Resolving the Role of Neutral Gas in Galaxy Evolution

加拿大天体物理学在未来十年的主要目标之一是了解星系的起源。揭开这个谜团是理解人类起源科学故事的重要一步，它解释了太阳形成的条件以及我们周围所有恒星的形成条件。我们大致知道恒星是由冷的分子气体云形成的，我们也知道这样形成的短命恒星会相对较快地进化和死亡，将它们的物质返还给下一代恒星。这种重子循环可以解释构成我们星球和我们身体的重元素是如何来自上一代恒星的。然而，驱动重子周期的实际物理原理却知之甚少。为了理解这个基本的周期，这项研究将使用一套新的望远镜观测来对控制星系演化的内部过程进行最好的普查。具体来说，这项研究将测量恒星形成过程如何随着星系内局部环境的变化而变化，回答诸如：在分子气体中恒星形成的速度有多快？是什么物理效应控制了这个速率？什么物理过程会影响气体转化为恒星的效率？垂死的恒星是如何激起或破坏它们的本地环境的？是什么导致气体云冷却并开始形成恒星？我们现在可以通过使用地球和太空中最好的望远镜对附近星系进行高分辨率的观测来解决这些问题。我们所有新观测的基本特征是，它们必须能够测量恒星形成的小细节（高分辨率）。我们用阿塔卡马大型毫米/亚毫米阵列收集了新的数据集，绘制出恒星形成气体云的特性，用哈勃太空望远镜和甚大望远镜研究新形成恒星的特性。我们的小组将利用这些数据来测量恒星形成的效率。我们还将使用詹姆斯·韦伯太空望远镜收集新数据，该望远镜将于2021年底发射，以观察处于形成中间的恒星，这将为恒星形成的速度提供新的见解。最后，我们正在使用甚大阵列来研究热气体，它充当中介：接收来自垂死恒星的物质，并冷却形成下一代的恒星形成云。这些观测将测量垂死的恒星如何破坏其局部环境，并为气体云如何开始形成恒星提供新的见解。这些都是理解星系演化的核心问题，但我们的进展有限，因为我们只能对我们自己银河系的恒星形成进行详细的研究。通过观察其他星系，我们终于可以“自上而下”地看到恒星的形成，这使我们能够看到恒星的形成是如何与更广泛的星系联系起来的。

One of the major goals for Canadian astrophysics over the next decade is to understand the origins of galaxies. Unravelling this mystery is a vital step in understanding the scientific story of our origins, explaining the conditions where the Sun formed but also all the stars around us. We understand broadly that stars form out of cold clouds of molecular gas, and we also understand that short-lived stars so formed will evolve and die relatively quickly, returning their material to be incorporated into the next generation of stars. This baryon cycle can explain how the heavy elements that make up our planet and our bodies came from a previous generation of stars. However, the actual physics that drives the baryon cycle is poorly understood. To understand this essential cycle, this research will use a suite of new telescope observations to make the best available census of these internal processes that control galaxy evolution. Specifically, this research will measure how the process of star formation changes in response to the local environments within galaxies, answering questions like: how quickly does star formation take place in molecular gas? What physical effects control that rate? What physical processes affect the efficiency of turning its gas into stars? How do dying stars stir up or destroy their local environments? What causes a cloud of gas to cool and start forming stars? We can now address these questions by making high resolution observations of nearby galaxies using some of the best telescopes on Earth and in space. The essential feature across all our new observations is that they must be able to measure the small details of star formation (high-resolution). We have collected new data sets with the Atacama Large Millimeter/submillimeter array to map out the properties of star forming clouds of gas and the Hubble Space Telescope and the Very Large Telescope to study the properties of the recently formed stars. Our group will use these data to measure the efficiency of star formation. We will also collect new data using the James Webb Space Telescope, which should launch at the end of 2021, to see the stars that are right in the middle of formation, which will provide new insights on how quickly star formation proceeds. Finally, we are using the Very Large Array to study the warm gas, which acts as an intermediary: receiving material from dying stars and cooling down to form the next generation of star-forming clouds. These observations will measure how dying stars disrupt their local environment as well as giving new insights into how gas clouds start forming stars. These are central questions to understanding galaxy evolution, but our progress has been limited because we could only make detailed studies of star formation in our own Milky Way galaxy. By observing other galaxies, we can finally see star formation from the "top down," which allows us to see how star formation connects back to the broader galaxy.