SOLIS II。太阳型原星系团OMC2-FIR4中碳链的增长
SOLIS II. Carbon-chain growth in the Solar-type protocluster OMC2-FIR4
摘要：
将碳原子锁定在分子中的星际传递可能是生命出现的关键因素之一。氰基多炔是在其两端由氢原子和氰基限定的碳链，因此它们可能是碳的优良储存器。最简单的成员HC 3 N在银河系星际介质中普遍存在，也在外部星系中发现。因此，了解氰基多炔在形成类似于我们太阳的恒星的区域中的生长，以及影响它的因素，特别重要。在IRAM/NOEMA大型计划SOLIS（太空生命种子）的框架中，我们获得了原星系团OMC 2-FIR 4中两个氰基多炔HC 3 N和HC 5 N的地图。由于我们的太阳被认为是诞生在一个丰富的星团中，OMC 2-FIR 4是太阳可能诞生的环境中最接近和最知名的代表之一。我们发现整个源的HC 3 N/HC 5 N丰度比在~ 1 - 30的范围内，在FIR 5和FIR 4的东部区域中具有最小值（< 10）。只有在以下条件下，化学模型才能重现< 10的比值：（1）宇宙线电离率$ζ$为~ $4 \times 10^{-14}$ s $^{-1}$ ;（2）气态元素比C/O接近1;（3）O和C基本上耗尽。大的$ζ$与以前的工作在FIR 4中测量的相当，并被解释为由于嵌入源的高能（> 10 MeV）粒子的通量。我们认为这些震源可能位于FIR 4和FIR 5以东。FIR 4上的温度梯度，T降低了约10 K，也可以解释观察到的HC 3 N/HC 5 N线比的变化，而不需要宇宙射线电离率梯度。然而，即使在这种情况下，为了重现观测结果，也需要高的恒定宇宙线电离率（$10^{-14}$ s $^{-1}$的量级）。
英文摘要：
The interstellar delivery of carbon atoms locked into molecules might be one of the key ingredients for the emergence of life. Cyanopolyynes are carbon chains delimited at their two extremities by an atom of hydrogen and a cyano group, so that they might be excellent reservoirs of carbon. The simplest member, HC3N, is ubiquitous in the galactic interstellar medium and found also in external galaxies. Thus, understanding the growth of cyanopolyynes in regions forming stars similar to our Sun, and what affects it, is particularly relevant. In the framework of the IRAM/NOEMA Large Program SOLIS (Seeds Of Life In Space), we have obtained a map of two cyanopolyynes, HC3N and HC5N, in the protocluster OMC2-FIR4. Because our Sun is thought to be born in a rich cluster, OMC2-FIR4 is one of the closest and best known representatives of the environment in which the Sun may have been born. We find a HC3N/HC5N abundance ratio across the source in the range ~ 1 - 30, with the smallest values (< 10) in FIR5 and in the Eastern region of FIR4. The ratios < 10 can be reproduced by chemical models only if: (1) the cosmic-ray ionisation rate $ζ$ is ~ $4 \times 10^{-14}$ s$^{-1}$; (2) the gaseous elemental ratio C/O is close to unity; (3) O and C are largely depleted. The large $ζ$ is comparable to that measured in FIR4 by previous works and was interpreted as due to a flux of energetic (> 10 MeV) particles from embedded sources. We suggest that these sources could lie East of FIR4 and FIR5. A temperature gradient across FIR4, with T decreasing by about 10 K, could also explain the observed change in the HC3N/HC5N line ratio, without the need of a cosmic ray ionisation rate gradient. However, even in this case, a high constant cosmic-ray ionisation rate (of the order of $10^{-14}$ s$^{-1}$) is necessary to reproduce the observations.
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