The first detection of near-infrared CN bands in active galactic nuclei: signature of star formation

摘要

We present the first detection of the near-infrared CN absorption band in thenuclear spectra of active galactic nuclei (AGN). This feature is a recent starformation tracer, being particularly strong in carbon stars. The equivalentwidth of the CN line correlates with that of the CO at 2.3 microns, as expectedin stellar populations (SP) with ages between ~ 0.2 and ~ 2 Gyr. The presenceof the 1.1 microns CN band in the spectra of the sources is taken as anunambiguous evidence of the presence of young/intermediate SP close to thecentral source of the AGN. Near-infrared bands can be powerful age indicatorsfor star formation connected to AGN, the understanding of which is crucial inthe context of galaxy formation and AGN feedback.