FRAMEx. V. Radio Spectral Shape at Central Subparsec Region of Active Galactic Nuclei
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Shuvo, Onic I., Megan C. Johnson, Nathan J. Secrest, Mario Gliozzi, Phillip J. Cigan, Travis C. Fischer, and Alexander J. Van Der Horst. “FRAMEx. V. Radio Spectral Shape at Central Subparsec Region of Active Galactic Nuclei.” The Astrophysical Journal 961, no. 1 (January 2024): 109. https://doi.org/10.3847/1538-4357/ad1388.
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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 Mark 1.0 Universal
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Abstract
We present results from the Very Long Baseline Array multifrequency (1.6, 4.4, 8.6, and 22 GHz), high-sensitivity (∼25 μJy beam⁻¹), subparsec-scale (<1 pc) observations and spectral energy distributions 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 subparsec-scale radio morphology, except for 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 the nearby interstellar medium. The spectral slopes are mostly gigahertz-peaked or curved, with a few showing steep, flat, or inverted spectra. We found that at the subparsec scale, the gigahertz-peaked spectra belong to the low-accreting, radio-loud AGNs, with a tendency to produce strong outflows, possibly small-scale jets, and/or have a coronal origin. In contrast, flat/inverted spectra suggest compact radio emission from the central regions of highly accreting AGNs, possibly associated with radio-quiet AGNs producing winds/shocks or nuclear star formation in the vicinity of black holes.