|Ph.D Student||Stern Jonathan|
|Subject||The Emission Properties of Type 1 Low Redshift AGN|
|Department||Department of Physics||Supervisor||Professor Ari Laor|
|Full Thesis text|
We study the properties of active galactic nuclei (AGN), and their relation to their host galaxies, based on a new sample of low redshift unobscured AGN. The sample is based on optical spectra from the SDSS survey, and supplemented by nearly complete photometric data from the GALEX ultraviolet survey, the ROSAT X-ray survey, and the 2MASS near-infrared survey. The sample spans four orders of magnitude in luminosity (1042<L<1046 erg s-1), and 3.5 orders of magnitude in black hole mass (106 < MBH < 10^9.5 MSun).
We find the following. The AGN hosts have the same luminosity distribution as non-emission line galaxies (NEG). The colors of AGN hosts are consistent with the colors of NEG at low luminosity, and become bluer with increasing AGN luminosity. This suggests that AGN are hosted by NEG with enhanced star formation. The observed optical-UV emission of unobscured AGN 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 the circumnuclear gas (10s -- 100s of parsecs from the nucleus) decreases with increasing AGN luminosity, in contrary to naive expectations. Also, the ratios of narrow emission line luminosities suggest that the circumnuclear gas metallicity is related to the host mass, similar to the relation between mass and metallicity observed in inactive galaxies. This relation can be used to probe the mass-metallicity relation in the hosts of high redshift quasars.
The metallicity of the accreting gas, derived from the broad emission lines, also appears to be related to the host mass.