The C iv forest as a probe of baryon acoustic oscillations

Abstract

Abstract In light of recent successes in measuring baryon acoustic oscillations (BAO) in quasar absorption using the Lyman α (Lyα) transition, I explore the possibility of using the 1548 Å transition of triply ionized carbon (C iv) as a tracer. While the Lyα forest is a more sensitive tracer of intergalactic gas, it is limited by the fact that it can only be measured in the optical window at redshifts z > 2. Quasars are challenging to identify and observe at these high redshifts, but the C iv forest can be probed down to redshifts z ≈ 1.3, taking full advantage of the peak in the redshift distribution of quasars that can be targeted with high efficiency. I explore the strength of the C iv absorption signal and show that the absorbing population on the red side of the Lyα emission line is dominated by C iv (and so will dominate over the potential BAO signal of other metals). As a consequence, I argue that forthcoming surveys may have a sufficient increase in quasar number density to offset the lower sensitivity of the C iv forest and provide competitive precision using both the C iv autocorrelation and the C iv-quasar cross-correlation at 〈z〉 ≈ 1.6.