We study of the properties of a new class of circumgalactic medium absorbers
identified in the Lyman-α forest: "Strong, Blended Lyman-α" (or
SBLA) absorption systems. We study SBLAs at 2.4<z<3.1 in SDSS-IV/eBOSS
spectra by their strong extended Lyman-α absorption complexes covering
138 km/s with an integrated log(NHI/cm−2)=16.04−0.06+0.05
and Doppler parameter b=18.1−0.4+0.7 km/s.
Clustering with the Lyman-α forest provides a large-scale structure
bias of b=2.34±0.06 and halo mass estimate of Mh≈1012h−1Msol for our SBLA sample. We measure the ensemble mean column
densities of 22 metal features in the SBLA composite spectrum and find that no
single-population multiphase model for them is viable. We therefore explore the
underlying SBLA population by forward modelling the SBLA absorption
distribution. Based on covariance measurements and favoured populations we find
that ≈25% of our SBLAs have stronger metals. Using silicon only we
find that our strong metal SBLAs trace gas with a log(nH/cm−3)>−2.45 for T=103.5K and show gas clumping on <255 parsec scales. We fit
multiphase models to this strong sub-population and find a low ionization phase
with nH=1cm−3, T=103.5K and [X/H]=0.8, an intermediate
ionization phase with log(nH/cm−3)=−3.35, T=103.5K and
[X/H]=−1.1, and a poorly constrained higher ionization phase. We find that
the low ionization phase traces cold, dense super-solar metallicity gas with a
clumping scale of just 0.009 parsecs.Comment: 28 pages, submitted to MNRA