We use the tapering effect of Halpha/[NII] rotation curves of spiral galaxies first noted by Goad & Roberts (1981) to investigate the internal extinction in disks. The scale length of exponential fits to the inner part of rotation curves depends strongly on the disk axial ratio. Preliminary modelling of the effect implies substantial opacity of the central parts of disks at a wavelength of 0.66 \mu. In addition, the average kinematic scale length of rotation curves, when corrected to face--on perspective, has a nearly constant value of about 1.7 h^{-1} kpc, for all luminosity classes. The interpretation of that effect, as the result of the increasing dominance of the baryonic mass in the inner parts of galaxies, yields a mean baryonic mass--to--light ratio in the I band \Upsilon_I= 2.7h M_sun/L_{sun,I}, within the inner 1.7 h^{-1} kpc of disks.
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机译：我们使用Goad＆Roberts（1981）首次注意到的螺旋星系的Halpha / [NII]旋转曲线的渐缩效应来研究磁盘内部的灭绝。旋转曲线内部的指数拟合的刻度长度在很大程度上取决于圆盘的轴向比率。效果的初步模型表明，在0.66μm的波长下，圆盘中心部分基本不透明。此外，对所有发光度类别而言，旋转曲线的平均运动尺度长度（当校正为面向正面时）的近似恒定值约为1.7 h ^ {-1} kpc。对这种效应的解释，是由于星系内部重子质量占主导地位的结果，在I波段中产生了重子质量与光的平均比。\ Upsilon_I = 2.7h M_sun / L_ {sun ，I}，位于内部1.7 h ^ {-1} kpc磁盘内。
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