2MASS wide-field extinction maps. V. Corona Australis
2MASS wide-field extinction maps. V. Corona Australis
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2MASS 广域消光图。
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
C. Lada
中科院分区：
文献类型：
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作者：
J. Alves;M. Lombardi;C. Lada
我们提出了一个近红外消光图的一个大的区域（870 deg^2 $）覆盖孤立的南冕复杂的分子云。我们达到了1-$sigma$的误差为0.02马格在K波段消光的分辨率为3弧分在整个地图。我们发现，南冕云是以前的CO和尘埃排放调查所揭示的三倍。该星云由一个45 pc长的复合体组成，从著名的星星形成的西端（头部，$N geq 10 ^{23}$ cm$^{-2}$）到弥散的东端（尾部，$N leq 10 ^{21}$ cm$^{-2}$）。值得注意的是，大约三分之二的复杂的大小和质量的谎言下A$_Vsim1$MAG。我们发现，PDF的云不能被描述为一个单一的对数正态函数。与之前的研究类似，我们发现在高柱密度下显著过量，但对数正态+幂律尾部拟合在低柱密度下不起作用。我们表明，在低柱密度附近的峰值观测PDF，PDF的振幅和形状都是由噪声在消光测量，使它不切实际的推导出内在的云PDF低于A$_K <$0.15马格。以上A$_K sim 0.15$马格，基本上是云的分子组成部分，PDF看起来最好由指数为$-3$的幂律来描述，但也可以描述为在非常低的柱密度处达到峰值的宽且相对低幅度的对数正态PDF的尾部。
We present a near-infrared extinction map of a large region ($sim$870 deg$^2$) covering the isolated Corona Australis complex of molecular clouds. We reach a 1-$sigma$ error of 0.02 mag in the K-band extinction with a resolution of 3 arcmin over the entire map. We find that the Corona Australis cloud is about three times as large as revealed by previous CO and dust emission surveys. The cloud consists of a 45 pc long complex of filamentary structure from the well known star forming Western-end (the head, $N geq10^{23}$ cm$^{-2}$) to the diffuse Eastern-end the tail, ($N leq10^{21}$ cm$^{-2}$). Remarkably, about two thirds of the complex both in size and mass lie beneath A$_Vsim1$ mag. We find that the PDF of the cloud cannot be described by a single log-normal function. Similar to prior studies, we found a significant excess at high column densities, but a log-normal + power-law tail fit does not work well at low column densities. We show that at low column densities near the peak of the observed PDF, both the amplitude and shape of the PDF are dominated by noise in the extinction measurements making it impractical to derive the intrinsic cloud PDF below A$_K <$ 0.15 mag. Above A$_K sim 0.15$ mag, essentially the molecular component of the cloud, the PDF appears to be best described by a power-law with index $-3$, but could also described as the tail of a broad and relatively low amplitude, log-normal PDF that peaks at very low column densities.