The Low-Redshift Intergalactic Medium

Abstract

The low-redshift Ly-alpha forest of absorption lines provides a probe of large-scale baryonic structures in the intergalactic medium, some of which may be remnants of physical conditions set up during the epoch of galaxy formation. We discuss our recent Hubble Space Telescope (HST) observations and interpretation of low-z Ly-alpha clouds toward nearby Seyferts and QSOs, including their frequency, space density, estimated mass, association with galaxies, and contribution to Omega-baryon. Our HST/GHRS detections of 70 Ly-alpha absorbers with N_HI > 10^12.6 cm-2 along 11 sightlines covering pathlength Delta(cz) = 114,000 km/s show f(>N_HI) ~ N_HI^{-0.63 +- 0.04} and a line frequency dN/dz = 200 +- 40 for N_HI > 10^12.6 cm-2 (one every 1500 km/s of redshift). A group of strong absorbers toward PKS 2155-304 may be associated with gas (400-800) h_75^-1 kpc from 4 large galaxies, with low metallicity (< 0.003 solar) and D/H < 2 x 10^-4. At low-z, we derive a metagalactic ionizing radiation field from AGN of J_0 = 1.3^{+0.8 -0.5} x 10^-23 ergs/cm2/s/Hz/sr and a Ly-alpha-forest baryon density Omega-baryon = (0.008 +- 0.004) h_75^-1 [J_-23 N_14 b_100]^{1/2} For clouds of characteristic size b = (100 kpc)b_100.

5 figures

References in corpus (4)

• The Deuterium Abundance Towards Q1937-1009
• The High-Redshift He II Gunn-Peterson Effect: Implications and Future Prospects
• Physical Properties of the Lyman Alpha Forest in a Cold Dark Matter Cosmology
• A Cluster of Low-Redshift Lyman-alpha Clouds toward PKS 2155-304. I. Limits on Metals and D/H

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• The Local Lyman-alpha Forest. II: Distribution of HI Absorbers, Doppler Widths, and Baryon Content
• Far Ultraviolet Spectroscopy of the Intergalactic and Interstellar Absorption Toward 3C 273
• The Local Lyman-alpha Forest. I: Observations with the GHRS/G160M on the Hubble Space Telescope
• An Extragalactic HI Cloud with No Optical Counterpart?
• Continuous statistics of the Lyman-alpha forest at 0 < z < 1.6: the mean flux, flux distribution, and autocorrelation from HST FOS spectra
• Implications for galaxy property estimation revealed by CO luminosity-FWHM relations in local star-forming galaxies