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The triply-ionized carbon forest from eBOSS: cosmological correlations with quasars in SDSS-IV DR14

Research output: Contribution to journalArticle

  • Michael Blomqvist
  • Matthew M. Pieri
  • Hélion Du Mas Des Bourboux
  • Nicolás G. Busca
  • Anže Slosar
  • Julian E. Bautista
  • Jonathan Brinkmann
  • Joel R. Brownstein
  • Kyle Dawson
  • Victoria De Sainte Agathe
  • Julien Guy
  • Will J. Percival
  • Ignasi Pérez-ràfols
  • James Rich
  • Donald P. Schneider
We present measurements of the cross-correlation of the triply-ionized carbon (CIV) forest with quasars using Sloan Digital Sky Survey Data Release 14. The study exploits a large sample of new quasars from the first two years of observations by the Extended Baryon Oscillation Spectroscopic Survey (eBOSS). The CIV forest is a weaker tracer of large-scale structure than the Lyα forest, but benefits from being accessible at redshifts z<2 where the quasar number density from eBOSS is high. Our data sample consists of 287,651 CIV forest quasars in the redshift range 1.4<z<3.5 and 387,315 tracer quasars with 1.2<z<3.5. We measure large-scale correlations from CIV absorption occuring in three distinct quasar rest-frame wavelength bands of the spectra referred to as the CIV forest, the SiIV forest and the Lyα forest. From the combined fit to the quasar-CIV cross-correlations for the CIV forest and the SiIV forest, the CIV redshift-space distortion parameter is βCIV=0.27 −0.14 −0.26 +0.16 +0.34 and its combination with the CIV linear transmission bias parameter is bCIV(1+βCIV)=−0.0183 −0.0014 −0.0029 +0.0013 +0.0025 (1σ and 2σ statistical errors) at the mean redshift z=2.00. Splitting the sample at z=2.2 to constrain the bias evolution with redshift yields the power-law exponent γ=0.60±0.63, indicating a significantly weaker redshift-evolution than for the Lyα forest linear transmission bias. Additionally, we demonstrate that CIV absorption has the potential to be used as a probe of baryon acoustic oscillations (BAO). While the current data set is insufficient for a detection of the BAO peak feature, the final quasar samples for redshifts 1.4<z<2.2 from eBOSS and the Dark Energy Spectroscopic Instrument (DESI) are expected to provide measurements of the isotropic BAO scale to ~7% and ~3% precision, respectively, at zsime1.6.
Original languageEnglish
Article number029
JournalJournal of Cosmology and Astroparticle Physics
Issue number05
Publication statusPublished - 8 May 2018


  • The triply-ionized carbon forest from eBOSS

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