Active Galactic Nuclei and their Hosts

Jonathan Stern

November 13, 2012

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Abstract: We study the properties of low redshift broad line AGN, and their relation to their host galaxies, based on a new sample derived from the SDSS survey. The sample is supplemented by data from the GALEX, ROSAT, and 2MASS surveys. We find the following. The average AGN hosts are regular non emission line galaxies (NEG), which become bluer with increasing AGN luminosity, suggesting a correlation of the AGN luminosity and the host star formation rate. The observed AGN optical-UV emission is subject to some reddening, and the intrinsic emission is blue, consistent with accretion disk model predictions. The narrow emission lines reveal that the covering factor of circumnuclear gas (10s – 100s pc) decreases with increasing AGN luminosity, and the gas metallicity follows the host mass, similar to the mass – metallicity relation of normal galaxies. The metallicity of the broad line region (0.01s – 0.1s pc) åÊalso appears to be related to the host mass.