Title: High energy extragalactic multimessenger backgrounds from starburst and dead galaxies Show Chinese title

Title: 高能星系外多信使背景来自星暴和死亡星系

Abstract: Starburst galaxies are $\gamma$-ray sources. Canonically, their emission is driven by hadronic cosmic rays (CRs) interacting with interstellar gas, forming $\gamma$-rays via the decay of neutral pions. Charged pions are also formed in this process. They decay into secondary leptons, including electrons and neutrinos. Starburst galaxies are therefore also expected to be neutrino sources, and their high-energy $\gamma$-ray emission may include a secondary leptonic component. Leptonic $\gamma$-rays may also originate from electrons directly energized by shocks within the interstellar medium of galaxies, or from pulsars and their surrounding halos. In the Milky Way, pulsars/pulsar halos are the dominant $\gamma$-ray source class. They are associated with stellar remnants or old stellar populations, and are presumably abundant in old galaxies. In this work, we show that the collective high-energy emission from galaxies can account for only a fraction of extragalactic neutrinos, but can form a major component of the extragalactic $\gamma$-ray background. Contrary to the traditional view, a substantial fraction of this radiation may originate from leptonic processes, including from old, quiescent galaxies. Show Chinese abstract

Abstract: 星暴星系是$\gamma$射线源。 通常情况下，它们的辐射是由强子宇宙射线（CRs）与星际气体相互作用产生的，通过中性π介子的衰变形成$\gamma$射线。 在这个过程中也会形成带电π介子。 它们衰变成次级轻子，包括电子和中微子。 因此，星暴星系也被预期为中微子源，其高能$\gamma$射线辐射可能包含一个次级轻子成分。 轻子$\gamma$射线也可能来自直接由星系星际介质中的激波加速的电子，或来自脉冲星及其周围晕。 在银河系中，脉冲星/脉冲星晕是主导的$\gamma$射线源类别。 它们与恒星残骸或古老的恒星种群有关，并且在古老星系中 presumably 很丰富。 在这项工作中，我们表明，星系的集体高能辐射只能解释一部分河外中微子，但可以成为河外$\gamma$射线背景的主要组成部分。 与传统观点相反，这种辐射的很大一部分可能起源于轻子过程，包括来自古老、静止的星系。