BASS XXXII: Studying the Nuclear Millimeter-wave Continuum Emission of AGNs with ALMA at Scales ≲100-200 pc
Baba, Shunsuke; Imanishi, Masatoshi; Ueda, Yoshihiro; Kawamuro, Taiki; Ricci, Claudio; Bauer, Franz E.; Stern, Daniel; Trakhtenbrot, Benny; Pfeifle, Ryan W.; Mushotzky, Richard F.; Izumi, Takuma; Baloković, Mislav; Ichikawa, Kohei; Sanders, David B.; Smith, Krista Lynne; Harrison, Fiona; Koss, Michael J.; den Brok, Jakob S.; Oh, Kyuseok; Powell, Meredith C.; Privon, George C.; Ricci, Federica; Shimizu, Taro; Kakkad, Darshan; Temple, Matthew J.; Rojas, Alejandra F.; Chang, Chin-Shin; Urry, Meg
Chile, Japan, China, United States, Italy, Israel, Germany, United Kingdom, South Korea, Switzerland
Abstract
To understand the origin of nuclear (≲100 pc) millimeter-wave (mm-wave) continuum emission in active galactic nuclei (AGNs), we systematically analyzed subarcsecond resolution Band-6 (211-275 GHz) Atacama Large Millimeter/submillimeter Array data of 98 nearby AGNs (z < 0.05) from the 70 month Swift/BAT catalog. The sample, almost unbiased for obscured systems, provides the largest number of AGNs to date with high mm-wave spatial resolution sampling (~1-200 pc), and spans broad ranges of 14-150 keV luminosity { $40\lt \mathrm{log}[{L}_{14-150}/(\mathrm{erg}\,{{\rm{s}}}^{-1})]\lt 45$ }, black hole mass $[5\lt \mathrm{log}({M}_{\mathrm{BH}}/{M}_{\odot })\lt 10$ ], and Eddington ratio ( $-4\lt \mathrm{log}{\lambda }_{\mathrm{Edd}}\lt 2$ ). We find a significant correlation between 1.3 mm (230 GHz) and 14-150 keV luminosities. Its scatter is ≈0.36 dex, and the mm-wave emission may serve as a good proxy of the AGN luminosity, free of dust extinction up to N H ~ 1026 cm-2. While the mm-wave emission could be self-absorbed synchrotron radiation around the X-ray corona according to past works, we also discuss different possible origins of the mm-wave emission: AGN-related dust emission, outflow-driven shocks, and a small-scale (<200 pc) jet. The dust emission is unlikely to be dominant, as the mm-wave slope is generally flatter than expected. Also, due to no increase in the mm-wave luminosity with the Eddington ratio, a radiation-driven outflow model is possibly not the common mechanism. Furthermore, we find independence of the mm-wave luminosity on indicators of the inclination angle from the polar axis of the nuclear structure, which is inconsistent with a jet model whose luminosity depends only on the angle.