星爆星系中的CS映射：致密气体的解缠和表征
Mapping CS in Starburst Galaxies: Disentangling and Characterising Dense Gas
摘要：
目的。我们观察到致密气体示踪CS在两个附近的星暴星系，以确定如何在星暴星系的环核区域的致密气体的条件变化。方法.利用IRAM-30 m望远镜，我们绘制了邻近星暴星系NGC 3079和NGC 6946的CS（2-1）和CS（3-2）线在环核区的分布。我们还在两个星系中检测到甲醛（H2 CO）和甲醇（CH 3OH）。我们勉强检测到同位素C34 S。结果我们在LTE条件下计算CS和CH 3OH的柱密度。使用这里积累的检测来指导我们的输入，我们链接的时间和深度依赖的化学模型与分子线辐射转移模型，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中心。结论.利用CH_3OH的转动图方法，我们得到了14 K的下限温度。除此之外，通过比较化学和辐射转移模型的观测，我们确定的致密气体的性质，跟踪CS（和CH 3OH）。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10^5到10^6个致密核心，对于两个目标星系，来自温暖（T = 100 - 400 K）、致密（n（H2）= 10^5-6 cm-3）核心的CS发射，可能具有高宇宙射线电离率（zeta = 100 zeta 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，导致在某些情况下需要一个数量级的密度较低的气体来复制观测。
英文摘要：
Aims. We 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. Methods. Using 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 the formaldehyde (H2CO) and methanol (CH3OH) in both galaxies. We marginally detect the isotopologue C34S. Results. We 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. Conclusions. Using 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 that there are a between 10^5 and 10^6 dense cores in our beam, for both target galaxies, emission of CS from warm (T = 100 - 400 K), dense (n(H2) = 10^5-6 cm-3) cores, possibly with a high cosmic ray ionisation rate (zeta = 100 zeta0) 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, leading to an order of magnitude less dense gas being required to replicate observations in some cases.
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