NGC 4261 AND NGC 4697: REJUVENATED ELLIPTICAL GALAXIES

摘要

Chandra images present evidence of a nonuniform spatial distribution of discrete X-ray sources in the elliptical galaxy NGC 4261. This nonuniform distribution is inconsistent with the optical morphology of NGC 4261 at greater than a 99.9% confidence level. Similar evidence is seen in one more elliptical galaxy (NGC 4697; 98% confidence level) out of five cases we investigated. NGC 4261 and NGC 4697 have old stellar populations (9-15 Gyr) and fine-structure parameters of 1 and 0, respectively, suggesting that no recent merging activity occurred. On the basis of simulations of galaxy interactions, we propose that the X-ray sources responsible for the nonuniform distribution are associated with young stellar populations, related to the rejuvenating fallback of material in tidal tails onto a relaxed merger remnant or to shock-induced star formation along the tidal tails.