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arXiv 2310.05693astro-ph.HEastro-ph.GA
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CONGRuENTS(宇宙线、中微子、伽马射线和射电非热谱)。II. 银河红外、射电和γ射线辐射之间的星系统计相关性

CONGRuENTS (COsmic-ray, Neutrino, Gamma-ray and Radio Non-Thermal Spectra). II. Population-level correlations between galactic infrared, radio, and γ-ray emission

Matt A. Roth, Mark R. Krumholz, Roland M. Crocker, Todd A. Thompson

AI总结:

利用CONGRuENTS模型模拟恒星形成星系的宇宙线输运与非热辐射,本文解释FIR-射电和FIR-γ相关及射电谱指数的物理起源,并预测射电谱曲率与π介子γ射线辐射的新相关。

摘要:

星系在其射电、γ射线和红外辐射之间遵循若干经验相关性,但这些相关性的物理起源仍不确定。本文使用CONGRuENTS模型研究恒星形成星系的宽波段非热辐射,该模型自洽地计算宇宙线强子和轻子的能量依赖输运及非热辐射,用以预测属性取自一项大深度巡天的合成星系样本的射电和γ射线辐射。我们表明,合成星系再现了观测到的关系,如远红外(FIR)-射电相关、FIR-γ相关以及射电谱指数分布,并利用模型解释这些关系的物理起源。结果显示,FIR-射电相关之所以出现,是因为由于流体静力学平衡和湍流发电机作用对气体属性施加的约束,最终以同步辐射形式辐射的宇宙线电子功率随星系恒星形成率的变化很弱;同样的物理过程决定不同星系中质子量能的程度,从而设定FIR-γ射线相关。我们进一步表明,星系射电谱指数主要源于热自由-自由辐射与宇宙线电子因轫致辐射及逃逸到星系晕而产生的能量依赖损失之间的竞争,而逆康普顿、同步辐射和电离过程对谱形的塑造通常起次要作用。除解释现有观测外,我们还通过分析预测了一种此前未见的相关性:星系射电谱曲率与其π介子驱动的γ射线辐射之间的相关,该预测可由未来设施检验。

英文摘要:

Galaxies obey a number of empirical correlations between their radio, γ-ray, and infrared emission, but the physical origins of these correlations remain uncertain. Here we use the CONGRuENTS model for broadband non-thermal emission from star-forming galaxies, which self-consistently calculates energy-dependent transport and non-thermal emission from cosmic ray hadrons and leptons, to predict radio and γ-ray emission for a synthetic galaxy population with properties drawn from a large deep-field survey. We show that our synthetic galaxies reproduce observed relations such as the FIR-radio correlation, the FIR-γ correlation, and the distribution of radio spectral indices, and we use the model to explain the physical origins of these relations. Our results show that the FIR-radio correlation arises because the amount of cosmic ray electron power ultimately radiated as synchrotron emission varies only weakly with galaxy star formation rate as a result of the constraints imposed on gas properties by hydrostatic balance and turbulent dynamo action; the same physics dictates the extent of proton calorimetry in different galaxies, and thus sets the FIR-γ-ray correlation. We further show that galactic radio spectral indices result primarily from competition between thermal free-free emission and energy-dependent loss of cosmic ray electrons to bremsstrahlung and escape into galactic halos, with shaping of the spectrum by inverse Compton, synchrotron, and ionisation processes typically playing a sub-dominant role. In addition to explaining existing observations, we use our analysis to predict a heretofore unseen correlation between the curvature of galaxies' radio spectra and their pion-driven γ-ray emission, a prediction that will be testable with upcoming facilities.

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