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S. O. Vasylyev, R. J. Buta (U. Alabama), H. Salo, E. Laurikainen (U. Oulu)
The distribution of bar strengths in disk galaxies is a fundamental property of the galaxy population that has only begun to be explored. We have applied the bar-spiral separation method of Buta, Block, and Knapen (2003, AJ, 126, 1148) to derive the distribution of maximum relative gravitational bar torques, Qb, for 147 spiral galaxies in the statistically well-defined Ohio State University Bright Galaxy Survey (Eskridge et al. 2002, ApJS, 143, 73) sample. Our goal is to examine the properties of bars as independently as possible of their associated spirals. We find that the relative frequency of bars declines approximately exponentially with increasing Qb, with more than 40% of the sample having Qb < 0.1. In the context of recurrent bar formation, this suggests that strongly-barred states are relatively short-lived compared to weakly-barred or non-barred states, while in the context of natural (spontaneous) bar formation, this suggests that the bar instability preferentially forms weak bars. The distribution of bar strengths undoubtedly includes a variety of bar formation and evolution processes that could possibly be deciphered with numerical modeling. We do not find compelling evidence for a bimodal distribution of bar strengths. Instead, the distribution is fairly smooth in the range 0.0 < Qb < 0.8.
Our analysis also provides a first look at spiral strengths Qs in the OSU sample, based on the same torque indicator. We are able to verify a possible weak correlation between Qs and Qb, in the sense that galaxies with the strongest bars tend also to have strong spirals.
This work was supported by NSF Grant AST 0205143 to the University of Alabama. Funding for the OSU Bright Galaxy Survey was provided by NSF grants AST-9217716 and AST-9617006, with additional funding from the Ohio State University.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.