指導教授：賀曾樸臺灣大學：天文物理研究所湯濟家Tang, Ji-JiaJi-JiaTang2014-11-252018-06-282014-11-252018-06-282014http://ntur.lib.ntu.edu.tw//handle/246246/261077目前為止，人們已經發現數十萬計個紅移六以下的類星體（quasar），但是在紅移六以上的類星體只有幾十個，這是因為以下三個主要原因。首先，紅移越大的類星體會越暗，其次，類星體的數量密度在高紅移較低。第三，觀測儀器的敏感度在長波長還有觀測涵蓋體積大小的情況下限制偵測類星體的能力。人們發展了一些方法來勘查高紅移類星體。目前已知利用類星體的光度在短於紅移過的Lyman-alpha譜線部分會降下來這個現象來做顏色篩選是非常強而有力的。這是因為在觀測路徑上的中性氫會吸收紅移小於類星體紅移的Lyman-alpha譜線的譜線。隨著Lyman-alpha譜線的紅移，我們需要波長更長的波段來涵蓋這個類星體特有的鮮明特徵。然而，例如棕矮星其他天體也會呈現相同特徵，因此我們非常需要增進顏色篩選法來篩檢掉那些污染物的能力以有效且穩定的篩選出預期中非常少的高紅移類星體。這個計畫的目標是尋找紅移大於5.5的類星體並同時增進顏色篩選法的條件。這個計畫所使用的資料主要來自公開資料，我們使用可見光波段的加法夏望遠鏡的傳統調查（Canada-France-Hawaii Telescope Legacy Survey）、近紅外波段的可見光和紅外巡天望遠鏡的銀河系外深景觀測（Visible and Infrared Survey Telescope for Astronomy Deep Extragalactic Observations survey）、中紅外波段的史匹哲太空紅外望遠鏡的銀河系外典型大量調查（Spitzer Extragalactic Representative Volume Survey）及廣域銀河系外紅外線調查（Spitzer Wide-Area Infrared Extragalactic Survey）還有來自私人資料中聯合王國紅外望遠鏡（United Kingdom Infrared Telescope）實施的紅外線中等深景調查（Infrared Medium-deep Survey）。我們在紅外線中等景深調查以及加法夏望遠鏡的傳統調查的天文陣列影像中擷取每個發光體，並做光度校正以做出資料表。同時我們也將直接公開的資料表跟我們的資料表做結合。作為結果的資料表涵蓋了從0.6到8.0微米的波段光度，並拿來與已知高紅移類星體以及棕矮星的許多顏色做比較。利用廣闊的涵蓋波段，我們提出了新的顏色篩選法來篩選類星體，特別注意利用棕矮星的光譜能量分布與類星體的冪律光譜能量分布不同的這一點來移除棕矮星，進而利用這個新的顏色篩選法找出了我們自己的類星體候選物。我們調查兩種由顏色選出的類星體的光度特性，分別是在i波段以及z波段上有光度降低現象的類星體，並且討論由低紅移類星體推演出來的光度函數是否與我們偵測到的類星體一致。People have discovered more than hundreds of thousands of quasars at a redshift below 6. However, there are only dozens of them discovered above redshift 6. There are three main reasons that cause this situation. First, the higher the redshift, the fainter the quasar. Second, the number density for quasars decreases at higher redshifts. Third, the sensitivity of the instrument especially at longer wavelengths and survey volume there limits detection of those quasars. People have been developing methods to explore higher-redshift quasars, and their color selection to utilize drop in magnitude below the redshifted Lyman alpha emission has been known to be very powerful. This is because the neutral hydrogen along the line of sight absorbs redshifted emission of quasar below its redshifted Lyman-alpha. As the Lyman-alpha is redshifted, the longer wavebands need to be covered to catch such a quasar-specific signature. However, there are some contaminants such as brown dwarf stars to those dropout sources, and improving color-selection criteria for removing those contaminants are highly desirable for efficient and robust detection of presumably very rare high redshift quasars. The goal of this project is to search for z>5.5 quasars while trying to improve the criteria for color selection. The data used in this project are mostly publicly available data. In particular, we utilize data from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) for the optical wavebands, Visible and Infrared Survey Telescope for Astronomy (VISTA) Deep Extragalactic Observations (VIDEO) survey for the near infrared wavebands, and the Spitzer Extragalactic Representative Volume Survey (SERVS) and Spitzer Wide-Area Infrared Extragalactic Survey (SWIRE) for the mid-infrared wavebands. Private data from the Infrared Medium-deep Survey (IMS) conducted by United Kingdom Infrared Telescope (UKIRT) are also analyzed. We have worked directly on the deep astronomical array images of IMS and CFHTLS for extracting sources and applying photometric calibrations to create catalogues. We also utilize publicly available catalogues to combine with our own catalogues. The resultant catalogues covering side wavelength ranges from 0.6 to 