2001ApJ...553..528D -
Astrophys. J., 553, 528-537 (2001/June-1)
The statistical and physical properties of the low-redshift Lyα forest observed with the Hubble space Telescope/STIS.
DAVE R. and TRIPP T.M.
Abstract (from CDS):
We examine the Lyα absorber population at z<0.3 detected in spectra of the quasars PG 0953+415 and H1821+643 taken with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We compare their statistical properties to those in carefully constructed mock quasar spectra drawn from a cosmological hydrodynamic simulation of a Λ-dominated cold dark matter universe. We find very good agreement in the column density and b-parameter distributions, down to the smallest observable absorbers with N_HI_~1012.3 cm^- 2^. The observed absorber population is complete for N_HI_≳1013 cm^- 2^, with a column density distribution slope of β=2.04±0.23 and a median b-parameter of 21 km.s–1 above this limit. The intergalactic gas giving rise to these weak absorbers is analogous to that at high redshift, located in diffuse large-scale structures that are highly photoionized by the metagalactic UV flux, though a greater number arise within shock-heated warm gas. The density, temperature, and column density of these absorbers follow similar relationships of those at high redshift, though with substantially larger scatter due to the shock-heated gas. The b-parameters typically have a significant contribution from thermal broadening, which facilitates a measurement of the low-z intergalactic medium temperature as traced by Lyα absorbers. From our simulation we estimate TIGM∼5000 K, with an upper limit of 104 K, at the mean density. The agreement in predicted and observed amplitude of the column density distributions allows us to measure the H I photoionization rate at z{d1}=0.17 to be Γ_HI_=10–13.3±0.7 s–1 (estimated modeling uncertainty), close to predictions based on quasar properties.
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Journal keyword(s):
Cosmology: Observations - Cosmology: Theory - Galaxies: Intergalactic Medium - Galaxies: Quasars: Absorption Lines - quasars: individual (PG 0953+415, H1821+643)
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