Quasar -- CIV forest cross-correlation with SDSS DR12

Abstract

We present a new determination of the large-scale clustering of the CIV forest (i.e., the absorption due to all CIV absorbers) using its cross-correlation with quasars in the Sloan Digital Sky Survey (SDSS) Data Release 12 (DR12). We fit a linear bias model to the measured cross-correlation. We find that the transmission bias of the CIV forest, $b_{Fc}$, at a mean redshift of $z=2.3$, obeys the relation $(1+\beta_c)b_{F c} = -0.024 \pm 0.003$. Here, $\beta_{c}$ is the linear redshift space distortion parameter of the CIV absorption, which can only be poorly determined at $\beta_c=1.1\pm 0.6$ from our data. This transmission bias is related to the bias of CIV absorbers and their host halos through the effective mean optical depth of the CIV forest, $\bar\tau_c$. Estimating a value $\bar \tau_c(z) \simeq 0.01$ from previous studies of the CIV equivalent width distribution, our measurement implies a CIV absorber bias near unity, with a large error due to uncertainties in both $\beta_c$ and $\bar\tau_c$. This makes it compatible with the higher DLA bias $b_{\rm DLA}\simeq 2$ measured previously from the cross-correlation of DLAs and the Lyman-$\alpha$ forest. We discuss the implications of the CIV absorber bias for the mass distribution of their host halos. More accurate determinations of $\bar \tau_c(z)$ and $\beta_c$ are necessary to obtain a more robust measurement of this CIV absorber bias.