D. R. Jiang

On the masses of black holes in radio-loud quasars

The central black hole masses of a sample of radio-loud quasars are estimated by using the data of H beta linewidth and the optical continuum luminosity. The vast majority of the quasars in this sample have black hole masses larger than 10(8) M(circle dot), while a few quasars may contain relatively smaller black holes. We found a significant anti-correlation between the radio loudness and the central black hole mass. It might imply that the jet formation is governed by the black hole mass.

A Narrow-Line Seyfert 1-Blazar Composite Nucleus in 2MASX J0324+3410

We report the identification of 2MASX J032441.19 + 341045.9 (hereafter 2MASX J0324 + 3410) with an appealing object that shows the dual properties of both a narrow-line Seyfert 1 galaxy (NLS1) and a blazar. Its optical spectrum, which has a H beta line width of about 1600 km s(-1) (FWHM), an [O III]-to-H beta line ratio of similar or equal to 0.12, and strong Fe II emission, clearly fulfills the conventional definition of NLS1s. On the other hand, 2MASX J0324 + 3410 also exhibits some behavior that is characteristic of blazars, including a flat radio spectrum above 1 GHz, a compact core plus a one-sided jet structure on milliarcsecond scale at 8.4 GHz, highly variable fluxes in the radio, optical, and X-ray bands, and a possible detection of TeV gamma-ray emission. On its optical image, obtained with the HST WFPC2, the active nucleus is displaced from the center of the host galaxy, which exhibits an apparent one-armed spiral structure extended to 16 kpc. The remarkable hybrid behavior of this object presents a challenge to current models of NLS1s and gamma-ray blazars.

Correlation between radio and broad line emission in radio loud quasars

We present a correlation between radio and broad-line emission for a sample of radio-loud quasars that supports a close Link between accretion processes and relativistic jets. BL Lac objects seem to follow the statistical behaviour of quasars, but with fainter broad-line emission.

EVN observation of three Broad Absorption Line quasars

We present the results of European VLBI Network observations of 3 Broad Absorption Line quasars at 1.6 GHz. They are all compact with linear sizes less than 1 kpc. The flat spectral source, J1556 + 3517, is unresolved at about 20 mas resolution, indicating that the orientation of the radio jet in this source is probably near the line of sight. J1312 + 2319 shows asymmetric two-sided structure on a scale of several hundred pc. This structure resembles that of Compact Symmetric Objects (CSO), however it has a bright central component at the present resolution. The jet orientation of J1312 + 2319 may be far from the line of sight. J0957 + 2356 is also unresolved, but with a steep spectrum, therefore the jet orientation in this source is unclear. These results are not consistent with the unification of BAL and non-BAL quasars by orientation.

The bulk kinetic power of radio jets in active galactic nuclei

Based on the Konigls inhomogeneous jet model, we estimate the jet parameters, such as bulk Lorentz factor Gamma, viewing angle theta and electron number density n(e) from radio very long-baseline interferometry and X-ray data for a sample of active galactic nuclei (AGNs) assuming that the X-rays are from the jet rather than the intracluster gas. The bulk kinetic power of jets is then calculated using the derived jet parameters. We find a strong correlation between the total luminosity of broad emission lines and the bulk kinetic power of the jets. This result supports the scenario that the accretion process is tightly linked with the radio jets, though how the disc and jet are coupled is not revealed by present correlation analysis. Moreover, we find a significant correlation between the bulk kinetic power and radio extended luminosity. This implies that the emission from the radio lobes is closely related with the energy flux transported through jets from the central part of AGNs.

The relation between extended radio and line emission for radio-loud quasars

We explore the relationship between the extended radio and line emission for a radio-loud quasar sample including both core-dominated and lobe-dominated quasars. A strong correlation is present between the extended radio and broad-line emission. The core emission is also correlated with the broad-line emission for core-dominated quasars in the sample. The statistical behaviour of the core emission of lobe-dominated quasars is rather different from that of core-dominated quasars. The extended radio luminosity is a good tracer for jet power, while the core luminosity can only be a jet power tracer for core-dominated quasars.

