[论文解读] Near-infrared and optical broadband surface photometry of 86 face-on disk dominated galaxies. IV. Using color profiles to study stellar and dust content of galaxies

Roelof S. de Jong|ArXiv.org|Apr 2, 1996

Impact of Light on Environment and Health被引用 5

一句话总结

本研究通过颜色剖面分析86个俯视螺旋星系的近红外与光学波段表面光度测量，探究恒星与尘埃含量。结果表明，颜色梯度主要由径向恒星年龄与金属量梯度解释，尘埃消光仅起次要作用，导致质量-光度比显著变化，从而加剧了旋转曲线分析中的“缺失光”问题。

ABSTRACT

The stellar and dust content of spiral galaxies as function of radius has been investigated using near-infrared and optical broadband surface photometry of 86 face-on spiral galaxies. Colors of galaxies correlate with the azimuthally averaged local surface brightness both within and among galaxies, with the lower surface brightness regions being bluer. The colors formed from different passband combinations correlate strongly indicating that they probably arise from the same physical process. A 3D radiative transfer model was developed to calculate the effect of dust absorption and scattering on the luminosity and color profiles of galaxies. Stellar synthesis models were used to investigate the effects of the star formation history and the metallicity on the broadband color profiles. Combining all optical and near-infrared data shows that the color gradients in this sample of face-on galaxies are best explained by a combined stellar age and metallicity gradient across the disk, with the outer regions being on average younger and of lower metallicity. Dust reddening probably plays only a minor role, as the dust models cannot produce reddening profiles that are compatible with the observations. The observed color differences implicate substantial M/L_lambda differences, both within galaxies and among galaxies. The variations are such that the ``missing light'' problem derived from rotation fitting becomes even worse. Late-type galaxies (T>=6) have lower metallicities and are often of younger average age than earlier types and have therefore an entirely different M/L_λin most passbands. The near-infrared passbands are recommended for studies where the M/L_λratios should not vary too much.

研究动机与目标

• 利用多波段光度测量，理解俯视盘状主导星系中恒星与尘埃组分的径向分布。
• 确定观测到的颜色梯度是由恒星群体性质还是尘埃消光效应引起。
• 评估恒星形成历史与金属量对宽带颜色剖面的影响。
• 评估尘埃在产生观测到的颜色梯度中的作用及其对质量-光度比（M/L）估计的影响。
• 考察M/L_lambda的变化如何影响星系旋转曲线研究中的“缺失光”问题。

提出的方法

• 获取86个俯视螺旋星系的近红外与光学波段表面光度测量。
• 使用多种滤波器组合（如B、V、R、I、K）构建方位平均颜色剖面。
• 应用三维辐射转移模型，模拟尘埃吸收与散射对亮度与颜色剖面的影响。
• 利用恒星合成模型，探究恒星形成历史与金属量对颜色剖面的影响。
• 结合光学与近红外数据，约束观测到的颜色梯度的物理成因。
• 将模型预测与观测到的颜色剖面比较，评估年龄、金属量与尘埃的相对贡献。

实验结果

研究问题

• RQ1 观测到的俯视螺旋星系的颜色梯度是由恒星群体梯度还是尘埃消光引起？
• RQ2 尘埃吸收与散射在多大程度上影响观测到的亮度与颜色剖面？
• RQ3 恒星年龄与金属量在星系盘面内的变化如何影响宽带颜色剖面？
• RQ4 这些恒星与尘埃特性对不同波段中质量-光度比（M/L_lambda）有何影响？
• RQ5 所推导出的M/L_lambda变化如何影响旋转曲线拟合中推断的“缺失光”问题？

主要发现

• 样本中的颜色梯度最合理地由径向恒星年龄与金属量梯度共同解释，外区恒星更年轻且金属量更低。
• 尘埃消光仅起次要作用，因尘埃模型在不产生显著偏差的情况下无法再现观测到的颜色剖面。
• 观测到的颜色差异导致质量-光度比（M/L_lambda）出现显著变化，无论在星系内部还是星系之间。
• 晚型星系（T ≥ 6）的金属量较低，且平均恒星年龄较早型星系更年轻，导致在大多数波段中M/L_lambda显著不同。
• 建议在需要稳定M/L_lambda比值的研究中使用近红外波段，因其对恒星群体变化的敏感性较低。
• 年龄与金属量梯度的综合作用加剧了由旋转曲线拟合推导出的“缺失光”问题，因为M/L_lambda随半径显著变化。