M51与HERA：II的完整的~（12）CO 2- 1图。总气体表面密度和引力稳定性
A complete 12CO 2--1 map of M51 with HERA: II. Total gas surface densities and gravitational stability
摘要：
到目前为止，星系中大规模恒星形成的开始及其与星系盘引力稳定性的联系还没有完全了解。附近的正面螺旋星系M51是研究这个主题的理想目标。本文结合M51及其伴星系的CO、尘埃、HI和恒星图，研究了H2/HI跃迁、气尘比和盘对引力坍缩的稳定性。利用HERA/IRAM-30 m的12 CO2 - 1图数据和HI VLA数据，结合分子气体图，研究了气体总表面密度和原子-分子气体的相变。将总气体表面密度与来自850微米SCUBA数据的灰尘表面密度进行比较。考虑到分子和原子气体的速度色散，以及2 MASS K波段观测得到的恒星表面密度，我们得到了盘的总Toomre Q参数。螺旋臂中的气体表面密度比臂间区域的气体表面密度高约2-3倍。分子与原子的表面密度比与流体静压力P_hydro近似呈幂律关系。M51中的气体表面密度分布显示出基本的指数分布，其尺度长度为h_gas=7.6 kpc，占总气体质量的55%，与指数尘埃盘的性质相当。与HI中观察到的速度宽度相反，CO速度分散显示与臂间区域相比，螺旋臂中的线宽增强。在Toomre Q-参数分析中，恒星分量的贡献是显著的，并且使组合Q-参数Q_tot降低了高达70%，接近引力不稳定性的阈值。在径向平均值中，Q_tot的值在1.5-3之间变化。Q_tot的图显示旋臂上的值约为1。
英文摘要：
To date the onset of large-scale star formation in galaxies and its link to gravitational stability of the galactic disk have not been fully understood. The nearby face-on spiral galaxy M51 is an ideal target for studying this subject. This paper combines CO, dust, HI, and stellar maps of M51 and its companion galaxy to study the H2/HI transition, the gas-to-dust ratios, and the stability of the disk against gravitational collapse. We combine maps of the molecular gas using 12CO 2--1 map HERA/IRAM-30m data and HI VLA data to study the total gas surface density and the phase transition of atomic to molecular gas. The total gas surface density is compared to the dust surface density from 850 micron SCUBA data. Taking into account the velocity dispersions of the molecular and atomic gas, and the stellar surface densities derived from the 2MASS K-band survey, we derive the total Toomre Q parameter of the disk. The gas surface density in the spiral arms is approximately 2-3 higher compared to that of the interarm regions. The ratio of molecular to atomic surface density shows a nearly power-law dependence on the hydrostatic pressure P_hydro. The gas surface density distribution in M51 shows an underlying exponential distribution with a scale length of h_gas=7.6 kpc representing 55% of the total gas mass, comparable to the properties of the exponential dust disk. In contrast to the velocity widths observed in HI, the CO velocity dispersion shows enhanced line widths in the spiral arms compared to the interarm regions. The contribution of the stellar component in the Toomre Q-parameter analysis is significant and lowers the combined Q-parameter Q_tot by up to 70% towards the threshold for gravitational instability. The value of Q_tot varies from 1.5-3 in radial averages. A map of Q_tot shows values around 1 on the spiral arms.
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