EGNoG调查：z~0.3正常星系中的气体激发
The EGNoG Survey: Gas Excitation in Normal Galaxies at z~0.3
摘要：
随着星系中分子气体的观测被推到恒星形成率较低的星系中，了解这些系统中气体的条件以正确推断它们的分子气体含量变得越来越重要。一氧化碳（CO）分子的旋转跃迁提供了一个很好的探测气体激发条件在这些星系。在本文中，我们提出了在毫米波天文学研究组合阵列（CARMA）的分子气体在正常星系（EGNoG）调查的演变的气体激发样品的结果。完整EGNoG样本的这一子集由四个z~0.3的星系组成，恒星形成速率为40-65 M太阳年^-1，恒星质量为~2x10^11 M太阳。利用CARMA的3 mm和1 mm波段，我们观测了这四个星系的CO（1-0）和CO（3-2）跃迁，以探测分子气体的激发。我们报告了在三个星系中对这两条谱线的强探测（第四条谱线的上限），平均谱线比r_31 = L '_CO（3-2）/L'_CO（1-0）为0.46 \pm 0.07（系统误差\lesssim 40%），这意味着CO（3-2）谱线的亚热激发。我们的结论是，在这些大质量的，高度恒星形成的星系中的气体的激发是与正常的恒星形成的星系，如本地螺旋，而不是像本地超亮红外星系恒星爆发系统是一致的。由于EGNoG气体激发样本星系是从主序星星系中选取的，我们认为这一结果适用于中高红移的主序星星系的研究，支持了在研究中发现恒星形成星系中z~1-2处的分子气体分数比局部观测值大一个数量级的假设。
英文摘要：
As observations of molecular gas in galaxies are pushed to lower star formation rate galaxies at higher redshifts, it is becoming increasingly important to understand the conditions of the gas in these systems to properly infer their molecular gas content. The rotational transitions of the carbon monoxide (CO) molecule provide an excellent probe of the gas excitation conditions in these galaxies. In this paper we present the results from the gas excitation sample of the Evolution of molecular Gas in Normal Galaxies (EGNoG) survey at the Combined Array for Research in Millimeter-wave Astronomy (CARMA). This subset of the full EGNoG sample consists of four galaxies at z~0.3 with star formation rates of 40-65 M_Sun yr^-1 and stellar masses of ~2x10^11 M_Sun. Using the 3 mm and 1 mm bands at CARMA, we observe both the CO(1-0) and CO(3-2) transitions in these four galaxies in order to probe the excitation of the molecular gas. We report robust detections of both lines in three galaxies (and an upper limit on the fourth), with an average line ratio, r_31 = L'_CO(3-2) / L'_CO(1-0), of 0.46 \pm 0.07 (with systematic errors \lesssim 40%), which implies sub-thermal excitation of the CO(3-2) line. We conclude that the excitation of the gas in these massive, highly star-forming galaxies is consistent with normal star-forming galaxies such as local spirals, not starbursting systems like local ultra-luminous infrared galaxies. Since the EGNoG gas excitation sample galaxies are selected from the main sequence of star-forming galaxies, we suggest that this result is applicable to studies of main sequence galaxies at intermediate and high redshifts, supporting the assumptions made in studies that find molecular gas fractions in star forming galaxies at z~1-2 to be an order of magnitude larger than what is observed locally.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
