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arXiv 1109.4255astro-ph.GA
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在螺旋附近年轻星团的NIR视图

NIR view on young stellar clusters in nearby spirals

P. Grosbol, H. Dottori

摘要:

近红外线观测可以详细研究大型螺旋星系中的年轻星团,这些星系在可见波段经常被沿臂的尘埃带高度遮蔽。用HAWK-I/VLT获得了10个螺旋的深度JHK图。这里给出NGC 2997的数据来说明样本的一般结果。(H-K)-(J-H)图表明,大多数小于700万年的星团被尘埃显著衰减,目视消光系数达到7等。(J-K)-Mk图中较年轻和较老的星团复合体之间的间隙表明,700万年左右的消光迅速减少,这可能是由于超新星爆炸后尘埃和气体的排出。星系团的光度函数符合指数为α ~ 2的幂律。星系团的亮度达到了Mk = -15等,对应的质量接近10^6 Mo,没有截止点的迹象。它们相对于主旋臂的方位角表明,质量最大的星团形成于旋臂区域,而较暗的星团也出现在旋臂之间。较老的簇更均匀地分布,相对于臂具有较弱的调制。

英文摘要:

Observations in the near-infrared (NIR) allow a detailed study of young stellar clusters in grand-design spiral galaxies which in visual bands often are highly obscured by dust lanes along the arms. Deep JHK-maps of 10 spirals were obtained with HAWK-I/VLT. Data for NGC 2997 are presented here to illustrate the general results for the sample. The (H-K)-(J-H) diagrams suggest that most stellar clusters younger than 7 Myr are significantly attenuated by dust with visual extinctions reaching 7 mag. A gap between younger and older cluster complexes in the (J-K)-Mk diagram indicates a rapid reduction of extinction around 7 Myr possibly due to expulsion of dust and gas after supernovae explosions. The cluster luminosity function is consistent with a power law with an exponent alpha ~ 2. Cluster luminosities of Mk = -15 mag are reached, corresponding to masses close to 10^6 Mo, with no indication of a cut-off. Their azimuthal angles relative to the main spiral arms show that the most massive clusters are formed in the arm regions while fainter ones also are seen between the arms. Older clusters are more uniformly distribution with a weaker modulation relative to the arms.

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