SPITZER SURVEY OF THE LARGE MAGELLANIC CLOUD, SURVEYING THE AGENTS OF A GALAXY'S EVOLUTION (SAGE). IV. DUST PROPERTIES IN THE INTERSTELLAR MEDIUM-猫眼课题宝

DOI：

10.1088/0004-6256/136/3/919

发表时间：

2005-06

期刊：

The Astronomical Journal

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

M. Meixner;K. Gordon;R. Indebetouw;J. Hora;B. Whitney;R. Blum;W. Reach;J. Bernard;M. Meade;B. Babler;C. Engelbracht;B. For;K. Misselt;U. Vijh;C. Leitherer;M. Cohen;E. Churchwell;F. Boulanger;J. Frogel;Y. Fukui;J. Gallagher;V. Gorjian;J. Harris;D. Kelly;A. Kawamura;Soyoung Kim;W. Latter;S. Madden;Ciska Markwick-Kemper;A. Mizuno;N. Mizuno;J. Mould;A. Nota;M. Oey;K. Olsen;T. Onishi;R. Paladini;N. Panagia;P. Pérez-González;H. Shibai;Sato Shuji;Linda J. Smith;L. Staveley-Smith;A. Tielens;T. Ueta;S. V. Dyk;K. Volk;M. Werner;D. Zaritsky

本文的目的是提出一个扩展的红外（IR）发射的大麦哲伦云（LMC）的星际介质（ISM）中的尘埃的初步分析结果。结合联合收割机Spitzer Survey the Agents of Galaxy Evolution（SAGE）和红外天文卫星（IRAS）的数据，将红外辐射与气体示踪剂H i、CO和Hα进行了关联。我们提出了一个全球性的分析，以及详细的建模的光谱能量分布（SED）的几个选定的地区。在3.6 μm到160 μm的所有红外波段都探测到与ISM的中性、分子和扩散电离相有关的尘埃的扩展发射。在我们模拟的所有区域中，各种尘埃物种的相对丰度与银河系（MW）中的相当相似。我们绘制了大尘埃颗粒的温度图。温度图显示了12.1-34.7 K范围内的变化，从内部到外部区域有系统的梯度，追踪了大质量恒星和单个H ii区域的一般分布，并显示了恒星棒中较温暖的尘埃。该图用于推导大尘埃颗粒的远红外（FIR）光学厚度。我们发现LMC中有两个主要偏离：（1）70 μm附近的过量中红外（MIR）发射，称为70 μm过量，以及（2）偏离FIR光学深度和气体柱密度之间的线性相关性，我们称之为FIR过量发射。70 μm的过剩从MW到LMC再到小麦哲伦云（SMC）逐渐增加，表明随着金属丰度的降低而演化。过剩是与中性和扩散电离气体，与最强的过剩区域位于一个环结构旁边的30 Dor。我们发现，70 μm的过量可以解释为一个非常小的颗粒的尺寸分布相对于MW的修改，并在选定的区域中的总尘埃质量的13%的相应的质量增加。最可能的解释是，70 μm的过量是由于扩散介质中较大颗粒的侵蚀产生了大的非常小的颗粒（VSG）。这种FIR过量可能是由于灰尘/气体比的固有变化，其将在整个LMC上比MW值低4.6至2.3倍，但从IR发射导出的XCO值将比从CO数据的维里分析导出的XCO值低约三倍。我们还调查了FIR过量与可用气体示踪剂中未检测到的额外气体组分相关的可能性。假设在所有ISM阶段中尘埃丰度恒定，则额外的气体组分将具有已知H i质量的两倍。我们表明，这是合理的，FIR过量是由于冷原子气体，光学厚在21厘米线，而由纯H2相没有CO排放的贡献仍然是一个可能的解释。

The goal of this paper is to present the results of a preliminary analysis of the extended infrared (IR) emission by dust in the interstellar medium (ISM) of the Large Magellanic Cloud (LMC). We combine Spitzer Surveying the Agents of Galaxy Evolution (SAGE) and Infrared Astronomical Satellite (IRAS) data and correlate the infrared emission with gas tracers of H i, CO, and Hα. We present a global analysis of the infrared emission as well as detailed modeling of the spectral energy distribution (SED) of a few selected regions. Extended emission by dust associated with the neutral, molecular, and diffuse ionized phases of the ISM is detected at all IR bands from 3.6 μm to 160 μm. The relative abundance of the various dust species appears quite similar to that in the Milky Way (MW) in all the regions we have modeled. We construct maps of the temperature of large dust grains. The temperature map shows variations in the range 12.1–34.7 K, with a systematic gradient from the inner to outer regions, tracing the general distribution of massive stars and individual H ii regions as well as showing warmer dust in the stellar bar. This map is used to derive the far-infrared (FIR) optical depth of large dust grains. We find two main departures in the LMC with respect to expectations based on the MW: (1) excess mid-infrared (MIR) emission near 70 μm, referred to as the 70 μm excess, and (2) departures from linear correlation between the FIR optical depth and the gas column density, which we refer to as FIR excess emission. The 70 μm excess increases gradually from the MW to the LMC to the Small Magellanic Cloud (SMC), suggesting evolution with decreasing metallicity. The excess is associated with the neutral and diffuse ionized gas, with the strongest excess region located in a loop structure next to 30 Dor. We show that the 70 μm excess can be explained by a modification of the size distribution of very small grains with respect to that in the MW, and a corresponding mass increase of ≃13% of the total dust mass in selected regions. The most likely explanation is that the 70 μm excess is due to the production of large very small grains (VSG) through erosion of larger grains in the diffuse medium. This FIR excess could be due to intrinsic variations of the dust/gas ratio, which would then vary from 4.6 to 2.3 times lower than the MW values across the LMC, but XCO values derived from the IR emission would then be about three times lower than those derived from the Virial analysis of the CO data. We also investigate the possibility that the FIR excess is associated with an additional gas component undetected in the available gas tracers. Assuming a constant dust abundance in all ISM phases, the additional gas component would have twice the known H i mass. We show that it is plausible that the FIR excess is due to cold atomic gas that is optically thick in the 21 cm line, while the contribution by a pure H2 phase with no CO emission remains a possible explanation.

SPITZER SURVEY OF THE LARGE MAGELLANIC CLOUD, SURVEYING THE AGENTS OF A GALAXY'S EVOLUTION (SAGE). IV. DUST PROPERTIES IN THE INTERSTELLAR MEDIUM

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