Anisotropic AGN Outflows and Enrichment of the Intergalactic Medium
  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.
