河外H_2O超脉泽辐射

H_2O Megamasers in Extragalaxies

介绍了近年来河外Ｈ２Ｏ超脉泽的主要观测结果。Ｈ２Ｏ超脉泽通常起源于活动星系核中央的拱核盘。它们主要寄生在 Ｓｅｒｆｅｒｔ ２星系或低电离核区。至今为止，已有２０个星系探测到Ｈ２Ｏ超脉泽。脉泽辐射的各向同性光度为１０～６０００Ｌ⊙。所有超脉泽星系显示出核的活动，显然，脉泽是由核活动所产生的射电和Ｘ射线光子或激波来抽运的。Ｈ２Ｏ超脉泽倾向存在于高倾斜度的星系，这使得沿视线上的分子柱密度增高，产生足够大的放大光深。最有可能产生Ｈ２Ｏ超脉泽辐射的星系应有一个包含着射电源的侧向的分子盘以及一个适当的抽运机制。

Main observational results and theoretical studies for H2O Megamasers are briefly reviewed. The H2O Megamaser emission often originates in thin circumnuclear disks near the centers of active galactic nuclei (AGN) and has been detected in 20 galaxies with isotropic luminosities of about 10-6000 L⊙. All of megamaser galaxies show evidence for nuclear activity, being classified as either Seyfert 2 or LINER, so there appears to be a link between the megamaser phenomenon and AGN. There was a trend for megamasers to occur preferentially in highly inclined host galaxies. The AGN apparently produces the seed radio photons and the X-ray photons or shock waves need to pump the maser material. The observed spectral characteristics support a model with inverted molecular gas located in front of the nuclear source that in part amplifies the background continuum.