2000/04/29 by J. M. Shull, J. Michael Shull, M. L. Giroux +28
Engineering · Physics and Astronomy · #Astrophysics (astro-ph) #FOS: Physical sciences #Radio Astronomy Observations and Technology #Real-time simulation and control systems #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0005011
To appear in ApJL (FUSE first-results issue), 4 pages + 3 figures (.ps)
arxiv created 2000/04/29 · openalex publication_date 2000/04/29 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
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> = 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.</b></b>