紅外線明亮星系的活躍星系核特性

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2013

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為了了解活躍星系核活動與恆星形成在星系演化中的相互影響,我們研究142個星系樣品,來自宇宙演化勘測視野(Cosmic Evolution Survey field),並且擁有X-ray與遠紅外線70μm觀測資料。我們的資料來自已公開之網路資料庫,X-ray來自錢德拉太空望遠鏡(Chandra)與XMM-牛頓太空望遠鏡(XMM-Newton); 遠紅外線70μm的資料則來自史匹哲太空望遠鏡(Spitzer)之多波段成像光度計(MIPS)觀測。儘管近紅外光測指數(color indexes)指出有恆星形成的存在,2-10 keV與全波段紅外光線(total infrared luminosity)的比值顯示,當固定全波段紅外光線能量時,2-10 keV的能量高出許多,暗示活躍星系核活動可能大於恆星形成活動。我們利用X-ray的硬指數(Hardness ratio)來當作”掩蔽活躍星系核”之指示標準,我們發現我們特殊的樣品選擇相對於單一X-ray的星系選擇有多餘的硬指數高值,可能與不同物理尺度的雲氣與灰塵有關。我們同時發現我們的樣品之冷灰塵溫度並不受X-ray有無的影響,灰塵溫度與活躍星系核活動之間可能沒有直接的關連。
In order to understand the mutual influence between active galactic nuclei (AGN) and star formation during the evolution of galaxies, we investigate 142 galaxies detected in both X-ray and 70μm observations in the COSMOS (Cos- mic Evolution Survey) field. All of our data are obtained from archive, X-ray point source catalogs from Chandra and XMM-Newton observation; far-infrared 70μm point source catalog from Spitzer-MIPS observation. Although the IRAC [3.6μm]-[4.5μm] vs. [5.8μm]-[8.0μm] colors of our sample indicate the existence of star formation, the ratio of rest frame 2-10 keV luminosity to total infrared lu- minosity (8-1000μm) shows comparatively higher X-ray flux than submillimeter galaxies for a given total infrared luminosity, indicating the possibility of higher AGN activity relative to star formation. When we characterize ”obscured AGN” by X-ray hardness ratio, we find that sources with exhibit both 70μm and X-ray emissions tend to have a higher hardness ratio compared to X-ray sources without 70μm emission, suggesting possible connection between the dust and gas across the various physical scales inside a galaxy. We also find that 70μm detected galaxies with X-ray emission and without X-ray emission show no significant dif- ference in cold dust temperature, suggesting that the AGN activity and the dust temperature may not be directly correlated.

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高紅移, 活躍星系, 紅外線, 星系, X-ray, 星系, high redshift, galaxy: active, infrared: galaxies, X-rays: galaxies

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