TY - JOUR
T1 - Emergence of a new H i 21-cm absorption component at z ∼1.1726 towards the γ-ray blazar PKS 2355-106
AU - Srianand, Raghunathan
AU - Gupta, Neeraj
AU - Petitjean, Patrick
AU - Momjian, Emmanuel
AU - Balashev, Sergei A.
AU - Combes, Françoise
AU - Chen, Hsiao Wen
AU - Krogager, Jens Kristian
AU - Noterdaeme, Pasquier
AU - Rahmani, Hadi
AU - Baker, Andrew J.
AU - Emig, Kimberly L.
AU - Józsa, Gyula I.G.
AU - Kloeckner, Hans Rainer
AU - Moodley, Kavilan
N1 - Publisher Copyright:
© 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
PY - 2022/10/1
Y1 - 2022/10/1
N2 - 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.
AB - 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.
KW - galaxies: ISM
KW - quasars: absorption lines
KW - quasars: individual PKS 2355-106
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U2 - 10.1093/mnras/stac1877
DO - 10.1093/mnras/stac1877
M3 - Article
AN - SCOPUS:85159324268
SN - 0035-8711
VL - 516
SP - 1339
EP - 1346
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 1
ER -