8.0 micrometers (μm) are examined in combination with colors of known high-redshift quasars and brown dwarfs. By utilizing the wide wavelength coverage, we propose our own color selection criteria for quasar selection. We pay special attention to eliminate brown dwarfs whose spectral energy distribution (SED) are quite different from the power-law like quasar SED. We create our own new catalogues of quasar candidates by utilizing the new criteria. We investigate photometric properties of such color-selected i- and z-dropout quasars, and discuss if expectation from the lower-redshift quasar luminosity function is consistent with our detection rate.Chapter 1. Introduction 1 1-1. Motivation of searching high redshift quasars．．．．．．．．．．．．1 1-2. Observational techniques of searching high redshift quasars．．．．．．4 1-3. Review of previous quasar surveys by dropout technique．．．．．．．5 1-4. Our strategy of searching high redshift quasars．．．．．．．．．．．8 Chapter 2. Observations and Catalogues 11 2-1. Observation fields．．．．．．．．．．．．．．．．．．．．．．11 2-1-1. CFHT-LS D1．．．．．．．．．．．．．．．．．．．．．．11 2-1-2. ELAIS N2．．．．．．．．．．．．．．．．．．．．．．．12 2-2. Image Dataset．．．．．．．．．．．．．．．．．．．．．．．．13 2-2-1. CFHT-LS in D1．．．．．．．．．．．．．．．．．．．．．13 2-2-2. CFHT-MegaPipe in ELAIS N2．．．．．．．．．．．．．．．14 2-2-3. IMS in ELAIS N2．．．．．．．．．．．．．．．．．．．．15 2-3. Catalogue Dataset．．．．．．．．．．．．．．．．．．．．．．16 2-3-1. VIDEO in D1．．．．．．．．．．．．．．．．．．．．．．16 2-3-2. SERVS in D1．．．．．．．．．．．．．．．．．．．．．．17 2-3-3. SWIRE in ELAIS N2．．．．．．．．．．．．．．．．．．．17 Chapter 3. Measurements and Analysis 19 3-1. Extracting and measuring sources on the images．．．．．．．．．．19 3-1-1. Source extraction．．．．．．．．．．．．．．．．．．．．20 3-1-2. Photometry．．．．．．．．．．．．．．．．．．．．．．21 3-1-3. SExtractor output．．．．．．．．．．．．．．．．．．．．23 3-2. Source size distribution of point-like objects．．．．．．．．．．．．24 3-2-1. Creating the synthetic point-like objects．．．．．．．．．．．25 3-2-2. Adding and extracting the synthetic point-like objects．．．．．．27 3-2-3. Determining FWHM range for point-like object selection．．．．28 3-3. Merging the catalogues between wavebands．．．．．．．．．．．．29 3-3-1. Matching the catalogues with topcat．．．．．．．．．．．．．29 3-3-2. Redundancy issue．．．．．．．．．．．．．．．．．．．．30 3-3-3. Statistics of false detection and false matching．．．．．．．．．31 3-4. Selection of point-like sources．．．．．．．．．．．．．．．．．33 3-5. Selecting dropout sources．．．．．．．．．．．．．．．．．．．34 3-6. Converting the flux counts into AB magnitudes．．．．．．．．．．．34 3-7. Merging with external catalogues．．．．．．．．．．．．．．．．35 Chapter 4. Characteristics of the Catalogues 36 4-1. Number of sources．．．．．．．．．．．．．．．．．．．．．．36 4-2. Magnitude distributions．．．．．．．．．．．．．．．．．．．．37 4-3. Detection limits．．．．．．．．．．．．．．．．．．．．．．．38 4-4. Completeness limits．．．．．．．．．．．．．．．．．．．．．38 4-5. Color correction．．．．．．．．．．．．．．．．．．．．．．．41 4-6. Falsely matched sources．．．．．．．．．．．．．．．．．．．．42 Chapter 5. Color-color Diagram Results 44 5-1. Developing our selection criteria for z-dropout quasars．．．．．．．．45 5-2. Color-color diagrams for g-, r-, and i-dropout quasars and their selection criteria．．．．．．．．．．．．．．．．．．．．．．．．．．．．．47 5-3. Color-color diagrams for z-dropout sources and their selection criteria．．49 5-4. Final examination on each preliminary candidate．．．．．．．．．．51 Chapter 6. Discussion．．．．．．．．．．．．．．．．．．．．．．．．54 6-1. Examination of the quasar candidates．．．．．．．．．．．．．．．54 6-2. Estimated number of quasars for the survey．．．．．．．．．．．．56 Bibliography 618035629 bytesapplication/pdf論文公開時間：2015/09/03論文使用權限：同意有償授權(權利金給回饋學校)類星體可見光－近紅外觀測計畫高紅移顏色篩選法thesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/261077/1/ntu-103-R01244002-1.pdf