Related papers: An ASKAP survey for HI absorption towards dust-obs…

Many radio galaxies show the presence of dense and dusty gas near the active nucleus. This can be traced by both 21cm HI absorption and soft X-ray absorption, offering new insight into the physical nature of the circumnuclear medium of…

HI absorption studies yield information on both AGN feeding and feedback processes. This AGN activity interacts with the neutral gas in compact radio sources, which are believed to represent the young or recently re-triggered AGN…

Recent targeted studies of associated HI absorption in radio galaxies are starting to map out the location, and potential cosmological evolution, of the cold gas in the host galaxies of Active Galactic Nuclei (AGN). The observed 21 cm…

We present MeerKAT observations searching for HI absorption in a sample of 17 powerful ($L_{\rm 1.4GHz}> 10^{27}$ W Hz$^{-1}$) radio sources at intermediate redshifts ($0.25<z<0.7$). The sample is well characterised at radio and optical…

At present neutral atomic hydrogen (HI) gas in galaxies at redshifts above $z \sim 0.3$ (the extent of 21-cm emission surveys in individual galaxies) and below $z \sim 1.7$ (where the Lyman-$\alpha$ line is not observable with ground-based…

Previous surveys for HI 21-cm absorption in z > 0.1 radio galaxies and quasars yield a 40% detection rate, which is attributed to unified schemes of active galactic nuclei (AGN). In this paradigm absorption is only witnessed in (close to)…

We report the discovery of a new 21-cm HI absorption system using commissioning data from the Boolardy Engineering Test Array of the Australian Square Kilometre Array Pathfinder (ASKAP). Using the 711.5 - 1015.5 MHz band of ASKAP we were…

We report the discovery of three HI absorbers toward low-power radio active galactic nuclei (AGNs) in a pilot HI absorption survey with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Compared to past studies, FAST…

We present results from a spectroscopically blind search for associated and intervening HI 21-cm and OH 18-cm absorption lines towards 88 AGNs at $2\le z\le5$ using the upgraded Giant Metrewave Radio Telescope (uGMRT). The sample of AGNs…

Different physical processes in galaxy evolution, such as galaxy mergers that lead to coalescence of dual Active Galactic Nuclei (AGN) and outflows emanating from the narrow line region, can leave their imprint on the optical spectra of AGN…

This review summarises what we have learnt in the last two decades based on HI 21-cm absorption observations about the cold interstellar medium (ISM) in the central regions of active galaxies and the interplay between this gas and the…

Using the Boolardy Engineering Test Array of the Australian Square Kilometre Array Pathfinder (ASKAP BETA), we have carried out the first $z = 0 - 1$ survey for HI and OH absorption towards the gravitationally lensed quasars PKSB1830$-$211…

We present the results of Hi line observations towards 26 Active Galactic Nuclei (AGN)-hosting and one star-forming dwarf galaxies (Mstar < 10^9.5 Msun) with the 19-beam spectral line receiver of FAST at 1.4 GHz. Our FAST observed targets…

We present the largest Galactic neutral hydrogen HI absorption survey to date, utilizing the Australian SKA Pathfinder Telescope at an unprecedented spatial resolution of 30''. This survey, GASKAP-HI, unbiasedly targets 2,714 continuum…

We analyse different photometric and spectroscopic properties of active galactic nuclei (AGNs) and quasars (QSOs) selected by their mid-IR power-law and X-ray emission from the COSMOS survey. We use a set of star-forming galaxies as a…

Using the WSRT, we carried out shallow HI absorption observations of a flux-selected (S > 50 mJy) sample of 93 radio AGN with available SDSS redshifts between 0.02 < z < 0.23. We study the gas properties of radio AGN down to fluxes not…

To understand the Active Galactic Nuclei (AGN) phenomenon and their impact on the evolution of galaxies, a complete AGN census is required; however, finding heavily obscured AGNs is observationally challenging. Here we use the deep and…

We have searched for redshifted neutral hydrogen 21cm absorption toward sources from the Stickel et al. `red quasar' sub-sample. Five of these red quasars have been searched for redshifted HI 21cm absorption to optical depth levels of a few…

We have observed the G23 field of the Galaxy And Mass Assembly (GAMA) survey using the Australian Square Kilometre Array Pathfinder (ASKAP) in its commissioning phase, to validate the performance of the telescope and to characterize the…

The energy released by active galactic nuclei (AGNs) is considered to have a profound impact on the cold gas properties of their host galaxies, potentially heating or removing the gas and further suppressing star formation. To understand…