The physics of Cosmic ray (CR) transport remains a key uncertainty in assessing whether CRs can produce galaxy-scale outflows consistent with observations. In this paper, we elucidate the physics of CR-driven galactic winds for CR transport dominated by diffusion. A companion paper considers CR streaming. We use analytic estimates validated by time-dependent spherically-symmetric simulations to derive expressions for the mass-loss rate, momentum flux, and speed of CR-driven galactic winds, suitable for cosmological-scale or semi-analytic models of galaxy formation. For CR diffusion coefficients $κ\gtrsim r_0 c_i$ where $r_0$ is the base radius of the wind and $c_i$ is the isothermal gas sound speed, the asymptotic wind energy flux is comparable to that supplied to CRs, and the outflow rapidly accelerates to supersonic speeds. By contrast, for $κ\lesssim r_0 c_i$, CR-driven winds accelerate more slowly and lose most of their energy to gravity, a CR analogue of photon-tired stellar winds. Given CR diffusion coefficients estimated using Fermi gamma-ray observations of pion decay, we predict mass-loss rates in CR-driven galactic winds of order the star formation rate for dwarf and disc galaxies. The dwarf galaxy mass-loss rates are small compared to the mass-loadings needed to reconcile the stellar and dark matter halo mass functions. For nuclear starbursts (e.g., M82, Arp 220), CR diffusion and pion losses suppress the CR pressure in the galaxy and the strength of CR-driven winds. We discuss the implications of our results for interpreting observations of galactic winds and for the role of CRs in galaxy formation.
Hadronic origin of multi-TeV gamma rays and neutrinos from low-luminosity active galactic nuclei: implications of past activities of the Galactic center
低光度活动星系核（LLAGNs）中的辐射低效吸积流（RIAFs）被认为是宇宙射线和中微子源，可能对观测到的漫射中微子强度有很大贡献。我们表明，这种情况下自然预测强子多TeV的伽马射线过剩银河系中心周围。在人马座A $^*$（Sgr A $^*$）的RIAF中加速的质子逃逸并与Sgr A $^*$周围的致密分子气体相互作用，这被称为中心分子区（CMZ），并产生伽马射线和中微子。基于与IceCube数据兼容的理论模型，我们计算了CMZ的伽马射线谱，发现如果Sgr A $^*$在过去比现在更活跃，那么高能立体系统可能已经探测到了具有$\gtrsim 1$ TeV的伽马射线。我们的模型预测中微子应该来自CMZ，其光谱与伽马射线光谱相似。我们还表明，这样的伽马射线过剩，预计一些附近的星系托管LLAGN。
