Discovery of water vapor megamaser emission from Mrk 1419 (NGC 2960): An analogue of NGC 4258?

Abstract

Water vapor emission at 22 GHz is reported from the nucleus of the LINER galaxy Mrk 1419 (NGC 2960). Single-dish spectra of the maser source show properties that are similar to those seen in NGC 4258, namely (1) a cluster of systemic ($V \sim V_{\rm sys}$) H 2 O features, (2) two additional H 2 O clusters, one red- and one blue-shifted with respect to V sys , (3) a likely acceleration of the systemic features (d V /d$t = 2.8 \pm 0.5$ km s -1 yr -1 ), and (4) no detectable velocity drifts ( -1 yr -1 ) in the red- and blue-shifted features. Interpreting the data in terms of the paradigm established for NGC 4258, i.e. assuming the presence of an edge-on Keplerian circumnuclear annulus with the systemic emission arising from the near side of its inner edge, the following parameters are derived: $V_{\rm rot} = 330$–600 km s -1 , $R \sim 0.13$–0.43 pc, binding mass $M \sim 10^{7}~M_{\odot}$, and mass density inside the disk $\rho \sim 10^{9}~M_{\odot}$ pc -3 . With the galaxy being approximately ten times farther away than NGC 4258, a comparison of linear and angular scales (the latter via Very Long Baseline Interferometry) may provide an accurate geometric distance to Mrk 1419 that could be used to calibrate the cosmic distance scale.