MOLECULAR HYDROGEN ABSORPTION FROM THE HALO OF A z ∼ 0.4 GALAXY
- The Pennsylvania State University, State College, PA 16802 (United States)
- Swinburne University of Technology, Victoria 3122 (Australia)
Lyman- and Werner-band absorption of molecular hydrogen (H{sub 2}) is detected in ∼50% of low-redshift (z<1) DLAs/sub-DLAs with N(H{sub 2}) > 10{sup 14.4} cm{sup −2}. However, the true origin(s) of the H{sub 2}-bearing gas remain elusive. Here we report a new detection of an H{sub 2} absorber at z{sub abs} = 0.4298 in the Hubble Space Telescope (HST)/Cosmic Origins Spectrograph spectra of quasar PKS 2128–123. The total N(H i) of 10{sup 19.50±0.15} cm{sup −2} classifies the absorber as a sub-DLA. H{sub 2} absorption is detected up to the J = 3 rotational level with a total logN(H{sub 2}) = 16.36 ± 0.08, corresponding to a molecular fraction of logf{sub H{sub 2}} = −2.84 ± 0.17. The excitation temperature of T{sub ex} = 206 ± 6 K indicates the presence of cold gas. Using detailed ionization modeling, we obtain a near-solar metallicity (i.e., [O/H] = −0.26 ± 0.19) and a dust-to-gas ratio of logκ∼−0.45 for the H{sub 2}-absorbing gas. The host galaxy of the sub-DLA is detected at an impact parameter of ρ ∼ 48 kpc with an inclination angle of i ∼ 48° and an azimuthal angle of Φ ∼ 15° with respect to the QSO sightline. We show that corotating gas in an extended disk cannot explain the observed kinematics of Mg ii absorption. Moreover, the inferred high metallicity is not consistent with the scenario of gas accretion. An outflow from the central region of the host galaxy, on the other hand, would require a large opening angle (i.e., 2θ>150{sup ∘}), much larger than the observed outflow opening angles in Seyfert galaxies, in order to intercept the QSO sightline. We thus favor a scenario in which the H{sub 2}-bearing gas is stemming from a dwarf-satellite galaxy, presumably via tidal and/or ram pressure stripping. Detection of a dwarf galaxy candidate in the HST/WFPC2 image at an impact parameter of ∼12 kpc reinforces such an idea.
- OSTI ID:
- 22862932
- Journal Information:
- Astrophysical Journal, Vol. 823, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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