A systematic observational study of radio properties of H2O megamaser Seyfert 2s: A Guide for H2O megamaser surveys

TL;DR

This study demonstrates that selecting radio-bright Seyfert 2 galaxies effectively identifies H2O megamasers at larger distances, aiding future surveys of obscured active galactic nuclei.

Contribution

It introduces a successful selection technique based on radio brightness to improve detection rates of H2O megamasers in Seyfert 2 galaxies.

Findings

Detection of one new megamaser source and one possible detection.

Higher detection rate at larger distances compared to previous studies.

Radio-bright nuclei are effective indicators for megamaser searches.

Abstract

Analyzing archival data from different telescopes, H2O megamaser Seyfert 2s appeared to exhibit higher nuclear radio luminosities than non-masing Seyfert 2s (Zhang et al. 2012). This has been confirmed by our follow-up study on multi-band (11, 6, 3.6, 2, 1.3 cm) radio properties of maser host Seyfert 2s, through systematic Effelsberg observations (Liu et al. 2017). The nuclear radio luminosity was supposed to be a suitable indicator to guide future AGN maser searches. Thus we performed a pilot survey with the Effelsberg telescope on H2O maser emission toward a small sample of radio-bright Seyfert 2 galaxies with relatively higher redshift (>0.04). Our pilot survey led to one new megamaser source and one additional possible detection, which reflects our success in selecting H2O megamaser candidates compared to previous observations (higher detection rate, larger distance). Our successful selection technique choosing Seyfert 2s with radio-bright nuclei may provide good guiding for future H2O megamaser surveys. Therefore we are conducting a large systematic survey toward a big Seyfert 2 sample with such radio-bright nuclei. Detections of luminous H2O masers at large distance (z>0.04) may hold the great potential to increase our knowledge on the central highly obscured but still very enigmatic regions of active Seyfert galaxies (Zhang et al. 2017).