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.
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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Keywords
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