Discovering young stars in the Gum 31 region with infrared observations

Context. The Gum 31 bubble, which contains the stellar cluster NGC 3324, is a poorly studied young region close to the Carina Nebula. Aims. We are aiming to characterise the young stellar and protostellar population in and around Gum31 and to investigate the star-formation process in this region. Methods. We identified candidate young stellar objects from Spitzer, WISE, and Herschel data. Combining these, we analysed the spectral energy distributions of the candidate young stellar objects. With density and temperature maps obtained from Herschel data and comparisons to a collect-and-collapse scenario for the region we are able to further constrain the characteristics of the region as a whole. Results. We find 661 candidate young stellar objects from WISE data; 91 protostar candidates are detected through Herschel observations in a 1.0 degrees x 1.1 degrees area. Most of these objects are found in small clusters or are well aligned with the H II bubble. We also identify the sources of Herbig-Haro jets. The infrared morphology of the region suggests that it is part of the larger Carina Nebula complex. Conclusions. The location of the candidate young stellar objects on the rim of the H II bubble is suggestive of their being triggered according to a collect-and-collapse scenario, which agrees well with the observed parameters of the region. Some candidate young stellar objects are found in the heads of pillars, which indicates radiative triggering of star formation. All in all, we find evidence that in the region different mechanisms of triggered star formation are at work. Correcting the number of candidate young stellar objects for contamination, we find similar to 600 young stellar objects in Gum 31 above our completeness limit of about 1 M-circle dot. Extrapolating the initial mass function down to 0.1 M-circle dot, we estimate a total population of similar to 5000 young stars for the region.