星系-星系碰撞中相对论粒子的激波加速
Shock acceleration of relativistic particles in galaxy-galaxy collisions
摘要：
所有没有射电强活动星系核的星系都遵循它们的全球FIR和射电同步辐射光度之间的紧密相关性，这被认为是大质量恒星形成的最终结果。两个面对面碰撞的星系对，UGC 12914/5和UGC 813/6偏离了这种相关性，并显示出过量的无线电发射，在这两种情况下，在很大程度上起源于连接两个星系盘的气体桥。假设在各自的星际介质（ISM）的主要气体动力学相互作用中释放的动能产生了冲击波，有效地加速原子核和电子的相对论能量，预计从桥区域的无线电同步辐射计算。一个简单的模型，在这些冲击的相对论粒子的加速与由此产生的无线电发射，其光谱指数和预期的高能伽马射线发射的计算。这个过程与恒星的形成无关。结果表明，碰撞过程中产生的非热能足以解释两个星系之间桥的射电辐射。目前计算的光谱指数也与观测值一致。另一方面，预期的伽马射线发射太低，即使用CTA等可预见的仪器也无法检测到。
英文摘要：
All galaxies without a radio-loud AGN follow a tight correlation between their global FIR and radio synchrotron luminosities, which is believed to be ultimately the result of the formation of massive stars. Two face-on colliding pairs of galaxies, UGC12914/5 and UGC 813/6 deviate from this correlation and show an excess of radio emission which in both cases originates to a large extent in a gas bridge connecting the two galactic disks. The radio synchrotron emission expected from the bridge region is calculated, assuming that the kinetic energy liberated in the predominantly gas dynamic interaction of the respective interstellar media (ISM) has produced shock waves that efficiently accelerate nuclei and electrons to relativistic energies. A simple model for the acceleration of relativistic particles in these shocks is presented together with a calculation of the resulting radio emission, its spectral index and the expected high-energy gamma-ray emission. This process is not related to star formation. It is found that the nonthermal energy produced in the collision is large enough to explain the radio emission from the bridge between the two galaxies. The calculated spectral index at the present time also agrees with the observed value. The expected gamma-ray emission, on the other hand, is too low by a factor of several to be detectable even with foreseeable instruments like CTA.
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