VLBI observations of seven BL Lacertae objects from RGB sample

We present EVN observations of seven BL Lac objects selected from the RGB sample. To investigate the intrinsic radiation property of BL Lac objects, we estimated the Doppler factor with the VLA or MERLIN core and the total 408 MHz luminosity for a sample of 170 BL Lac objects. The intrinsic ( comoving) synchrotron peak frequency was then calculated by using the estimated Doppler factor. Assuming a Lorentz factor of 5, the viewing angle of jets was constrained. The high-resolution VLBI images of seven sources all show a core-jet structure. We estimated the proper motions of three sources with the VLBI archive data, and find that the apparent speed increases with the distance of components to the core for all of them. In our BL Lacs sample, the Doppler factor of LBLs is systematically larger than that of IBLs and HBLs. We find a significant anti-correlation between the total 408 MHz luminosity and the intrinsic synchrotron peak frequency. However, the scatter is much larger than for the blazar sequence. Moreover, we find a significant positive correlation between the viewing angle and the intrinsic synchrotron peak frequency. The BL Lac objects show a continuous distribution on the viewing angle. While LBLs have a smaller viewing angle than that of IBLs and HBLs, IBLs are comparable to HBLs. We conclude that the intrinsic synchrotron peak frequency is not only related to the intrinsic radio power ( though with a large scatter), but also to the viewing angle for the present sample.

Time Delay Effect on the Cosmic Background Radiation from Static Gravitational Potential of Clusters

We present a quantitative analysis of the time delay effect of the static gravitational potential of galaxy clusters on the cosmic background radiation (CBR). This is primarily motivated by growing observational evidence that clusters have essentially experienced no evolution since redshift z ≈ 1, indicating that the contribution of a time-dependent potential to the CBR anisotropy discussed in the literature could be rather small for dynamically relaxed clusters. Using the softened isothermal sphere model and the universal density profile for the mass distribution of rich clusters, we calculate the CBR anisotropy by the time delay effect and compare it with those generated by the thermal and kinematic Sunyaev-Zeldovich (S-Z) effects, as well as by the transverse motion of clusters. While it is unlikely that the time delay effect is detectable in the current S-Z measurement, because of its small amplitude of 10-6-10-7 and its achromaticity, it nevertheless leads to an uncertainty of ~10% in the measurement of the kinematic S-Z effect of clusters. Future cosmological application of the peculiar velocity of clusters to be measured through the S-Z effect should therefore take this uncertainty into account.

The compact structure of radio-loud broad absorption line quasars

We present the results of EVN+MERLIN very long baseline interferometry (VLBI) polarization observations of eight broad absorption line (BAL) quasars at 1.6 GHz, including four low-ionization BAL quasars (LoBALs) and four high-ionization BAL quasars (HiBALs) with either steep or flat spectra on Very Large Array (VLA) scales. Only one steep-spectrum source, J1122+3124, shows two-sided structure on the scale of 2 kpc. The other four steep-spectrum sources and three flat-spectrum sources display either an unresolved image or a core–jet structure on scales of less than 300 pc. In all cases, the marginally resolved core is the dominant radio component. Linear polarization in the cores has been detected in the range of a few to 10 per cent. Polarization, together with high brightness temperatures (from 2 × 10 9 to 5 × 10 10 K), suggests a synchrotron origin for the radio emission. There is no apparent difference in the radio morphologies or polarization between low-ionization and high-ionization BAL quasi-stellar objects (QSOs) or between flat- and steep-spectrum sources. We discuss the orientation of BAL QSOs with both flat and steep spectra, and consider a possible evolutionary scenario for BAL QSOs. In this scenario, BAL QSOs are probably a young population of radio sources that are compact steep spectrum or GHz peaked radio source analogues at the low end of radio power.

The Inhomogeneous Jet Parameters in Active Galactic Nuclei

The Konigl inhomogeneous jet model is applied to investigate the properties of the jets in active galactic nuclei (AGNs). A sample of AGNs that includes measurements of the angular size and radio flux density of the VLBI core, proper motion of the components in the jet, and X-ray flux density is collected. The inhomogeneous jet parameters are derived with the same assumptions for all sources. A comparison among the parameters of different types of sources in the sample is presented. It is found that most of EGRET sources have higher Doppler factors delta, larger Lorentz factors gamma, and smaller viewing angles theta as compared to the other sources in the sample. The statistical analyses show that the derived Doppler factor delta is strongly correlated with the observed 22 GHz brightness temperature. Furthermore, there is a correlation between the relative gamma-ray luminosity and the Doppler factor delta. The implications of these results are discussed.