Oral Presentation

Discovery of a Tight Correlation between Mm-wave and X-ray emission for Hard X-ray Selected Nearby AGNs

Author(s): Taiki Kawamuro (RIKEN)

Presenter: Taiki Kawamuro (RIKEN)

Active galactic nuclei (AGNs) emit radiation over a wide range of wavelengths from radio to gamma rays, and by decomposing their spectral energy distributions (SEDs), we have discussed their structures such as X-ray emitting coronae, accretion disks, obscuring tori, and jets. In such a situation, AGN emission in the millimeter-wave (mm-wave) band has not been well understood due to the contaminating light from host galaxies and the low sensitivities of past telescopes. However, thanks to recent ALMA observations with high spatial resolution and sensitivity, it has been reported that synchrotron self-absorption emission from a region on a scale of the X-ray emitting corona may be significant in the mm-wave band. In order to better understand AGN mm-wave emission, we systematically analyzed high-resolution (less than 1") ALMA Band-6 (1.1--1.4 mm) data of 98 objects among nearby AGNs (redshifts below 0.05) detected in the Swift/BAT 70-month hard-X-ray catalog. The achieved spatial resolutions are in a range ~ 1--200 pc, and we detected significant (above 5 sigma) mm-wave emission from the galactic nuclei of 89 objects. For the first time, we then found a strong correlation between mm-wave and X-ray emission with a slope of ∼ 1 and a standard deviation of 0.36 dex. This suggests that the mm-wave emission may be the synchrotron radiation from the vicinity of the X-ray corona, as has been suggested. As possibilities other than that scenario, we also considered the dust torus, outflow-derived shock waves, and jets. The torus would be unlikely, because the slope of the observed mm-wave spectrum is basically flatter than expected for thermal radiation. In addition, we found no tendency for the mm-wave luminosity to increase with Eddington ratio, while it was predicted by a radiation-driven outflow model. Furthermore, the independence of mm-wave luminosity on the viewing angle is found to be inconsistent with a simple jet model in which the luminosity depends only on the angle.