Volume 619, November 2018
|Number of page(s)||14|
|Published online||19 November 2018|
Dissecting cold gas in a high-redshift galaxy using a lensed background quasar⋆
1 Institut d’Astrophysique de Paris, CNRS-SU, UMR7095, 98bis bd Arago, 75014 Paris, France
e-mail: firstname.lastname@example.org, email@example.com
2 Department of Chemistry and Physics, Saint Michael’s College, One Winooski Park, Colchester, VT, 05439, USA
3 Centre for Extragalactic Astronomy, Durham University, South Road, Durham, DH1 3LE, UK
4 Institute for Computational Cosmology, Durham University, South Road, Durham, DH1 3LE, UK
5 The Cosmic Dawn Center, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
6 Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA, 95064, USA
7 University of California Observatories, Lick Observatory, 1156 High Street, Santa Cruz, CA, 95064, USA
8 Department of Physics, Broida Hall, University of California, Santa Barbara, CA, 93106, USA
9 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
10 Ioffe Institute, Polytechnicheskaya ul. 26, Saint Petersburg, 194021, Russia
11 Institute of Physics, Laboratory of Astrophysics, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
12 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218, USA
13 Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD, 21218, USA
14 European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
Accepted: 31 August 2018
We present a study of cold gas absorption from a damped Lyman-α absorber (DLA) at redshift zabs = 1.946 toward two lensed images of the quasar J144254.78+405535.5 at redshift zQSO = 2.590. The physical separation of the two lines of sight at the absorber redshift is dabs = 0.7 kpc according to our lens model. We observe absorption lines from neutral carbon and H2 along both lines of sight, indicating that cold gas is present on scales larger than dabs. We measure the column densities of H I to be log N(HI) = 20.27 ± 0.02 and 20.34 ± 0.05 and those of H2 to be log N(H2) = 19.7 ± 0.1 and 19.9 ± 0.2. The metallicity inferred from sulphur is consistent with solar metallicity for both sightlines: [S/H]A = 0.0 ± 0.1 and [S/H]B = −0.1 ± 0.1. Based on the excitation of low rotational levels of H2, we constrain the temperature of the cold gas phase to be T = 109 ± 20 and T = 89 ± 25 K for the two lines of sight. From the relative excitation of fine-structure levels of C I, we constrain the hydrogen volumetric densities to lie in the range of 40 − 110 cm−3. Based on the ratio of observed column density and volumetric density, we infer the average individual “cloud” size along the line of sight to be l ≈ 0.1 pc. Using the transverse line-of-sight separation of 0.7 kpc together with the individual cloud size, we are able to place an upper limit to the volume filling factor of cold gas of fvol < 0.1%. Nonetheless, the projected covering fraction of cold gas must be large (close to unity) over scales of a few kpc in order to explain the presence of cold gas in both lines of sight. Compared to the typical extent of DLAs (∼10 − 30 kpc), this is consistent with the relative incidence rate of C I absorbers and DLAs.
Key words: galaxies: high-redshift / cosmology: observations / quasars: absorption lines / gravitational lensing: strong / galaxies: ISM
The reduced spectra (FITS files) are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/619/A142
© ESO 2018
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