Searching for new OH megamasers out to redshifts z>1

TL;DR

This study conducted a systematic search for OH megamasers in ULIRGs at redshifts up to 1.5, resulting in nine new detections at lower redshifts and constraining the occurrence and luminosity of OHMs at higher redshifts.

Contribution

First large systematic search for OH megamasers at z>0.25, providing new detections, upper limits, and an updated luminosity function to understand their evolution.

Findings

Nine new OHM detections at z<0.25.

Constraints on OHM brightness in the sample.

OH luminosity function slope of -0.66.

Abstract

We have carried out a search for 18-cm OH megamaser (OHM) emission with the Green Bank Telescope. The targeted galaxies comprise a sample of 121 ULIRGs at 0.09<z<1.5, making this the first large, systematic search for OHMs at z>0.25. Nine new detections of OHMs are reported, all at redshifts z<0.25. For the remainder of the galaxies, observations constrain the upper limit on OH emission; this rules out OHMs of moderate brightness (L_OH > 10^3 L_sun) for 26% of the sample, and extremely bright OHM emission (L_OH > 10^4 L_sun) for 73% of the sample. Losses from RFI result in the OHM detection fraction being significantly lower than expected for galaxies with L_IR >10^12 L_sun. The new OHM detections are used to calculate an updated OH luminosity function, with \Phi[L]\simL_OH^{-0.66}; this slope is in agreement with previous results. Non-detections of OHMs in the COSMOS field constrain the predicted sky density of OHMs; the results are consistent with a galaxy merger rate evolving as (1+z)^m, where m<6.