通过Breakthrough Listen对河外发射机的限制
Constraints on extragalactic transmitters via Breakthrough Listen
摘要：
突破性倾听计划已经开始对银河系附近的恒星进行全面的SETI调查，这比以前的努力要好得多，因为测量范围很广。SETI调查传统上忽略了一个事实，即除了前景目标恒星外，它们对许多背景物体都很敏感。为了更好地了解和利用视野中存在的河外天体，利用阿拉丁天图集和NED对100米格林班克望远镜在1.1-1.9千兆赫观测时偶然观测到的河外天体进行了初步普查。对于469个目标场（假设径向视场的半高宽为4.2弧分），NED总共识别了143024个河外天体，包括各种天体物理学上的外来天体，例如各种类型的AGN，射电星系，相互作用星系和一个已确认的引力透镜系统。几个附近的星系，星系团和星系团的识别，允许SETI调查探测的参数空间显着扩展。约束放置在潜在的外星发射机的光度函数假设它遵循一个简单的幂律和限制与这些巨大的恒星系统相关的非常强大的外星发射机的流行也被确定。它表明，最近的突破倾听计划，事实上，许多以前的SETI无线电调查，对遥远宇宙中外星智慧的流行程度的限制比通常充分认识到的更强。
英文摘要：
The Breakthrough Listen Initiative has embarked on a comprehensive SETI survey of nearby stars in the Milky Way that is vastly superior to previous efforts as measured by a wide range of different metrics. SETI surveys traditionally ignore the fact that they are sensitive to many background objects, in addition to the foreground target star. In order to better appreciate and exploit the presence of extragalactic objects in the field of view, the Aladin sky atlas and NED were employed to make a rudimentary census of extragalactic objects that were serendipitously observed with the 100-m Greenbank telescope observing at 1.1-1.9 GHz. For 469 target fields (assuming a FWHM radial field-of-view of 4.2 arcminutes), NED identified a grand total of 143024 extragalactic objects, including various astrophysical exotica e.g. AGN of various types, radio galaxies, interacting galaxies, and one confirmed gravitational lens system. Several nearby galaxies, galaxy groups and galaxy clusters are identified, permitting the parameter space probed by SETI surveys to be significantly extended. Constraints are placed on the luminosity function of potential extraterrestrial transmitters assuming it follows a simple power law and limits on the prevalence of very powerful extraterrestrial transmitters associated with these vast stellar systems are also determined. It is demonstrated that the recent Breakthrough Listen Initiative, and indeed many previous SETI radio surveys, place stronger limits on the prevalence of extraterrestrial intelligence in the distant Universe than is often fully appreciated.
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