Multi-frequency Radio Astronomy as a Tool to Study Active Galaxies and Cosmology

多频射电天文学作为研究活动星系和宇宙学的工具

• 批准号: 9905652
• 负责人: Erick Guerra
• 金额: $ 1.76万
• 依托单位: Rowan University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-07-01 至 2000-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9905652&HistoricalAwards=false
• 关键词: Multi; frequency; Radio; Astronomy; Tool

AbstractGuerra AST 99-05625Multi-frequency radio observations and theoretical studies of active galaxies will be carried out. The analysis of the data obtained will be used to address issues concerning the physics of active galaxies and the Big Bang cosmology. Telescopes operating at radio wavelengths at the National Radio Astronomy Observatory (NRAO) will be utilized, including the NRAO 140-foot telescope in Green Bank, West Virginia and the NRAO Very Large Array (VLA) in New Mexico. The results obtained will be used to launch more ambitious radio observing campaigns to further the same goals. This research is comprised of two components. In the first component, radio-loud active galaxies which have "inverted spectra" (i.e., are brighter at higher radio frequency than lower radio frequency) have been selected from the VLA Faint Images of the Radio Sky at Twenty-centimeters (FIRST) survey and the Green Bank six centimeter (GB6) radio catalogs. These inverted-spectrum radio sources may be a small part of a class of radio sources that have been difficult to detect up to this date. Existing radio source catalogs are biased against the detection of inverted spectrum radio sources since they are faintest at the radio frequencies used for observations to compile existing catalogs (4.8 GHz in frequency and lower). However, models of radio-loud active galaxies predict inverted-spectrum radio sources as the precursors to other classes of radio sources (e.g., flat-spectrum radio sources). Inverted-spectrum radio sources can be brightest at frequencies well above 4.8 GHz, even above 20 GHz. A class of extra-galactic radio sources that is brightest above 20 GHz would be a significant foreground contamination to cosmic microwave background (CMB) anisotropy measurements such as will be made by NASA's Microwave Anisotropy Probe (MAP), which is scheduled to be launched in 2001.The data obtained at the NRAO 140-foot telescope and other facilities will be used to place upper limits on foreground contamination of the CMB anisotropy and to study the evolution of inverted-spectrum radio sources into other classes of radio-loud active galaxies. Ultimately, these data will be used to devise optimal strategies for radio surveys of the sky in the frequency range from 15 GHz to 43 GHz. Surveys of the radio "sky" at these frequencies are the best method for obtaining data for detecting inverted-spectrum radio sources.The second component of this research project is a study of the gaseous environments of powerful extended radio sources. The environments of powerful extended radio sources appear to be gas-rich clusters of galaxies. These radio sources are detected farther, both in space and time, than galaxy clusters that are detected in the visible light or X-ray wavelengths. Thus, environments surrounding powerful extended radio sources can be used to probe cluster evolution father back in time than clusters detected by other methods.A method to measure the properties of the gas in a cluster utilizes the Sunyaev-Zel'dovich (S-Z) effect. Radio sources with a predicted S-Z signal from their environments greater than the radio emission from the active galaxy itself will be selected from the Third Cambridge Revised Catalog (3CR) sample of powerful extended radio sources. Radio maps at frequencies up to 43 GHz will be collected and used to compute the radio signal above 100 GHz from the active galaxy. These radio maps will be obtained from the VLA archives and the remainder will be obtained by observations at the VLA. The S-Z signal will be computed on the basis of the interaction of the radio source with the surrounding gas. A target list for observations of the S-Z effect will be determined from these data.

AbstractGuerra AST 99- 05625将对活动星系进行多频射电观测和理论研究。 对所获得数据的分析将用于解决有关活动星系物理学和大爆炸宇宙学的问题。将利用国家射电天文台的射电波长望远镜，包括西弗吉尼亚州绿色班克的国家射电天文台140英尺望远镜和新墨西哥州的国家射电天文台甚大阵列。所取得的成果将用于开展更雄心勃勃的无线电观测活动，以促进实现同样的目标。本研究由两部分组成。在第一个组成部分中，射电大声活动星系具有“倒谱”（即，在较高的无线电频率比较低的无线电频率更亮）已被选定的VLA微弱图像的无线电天空在二十厘米（第一）调查和绿色银行六厘米（GB 6）无线电目录。这些倒频谱射电源可能是迄今为止难以探测到的一类射电源的一小部分。现有的射电源目录对倒频谱射电源的检测有偏见，因为它们在用于观测的无线电频率下最微弱，以编制现有的目录（频率为4.8 GHz或更低）。然而，射电大声活动星系的模型预测倒谱射电源是其他类别射电源的前兆（例如，平谱射电源）。反频谱射电源在频率远高于4.8 GHz，甚至高于20 GHz时最亮。一类最亮超过20 GHz的河外射电源将是对宇宙微波背景（CMB）各向异性测量的重大前景污染，例如将由美国宇航局的微波各向异性探测器（MAP）进行测量，该卫星计划于2001年发射。将使用100英尺望远镜和其他设施确定CMB各向异性前景污染的上限，并研究倒频谱射电源演变成其他类别的射电大声活动星系。最终，这些数据将用于设计15 GHz至43 GHz频率范围内的天空无线电勘测的最佳策略。在这些频率上对无线电“天空”进行测量是获得探测倒频谱无线电源的数据的最佳方法，本研究项目的第二个组成部分是对强扩展无线电源的气体环境进行研究。 强大的扩展射电源的环境似乎是富含气体的星系团。这些射电源在空间和时间上都比在可见光或X射线波长下探测到的星系团更远。因此，在强扩展射电源周围的环境中，可以探测到比其他方法探测到的星系团更早的星系团演化。一种测量星系团中气体性质的方法利用了Sunyaev-Zel'dovich（S-Z）效应。从第三次剑桥修订星表（3CR）强扩展射电源样本中选择来自其环境的预测S-Z信号大于活动星系本身的射电发射的射电源。将收集频率高达43 GHz的无线电地图，并用于计算来自活动星系的100 GHz以上的无线电信号。这些无线电地图将从甚大线阵档案馆获得，其余的将通过在甚大线阵的观测获得。S-Z信号将根据射电源与周围气体的相互作用来计算。将根据这些数据确定观察S-Z效应的目标列表。