A gravitationally lensed water maser in the early Universe

TL;DR

This paper reports the discovery of a highly luminous water maser at redshift 2.64 in a gravitationally lensed galaxy, suggesting that maser luminosities and densities were higher in the early Universe than previously expected.

Contribution

First detection of a water maser at high redshift using gravitational lensing, indicating increased maser activity in the early Universe.

Findings

Discovered a water maser with 10,000 L_solar luminosity at z=2.64

Maser luminosity exceeds local universe counterparts

Implicates higher maser volume densities at high redshift

Abstract

Water masers are found in dense molecular clouds closely associated with supermassive black holes in the centres of active galaxies. Based upon the understanding of the local water maser luminosity function, it was expected that masers at intermediate and high redshifts would be extremely rare, but galaxies at redshifts z > 2 might be quite different from those found locally, not least because of more frequent mergers and interaction events. Using gravitational lensing as a tool to enable us to search higher redshifts than would otherwise be possible, we have embarked on a survey of lensed galaxies, looking for masers. Here we report the discovery of a water maser at redshift 2.64 in the dust- and gas-rich gravitationally lensed type 1 quasar MG J0414+0534, which, with an isotropic luminosity of 10,000 L_solar, is twice as luminous as the most powerful local water maser, and half that of the most distant maser previously known. Using the locally-determined luminosity function, the probability of finding a maser this luminous associated with any single active galaxy is 10^{-6}. The fact that we saw such a maser in the first galaxy we observed must mean that the volume densities and luminosities of masers are higher at redshift 2.64.