Discovering young stars in the Gum 31 region with infrared observations
  Context. The Gum 31 bubble containing 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 Gum 31 and to investigate the star-formation process
in this region.
  Methods. We identify candidate young stellar objects from Spitzer, WISE, and
Herschel data. Combining these, we analyse 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. 661 candidate young stellar objects are found from WISE data, 91
protostar candidates are detected through Herschel observations in a 1.0 deg x
1.1 deg 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 in the rim
of the H II bubble is suggestive of their being triggered by 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 points towards radiative triggering of star formation. Thus, 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 ~ 600 young stellar objects in Gum 31 above our
completeness limit of about 1 M_sol. Extrapolating the intital mass function
down to 0.1 M_sol, we estimate a total population of ~ 5000 young stars for the
region.
