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تسجيل مستخدم جديدThe Assembly and Evolution of Spiral Disks
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Matthew Bershady
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We explore how the growth rate of spiral disks can be measured via analyses of the scatter in the Tully-Fisher (TF) relation of local and intermediate redshift galaxies. As an initial step, we show it is possible to construct a low-dispersion TF relation for nearly face-on, nearby spirals. We find these spiral disks are non-circular, (a mean ellipticity of 6%), which accounts for about 0.1 mag of the intrinsic scatter in the nearby TF relation of even the most ``normal looking spirals. If this ellipticity is induced by matter accretion, we expect to find greater disk ellipticity or disturbance in the past. We find evidence that more extreme outliers of the intermediate-redshift TF relation are more morphologically and kinematically disturbed. Whether this effect reflects a redshift trend or selection bias of local samples needs to be addressed.
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galaxy pairs. The main results from both so far are a semi-transparent disk with more opaque arms, and a relation between surface brightness and disk opacity. In the Spitzer era, SED models of spiral disks add a new perspective on the role of dust in spiral disks. Combined with the overall opacity from galaxy counts, they yield a typical optical depth of the dusty ISM clouds: 0.4 that implies a size of ~60 pc. Work on galaxy counts is currently ongoing on the ACS fields of M51, M101 and M81. Occulting galaxies offer the possibility of probing the history of disk opacity from higher redshift pairs. Evolution in disk opacity could influence distance measurements (SN1a, Tully-Fisher relation). Here, we present first results from spectroscopically selected occulting pairs in the SDSS. The redshift range for this sample is limited, but does offer a first insight into disk opacity evolution as well as a reference for higher redshift measurements.
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