2023MNRAS.521.1958T

The far-infrared source IRAS 23139+5939 (G111.25-0.77) is a well-studied massive star-forming region at the centre of a dense molecular clump. It is associated with a low-luminosity and variable methanol maser, a number of water maser clusters, and several compact H II regions. We present new sub-arcsec-resolution broad- and narrow-band near- and mid-infrared calibrated images. These were analysed together with Wide-field Infrared Survey Explorer images and longer wavelength published data. We establish that IRAS 23139+5939 is a multiple massive young stellar object (YSO) with a spectral energy distribution characteristic of a Class I object. Its deeply embedded (A_V = 21) central YSOs have a total luminosity of 3 × 10⁴ L_⊙ and a mass of 16 M_⊙. We find several small knots of H₂ emission in its vicinity, bordering a large CO outflow driven by the protostar. Their distribution suggests the presence of several YSOs with jets. A young embedded stellar cluster of size ∼40 arcsec (0.65 pc) is found around the massive protostar, with evidence of protoplanetary discs in more than 50 per cent of the likely members. We also report a large arc of H₂ emission surrounding a nearby H α-emission star displaying a large infrared excess, with a total luminosity of 1.5 × 10³ L_⊙. Gaia Data Release 3 and very long baseline interferometry parallaxes indicate a common distance of 3.34 kpc to these two YSOs, a distance similar to that to Sh2-157, a nearby massive star-forming region, which appears connected to IRAS 23139+5939 by a warm dust filament.