Emergence of a new HI 21-cm absorption component at z~1.1726 towards the gamma-ray blazar PKS~2355-106

Abstract

We report the emergence of a new HI 21-cm absorption at z_abs = 1.172635 in the damped Lyman-alpha absorber (DLA) towards the gamma-ray blazar PKS 2355-106 (z_em~1.639) using science verification observations (June 2020) from the MeerKAT Absorption Line Survey (MALS). Since 2006, this DLA is known to show a narrow HI 21-cm absorption at z_abs = 1.173019 coinciding with a distinct metal absorption line component. We do not detect significant HI 21-cm optical depth variations from this known HI component. A high resolution optical spectrum (August 2010) shows a distinct Mg I absorption at the redshift of the new HI 21-cm absorber. However, this component is not evident in the profiles of singly ionized species. We measure the metallicity ([Zn/H] = -(0.77\pm0.11) and [Si/H]= -(0.96\pm0.11)) and depletion ([Fe/Zn] = -(0.63\pm0.16)) 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 slightly larger N(Mg I)/N(Si II) ratio. The two HI 21-cm absorbers belong to this velocity range. The emergence of z_abs = 1.172635 can be understood if there is a large optical depth gradient over a length scale of ~0.35 pc. However, the gas producing the z_abs = 1.173019 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.

arXiv comment8 pages, 7 figures and accepted for publication in MNRAS

References in corpus (35)

• The Zwicky Transient Facility: System Overview, Performance, and First Results
• The chemical make-up of the Sun: A 2020 vision
• The Third Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope
• The Zwicky Transient Facility: Surveys and Scheduler
• The VLT-UVES survey for molecular hydrogen in high-redshift damped Lyman-alpha systems: Physical conditions in the neutral gas
• The spin temperature of high-redshift damped Lyman-$\alpha$ systems
• Connecting radio variability to the characteristics of gamma-ray blazars
• Molecular hydrogen at z=1.973 toward Q0013-004: Dust depletion pattern in damped Lyman-alpha systems
• Hot Halos around High Redshift Protogalaxies: Observations of O VI and N V Absorption in Damped Lyman Alpha systems
• Discovery of a Perseus-like cloud in the early Universe: HI-to-H2 transition, carbon monoxide and small dust grains at zabs=2.53 towards the quasar J0000+0048
• Connection between optical and gamma-ray variability in blazars
• On significance of VLBI/Gaia position offsets
• Partial coverage of the Broad Line Region of Q1232+082 by an intervening H2-bearing cloud
• The VSOP 5 GHz Active Galactic Nucleus Survey: V. Imaging Results for the Remaining 140 sources
• A complete sample of 21-cm absorbers at z~1.3: Giant Metrewave Radio Telescope Survey Using MgII Systems
• Toward a Direct Measurement of the Cosmic Acceleration
• Drastic changes in the molecular absorption at redshift z=0.89 toward the quasar PKS 1830-211
• Search for cold gas in strong MgII absorbers at 0.5<z<1.5: nature and evolution of 21-cm absorbers
• Atomic and Ionized Microstructures in the Diffuse Interstellar Medium
• Constraining the variation of fundamental constants at z ~ 1.3 using 21-cm absorbers
• Parsec-scale structures and diffuse bands in a translucent interstellar medium at z 0.079
• Spatial and Temporal Variations in Small-Scale Galactic HI Structure Toward 3C~138
• The First Large Absorption Survey in HI (FLASH): I. Science Goals and Survey Design
• Variable 21cm absorption at z=0.3127
• HI content, metallicities and spin temperatures of damped and sub-damped Lyman alpha systems in the redshift desert (0.6 < z < 1.7)
• Blind HI and OH absorption line search: first results with MALS and uGMRT processed using ARTIP
• Relative abundance pattern along the profile of high redshift Damped Lyman-alpha systems
• Revealing HI gas in emission and absorption on pc to kpc scales in a galaxy at z ~ 0.017
• Tiny scale opacity fluctuations from VLBA, MERLIN and VLA observations of HI absorption toward 3C 138
• Mapping kiloparsec-scale structures in the extended HI disc of the galaxy UGC 00439 by HI 21-cm absorption
• Partial covering of emission regions of Q 0528-250 by intervening H${}_2$ clouds
• Detecting cold gas at intermediate redshifts: GMRT survey using Mg II systems
• The inhomogeneous ISM toward PKS1830-211 SW - A detailed view on molecular gas at a look-back time of 7.5 Gyr
• LOFAR Deep Fields: Probing a broader population of polarized radio galaxies in ELAIS-N1
• Time variations of narrow absorption lines in high resolution quasar spectra

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