探测来自3.6 $μ$ m处低质量分子核的散射光--全球效应对核区观测的影响
Detecting scattered light from low-mass molecular cores at 3.6 $μ$m - Impact of global effects on the observation of coreshine
摘要：
最近从低质量核心（所谓的“核心”）发现的3-5 $μ$ m的散射光揭示了1 $μ$ m左右的颗粒的存在，这比在低密度星际介质中发现的颗粒要大。但到目前为止，在调查的100多个核心中，只有大约一半显示出这种效果。这促使进一步研究这一检出率的起源。从三维连续辐射转移方程，我们得到预期的散射光强度从一个核心放置在一个任意方向从地球上看。我们使用单次散射的近似，考虑消光到2阶泰勒近似，忽略尘埃粒度分布的空间梯度。对于给定的晶粒尺寸分布，计算了散射的方向特性对检测来自芯的散射光的影响，并讨论了附加辐射场分量等局部效应。一个核心的表面亮度轮廓与1D密度分布计算不同的银河系的位置，并将结果进行比较的近似检测限。我们发现，对于光学薄辐射和恒定的尺寸分布，可以推导出一个简单的限制，用于检测散射光从低质量的核心，适用于晶粒尺寸小于0.5 $μ$ m。核心的消光使银河平面的明亮部分无法被探测到，特别是在银河中心附近。对于从颗粒尺寸超过0.5 $μ$ m的低质量核心接收的散射光，散射的方向特性有利于检测银河系中心上方和下方的散射光，并在一定程度上靠近银河系反中心。我们确定了当地的入射辐射场作为主要的未知因素，从这个简单的计划造成的偏差。
英文摘要：
Recently discovered scattered light at 3-5 $μ$m from low-mass cores (so-called "coreshine") reveals the presence of grains around 1 $μ$m, which is larger than the grains found in the low-density interstellar medium. But only about half of the 100+ cores investigated so far show the effect. This prompts further studies on the origin of this detection rate. From the 3D continuum radiative transfer equation, we derive the expected scattered light intensity from a core placed in an arbitrary direction seen from Earth. We use the approximation of single scattering, consider extinction up to 2nd-order Taylor approximation, and neglect spatial gradients in the dust size distribution. The impact of the directional characteristics of the scattering on the detection of scattered light from cores is calculated for a given grain size distribution, and local effects like additional radiation field components are discussed. The surface brightness profiles of a core with a 1D density profile are calculated for various Galactic locations, and the results are compared to the approximate detection limits. We find that for optically thin radiation and a constant size distribution, a simple limit for detecting scattered light from a low-mass core can be derived that holds for grains with sizes smaller than 0.5 $μ$m. The extinction by the core prohibits detection in bright parts of the Galactic plane, especially near the Galactic center. For scattered light received from low-mass cores with grain sizes beyond 0.5 $μ$m, the directional characteristics of the scattering favors the detection of scattered light above and below the Galactic center, and to some extent near the Galactic anti-center. We identify the local incident radiation field as the major unknown causing deviations from this simple scheme.
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