arXiv 1906.087792019-06-20astro-ph.GA

EMPIRE：IRAM 30米高密度天然气勘探

EMPIRE: The IRAM 30-m Dense Gas Survey of Nearby Galaxies

María J. Jiménez-Donaire, F. Bigiel, A. K. Leroy, A. Usero, D. Cormier, J. Puschnig, M. Gallagher, A. Kepley, A. D. Bolatto, S. García-Burillo, A. Hughes, C. Kr… 展开作者

María J. Jiménez-Donaire, F. Bigiel, A. K. Leroy, A. Usero, D. Cormier, J. Puschnig, M. Gallagher, A. Kepley, A. D. Bolatto, S. García-Burillo, A. Hughes, C. Kramer, J. Pety, E. Schinnerer, A. Schruba, K. Schuster, F. Walter

备注：: Accepted for publication in ApJ
DOI：: 10.3847/1538-4357/ab2b95

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摘要：

我们目前的帝国，IRAM 30米的大型计划，映射$λ= 3{-}4$毫米致密气体示踪剂在$\sim 1{-}2\,$千秒差距的分辨率在整个恒星形成盘附近的9个，大质量的，螺旋星系。我们描述了EMPIRE的观测和还原策略，并给出了HCN（1-0），HCO $^+$（1-0），HNC（1-0）和CO（1-0）的新的全星系图。我们探讨了如何HCN-CO和IR-HCN的比例，观测代理的致密气体分数和致密气体恒星的形成效率，取决于宿主星系和当地的环境。我们发现，致密气体的分数与恒星表面密度，气体表面密度，分子与原子的气体比例，和动态平衡压力。在EMPIRE中，每单位致密气体的恒星形成率与这些相同的环境参数反相关。因此，虽然稠密的气体在许多螺旋星系的中心区域看起来很丰富，但这些气体在形成恒星时似乎相对低效。这些结果与以前对附近星系和银河系中央分子带的研究结果在定性上一致。一阶，EMPIRE表明，在一个星系盘的条件设置的气体密度分布和HCN跟踪的致密气体显示环境依赖于恒星形成的关系。然而，我们的研究结果也显示了显着的（$\pm 0.2$ dex）星系到星系的变化。我们认为，气体结构低于我们的观察尺度和动力学效应也可能发挥重要作用。

英文摘要：

We present EMPIRE, an IRAM 30-m large program that mapped $λ= 3{-}4$ mm dense gas tracers at $\sim 1{-}2\,$kpc resolution across the whole star-forming disk of nine nearby, massive, spiral galaxies. We describe the EMPIRE observing and reduction strategies and show new whole-galaxy maps of HCN(1-0), HCO$^+$(1-0), HNC(1-0) and CO(1-0). We explore how the HCN-to-CO and IR-to-HCN ratios, observational proxies for the dense gas fraction and dense gas star formation efficiency, depend on host galaxy and local environment. We find that the fraction of dense gas correlates with stellar surface density, gas surface density, molecular-to-atomic gas ratio, and dynamical equilibrium pressure. In EMPIRE, the star formation rate per unit dense gas anti-correlates with these same environmental parameters. Thus, although dense gas appears abundant the central regions of many spiral galaxies, this gas appears relatively inefficient at forming stars. These results qualitatively agree with previous work on nearby galaxies and the Milky Way's Central Molecular Zone. To first order, EMPIRE demonstrates that the conditions in a galaxy disk set the gas density distribution and that the dense gas traced by HCN shows an environment-dependent relation to star formation. However, our results also show significant ($\pm 0.2$ dex) galaxy-to-galaxy variations. We suggest that gas structure below the scale of our observations and dynamical effects likely also play an important role.

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