Evolution of CIV Absorbers. II. Where does CIV live?

Abstract

We use the observed cumulative statistics of CIV absorbers and dark matter halos to infer the distribution of CIV-absorbing gas relative to galaxies at redshifts $0\!\leq\!z\!\leq\!5$. We compare the cosmic incidence $dN/dX$ of CIV absorber populations and galaxy halos, finding that massive $L \geq L_{\star}$ halos alone cannot account for all the observed $W_r \geq 0.05$~{\AA} absorbers. However, the $dN/dX$ of lower mass halos exceeds that of $W_r \geq 0.05$~{\AA} absorbers. We also estimate the characteristic gas radius of absorbing structures required for the observed CIV $dN/dX$, assuming each absorber is associated with a single galaxy halo. The $W_r \geq 0.3$~{\AA} and $W_r \geq 0.6$~{\AA} CIV gas radii are $\sim30-70\%$ ($\sim20-40\%$) of the virial radius of $L_{\star}$ ($0.1L_{\star}$) galaxies, and the $W_r \geq 0.05$~{\AA} gas radius is $\sim100-150\%$($\sim60-100\%$) of the virial radius of $L_{\star}$ ($0.1L_{\star}$) galaxies. For stronger absorbers, the gas radius relative to virial radius rises across Cosmic Noon and falls afterwards, while for weaker absorbers, the relative gas radius declines across Cosmic Noon and then dramatically rises at $z\!<\!1$. A strong luminosity-dependence of gas radius implies highly extended CIV envelopes around massive galaxies before Cosmic Noon, while a luminosity-independent gas radius implies highly extended envelopes around dwarf galaxies after Cosmic Noon. From available absorber-galaxy and CIV evolution data, we favor a scenario in which low-mass galaxies enrich the volume around massive galaxies at early epochs and propose that the outer halo gas ($>0.5R_v$) was produced primarily in ancient satellite dwarf galaxy outflows, while the inner halo gas ($<0.5R_v$) originated from the central galaxy and persists as recycled accreting gas.