论文标题
极为金属贫困的星系DDO中的CS发射弱70
Weak CS Emission in an Extremely Metal-poor Galaxy DDO 70
论文作者
论文摘要
在大多数星系中，如银河系，在分子气云中形成恒星。与追踪大部分分子气体的CO发射不同，HCN和CS分子的旋转过渡主要探测分子气的致密相，分子气的致密相位与远红外的光度和恒星形成速率具有紧密而几乎是线性的关系。但是，目前尚不清楚是否以非常低的金属性存在致密分子气体，并且是否存在与恒星形成相关。在这项工作中，我们报告了CS $ j $ = 5 $ \ rightarrow $ 4排放线〜70的Alma观察结果，这是一个附近的富含气体的矮人银河系，带有$ \ sim7 \％\％$ $ $太阳金属。我们没有检测到所有具有强大CO发射的区域的CS发射。从共同的团块中堆叠所有CS光谱后，我们发现CS $ j $ = 5 $ \ rightArow $ 4过渡的边际检测，以$ \ sim 3.3 $的信噪比。这个3- $σ$上限与$ l^\ prime _ {\ rm cs} $ - $ l _ {\ rm ir} $和$ l^\ prime _ {\ rm cs} $ - sfr在本地星系中以元素形成的星系和密集的团块中的米尔基（Milky Way）属于较弱的sf insife and s fressife and s fressife and ser fression c.sm sf。我们讨论在低金属性下抑制CS发射的可能机制。
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.
