Parsec-scale morphology and spectral index distribution in faint high frequency peakers

TL;DR

This study uses VLBA observations at 8.4 and 15.3 GHz to analyze the parsec-scale structure and spectral index distribution of faint high frequency peaking radio sources, revealing insights into their morphology, magnetic fields, and evolutionary stages.

Contribution

It provides the first detailed parsec-scale morphological and spectral analysis of faint HFP sources, distinguishing young radio sources from blazar-like objects and examining magnetic field properties.

Findings

64% of sources are resolved into subcomponents.

Resolved sources show characteristics of young radio sources or blazars.

Magnetic fields in components are tens of milliGauss, affecting source evolution.

Abstract

We investigate the parsec-scale structure of 17 high frequency peaking radio sources from the faint HFP sample. VLBA observations were carried out at two adjacent frequencies, 8.4 and 15.3 GHz, both in the optically-thin part of the spectrum, to obtain the spectral index information. We found that 64% of the sources are resolved into subcomponents, while 36% are unresolved even at the highest frequency. Among the resolved sources, 7 have a morphology and a spectral index distribution typical of young radio sources, while in other 4 sources, all optically associated with quasars, the radio properties resemble those of the blazar population. The equipartition magnetic field of the single components are a few tens milliGauss, similar to the values found in the hotspots of young sources with larger sizes. Such high magnetic fields cause severe radiative losses, precluding the formation of extended lobe structures emitting at centimeter wavelengths. The magnetic fields derived in the various components of individual source are usually very different, indicating a non self-similar source evolution, at least during the very first stages of the source growth.