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arXiv 0810.2391astro-ph
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螺旋星系中恒星形成的几何时标

Geometrically Derived Timescales for Star Formation in Spiral Galaxies

D. Tamburro, H. -W. Rix, F. Walter, E. Brinks, W. J. G. de Blok, R. C. Kennicutt, M. -M. Mac Low

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Accepted for publication in the AJ special THINGS issue. For a high-resolution version visit: http://www.mpia.de/THINGS/Publications.html
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摘要：

我们估计一个特征的时间尺度恒星形成的旋臂盘星系，从原子氢（HI）的尘埃笼罩的大质量恒星。绘制高分辨率HI数据HI邻近星系巡天和24 $μ$米图像斯皮策红外邻近星系巡天我们测量的HI和24 $μ$米发射率峰值之间的平均角偏移作为半径的函数，为样本的14个附近的盘星系。我们模拟这些偏移假设一个瞬时的运动学模式的速度，$Ω_p$，和一个时标，t（HI-->24 $μ$ m），密集的\hi阶段和形成的大质量恒星，加热周围的尘埃之间的特征时间跨度。拟合$Ω_p$和t（HI-->24 $μ$ m），我们发现观测到的角度偏移（\hi和24 $μ$ m发射）的径向依赖性与这个简单的处方是一致的;由此产生的螺旋图案的共转半径通常是$R_{cor}\simeq 2.7 R_{s}$，与独立的估计一致。样品的t（HI-->24 $μ$ m）的结果值在1--400万年的范围内。我们已经探讨了非圆形气体运动对t（HI-->24 $μ$ m）估计值的可能影响，并发现它基本上小于因子2。这意味着在螺旋臂中随后的恒星形成的最强烈阶段的时间尺度很短，并且意味着相当大一部分分子云在形成恒星之前只存在了几百万年。然而，我们的分析并不排除一些分子云持续相当长的时间。如果旋臂中的大部分恒星形成都发生在这个短间隔t（HI-->24 $μ$ m）内，那么恒星形成必须是低效的，以避免气藏的短期耗尽。

英文摘要：

We estimate a characteristic timescale for star formation in the spiral arms of disk galaxies, going from atomic hydrogen (HI) to dust-enshrouded massive stars. Drawing on high-resolution HI data from The HI Nearby Galaxy Survey and 24$μ$m images from the Spitzer Infrared Nearby Galaxies Survey we measure the average angular offset between the HI and 24$μ$m emissivity peaks as a function of radius, for a sample of 14 nearby disk galaxies. We model these offsets assuming an instantaneous kinematic pattern speed, $Ω_p$, and a timescale, t(HI-->24$μ$m), for the characteristic time span between the dense \hi phase and the formation of massive stars that heat the surrounding dust. Fitting for $Ω_p$ and t(HI-->24$μ$m), we find that the radial dependence of the observed angular offset (of the \hi and 24$μ$m emission) is consistent with this simple prescription; the resulting corotation radii of the spiral patterns are typically $R_{cor}\simeq 2.7 R_{s}$, consistent with independent estimates. The resulting values of t(HI-->24$μ$m) for the sample are in the range 1--4 Myr. We have explored the possible impact of non-circular gas motions on the estimate of t(HI-->24$μ$m) and have found it to be substantially less than a factor of 2. This implies that a short timescale for the most intense phase of the ensuing star formation in spiral arms, and implies a considerable fraction of molecular clouds exist only for a few Myr before forming stars. However, our analysis does not preclude that some molecular clouds persist considerably longer. If much of the star formation in spiral arms occurs within this short interval t(HI-->24$μ$m), then star formation must be inefficient, in order to avoid the short-term depletion of the gas reservoir.

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