arXiv 2005.039072020-05-08astro-ph.GA

极端贫金属星系DDO 70中的弱CS发射

Weak CS Emission in an Extremely Metal-poor Galaxy DDO 70

Kaiyi Du, Yong Shi, Zhi-Yu Zhang, Junzhi Wang, Yu Gao

备注：: 5 pages, 4 figures. Accepted for publication in MNRAS Letters
DOI：: 10.1093/mnrasl/slaa086

摘要：

在大多数像银河系这样的星系中，恒星形成于分子气体云中。与追踪大部分分子气体的CO发射不同，HCN和CS分子的转动跃迁主要探测分子气体的致密相，这与远红外光度和恒星形成率有紧密的几乎线性的关系。然而，目前还不清楚致密的分子气体是否存在于非常低的金属丰度，如果存在，它是如何与恒星形成相关的。本文报道了DDO~70的CS $J$ =5 $\rightarrow$ 4发射线的ALMA观测结果。DDO~70是一个具有$\sim7\%$太阳金属丰度的富气矮星系。我们没有检测到CS排放与强CO排放的所有地区。在叠加所有来自CO明亮团块的CS光谱之后，我们发现在$\sim 3.3$的信噪比下，不超过CS $J$ =5 $\rightarrow$ 4跃迁的边缘检测。这个3- $σ$的上限偏离了银河系中的本地恒星形成星系和致密团块中发现的$L^\prime_{\rm CS}$ - $L_{\rm IR}$和$L^\prime_{\rm CS}$ -SFR关系，这意味着在给定的红外光度和SFR下CS发射较弱。我们讨论了在低金属丰度下抑制CS发射的可能机制。

英文摘要：

In most galaxies like the Milky Way, stars form in clouds of molecular gas. Unlike the CO emission that traces the bulk of molecular gas, the rotational transitions of HCN and CS molecules mainly probe the dense phase of molecular gas, which has a tight and almost linear relation with the far-infrared luminosity and star formation rate. However, it is unclear if dense molecular gas exists at very low metallicity, and if exists, how it is related to star formation. In this work, we report ALMA observations of the CS $J$=5$\rightarrow$4 emission line of DDO~70, a nearby gas-rich dwarf galaxy with $\sim7\%$ solar metallicity. We did not detect CS emission from all regions with strong CO emission. After stacking all CS spectra from CO-bright clumps, we find no more than a marginal detection of CS $J$=5$\rightarrow$4 transition, at a signal-to-noise ratio of $\sim 3.3$. This 3-$σ$ upper limit deviates from the $L^\prime_{\rm CS}$-$L_{\rm IR}$ and $L^\prime_{\rm CS}$-SFR relationships found in local star forming galaxies and dense clumps in the Milky Way, implying weaker CS emission at given IR luminosity and SFR. We discuss the possible mechanisms that suppress CS emission at low metallicity.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

摘要：

英文摘要：

相关论文