Tidal Dwarf Galaxies as Laboratories for Understanding the Origins of Star Formation

现代天体物理学的基本挑战之一是理解触发和调节恒星形成的物理机制。一个关键的悬而未决的问题是，在将气体转化为恒星的过程中，包括气体动力学和磁场在内的环境的作用和相对重要性。潮汐矮星系被认为是由引力约束的气体凝聚形成的，而恒星在星系相互作用期间被潮汐引力从其母星系中剥离出来。这使得它们成为研究极端环境中恒星形成物理的理想实验室，这是理解恒星在宇宙早期是如何形成的基础。在博士学位的第一年，我们将开始一项开创性的研究(‘ALMA解析潮汐矮小星系中的巨型分子云’，Querejeta等人。2021年在相互作用系统ARP 94中的原型TDG J1023+1954的https://doi.org/10.1051/0004-6361/202038955)。我们将使用Jansky甚大阵列(从1.4 GHz到22 GHz)的数据来搜索和成像该星系中的射电连续辐射。这将使我们能够追踪TDG上恒星形成的历史，搜索残存恒星形成的射电信号，并确定射电发射的极化分布和强度，以绘制可能穿过气体的磁场图。要使用CASA(通用天文软件应用程序)处理JVLA数据集，预计将访问曼彻斯特大学的ALMA节点。由于Covid 19的限制，确切的日期还没有确定。在接下来的几年里，我们将对另外10个TDG样本进行大量的ALMA致密分子气体调查，这将使我们能够将J1023+1954放在更广泛的背景下，并将其性质与更大的银河型螺旋星系进行比较。利用现有的ALMA 12米望远镜观测，我们将致力于表征这个样本中扩散气体的比例，同时，我们将申请使用ALMA紧凑型阵列来观察其分子气体。使用阿塔卡马大型毫米波阵列的提案将于2022年4月提交，预计获胜时间将是直截了当的。卡罗尔·蒙代尔教授将是巴斯的首席导师，凯瑟琳·米切尔教授将是第二任导师。此外，两名外部监督员Ute Lienfeld博士(西班牙格拉纳达大学)和Miguel Querejeta博士(马德里国家天文台)将参与该项目。他们是多波长天文学和星系研究方面的专家，对厘米和毫米波段的无线电干涉测量和星系中多相气体的研究有特别的了解，这是本博士项目的中心课题。还将有机会与更广泛的合作网络合作，其中包括马克斯·普朗克研究所(德国海德堡)、欧洲南方天文台(德国慕尼黑)和卡迪夫大学的学者。

One of the fundamental challenges of modern astrophysics is understanding the physical mechanisms that trigger and regulate star formation. A key outstanding question is the role and the relative importance of the environment, including gas dynamics and magnetic fields, in this process that transforms gas into stars.Tidal Dwarf Galaxies are thought to form from gravitationally bound condensations of gas and stars that were torn out from their parent galaxy by tidal forces during galaxy interactions.This makes them ideal laboratories to study the physics of star formation in extreme environments, fundamental in order to understand how stars formed during the early days of the Universe, where galaxy collisions were more frequent than today.In year 1 of the PhD we will begin by extending a groundbreaking study ('ALMA Resolves Giant Molecular Clouds in a Tidal Dwarf Galaxy' Querejeta et al. 2021 https://doi.org/10.1051/0004-6361/202038955) of the archetypal TDG J1023+1954 in the interacting system Arp 94. We will use data from the Jansky Very Large Array (from 1.4 to 22 GHz) to search for and image radio continuum emission in this galaxy. This will allow us to trace the history of star formation across the TDG, search for radio signatures of relic star formation, and determine the distribution and magnitude of polarization of the radio emission, to map the magnetic field that may be threaded through the gas.To process the JVLA dataset using CASA, (Common Astronomy Software Applications) it is expected to visit the Manchester University ALMA node. Due to Covid 19 restrictions, the exact date is not confirmed yet.In subsequent years we will perform a substantial ALMA survey of dense molecular gas for a sample of 10 further TDGs, which will enable us to put J1023+1954 into a wider context and to compare its properties with larger, Milky Way type spiral galaxies.Using existing archival ALMA 12 m telescope observations, we will aim to characterize the fraction of diffuse gas in this sample and, in parallel, we will apply to use the ALMA Compact Array to observe its molecular gas. The submission of the proposal to use the Atacama Large Millimeter Array is set in April 2022, for which it is expected winning time will be straightforward.Professor Carole Mundell will be the primary supervisor in Bath, and Professor Cathryn Mitchell will be the second supervisor. In addition, two external supervisors, Dr Ute Lisenfeld (University of Granada, Spain) and Dr Miguel Querejeta (Observatorio Astronómico Nacional, Madrid) will form part of the project. They are experts in multi-wavelength astronomy and galaxy studies, with particular knowledge of radio interferometry at cm and mm wavebands and the study of the multi-phase gas in galaxies, central topics in this PhD project. There will also be an opportunity to work with a wider collaboration network that includes academics at Max-Planck Institute (Heidelberg, Germany), the European Southern Observatory (Munich, Germany) and the University of Cardiff.