HI Absorption in Low-power Radio AGNs Detected by FAST

Abstract

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 observations have explored lower radio powers by $\sim$0.4 dex and detected these weakest absorbers at given redshifts. By comparing the gas properties and kinematics of sources along radio powers, we aim to explore the interplay between AGN and the surrounding interstellar medium (ISM). Compared to brighter sources at similar redshifts, our observations suggest a slightly lower detection rate of HI absorption lines ($\sim$$11.5\%$) in low-power radio AGNs with $\text{log}(P_{\text{1.4 GHz}}/{\text{W Hz}}^{-1})=21.8-23.7$. The low-power sources with $\text{log}(P_{\text{1.4 GHz}}/{\text{W Hz}}^{-1})<23$ have a lower detection rate of $\sim$$6.7\%$. Due to the incompleteness of the sample, these detection rates may represent the lower limits. The selection of more extended sources and dilution by HI emission at lower redshifts may contribute to the lower detection rate of HI absorption lines. These detected absorbers present relatively narrow line widths and comparable column densities consistent with previous observations. One absorber has a symmetric profile with a large velocity offset, while the other two show asymmetric profiles that can be decomposed into multiple components, suggesting various possibilities of gas origins and kinematics. These HI absorbers may have connections with rotating disks, gas outflows, galactic gas clouds, gas fueling of the AGN, and jet-ISM interactions, which will be further investigated with the upcoming systematic survey and spatially resolved observations.

12 pages, 5 figures, accepted for publication in ApJ

References in corpus (22)

• The Sixteenth Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
• The Five-Hundred-Meter Aperture Spherical Radio Telescope (FAST) Project
• GALEX-SDSS-WISE Legacy Catalog (GSWLC): Star Formation Rates, Stellar Masses and Dust Attenuations of 700,000 Low-redshift Galaxies
• The Fundamental Performance of FAST with 19-beam Receiver at L Band
• Interacting galaxies on FIRE-2: The connection between enhanced star formation and interstellar gas content
• The HI absorption "Zoo"
• Luminosity and Redshift Dependence of the Covering Factor of AGNs viewed with WISE and SDSS
• A search for HI absorption in nearby radio galaxies using HIPASS
• HI-MaNGA: Tracing the physics of the neutral and ionized ISM with the second data release
• What triggers a radio AGN? The intriguing case of PKSB 1718-649
• A Giant Metrewave Radio Telescope search for associated H{\sc i} 21\,cm absorption in GHz-peaked-spectrum sources
• Probing the gas content of radio galaxies through HI absorption stacking
• A circumnuclear disk of atomic hydrogen in Centaurus A
• The parsec-scale HI outflows in powerful radio galaxies
• Giant Metrewave Radio Telescope detection of associated HI 21cm absorption at $z=1.2230$ towards TXS1954+513
• On the HI Content of MaNGA Major Merger Pairs
• The HI absorption zoo: JVLA extension to $z\sim 0.4$
• Extragalactic HI 21-cm absorption line observations with the Five-hundred-meter Aperture Spherical radio Telescope
• Peering into the Milky Way by FAST: I. Exquisite HI structures in the inner Galactic disk from the piggyback line observations of the FAST GPPS survey
• Distance of PSR B0458+46 indicated by FAST HI absorption observations
• Detections of 21-cm absorption with a blind FAST survey at z $⩽$ 0.09
• HI 21-cm absorption in radio-loud AGN with double-peaked [OIII] emission

Cited by in corpus (3)

• The FAST HI 21-cm absorption blind survey. II. -- Statistic Exploration for Associated and Intervening systems
• FASHI: An untargeted survey of the 21 cm HI absorption galaxies with FAST
• HI gas in the rejuvenated radio galaxy PKS 2014-55