Spatially Resolved Water Emission from Gravitationally Lensed Dusty Star-forming Galaxies at z ∼ 3
Abstract
Water (H2O), one of the most ubiquitous molecules in the universe, has bright millimeter-wave emission lines that are easily observed at high redshift with the current generation of instruments. The low-excitation transition of H2O, p - {{{H}}}2{{O}}({2}0,2}-{1}1,1}) (ν rest = 987.927 GHz), is known to trace the far-infrared (FIR) radiation field independent of the presence of active galactic nuclei (AGNs) over many orders of magnitude in FIR luminosity ({L}FIR}). This indicates that this transition arises mainly due to star formation. In this paper, we present spatially (∼0.″5 corresponding to ∼1 kiloparsec) and spectrally resolved (∼100 kms-1) observations of p - {{{H}}}2{{O}}({2}0,2}-{1}1,1}) in a sample of four strong gravitationally lensed high-redshift galaxies with the Atacama Large Millimeter/submillimeter Array. In addition to increasing the sample of luminous (>1012 L ⊙) galaxies observed with H2O, this paper examines the {L}{{{H}}2{{O}}}/{L}FIR} relation on resolved scales for the first time at high redshift. We find that {L}{{{H}}2{{O}}} is correlated with {L}FIR} on both global and resolved kiloparsec scales within the galaxy in starbursts and AGN with average {L}{{{H}}2{{O}}}/{L}FIR} = {2.76}-1.21+2.15 × {10}-5. We find that the scatter in the observed {L}{{{H}}2{{O}}}/{L}FIR} relation does not obviously correlate with the effective temperature of the dust spectral energy distribution or the molecular gas surface density. This is a first step in developing p - {{{H}}}2{{O}}({2}0,2}-{1}1,1}) as a resolved star formation rate calibrator.