Multi-frequency investigation of the parsec- and kilo-parsec-scale radio structures in high-redshift quasar PKS 1402+044

TL;DR

This study examines the multi-frequency radio properties of the high-redshift quasar PKS 1402+044 over seven years, revealing a core-jet structure, spectral evolution, and jet dynamics consistent with shock-in-jet models.

Contribution

It provides the first detailed multi-frequency, long-term radio analysis of a high-redshift quasar, including jet morphology, spectral index variation, and proper motion constraints.

Findings

PKS 1402+044 exhibits a core-jet morphology from parsec to kilo-parsec scales.

The jet's spectral index steepens with distance from the core.

The jet's brightness temperature variation aligns with shock-in-jet models.

Abstract

We investigate the frequency-dependent radio properties of the jet of the luminous high-redshift (z = 3.2) radio quasar PKS 1402+044 (J1405+0415) by means of radio interferometric observations. The observational data were obtained with the VLBI Space Observatory Programme (VSOP) at 1.6 and 5 GHz, supplemented by other multi-frequency observations with the Very Long Baseline Array (VLBA; 2.3, 8.4, and 15 GHz) and the Very Large Array (VLA; 1.4, 5, 15, and 43 GHz). The observations span a period of 7 years. We find that the luminous high-redshift quasar PKS 1402+044 has a pronounced "core-jet" morphology from the parsec to the kilo-parsec scales. The jet shows a steeper spectral index and lower brightness temperature with increasing distance from the jet core. The variation of brightness temperature agrees well with the shock-in-jet model. Assuming that the jet is collimated by the ambient magnetic field, we estimate the mass of the central object as ~10^9 M_sun. The upper limit of the jet proper motion of PKS 1402+044 is 0.03 mas/yr (~3c) in the east-west direction.