Blind H I and OH Absorption Line Search: First Results with MALS and uGMRT Processed Using ARTIP

We present details of the Automated Radio Telescope Imaging Pipeline (ARTIP) and the results of a sensitive blind search for H I and OH absorbers at z < 0.4 and z < 0.7, respectively. ARTIP is written in Python 3.6, extensively uses the Common Astronomy Software Application tools and tasks, and is designed to enable the geographically distributed MeerKAT Absorption Line Survey (MALS) team to collaboratively process large volumes of radio interferometric data. We apply it to the first MALS data set obtained using the 64-dish MeerKAT radio telescope and 32 K channel mode of the correlator. With merely 40 minutes on target, we present the most sensitive spectrum of PKS 1830-211 ever obtained and characterize the known H I (z = 0.19) and OH (z = 0.89) absorbers. We further demonstrate ARTIP's capabilities to handle realistic observing scenarios by applying it to a sample of 72 bright radio sources observed with the upgraded Giant Metrewave Radio Telescope (uGMRT) to blindly search for H I and OH absorbers. We estimate the numbers of H I and OH absorbers per unit redshift to be n₂₁(z ∼ 0.18) < 0.14 and n_OH(z ∼ 0.40) < 0.12, respectively, and constrain the cold gas covering factor of galaxies at large impact parameters (50 kpc < ρ < 150 kpc) to be less than 0.022. Due to the small redshift path, Δz ∼ 13 for H I with column density >5.4 × 10¹⁹ cm^-2, the survey has probed only the outskirts of star-forming galaxies at ρ > 30 kpc. MALS with the expected Δz ∼ 10^3-4 will overcome this limitation and provide stringent constraints on the cold gas fraction of galaxies in diverse environments over 0 < z < 1.5.