EDP Sciences
Free access
Issue
A&A
Volume 400, Number 1, March II 2003
Page(s) 81 - 93
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20021910


A&A 400, 81-93 (2003)
DOI: 10.1051/0004-6361:20021910

Propagation velocities of gas rings in collisional ring galaxies

E. I. Vorobyov1 and D. Bizyaev2

1  Institute of Physics, Stachki 194, Rostov-on-Don, Russia, and Isaac Newton Institute of Chile, Rostov-on-Don Branch
2  Sternberg Astronomical Institute, Universitetsky prospect 13, Moscow, Russia; Isaac Newton Institute of Chile, Moscow Branch; Department of Physics, UTEP, El Paso, Texas, USA
    e-mail: dmbiz@sai.msu.ru

(Received 12 August 2002 / Accepted 16 December 2002 )

Abstract
The propagation velocity of the first gas ring in collisional ring galaxies, i.e. the velocity at which the maximum in the radial gas density profile propagates radially in the galactic disk, is usually inferred from the radial expansion velocity of gas in the first ring. Our numerical hydrodynamics modeling of ring galaxy formation however shows that the maximum radial expansion velocity of gas in the first ring ( $v_{\rm gas}$) is invariably below the propagation velocity of the first gas ring itself ( $v_{\rm
ring}$ ). Modeling of the Cartwheel galaxy indicates that the outer ring is currently propagating at $v_{\rm ring} \approx 100$ km s -1, while the maximum radial expansion velocity of gas in the outer ring is currently $v_{\rm gas} \approx 65$ km s -1. The latter value is in marginal agreement with the measurements of Higdon (1996) based on HI kinematics. Modeling of the radial B-V/V-K color gradients of the Cartwheel ring galaxy also indicates that the outer ring is propagating at $v_{\rm ring} \ge 90$ km s -1 for the adopted distance to the galaxy of 140 Mpc. On the other hand, the azimuthally averaged $\rm H\alpha$ surface brightness profile of the Cartwheel's outer ring does not peak exterior to those in K- and B -bands, contrary to what would be expected for such a high propagation velocity. We show that a combined effect of 41 $^{\circ}$ inclination, finite thickness, and warping of the Cartwheel's disk might be responsible for the lack of angular difference in the peak positions. Indeed, the radial $\rm H\alpha$ surface brightness profiles obtained along the Cartwheel's major axis, where effects of inclination and finite thickness are minimized, do peak exterior to those at K- and B-bands. The angular difference in peak positions implies $v_{\rm
ring}$ = 110 km s -1, which is in agreement with the model predictions. We briefly discuss the utility of radio continuum emission and spectral line equivalent widths for determining the propagation velocity of gas rings in collisional ring galaxies.


Key words: galaxies: individual: The Cartwheel -- galaxies: photometry

Offprint request: E. I. Vorobyov, eduard_vorobev@mail.ru

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