A Caltech Library Service

APM z ≳ 4 survey: distribution and evolution of high column density HI absorbers

Storrie-Lombardi, L. J. and Irwin, M. J. and McMahon, R. G. (1996) APM z ≳ 4 survey: distribution and evolution of high column density HI absorbers. Monthly Notices of the Royal Astronomical Society, 282 (4). pp. 1330-1342. ISSN 0035-8711. doi:10.1093/mnras/282.4.1330.

[img] PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


Eleven candidate damped Lyα absorption systems were identified in 27 spectra of the quasars from the APM z ≳ 4 survey covering the redshift range 2.8 ≤ z_(absorption) ≤ 4.4 (eight with z_(absorption) > 3.5). High-resolution echelle spectra (0.8-Å FWHM) have been obtained for three quasars, including two of the highest redshift objects in the survey. Two damped systems have confirmed H i column densities of N_(HI) ≥ 10^(20.3) atom cm^(−2), with a third falling just below this threshold. We have discovered the highest redshift damped Lyα absorber known at z = 4.383 in QSO BR 1202 — 0725. The APM QSOs provide a substantial increase in the redshift path available for damped surveys for z > 3. We combine this high-redshift sample with other quasar samples covering the redshift range 0.008 < z < 4.7 to study the redshift evolution and the column density distribution function for absorbers with log N_(HI) ≥ 17.2. In the Hi column density distribution f (N) = kN^(−β) we find evidence for breaks in the power law, flattening for 17.2 ≤ log N_(HI) ≲ 21 and steepening for log N_(HI) > 21.2. The breaks are more pronounced at higher redshift. The column density distribution function for the data with log N_(HI) ≥ 20.3 is better fitted with the form f (N) = (f_*/N_*) (N/N_*)^(−β)exp (— N/N_*) with log N_* = 21.63 ± 0.35, β = 1.48 ± 0.30, and f_* = 1.77 × 10^(−2). We study the evolution of the number density per unit redshift of the damped systems by fitting the sample with the customary power law N(z) = N_o(1 + z)^γ. For a population with no intrinsic evolution in the product of the absorption cross-section and comoving spatial number density this will give γ = 1/2 (Ω = 1) or γ = 1 (Ω = 0). The best maximum-likelihood fit for a single power law is γ = 1.3 ± 0.5 and N_o = 0.041_(−0.02)^(+0.03), consistent with no intrinsic evolution even though the value of γ is also consistent with that found for the Lyman limit systems where evolution is detected at a significant level. However, redshift evolution is evident in the higher column density systems with an apparent decline in N(z) for z > 3.5.

Item Type:Article
Related URLs:
URLURL TypeDescription
Storrie-Lombardi, L. J.0000-0002-5987-5210
Additional Information:© 1996 Royal Astronomical Society. Accepted 1996 June 7. Received 1996 June 6; in original form 1995 November 29. We thank Bob Carswell for providing software for and assistance with the data reduction and profile fitting of the spectra. USL acknowledges support from an Isaac Newton Studentship, the Cambridge Overseas Trust and a University of California President's Post-doctoral Fellowship. RGM acknowledges the support of the Royal Society.
Funding AgencyGrant Number
Isaac Newton StudentshipUNSPECIFIED
Cambridge Overseas TrustUNSPECIFIED
University of CaliforniaUNSPECIFIED
Subject Keywords:galaxies: evolution, galaxies: formation, quasars: absorption lines, quasars: individual: BR 1033—0327, BRI 1108—0747, BR 1202—0725, cosmology: miscellaneous
Issue or Number:4
Record Number:CaltechAUTHORS:20170322-085928896
Persistent URL:
Official Citation:APM z>~4 survey: distribution and evolution of high column density HI absorbers Storrie-Lombardi, L. J., Irwin, M. J., & McMahon, R. G. Monthly Notices of the Royal Astronomical Society, Volume 282, Issue 4, pp. 1330-1342.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75301
Deposited By: Ruth Sustaita
Deposited On:22 Mar 2017 17:47
Last Modified:15 Nov 2021 16:32

Repository Staff Only: item control page