A successful search for intervening 21 cm HI absorption in galaxies at 0.4 < z <1.0 with the Australian Square Kilometre Array Pathfinder (ASKAP)

Abstract

We have used the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope to search for intervening 21 cm neutral hydrogen (HI) absorption along the line of sight to 53 bright radio continuum sources. Our observations are sensitive to HI column densities typical of Damped Lyman Alpha absorbers (DLAs) in cool gas with an HI spin temperature below about 300-500 K. The six-dish Boolardy Engineering Test Array (BETA) and twelve-antenna Early Science array (ASKAP-12) covered a frequency range corresponding to redshift $0.4<z<1.0$ and $0.37<z<0.77$ respectively for the HI line. Fifty of the 53 radio sources observed have reliable optical redshifts, giving a total redshift path $\Delta z$ = 21.37. This was a spectroscopically-untargeted survey, with no prior assumptions about the location of the lines in redshift space. Four intervening HI lines were detected, two of them new. In each case, the estimated HI column density lies above the DLA limit for HI spin temperatures above 50-80 K, and we estimate a DLA number density at redshift $z\sim 0.6$ of $n(z)=0.19\begin{array}{c}+0.15\\ -0.09\end{array}$. This value lies somewhat above the general trend of $n(z)$ with redshift seen in optical DLA studies. Although the current sample is small, it represents an important proof of concept for the much larger 21cm First Large Absorption Survey in HI (FLASH) project to be carried out with the full 36-antenna ASKAP telescope, probing a total redshift path $\Delta z\sim 50,000$.

21 pages, 11 figures. Accepted for publication in MNRAS

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Cited by in corpus (20)

• The First Large Absorption Survey in HI (FLASH): I. Science Goals and Survey Design
• MUSE-ALMA Haloes VII: Survey Science Goals & Design, Data Processing and Final Catalogues
• Extragalactic HI 21-cm absorption line observations with the Five-hundred-meter Aperture Spherical radio Telescope
• A statistical measurement of the HI spin temperature in DLAs at cosmological distances
• HI absorption at z~0.7 against the lobe of the powerful radio galaxy PKS 0409-75
• The distribution and properties of DLAs at z $\le$ 2 in the EAGLE simulations
• FLASH Pilot Survey: Detections of associated 21 cm HI absorption in GAMA galaxies at 0.42 < z <1.00
• Detections of 21-cm absorption with a blind FAST survey at z $⩽$ 0.09
• A census of compact sources at 162MHz: first data release from the MWA Phase II IPS Survey
• Probing galaxy evolution through HI 21-cm emission and absorption: current status and prospects with the Square Kilometre Array
• Intervening or associated? Machine learning classification of redshifted H I 21-cm absorption
• Reconciling X-ray and 21cm HI absorption gas column densities toward obscured AGN
• Observations of cold extragalactic gas clouds at $z=0.45$ towards PKS 1610-771
• Unveiling the Universe with Emerging Cosmological Probes
• Modeling Post-Reionization HI Distributions in Fuzzy Dark Matter Cosmologies Using Conditional Normalizing Flows
• The galaxy counterpart and environment of the dusty Damped Lyman-alpha Absorber at z=2.226 towards Q1218+0832
• The FAST HI 21-cm absorption blind survey. II. -- Statistic Exploration for Associated and Intervening systems
• Statistical distribution of HI 21cm intervening absorbers as potential cosmic acceleration probes
• A search for HI absorption in distant star-forming galaxies with ASKAP-FLASH -- I. Selection and analysis of the radio sample
• HI 21-cm Absorption Associated with Foreground Galaxies on Top of Quasars