漩涡星系巡天中的CO同位素谱线图集（CLAWS）
A CO isotopologue Line Atlas within the Whirlpool galaxy Survey (CLAWS)
摘要：
我们提出的CO同位素线图集内的漩涡星系调查（CLAWS）的基础上IRAM 30米的大型计划，提供了一个基准研究的众多，微弱的CO同位素在毫米波长制度的整个光盘M51（NGC 5194）。该调查的核心目标是使用低J CO同位素线来约束CO激发和化学，并由此约束气体的局部物理条件。在这篇调查论文中，我们描述了CLAWS观察和数据简化策略。我们绘制了CO同位素$^{12}$ CO，$^{13}$ CO，C $^{18}$ O和C $^{17}$ O，以及1 mm和3 mm窗口内的几条补充线（CN（1-0），CS（2-1），CH $_3$ OH（2- 1），HC $^+$ N（1-0 -9））。149小时的总观测时间提供了前所未有的灵敏度。我们使用这些数据来详细探索几个CO同位素线比，研究它们的径向（和方位角）的趋势，并调查线比的变化是否源于ISM属性，如气体温度，密度或化学丰度的变化。例如，我们发现$^{13}$ CO}/ $^{12}$ CO、C $^{18}$ O/ $^{12}$ CO和C $^{18}$ O/ $^{13}$ CO谱线比在它们的J=1-0跃迁中的负径向趋势。我们还发现了局部环境的变化，例如与螺旋臂区域相比，臂间区域中的$^{12}$ CO（2-1）/（1-0）或$^{13}$ CO/ $^{12}$ CO（1-0）线比率更高。我们建议，上述CO线比的变化最有可能是由于光学深度的变化，而丰度的变化，由于选择性核合成在银河系范围内的规模也可以发挥作用。我们还研究了CO谱线能量分布（SLED）使用档案JCMT $^{12}$ CO（3-2）数据，并发现了变化的SLED的形状与当地的环境参数进一步的变化在光学深度，气体温度或密度。
英文摘要：
We present the CO isotopologue Line Atlas within the Whirpool galaxy Survey (CLAWS) based on an IRAM 30-m large programme which provides a benchmark study of numerous, faint CO isotopologues in the mm-wavelength regime across the full disc of M51 (NGC 5194). The survey's core goal is to use the low-J CO isotopologue lines to constrain CO excitation and chemistry, and therefrom the local physical conditions of the gas. In this survey paper, we describe the CLAWS observing and data reduction strategies. We map the J=1-0 and 2-1 transitions of the CO isotopologues $^{12}$CO,$^{13}$CO, C$^{18}$O and C$^{17}$O, as well as several supplementary lines within the 1 mm and 3 mm window (CN(1-0), CS(2-1), CH$_3$OH(2-1), N$_2$H$^+$(1-0), HC$_3$N(10-9)) at ~1 kpc resolution. A total observation time of 149 h offers unprecedented sensitivity. We use these data to explore several CO isotopologue line ratios in detail, study their radial (and azimuthal) trends and investigate whether changes in line ratios stem from changes in ISM properties such as gas temperatures, densities or chemical abundances. For example, we find negative radial trends for the $^{13}$CO}/$^{12}$CO, C$^{18}$O/$^{12}$CO and C$^{18}$O/$^{13}$CO line ratios in their J=1-0 transitions. We also find variations with local environment, such as higher $^{12}$CO(2-1)/(1-0) or $^{13}$CO/$^{12}$CO(1-0) line ratios in interarm regions compared to spiral arm regions. We propose that these aforementioned variations of CO line ratios are most likely due to a variation of the optical depth, while abundance variations due to selective nucleosynthesis on a galaxy-wide scale could also play a role. We also study the CO spectral line energy distribution (SLED) using archival JCMT $^{12}$CO(3-2) data and find a variation of the SLED shape with local environmental parameters further underlying changes in optical depth, gas temperatures or densities.
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