仙后座和仙王座的费米观测：外星系弥漫的gamma-ray发射
Fermi observations of Cassiopeia and Cepheus: diffuse gamma-ray emission in the outer Galaxy
摘要：
本文分析了费米大天区望远镜在银河系第二象限100度< l < 145度和-15度< b < +30度区域测量到的星际伽马射线辐射。这一区域包括仙后座、仙王座和北极星耀斑的显著的古尔德带云，以及更远距离的原子和分子复合体，如英仙座臂中与NGC 7538相关的复合体。而且每个星系中都存在大质量的复合体，这使得这个区域非常适合探测宇宙射线和太阳圈以外的星际介质。古尔德带中气体的伽马射线发射率光谱与基于当地测量的宇宙射线光谱的预期一致。伽马射线发射率从古尔德带到英仙座臂逐渐降低，但测量到的梯度比宇宙射线源在银河系内部达到峰值的预期要平坦，这一点由天文学家提出。我们发现Xco=N（H2）/W（CO）的转换因子从古尔德带的（0.87 +- 0.05）10^20 cm^-2（K km s^-1）^-1增加到英仙座臂的（1.9 +- 0.2）10^20 cm^-2（K km s^-1）^-1。在古尔德带中，通过相关的过量尘埃和伽马射线发射，发现了没有被无线电和微波探测正确追踪的暗气体：其质量约为CO追踪质量的50%。
英文摘要：
We present the analysis of the interstellar gamma-ray emission measured by the Fermi Large Area Telescope toward a region in the second Galactic quadrant at 100 deg < l < 145 deg and -15 deg < b < +30 deg. This region encompasses the prominent Gould-Belt clouds of Cassiopeia, Cepheus and the Polaris flare, as well as atomic and molecular complexes at larger distances, like that associated with NGC 7538 in the Perseus arm. The good kinematic separation in velocity between the local, Perseus, and outer arms, and the presence of massive complexes in each of them make this region well suited to probe cosmic rays and the interstellar medium beyond the solar circle. The gamma-ray emissivity spectrum of the gas in the Gould Belt is consistent with expectations based on the locally measured cosmic-ray spectra. The gamma-ray emissivity decreases from the Gould Belt to the Perseus arm, but the measured gradient is flatter than expectations for cosmic-ray sources peaking in the inner Galaxy as suggested by pulsars. The Xco=N(H2)/W(CO) conversion factor is found to increase from (0.87 +- 0.05) 10^20 cm^-2 (K km s^-1)^-1 in the Gould Belt to (1.9 +- 0.2) 10^20 cm^-2 (K km s^-1)^-1 in the Perseus arm. We derive masses for the molecular clouds under study. Dark gas, not properly traced by radio and microwave surveys, is detected in the Gould Belt through a correlated excess of dust and gamma-ray emission: its mass amounts to ~50% of the CO-traced mass.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
