Volume-Limited Dependent Galactic Model Parameters
Volume-Limited Dependent Galactic Model Parameters
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DOI：
10.1071/as07006
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发表时间：
2007-11
影响因子：
6.3
通讯作者：
S. Karaali;S. Bilir;E. Yaz;E. Hamzaoğlu;R. Buser
中科院分区：
文献类型：
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作者：
S. Karaali;S. Bilir;E. Yaz;E. Hamzaoğlu;R. Buser
摘要 我们估计了银经度l = 60°、l = 90°和l = 180°的三个中纬度场的34组银河模型参数，并讨论了它们对体积的依赖关系。此外，我们还确认了这些参数随绝对星等和银河经度的变化。两个视场中的恒星样本受到明亮且单位绝对星等间隔的限制，4 < M g ≤ 5 和 5 < M g ≤ 6，而对于第三视场（l = 60°），采用更大的绝对星等间隔，4 < M g ≤ 10。恒星样本的极限视星等为 g 0 = 15 和 g 0 = 22.5 星等，这提供了线中距离内的空间密度视线范围为∼0.9和25 kpc。薄盘的银河模型参数与体积无关。然而，除了厚圆盘的尺度长度之外，厚圆盘和光晕的那些确实在随体积变化方面表现出惊人的趋势。厚盘的局部空间密度增加，而同一星系成分的尺度高度单调减少。然而，两个模型参数在大距离处都接近渐近值。通过将密度定律拟合到针对所有体积评估的空间密度来估计的光环的相对局部空间密度是恒定的，除了小体积之外。然而，它取决于绝对星等和银河经度。对于厚盘占主导地位的体积，晕轴比突然增加，而对于较大体积，晕轴比逐渐接近渐近值，表明在银河系最外层区域从盘状结构到球形结构的连续过渡。银河模型参数随绝对星等的变化可以通过其对恒星光度的依赖性来解释，而短距离处随体积和银河经度的变化是分析中的偏差。
Abstract We estimate 34 sets of Galactic model parameters for three intermediate-latitude fields with Galactic longitudes l = 60°, l = 90°, and l = 180°, and we discussed their dependence on the volume. Also, we confirm the variation of these parameters with absolute magnitude and Galactic longitude. The star samples in two fields are restricted with bright and unit absolute-magnitude intervals, 4 < M g ≤ 5, and 5 < M g ≤ 6, whereas for the third field (l = 60°) a larger absolute-magnitude interval is adopted, 4 < M g ≤ 10. The limiting apparent magnitudes of the star samples are g 0 = 15 and g 0 = 22.5 mag, which provide space densities within distances in the line of sight of ∼0.9 and 25 kpc. The Galactic model parameters for the thin disc are not volume dependent. However, the ones for the thick disc and halo do show spectacular trends in their variation with volume, except for the scalelength of the thick disc. The local space density of the thick disc increases, whereas the scaleheight of the same Galactic component decreases monotonically. However, both model parameters approach asymptotic values at large distances. The relative local space density of the halo estimated by fitting the density laws to the space densities evaluated for all volumes is constant, except for the small ones. However it is absolute-magnitude and Galactic longitude dependent. The axial ratio of the halo increases abruptly for the volumes where a thick disc is dominant, whereas it approaches an asymptotic value gradually for larger volumes, indicating a continuous transition from a disc-like structure to a spherical one at the outermost region of the Galaxy. The variation of the Galactic model parameters with absolute magnitude can be explained by their dependence on the stellar luminosity, whereas the variation with volume and Galactic longitude at short distances is a bias in analysis.