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arXiv 1202.1803astro-ph.COastro-ph.GA
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发光红外星系II中的分子气体:极端物理条件及其对X_{co}因子的影响

The molecular gas in Luminous Infrared Galaxies II: extreme physical conditions, and their effects on the X_{co} factor

Padelis P. Papadopoulos, Paul van der Werf, E Xilouris, Kate G. Isaak, Yu Gao

摘要:

在这项工作中,我们总结了我们的CO线调查的发光红外星系(LIRGs:L_{IR} >=10^{11} L_{sol})在本地宇宙(文件\,我),通过集中在其平均ISM性质的影响,总分子气体质量估计通过所谓的X_{co} =M(H_2)/ L_{co,1-0}因素。全球CO谱线能量分布(SLED)的单相辐射转移模型< X_{co} >在一个显著的平均气体密度、温度和动力学状态范围内产生了X_{co}分布:\sim(0.6+/-0.2)M_{sol}(K km s^{-1} pc ^2)^{-1}。后者是决定X_{co}的最重要的参数,未结合态的值较低,自引力态的值最高。然而,在许多(U)LIRG中,(J=3- 2,4- 3,和/或J=6- 5)或文献中的HCN谱线数据允许在高密度下单独评估气体质量(&gt;=10^{4} cm^{-3})而不是简单的单相分析,我们发现{ \it近银河系X_{co}(3-6)\,M_sol\,(K\,km^{-1 $&gt;\,pc^2)^{-1}值成为可能。}我们进一步表明,在ULIRGs的高度湍流分子气体的高密度组件将是常见的,可以是足够大的高X_{co}占主导地位的平均值为整个星系。......... ...因此,这可能导致系统性地低估了ULIRGs中的分子气体质量。

英文摘要:

In this work we conclude the analysis of our CO line survey of Luminous Infrared Galaxies (LIRGs: L_{IR}>=10^{11}L_{sol}) in the local Universe (Paper\,I), by focusing on the influence of their average ISM properties on the total molecular gas mass estimates via the so-called X_{co}=M(H_2)/L_{co,1-0} factor. One-phase radiative transfer models of the global CO Spectral Line Energy Distributions (SLEDs) yield an X_{co} distribution with: <X_{co}>\sim(0.6+/-0.2) M_{sol}(K km s^{-1} pc^2)^{-1} over a significant range of average gas densities, temperatures and dynamical states. The latter emerges as the most important parameter in determining X_{co}, with unbound states yielding low values and self-gravitating states the highest ones. Nevertheless in many (U)LIRGs where available higher-J CO lines (J=3--2, 4--3, and/or J=6--5) or HCN line data from the literature allow a separate assessment of the gas mass at high densities (>=10^{4} cm^{-3}) rather than a simple one-phase analysis we find that {\it near-Galactic X_{co} (3-6)\, M_sol\,(K\,km^{-1}\,pc^2)^{-1} values become possible.} We further show that in the highly turbulent molecular gas in ULIRGs a high-density component will be common and can be massive enough for its high X_{co} to dominate the average value for the entire galaxy. ......... ...this may have thus resulted to systematic underestimates of molecular gas mass in ULIRGs.

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