The Initial Mass Functions in the Super-Star Clusters NGC 1569A and NGC 1705-1
The Initial Mass Functions in the Super-Star Clusters NGC 1569A and NGC 1705-1
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DOI：
10.1086/306291
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发表时间：
1998-05
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影响因子：
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通讯作者：
A. Sternberg
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文献类型：
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作者：
A. Sternberg
我使用最近的光度和恒星速度色散测量的超级星团（SSC）的NGC 1569 A和NGC 1705-1，以确定他们现在的光度/质量比（LV/M）。然后，我使用推断的LV/M，人口合成模型的演变星星集群，以约束这些对象的初始质量函数（IMF）。我发现1569 A年的（LV/M）流率= 28.9，1705-1年的（LV/M）流率= 126。因此，在1569年，对于扩展到0.1 M的m-αdm IMF，IMF是陡峭的，α ~ 2.5。这意味着1569 A中的大部分恒星质量都包含在低质量（<1 M嫌）恒星中;然而，1705-1中的IMF要么是平坦的，α = 2，要么在1 ~ 3 M嫌的质量下限处被截断。我比较推断的IMF与银河系球状星团的质量函数（MF）。1569 A似乎有足够的低质量恒星，使其有可能演化成类似于银河系球状星团的天体;然而，1705-1中明显缺乏低质量恒星可能使这个SSC很难成为球状星团。如果1705-1中的星团质量确实是由低质量恒星所主导，那么这个SSC中大的LV/M可能是最大质量恒星在靠近星团核心的地方形成的证据。
I use recent photometric and stellar velocity dispersion measurements of the super-star clusters (SSCs) NGC 1569A and NGC 1705-1 to determine their present-day luminosity/mass ratios (LV/M). I then use the inferred LV/M, together with population synthesis models of evolving star clusters, to constrain the initial mass functions (IMFs) in these objects. I find that (LV/M)☉ = 28.9 in 1569A and (LV/M)☉ = 126 in 1705-1. It follows that in 1569A the IMF is steep with α ~ 2.5 for m-αdm IMFs that extend to 0.1 M☉. This implies that most of the stellar mass in 1569A is contained in low-mass (<1 M☉) stars; however, in 1705-1 the IMF is either flat, with α ≲ 2, or it is truncated at a lower mass limit between 1 and 3 M☉. I compare the inferred IMFs with the mass functions (MFs) of Galactic globular clusters. It appears that 1569A has a sufficient reservoir of low-mass stars for it plausibly to evolve into an object similar to Galactic globular clusters; however, the apparent deficiency of low-mass stars in 1705-1 may make it difficult for this SSC to become a globular cluster. If low-mass stars do dominate the cluster mass in 1705-1, the large LV/M in this SSC may be evidence that the most massive stars have formed close to the cluster cores.