A gravitationally lensed water maser in the early Universe

Abstract

Water masers are found in dense molecular clouds closely associated with supermassive black holes at the centres of active galaxies. On the basis of the understanding of the local water-maser luminosity function, it was expected that masers at intermediate and high redshifts would be extremely rare. However, galaxies at redshifts z> 2 might be quite different from those found locally, not least because of more frequent mergers and interaction events. Here we use gravitational lensing to search for masers at higher redshifts than would otherwise be possible, and find a water maser at redshift 2.64 in the dust- and gas-rich, gravitationally lensed type-1 quasar MG J0414+0534 (refs 6-13). The isotropic luminosity is 10,000 (, solar luminosity), which is twice that of 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 see such a maser in the first galaxy we observe must mean that the volume densities and luminosities of masers are higher at redshift 2.64.

Water vapour at high redshift: Arecibo monitoring of the megamaser in MG J0414+0534

“…1). This spectrum confidently confirms the presence of the water maser line that was detected in the discovery spectra obtained with Effelsberg and the EVLA (Impellizzeri et al 2008). In addition, it shows a weak satellite emission feature, detected with a signal-to-noise ratio (SNR) of three, which is displaced by about +800 km s −1 from the main line.…”

“…By observing gravitational lens systems, we used the lens as a "cosmic telescope" to probe a luminosity regime that is otherwise not reachable with current instrumentation. Our first confirmed high-redshift water maser was found toward the lensed quasar MG J0414+0534 at z = 2.64, which is by far the most distant object known to host water maser emission (Impellizzeri et al 2008). The previously reported (unlensed) H 2 O apparent isotropic luminosity of ∼10 000 L places the maser in MG J0414+0534 among the most luminous water masers ever detected and suggests that the emission is associated with the AGN of the quasar.…”

“…This line broadening is responsible for the higher intrinsic isotropic luminosity we measure (26 000 L ) w.r.t. that reported by Impellizzeri et al (2008) (10 000 L ). The line velocity is also different.…”

“…The discovery of water masers at cosmological distances (z > 1.5) would allow us to study the parsec-scale environment around powerful radio sources, to investigate the A&A 529, A150 (2011) physical conditions of the molecular gas in the inner parsecs of quasars, and to measure their black-hole masses not only in the local but also in the early universe. We have recently performed a survey of gravitationally lensed quasars with the Effelsberg radio telescope to find water masers at cosmological redshifts (Impellizzeri et al 2008;McKean et al 2011). By observing gravitational lens systems, we used the lens as a "cosmic telescope" to probe a luminosity regime that is otherwise not reachable with current instrumentation.…”

Dusty star-forming galaxies at high redshift

“…The early studies typically detected water masers (e.g. Barvainis & Antonucci, 2005;Impellizzeri et al, 2008), though in recent years, nonmasing sources at high-z have been procured as well . Riechers et al (2013b) impressively detected seven H 2 O lines in the z = 6.34 galaxy HFLS3.…”