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Physical condition of the molecular gas at the centre of NGC 1097
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
2011 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 414, no 1, 529-537 p.Article in journal (Refereed) Published
Abstract [en]

We have used the X(CO) conversion factor, local thermodynamic equilibrium and large velocity gradient approximation to parametrize the cold and warm phases 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 x 10(3) M(circle dot) pc(-3) and a CO column density of 1.2 x 10(-2) M(circle dot) pc(-2). A two-component model results in 85 per cent 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 on to the supermassive black hole in this prototype low-ionization nuclear emission-line region/Seyfert 1 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 of 10. Finally, we have calculated the X(CO) conversion factor for the centre of NGC 1097 using an independent estimation of the surface density to the CO emission and obtained X(CO) = (2.8 +/- 0.5) x 10(20) cm(-2) (K km s(-1))(-1) at a radius 10.5 arcsec and X(CO) = (5.0 +/- 0.5) x 10(20) cm(-2) (K km s(-1))(-1) at a radius 7.5 arcsec. With the approach and analysis described in this paper, we have demonstrated that important physical properties can be derived to a resolution beyond the single-dish resolution element; however, caution is necessary while interpreting the results.

Place, publisher, year, edition, pages
2011. Vol. 414, no 1, 529-537 p.
Keyword [en]
galaxies: fundamental parameters, galaxies: individual: NGC 1097
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:su:diva-67858DOI: 10.1111/j.1365-2966.2011.18419.xISI: 000292141600060OAI: oai:DiVA.org:su-67858DiVA: diva2:471609
Note

authorCount :4

Available from: 2012-01-02 Created: 2012-01-02 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Rearrangement of gas in disc galaxies
Open this publication in new window or tab >>Rearrangement of gas in disc galaxies
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Active galactic nuclei and bursts of star formation are two distinct phenomena that amply change their host environments. They are present in a significant number of galaxies at all redshifts. In this thesis, we aim toward a better understanding of the physical processes that allow for the formation and maintenance of these two phenomena. We focus on the study of the physical conditions of the interstellar gas in the central kiloparsec region of the barred active galaxy NGC 1097 (Paper I). In Paper I we present different CO transitions and the consequent analysis realized in order to derive the molecular gas content together with the molecular mass inflow toward the centre of the galactic gravitational potential well. To completely understand the physical processes that drive such gas rearrangement, a coherent picture for a dynamical system has to be considered. We have developed a code, Paper II, in order to model the dynamics of a predominantly rotating system with an arbitrary mass distribution. The formalism we have used is based on analytical solutions of the first order approximation of the equations of motion of a smooth medium that may be subject to dissipation. The most important free parameter to constrain the boundary conditions of the model is the angular frequency of the perturbing pattern, which may be assumed virtually invariant over significant ranges of galactocentric radii. We constrain the pattern velocity using the Tremaine-Weinberg method (Paper III). Hence, we have prepared all procedures needed to comprehend the physical processes that sustain the nuclear activity and bursts of star formation: the amount of gas in the region and the dynamics of the system. In Paper IV, we model the neutral and ionized gas kinematics in NGC 1097 and apply a combination of the methods described in Paper II and Paper III to comprehend the rearrangement of gas in the galaxy. In order to observationally discern the gas inflow in the nuclear region at a higher resolution, we apply the methods developed and used in this thesis to Cycle-0 ALMA observations of our target galaxy, and we confirm that we are able to follow the streaming of gas from 20 kiloparsec distances down to 40 parsecs from its central central supermassive black hole (Paper V).

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University, 2013. 54 p.
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-88636 (URN)978-91-7447-673-6 (ISBN)
Public defence
2013-06-05, sal FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Submitted. Paper 5: Submitted.

Available from: 2013-05-14 Created: 2013-03-23 Last updated: 2013-04-25Bibliographically approved

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