Physical Condition of Molecular Gas at the Centre of the active galaxy NGC 1097

Details Physical Condition of Molecular Gas at the Centre of the active galaxy NGC 1097 Physical Condition of Molecular Gas at the Centre of the active galaxy NGC 1097

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p.304p&link_type=abstract

The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole

Astronomy and Astrophysics

Astronomy

Scientific paper

We have used the Xco conversion factor, Local Thermal Equilibrium and Large Velocity Gradient approximation to parametrize the cold and warm phase of the interstellar medium from five different low transitions of the CO molecule in the central 21 arcsec (kpc) region of NGC 1097. We have applied a one-component model and derived a typical kinetic temperature of about 33 K, a molecular Hydrogen density of 4.9×103 M&sun; pc-3 and a CO column density of 1.2× 10-2 M&sun; pc-2. A two-component model results in 85% cold-to-total gas fraction in the presence of a 90 K warm counterpart. Furthermore, we ``resolve" the spatially unresolved single dish observations by selecting velocity channels that in an interferometric velocity map correspond to specific regions. We have selected five such regions and found that the physical properties in these regions are comparable to those derived from the full line profile. This implies that the central kpc of NGC 1097 is rather homogeneous in nature, and, although the regions are not uniquely located within the ring, the star formation along the ring is homogeneously distributed (in agreement with recent Herschel observations). We have further revised the mass inflow rate onto the Supermassive Black Hole in this prototype LINER/Sy1 galaxy and found that, accounting for the total interstellar medium and applying a careful contribution of the disc thickness and corresponding stability criterion, increases the previous estimations by a factor 10. Finally we have calculated the Xco conversion factor for the centre of NGC 1097 using an independent estimation of the surface density to the CO emission, and obtained Xco=(2.8%B m0.5)× 1020 cm-2 (K km s-1)-1 at radius 10.5 arcsec and Xco=(5.0%B m0.5)×1020 cm-2 (K km s-1)-1 at radius 7.5 arcsec. With the approach and analysis described in here we have demonstrated that important physical properties can be derived to a resolution beyond the single dish resolution element, however, caution is necessary for interpreting the results. To obtain a more accurate description of the molecular gas at the nuclear region, observations of higher transitions with ALMA will help overcome most of the limitations that we have faced in the current work.

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