The incidence and evolution of Active Galactic Nuclei in 2865 COSMOS radio sources

使用甚长基线干涉测量(VLBI)技术的观测传统上是以精心挑选的样品为目标，以研究它们的性质和环境的特定方面。造成这种情况的部分原因是足够明亮的光源相对稀少(或者更确切地说是缺乏灵敏度)，但主要是由于成像分散在大范围内的多个光源所固有的技术困难。这两个方面在过去几年中都发生了重大变化，使观察员能够用VLBI图像补充敏感的广域射电观测。我们在甚长基线阵列上获得了276小时的观测时间，对宇宙调查中发现的所有2865个射电天体进行了成像。观测将使用我们在以前的宽视场VLBI观测中与其他工作人员共同开发的新的相关和校准技术。由于宇宙2平方度场中所有已知的射电发射体都是目标，在没有应用其他选择的情况下，数据将第一次产生大量星系中通量受限的VLBI探测物体的样本。此外，我们还从VLBA获得了200小时的数据，以对100平方度区域内第一次(20厘米处的无线电天空微弱图像)调查的所有来源进行成像。这些数据集加在一起，将能够调查从Jy级到100uJy以下的VLBI射电源。该项目的主要科学目标是研究射电活动星系核的发生率和影响。我们将(I)确定哪些天体拥有致密的核心；(Ii)确定这些天体如何影响其所在星系的恒星形成；以及(Iii)研究吸积模式随红移的变化。此外，我们预计将为调查数据的其他意外用例和后续观察提供大量投入。COSMOS领域拥有无与伦比的光学、红外、X射线和光谱覆盖，通过与COSMOS项目成员的合作，我们可以访问这些数据。

Observations using the Very Long Baseline Interferometry (VLBI) technique traditionally target carefully selected samples, to study particular aspects of their properties and surroundings. This situation is caused partly by the relative sparsity of sufficiently bright sources (or rather a lack of sensitivity), but mostly by the inherent technical difficulties of imaging multiple sources scattered across wide fields. Both aspects have undergone significant changes in the past few years, allowing observers to complement sensitive, wide-area radio observations with VLBI images. We have acquired 276h of observing time at the Very Long Baseline Array, to image all 2865 radio objects found in the COSMOS survey. The observations are going to use the new correlation and calibration techniques that we have developed with other workers in the field in previous wide-field VLBI observations. Since all known radio emitters in the COSMOS 2 sq-deg field are targeted, without other selection applied, the data will yield, for the first time, a sample of flux-limited, VLBI-detected objects in a large variety of galaxies. Furthermore, we have access to 200h of data from the VLBA to image all sources from the FIRST (Faint Images of the Radio Sky at Twenty Centimeters) survey in a 100 sq-deg region. Together these data sets will allow the investigation of VLBI radio sources from the Jy level to below 100 uJy. The main scientific goal of this project is to study the incidence and impact of radio-emitting AGN. We will (i) determine which objects host compact cores; (ii) determine how these objects affect the star formation in their host galaxies; and (iii) investigate the changes in accretion modes as a function of redshift. Furthermore, we anticipate significant input for additional, unexpected use cases of the survey data and input for follow-up observations. The COSMOS field has unrivalled optical, IR, X-ray, and spectroscopic coverage, and through a collaboration with members of the COSMOS project we have access to the data.