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arXiv 0710.1180astro-ph
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OSUBSGS样品的光学和近红外线强度比较

Comparison of bar strengths in optical and near-infrared for the OSUBSGS sample

T. Speltincx, E. Laurikainen, H. Salo

摘要:

我们使用的引力棒扭矩方法比较酒吧的强度(最大的切向力归一化径向力)在B和H波段图像的152个星系从俄亥俄州立大学明亮的螺旋星系调查。我们的主要动机是检查有多大的差异,在休息帧波长可能会影响比较酒吧的强度在低和高红移的意见。在这两个带之间,我们发现平均棒强度比Q_B/H= 1.25,该因子几乎与形态类型无关。结果表明,Q_B/H > 1主要是由于B带径向力的凸起稀释减小所致。棒矩法需要根据星系盘的径向尺度长度和星系的形态类型来估计星系的垂直尺度高度。由于在高红移时并不总是能够以可靠的方式确定这两个值,因此我们还检查了根据对应于20 mag/arcsec的K波段表面亮度的半径估算的垂直标度高度^[2],也得到了类似的结果。此外,我们做了一个简单的测试的可用性的酒吧扭矩方法在高红移检查图像退化的影响(最近邻采样没有任何调整的噪声水平):我们发现,估计酒吧的强度变化+/- 10%,只要酒吧的总范围至少是10个像素。总的来说,我们表明,重力酒吧扭矩方法应该提供一个熟练的工具,量化酒吧的强度也在高红移。

英文摘要:

We use a gravitational bar torque method to compare bar strengths (the maximum tangential force normalized by radial force) in B and H-band images of 152 galaxies from the Ohio State University Bright Spiral Galaxy Survey. Our main motivation is to check how much the difference in the rest-frame wavelength could affect comparisons of bar strengths in low and high redshift observations. Between these two bands we find an average bar strength ratio Q_B/H= 1.25 which factor is nearly independent of the morphological type. We show that Q_B/H > 1 is mostly due to reduced bulge dilution of radial forces in the B-band. The bar torque method needs an estimate for the vertical scale height of the galaxy, based on the radial scale length of the disk and the galaxy's morphological type. Since these two might not always be possible to determine at high redshifts in a reliable manner, we also checked that similar results are obtained with vertical scale heights estimated from the radii corresponding to the K-band surface brightness of 20 mag/arcsec^2. Also, we made a simple test of the usability of the bar torque method at high redshifts by checking the effects of image degradation (nearest neighbour sampling without any adjustment of noise levels): we found that the estimated bar strengths varied by +/- 10% at most as long as the total extent of the bar was at least 10 pixels. Overall, we show that the gravitational bar torque method should provide a proficient tool for quantifying bar strengths also at high redshifts.

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