Constraints on the presence of water megamaser emission in z~2.5 ultraluminous infrared starburst galaxies

TL;DR

This study searched for water megamaser emission in two high-redshift starburst galaxies but found no evidence, suggesting such emission is rare in similar unlensed galaxies, and provided limits for future surveys.

Contribution

First deep limits on H2O megamaser emission in z~2.5 starburst galaxies, informing future high-redshift megamaser surveys and understanding of galaxy evolution.

Findings

No H2O megamaser detected in the two galaxies.

Set upper limits on H2O line luminosities for both targets.

Predicted detection prospects based on a known high-redshift megamaser.

Abstract

We present Expanded Very Large Array and Arecibo observations of two lensed submm galaxies at z~2.5, in order to search for redshifted 22.235 GHz water megamaser emission. Both SMM J14011+0252 and SMM J16359+6612 have multi-wavelength characteristics consistent with ongoing starburst activity, as well as CO line emission indicating the presence of warm molecular gas. Our observations do not reveal any evidence for H2O megamaser emission in either target, while the lensing allows us to obtain deep limits to the H_2O line luminosities, L(H2O) < 7470 Lsun (3-sigma) in the case of SMM J14011+0252, and L(H2O) < 1893 Lsun for SMM J16359+6612, assuming linewidths of 80 km/s. Our search for, and subsequent non-detection of H2O megamaser emission in two strongly lensed starburst galaxies, rich in gas and dust, suggests that such megamaser emission is not likely to be common within the unlensed population of high-redshift starburst galaxies. We use the recent detection of strong H2O megamaser emission in the lensed quasar, MG J0414+0534 at z = 2.64 to make predictions for future EVLA C-band surveys of H2O megamaser emission in submm galaxies hosting AGN.