CAJ | 학술논문

利用天体光谱上DLAs系统吸收线测定星际或星系际介质的金属元素丰度，是研究星系际介质和星系化学演化的基础。目前主要有三种测定元素柱密度的方法：生长曲线法、谱线轮廓拟合法和视光深法。古老的生长曲线法目前主要应用于光谱分辨率不高的观测，而且常常只用于气体云光学薄的情形，但是这种方法不受仪器轮廓的影响。在当今光谱分辨率观测普遍较高以及计算机技术相当发达的情况下，谱线轮廓拟合法和视光深法获得了更多的应用，尤其是谱线轮廓拟合法。只是它有较多的自由参数需要确定，从而需要大量的计算时间，有时会出现几个不同收敛解的情况；另外，在谱线混合严重的情况下这种方法也会引入较多的偏差。至于介于这两种方法之间的视光深法，由于简单而可靠，当今也受到部分研究者的偏爱；只是由于谱线隐性饱和的存在，使这种方法的应用受到限制。
이용천체광보상DLAs계통흡수선측정성제혹성계제개질적금속원소봉도，시연구성계제개질화성계화학연화적기출。목전주요유삼충측정원소주밀도적방법：생장곡선법、보선륜곽의합법화시광심법。고로적생장곡선법목전주요응용우광보분변솔불고적관측，이차상상지용우기체운광학박적정형，단시저충방법불수의기륜곽적영향。재당금광보분변솔관측보편교고이급계산궤기술상당발체적정황하，보선륜곽의합법화시광심법획득료경다적응용，우기시보선륜곽의합법。지시타유교다적자유삼수수요학정，종이수요대량적계산시간，유시회출현궤개불동수렴해적정황；령외，재보선혼합엄중적정황하저충방법야회인입교다적편차。지우개우저량충방법지간적시광심법，유우간단이가고，당금야수도부분연구자적편애；지시유우보선은성포화적존재，사저충방법적응용수도한제。
In the first of our series review paper about Damped Lyman Alpha systems (DLAs), we have mainly given a detailed introduction to the recent progress in DLA surveys. In this second paper of the series, we will review the main methods of measuring the metal column density in the gas clouds along the line of sight towards the background QSOs. <br> There are three main methods of measuring the metal column density of gas clouds:Curve of Growth;Line Profile Fitting and Apparent Optical Depth methods. The method of Curve of Growth (COG) was developed in about half a century ago. So far it has been mainly applied in observations with the low spectral resolution. Though the COG is unaffected by the instrumental profile, it is widely used in the case of optical thin gas clouds. In recent years, most of the observations are done with high resolution spectrographs, therefore the acquired spectra are of very high spectral resolution. In this case the Line Profile Fitting method (LPTM) and the Apparent Optical Depth method (AODM) are more frequently adopted by most of astronomers. The LPTM is often used in measuring the column density of gas, but it has more fitting parameters. So, it will consume more time of calculation and sometimes will result in several convergence solutions. It will also introduce more deviations when a line is blended seriously with other lines. The AODM is adopted by some groups since it is more simple and reliable in some cases. But this method suffers from the indirect line saturation in spectra, so it is only used in some special cases.