DD.7.05 — Giant Shocks in the Fermi Bubbles and the Origin of the Microwave Haze

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Aug 10th at 3:15 PM until 3:30 PM

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Author(s): Roland M Crocker1, Geoffrey Vincent Bicknell1, Andrew Taylor2, Ettore Carretti3

Institution(s): 1. Australian National University, 2. Dublin Institute for Advanced Study, 3. Observatory of Cagliari - INAF

Analysis of γ-ray data provided by the Fermi-LAT has revealed giant, hard-spectrum γ-ray lobes emanating from the Galactic nucleus (and extending to |b| ∼ 50°). These `Fermi Bubbles' have hard-spectrum, total-intensity microwave (∼20-40 GHz) counterparts in their lower reaches (the microwave `Haze' extending to |b| ∼ 35°) and, on large scales, are subsumed by steep spectrum, polarised radio (2-20 GHz) structures (the `S-PASS Lobes' extending to |b| ∼ 60°). We present a unified model for these disparate, non-thermal phenomena in which the Bubbles are inflated by a wind driven by star formation in the central molecular zone of the Galactic Center. Giant reverse shocks located ~1 kpc above and below the nucleus in the interior of the Bubbles accelerate relativistic electrons, accounting for the microwave haze associated with them. The γ-rays are produced by hadronic emission through shock accelerated relativistic protons interacting with dense, thermally unstable clouds within the Bubbles but concentrated near their edges. The Bubbles are currently slowly expanding, with ages of a few x 100 Myr. Lower energy, non-thermal electrons accelerated at the shocks reach the edges of the Bubbles and escape from their upper regions accounting for the steep spectrum, polarized radio emission covering the Bubbles and extending beyond them at high Galactic latitudes.