Radio Active Galactic Nucleus In SDSS And FIRST

According to unification scheme, active galactic nuclei (AGNs) have the same structure as long as they belong to the same parent population, and their obser-vation characteristics are attributed solely to the different viewing angles. An AGN appears as broad lined (Type 1) or narrow lined (Type 2) depending on whether our line of sight is blocked by a dusty torus or not; a radio AGN appears as compact, flat spectral radio source when it is viewed along the radio axis and as extended, steep spectral source when viewed off axis. The exact division for the different types depends likely on the intrinsic source parameters, such as black hole mass, accretion rate and jet velocity. In addition, these parameters may also determine what parent population the AGN belongs, such as existence of radio jet, broad line region. In this thesis, I explore such an extension of the unifica-tion scheme using large AGN samples drawn from the Sloan Digital Sky Survey (SDSS) and the radio source catalog of Faint Image of Radio Sky at Twenty cm (FIRST).In Chapter 1, I first introduce the taxonomy, and structure of a typical AGN, and then briefly review the two unification schemes based on the dusty torus obscuration for two types of Seyfert galaxies and based on the jet orientation for radio loud AGNs. I also outline briefly the observation evidences for different accretion modes, and structures of AGN.In Chapter 2, I present a detailed study of selection effect of radio quasars on the bimodality of radio loudness and unification of radio quasars. I extract a uniformed sample, consisting of 859 extended and 2782 compact radio quasars by matching quasar catalog of SDSS Data Release 3 (DR3) and FIRST survey. I analysis my sample within limited redshift and optical magnitude, and find that the incompleteness due to small beam size of FIRST is low above the 3 mJy level, and I find that the 2" cutout will cause-16.8%extended flux be underestimated. I also find the extended sources tend to be more luminous than the compact ones, though their optical luminosity is similar. This may implied that the radio loudness of radio quasars were bimodal intrinsically. When the jet of radio quiet quasars oriented towards us, they appear to be compact sources, and Doppler enhancement make them be detected by FIRST. On the contrary, when the jet perpendicular to us, the radio quiet quasars could not be detect by FIRST in extended morphology.In Chapter 3, I study the dependence of covering factor on some parameters in a radio strong (P1.4GHz≥1023W Hz-1) AGN sample selected by matching the spectroscopic catalog of SDSS DR4 and FIRST. My sample includes 711 type 2 objects and 286 type 1 objects with z≤0.35. After correcting for several selection effects, I find that:(1) type 1 fraction f1 keeps at a constant of～20% in the [OIII] luminosity range of 40.7< log(L[OIII]/erg s-1)< 43.5. This result is significantly different from previous studies, and the difference can be explained by extinction correction and different treatment of selection effects. (2)f1 rises with black hole mass from～20%below 108M(?)to 30% above that. This coincides with the decrease of the fraction of highly-inclined disk galaxies with black hole mass, implying a population of Seyfert galaxies seen as Type-2 due to galaxy-scale obscuration in disk when the host galaxy type transfer from bulge-dominant to disk-dominant. (3) f1 is independent of the Eddington ratio for its value between 0.01 and 1; (4)f1 ascends from 15%to 30%in the radio power range of 23< log(P1.4GHz/WHz-1)< 24, then remain a constant at-30%until 1026 W Hz-1. My results show that the torus opening angle does not change with the nuclear luminosity, thus do not support'receding torus'model, but are consistent with the "Starved/Eddington tuned" two population models.The summary and discussion are presented in the last Chapter.