A Molecular Gas Study of the Initial and Final Stages of the Ultraluminous Infrared Galaxy Phenomenon

AST-0080881EVANSU 超光度红外星系 (ULIG) 被观察到是紧密相互作用/合并的星系。 ULIG中的核环恒星形成和活跃星系核（AGN）活动都被认为是由分子气体提供燃料的，并且这两个过程产生的强紫外光辐射被尘埃吸收并以红外波长重新发射。光学明亮的 QSO 可能是 ULIG 阶段的进化最终产品。 光学明亮的 QSO 的出现可能是流出物和超新星清除了大部分遮蔽 QSO 核的尘埃后的结果。将进行两个项目，为 ULIG 现象的早期和最终阶段提供潜在线索。第一个是 ULIG 祖细胞的分子气体特性的研究。具体来说，正在对 ULIG 的一氧化碳（CO）（1 到 0 过渡）线辐射进行观测调查，其核仍然广泛分离，以确定祖星系的相对分子气体含量。正在将 CO 数据与这些 ULIG 的地基和空基光学到近红外图像进行比较，以验证分子气体相对于恒星核的位置。对核间隔约为 5 秒差距的 5 个 ULIG 的初步分析表明，具有温暖的、类似 Seyfert 的红外通量比的 ULIG 具有仅与 AGN 相关的 CO，而具有冷的、类似星爆的通量比的 ULIG 具有与两个原子核相关的 CO。这种二分法可能表明不同主要能源的合并在合并过程的早期变得超发光的方式。第二个项目是在 QSO 样本中寻找早期 ULIG 相的分子气体残余物。该样本由 17 个红外过量 QSO 组成，据信代表了严重遮挡的 ULIG 和经典光学 QSO 之间的过渡阶段。该样品之前已在光学/近红外波长下成像。这些研究表明存在未解析的明亮核，其下方有旋臂和潮汐尾，以及发光的年轻星团。这些 QSO 的 CO 观测将提供所需的统计样本，以便直接比较它们的分子气体性质与 ULIG 的分子气体性质，以及与最近在 CO 中检测到的富含气体、高红移 ULIG 和 QSO 的数量进行比较。研究结果将帮助天文学家了解星系和 QSO 之间的差异。这两个项目都将利用在加州理工学院运营的欧文斯谷毫米波阵列获得的观测数据。 该项目和欧文斯谷毫米波阵列得到了天文科学部的资金支持。 ***

AST-0080881EVANSUltraluminous infrared galaxies (ULIGs) are observed to be closely interacting/ merging galaxies. Both circumnuclear star formation and active galactic nuclear (AGN) activity in ULIGs are believed to be fueled by molecular gas, and the strong ultraviolet-to-optical radiation generated by both processes is absorbed by dust and re-emitted at infrared wavelengths. Optically bright QSOs may be an evolutionary end product of the ULIG phase. The appearance of optically bright QSOs may be the result after outflows and supernovae have cleared much of the dust responsible for obscuring the QSO nucleus.Two projects will be carried out that will provide potential clues to the early and final stages of ULIG phenomenon. The first is a study of the molecular gas properties of ULIG progenitors. Specifically, an observational survey of the Carbon monoxide (CO) (1 to 0 transition) line radiation of ULIGs, whose nuclei are still widely separated, is being undertaken in order to determine the relative molecular gas content of the progenitor galaxies. The CO data are being compared with ground-based and space-based optical to near-infrared images of these ULIGs to verify the location of the molecular gas relative to the stellar nuclei. Preliminary analysis of five ULIGs with nuclear separations of about 5 parsecs shows that ULIGs with warm, Seyfert-like infrared flux ratios have CO associated with only the AGN, whereas ULIGs with cool, starburst-like flux ratios has CO associated with both nuclei. Such a dichotomy may indicate the manner in which mergers with different primary power sources become ultraluminous early in the merger process.The second project is a search for molecular gas remnants of an early ULIG phase in a sample of QSOs. The sample consists of a family of 17 infrared excess QSOs believed to represent the transition stage between the heavily obscured ULIGs and the classic, optical QSOs. The sample has been previously imaged at optical/near infrared wavelengths. These studies have shown evidence of unresolved bright nuclei with underlying spiral arms and tidal tails, as well as luminous young star clusters. The CO observations of these QSOs will provide the statistical sample needed for a direct comparison of their molecular gas properties to those of ULIGs, as well as to the population of gas-rich, high redshift ULIGs and QSOs recently detected in CO.The results of the research will help astronomers understand the differences between galaxies and QSOs.Both of these projects will make use of observational data taken at the Owens Valley Millimeter Array that is operated by Caltech. This project and the Owens Valley Millimeter Array are supported by funds from the Division of Astronomical Sciences. ***