Anisotropic AGN Outflows and Enrichment of the Intergalactic Medium

TL;DR

This study models anisotropic AGN outflows and their role in enriching the intergalactic medium, showing that such outflows can significantly enrich the universe, especially under certain parameters, with anisotropy influencing the enrichment pattern.

Contribution

Introduces a semi-analytical model for anisotropic AGN outflows integrated into cosmological simulations, revealing their impact on IGM metal enrichment over cosmic time.

Findings

AGN outflows enrich up to 100% of the universe by present day.

Anisotropic outflows preferentially enrich underdense regions.

Enrichment depends on outflow kinetic fraction, AGN lifetime, and clustering.

Abstract

We investigate the cosmological-scale influence of outflows driven by AGNs on metal enrichment of the intergalactic medium. AGNs are located in dense cosmological structures which tend to be anisotropic. We designed a semi-analytical model for anisotropic AGN outflows which expand away along the direction of least resistance. This model was implemented into a cosmological numerical simulation algorithm for simulating the growth of large-scale structure in the universe. Using this modified algorithm, we perform a series of 9 simulations inside cosmological volumes of size $(128 h^{-1}{\rm Mpc})^3$, in a concordance $\Lambda$CDM universe, varying the opening angle of the outflows, the lifetimes of the AGNs, their kinetic fractions, and their level of clustering. For each simulation, we compute the volume fraction of the IGM enriched in metals by the outflows. The resulting enriched volume fractions are relatively small at $z \gtrsim 2.5$, and then grow rapidly afterward up to $z = 0$. We find that AGN outflows enrich from 65% to 100% of the entire universe at the present epoch, for different values of the model parameters. The enriched volume fraction depends weakly on the opening angle of the outflows. However, increasingly anisotropic outflows preferentially enrich underdense regions, a trend found more prominent at higher redshifts and decreasing at lower redshifts. The enriched volume fraction increases with increasing kinetic fraction and decreasing AGN lifetime and level of clustering.