2025ApJ...983...96K

We report the detection of H₂O maser emission in 4 out of 77 (5.2%) mid-IR red galaxies that meet the color criteria of W1 - W2 > 0.5 and W1 - W4 > 7 and are classified as Type 2 active galactic nuclei (AGNs) based on optical, near-IR, and mid-IR spectral energy distribution (SED) fitting. Here, W1, W2, and W4 represent the IR magnitudes at 3.4, 4.6, and 22 μm, respectively, as measured by the Wide-field Infrared Survey Explorer. Three of the four newly identified maser galaxies are classified as either Seyfert 2 or low-ionization nuclear emission-line region systems, but none are disk maser systems. Our analysis indicates that AGN identifications based solely on SED fitting are unreliable, resulting in an unexpectedly low megamaser detection rate. By restricting our sample to optically classified Type 2 AGNs that satisfy the mid-IR color criteria, we achieve a maser detection rate of ∼13%-18%, aligning with previous predictions for mid-IR red sources. These selection criteria are one of the most effective methods to date for facilitating new maser detections, particularly in light of the recent identification of additional Type 2 AGNs identified from ongoing galaxy and AGN surveys.