Continuum removal in Hα extragalactic measurements
Continuum removal in Hα extragalactic measurements
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DOI：
10.1111/j.1365-2966.2011.19869.x
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发表时间：
2011-10
影响因子：
4.8
通讯作者：
O. Spector;I. Finkelman;N. Brosch
中科院分区：
文献类型：
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作者：
O. Spector;I. Finkelman;N. Brosch
本文指出了河外Hα辐射测量中的一个重要误差来源，并提出了减小误差的方法. Hα线用于估算星星的形成速率，通常通过窄带和宽带成像来测量，这两个波段都包括H α线.图像分析依赖于对潜在连续体的准确去除。详细讨论了河外扩展源发射线的等效宽度和通量的推导，以及所需的测光定标。我们描述了常用的连续减法程序，并讨论了它们引入的不确定性。具体来说，我们分析的颜色效应引入的错误。我们表明，在测量的Hα等效宽度的颜色效应引起的误差可能会导致低估高达40%和高估高达10%，这取决于底层星系的恒星人口和连续减法程序使用。我们还表明，这些错误可能会导致偏差的调查结果，并低估宇宙星星的形成率在低红移（低z点的Madau图）。我们提出了一种方法，以显着减少这些错误使用一个单一的颜色测量。
We point out an important source of error in measurements of extragalactic Hα emission and suggest ways to reduce it. The Hα line, used for estimating star formation rates, is commonly measured by imaging in a narrow band and a wide band, both of which include the line. The image analysis relies on the accurate removal of the underlying continuum. We discuss in detail the derivation of the emission-line’s equivalent width and flux for extragalactic extended sources, and the required photometric calibrations. We describe commonly used continuum-subtraction procedures, and discuss the uncertainties that they introduce. Specifically, we analyse errors introduced by colour effects. We show that the errors in the measured Hα equivalent width induced by colour effects can lead to underestimates as large as 40 per cent and overestimates as large as 10 per cent, depending on the underlying galaxy’s stellar population and the continuum-subtraction procedure used. We also show that these errors may lead to biases in results of surveys, and to the underestimation of the cosmic star formation rate at low redshifts (the low z points in the Madau plot). We suggest a method to significantly reduce these errors using a single colour measurement.