LBA observations for project V620 semester 2022OCTS

Ultra-high-redshift radio galaxies (UHzRGs; z > 5) are unique tracers of supermassive black hole growth and massive galaxy formation in the early Universe. A novel UHzRG selection technique was developed that makes use of broadband data (70-230 MHz) from the MWA GLEAM survey. A total of 14 high-priority targets have been identified using this technique that also have very faint near-infrared K-band host galaxy magnitudes from deep VLT imaging. Here, we propose 2.3-GHz LBA observations of two of these new UHzRG candidates, GLEAM J1033 and GLEAM J1037. Both of these compact radio sources (largest angular sizes 0.9 and 2.6 arcsec) have K > 24 (AB) and are therefore excellent candidates for being at z > 5 and possibly within the epoch of reionisation. VLBI observations of GLEAM J1033 and J1037 will provide highly valuable information on the growth and evolution of powerful radio sources at potentially a very early cosmic epoch. In particular, by resolving the radio structures of both sources, we will obtain estimates for a number of properties of the radio jets, including the jet power, equipartition magnetic field strength and bulk Lorentz factor, and we will also constrain the black hole mass and accretion rate.

超高红移射电星系（Ultra-high-redshift radio galaxies, UHzRGs；z>5）是早期宇宙中超大质量黑洞演化与大质量星系形成的独特示踪剂。本研究开发了一种全新的UHzRG筛选技术，该技术利用了默奇森宽场阵列（Murchison Widefield Array, MWA）GLEAM巡天项目的70-230 MHz宽带观测数据。通过该技术共筛选出14个高优先级目标，这些目标的宿主星系在近红外K波段的星等极暗，其观测数据来自甚大望远镜（Very Large Telescope, VLT）的深场成像。在此，我们提议对其中两个新发现的UHzRG候选体——GLEAM J1033与GLEAM J1037——开展2.3 GHz频段的甚长基线阵列（Long Baseline Array, LBA）观测。这两个致密射电源的最大角尺度分别为0.9角秒与2.6角秒，其K波段星等（AB系统）均大于24，因此是红移z>5、甚至可能处于再电离纪元的优质候选体。对GLEAM J1033与GLEAM J1037开展甚长基线干涉测量（Very Long Baseline Interferometry, VLBI）观测，将为探究极早期宇宙中强射电源的形成与演化提供极具价值的信息。具体而言，通过解析这两个源的射电结构，我们将能够估算射电喷流的多项属性，包括喷流功率、均分磁场强度与整体洛伦兹因子，同时还能限定黑洞质量与吸积率。