錢卓南天深空觀測中不同類型活躍星系核受環境影響之研究

Environmental effects on different types of AGNs in Chandra Deep Field South

姚漢林

指導教授 ： 陳林文

國立臺灣師範大學/理學院/地球科學系/碩士(2007年)

摘要

我們藉由研究宇宙間的大尺度結構（如星系團或星系團合併）與 Chandra Deep Field South（CDFS）觀測到的不同類型活躍星系核（AGN）之間的關聯，探討 AGN 的演化受到周圍環境影響的程度。在本研究中 AGN資料是由 CDFS 及 Extended-CDFS（E-CDFS）X射線源合併而來的，所有可分析的 AGN 共 889 筆；而可見光星系目錄是具有多波段觀測及光度紅移的 COMBO-17 觀測資料，在我們所分析的紅移範圍中（z = 0.2 ~ 1.2）共約有 11,500 筆。透過星系–AGN 二點交互相關函數分析、星系二維密度分析以及分析實際以 Friend-of-Friend（FoF）星系團尋找演算法找到的高密度星系區周圍 AGN 分佈，我們發現 Type 1 AGN 與高密度星系區的中心部分關聯性較強；且在這個區域 Type 1 AGN 與星系的比例，存在高於平均比例的趨勢。而關於 Type 2 AGN 大量出現在低紅移處的原因，應該也與高密度星系區有關。在不同的分析下，我們都看到 Type 2 AGN 與成團星系結構存在關聯性。另外，在距離高密度星系區中心 0.5 Mpc 之外圍區域，Type 2 AGN 出現的機率高於 Type 1 AGN，而且我們同樣也在高密度星系區周圍（~ 0.5 Mpc）看到 Type 2 AGN 與星系的比例具有高於平均比例之趨勢。這代表宇宙間可能存在許多尚未觀測到的大尺度結構（由較暗的星系組成），而大尺度結構內星系因為彼此的交互作用而產生大量的 Type 2 AGN。雖然在探討更大尺度的環境（如星系團合併）與 AGN 演化的關聯分析中，由於分析資料的限制，因此沒有具體的證據支持 AGN 的演化受更大尺度環境影響；但在星系團（群）尺度下，我們的結果顯示 AGN 的演化確實受到高密度星系區的影響。我們的結果可提供關於研究 AGN 的演化起源問題的參考，而未來更多深空的觀測也許可以提供我們檢視這些與 AGN 有關聯的大尺度結構之特質，以更進一步了解環境如何影響 AGN 演化的問題。

關鍵字

活躍星系核 ； 星系團 ； 星系團合併

並列摘要

We investigate the relation between cosmic structures and active galactic nuclei (AGNs) observed in Chandra Deep Field South (CDFS) to study how the evolution of galaxies was affected by environments (eg, galaxy clusters or cluster mergers). A total of 889 X-ray sources, compiled from CDFS and the Extended Chandra Deep Field South (E-CDFS) surveys, are analyzed in the study. An optical catalog of galaxies with multi-colour photometry in the same field is extracted from COMBO-17, which includes about 11,500 (MR≦-19.19) objects with photometric redshifts between 0.2 and 1.2. Using the cross-correlation functions ω(θ) of X-ray AGN and galaxies, 2D galaxies density distribution, and Friends-of-Friends (FoF) algorithm analyses, we note that Type 1 AGNs (with hardness ratio HR<-0.2) are spatially cross-correlated with the center of high number density of galaxies region (HNDoGR), and the Type 1 AGN to galaxy ratio in these regions tends to be higher than average. Moreover, our analyses also reveal a correlation between Type 2 AGNs (HR>-0.2) and galaxies structure; further analyses indicate the number of Type 2 AGNs is much larger than Type 1 AGNs on the outskirts of HNDoGR (~ 0.5 Mpc), and the Type 2 AGN to galaxy ratio around the HNDoGR (~ 0.5 Mpc ) tends to be higher than average. These results may infer that the large number of Type 2 AGNs appearing at low redshift could be associated with HNDoGRs, which are undetected large scale structures (LSS) composed of faint galaxies in the low-redshift universe, the interaction of galaxies in the outer part of the faint LSS can provide a mechanism to boost the formation of Type 2 AGNs. On the other hand, our analyses do not show obvious evidence that the evolution of AGNs is related to larger scale environment such as cluster mergers. With our results demonstrating the different correlations between Type 1/2 AGNs and HNDoGR, deeper observations in the future can offer more data to analyze the properties of faint LSS with AGNs embedded, and to provide new clues to the origins
of the different types of AGNs.

並列關鍵字

AGN ； galaxy cluster ； cluster merger

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