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تسجيل مستخدم جديدThe Vcirc-sigma0 Relation of Galaxies
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Courteau et al. (2007a) reported on the dependence of the ratio of a galaxys maximum circular velocity, Vcirc, to its central velocity dispersion, sigma0, on morphology, or equivalently total light concentration. This Vcirc-sigma0 concentration relation, which involves details about the local and global galaxy physics, poses a fundamental challenge for galaxy structure models. Furthermore, not only must these models reproduce the Vcirc-sigma0 relation and its various dependences, they must simultaneously match other fundamental scaling relations such as the velocity-size-luminosity and color-luminosity relations of galaxies. We focus here on the interpretation of parameters that enter the Vcirc-sigma0 relation to enable proper data-model comparisons and follow-up studies by galaxy modelers and observers.
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We explore the dependence of the ratio of a galaxys circular velocity, Vcirc, to its central velocity dispersion, sigma_0, on morphology, or equivalently total light concentration. Such a dependence is expected if light traces the mass. Over the full
range of galaxy types, masses and brightnesses, and assuming that the gas velocity traces the circular velocity, we find that galaxies obey the relation log(Vcirc/sigma_0)= 0.63-0.11*C28 where C28=5log(r80/r20) and the radii are measured at 80 percent and 20 percent of the total light. Massive galaxies scatter about the Vcirc = sqrt(2)*sigma_0 line for isothermal stellar systems. Disk galaxies follow the simple relation Vcirc/sigma_0=2(1-B/T), where B/T is the bulge-to-total light ratio. For pure disks, C28~2.8, B/T -> 0, and Vcirc~=2*sigma_0. Self-consistent equilibrium galaxy models from Widrow & Dubinski (2005) constrained to match the size-luminosity and velocity-luminosity relations of disk galaxies fail to match the observed Vcirc/sigma_0 distribution. Furthermore, the matching of dynamical models for Vcirc(r)/sigma(r) with observations of dwarf and elliptical galaxies suffers from limited radial coverage and relatively large error bars; for dwarf systems, however, kinematical measurements at the galaxy center and optical edge suggest Vcirc(Rmax) > 2*sigma_0 (in contrast with past assumptions that Vcirc = sqrt(2)*sigma_0 for dwarfs.) The Vcirc-sigma_0-C28 relation has direct implications for galaxy formation and dynamical models, galaxy scaling relations, the mass function of galaxies, and the links between respective formation and evolution processes for a galaxys central massive object, bulge, and dark matter halo.
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