Emergence of a new H i 21-cm absorption component at z ∼ 1.1726 towards the γ-ray blazar PKS 2355-106

Author:

Srianand Raghunathan1ORCID,Gupta Neeraj1,Petitjean Patrick2,Momjian Emmanuel3,Balashev Sergei A45ORCID,Combes Françoise6,Chen Hsiao-Wen7ORCID,Krogager Jens-Kristian8,Noterdaeme Pasquier29,Rahmani Hadi10,Baker Andrew J1112,Emig Kimberly L13,Józsa Gyula I G1415,Kloeckner Hans-Rainer14,Moodley Kavilan1617

Affiliation:

1. IUCAA , Postbag 4, Ganeshkind, Pune 411007, India

2. Institut d’Astrophysique de Paris, Sorbonne Université and CNRS , 98bis boulevard Arago, F-75014 Paris, France

3. National Radio Astronomy Observatory , PO Box O, Socorro, NM 87801, USA

4. Ioffe Institute , Politekhnicheskaya 26, 194021 Saint Petersburg, Russia

5. HSE University , Saint Petersburg, 190121, Russia

6. Observatoire de Paris, Collège de France, PSL University , Sorbonne University, CNRS, LERMA, Paris, 75014, France

7. Department of Astronomy & Astrophysics, The University of Chicago , 5640 South Ellis Avenue, Chicago, IL 60637, USA

8. Université Lyon1 , ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, F-69230 Saint-Genis-Laval, France

9. Franco-Chilean Laboratory for Astronomy , IRL 3386, CNRS and U. de Chile , Casilla 36-D, Santiago, Chile

10. School of Astronomy, Institute for Research in Fundamental Sciences (IPM) , PO Box 19395-5531 Tehran, Iran

11. Department of Physics and Astronomy, Rutgers, the State University of New Jersey , 136 Frelinghuysen Road, Piscataway, NJ 08854-8019, USA

12. Department of Physics and Astronomy, University of the Western Cape , Robert Sobukwe Road, Bellville 7535, South Africa

13. National Radio Astronomy Observatory , 520 Edgemont Road, Charlottesville, VA 22903, USA

14. Max-Planck-Institut für Radioastronomie , Auf dem Hügel 69, D-53121 Bonn, Germany

15. Department of Physics and Electronics, Rhodes University , PO Box 94, Makhanda, 6140, South Africa

16. Astrophysics Research Centre, University of KwaZulu-Natal , Westville Campus, Durban 4041, South Africa

17. School of Mathematics, Statistics & Computer Science, University of KwaZulu-Natal , Westville Campus, Durban 4041, South Africa

Abstract

ABSTRACT We report the emergence of a new H i 21-cm absorption at zabs = 1.172 635 in the damped Lyα absorber (DLA) towards the γ-ray blazar PKS 2355-106 (zem∼1.639) using science verification observations (2020 June) from the MeerKAT Absorption Line Survey (MALS). Since 2006, this DLA is known to show a narrow H i 21-cm absorption at zabs = 1.173019 coinciding with a distinct metal absorption-line component. We do not detect significant H i 21-cm optical depth variations from this known H i component. A high-resolution optical spectrum (2010 August) shows a distinct Mg i absorption at the redshift of the new H i 21-cm absorber. However, this component is not evident in the profiles of singly ionized species. We measure the metallicity ([Zn/H] = −(0.77 ± 0.11) and [Si/H]= −(0.96 ± 0.11)) and depletion ([Fe/Zn] = −(0.63 ± 0.16)) for the full system. Using the apparent column density profiles of Si ii, Fe ii, and Mg i, we show that the depletion and the N(Mg i)/N(Si ii) column density ratio systematically vary across the velocity range. The region with high depletion tends to have a slightly larger N(Mg i)/N(Si ii) ratio. The two H i 21-cm absorbers belong to this velocity range. The emergence of zabs = 1.172 635 can be understood if there is a large optical depth gradient over a length-scale of ∼0.35 pc. However, the gas producing the zabs = 1.173 019 component must be nearly uniform over the same scale. Systematic uncertainties introduced by the absorption-line variability has to be accounted for in experiments measuring the variations of fundamental constants and cosmic acceleration even when the radio emission is apparently compact as in PKS 2355-106.

Funder

National Research Foundation

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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