LBA observations for project V605 semester 2021APRS

High-redshift radio galaxies (HzRGs) are unique tracers of massive galaxy formation in the early Universe. We have developed a novel HzRG selection technique that makes use of broadband data from the MWA GLEAM survey. In our pilot study of four sources, we found the second-most distant radio galaxy currently known (z=5.55). In addition, there is the exciting possibility that a second source, GLEAM 0917, is at an even higher redshift, between z=7-9, i.e. well within the Epoch of Reionization. This ‘oddball’ has some unusual properties, and we are currently conducting a multi-wavelength study of GLEAM 0917, including ongoing Hubble Space Telescope observations. The radio emission is point-like in our highest-resolution radio data set (ALMA 100 GHz; largest angular size < 0.5 arcsec). Here, we propose to obtain an LBA 13-cm observation of GLEAM 0917, offering an increase of up to a factor of 200 in angular resolution compared to the ALMA data. By resolving the radio structure of the source, we will obtain estimates for a number of properties of the radio jets, including the bulk Lorentz factor, jet power and equipartition magnetic field strength. We will also investigate whether faint extension in our Hubble 1.05 micron image, possibly Lyman alpha emission, is coincident with extended radio structure. Very-high-resolution radio observations of GLEAM 0917 will provide highly valuable information on the growth and evolution of a powerful radio source at potentially a very early cosmic epoch.

高红移射电星系（High-redshift radio galaxies, HzRGs）是早期宇宙中大质量星系形成的独特示踪剂。我们开发了一种新颖的HzRG选源技术，该技术利用了默奇森宽场阵列（Murchison Widefield Array, MWA）GLEAM巡天的宽带数据。在针对4个源的先导研究中，我们发现了目前已知的第二遥远射电星系（红移z=5.55）。此外，另有一个令人振奋的潜在发现：第二颗源GLEAM 0917的红移可能更高，处于z=7至9之间，即完全处于再电离纪元范围内。这一"异类"源具备若干非同寻常的特性，我们目前正对GLEAM 0917开展多波段研究，其中包括正在进行的哈勃空间望远镜（Hubble Space Telescope, HST）观测。在我们最高分辨率的射电数据集（阿塔卡马大型毫米/亚毫米波阵列（Atacama Large Millimeter/submillimeter Array, ALMA）100 GHz观测数据）中，该射电辐射呈点源形态，最大角尺寸小于0.5角秒。在此，我们提议对GLEAM 0917开展长基线阵列（Long Baseline Array, LBA）13厘米波段观测，相较ALMA数据，该观测的角分辨率最高可提升200倍。通过解析该源的射电结构，我们将能够估算射电喷流的多项特性，包括整体洛伦兹因子、喷流功率以及均分磁场强度。我们还将探究哈勃1.05微米图像中疑似莱曼α发射的微弱延展结构，是否与延展射电结构重合。对GLEAM 0917开展极高分辨率射电观测，将为探究潜在极早期宇宙中强射电源的生长与演化提供极具价值的信息。