E+A galaxies with blue cores: Active galaxies in transition

Hubble Space Telescope (HST) ACS images reveal blue cores in four E+A, or post-starburst, galaxies. Follow-up spectroscopy shows that these cores have LINER spectra. The existence of LINERs, consistent with those in many elliptical galaxies, is yet one more piece of evidence that these postmerger, post-starburst, bulge-dominated galaxies will evolve into normal elliptical galaxies. More interestingly, if LINERs are powered by low-luminosity active galactic nuclei (AGNs), their presence in these E+A's suggests that any rapid growth phase of the central black hole ended in rough concert with the cessation of star formation. This result emphasizes the importance of E+A's for exploring how the evolution of black holes and AGNs may be tied to that of galactic bulges.