Different evolutionary stages in the massive star-forming region S255 complex

Aims. Massive stars formin clusters, and they are often found in different evolutionary stages located close to each other. To understand evolutionary and environmental effects during the formation of high-mass stars, we observed three regions of massive star formation at different evolutionary stages, and all are found that in the same natal molecular cloud. Methods. The three regions, S255IR, S255N, and S255S, were observed at 1.3 mm with the submillimeter array (SMA), and follow-up short spacing information was obtained with the IRAM 30 m telescope. Near infrared (NIR) H + K-band spectra and continuum observations were taken for S255IR with VLT-SINFONI to study the different stellar populations in this region. Results. This combination of millimeter (mm) and near infrared data allow us to characterize different stellar populations within the young forming cluster in detail. While we find multiple mm continuum sources toward all regions, their outflow, disk, and chemical properties vary considerably. The most evolved source S255IR exhibits a collimated bipolar outflow visible in CO and H-2 emission, and the outflows from the youngest region S255S are still small and fairly confined in the regions of the mm continuum peaks. Also the chemistry toward S255IR is the most evolved, exhibiting strong emission from complex molecules, while much fewer molecular lines are detected in S255N, and in S255S we detect only CO isotopologues and SO lines. Also, rotational structures are found toward S255N and S255IR. Furthermore, a comparison of the NIR SINFONI and mm data from S255IR clearly reveal two different (proto) stellar populations with an estimated age difference of approximately 1 Myr. Conclusions. A multiwavelength spectroscopy and mapping study reveals different evolutionary phases of the star formation regions. We propose the triggered outside-in collapse star formation scenario for the bigger picture and the fragmentation scenario for S255IR.