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We report the discovery of two remarkable high-opacity HI 21cm absorbers against low-luminosity active galactic nuclei (AGNs), at $z = 1.2166$ towards J0229+0044 and at $z=1.1630$ towards J0229+0053. The absorbers were detected in an unbiased Giant Metrewave Radio Telescope survey for HI 21cm absorption against radio sources in the DEEP2 survey fields, covering $z \approx 0.73-1.53$, and including sources without known redshifts. The velocity-integrated HI 21cm optical depths are $(74.2 \pm 7.8)$ km s$^{-1}$ (J0229+0044) and $(78.41 \pm 0.81)$ km s$^{-1}$ (J0229+0053), higher than that of any known redshifted HI 21cm absorber at $z > 0.12$, and implying high H{\sc i} column densities, $> 10^{22}$ cm$^{-2}$. The emission redshift of J0229+0044 is consistent with the HI 21cm absorption redshift, while the strength and velocity spread of the absorption against J0229+0053 suggest that it too arises from gas in the AGN environment: both absorbers are thus likely to be "associated" systems. The two AGNs have low rest-frame 1.4 GHz radio and 1215 Angstrom ultraviolet luminosities ($\lesssim 10^{26.1}$ W Hz$^{-1}$ and $\lesssim 10^{21.7}$ W Hz$^{-1}$, respectively), both significantly lower than the typical luminosities of AGNs against which HI 21cm searches have hitherto been carried out at $z \gtrsim 1$. The paucity of HI 21cm absorbers at $z \gtrsim 1$ may be due to a luminosity bias in high-$z$ AGN samples that have been searched for HI 21cm absorption, where the high AGN ultraviolet luminosity affects physical conditions in its environment, ionizing the neutral hydrogen.

Giant Metrewave Radio Telescope Detections of Two High-opacity Hi 21 cm Absorbers at z ≈ 1.2