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Pattern Speeds of Bars and Spiral Arms from Hα Velocity Fields
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
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2009 (English)In: Astrophysical Journal, ISSN 0004-637X, 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.

Place, publisher, year, edition, pages
2009. Vol. 704, 1657-1675 p.
Keyword [en]
galaxies: evolution, galaxies: ISM, galaxies: kinematics and dynamics, galaxies: spiral, galaxies: structure
National Category
Natural Sciences
URN: urn:nbn:se:su:diva-31995DOI: 10.1088/0004-637X/704/2/1657ISI: 000270486200049ISBN: 0004-637XOAI: diva2:279159
Available from: 2009-12-01 Created: 2009-12-01 Last updated: 2013-03-25Bibliographically 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
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)

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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