Implications of Nonthermal Motions for Statistics of Lyman-Alpha Forest Clouds

Abstract

view Abstract Citations (5) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Implications of Nonthermal Motions for Statistics of Lyman-Alpha Forest Clouds Kulkarni, Varsha P. ; Fall, S. Michael Abstract We investigate the effects of nonthermal bulk motions within Lyα forest clouds on some observationally derived statistics of these clouds. We calculate the absorption-line profiles and curves of growth for three illustrative cases of single-peaked, non-Maxwellian velocity distributions. We then calculate the distributions in H I column density f(N) and velocity dispersion f(o) for Lyα forest clouds, using the corresponding distributions derived under the Maxwellian assumption, while also maintaining consistency with measurable line properties (Lyα central intensity and Lyα equivalent width, or Lyman alpha and Lyβ equivalent widths). We find that, for systems with saturated Lyα lines, in the case of velocity distributions with shorter tails than the Maxwellian, f(N) is steeper at log N ≳ 15.2 than f(N) in the Maxwellian case. On the other hand, in the case of velocity distributions with longer tails than the Maxwellian, f(N) is shallower at log N ≳ 15.9 than f(N) in the Maxwellian case. The effect found here is not expected to be relevant for log N ≳ 17.2, where f(N) is derived from quantities independent of the velocity distribution. The f(σ) also depends on the velocity distribution, but less so than f(N). Finally, using some published high-resolution observations, we find that, even for samples that show no N-σ correlation in the case of the Maxwellian velocity distribution, a significant positive correlation exists in the cases of the velocity distributions with shorter tails than the Maxwellian, while a significant negative correlation exists in the cases of the velocity distributions with longer tails than the Maxwellian. Our results imply that various properties derived from f(N), such as the effective photoelectric opacity of the Lyα forest clouds to the ionizing background at high redshifts, could differ from previous estimates if the velocity distribution within Lyα forest clouds were non-Maxwellian. Publication: The Astrophysical Journal Pub Date: November 1995 DOI: 10.1086/176370 Bibcode: 1995ApJ...453...65K Keywords: GALAXIES: INTERGALACTIC MEDIUM; GALAXIES: QUASARS: ABSORPTION LINES full text sources ADS |