The evolution of the low-frequency radio AGN population to z ≃ 1.5 in the ELAIS N1 field

ABSTRACT We study the cosmic evolution of radio sources out to z ≃ 1.5 using a GMRT 610 MHz survey covering ∼1.86 deg2 of the ELAIS N1 field with a minimum/median rms noise 7.1/19.5 μJy beam−1 and an angular resolution of 6 arcsec. We classify sources as star forming galaxies (SFGs), radio-quiet (RQ) and radio-loud (RL) Active Galactic Nuclei (AGNs) using a combination of multiwavelength diagnostics and find evidence in support of the radio emission in SFGs and RQ AGN arising from star formation, rather than AGN-related processes. At high luminosities, however, both SFGs and RQ AGN display a radio excess when comparing radio and infrared star formation rates. The vast majority of our sample lie along the $\rm {SFR - \mathit{ M}_{\star }}$ ‘main sequence’ at all redshifts when using infrared star formation rates. We derive the 610 MHz radio luminosity function for the total AGN population, constraining its evolution via continuous models of pure density and pure luminosity evolution with $\rm {\Phi ^{\star }\, \propto \, (\, 1+\, \mathit{ z})^{(2.25\pm 0.38)-(0.63\pm 0.35)z}}$ and $\rm {\mathit{ L}_{610\, MHz}\, \propto \, (\, 1+\, \mathit{ z})^{(3.45\pm 0.53)-(0.55\pm 0.29)\mathit{ z}}}$, respectively. For our RQ and RL AGN, we find a fairly mild evolution with redshift best fitted by pure luminosity evolution with $\rm {\mathit{ L}_{610\, MHz}\, \propto \, (\, 1+\, \mathit{ z})^{(2.81\pm 0.43)-(0.57\pm 0.30)\mathit{ z}}}$ for RQ AGN and $\rm {\mathit{ L}_{610\, MHz}\, \propto \, (\, 1+\, \mathit{ z})^{(3.58\pm 0.54)-(0.56\pm 0.29)\mathit{ z}}}$ for RL AGN. The 610 MHz radio AGN population thus comprises two differently evolving populations whose radio emission is mostly SF-driven or AGN-driven, respectively.

Accretion into Black Hole, and Formation of Magnetically Arrested Accretion Disks

The exact time-dependent solution is obtained for a magnetic field growth during a spherically symmetric accretion into a black hole (BH) with a Schwarzschild metric. Magnetic field is increasing with time, changing from the initially uniform into a quasi-radial field. Equipartition between magnetic and kinetic energies in the falling gas is supposed to be established in the developed stages of the flow. Estimates of the synchrotron radiation intensity are presented for the stationary flow. The main part of the radiation is formed in the relativistic region r ≤ 7 r g , where r g is a BH gravitational radius. The two-dimensional stationary self-similar magnetohydrodynamic solution is obtained for the matter accretion into BH, in a presence of a large-scale magnetic field, under assumption, that the magnetic field far from the BH is homogeneous and its influence on the flow is negligible. At the symmetry plane perpendicular to the direction of the distant magnetic field, the dense quasi-stationary disk is formed around BH, which structure is determined by dissipation processes. Solutions of the disk structure have been obtained for a laminar disk with Coulomb resistivity and for a turbulent disk. Parameters of the shock forming due to matter infall onto the disk are obtained. The radiation spectrum of the disk and the shock are obtained for the 10 M ⊙ BH. The luminosity of such object is about the solar one, for a characteristic galactic gas density, with possibility of observation at distances less than 1 kpc. The spectra of a laminar and a turbulent disk structure around BH are very different. The laminar disk radiates mainly in the ultraviolet, the turbulent disk emits a large part of its flux in the infrared. It may occur that some of the galactic infrared star-like sources are a single BH in the turbulent accretion state. The radiative efficiency of the magnetized disk is very high, reaching ∼ 0.5 M ˙ c 2 . This model of accretion was called recently as a magnetically arrested disk (MAD). Numerical simulations of MAD and its appearance during accretion into neutron stars, are considered and discussed.