After over three decades of unsuccessful attempts, we report the first detection of molecular gas emission in Malin 1, the largest spiral galaxy observed to date, and one of the most iconic giant low surface brightness galaxies. Using Atacama Large Millimeter/submillimeter Array, we detect significant ¹²CO (J = 1–0) emission in the galaxy’s central region and tentatively identify CO emission across three regions on the disk. These observations allow for a better estimate of the H₂ mass and molecular gas mass surface density, both of which are remarkably low given the galaxy’s scale. By integrating data on its H i mass, we derive a very low molecular-to-atomic gas mass ratio. Overall, our results highlight the minimal presence of molecular gas in Malin 1, contrasting sharply with its extensive, homogeneous atomic gas reservoir. For the first time, we position Malin 1 on the Kennicutt–Schmidt diagram, where it falls below the main sequence for normal spirals, consistent with previous upper limits but now with more accurate figures. These findings are crucial for constraining our understanding of star formation processes in environments characterized by extremely low molecular gas densities and for refining models of galaxy formation, thereby improving predictions concerning the formation, evolution, and distribution of these giant, elusive galaxies.

中文翻译：

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在巨大的低表面亮度星系 Malin 1 中首次检测到分子气体


经过三十多年的失败尝试，我们报告了在马林 1 号中首次检测到分子气体发射，这是迄今为止观测到的最大的螺旋星系，也是最具标志性的巨型低表面亮度星系之一。使用阿塔卡马大型毫米/亚毫米阵列，我们在星系的中心区域检测到显著的 ¹²CO （J = 1-0） 发射，并初步确定了盘上三个区域的 CO 发射。这些观测结果可以更好地估计 H₂ 质量和分子气体质量表面密度，考虑到星系的尺度，这两者都非常低。通过对其 H i 质量进行积分，我们得出了非常低的分子与原子气体质量比。总体而言，我们的结果突出了 Malin 1 中分子气体的存在极少，与其广泛、均匀的原子气储层形成鲜明对比。我们首次将 Malin 1 定位在 Kennicutt-Schmidt 图上，它低于法向螺旋的主序列，与之前的上限一致，但现在的数字更准确。这些发现对于限制我们对以极低分子气体密度为特征的环境中恒星形成过程的理解以及完善星系形成的模型至关重要，从而改进对这些巨大、难以捉摸的星系的形成、演化和分布的预测。