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

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 AGN feedbacks. For each simulation, by considering a wide range of metagalactic ionizing UV background (UVB), we show the statistical properties such as distribution functions of column density (N), b-paramerer and velocity spread (ΔV90), the relationship between N and b-parameter and the fraction of Lyα 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.

An Exploration of AGN and Stellar Feedback Effects in the Intergalactic Medium via the Low-redshift Lyα Forest

“…The next step to determine the extent of the degeneracy between the UVB, stellar feedback, and AGN feedback in these subgrid models is to employ machine-learning techniques to the CAMELS project simulations to determine best fits. Many other studies have noted degeneracies between UVB and AGN feedback effects on the forest, and it is clear that constraining feedback models to additional observables will be necessary to unravel the relationship (Burkhart et al 2022;Tillman et al 2023;Mallik et al 2023;Khaire et al 2023). This will not only help simulations reproduce a wider range of observables, but will aid in the construction of new more physical feedback models.…”

“…While the effects of some AGN feedback models on the statistics of the forest are degenerate with a rescaling of the assumed UVB (e.g., see Burkhart et al 2022;Khaire et al 2023;Mallik et al 2023), other AGN models had different, idiosyncratic effects, highlighting the importance of including feedback subgrid models within cosmological simulations (Tillman et al 2023). The unique effects seen on the Lyα forest column density distribution function (CDD) due to AGN jet feedback (Tillman et al 2023) are primarily attributed to the far-reaching heating effects that the jet feedback has on the large-scale environment (see Tonnesen et al 2017 for a discussion of the dependence of the CDD on the large-scale environment).…”

Low- and High-velocity O vi in Milky Way-like Galaxies: The Role of Stellar Feedback

“…The spectral shape of the UV background has been shown to affect oxygen abundance (Aguirre et al 2008) and statistics of O VI absorbers in the IGM (Oppenheimer & Davé 2009). A comparison of various UV backgrounds has been presented in Figure 1 of Mallik et al (2023), including the one (Haardt & Madau 1996) we adopted. The energy of ∼114 eV required for photoionizing O V corresponds to the high-energy tail of the spectral energy distribution (SED) of the background radiation field.…”

Impact of Helium ii Resonant Absorption on the Ultraviolet Background Modeled in Three Dimensions

“…The abundances of C IV and Si IV are particularly useful observationally. Both have transitions that can be detected in high-redshift CGM, which allows us to examine the CGM's density, temperature, and metallicity (Mallik et al 2023). However, the kinship between the two ions diverges when their abundances are calculated in cosmological models.…”