2MASS J16213110-5025151 , the SIMBAD biblio

We report the discovery of a young massive stellar cluster embedded in an extended H II region, invisible at optical wavelengths where the extinction is A_V~28 mag, associated with the IRAS source 16177-5018. J-, H-, and narrowband K-imaging photometry combined with the K_sTwo Micron All Sky Survey data show the presence of sources with excess infrared emission at 2.2 µm, concentrated in an area of about 1 pc² around a massive young stellar object identified as the IRAS source. This object has a near mid-infrared spectral index between 2.2 and 25 µm α(IR)=dlog(λF_λ)/dlogλ=4.78, characteristic of compact H II regions, with bolometric luminosity inferred from the integrated near-to-far-infrared flux density of 2.8x10⁵L_☉, which corresponds to a zero-age main-sequence star of about 42 M_☉. From the color-magnitude diagram we were able to classify the majority of the cluster members as reddened massive stars earlier than spectral type B5.