A pilot search for extragalactic OH absorption with FAST

Journal article

OH absorption is currently the only viable way to detect OH molecules in non-masing galaxies at cosmological distances. There have been only six such detections at z > 0.05 to date and so it is hard to put a statistically robust constraint on OH column densities in distant galaxies. We carried out a pilot OH absorption survey towards eight associated and one intervening H i 21-cm absorbers using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We were able to constrain the OH abundance relative to H i ([OH]/[H i]) to be lower than 10-6 ∼10-8 for redshifts z [0.1919, 0.2241]. Although no individual detection was made, stacking three associated absorbers free of RFI provides a sensitive OH column density 3σ upper-limit $\sim 1.57 ×1014(TxOH/10\,\mathrmK)(1/fcOH}cm-2, which corresponds to a [OH]/[H i] < 5.45 × 10-8. Combining with archival data, we show that associated absorbers have a slightly lower OH abundance than intervening absorbers. Our results are consistent with a trend of decreasing OH abundance with decreasing redshift.

Authors: Zheng, Z; Li, D; Sadler, EM; Allison, JR; Tang, N

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 499
• Issue: 3
• Pages: 3085-3093
• Publication date: 2020-10-01
• Acceptance date: 2020-09-29
• DOI: 10.1093/mnras/staa3033
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: galaxies: evolution; radio lines: galaxies; quasars: absorption line; galaxies: ISM; FFR; ISM: abundances; radio lines: ISM