Exploring the Host Galaxies of Unusual Astrophysical Transients

大多数天体物理瞬变现象都是由两种来源之一引起的--物质吸积到致密源上，释放其引力势，或者当一颗星星达到其生命的尽头并与其邻居合并或在其自身重量下崩溃时突然释放能量。在这两种情况下，特别是后者，对瞬变的宿主星系及其恒星种群的研究可以深入了解塑造事件的祖先和环境。核心坍缩伽马射线暴（GRB）是宇宙中能量最高的爆炸，有些能量高达1054 ergs-1。伽玛射线暴有一系列的光度和不同的光谱和时间轮廓。附近的少数几次爆发为研究伽玛暴的宿主提供了最好的机会。这些可能与WISE IR巡天中探测到的少量GRB宿主的位置相对应。我们手头有数据，包括VLT/X-Shooter光谱，WHT数据和ATCA无线电观测，探索这些物体，这些将成为该项目的最初重点。WISE天体的性质将被确定--它们是偶然排列的，附近的星星形成的星系，还是更遥远的尘埃星系？我们的工作将是寻找潜在的伽玛射线暴宿主星系，利用它来确定星系的星星形成率和化学成分。它们是否具有预期的性质，因为它们产生了伽马射线暴？然后，这项研究将扩展到其他类别的不寻常的天体物理瞬变（可能包括引力波源，或更奇特的瞬变，如FRB或TDE）的宿主星系。这样的瞬变揭示了直接观察非常具有挑战性的结构和恒星种群。因此，它们对于估算宇宙中形成的被遮蔽的星星的比例、限制伽马射线暴和其他瞬态祖先形成的条件，甚至限制恒星相互作用和恒星生命的终结--这是引力波天文学新时代的一个特别突出的问题--都是至关重要的。

Most astrophysical transients arise from one of two sources - the accretion of material onto a compact source, releasing its gravitational potential, or the sudden release of energy when a star reaches the end of its life and merges with its neighbour or collapses under its own weight. In both cases, but particularly the latter, the study of the transient's host galaxy and its stellar populations can lend insights into the progenitor and environment that shape the event. Core collapse gamma-ray bursts (GRBs) are the most energetic explosions in the Universe, with some reaching isotropic energies as high as 1054 ergs s-1. GRBs have a range of luminosities and different spectral and temporal profiles. The handful of nearby bursts offer the best opportunities to study the hosts of GRBs. It is possible that these correspond in position to the small number of GRB hosts detected in the WISE IR survey. We have data in hand, including VLT/X-Shooter spectra, WHT data and ATCA radio observations, exploring these objects, and these will form the initial focus of this project. The nature of the WISE objects will be determined - are they chance alignments, nearby star forming galaxies, or more distant dusty galaxies? Work will be done to characterise potential GRB host galaxies, using to determine the star formation rates and chemical compositions of the galaxies. Do they have the expected properties, given that they produced a GRB?This study will then be extended to the host galaxies of further classes of unusual astrophysical transients (potentially including gravitational wave sources, or more exotic transients such as FRBs or TDEs). Such transients reveal structures and stellar populations that are very challenging to observe directly. Hence they may be critical for estimating the fraction of obscured star formation in the Universe, constraining the conditions under which GRB and other transient progenitors can form, and even placing limits on stellar interactions and the end of stellar life - a particularly salient point in this new era of gravitational wave astronomy.