arXiv 0903.22222009-03astro-ph.GA

拱星团的大质量恒星初始质量函数

The massive star initial mass function of the Arches cluster

Pablo Espinoza, Fernando J. Selman, Jorge Melnick

备注：: Accepted for publication in Astronomy and Astrophysics. 22 pages, 21 figures. Image quality of figures is now improved, and we replaced Fig.A.1
DOI：: 10.1051/0004-6361/20078597

摘要：

银河系中心附近的巨大拱门星团应该是研究极端条件下大质量恒星形成的理想实验室。但这是要付出高昂代价的：这个星团隐藏在几十个视觉等级的灭绝之后。严重的拥挤需要空间或AO辅助仪器来解析恒星星族，即使使用最好的仪器解释数据也远非直接。使用NICMOS和地面上最先进的AO成像仪进行的几次调查显示，星团的整体IMF头重脚轻，中心附近的IMF非常平坦。然而，有几种效应可能会使这些结果产生偏差，特别是强微分消光和在强红化存在下将观测转换为标准测光系统的问题。我们提出了新的观测获得的NAOS-Conica（NACO）AO成像仪的VLT。在NACO的自然光度系统中工作避免了光度变换的问题，并且我们使用贝叶斯方法从宽带IR颜色确定质量和红度。得到了IMF高质量端（$M>10M_{\sun}$）的$Γ=-1.1 \pm 0.2$的全局值，并得出结论，对于拱形簇，不能丢弃Salpeter斜率的幂律。国际货币基金组织向中心的扁平化得到了证实，但没有以前想象的那么严重。我们发现$Γ=-0.88\pm0.20$，这是不符合以前的决定。在0.4 pc的范围内，我们得到了该星团的$\sim2.0(\pm0.6)\times10^{4}M_{\sun}$总质量和中心质量密度$ρ= 2(\pm0.4)\times10^{5} M_{\sun}pc^{-3}$，证实了拱门是银河系中已知的年轻大质量星团。

英文摘要：

The massive Arches cluster near the Galactic center should be an ideal laboratory for investigating massive star formation under extreme conditions. But it comes at a high price: the cluster is hidden behind several tens of magnitudes of visual extinction. Severe crowding requires space or AO-assisted instruments to resolve the stellar populations, and even with the best instruments interpreting the data is far from direct. Several investigations using NICMOS and the most advanced AO imagers on the ground revealed an overall top-heavy IMF for the cluster, with a very flat IMF near the center. There are several effects, however, that could potentially bias these results, in particular the strong differential extinction and the problem of transforming the observations into a standard photometric system in the presence of strong reddening. We present new observations obtained with the NAOS-Conica (NACO) AO-imager on the VLT. The problem of photometric transformation is avoided by working in the natural photometric system of NACO, and we use a Bayesian approach to determine masses and reddenings from the broad-band IR colors. A global value of $Γ=-1.1 \pm 0.2$ for the high-mass end ($M>10M_{\sun}$) of the IMF is obtained, and we conclude that a power law of Salpeter slope cannot be discarded for the Arches cluster. The flattening of the IMF towards the center is confirmed, but is less severe than previously thought. We find $Γ=-0.88\pm0.20$, which is incompatible with previous determinations. Within 0.4 pc we derive a total mass of $\sim2.0(\pm0.6)\times10^{4}M_{\sun}$ for the cluster and a central mass density $ρ= 2(\pm0.4)\times10^{5} M_{\sun}pc^{-3}$ that confirms Arches as the densest known young massive cluster in the Milky Way.

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