English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We report the emergence of a new HI 21-cm absorption at z_abs = 1.172635 inthe damped Lyman-alpha absorber (DLA) towards the gamma-ray blazar PKS 2355-106(z_em~1.639) using science verification observations (June 2020) from theMeerKAT Absorption Line Survey (MALS). Since 2006, this DLA is known to show anarrow HI 21-cm absorption at z_abs = 1.173019 coinciding with a distinct metalabsorption line component. We do not detect significant HI 21-cm optical depthvariations from this known HI component. A high resolution optical spectrum(August 2010) shows a distinct Mg I absorption at the redshift of the new HI21-cm absorber. However, this component is not evident in the profiles ofsingly 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 fullsystem. Using the apparent column density profiles of Si II, Fe II and Mg I weshow that the depletion and the N(Mg I)/N(Si II) column density ratiosystematically vary across the velocity range. The region with high depletiontends to have slightly larger N(Mg I)/N(Si II) ratio. The two HI 21-cmabsorbers belong to this velocity range. The emergence of z_abs = 1.172635 canbe 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 benearly uniform over the same scale. Systematic uncertainties introduced by theabsorption line variability has to be accounted for in experiments measuringthe variations of fundamental constants and cosmic acceleration even when theradio emission is apparently compact as in PKS 2355-106.

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