通过平衡恒星反馈与气体吸积来解释早期星系的小型熄火模型

中文摘要 AI 辅助

詹姆斯·韦布空间望远镜（JWST）发现了一类低质量、早期星系，它们在数千万年（tens of Myr）内保持着极低的恒星形成水平。这些“小型熄火”（mini-quenched）星系是JWST带来的众多惊喜之一，至今仍缺乏稳健的解释。我们旨在解释这些星系的几个重要性质，即控制其恒星形成与熄火的时间尺度。我们采用一个简单模型，将恒星反馈与束缚气体于红移 $z \sim 6$ 星系的引力相结合，在合理的参数选择下，该模型能够产生与观测到的小型熄火星系规模相当的星系中的小型熄火现象——其总恒星质量最高可达 $\sim 10^{10} M_{\odot}$。在我们的模型中，被抛出的星际气体形成一个球壳，在熄火过程中向外膨胀。我们的新颖改进在于允许这个膨胀的球壳阻止吸积气体落入星系，而其他模型中的球壳则不与吸积气体相互作用。利用我们的模型，如果星系各向同性地吸积气体，我们发现恒星反馈能够以合理的星系形成参数值重现观测到的小型熄火时间尺度。然而，在低晕质量下，我们模型的熄火时间尺度过长（$> 100$ Myr）。对于长熄火时间的一个潜在解决方案是星系通过纤维状结构（filaments）进行吸积，在这种情况下，只有部分球壳与吸积气体相互作用，熄火时间尺度缩短至更可接受的值。然而，反馈产生的冲压压力（ram pressure）无法阻止具有极小张角的纤维状结构，正如某些晕形成模型中出现的情况，这使得小型熄火无法发生。最后，我们利用该模型估算正在经历小型熄火的星系比例，发现该比例可能很大。

英文摘要

The James Webb Space Telescope (JWST) has discovered a population of low-mass, early galaxies with very low levels of star formation over tens of Myr. These "mini-quenched" galaxies were one of the many surprises from JWST and still require a robust explanation. We seek to explain a few important properties of these galaxies, namely the timescales governing their star formation and quenching. We use a simple model that pairs stellar feedback with the forces binding gas to a $z \sim 6$ galaxy, and with plausible parameter choices, this model produces mini-quenching in galaxies approximately as large as observed mini-quenched galaxies -- up to total stellar masses of $\sim 10^{10} M_{\odot}$. In our model, the ejected interstellar gas forms into a spherical shell that expands outward during quenching. Our novel improvement is allowing this expanding shell to prevent accreting gas from falling in, in contrast to other models whose shells do not interact with accreting gas. Using our model, if a galaxy accretes isotropically, we find that stellar feedback can reproduce observed timescales of mini-quenching with plausible galaxy-formation parameter values. However, at low halo masses, the quenching timescale of our model is too long ($> 100$ Myr). A potential solution for a long quenching time is for the galaxy to accrete via filaments, in which case only a portion of the shell interacts with the accreting gas and the quenching timescale decreases to more accepted values. However, the ram pressure from feedback cannot stop filaments with very small opening angles, as occur in some halo formation models, making mini-quenching impossible. Finally, we use this model to estimate the fraction of galaxies undergoing mini-quenching, finding that it can be large.

发表机构

• University of California（加州大学）

机构由 AI 辅助整理，请以论文原文为准。

补充信息

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37 pages, 10 figures