Molecular Hydrogen Absorption in the [CLC][ITAL]z[/ITAL][/CLC] = 1.97 Damped L[CLC]y[/CLC]α Absorption System toward Quasi-Stellar Object Q0013−004

Open Access
Publisher Website
Google Scholar
Abstract
We present a new ultraviolet spectrum of the quasi-stellar object Q0013-004 with 0.9 Å resolution obtained with the Multiple Mirror Telescope Blue Spectrograph. The υ = 0-0, 1-0, 2-0, and 3-0 Lyman bands of H2 associated with the z = 1.9731 damped Lyα absorption-line system have been detected. The H2 column density is N(H2) = 6.9(±1.6) × 1019 cm-2, and the Doppler parameter b = 15 ± 2 km s-1. The populations of different rotational levels are measured and used to derive the excitation temperatures. The estimated kinetic temperature TK ~ 70 K, and the total particle number density n(H) ~ 300 cm-3. The UV photoabsorption rate β0 ~ 6.7 × 10-9 s-1, about a factor of a few times greater than that in a typical diffuse Milky Way interstellar cloud. The total hydrogen column density is N(H) = 6.4(±0.5) × 1020 cm-2. The fractional H2 abundance f = 2N(H2)/[2N(H2) + N(H I)] ~ 0.22 ± 0.05 is the highest among all observed damped Lyα absorbers. The high fractional H2 abundance is consistent with the inferred presence of dust and strong C I absorption in this absorber.
All Related Versions