Discovery of OH Absorption from a Galaxy at z ∼ 0.05: Implications for Large Surveys with SKA Pathfinders

Abstract

Abstract We present the first detection of OH absorption in diffuse gas at z > 0, along with another eight stringent limits on OH column densities for cold atomic gas in galaxies at 0 < z < 0.4. The absorbing gas detected toward Q0248+430 (z q = 1.313) originates from a tidal tail emanating from a highly star-forming galaxy G0248+430 (z g = 0.0519) at an impact parameter of 15 kpc. The measured column density is N(OH) = (6.3 ± 0.8) × 1013 cm−2, where and T ex are the covering factor and the excitation temperature of the absorbing gas, respectively. In our Galaxy, the column densities of OH in diffuse clouds are of the order of N(OH) ∼ 1013–14 cm−2. From the incidence (number per unit redshift; n 21) of H i 21 cm absorbers at 0.5 < z < 1 and assuming no redshift evolution, we estimate the incidence of OH absorbers (with log N(OH) > 13.6) to be n OH = at z ∼ 0.1. Based on this we expect to detect such OH absorbers from the MeerKAT Absorption Line Survey (MALS). Using H i 21 cm and OH 1667 MHz absorption lines detected toward Q0248+430, we estimate (ΔF/F) = (5.2 ± 4.5) × 10−6, where , α is the fine structure constant, μ is the electron–proton mass ratio, and g p is the proton gyromagnetic ratio. This corresponds to Δα/α(z = 0.0519) = (1.7 ± 1.4) × 10−6, which is among the stringent constraints on the fractional variation of α.