Molecular hydrogen absorption in the z = 1.97 damped Lyα absorption system toward quasi-stellar object Q0013-004

Jian Ge, Jill Bechtold

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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 v = 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.

Original languageEnglish (US)
Pages (from-to)L73-L77
JournalAstrophysical Journal
Issue number2 PART II
StatePublished - Jan 1 1997



  • ISM: molecules
  • Quasars: absorption lines
  • Quasars: individual (Q0013-004)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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