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Rearrangement of gas in disc galaxies
Stockholm University, Faculty of Science, Department of Astronomy.
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: urn:nbn:se:su:diva-88636ISBN: 978-91-7447-673-6 (print)OAI: oai:DiVA.org:su-88636DiVA: diva2:612652
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
List of papers
1. Physical condition of the molecular gas at the centre of NGC 1097
Open this publication in new window or tab >>Physical condition of the molecular gas at the centre of NGC 1097
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.

Keyword
galaxies: fundamental parameters, galaxies: individual: NGC 1097
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-67858 (URN)10.1111/j.1365-2966.2011.18419.x (DOI)000292141600060 ()
Note

authorCount :4

Available from: 2012-01-02 Created: 2012-01-02 Last updated: 2017-12-08Bibliographically approved
2. Analytic gas orbits in an arbitrary rotating galactic potential using the linear epicyclic approximation
Open this publication in new window or tab >>Analytic gas orbits in an arbitrary rotating galactic potential using the linear epicyclic approximation
2012 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 421, no 2, 1089-1102 p.Article in journal (Refereed) Published
Abstract [en]

A code, EPIC5, has been developed which computes, in the two-dimensional case, the initially circular orbits of guiding centra in an arbitrary axisymmetric potential with an arbitrary, weak perturbing potential in solid body rotation. This perturbing potential is given by its Fourier expansion. The analytic solution solves the linear epicyclic approximation of the equations of motion. To simulate the motion of interstellar matter and to damp the Lindblad resonances, in these equations we have introduced a friction which is proportional to the deviation from circular velocity. The corotation resonance is also damped by a special parameter. The program produces, in just a few seconds, orbital and density maps, as well as line-of-sight velocity maps for a chosen orientation of the galaxy. We test EPIC5 by comparing its results with previous simulations and observations from the literature, which gives satisfactory agreement. The aim is that this program should be a useful complement to elaborate numerical simulations. Particularly so are its abilities to quickly explore the parameter space, to construct artificial galaxies and to isolate various single agents important for developing the structure of interstellar matter in disc galaxies. The EPIC5 code can be obtained from npi@astro.su.se.

Keyword
galaxies: kinematics and dynamics, galaxies: spiral
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-76054 (URN)10.1111/j.1365-2966.2011.20367.x (DOI)000302695600013 ()
Note
3Available from: 2012-05-08 Created: 2012-05-08 Last updated: 2017-12-07Bibliographically approved
3. Pattern Speeds of Bars and Spiral Arms from Hα Velocity Fields
Open this publication in new window or tab >>Pattern Speeds of Bars and Spiral Arms from Hα Velocity Fields
Show others...
2009 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 704, 1657-1675 p.Article in journal (Refereed) Published
Abstract [en]

We have applied the Tremaine-Weinberg method to 10 late-type barred spiral galaxies using data cubes, in Hα emission, from the FaNTOmM and GHAFAS Fabry-Perot spectrometers. We have combined the derived bar (and/or spiral) pattern speeds with angular frequency plots to measure the corotation radii for the bars in these galaxies. We base our results on a combination of this method with a morphological analysis designed to estimate the corotation radius to bar-length ratio using two independent techniques on archival near-infrared images, and although we are aware of the limitation of the application of the Tremaine-Weinberg method using Hα observations, we find consistently excellent agreement between bar and spiral arm parameters derived using different methods. In general, the corotation radius, measured using the Tremaine-Weinberg method, is closely related to the bar length, measured independently from photometry and consistent with previous studies. Our corotation/bar-length ratios and pattern speed values are in good agreement with general results from numerical simulations of bars. In systems with identified secondary bars, we measure higher Hα velocity dispersion in the circumnuclear regions, whereas in all the other galaxies, we detect flat velocity dispersion profiles. In the galaxies where the bar is almost purely stellar, Hα measurements are missing, and the Tremaine-Weinberg method yields the pattern speeds of the spiral arms. The excellent agreement between the Tremaine-Weinberg method results and the morphological analysis and bar parameters in numerical simulations suggests that although the Hα emitting gas does not obey the continuity equation, it can be used to derive the bar pattern speed. In addition, we have analyzed the Hα velocity dispersion maps to investigate signatures of secular evolution of the bars in these galaxies. The increased central velocity dispersion in the galaxies with secondary bars suggests that the formation of inner bars or disks may be a necessary step in the formation of bulges in late-type spiral galaxies.

