A Search for H2O Megamasers in High-z Type-2 AGNs

TL;DR

This study conducted a search for H2O megamasers in high-redshift type-2 AGNs using large radio telescopes, finding only one known luminous megamaser and setting constraints on the prevalence of such phenomena.

Contribution

First systematic search for H2O megamasers in high-z type-2 AGNs, providing insights into their occurrence and properties at cosmological distances.

Findings

Detected one luminous water megamaser in the sample.

Most high-z type-2 AGNs do not host detectable megamasers.

Results constrain the luminosity function of water masers at high redshift.

Abstract

We report a search for H2O megamasers in 274 SDSS type-2 AGNs (0.3 < z < 0.83), half of which can be classified as type-2 QSOs from their [OIII] 5007 luminosity, using the Robert C. Byrd Green Bank Telescope (GBT) and the Effelsberg 100-m radio telescope. Apart from the detection of the extremely luminous water vapor megamaser SDSS J080430.99+360718.1, already reported by Barvainis & Antonucci (2005), we do not find any additional line emission. This high rate of non-detections is compared to the water maser luminosity function created from the 78 water maser galaxies known to date and its extrapolation towards the higher luminosities of "gigamasers" that we would have been able to detect given the sensitivity of our survey. The properties of the known water masers are summarized and discussed with respect to the nature of high-z type-2 AGNs and megamasers in general. In the appendix, we list 173 additional objects (mainly radio galaxies, but also QSOs and galaxies) that were observed with the GBT, the Effelsberg 100-m radio telescope, or Arecibo Observatory without leading to the detection of water maser emission.