Mapping CS in starburst galaxies: Disentangling and characterising dense gas
Mapping CS in starburst galaxies: Disentangling and characterising dense gas
复制标题
绘制星暴星系中的 CS 地图：解开和表征致密气体
DOI：
10.1051/0004-6361/201425502
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发表时间：
2015
影响因子：
6.5
通讯作者：
Kelly G
中科院分区：
文献类型：
--
作者：
Kelly G
利用IRAM-30 m望远镜，对两个邻近星暴星系的CS（2 - 1）和CS（3 - 2）线进行了观测，并对它们的分布进行了分析。我们还在两个星系中检测到甲醛（H2 CO）和甲醇（CH 3OH）。结果在LTE条件下计算了CS和CH 3OH的柱密度。使用检测积累在这里，以指导我们的输入，我们链接的时间和深度依赖的化学模型与分子线辐射传输模型，我们重现的意见，显示CS存在的条件是如何可能会有所不同，远离银河系centrs.ConclusionsUsing的旋转图方法为CH 3OH，我们得到的下限温度为14 K。除此之外，通过将化学和辐射传输模型与观测结果进行比较，我们确定了CS（和CH 3OH）追踪的致密气体的性质。我们还估计了稠密气体的数量。我们发现，假设在我们的光束中有105到106个致密的核心，对于两个目标星系，来自温暖（T= 100−400 K）、致密（n（H2）= 105− 6 cm-3）的核心的CS辐射，可能具有高宇宙射线电离率（n = 100 cm-0），最好地描述了我们中心指向的条件。在NGC 6946中，离中心较远的地方的环境通常较冷和/或密度较小，而在NGC 3079中，环境较为均匀。包含冲击允许更有效的CS形成，这意味着在某些情况下需要密度低一个数量级的气体来复制观测结果。
AimsWe observe the dense gas tracer CS in two nearby starburst galaxies to determine how the conditions of the dense gas varies across the circumnuclear regions in starburst galaxies.MethodsUsing the IRAM-30m telescope, we mapped the distribution of the CS(2−1) and CS(3−2) lines in the circumnuclear regions of the nearby starburst galaxies NGC 3079 and NGC 6946. We also detected formaldehyde (H2CO) and methanol (CH3OH) in both galaxies. We marginally detect the isotopologue C34S.ResultsWe calculate column densities under LTE conditions for CS and CH3OH. Using the detections accumulated here to guide our inputs, we link a time and depth dependent chemical model with a molecular line radiative transfer model; we reproduce the observations, showing how conditions where CS is present are likely to vary away from the galactic centres.ConclusionsUsing the rotational diagram method for CH3OH, we obtain a lower limit temperature of 14 K. In addition to this, by comparing the chemical and radiative transfer models to observations, we determine the properties of the dense gas as traced by CS (and CH3OH). We also estimate the quantity of the dense gas. We find that, provided there are between 105and 106dense cores in our beam, for both target galaxies, emission of CS from warm (T= 100−400 K), dense (n(H2) = 105−6cm-3) cores, possibly with a high cosmic ray ionisation rate (ζ= 100ζ0) best describes conditions for our central pointing. In NGC 6946, conditions are generally cooler and/or less dense further from the centre, whereas in NGC 3079, conditions are more uniform. The inclusion of shocks allows for more efficient CS formation, which means that gas that is less dense by an order of magnitude is required to replicate observations in some cases.