Active galactic nuclei and their host galaxies

In recent years there has been rapid progress in the research of active galactic nuclei (AGNs), such as central super-massive black holes (sbh), accretion processes, and their host galaxies. Using data from rosat point sources, we found that the soft x-ray spectra of narrow-line seyfert 1 galaxies (nls1s) and blazars become harder during x-ray flux increases, while the spectra of broad-line AGNs (bl AGNs) become softer. From asca data, we found that nls1s and bl AGNs follow the same σ²-m_mbh relation, where σ² is the excess variance in the hard x-ray band. With the accretion efficiency of AGNs, we found that most of the radio-loud quasars possibly possess a kerr sbh, while the seyfert 1 galaxies and radio-quiet quasars possess schwarzschild sbh. We also studied the relation between the central black holes and their host galaxies. It was found that nls1s appear to have genuinely lower mbh/bulge mass ratios. And the width of the [o IIi] line is not a good tracer of host velocity dispersion. Nls1s play a special role in our understanding of the evolution of galaxies and their central sbhs.