A COSMIC-RAY-DOMINATED INTERSTELLAR MEDIUM IN ULTRA LUMINOUS INFRARED GALAXIES: NEW INITIAL CONDITIONS FOR STAR FORMATION
A COSMIC-RAY-DOMINATED INTERSTELLAR MEDIUM IN ULTRA LUMINOUS INFRARED GALAXIES: NEW INITIAL CONDITIONS FOR STAR FORMATION
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DOI：
10.1088/0004-637x/720/1/226
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发表时间：
2010-09
期刊：
影响因子：
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通讯作者：
P. Papadopoulos
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文献类型：
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作者：
P. Papadopoulos
高密度的星星形成是典型的合并/星暴事件，为超亮红外星系（ULIRGs）的大红外光度提供动力。（LIR（8-1000 μm）<$1012 L返）导致了极高的宇宙射线（CR）能量密度，其能量密度为UCR 100 ×（103-104）UCR，Gal透过星际介质，这是这类系统中超新星遗迹数量密度大的直接结果。与从众多恒星形成（SF）地点发出的远紫外光子不同，ULIRG中这些大的CR能量密度将在其紧凑的SF体积中加热并提高致密（n > 104 cm−3）紫外屏蔽气体核心的电离分数。这样的条件可以把大部分在这样的系统中发现的大分子气体质量和它们的高红移对应物（109-1010 M）变成巨大的CR主导区域（CRDR），而不是光子主导区域（PDR）的集合，后者在红外发光度较低的系统中占主导地位，其中星星的形成和分子气体分布更加广泛。CRDR中的分子气体最低温度为Tkin（80-160）K，并且在其被紫外线屏蔽的致密核心中具有非常高的电离分数x（e）> 10−6，这反过来将从根本上改变此类系统中星星形成的初始条件。CRDR的观测测试可以通过高J CO和13 CO谱线或任何重转子分子的多J跃迁（例如，HCN）及其同位素。在致密的紫外屏蔽气体中，非常高的电离分数的化学特征，如低[DCO+]/[HCO+]和高[HCO+]/[CO]丰度比，将是在极端的星爆CRDR的很好的探针。这些测试，沿着直接测量的高CO线亮度温度预计在ULIRGs中发现的致密气体盘的区域，将很快成为可行的亚弧秒干涉成像能力和灵敏度在毫米/亚毫米波长的改善，在阿尔马的时代。
The high-density star formation typical of the merger/starburst events that power the large IR luminosities of ultraluminous infrared galaxies (ULIRGs) (LIR(8–1000 μm) ≳1012 L☉) throughout the universe results in extraordinarily high cosmic-ray (CR) energy densities of UCR ∼ few ×(103–104) UCR,Gal permeating their interstellar medium, a direct consequence of the large supernova remnant number densities in such systems. Unlike far-UV photons emanating from numerous star-forming (SF) sites, these large CR energy densities in ULIRGs will volumetrically heat and raise the ionization fraction of dense (n > 104 cm−3) UV-shielded gas cores throughout their compact SF volumes. Such conditions can turn most of the large molecular gas masses found in such systems and their high redshift counterparts (∼109–1010 M☉) into giant CR-dominated regions (CRDRs) rather than ensembles of photon-dominated regions (PDRs) which dominate in less IR-luminous systems where star formation and molecular gas distributions are much more extended. The molecular gas in CRDRs will have a minimum temperature of Tkin ∼ (80–160) K, and very high ionization fractions of x(e) > 10−6 throughout its UV-shielded dense core, which in turn will fundamentally alter the initial conditions for star formation in such systems. Observational tests of CRDRs can be provided by high-J CO and 13CO lines or multi-J transitions of any heavy rotor molecules (e.g., HCN) and their isotopologs. Chemical signatures of very high ionization fractions in dense UV-shielded gas such as low [DCO+]/[HCO+] and high [HCO+]/[CO] abundance ratios would be good probes of CRDRs in extreme starbursts. These tests, along with direct measurements of the high CO line brightness temperatures expected over the areas of compact dense gas disks found in ULIRGs, will soon be feasible as sub-arcsecond interferometric imaging capabilities and sensitivity at millimeter/submillimeter wavelengths improve in the era of ALMA.