1. Dissecting cold gas in a high-redshift galaxy using a lensed background quasar
- Author
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Krogager, J.-K., Noterdaeme, P., O'Meara, J. M., Fumagalli, M., Fynbo, J. P. U., Prochaska, J. X., Hennawi, J., Balashev, S., Courbin, F., Rafelski, M., Smette, A., Boisse, P., O’Meara, J., Krogager, J, Noterdaeme, P, O'Meara, J, Fumagalli, M, Fynbo, J, Prochaska, J, Hennawi, J, Balashev, S, Courbin, F, Rafelski, M, Smette, A, Boisse, P, Institut d'Astrophysique de Paris (IAP), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Dark Cosmology Centre (DARK), Niels Bohr Institute [Copenhagen] (NBI), Faculty of Science [Copenhagen], University of Copenhagen = Københavns Universitet (KU)-University of Copenhagen = Københavns Universitet (KU)-Faculty of Science [Copenhagen], University of Copenhagen = Københavns Universitet (KU)-University of Copenhagen = Københavns Universitet (KU), A.F. Ioffe Physical-Technical Institute, Russian Academy of Sciences [Moscow] (RAS), Laboratoire d'Astrophysique, Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratoire d'astrophysique de l'observatoire de Besançon (UMR 6091) (LAOB), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC), Laboratoire de Mécanique des Systèmes et des Procédés (LMSP), and Centre National de la Recherche Scientifique (CNRS)
- Subjects
Absorption spectroscopy ,Hydrogen ,Gravitational lensing: strong ,absorption lines [quasars] ,Metallicity ,chemistry.chemical_element ,FOS: Physical sciences ,h-and-k ,Astrophysics ,lyman-alpha systems ,physical conditions ,01 natural sciences ,Cosmology: observation ,0103 physical sciences ,Quasars: absorption line ,010306 general physics ,Absorption (electromagnetic radiation) ,010303 astronomy & astrophysics ,Physics ,molecular-hydrogen absorption ,mg ii ,Line-of-sight ,star-formation ,ISM [galaxies] ,Galaxies: high-redshift ,Astronomy and Astrophysics ,Quasar ,Quasars: absorption lines ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,Redshift ,ii systems ,observations [cosmology] ,Galaxies: ISM ,ly-alpha ,chemistry ,Space and Planetary Science ,cosmology: observations ,damped lyman ,strong [gravitational lensing] ,Astrophysics of Galaxies (astro-ph.GA) ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] ,neutral medium ,high-redshift [galaxies] - Abstract
We present a study of cold gas absorption from a damped Lyman-$\alpha$ absorber (DLA) at redshift $z_{\rm abs}=1.946$ towards two lensed images of the quasar J144254.78+405535.5 at redshift $z_{\rm QSO} = 2.590$. The physical separation of the two lines of sight at the absorber redshift is $d_{\rm abs}=0.7$~kpc based on our lens model. We observe absorption lines from neutral carbon and H$_2$ along both lines of sight indicating that cold gas is present on scales larger than $d_{\rm abs}$. We measure column densities of HI to be $\log N(\rm H\,\i) = 20.27\pm0.02$ and $20.34\pm0.05$ and of H$_2$ to be $\log N(\rm H_2) = 19.7\pm0.1$ and $19.9\pm0.2$. The metallicity inferred from sulphur is consistent with Solar metallicity for both sightlines: $[{\rm S/H}]_A = 0.0\pm0.1$ and $[{\rm S/H}]_B = -0.1\pm0.1$. Based on the excitation of low rotational levels of H$_2$, we constrain the temperature of the cold gas phase to be $T=109\pm20$ and $T=89\pm25$ K for the two lines of sight. From the relative excitation of fine-structure levels of CI, we constrain the hydrogen volumetric densities 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 $l\approx0.1$ pc. Using the transverse line-of-sight separation of 0.7 kpc together with the individual cloud size, we are able to put an upper limit to the volume filling factor of cold gas of $f_{\rm vol} < 0.2$ %. 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 CI absorbers and DLAs., Comment: 12 pages + 5 pages of appendix. Accepted for publication in A&A
- Published
- 2018
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