Spatial resolution bias in the mid-infrared Starburst/AGN classification

Abstract

We present the effects of limited spatial resolution to the observed mid-infrared (MIR) spectrum of an active galactic nucleus (AGN) surrounded by a disk with massive star forming regions. Using MIR observations of the face-on nearby Seyfert 1 galaxy NGC 6814, we vary the observing aperture and examine the evolution of the observed AGN/starburst fraction with our MIR diagnostic. We show that the spatial resolution of ISOCAM is sufficient to disentangle AGN from starburst features in nuclear regions of nearby galaxies (D<50Mpc). However, with the exception of a few ultra-luminous galaxies, dilution effects hide completely the AGN contribution in more distant galaxies.

4 pages, 3 figures. To appear in the Proceedings of the XIXth Rencontres de Moriond, `Building the Galaxies: from the Primordial Universe to the Present', p. 79, 1999 eds F. Hammer, T.X.T. Thuan, V. Cayatte, B. Guiderdoni and J. Tran Than Van