VLBI Observations of a sample of Palomar-Green quasars II: characterizing the parsec-scale radio emission

ABSTRACT This study uses multifrequency very long baseline interferometry (VLBI) to study the radio emission from 10 radio-quiet quasars (RQQs) and four radio-loud quasars (RLQs). The diverse morphologies, radio spectra, and brightness temperatures observed in the VLBI images of these RQQs, together...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2023-11, Vol.525 (4), p.6064-6083
Main Authors: Wang, Ailing, An, Tao, Zhang, Yingkang, Cheng, Xiaopeng, Ho, Luis C, Kellermann, Kenneth I, Baan, Willem A
Format: Article
Language:English
Subjects:
Active galactic nuclei
Astronomical models
Brightness temperature
Emission spectra
High resolution
Image resolution
Quasars
Radio emission
Radio spectra
Spectral emissivity
Star & galaxy formation
Star formation
Synchrotron radiation
Very long base interferometry
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Summary:ABSTRACT This study uses multifrequency very long baseline interferometry (VLBI) to study the radio emission from 10 radio-quiet quasars (RQQs) and four radio-loud quasars (RLQs). The diverse morphologies, radio spectra, and brightness temperatures observed in the VLBI images of these RQQs, together with the variability in their GHz spectra and VLBI flux densities, shed light on the origins of their nuclear radio emission. The total radio emission of RQQs appears to originate from non-thermal synchrotron radiation due to a combination of active galactic nuclei and star formation activities. However, our data suggest that the VLBI-detected radio emission from these RQQs is primarily associated with compact jets or corona, with extended emissions such as star formation and large-scale jets being resolved by the high resolution of the VLBI images. Wind emission models are not in complete agreement the VLBI observations. Unlike RLQs, where the parsec-scale radio emission is dominated by a relativistically boosted core, the radio cores of RQQs are either not dominant or are mixed with significant jet emission. RQQs with compact cores or core-jet structures typically have more pronounced variability, with flat or inverted spectra, whereas jet-dominated RQQs have steep spectra and unremarkable variability. Future high-resolution observations of more RQQs could help to determine the fraction of different emission sources and their associated physical mechanisms.
ISSN:0035-8711
1365-2966
DOI:10.1093/mnras/stad2651