Exploring the voids: Luminosity functions and magnetic field

Abstract

We present semi-analytical models for magnetisation of the void inter-galactic medium (IGM) by outflows from void galaxies. The number density of dark matter haloes in an under-dense region (i.e., void) is obtained using the excursion set method extended for such low density environment. The star formation in such haloes has been estimated, taking account of the negative feedback by supernovae. The galaxy formation/evolution model is tuned to provide the r-band luminosity function, the stellar mass function and also the color of void galaxies as obtained from recent observations. This star formation model is used to study possible outflows from void galaxies driven by the hot thermal gas and cosmic ray pressures. These outflows drag the magnetic fields present in those galaxies to the void IGM. We show that such a model can magnetise ∼30% of the void IGM with the magnetic field strength of 10−12−10−10 G while considering only magnetic flux freezing condition. Along with this, the megapersec size of individual outflows can explain the non-detection of GeV photons in TeV blazars that put a lower limit of 10−16 G for void IGM magnetic field with a Mpc coherent length scale.