椭圆星系中的星系际尘埃

Interstellar Dust in Elliptical Galaxies

该文总结了近年来椭圆星系中尘埃起源研究中的一些关键问题,包括尘埃大小的分布及其组成、椭圆星系恒星质量损失速率、尘埃的两种加热机制(恒星辐射加热和电子-尘埃碰撞加热),以及由此导致的尘埃温度分布;尘埃的总质量估算;由热离子导致的尘埃破坏速率,以及与此相关联的椭圆星系热气体分布,等等.综合考虑这些因素,作者认为热气体分布对于椭圆星系中尘埃存在和破坏的影响不可忽视,椭圆星系中星系内部恒星质量损失产生尘埃的起源可能占据着非常重要的地位.

The origin of the dust in elliptical galaxies could be internal from stellar mass loss or external from merger. The former one was considered to be insufficient comparing with the observation, this standpoint came from the calculation of dust mass, the lacking of relationship between infrared and optical radiation, and the difference of angle momentum between gas and stars. In this paper, we summarize the internal origin and properties of dust in elliptical galaxies, including the size and composition; stellar mass loss rate; two heat mechanisms for dust： heating by stellar radiation field and by electron-dust collision, and the dust temperature distribution; the total mass of dust; the sputtering rate of hot ions, and the hot gas distribution in elliptical galaxies. The most important factors for the existence and destruction of dust are the stellar mass loss rate and the hot gas distribution. The stellar mass loss rate is extrapolated by the relation between radiation and dust mass in our Galaxy, which has the uncertainty at least by a factor of 4. X-ray observations indicate that hot gas in elliptical galaxies always have irregular content and distribution. The X-ray luminosities of elliptical galaxies with equal optical luminosity could have a scatter of two orders of magnitude, and the gas distribution is also chaotic. The recent Spitzer observations show that dust in some elliptical galaxies should have internal origin. There are two possible ways： dust from the stellar mass loss may directly merge with the hot gas and be destructed; dust could be formed in the central disk as observed in many elliptical galaxies, the central AGN activity could transport the central dust outward through buoyant outflow. We conclude that internal origin of dust from the stellar mass loss is important in giant elliptical galaxies.