Detection of molecular hydrogen in a near Solar-metallicity damped Lyman-alpha system at zabs ~ 2 toward Q 0551-366 ≈ 2

Details Detection of molecular hydrogen in a near Solar-metallicity damped Lyman-alpha system at zabs ~ 2 toward Q 0551-366 ≈ 2 Detection of molecular hydrogen in a near Solar-metallicity damped Lyman-alpha system at zabs ~ 2 toward Q 0551-366 ≈ 2

Sep 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002a%26a...392..781l&link_type=abstract

Astronomy and Astrophysics, v.392, p.781-789 (2002)

Astronomy and Astrophysics

Astrophysics

44

Cosmology: Observations, Galaxies: Halos, Galaxies: Ism, Quasars: Absorption Lines -, Quasars: Individual: Q 0551-366

Scientific paper

We report the detection of H2, C I, C I *, C I ** and Cl I lines in a near Solar-metallicity ([Zn/H]=-0.13) damped Lyman-alpha (DLA) system at zabs=1.962 observed on the line of sight to the quasar Q 0551-366. The iron-peak elements, X=Fe, Cr and Mn are depleted compared to zinc, [X/Zn] ~ -0.8, probably because they are tied up onto dust grains. Among the three detected H2-bearing clouds, spanning 55 km s-1 in velocity space, we derive a total molecular hydrogen column density N(H2)=2.6x 1017 cm-2 and a mean molecular fraction f=2N(H2)/(2N(H2)+N(H I))=1.7x 10-3. The depletion of heavy elements (S, Si, Mg, Mn, Cr, Fe, Ni and Ti) in the central component is similar to that observed in the diffuse neutral gas of the Galactic halo. This depletion is approximately the same in the six C I-detected components independently of the presence or absence of H2. The gas clouds in which H2 is detected always have large densities, nH>30 cm-3, and low temperatures, T01<~ 100 K. This shows that presence of dust, high particle density and/or low temperature is required for molecules to be present. The photo-dissociation rate derived in the components where H2 is detected suggests the existence of a local UV radiation field similar in strength to the one in the Galaxy. Star formation therefore probably occurs near these H2-bearing clouds. Based on observations carried out at the European Southern Observatory (ESO) under prog. ID No. 66.A-0624 with the UVES spectrograph installed at the Very Large Telescope (VLT) on Cerro Paranal, Chile.

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