Dust properties of the dark cloud IC 5146 - Submillimeter and NIR imaging
Dust properties of the dark cloud IC 5146 - Submillimeter and NIR imaging
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暗云 IC 5146 的灰尘特性 - 亚毫米和近红外成像
DOI：
10.1051/0004-6361:20021823
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发表时间：
2002
影响因子：
6.5
通讯作者：
C. Lada
中科院分区：
文献类型：
--
作者：
C. Kramer;J. Richer;B. Mookerjea;J. Alves;C. Lada
本文报道了在James Clerk Maxwell望远镜（JCMT）上用SCUBA对ic5146中850 μ m和450 μ m的分子脊进行亚毫米尘埃连续体研究的结果。绘制的区域大小为${\sim}14'\times2\farcm5$ (${\sim}2\rm \,pc\times0.3\,pc$)，由至少四个致密的核组成，这些核很可能是恒星前的。为了研究山脊及其内嵌核心的尘埃特性，我们将Lada et al.（1999）从背景巨星的近红外颜色中获得的尘埃发射数据与尘埃消光数据结合起来。山脊显示了10等以上的尘埃消失，在核心上升到35等。
由连续通量比构建的尘埃温度图显示了显著的温度梯度：我们发现外围和核心之间的温度高达20 K，核心本身的温度降至10 K。岩心本身几乎是等温的，尽管它们的平均温度在10k到18k之间变化。我们利用消光数据推导出另外一张由$\kappa'=\kappa_{850}/\kappa_{V}$参数化的尘埃发射率图。$\kappa'$的平均值与Mathis（1990）的正则值非常吻合。我们发现，当粉尘温度从${\sim}20$ K降低到${\sim}12$ K时，$\kappa'$从${\sim}1.3\times10^{-5}$增加到${\sim}5\times10^{-5}$，增加了${\sim}4$倍。蒙特卡罗模拟表明，对于估计的校准不确定度，这种变化是显著的。这与Ossenkopf ＆ Henning（1994）的星前核心尘埃演化模型相一致，该模型预测，在寒冷、致密的云内部，颗粒凝固和颗粒表面冰的形成导致$850\,\mu$ m尘埃不透明度的显著增加。这一解释进一步得到了先前在IC 5146核心之一中检测到的CO气相耗尽的支持（Kramer et al. 1999）。然而，需要对短波长的尘埃通量进行观测来验证这一结果。
We present the results of a submillimeter dust continuum study of a molecular ridge in IC 5146 carried out at 850 μ m and 450 μ m with SCUBA on the James Clerk Maxwell Telescope (JCMT). The mapped region is ${\sim}14'\times2\farcm5$ in size (${\sim}2\rm \,pc\times0.3\,pc$) and consists of at least four dense cores which are likely to be prestellar in nature. To study the dust properties of the ridge and its embedded cores, we combined the dust emission data with dust extinction data obtained by Lada et al. (1999) from the NIR colors of background giant stars. The ridge shows dust extinctions above ~10 mag, rising up to 35 mag in the cores.
A map of dust temperatures, constructed from the continuum flux ratios, shows significant temperature gradients: we find temperatures of up to ~20 K in the outskirts and between the cores, and down to ~10 K in the cores themselves. The cores themselves are almost isothermal, although their average temperatures vary between 10 K and 18 K. We used the extinction data to derive in addition a map of the dust emissivity parametrized by $\kappa'=\kappa_{850}/\kappa_{V}$. The average value of $\kappa'$ agrees well with the canonical value of Mathis (1990). We find that $\kappa'$ increases by a factor of ${\sim}4$ from ${\sim}1.3\times10^{-5}$ to ${\sim}5\times10^{-5}$ when the dust temperature decreases from ${\sim}20$ K to ${\sim}12$ K. A Monte Carlo simulation shows that this change is significant with regard to the estimated calibration uncertainties. This is consistent with models of dust evolution in prestellar cores by Ossenkopf & Henning (1994) which predict that grain coagulation and the formation of ices on grain surfaces in the cold, dense cloud interiors lead to a significant increase of the $850\,\mu$m dust opacity. This interpretation is furthermore supported by the previous detection of gas-phase depletion of CO in one of the IC 5146 cores (Kramer et al. 1999). Observations of dust fluxes at short wavelengths are however needed to verify this result.