THE CENTRAL MOLECULAR GAS STRUCTURE IN LINERS WITH LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI: EVIDENCE FOR GRADUAL DISAPPEARANCE OF THE TORUS

By F. Muller-S'anchez, M. Prieto, M. Mezcua, R. Davies, M. Malkan, M. I. D. A. D. Canarias, U. L. Laguna, U. California, Los Angeles, Max Planck Institute for Radioastronomy and 2 more. 2012

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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 NH > 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.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

Active galactic nuclei: what’s in a name? (2017, background): “A clear case among the observational evidence (e.g. Chiaberge et al. 1999; Maoz et al. 2005; Müller-Sánchez et al. 2013) is the nearby LEG M87, that has been shown to lack the thermal radiation of the torus (Whysong and Antonucci 2004; Perlman et al. 2007).”
A characteristic oxygen abundance gradient in galaxy disks unveiled with CALIFA (2013, result): “Recent results, which are based on the analysis of the SFH of CALIFA data, found undisputed evidence of the insideout growth of the stellar mass in galaxies (Pérez et al. 2013), at least for galaxies more massive than 7 × 1010 M .”
Constraining the galaxy–halo connection over the last 13.3 Gyr: star formation histories, galaxy mergers and structural properties (2017, methodology): “…of the “fossil record” method, the global and radial stellar mass assembly histories of galaxies of different masses have recently been inferred from spectroscopic surveys of local galaxies under the assumption of no radial displace- ments of stars (Pérez et al. 2013; Ibarra-Medel et al. 2016).”
OVERVIEW OF THE SDSS-IV MaNGA SURVEY: MAPPING NEARBY GALAXIES AT APACHE POINT OBSERVATORY (2014, background): “More generally, it appears that various processes conspire to produce “inside-out” star formation histories, with earlier, more rapid formation occurring in the centers of galaxies, at least with masses above M∗ (e.g., Pérez et al. 2013).”
The star formation history of CALIFA galaxies: Radial structures (2013, methodology): “This trend confirms again that galaxies more massive than ∼ 1010M grow inside-out (Pérez et al. 2013).”
SDSS IV MaNGA – metallicity and nitrogen abundance gradients in local galaxies (2017, background): “The insideout growth scenario is further supported by observations of colour gradients (Bell & de Jong 2000; Muñoz-Mateos et al. 2007) and spectroscopically-inferred age profiles of disc galaxies (Pérez et al. 2013; González Delgado et al. 2015; Ibarra-Medel et al. 2016).”
The CALIFA survey across the Hubble sequence: Spatially resolved stellar population properties in galaxies (2015, methodology): “The inversion of the gradient in late type spirals and in low mass spirals may be an indicator of the secular processes or the outside-in formation scenario in these galaxies (Pérez et al. 2013).”
Stellar population gradients in galaxy discs from the CALIFA survey - The influence of bars (2014, methodology): “To check the extent of this dependence, we have compared our results with those obtained using STARLIGHT (Cid Fernandes et al. 2005) together with a set of models combination of V10 and González Delgado et al. (2005) for young stars (see Pérez et al. 2013 and González Delgado et al. 2014).”