2000/10/17 by R. Buta, David L. Block, D. L. Block · 1 citation
Physics and Astronomy · #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/319736
Accepted for publication in the Astrophysical Journal (LaTex, 30 pages + 3 figures); Figs. 1 and 3 are in color and are also available at http://bama.ua.edu/~rbuta/bars/
arxiv created 2000/10/17 · openalex publication_date 2001/03/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
The division of galaxies into "barred" (SB) and "normal" (S) spirals is a fundamental aspect of the Hubble galaxy classification system. This "tuning fork" view was revised by de Vaucouleurs, whose classification volume recognized apparent "bar strength" (SA, SAB, SB) as a continuous property of galaxies called the "family." However, the SA, SAB, and SB families are purely visual judgments that can have little bearing on the actual bar strength in a given galaxy. Until very recently, published bar judgments were based exclusively on blue light images, where internal extinction or star formation can either mask a bar completely or give the false impression of a bar in a nonbarred galaxy. Near-infrared camera arrays, which principally trace the old stellar population in both normal and barred galaxies, now facilitate a quantification of bar strength in terms of their gravitational potentials and force fields. In this paper, we show that the maximum value, Q b , of the ratio of the tangential force to the mean axisymmetric radial force in a barred disk galaxy is a quantitative measure of the strength of a bar. Q b does not measure bar ellipticity or bar shape but rather depends on the actual forcing due to the bar embedded in its disk. We show that a wide range of true bar strengths characterizes the category "SB," while the de Vaucouleurs category "SAB" corresponds to a narrower range of bar strengths. We present Q b values for 36 galaxies, and we incorporate our bar classes into a dust-penetrated classification system for spiral galaxies.