2019ApJ...880...92J

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 - H₂O(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 - H₂O(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_H2O_/LFIR_ relation on resolved scales for the first time at high redshift. We find that L_H2O_ is correlated with L_FIR on both global and resolved kiloparsec scales within the galaxy in starbursts and AGN with average L_H2O_/LFIR_=2.76-1.21_^+2.15×10^–5. We find that the scatter in the observed L_H2O_/LFIR_ 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 - H₂O(2_0,2-1_1,1) as a resolved star formation rate calibrator.