Astrophys. J., 817, 111 (2016/February-1)
An HST/COS survey of the low-redshift intergalactic medium. I. Survey, methodology, and overall results.
DANFORTH C.W., KEENEY B.A., TILTON E.M., SHULL J.M., STOCKE J.T., STEVANS M., PIERI M.M., SAVAGE B.D., FRANCE K., SYPHERS D., SMITH B.D., GREEN J.C., FRONING C., PENTON S.V. and OSTERMAN S.N.
Abstract (from CDS):
We use high-quality, medium-resolution Hubble Space Telescope/Cosmic Origins Spectrograph (HST/COS) observations of 82 UV-bright active galactic nuclei (AGNs) at redshifts zAGN
< 0.85 to construct the largest survey of the low-redshift intergalactic medium (IGM) to date: 5138 individual extragalactic absorption lines in H i and 25 different metal-ion species grouped into 2611 distinct redshift systems at zabs
< 0.75 covering total redshift pathlengths Δz_ H i_= 21.7 and Δz_O vi_= 14.5. Our semi-automated line-finding and measurement technique renders the catalog as objectively defined as possible. The cumulative column density distribution of H i systems can be parametrized d N(>N)/dz = C14
, with C14
= 25±1 and β = 1.65±0.02. This distribution is seen to evolve both in amplitude, C14
∝ (1 + z)2.3±0.1
, and slope β(z) = 1.75-0.31 z for z ≤ 0.47. We observe metal lines in 418 systems, and find that the fraction of IGM absorbers detected in metals is strongly dependent on NH1
. The distribution of O vi absorbers appears to evolve in the same sense as the Lyα forest. We calculate contributions to Ωb
from different components of the low-z IGM and determine the Lyα decrement as a function of redshift. IGM absorbers are analyzed via a two-point correlation function in velocity space. We find substantial clustering of H i absorbers on scales of Δv = 50-300 km/s with no significant clustering at Δv ≳ 1000 km/s. Splitting the sample into strong and weak absorbers, we see that most of the clustering occurs in strong, N_H i_≳ 1013.5
/cm2, metal-bearing IGM systems. The full catalog of absorption lines and fully reduced spectra is available via the Mikulski Archive for Space Telescopes (MAST) as a high-level science product at http://archive.stsci.edu/prepds/igm/.
cosmological parameters - cosmology: observations - intergalactic medium - quasars: absorption lines - surveys
VizieR on-line data:
<Available at CDS (J/ApJ/817/111): table1.dat table2.dat linelist.dat systems.dat igm/*>
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