uGMRT detection of associated HI 21 cm absorption at $z\approx 3.5$

Abstract

We report a uGMRT detection of HI 21-cm absorption associated with the radio source 8C 0604+728, at $z=3.52965$. The source is at the highest redshift at which associated HI 21-cm absorption has been discovered to date, surpassing earlier known absorber at $z\approx 3.39$. We estimate ultraviolet luminosities of $(3.2\pm 0.1)\times 10^{23}\mathrm{W}\mathrm{H}{\mathrm{z}}^{-1}$ and $(6.2\pm 0.2)\times 10^{23}\mathrm{W}\mathrm{H}{\mathrm{z}}^{-1}$ , and ionising photon rates of $(1.8\pm 0.1)\times 10^{56}{\mathrm{s}}^{-1}$ and $(5.0\pm 0.1)\times 10^{56}{\mathrm{s}}^{-1}$, using data at different epochs; the source shows year-scale variability in both its luminosity and photon rate. The luminosity and photon rate at later epochs are $\approx 6.2$ and $\approx 1.7$ times higher than thresholds suggested in the literature above which all the neutral hydrogen in the AGN host galaxy is expected to be ionised. The detection demonstrates that neutral hydrogen can survive in the host galaxies of AGNs with high ultraviolet luminosities. We estimate a high equivalent width ratio of $15.2$ for the $\mathrm{Ly}\alpha$ and HeII emission lines detected in the optical spectrum, that is consistent with AGN photoionisation models. However, a significant contribution from young stellar populations to the excess $\mathrm{Ly}\alpha$ flux cannot be ruled out.

7 pages, 4 Figures, one table. Accepted for publication in MNRAS, corrected few typos in section 3.3 and summary

References in corpus (11)

• The Gaia mission
• The UCSD Radio-Selected Quasar Survey for Damped Lyman alpha System
• Ly-alpha excess in high redshift radio galaxies: a signature of star formation
• Statistical properties of damped Lyman-alpha systems from Sloan Digital Sky Survey DR12
• A Giant Metrewave Radio Telescope search for associated H{\sc i} 21\,cm absorption in GHz-peaked-spectrum sources
• HI 21cm absorption at $z\sim 3.39$ towards PKS 0201+113
• A comparative study of intervening and associated HI 21-cm absorption profiles in redshifted galaxies
• A Multi-Epoch VLBI Survey of the Kinematics of CJF Sources; Part I: Model-Fit Parameters and Maps
• Giant Metrewave Radio Telescope detection of associated HI 21cm absorption at $z=1.2230$ towards TXS1954+513
• Ionisation of the atomic gas in redshifted radio sources
• The Extreme Ultraviolet Variability of Quasars

Cited by in corpus (3)

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