MeerKAT

Abstract:

We describe a major study of radio source host galaxies being carried out with the HST and ground-based facilities. Our sample is selected from 4 complete samples with different radio flux-density limits, giving a range of three orders of magnitude in radio luminosity at a fixed epoch (z=0.5). High-resolution HST WFPC2 imaging shows that all 44 radio galaxies have flux distributions well fit by an r1/4 law and lying on the Kormendy relation defined by lower redshift ellipticals with a shift in the zero-point to account for passive evolution. Spectroscopic follow-up enables stellar velocity dispersions to be determined and black hole masses estimated. The clustering environments of the radio galaxies are being probed via multi-colour wide-field imaging. Together, these data allow a detailed investigation of how factors such as clustering environment, close interactions and star-formation history affect the accretion rate, ionizing luminosity and jet production from supermassive black holes. © 2003 Elsevier B.V. All rights reserved.

Abstract:

In this paper we demonstrate that a large, unexplored reservoir of information about pulsar emission exists, that is directly linked to the radiating particles and their radiation process: We present a study of flux density measurements of individual pulses simultaneously observed at four different frequencies. Correcting for effects caused by the interstellar medium, we derive intrinsic flux density spectra of individual radio pulses observed at several frequencies for the first time. Pulsar B0329+54 was observed at 238, 626, 1412 and 4850 MHz, while observations of PSR B1133+16 were made at 341, 626, 1412 and 4850 MHz, We derive intrinsic pulse-to-pulse modulation indices which show a minimum around 1 GHz. Correlations between the flux densities of different frequency pairs worsen as the frequency separation widens and also tend to be worse for outer profile components. The single pulse spectra of PSR B0329+54 resemble the spectra of the integrated profile. However, the spectral index distributions for the single pulses of PSR B1133+16 show significant deviations from a Gaussian. This asymmetry is caused by very strong pulses with flux densities exceeding the mean value by more than a factor of ten. These strong pulses occur preferentially at the trailing edge of the leading component and appear to be broadband in most cases. Their properties are similar to those of so-called giant pulses, suggesting that these phenomena are related.

Abstract:

We investigate circular polarization in pulsar radio emission through simultaneous observations of PSR B1133+16 at two frequencies. In particular, we investigate the association of the handedness of circular polarization with the orthogonal polarization mode phenomenon at two different frequencies. We find the association to be significant across the pulse for PSR B1133+16, making a strong case for orthogonal polarization modes determining the observed circular polarization. The association however is not perfect and decreases with frequency. Based on these results and assuming emission occurs in super-posed orthogonal polarization modes, we present a technique of mode decomposition based on single pulses. Average profiles of the polarization of each mode can then be computed by adding the individual mode-separated single pulses. We show that decomposing single pulses produces different average profiles for the orthogonal polarization modes from decomposing average profiles. Finally, we show sample single pulses and discuss the implications of the frequency dependence of the correlation of the circular polarization with the orthogonal polarization mode phenomenon.

Abstract:

We present the results of deep VLT-ISAAC Ks-band imaging of four z∼1.5 flat-spectrum quasars selected from the Parkes half-Jansky flat spectrum sample. We find that the hosts of these flat-spectrum quasars are consistent with lying on the K-z Hubble relation for radio galaxies. This implies that the flat-spectrum quasar hosts fall in line with the expectations from orientation based unified schemes and also that they contain black holes of similar mass. Moreover, the width of the Hβ broad emission line in these objects tends to be narrower than in their misaligned (low-frequency selected quasar) counterparts, implying that the width of the Hβ broad emission line depends on source inclination, at least for radio-loud quasars, in line with previous studies. © 2003 Elsevier B.V. All rights reserved.