FRAMEx. V. Radio Spectral Shape at Central Sub-parsec Region of AGNs
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Author/Creator ORCID
Date
2023-12-07
Type of Work
Department
Program
Citation of Original Publication
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Public Domain
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Abstract
We present results from the Very Long Baseline Array (VLBA) multi-frequency (1.6, 4.4, 8.6, 22 GHz),
high-sensitivity (∼25 µJy beam⁻¹
), sub-parsec scale (<1 pc) observations and Spectral Energy Distributions (SEDs) for a sample of 12 local active galactic nuclei (AGNs), a subset from our previous
volume-complete sample with hard X-ray (14–195 keV) luminosities above 10⁴² erg s⁻¹
, out to a distance of 40 Mpc. All 12 of the sources presented here were detected in the C (4.4 GHz) and X (8.6
GHz) bands, 75% in the L band(1.6 GHz), and 50% in the K band (22 GHz). Most sources showed
compact, resolved/slightly resolved, central sub-parsec scale radio morphology, except a few with extended outflow-like features. A couple of sources have an additional component that may indicate the
presence of a dual-core, single or double-sided jet or a more intricate feature, such as radio emission
resulting from interaction with nearby ISM. The spectral slopes are mostly GHz-peaked or curved, with
a few showing steep, flat, or inverted spectra. We found that in the sub-parsec scale, the GHz-peaked
spectra belong to the low-accreting, radio-loud AGNs with a tendency to produce strong outflows, possibly small-scale jet, and/or have a coronal origin. In contrast, flat/inverted spectra suggest compact
radio emission from highly-accreting AGNs’ central region, possibly associated with radio-quiet AGNs
producing winds/shocks or nuclear star formation in the vicinity of black holes.