10⁵ M_⊙ in the ionized gas. We suggest that photo-ionization by young stars is a viable emission mechanism and star formation due to accretion events or mergers may be common in these galaxies.