GMRT observations of hydroxyl megamaser (OHM) candidates from the ALFALFA survey

Abstract

We present the results of our observations using the Giant Meterwave Radio Telescope (GMRT) to investigate the radio continuum and hydroxyl (OH) line emission of ten OH megamaser (OHM) candidates from the Arecibo Legacy Fast ALFA (ALFALFA) survey. Among these candidates, we identified two sources, AGC 115713 and AGC 249507, displaying compact OH line emission that is spatially associated with radio continuum emission. These characteristics are aligned with the typical properties of OHM galaxies. Furthermore, the infrared (IR) properties of these two galaxies are consistent with those of known OHM galaxies. Of the two sources, AGC 249507 has been confirmed through optical redshift, whereas AGC 115713 is aligned with a WISE color selection criterion in the literature, providing additional support for this source being an OHM galaxy, rather than a nearby H I galaxy. On the contrary, no significant spectral line emission was detected in the remaining eight OHM candidates using our full GMRT dataset. This suggests that the spectral line emission initially detected by the ALFALFA survey may have been significantly resolved in the high-resolution observations used in this work. Additionally, the absence of radio continuum emission in six candidates also distinguishes them from known OHM galaxies documented in the literature. These findings support the notion that OHM emission may be distributed on a subarcsecond scale, underscoring the utility of arcsecond-scale observations in confirming OHM candidates, particularly those lacking optical redshift data.