Far-infrared observations of a massive cluster forming in the Monoceros R2 filament hub.

We present far-infrared observations of Monoceros R2 (a giant molecular cloud at approximately 830 pc distance, containing several sites of active star formation), as observed at 70 m, 160 m, 250 m, 350 m, and 500 m by the Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging Receiver (SPIRE) instruments on the Space Observatory as part of the imaging survey of OB young stellar objects (HOBYS) Key programme. The data are complemented by SCUBA-2 data in the submillimetre range, and WISE and data in the mid-infrared. In addition, CO data from the IRAM 30-m Telescope are presented, and used for kinematic information. Sources were extracted from the maps with , and from the fluxes measured, spectral energy distributions were constructed, allowing measurements of source mass and dust temperature. Of 177 sources robustly detected in the region (a detection with high signal-to-noise and low axis ratio at multiple wavelengths), including protostars and starless cores, 29 are found in a filamentary hub at the centre of the region (a little over 1% of the observed area). These objects are on average smaller, more massive, and more luminous than those in the surrounding regions (which together suggest that they are at a later stage of evolution), a result that cannot be explained entirely by selection effects. These results suggest a picture in which the hub may have begun star formation at a point significantly earlier than the outer regions, possibly forming as a result of feedback from earlier star formation. Furthermore, the hub may be sustaining its star formation by accreting material from the surrounding filaments.