arXiv 0707.23452007-07-16astro-ph

M33中特别有效的恒星形成

Particularly Efficient Star Formation in M33

E. Gardan, J. Braine, K. F. Schuster, N. Brouillet, A. Sievers

备注：: 16 pages, 15 figures
DOI：: 10.1051/0004-6361:20077711

摘要：

星系的恒星形成率是星系所有红移和演化阶段的重要参数。为了了解增加SF率在中等红移星系的一种可能性是研究恒星形成的本地星系的属性经常发现在这个较早的时代，如低金属丰度和小尺寸。我们提出了敏感的观测分子气体在M33，一个小的本星系群螺旋在840千秒差距的距离，其中股票的许多特征的中间红移星系。在IRAM 30米望远镜上用HERA外差天线阵在CO（2- 1）线上进行了观测。在M33的北部观察到11 \arcmin $\times$ 22 \arcmin区域，达到几个10 $^{3}$ \msol的检测阈值。在这一区域，SF（8 \mum、24 \mum、\Ha、FUV）的CO排放和示踪物之间的相关性非常好，CO在极北的地方被探测到，这表明即使在太阳下金属丰度的小螺旋中，分子气体也在盘的远处形成。一个主要的分子云被发现在一个臂间区域没有HI峰和很少，如果没有任何迹象SF-没有一个完整的调查，这种云将永远不会被发现。径向依赖的CO排放的尺度长度类似的尘埃排放，比\Ha或FUV扩展。然而，如果$\ratioo$比率与金属丰度成反比，则H $_2$的标度长度变得与\Ha或FUV相似。将SF率与H $_2$质量进行比较，表明M 33像它类似的中等红移星系一样，具有比大的局部宇宙螺旋更高的SF效率。

英文摘要：

The Star Formation (SF) rate in galaxies is an important parameter at all redshifts and evolutionary stages of galaxies. In order to understand the increased SF rates in intermediate redshift galaxies one possibility is to study star formation in local galaxies with properties frequently found at this earlier epoch like low metallicity and small size. We present sensitive observations of the molecular gas in M 33, a small Local Group spiral at a distance of 840 kpc which shares many of the characteristics of the intermediate redshift galaxies. The observations were carried out in the CO(2--1) line with the HERA heterodyne array on the IRAM 30 m telescope. A 11\arcmin$\times$22\arcmin region in the northern part of M 33 was observed, reaching a detection threshold of a few 10$^{3}$ \msol. The correlation in this field between the CO emission and tracers of SF (8\mum, 24\mum, \Ha, FUV) is excellent and CO is detected very far North, showing that molecular gas forms far out in the disk even in a small spiral with a subsolar metallicity. One major molecular cloud was discovered in an interarm region with no HI peak and little if any signs of SF -- without a complete survey this cloud would never have been found. The radial dependence of the CO emission has a scale length similar to the dust emission, less extended than the \Ha or FUV. If, however, the $\ratioo$ ratio varies inversely with metallicity, then the scale length of the H$_2$ becomes similar to that of the \Ha or FUV. Comparing the SF rate to the H$_2$ mass shows that M 33, like the intermediate redshift galaxies it resembles, has a significantly higher SF efficiency than large local universe spirals.

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