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Properties of molecular gas in the bar of maffei 2

机译：马菲2棒中的分子气体性质

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摘要

We investigated the physical properties of molecular gas in one of the nearest barred spiral galaxies, Maffei 2, using the ~(12)CO (J = 1-0) emission line taken for the Nobeyama CO Atlas of Nearby Spiral Galaxies. Position- velocity diagrams perpendicular to the apparent major axis of the bar show an abrupt velocity change across the bar, which is caused by molecular gas motion of ～100km s ~(-1) along the leading edges of the bar. The distribution of the peak temperature (Tpeak), velocity width (δV), and integrated intensity of the ~(12)CO spectra (ICO) in the ridges of the bar is quite different from that in the spiral arms in Tpeak-δV -ICO space, suggesting that molecular-gas properties are different in these regions. Simple model calculations assuming an ensemble of uniform and spherical molecular clouds in a large velocity-gradient approximation indicate that molecular gas in the bar ridge regions may be gravitationally unbound, which suggests that molecular gas is hard to become dense, and to form stars. Moreover, the gravitationally unbound condition makes the CO-to-H _2 conversion factor in the bar ridges smaller than in the arms. A lower star-formation efficiency in bars indicated by previous studies is caused by such a condition that molecular gas is gravitationally unbound, as well as by an overestimation of molecular gas mass in the bar regions relative to spiral arms using a constant CO-to-H _2 conversion factor.
机译：我们使用了附近螺旋星系的Nobeyama CO图集拍摄的〜（12）CO（J = 1-0）发射谱线，研究了最接近的禁止旋涡星系之一Maffei 2中分子气体的物理性质。垂直于条的视主轴的位置速度图显示条上的突然速度变化，这是由于沿条的前缘约100km s〜（-1）的分子气体运动引起的。棒形脊中的峰值温度（Tpeak），速度宽度（δV）和〜（12）CO谱图（ICO）的积分强度与Tpeak-δV-中的螺旋臂中的分布有很大不同ICO空间，表明这些区域的分子气体性质不同。简单的模型计算假设以大的速度-梯度近似方式获得了均匀且球形的分子云集合，这表明在条形脊区域中的分子气体可能在重力上没有约束力，这表明分子气体很难变得稠密并形成恒星。此外，重力不受约束的条件使棒状脊中的CO到H _2的转换因子比臂中的小。以前的研究表明，棒中较低的恒星形成效率是由于以下条件引起的：分子气体在重力作用下未结合，以及使用恒定的CO-to-tos值高估了棒区域中相对于螺旋臂的分子气体质量H _2转换因子。

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