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. Followup 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.