The Central Molecular Gas Structure in LINERs with Low-luminosity Active Galactic Nuclei: Evidence for Gradual Disappearance of the Torus

Müller-Sánchez, F.; Malkan, M. A.; Elitzur, M.; Davies, R. I.; Mezcua, M.; Prieto, M. A.
Bibliographical reference

The Astrophysical Journal Letters, Volume 763, Issue 1, article id. L1, 6 pp. (2013).

Advertised on:
1
2013
Number of authors
6
IAC number of authors
3
Citations
38
Refereed citations
37
Description
We present observations of the molecular gas in the nuclear environment of three prototypical low-luminosity active galactic nuclei (LLAGNs), based on VLT/SINFONI AO-assisted integral-field spectroscopy of H2 1-0 S(1) emission at angular resolutions of ~0.''17. On scales of 50-150 pc, the spatial distribution and kinematics of the molecular gas are consistent with a rotating thin disk, where the ratio of rotation (V) to dispersion (σ) exceeds unity. However, in the central 50 pc, the observations reveal a geometrically and optically thick structure of molecular gas (V/σ < 1 and N H > 1023 cm–2) that is likely to be associated with the outer extent of any smaller scale obscuring structure. In contrast to Seyfert galaxies, the molecular gas in LLAGNs has a V/σ < 1 over an area that is ~9 times smaller and column densities that are on average ~3 times smaller. We interpret these results as evidence for a gradual disappearance of the nuclear obscuring structure. While a disk wind may not be able to maintain a thick rotating structure at these luminosities, inflow of material into the nuclear region could provide sufficient energy to sustain it. In this context, LLAGNs may represent the final phase of accretion in current theories of torus evolution. While the inflow rate is considerable during the Seyfert phase, it is slowly decreasing, and the collisional disk is gradually transitioning to become geometrically thin. Furthermore, the nuclear region of these LLAGNs is dominated by intermediate-age/old stellar populations (with little or no ongoing star formation), consistent with a late stage of evolution. Based on observations at the European Southern Observatory VLT (082.B-0709 and 084.B-0568).
Related projects
Project Image
The Central PARSEC of Galaxies using High Spatial Resolution Techniques
PARSEC is a multi-wavelength investigation of the central PARSEC of the nearest galaxies. We work on black-hole accretion and its most energetic manifestations: jets and hot spots, and on its circumnuclear environment conditions for star formation. We resort to the highest available angular resolution observations from gamma-rays to the centimetre
Almudena
Prieto Escudero