用从X射线到射电波长的多重选择技术确定COSMOS中红化类星体的比例
Determining the fraction of reddened quasars in COSMOS with multiple selection techniques from X-ray to radio wavelengths
摘要：
被内在或居间的尘埃云变红的类星体子种群在光学类星体调查中被低估了。通过定义一个完整的父样本的最明亮的和空间未解决的类星体在宇宙领域，我们量化到何种程度，这个子人口是根本的，我们了解的类星体的真实人口。通过使用COSMOS领域各种调查的多波长数据，我们建立了一个由33个比$J=20$等亮的类星体组成的母样本，这些类星体通过可靠的X射线到无线电波长选择技术进行识别。使用NOT/ALFOSC对之前没有被瞄准的四个候选类星体进行了光谱跟踪，以获得样品的100%红移完整性。高$A_V$类星体（HAQs）是从光学/近红外光度测量中选出的一类特殊的类星体，它对母体样品的$21\%^{+9}_{-5}$有贡献。由我们的母样本代表的明亮的空间未分辨类星体的全部人口由$39\%^{+9}_{-8}$红化类星体组成，定义为具有$A_V>0.1$，以及假设小麦哲伦云的消光曲线具有$E(B-V)>0.1$的样本的$21\%^{+9}_{-5}$。我们表明，HAQ选择工作以及选择红化类星体，但有些被错过，因为他们的光谱太蓝，通过$g-r$的颜色削减HAQ选择。这可能是由于尘埃红化程度较低或光谱异常所致。我们发现，类星体的贡献光从宿主星系的分数是最主要的$z \lesssim 1$。在较高的红移的人口的空间未解决的类星体选择我们的父样本被发现是代表的全部人口在$J<20$马格。这项工作量化的偏见，对红化类星体的研究是完全基于光学调查。
英文摘要：
The sub-population of quasars reddened by intrinsic or intervening clouds of dust are known to be underrepresented in optical quasar surveys. By defining a complete parent sample of the brightest and spatially unresolved quasars in the COSMOS field, we quantify to which extent this sub-population is fundamental to our understanding of the true population of quasars. By using the available multiwavelength data of various surveys in the COSMOS field, we built a parent sample of 33 quasars brighter than $J=20$ mag, identified by reliable X-ray to radio wavelength selection techniques. Spectroscopic follow-up with the NOT/ALFOSC was carried out for four candidate quasars that had not been targeted previously to obtain a 100\% redshift completeness of the sample. The population of high $A_V$ quasars (HAQs), a specific sub-population of quasars selected from optical/near-infrared photometry, is found to contribute $21\%^{+9}_{-5}$ of the parent sample. The full population of bright spatially unresolved quasars represented by our parent sample consists of $39\%^{+9}_{-8}$ reddened quasars defined by having $A_V>0.1$, and $21\%^{+9}_{-5}$ of the sample having $E(B-V)>0.1$ assuming the extinction curve of the Small Magellanic Cloud. We show that the HAQ selection works well for selecting reddened quasars, but some are missed because their optical spectra are too blue to pass the $g-r$ color cut in the HAQ selection. This is either due to a low degree of dust reddening or anomalous spectra. We find that the fraction of quasars with contributing light from the host galaxy is most dominant at $z \lesssim 1$. At higher redshifts the population of spatially unresolved quasars selected by our parent sample is found to be representative of the full population at $J<20$ mag. This work quantifies the bias against reddened quasars in studies that are based solely on optical surveys.
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