WISE Green Objects (WGOs): The Massive Star Candidates in the Whole Galactic Plane (∣b∣ < 2°)

Abstract

Abstract Massive young stellar objects (MYSOs) play a crucial role in star formation. Given that MYSOs were previously identified based on the extended structure and the observational data for them is limited, screening the Wide-field Infrared Survey Explorer (WISE) objects showing green features (for the common coding of the 4.6 μm band as the green channel in three-color composite WISE images) will yield more MYSO candidates. Using WISE images in the whole Galactic plane (0° < l < 360° and ∣b∣ < 2°), we identified sources with strong emissions at the 4.6 μm band, then according to morphological features divided them into three groups. We present a catalog of 2135 WISE Green Objects (WGOs). 264 WGOs have an extended structure. 1366 WGOs show compact green features but without extended structure. 505 WGOs have neither extended structure nor green features, but the intensity at 4.6 μm is numerically at least 4.5 times that of 3.4 μm. According to the analysis of the coordinates of WGOs, we find WGOs are mainly distributed in ∣l∣ < 60°, coincident with the position of the giant molecular clouds in ∣l∣ > 60°. Matching results with various masers show that those three groups of WGOs are at different evolutionary stages. After crossmatching WGOs with published YSO survey catalogs, we infer that ∼50% of WGOs are samples of newly discovered YSOs. In addition, 1260 WGOs are associated with Hi-GAL sources, according to physical parameters estimated by spectral energy distribution fitting, of which 231 are classified as robust MYSOs and 172 as candidate MYSOs.