arXiv 1003.51022010-03astro-ph.GA

高红外消光云中大质量恒星形成的初始阶段。I.物理参数

Initial phases of massive star formation in high infrared extinction clouds. I. Physical parameters

K. L. J. Rygl, F. Wyrowski, F. Schuller, K. M. Menten

备注：: 26 pages, 14 figures, 9 tables. Accepted for publication in Astronomy and Astrophysics, small corrections implemented
DOI：: 10.1051/0004-6361/200913510

摘要：

大质量恒星形成的最早阶段是在寒冷和密集的红外暗云（IRDC）中发现的。由于IRDC的检测方法对背景辐射的局部性质非常敏感，我们在这里提出了一种替代方法，通过使用红外消光图来搜索银河系平面中的高柱密度。我们发现了1到5千秒差距之间的云，其中许多是以前的调查所遗漏的。通过研究这些云的子样本的物理条件，我们的目标是更好地了解大质量恒星形成的初始条件。我们根据斯皮策IRAC两个最短波长波段之间3.6-4.5微米的颜色过剩绘制了银河系平面的消光图，达到了约100等的视觉消光比和9 × 10^22 cm^-2的柱密度。由此，我们编制了一个新的冷而紧凑的高消光云样本。我们在IRAM 30米望远镜上使用MAMBO阵列来研究云的形态，质量和密度以及其中的致密团块。后者随后用100米埃费尔斯堡望远镜进行了氨的定点观测，以确定旋转温度和运动距离。银河平面的消光图描绘了像旋臂这样的大尺度结构。1.2毫米的发射图显示，高消光云包含扩展的冷尘埃发射，从对流结构到仍然弥漫的云。大多数云在24微米内是黑暗的，但有几个已经显示出通过脉泽发射或明亮的红外源形成恒星的迹象，这表明高消光云包含各种演化阶段。观测结果表明，从黑暗，寒冷和弥漫的云，到具有更强的1.2毫米峰值的云，最后是具有许多强大的1.2毫米峰值的云，这些云也更温暖，更动荡，并且已经有一些恒星形成的路标。

英文摘要：

The earliest phases of massive star formation are found in cold and dense infrared dark clouds (IRDCs). Since the detection method of IRDCs is very sensitive to the local properties of the background emission, we present here an alternative method to search for high column density in the Galactic plane by using infrared extinction maps. We find clouds between 1 and 5 kpc, of which many were missed by previous surveys. By studying the physical conditions of a subsample of these clouds, we aim at a better understanding of the initial conditions of massive star formation. We made extinction maps of the Galactic plane based on the 3.6-4.5 microns color excess between the two shortest wavelength Spitzer IRAC bands, reaching to visual extinctions of ~100 mag and column densities of 9x10^22 cm^-2. From this we compiled a new sample of cold and compact high extinction clouds. We used the MAMBO array at the IRAM 30m telescope to study the morphology, masses and densities of the clouds and the dense clumps within them. The latter were followed up by pointed ammonia observations with the 100m Effelsberg telescope, to determine rotational temperatures and kinematic distances. Extinction maps of the Galactic plane trace large scale structures such as the spiral arms. The 1.2 mm emission maps reveal that the high extinction clouds contain extended cold dust emission, from filamentary structures to still diffuse clouds. Most of the clouds are dark in 24 microns, but several show already signs of star formation via maser emission or bright infrared sources, suggesting that the high extinction clouds contain a variety of evolutionary stages. The observations suggest an evolutionary scheme from dark, cold and diffuse clouds, to clouds with a stronger 1.2 mm peak and to finally clouds with many strong 1.2 mm peaks, which are also warmer, more turbulent and already have some star formation signposts.

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