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研究生： 黃鼎耆
Huang, Ting-Chi
論文名稱： 藉由擬合中紅外線波段的光譜能帶分佈來篩選AKARI北黃極深域內的活躍星系核
AGN selection by 18-band SED fitting in mid-infrared in the AKARI NEP deep field
指導教授： 後藤友嗣
Goto, Tomotsugu
口試委員: 大山陽一
Oyama, Youichi
賴詩萍
Lai, Shih-Ping
學位類別： 碩士
Master
系所名稱： 理學院 - 物理學系
Department of Physics
論文出版年： 2017
畢業學年度： 105
語文別： 英文
論文頁數： 43
中文關鍵詞： 活躍星系核 、光譜能帶分佈 、恆星形成星系 、星爆星系
外文關鍵詞： active, spectral, star-forming, starburst
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    • 藉由擬合中紅外線波段的光譜能帶分佈，我們發展出了一套有效篩選活躍星系核的方法。活躍星系核常被氣體和塵埃所遮蔽，因此不容易使用可見光、紫外線或X光的望遠鏡來觀測。但因為氣體和塵埃吸收紫外線後會產生熱輻射並以紅外線傳遞，所以我們可以使用紅外線望遠鏡。而另一方面，恆星形成星系(星爆星系)也在中紅外線波段有高強度的多環芳香烴發射譜線，所以建立一個準確的方法來篩選活躍星系核是必須且重要的。然而，在過去的中紅外線研究中，望遠鏡可用的濾鏡只有三、四個，也因此受到了限制。我們使用AKARI太空望遠鏡，其擁有連續分布在近、中紅外波段的九個濾鏡，並結合WISE和Spitzer的觀測資料，總共使用了十八個能帶來篩選活躍星系核。在AKARI北黃極深域裡，我們從4682個星系中篩選出了1388個活躍星系核。同時也表示了活躍星系核比率為29.6$
    m$0.8$\%$（其中有47$\%$為西弗1.8和西弗2型）。跟過去WISE和Spitzer雙色圖的篩選做比較，顯示出過去的方法會遺漏西弗類型的活躍星系核。我們透過疊加輻射通量並擬合中位數測試出結果是可信的。以Chandra望遠鏡的觀測結果作為標準和過去的篩選方法做比較，在X光活躍星系核的樣本裡面，我們找回的活躍星系核數量比過去方法多了20$\%$。

    We have developed an efficient Active Galactic Nucleus (AGN) selection method using 18-band Spectral Energy Distribution (SED) fitting in mid-infrared (mid-IR). AGNs are often obscured by gas and dust, and those obscured AGNs tend to be missed in optical, UV and soft X-ray observations. Mid-IR light can help us to recover them in an obscuration free way using their thermal emission. On the other hand, Star-Forming Galaxies (SFG) also have strong PAH emission features in mid-IR. Hence, establishing an accurate method to separate populations of AGN and SFG is important. However, in previous mid-IR surveys, only 3 or 4 filters were available, and thus the selection was limited. We combined AKARI's continuous 9 mid-IR bands with WISE and Spitzer data to create 18 mid-IR bands for AGN selection. Among 4682 galaxies in the AKARI NEP deep field, 1388 are selected to be AGN hosts, which implies an AGN fraction of 29.6$
    m$0.8$\%$ (among them 47$\%$ are Seyfert 1.8 and 2). Comparing the result from SED fitting into WISE and Spitzer colour-colour diagram reveals that Seyferts are often missed by previous studies. Our result has been tested by stacking median magnitude for each sample. Using X-ray data from Chandra, we compared the result of our SED fitting with WISE's colour box selection. We recovered more X-ray detected AGN than previous methods by 20$\%$.

    1 Introduction 1 2 Data and Analysis 2 2.1 Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.2 SED fitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 Results 6 3.1 AGN Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1.1 SED AGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1.2 Colour AGN . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2 Examination by X-ray AGN . . . . . . . . . . . . . . . . . . . . . . 15 3.3 Examination by stacked median magnitude . . . . . . . . . . . . . . 15 4 Discussion 17 4.1 SED AGN missed in colour method . . . . . . . . . . . . . . . . . . 24 4.2 Colour AGN missed in SED fitting . . . . . . . . . . . . . . . . . . 24 4.3 Implication for Luminosity Function of AGN . . . . . . . . . . . . . 27 4.4 Relaxed selection and AGN fraction . . . . . . . . . . . . . . . . . . 27 4.5 Comparision with another template . . . . . . . . . . . . . . . . . . 29 4.6 Future prospects . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 5 Summary 32 A SWIRE template 35 B CFHT u ∗ -band data reduction in the AKARI NEP field 36 B.1 Observation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 B.2 Data reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 C Comments from the oral defense 38 C.1 What are the stars in the AGN colour box? . . . . . . . . . . . . . 38 C.2 Reduced χ 2 distribution . . . . . . . . . . . . . . . . . . . . . . . . 38 C.3 Why is the recovering rate of X-ray AGN not 100%? . . . . . . . . 41

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