The physics of megamaser AGN
Abstract
Many local active galactic nuclei (AGN) show water vapor molecule maser emission at 22 GHz. Using Very Long Baseline Interferometry (VLBI) radio interferometry, this emission can be spatially mapped, showing in some sources a nearly edge-on, disk-like structure, in keplerian motion around a supermassive black hole (SMBH). Together with radio emission, hard X-rays are an important way to test and probe the physics of AGN, especially the most obscured ones. Very few local, VLBI-mapped, with high quality hard X-ray observations AGN are known today, but it is clear that disk megamasers are preferentially found in Compton thick (NH > 1.5x10^{24}) Seyfert 2 (Sy2) AGN, hinting towards a connection between high obscuration and maser emission. We show that, using a well defined sample of 15 local Sy2 megamasers with both radio VLBI mapping and NuSTAR hard X-ray spectral coverage, a simple analytical model with spatial continuity and same density profile between the maser disk and the torus allows to recover obscuring column densities in parsec-scale tori in good agreement with the NuSTAR measurements. Moreover, we provide a simple geometrical interpretation for the rarity of maser disk emitting sources and their connection with high obscuring columns in Sy2 AGN, together with hints of a slightly different torus density profile between Compton thin and Compton thick sources.
- Publication:
-
TORUS2015: The AGN Unification Scheme After 30 Years
- Pub Date:
- September 2015
- Bibcode:
- 2015toru.conf..O07M
- Keywords:
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- Active Galactic Nuclei