[论文解读] Aperture corrections for disk galaxy properties derived from the CALIFA survey. Balmer emission lines in spiral galaxies

J. Iglésias-Páramo, J. M. Vı́lchez+38 more|DIGITAL.CSIC (Spanish National Research Council (CSIC))|Apr 5, 2013

Galaxies: Formation, Evolution, Phenomena参考文献 28被引用 31

一句话总结

本研究利用CALIFA巡天提供的空间分辨光谱，对104个旋涡星系的巴尔默发射线进行了孔径修正。研究发现，Hα光度和f(Hα)/f(Hβ)比值在0.3至2.5 R₅₀的孔径范围内表现出低分散性，修正结果可靠；而Hα等效宽度则显示高分散性，导致无法获得可靠的孔径修正，并引发使用小孔径时可能将星系错误分类为宁静星系的担忧。

ABSTRACT

This work investigates the effect of the aperture size on derived galaxy properties for which we have spatially-resolved optical spectra. We focus on some indicators of star formation activity and dust attenuation for spiral galaxies that have been widely used in previous work on galaxy evolution. We have used 104 spiral galaxies from the CALIFA survey for which 2D spectroscopy with complete spatial coverage is available. From the 3D cubes we have derived growth curves of the most conspicuous Balmer emission lines (Halpha, Hbeta) for circular apertures of different radii centered at the galaxy's nucleus after removing the underlying stellar continuum. We find that the Halpha flux (f(Halpha)) growth curve follows a well defined sequence with aperture radius showing low dispersion around the median value. From this analysis, we derive aperture corrections for galaxies in different magnitude and redshift intervals. Once stellar absorption is properly accounted for, the f(Halpha)/f(Hbeta) ratio growth curve shows a smooth decline, pointing towards the absence of differential dust attenuation as a function of radius. Aperture corrections as a function of the radius are provided in the interval [0.3,2.5]R_50. Finally, the Halpha equivalent width (EW(Halpha)) growth curve increases with the size of the aperture and shows a very large dispersion for small apertures. This large dispersion prevents the use of reliable aperture corrections for this quantity. In addition, this result suggests that separating star-forming and quiescent galaxies based on observed EW(Halpha) through small apertures is likely to result in low EW(Halpha) star-forming galaxies begin classified as quiescent.

研究动机与目标

• 量化光谱巡天中有限天空覆盖度对星系性质测量的孔径效应影响。
• 评估关键恒星形成指标（如Hα光度、f(Hα)/f(Hβ)比值和Hα等效宽度）的孔径修正可靠性。
• 确定小孔径是否会导致基于EW(Hα)将星系系统性误分类为宁静星系。
• 为现有及未来星系巡天提供经验孔径修正关系。

提出的方法

• 从CALIFA巡天获取104个具有完整空间覆盖的旋涡星系的三维光谱立方体。
• 使用以星系核为中心、半径不同的圆形孔径，提取Hα和Hβ发射线的生长曲线。
• 在测量线光度和等效宽度前，先去除背景恒星连续谱。
• 通过比较孔径内光度与全空间覆盖下总光度，计算孔径修正。
• 通过分析中位生长曲线的分散性，评估修正的可靠性。
• 利用f(Hα)/f(Hβ)的径向分布推断尘埃消光趋势及其径向依赖性。

实验结果

研究问题

• RQ1 孔径大小如何影响旋涡星系中Hα和Hβ发射线的测量光度？
• RQ2 f(Hα)/f(Hβ)比值随孔径半径的变化程度如何，是否反映尘埃消光的径向梯度？
• RQ3 鉴于其径向可变性，能否为Hα等效宽度建立可靠的孔径修正？
• RQ4 小孔径对基于EW(Hα)将星系分类为星形成与宁静星系的影响如何？
• RQ5 倾角（面朝向与侧向）如何影响小孔径下EW(Hα)的观测分散性？

主要发现

• Hα光度生长曲线在0.3至2.5 R₅₀的孔径范围内围绕中位值表现出低分散性，表明其行为具有良好的定义性和可重复性。
• f(Hα)/f(Hβ)比值随孔径半径增大而平滑下降，表明尘埃消光的径向变化极小。
• f(Hα)和f(Hα)/f(Hβ)的中位孔径修正在0.3–2.5 R₅₀范围内可靠且适用。
• Hα等效宽度生长曲线在小孔径（r/R₅₀ ≤ 1.3）时表现出高分散性（σ > 0.3），导致无法建立可靠的孔径修正。
• 对于总EW(Hα) = 6 Å的面朝向旋涡星系，有50%的概率在孔径小于R₅₀时观测到EW(Hα) ≤ 3 Å，存在被错误分类为宁静星系的风险。
• EW(Hα)在径向方向上的大分散性意味着小孔径测量结果不可靠，尤其在面朝向系统中更为显著。