Open AccessA 22‐GHz search for molecular absorption at z ∼ 3 with the upgraded ATCA
Author(s) -
Curran S. J.,
Murphy M. T.,
Webb J. K.,
Pihlström Y. M.
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2003.06273.x
Subject(s) - physics , quasar , redshift , astrophysics , photoionization , absorption (acoustics) , telescope , astronomy , absorption spectroscopy , galaxy , ionization , optics , ion , quantum mechanics
We report a λ≳ 1 cm search for rotational molecular absorption towards quasars, now possible with the upgraded Australia Telescope Compact Array (ATCA). The targets were PKS 0201+113, PKS 0336–017 and Q 0537–286, where known damped Lyman‐alpha absorption systems (DLAs) could cause redshifted molecular absorption in the 12‐mm band of the telescope. We place 3σ upper limits on any HCO + 0 → 1 absorption features of <30 mJy per 3.4 km s −1 channel. The non‐detections could be attributed to the inherent low metallicities in DLAs leading to generally low H 2 , and thus HCO + , column densities. In general, the detection of molecular rotational transitions in DLAs could be further hindered by a lower than expected CO‐to‐H 2 conversion ratio, whether due either to photoionization of carbon or to its relative under‐abundance at high redshift.