Evolution of Gas and Stars in the Merger Galaxy NGC 1316 (Fornax A)

Abstract

We present optical and archival X-ray data on the disturbed-morphology radio elliptical galaxy NGC 1316 (Fornax A), which displays numerous low surface brightness shells, loops, and tails. An extended (81A ] 27A, or 9 kpc ] 3 kpc) emission-line region (EELR) at a projected distance of 35 kpc from the nucleus has been discovered in an approximately 90 kpc ] 35 kpc, 3.0 ] 109 tidal tail. The position L B_ and extreme size of the EELR suggest that it is related to the merger process. We suggest that the ion-ization mechanism of the EELR is shock excitation and that the gas is a remnant from the merger progenitor. X-ray emission is detected near two tidal tails. Hot, D5 ] 106 K, gas is probably the predominant gas component in the tidal-tail interstellar medium. However, based on the current tidal-tail (cold ] warm ] hot) gas mass, a large fraction of the progenitor gas may already reside in the nucleus of NGC 1316. The numerous and varied tidal-tail system suggests that a disk-disk or disk-E merger could have taken place º1 Gyr ago, while a low-mass, gas-rich galaxy would have started to merge D0.5 Gyr ago.