γ-rays and the far-infrared–radio continuum correlation reveal a powerful Galactic Centre wind

Abstract

We consider the thermal and non-thermal emission from the inner 200 pc of the Galaxy. The radiation from this almost starburst-like region is ultimately driven dominantly by ongoing massive star formation. We show that this region's radio continuum (RC) emission is in relative deficit with respect to the expectation afforded by the far-infrared-radio continuum correlation (FRC). Likewise we show that the region's γ -ray emission falls short of that expected given its star formation and resultant supernova rates. These facts are compellingly explained by positing that a powerful (400-1200 km s −1 ) wind is launched from the region. This wind probably plays a number of important roles including advecting positrons into the Galactic bulge thus explaining the observed ∼kpc extension of the 511 keV positron annihilation signal around the GC. We also show that the large-scale GC magnetic field falls in the range ∼100-300 µG and that -in the time they remain in the region -GC cosmic rays do not penetrate into the region's densest molecular material.

Cosmic rays and the magnetic field in the nearby starburst galaxy NGC 253 III. Helical magnetic fields in the nuclear outflow

“…Assuming that the outflow is driven by the starburst, the energy input in NGC 253 is thus a factor of 100 higher than in the Milky Way. Nevertheless, the Milky Way is able to launch a powerful galactic wind from its central region, as indicated by the strong deficiency in the radio emission compared to the FIR luminosity (Crocker et al 2011b). Also, the gamma ray emission is deficient compared to the star formation and supernova rates, which can be explained by the advection of cosmic rays in the wind, escaping into the halo.…”

A Unified Model of the Fermi Bubbles, Microwave Haze, and Polarized Radio Lobes: Reverse Shocks in the Galactic Center’s Giant Outflows

“…The complement to these points is that the nucleus is underluminous in both diffuse γ-ray and radio continuum emission given how much star formation occurs there (Crocker et al 2011a(Crocker et al , 2011bCrocker 2012), and this seems to be because both cosmic-ray electrons and ions are advected out of the region in the large-scale outflow before they can radiate. Thus, these particles radiate on the size scale of the bubbles into which the nuclear outflow delivers them.…”

“…The nucleus directly accelerates a population of hardspectrum primary electrons that is advected from the region before it can lose much energy radiatively in situ (Crocker et al 2011a(Crocker et al , 2011bCrocker 2012;Carretti et al 2013). These electrons cool adiabatically and radiatively in the expanding outflow (R1) until they encounter the giant reverse shock in either bubble where they are reaccelerated.…”

Stochastic non-circular motion and outflows driven by magnetic activity in the Galactic bulge region

“…Recently, the existence of outflows or winds in the Galactic center region is extensively discussed (Everett et al 2008;Crocker et al 2011), and it might be closely linked to the formation mechanisms of the Fermi bubbles via magnetic activity (Carretti et al 2013). Our simulation is not directly applicable to the Fermi bubbles since the simulation does not cover the region near the polar axis.…”