ﻻ يوجد ملخص باللغة العربية
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. These absorbers appear to contain a significant fraction of the low-z baryons and were a major discovery of the HST spectrographs. Using FUSE data, with 40 mA (4-sigma) Lyb detection limits, we have employed the equivalent width ratio of Lyb/Lya and occasionally higher Lyman lines, to determine the doppler parameter, b, and accurate column densities, N(HI), for moderately saturated lines. We detect Lyb absorption corresponding to all Lya lines with EW > 200 mA. The Lyb/Lya ratios yield a preliminary distribution function of doppler parameters, with mean <b> = 31.4 +/- 7.4 km/s and median b = 28 km/s, comparable to values at redshifts z = 2.0-2.5. If thermal, these b-values correspond to T(HI) ~ 50,000 K, although the inferred doppler parameters are considerably less than the widths derived from Lya profile fitting, <b(dopp)/b(width)> = 0.52. The typical increase in column density over that derived from profile fitting is Delta[log N(HI)] = 0.3, but ranges up to 1.0 dex. Our data suggest that the low-z Lya absorbers contain sizable non-thermal motions or velocity components in the line profile, perhaps arising from cosmological expansion and infall.
We present FUSE observations of the HeII Lyman alpha forest in the redshift range 2.3 < z < 2.7 towards HS1700+6416. Between October 2002 and February 2003, the brightness of the QSO increased by a factor 2. Therefore, with an exposure time of 203 ks
We present the far-UV spectrum of the quasar HS1700+6416 taken with FUSE. This QSO provides the second line of sight with the HeII absorption resolved into a Ly alpha forest structure. Since HS1700+6416 is slightly less redshifted (z=2.72) than HE234
Absorption between the rest-frame wavelengths of 973 and 1026 Angstroms in quasar spectra arises from two sources (apart from occasional metals): one is due to Lyman-alpha (Lya) absorption by materials at a low redshift, and the other from Lyman-beta
We compare the low redshift (z ~ 0.1) Lyman-alpha forest from hydrodynamical simulations with data from the Cosmic Origin Spectrograph (COS). We find tension between the observed number of lines with b-parameters in the range 25-45 km/s and the predi
We present an analysis of the evolution of the Lyman-series forest into the epoch of reionization using cosmological radiative transfer simulations in a scenario where reionization ends late. We explore models with different midpoints of reionization