Role of ionizing background on the statistics of metal absorbers in hydrodynamical simulations

Abstract

ABSTRACT We study the statistical properties of O vi, C iv, and Ne viii absorbers at low-z (i.e. z < 0.5) using Sherwood simulations with ‘WIND’ only and ‘WIND + AGN’ feedback and massive black-II simulation that incorporates both ‘WIND’ i.e. outflows driven by stellar feedback and active galactic nucleus (AGN) feedbacks. For each simulation, by considering a wide range of metagalactic ionizing ultraviolet background (UVB), we show the statistical properties such as distribution functions of column density (N), b-parameter and velocity spread (ΔV90), the relationship between N and b-parameter, and the fraction of Ly α absorbers showing detectable metal lines as a function of N(H i) are influenced by the UVB used. This is because UVB changes the range in density, temperature, and metallicity of gas contributing to a given absorption line. For simulations considered here, we show the difference in some of the predicted distributions between different simulations is similar to the one obtained by varying the UVB for a given simulation. Most of the observed properties of O vi absorbers are roughly matched by Sherwood simulation with ‘WIND + AGN’ feedback when using the UVB with a lower O vi ionization rate. However, this simulation fails to produce observed distributions of C iv and fraction of H i absorbers with detectable metals. Therefore, in order to constrain different feedback processes and/or UVBs, using observed properties of H i and metal ions, it is important to perform simultaneous analysis of various observable parameters.