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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 693808.0, MPI für Astronomie / Publikationen_mpia
A high molecular fraction in a subdamped absorber at z = 0.56
Authors:Crighton, Neil H. M.; Bechtold, Jill; Carswell, Robert F.; Davé, Romeel; Foltz, Craig B.; Jannuzi, Buell T.; Morris, Simon L.; O'Meara, John M.; Prochaska, J. Xavier; Schaye, Joop; Tejos, Nicolas
Date of Publication (YYYY-MM-DD):2013
Title of Journal:Monthly Notices of the Royal Astronomical Society
Issue / Number:1
Start Page:178
End Page:193
Review Status:Internal review
Audience:Experts Only
Abstract / Description:Measuring rest-frame ultraviolet rotational transitions from the Lyman and Werner bands in absorption against a bright background continuum is one of the few ways to directly measure molecular hydrogen (H2). Here, we report the detection of absorption from H2 at z = 0.56 in a subdamped Lyα system with neutral hydrogen column density NHI = 1019.5 ± 0.2 cm-2. This is the first H2 system analysed at a redshift of <1.5 beyond the Milky Way halo. It has a surprisingly high molecular fraction: log10 fH2 > -1.93 ± 0.36 based on modelling the line profiles, with a robust model-independent lower limit of fH2 > 10-3. This is higher than fH2 values seen along sightlines with similar NHI through the Milky Way disc and the Magellanic Clouds. The metallicity of the absorber is 0.19+0.21-0.10 solar, with a dust-to-gas ratio of <0.36 of the value in the solar neighbourhood. Absorption from associated low-ionization metal transitions such as O I and Fe II is observed in addition to O VI. Using CLOUDY models, we show that there are three phases present; a ˜100 K phase giving rise to H2, a ˜104 K phase where most of the low-ionization metal absorption is produced; and a hotter phase associated with O VI. Based on similarities to high-velocity clouds in the Milky Way halo showing H2, and the presence of two nearby galaxy candidates with impact parameters of ˜10 kpc, we suggest that the absorber may be produced by a tidally stripped structure similar to the Magellanic Stream.
Free Keywords:ISM: molecules; galaxies: haloes; quasars: absorption lines
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:ISSN:0035-8711 %R 10.1093/mnras/stt714 [ID No:1]
URL:http://cdsads.u-strasbg.fr/abs/2013MNRAS.433..178C [ID No:2]
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