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arXiv 1104.3669astro-ph.CO
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相互作用星系M51的HII区光度函数

HII Region Luminosity Function of the Interacting Galaxy M51

Jong Hwan Lee, Narae Hwang, Myung Gyoon Lee

摘要:

我们提出了一个研究的HII区域在M51使用哈勃太空望远镜ACS图像作为哈勃遗产计划的一部分。我们已经在M51中编目了大约19,600个HII区,其Ha光度在L = 10^{35.5} erg/s到10^{39.0} erg/s之间。M51中HII区(HII LF)的Ha光度函数可用双幂律表示,其明亮部分的指数α =-2.25 \pm 0.02,暗部分的指数α =-1.42 \pm 0.01,在L= 10^{37.1} erg/s的折点处分离。这种断裂在以前对M51 HII区的研究中没有发现。与模拟的HII LF的比较表明,这种破裂是由HII区电离源的跃迁引起的,从低质量的星团(~ 10^3 M_sun,包括几颗OB星)到更大质量的星团(包括几十颗OB星)。在M_(51)的不同部位,L < 10^{37.1} erg/s的H Ⅱ低频具有不同的斜率:臂间区的H Ⅱ低频比臂区和核区的H Ⅱ低频陡。这种观察到的HII LF的差异可以解释为进化效应,即臂间区域的HII区域比M51其他部分的HII区域相对更古老。

英文摘要:

We present a study of HII regions in M51 using the Hubble Space Telescope ACS images taken as part of the Hubble Heritage Program. We have catalogued about 19,600 HII regions in M51 with Ha luminosity in the range of L = 10^{35.5} erg/s to 10^{39.0} erg/s. The Ha luminosity function of HII regions (HII LF) in M51 is well represented by a double power law with its index alpha=-2.25\pm0.02 for the bright part and alpha=-1.42\pm0.01 for the faint part, separated at a break point L= 10^{37.1} erg/s. This break was not found in previous studies of M51 HII regions. Comparison with simulated HII LFs suggests that this break is caused by the transition of HII region ionizing sources, from low mass clusters (with ~ 10^3 M_sun, including several OB stars) to more massive clusters (including several tens of OB stars). The HII LFs with L < 10^{37.1} erg/s are found to have different slopes for different parts in M51: the HII LF for the interarm region is steeper than those for the arm and the nuclear regions. This observed difference in HII LFs can be explained by evolutionary effects that HII regions in the interarm region are relatively older than those in the other parts of M51.

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