Keyword
galaxies: evolution, galaxies: ISM, galaxies: kinematics and dynamics, galaxies: spiral, galaxies: structure
National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-31995 (URN)10.1088/0004-637X/704/2/1657 (DOI)000270486200049 ()0004-637X (ISBN)
Available from: 2009-12-01 Created: 2009-12-01 Last updated: 2017-12-12Bibliographically approved
4. Bar pattern speed and position of the circumnuclear ringin NGC 1097
Open this publication in new window or tab >>Bar pattern speed and position of the circumnuclear ringin NGC 1097
Show others...
2014 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 438, no 2, 971-982 p.Article in journal (Refereed) Published
Abstract [en]

We present the first galactic-scale model of the gas dynamics of the prototype barred Seyfert 1 galaxy NGC 1097. We use large scale FaNTOmM Fabry-Perot interfer-ometric data covering the entire galactic disc and combined the distribution andkinematics maps with high resolution two-dimensional spectroscopy from the Gemini telescope. We build a dynamical model for the gravitational potential by applying the analytic solution to the equations of motion, with in the epicyclic approximation. Our model reproduces all the significant kinematic and structural signatures of thisgalaxy. We find that the primary bar is 7.9±0.6 kpc long and has a pattern speedof 36 ± 2 km s−1 kpc−1. This places the corotation radius at 8.6±0.5 kpc, the outer Lindblad resonance at 14.9±0.9 kpc and two inner Lindblad resonances at 60±5 pcand 2.9±0.1 kpc. These derivations lead to a ratio of the corotation radius over barlength of 1.0–1.2, which is in concordance with simulations of barred galaxies. Our model presents evidence that the circumnuclear ring in this galaxy is not located near any of the resonance radii in this galaxy. The ring might have once formed at the outer inner Lindblad resonance radius, and it has been migrating inward, toward the centre of the galactic gravitational potential.

Keyword
galaxies: active, galaxies: evolution, galaxies: kinematics and dynamics, galaxies: structure
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-88634 (URN)10.1093/mnras/stt2162 (DOI)000330955900006 ()
Available from: 2013-03-23 Created: 2013-03-23 Last updated: 2017-12-06Bibliographically approved
5. ALMA FOLLOWS STREAMING OF DENSE GAS DOWN TO 40 PC FROM THE SUPERMASSIVE BLACKHOLE IN NGC 1097
Open this publication in new window or tab >>ALMA FOLLOWS STREAMING OF DENSE GAS DOWN TO 40 PC FROM THE SUPERMASSIVE BLACKHOLE IN NGC 1097
Show others...
2013 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, Vol. 770, no 2, L27- p.Article in journal (Refereed) Published
Abstract [en]

We present a kinematic analysis of the dense gas in the central 200 parsecs of thenearby galaxy NGC1097, based on Cycle 0 observations with the Atacama LargeMillimeter/sub-millimeter Array (ALMA). We use the HCN(4-3) line to trace the densest interstellar molecular gas (nH2 ~ 10^8 cm-3), and quantify its kinematics by means of Fourier decomposition. We find a striking similarity between the ALMA kinematic data and the analytic spiral in ow model that we have previously constructed based onionized gas velocity fields on larger scales. We are able to follow dense gas streamingdown to 40 pc distance from the supermassive black hole in this Seyfert 1 galaxy. In order to fulll marginal stability, we deduce that the dense gas is conned to a very thin disc, with 6.0+2.2-2.7 10^6 Msun dynamical mass inside a radius of 40 pc. Finally, we derive a dense gas in ow rate of 0.09Msun yr-1 at 40 pc radius. Combined with previous valuesfrom the H and CO gas, we calculate a combined molecular and ionized gas in ow rateof 0.2Msun yr-1 at 40 pc distance from the central supermassive black hole of NGC1097.

Keyword
galaxies: active, galaxies: individual (NGC 1097), galaxies: kinematics and dynamics
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-88635 (URN)10.1088/2041-8205/770/2/L27 (DOI)000320709900011 ()
Available from: 2013-03-23 Created: 2013-03-23 Last updated: 2013-12-11Bibliographically approved

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