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arXiv 0810.0473astro-ph
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在M33中的恒星形成：盘上的多波长特征

Star formation in M33: multiwavelength signatures across the disk

S. Verley, E. Corbelli, C. Giovanardi, L. K. Hunt

备注：
14 pages, 13 figures, 3 tables, accepted by A&A
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摘要：

目标。我们使用不同的示踪剂，如哈，紫外线（UV）和红外线（IR）的各种波长的排放，研究整个磁盘的尘埃和恒星形成（SF）的条件M33。方法.我们得出的径向分布的尘埃，老的和年轻的恒星星族使用斯皮策和GALEX数据，补充地面光学数据和现有的调查原子和分子气体。我们将离散源对红外亮度的贡献与漫反射发射分开。结果在8和24微米，离散源占40%的红外辐射在最里面的3千秒差距，并为20%进一步。我们发现，随机发射从非常小的颗粒在弥漫的星际介质仅占10%的弥漫24 μ m的排放量，和尘埃拱壳的未解决的，进化的AGB星（碳星）是一个可行的选择。8微米的轮廓表明，多环芳烃排放量下降更快的半径比灰尘连续。在环形区域，0.24千秒差距宽，我们发现一个平均消光值为恒星连续AV = 0.25马格与弱依赖于半径，符合浅金属丰度梯度观察。从160 μ m的发射得到的尘埃不透明度从SF盘的中心到边缘反而降低了10倍。结论.使用消光校正的UV和Ha地图，我们发现在M33的全球SF率，在过去的1亿年，为0.45 +- 0.10百万年。FIR（远红外）和TIR（全红外）亮度可以跟踪SF，即使需要高转换因子来恢复有效速率。如果碳星为M33中弥漫的24 μ m辐射提供动力，这可以追踪1 Gyr前的恒星形成，并提供星系SF历史的更完整视图。[删节]

英文摘要：

Aims. We use different tracers, such as Ha, ultraviolet (UV), and infrared (IR) emissions at various wavelengths, to study the dust and star-formation (SF) conditions throughout the disk of M33. Methods. We derive the radial distribution of dust, of the old and young stellar population using Spitzer and GALEX data, complemented by ground-based optical data and available surveys of atomic and molecular gas. We separate the contribution of discrete sources to the IR brightness from the diffuse emission. Results. At 8 and 24 um, discrete sources account for 40% of the IR emission in the innermost 3 kpc, and for 20% further out. We find that stochastic emission from very small grains in the diffuse interstellar medium accounts for only 10% of the diffuse 24 um emission, and that dusty circumstellar shells of unresolved, evolved AGB stars (carbon stars) are a viable alternative. The 8 um profile suggests that PAH emission declines faster with radius than the dust continuum. In annular regions, 0.24 kpc wide, we find a mean extinction value for stellar continuum AV = 0.25 mag with a weak dependence on radius, consistent with the shallow metallicity gradient observed. Dust opacity derived from the 160 um emission decreases instead by a factor 10 from the center to edge of the SF disk. Conclusions. Using extinction corrected UV and Ha maps we find the global SF rate in M33, over the last 100 Myr, to be 0.45 +- 0.10 M yr-1. FIR (far-IR) and TIR (total-IR) luminosities can trace SF even though a high conversion factor is required to recover the effective rate. If carbon stars are powering the diffuse 24 um emission in M33 this can trace star formation 1 Gyr ago and provide a more complete view of the SF history of the galaxy. [abridged]

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