Researches On The Central Black Hole Masses And Emissions Of AGNs

In this thesis, we present the studies of the relationships between the central black holemasses and radio properties, the interactions between the radio jets and accretion disc,and the properties of emission lines for radio-loud quasars.The energy released from the accretion process upon central black holes is believed topower the quasars. In such scenario, the black hole mass is one of the most importantphysical quantity. The radio-loud quasars are characteristic of powerful radio jets, and thejets are probably powered by the rotating black hole, or accelerated by the magnetic field ofthe accretion disc. Several recent researches discovered the relationships between the blackhole masses and radio activities. But, the number of radio-loud quasars included in thesework is relatively small, we performed a study for a sample of 86 radio-loud quasars forfurther understanding the relationships between the black hole masses and radio activities.The central black-hole masses of radio-loud quasars are estimated by using the data of Hβline-width and the optical continuum luminosity. We found the vast majority of the quasarsin this sample have black-hole masses higher than 10~8M_⊙, while a few quasars may containrelatively smaller black-holes〈10~8M_⊙. Our results are confirmed by a recent researchon PHFS. There are a tendency of the radio luminosity increasing with the central blackhole mass. We found a significant anti-correlation between radio-loudness and the centralblack-hole mass. It might imply that the jet formation is related with the black-hole mass.Many quasars show a big blue bump in the optical/UV continuum, which is usuallythought to origin from the thermal emission from the accretion disc. The optical/UVcontinuum is determined by the physical conditions of the accretion disc. So, the observedcontinuum of quasars could reflect the properties of accretion disc. Recent numericalsimulations indicate the jets probably accelerated from the inner region of accretion discnear the black hole. Some studies show the interactions between the jets and accretiondiscs may be important, and the outflows from the accretion disc could significantly alterthe temperature distribution in the inner region of the accretion disc. We studied therelationships between the ratio of radio to optical luminosities and the continuum spectralindex in blue/UV bands for a low-frequency radio selected quasar sample, and found asignificant anti-correlation. It might indicate that the continuum shape in blue/UV bandsis related to the ratio of jet to accretion power. The results may imply that the spectra and structure of accretion discs are probably affected by the interactions between jets anddiscs.Strong emission-lines are the main characteristic of the optical spectra of AGN. Thedynamics of the broad emission line cloud directly reflect the inner gravitational field or theemission properties of AGN, and one of the effective means to understand AGN could bethrough analysing the strength and profile of various types of emission-lines. The inverse-compton process of soft photons upon high-energy electrons is probably responsible for theγ-ray emission. One possible origin of soft photon is from the emission of the broad-lineclouds. However, there is no obvious evidence on the relationships ofγ-ray emission and thestrength of emission-lines at present. The optical spectral observations for EGRET AGNslack of emission line data are useful for the further research onγ-ray radiation mechanism.For quasars, the central black hole masses could be estimated using the optical continuumluminostiy and the boad emission line width from the single spectra. We performed thespectral observations on ten EGRET AGNs and thirteen radio-loud quasars. Using 2.16mtelescope in the Xinglong station of NAO, we have measured the flux, equivalent widthand FWHM of broad H/β, MgⅡ, [OⅢ]λ5007 for two EGRET AGNs and six quasars. Forfive of six radio-loud quasars, combining the results of literature and ours, we found theFWHM of broad Hβline is varying. For the rest one, we found no broad Hβemission linedata available in the literature, and we present our measurements on this source. Finally,we estimated the central black hole masses for all eight sources, and found all the blackhole masses are higher than 3×10~8M_⊙.