OH Megamasers and Galaxy Evolution

许多星系的核心都有高能量的过程，这些过程被认为最终是由超大质量黑洞周围区域的强大引力场提供动力的。在特殊情况下，围绕或坠入星系核区的气体可以产生发光脉泽(微波激光)，它被观察到是从星系核发出的一条强烈的射电谱线。这种“超级激光器”-之所以这样叫，是因为它们的亮度大约是银河系中发现的年轻恒星的典型脉泽的一百万倍-是由激发的H2O或OH分子产生的。尤其是巨型激光，只有在合并星系的核心中才能发现，而且亮度足够大，在宇宙学距离内都能观察到。这项研究旨在刻画和理解星系合并与OH超强激光产生之间的关系，最终目的是利用OH超强激光作为宇宙时间的函数来追踪星系合并的历史。星系的数量随时间的演化尚不清楚，尽管它很可能是星系演化过程中的一个重要元素。这项研究将(1)从阿雷西博天文台对合并星系进行的广泛的OH谱线调查中建立OH超伽马激光的空间密度，(2)通过对谱线强度可变性的研究确定这些系统中OH超伽马激光的空间尺度，(3)从Palomar天文台的光学光谱确定最有利于产生OH超伽马激光的宿主类型，以及(4)描述作为高红移合并星系的指示器的OH超伽马激光的潜在用途。***

AST 0098526Giovanelli The nuclei of many galaxies harbor highly energetic processes, which are thought to be powered ultimately by strong gravitational fields in the regions surrounding supermassive black holes. In special circumstances, gas orbiting or falling into the nuclear regions of galaxies can produce a luminous maser (a microwave laser) which is observed as a strong radio spectral line emanating from a galactic nucleus. Such "megamasers" --- so called because they are roughly a million times more luminous than typical masers associated with young stars found in the Milky Way --- are produced by excited H2O or OH molecules. OH megamasers in particular are foundonly in the nuclei of merging galaxies and are luminous enough to be observable at cosmological distances. The study proposed here aims to characterize and understand the relationship between merging galaxies and the production of OH megamasers with the ultimate goal of using OH megamasers to trace the merging history of galaxies as a function of cosmic time. The number evolution of galaxies with time is not yet known, although it is likely to be an important element in the galaxy evolution process. This study will (1) establish the space density of OH megamasers from a broad OH spectral line survey of merging galaxies at the Arecibo Observatory, (2) determine the spatial scale of OH masing in these systems from a study of line intensity variability, (3) characterize the type of host most favorable to producing an OH megamaser from optical spectroscopy at Palomar Observatory, and (4) characterize the potential use of OH megamasers as indicators of merging galaxies at high redshift. ***