Related papers: The Low-Redshift Intergalactic Medium

I discuss recent 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_b. Our HST/GHRS…

We have conducted pointed redshift surveys for galaxies in the direction of bright AGN whose HST far-UV spectra contain nearby (cz <~ 30,000 kms), low column density (12.5 <= log N_{HI} (cm s^{-2}) <= 14.5) Ly-alpha forest absorption…

We present a study of the Ly\alpha forest at z<0.4 from which we conclude that at least 20% of the total baryons in the universe are located in the highly-ionized gas traced by broad Ly\alpha absorbers. The cool photoionized low-z…

We present further observational results on our Lya-only absorber identification project at low and intermediate redshifts. We combine CFHT/MOS imaging and spectroscopic observations of 25 galaxies in the field of the quasar 3C286 (z_e =…

In Paper I of this series (astro-ph/9911117) we described observations of 15 extragalactic targets taken with the Hubble Space Telescope GHRS/G160M grating for studies of the low-z Lya forest. We reported the detection of 110 Lya absorbers…

We present HST and FUSE observations of the intergalactic absorption toward PG1116+215 in the 900-3000 A spectral region. We detect 25 Ly-alpha absorbers at rest-frame equivalent widths W_r > 30 mA, yielding (dN/dz)_Ly-alpha = 154+/-18 over…

We describe recent discoveries of low column density [N(HI) < 10^14.5 cm^-2] H I Ly-alpha absorbers made with the Hubble Space Telescope (HST), which have allowed us a first look at gas in local intergalactic space between us and the "Great…

Ultraviolet spectrographs aboard the Hubble Space Telescope (HST) and the Far Ultraviolet Spectroscopic Explorer (FUSE) have proved their value as sensitive probes of the low-density intergalactic medium (IGM) at low redshifts (z < 0.1).…

We examine the Ly-alpha absorber population at z<0.3 detected in spectra of the QSOs PG0953+415 and H1821+643 taken with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. We compare their statistical properties to…

We present a new method for probing the physical conditions and metal enrichment of the Intergalactic Medium: the composite spectrum of Ly-alpha forest absorbers. We apply this technique to a sample of 9480 Ly-alpha absorbers with redshift…

We identify a concordant model for the intergalactic medium (IGM) at redshift z=1.9 that uses popular values for cosmological and astrophysical parameters and accounts for all baryons with an uncertainty of 6%. We have measured the amount…

In this work we shall sketch a further piece of evidence for the plausibility of hypothesis of galactic origin of Ly-$\alpha$ forest absorption systems. Two basic premises of our discussion are (1) HDF redshift surface densities in the…

We present the target selection, observations, and data reduction and analysis process for a program aimed at discovering numerous, weak (equivalent width < 100 mA) Lya absorption lines in the local Universe (0.003 < z < 0.069). The purpose…

Detecting HI using redshifted Ly-alpha absorption lines is 1e6 times more sensitive than using the 21cm emission line. We review recent discoveries of HI Ly-alpha absorbers made with the Hubble Space Telescope (HST) which have allowed us a…

We describe a moderate-resolution (20-25 km/s) FUSE study of the low-redshift intergalactic medium. We report on studies of 7 extragalactic sightlines and 12 Ly-beta absorbers that correspond to Ly-alpha lines detected by HST/GHRS and STIS.…

Estimates of Omega_baryon from primordial nucleosynthesis together with standard assumptions about the ionization state of low column density Lyman alpha forest clouds can be used to determine an upper limit for the cloud thickness along…

We discuss the origin and physical nature of the Lya forest absorption systems as found in hydrodynamical simulations of the Intergalactic Medium in a standard Cold Dark Matter cosmology (Omega=1, H0=50 km/s/Mpc, sigma_8=0.7). The…

We describe our surveys of low column density Lyman-alpha absorbers [N(HI) = 10^(12.5-16.0) cm^-2], which show that the warm photoionized IGM contains 30% of all baryons at z < 0.1. This fraction is consistent with cosmological simulations,…

Spectra from the Keck HIRES instrument of the Lyman alpha forests in the lines of sight to the A and C components of the gravitationally lensed QSO Q1422+231 were used to investigate the structure of the intergalactic medium at mean…

We present HST STIS/G140M spectra of 15 extragalactic targets, which we combine with GHRS/G160M data to examine the statistical properties of the low-z Ly-alpha forest. We evaluate the physical properties of these Ly-alpha absorbers and…