It is currently accepted that intrinsically compact and bright radio sources characterized by a convex spectrum peaking at frequencies ranging from 100 MHz to a few GHz are young objects. Following the evolutionary models, these objects would evolve into the population of classical radio galaxies. However, the fraction of young radio sources in flux density-limited samples is much larger than what expected from the number counts of large radio sources. This may suggest that for some reason a significant fraction of young objects would never become large radio galaxies with sizes up to a few Mpc. The discovery of the young radio source PKS 1518+047 characterized by an uncommonly steep spectrum confirms that the radio emission may switch off shortly after its onset. Then the source spectrum steepens and evolves due to energy losses. If the interruption is not temporary, the fate of the fading sources is to disappear at frequencies lower than those explored by current radio telescopes. Fossils of past activities have been recently found at pc-scale distances from newly born radio sources, suggesting the presence of short-lived objects with an intermittent radio emission.
Evolution in the Black Hole - Galaxy Scaling Relations and the Duty Cycle of Nuclear Activity in Star-Forming Galaxies
本文测量了69个Herschel探测到的宽线活动星系核（BLAGN）在M_BH-M_* 平面上的位置和演化矢量。BLAGN选自COSMOS和CDF-S场，并且跨越红移范围0.2< z<2.1。黑洞质量的计算使用档案光谱学和单历元维里质量估计，和星系总恒星质量的计算通过拟合光谱能量分布（减去BLAGN分量）。分别使用Chandra/XMM-牛顿X射线和Herschel远红外数据计算了黑洞和星系的质量增长率，这些数据是BLAGN吸积和星系恒星形成率的可靠测量。我们使用蒙特卡罗模拟来解释我们的样本中的偏差，由于选择限制和星系恒星质量分布的大质量末端的陡峭斜率。我们发现我们的样本与M_BH-M_* 关系从z~2到z~0没有演化是一致的。BLAGN和它们的宿主星系如果偏离了黑洞质量星系总恒星质量的关系，则它们的演化矢量往往与它们的质量比反相关：也就是说，具有超大质量（欠大质量）黑洞的星系往往具有低（高）的比吸积率与比恒星形成率之比。我们还使用测量的增长率来估计我们的星系的首选AGN占空比，以最一致地演变到本地M_BH-M_Bul关系。在恒星形成历史呈指数下降的合理假设下，数据表明恒星形成星系中的BLAGN占空比为10%（z 1时1 σ范围为1-42%<1 and 2-34% at z>）。
Popcorn in the sky: Identifying primordial black holes in the gravitational-wave background
Université Libre de Bruxelles（布鲁塞尔自由大学）；Universiteit Antwerpen（安特卫普大学）；University of Cambridge（剑桥大学）；King’s College London, University of London（伦敦大学国王学院）
MIGHTEE: The dark matter haloes, duty cycle and mechanical feedback from radio-AGN up to $z \sim 2.5$
University of Oxford（牛津大学）；School of Physics and Astronomy, Institute for Astronomy, University of Edinburgh（爱丁堡大学天体物理与天文学院天体物理研究所）；Department of Physics and Astronomy, University of the Western Cape（西开普大学物理与天文系）
