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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents



ID: 606482.0, MPI für Astronomie / Publikationen_mpia
High-resolution mapping of the physical conditions in two nearby active galaxies based on 12CO(1-0), (2-1), and (3-2) lines
Authors:Boone, F.; García-Burillo, S.; Combes, F.; Lim, J.; Ho, P.; Baker, A. J.; Matsushita, S.; Krips, M.; Dinh, V. T.; Schinnerer, E.
Date of Publication (YYYY-MM-DD):2011
Journal Abbrev.:Astronomy and Astrophysics
Volume:525
Audience:Not Specified
Abstract / Description:We present a detailed analysis of high resolution observations of the three lowest CO transitions in two nearby active galaxies, NGC 4569 and NGC 4826. The CO(1-0) and (2-1) lines were observed with the Plateau de Bure Interferometer and the CO(3-2) line with the Submillimeter Array. Combining these data allows us to compare the emission in the three lines and to map the line ratios, R21 = ICO(2-1)/ICO(1-0) and R32 = ICO(3-2)/ICO(1-0) at a resolution of ~2”, i.e., a linear resolution of 160 pc for NGC 4569 and 40 pc for NGC 4826. In both galaxies the emission in the three lines is similarly distributed spatially and in velocity, and CO is less excited (R32 < 0.6) than in the Galactic Center or the centers of other active galaxies studied so far. According to a pseudo-LTE model the molecular gas in NGC 4569 is cold and mainly optically thick in the CO(1-0) and (2-1) lines; less than 50% of the gas is optically thin in the CO(3-2) line. LVG modeling suggests the presence of an elongated ring of cold and dense gas coinciding with the inner Lindblad resonance (ILR) of the stellar bar in agreement with a previous analysis of the kinematics. More excited gas is resolved in the circumnuclear disk of NGC 4826. According to our pseudo-LTE model this corresponds to warmer gas with a ~20% of the CO(3-2) emission being optically thin. LVG modeling indicates the presence of a semicircular arc of dense and cold gas centered on the dynamical center and ~70 pc in radius. The gas temperature increases and its density decreases toward the center. A near side/far side asymmetry noticeable in the CO, R32 and Paα maps suggests that opacity effects play a role. Examining published CO maps of nearby active galaxies we find similar asymmetries suggesting that this could be a common phenomenon in active galaxies. These mainly qualitative results open new perspectives for the study of active galaxies with the future Atacama Large Millimeter/submillimeter Array. Based on observations carried out with the Submillimeter Array (SMA), a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics that is funded by the Smithsonian Institution and the Academia Sinica.Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).Appendix and Figs. 1, 5, 16-20, 23, 24 are only available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A>
Free Keywords:galaxies: active; galaxies: ISM; galaxies: individual: NGC 4569; galaxies: individual: NGC 4826
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:URL:http://cdsads.u-strasbg.fr/abs/2011A%26A...525A..1...
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