文章基本信息

标题：Probing the clumping structure of giant molecular clouds through the spectrum, polarisation and morphology of X-ray reflection nebulae
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作者：Margherita Molaro ; Margherita Molaro ; Rishi Khatri 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2016
卷号：589
页码：1-15
DOI：10.1051/0004-6361/201527760
语种：English
出版社：EDP Sciences
摘要：We introduce a new method for probing global properties of clump populations in giant molecular clouds (GMCs) in the case where these act as X-ray reflection nebulae (XRNe), based on the study of the clumping’s overall effect on the reflected X-ray signal, in particular on the Fe K-α line’s shoulder. We consider the particular case of Sgr B2, one of the brightest and most massive XRN in the Galactic center (GC) region. We parametrise the gas distribution inside the cloud using a simple clumping model with theslope of the clump mass function (α), the minimum clump mass (mmin), the fraction of the cloud’s mass contained in clumps (fDGMF), and the mass-size relation of individual clumps as free parameters, and investigate how these affect the reflected X-ray spectrum. In the case of very dense clumps, similar to those presently observed in Sgr B2, these occupy a small volume of the cloud and present a small projected area to the incoming X-ray radiation. We find that these contribute negligibly to the scattered X-rays. Clump populations with volume-filling factors of >10-3 do leave observational signatures, that are sensitive to the clump model parameters, in the reflected spectrum and polarisation. Future high angular resolution X-ray observations could therefore complement the traditional optical and radio observations of these GMCs, and prove to be a powerful probe in the study of their internal structure. Clumps in GMCs should further be visible both as bright spots and regions of heavy absorption in high resolution X-ray observations. We therefore also study the time-evolution of the X-ray morphology, under illumination by a transient source, as a probe of the 3D distribution and column density of individual clumps by future X-ray observatories.
关键词：Galaxy: center;scattering;polarization;ISM: structure