Fermi bubbles: the collimated outburst needed to explain forward-shock edges

ABSTRACT The bipolar, non-thermal, high-latitude lobes known as the Fermi bubbles (FBs) are thought to originate from a massive energy release near Galactic Centre (GC). We constrain FB engine and circumgalactic medium (CGM) by analytically numerically modelling edges strong forward shocks, inferred recent observations. A non-directed produces shocks too spherical account for observations even maximally disc, critical CGM rotation, or injection effectively offset GC. In contrast, collimated nearly perpendicular disc can in both ballistic (free expansion) slowdown regimes, we show using simple stratified evolution model verified hydrodynamic simulations. FBs still their regime require (at z ? 100 pc heights our model) with half-opening angle ? 4°, normalized velocity ??2 ? v/(0.01c) ? 0.4, an $E\gtrsim 2\beta _{-2}^2\times 10^{55}$ erg, launched $\mathbb {T}\simeq 3.3\beta _{-2}^{-1}$ Myr ago, showing distinctive low-pressure region behind bubble head. Slowing-down (mass accumulated) faster injection, thinner jet, smaller E/(??2?)2, comparable {T}$, follow stage that must reach height zs 5 kpc.