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In Paper III of our series A Uniform Analysis of the Ly-alpha forest at z=0 - 5, we presented a set of 270 quasar spectra from the archives of the Faint Object Spectrograph on the Hubble Space Telescope. A total of 151 of these spectra, yielding 906 lines, are suitable for using the proximity effect signature to measure J( u_0), the mean intensity of the hydrogen-ionizing background radiation field, at low redshift. Using a maximum likelihood technique and the best estimates possible for each QSOs Lyman limit flux and systemic redshift, we find J( u_0)= 7.6^+9.4_-3.0 x 10^-23 ergs s^-1 cm^-2 Hz^-1 sr^-1 at at 0.03 < z < 1.67. This is in good agreement with the mean intensity expected from models of the background which incorporate only the known quasar population. When the sample is divided into two subsamples, consisting of lines with z < 1 and z > 1, the values of J( u_0) found are 6.5^+38._-1.6 x 10^-23 ergs s^-1 cm^-2 Hz^-1 sr^-1, and 1.0^+3.8_-0.2 x 10^-22 ergs s^-1 cm^-2 Hz^-1 sr^-1, respectively, indicating that the mean intensity of the background is evolving over the redshift range of this data set. Relaxing the assumption that the spectral shapes of the sample spectra and the background are identical, the best fit HI photoionization rates are found to be 6.7 x 10^-13 s^-1 for all redshifts, and 1.9 x 10^-13 s^-1 and 1.3 x 10^-12 s^-1 for z < 1 and z > 1, respectively. This work confirms that the evolution of the number density of Ly-alpha lines is driven by a decrease in the ionizing background from z ~ 2 to z ~ 0 as well as by the formation of structure in the intergalactic medium. (Abridged)
We present a measurement of the mean intensity of the hydrogen-ionizing background radiation field at low redshift using 906 Ly-alpha absorption lines in 151 quasar spectra from the archives of the Faint Object Spectrograph on the Hubble Space Telesc
We analyzed the absorption line spectra of all quasars observed with the high resolution gratings of the Faint Object Spectrograph on board the Hubble Space Telescope. We examined 788 spectra for 334 quasars, and present line lists and identification
We present results on the evolution and clustering of Ly-alpha lines at low z. The sample contains 1298 Ly-alpha lines from 165 quasar spectra mined from the archives of the HST/FOS. Our sample extends to z=1.7, slightly higher than the sample analyz
We compare a sample of five high-resolution, high S/N Ly$alpha$ forest spectra of bright $6<z lesssim 6.5$ QSOs aimed at spectrally resolving the last remaining transmission spikes at $z>5$ with those obtained from mock absorption spectra from the Sh
Context. Searching for high-redshift galaxies is a field of intense activity in modern observational cosmology that will continue to grow with future ground-based and sky observatories. Over the last few years, a lot has been learned about the high-z