CIV Absorbers in z>4 Quasars: Tracing Early Galactic Halos Evolution

Abstract

We use 29 z>4 quasar spectra to build a homogeneous sample of high-redshift CIV absorbers. We use these data to calculate the number density, n(z), of W_rest(CIV)>0.30 A CIV doublets. We find that n(z) increases with time from z ~ 4.5. In addition, W_rest(CIV)>0.15 A CIV systems are more numerous than the former at all redshifts. On the contrary, n(z) of W_rest(MgII)>0.30 A MgII doublets decreases with time, in agreement with results from studies of LLS number densities. Below z<3, none of all the classes of absorbers show signs of evolution. We interpret this as the formation of galactic envelopes from smaller halos. Furthermore, the doublet ratio DR=W(CIV 1548)/W(CIV 1550) is found to decrease with time, a signature of the increase of the mean CIV column density. Finally, the W(SiIV 1393)/W(CIV 1548) ratios in strong absorbers (W_rest(CIV 1548) > 0.50 A) is found to be approximately constant from z=3.5 to z=2.5 and then to decrease with time. This result suggests that the highest column density absorbers are not sensitive to changes in the ionization continuum.

20 pages, 8 figures, accepted for publication in Astronomy & Astrophysics. A&A style file added to fit overseas paper format

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Cited by in corpus (6)

• A Homogeneous Sample of Sub-DLAs III: Total Gas Mass Omega_(HI+HeII) at z>2
• Evolution of CIV Absorbers I. The Cosmic Incidence
• Examining the Decline in the C IV Content of the Universe over 4.3 < z < 6.3 using the E-XQR-30 Sample
• MUSE unravels the ionisation and origin of metal enriched absorbers in the gas halo of a z = 2.92 radio galaxy
• Evolution of CIV Absorbers. II. Where does CIV live?
• The Cosmic Evolution of CIV Absorbers at $1.4<z<4.5$: Insights from $100,000$ Systems in DESI Quasars