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تسجيل مستخدم جديدSigma-drop in galaxies and the sigma-metallicity degeneracy
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تأليف
Mina Koleva
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In some galaxies, the central velocity dispersion, sigma, is depressed with respect to the surroundings. This sigma-drop phenomenon may have different physical origins, bearing information about the internal dynamics of the host galaxy. In this article, we stress the importance also of observational artifacts due to the sigma-metallicity degeneracy: when a spectrum of a population is compared with a template of miss-matched metallicity, the velocity dispersion may be wrongly estimated. A sigma-drop may appear in place of a metallicity peak. The discussion is illustrated using VLT/FORS spectra of diffuse elliptical galaxies. Some of the sigma-drop galaxies reported in the literature may be analysis artifacts.
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Context: Local reductions of the stellar velocity dispersion in the central regions of galaxies are known as sigma-drops. Knowing the origin of these features can lead to better understanding of inner galactic dynamics. Aims: We present a sample of
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igma^{+} bar{Sigma}^{-}$ decays. The relative phases of the form factors $DeltaPhi$ have been measured to be $(-15.5pm0.7pm0.5)^{circ}$ and $(21.7pm4.0pm0.8)^{circ}$ with $J/psi$ and $psi(3686)$ data, respectively. The non-zero value of $DeltaPhi$ allows for a direct and simultaneous measurement of the decay asymmetry parameters of $Sigma^{+}rightarrow p pi^{0}~(alpha_0 = -0.998pm0.037pm0.009)$ and $bar{Sigma}^{-}rightarrow bar{p} pi^{0}~(bar{alpha}_0 = 0.990pm0.037pm0.011)$, the latter value being determined for the first time. The average decay asymmetry, $(alpha_{0} - bar{alpha}_{0})/2$, is calculated to be $-0.994pm0.004pm0.002$. The CP asymmetry $A_{rm CP,Sigma} = (alpha_0 + bar{alpha}_0)/(alpha_0 - bar{alpha}_0) = -0.004pm0.037pm0.010$ is extracted for the first time, and is found to be consistent with CP conservation.
We analyze new measurements of the Mg_2 central line strength index and velocity dispersion (sigma) for the galaxies of the ENEAR survey. The observations are now complete (da Costa et al. 2000) and the sample contains 1223 early-type galaxies. We al
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