A Massive Molecular Torus inside a Gas-poor Circumnuclear Disk in the Radio Galaxy NGC 1052 Discovered with ALMA
Seiji Kameno, Satoko Sawada-Satoh, C. M. Violette Impellizzeri, Daniel Espada, Naomasa Nakai, Hajime Sugai, Yuichi Terashima, Kotaro Kohno, Minju Lee, Sergio Martín
Abstract
Abstract We report ALMA observations of NGC 1052 to search for mass accretion in a gas-poor active galactic nucleus. We detected CO emission representing a rotating ring-like circumnuclear disk (CND) seen edge-on with a gas mass of 5.3 × 10 5 M ⊙ . The CND has smaller gas mass than that in typical Seyfert galaxies with circumnuclear star formation and is too gas-poor to drive mass accretion onto the central engine. The continuum emission casts molecular absorption features of CO, HCN, HCO + , SO, SO 2 , CS, CN, and H 2 O, with H 13 CN and HC 15 N and vibrationally excited ( v 2 = 1) HCN and HCO + . Broader absorption line widths than CND emission-line widths imply the presence of a geometrically thick molecular torus with a radius of 2.4 ± 1.3 pc and a thickness ratio of 0.7 ± 0.3. We obtain an H 2 column density of (3.3 ± 0.7) × 10 25 cm −2 using H 12 CN, H 13 CN, and HCO + absorption features and adopting abundance ratios of 12 C to 13 C and HCO + to H 2 , and we derived a torus gas mass of (1.3 ± 0.3) × 10 7 M ⊙ , which is ∼9% of the central black hole mass. The molecular gas in the torus is clumpy, with an estimated covering factor of . The gas density of the clumps inside the torus is inferred to be (6.4 ± 1.3) × 10 7 cm −3 , which meets the excitation conditions for an H 2 O maser. The specific angular momentum in the torus exceeds the flat rotation curve extrapolated from that of the CND, indicating a Keplerian rotation inside a 14.4 pc sphere of influence.