2011A&A...530A..34P

The Great Nebula in Carina is a giant HII region and a superb location in which to study the physics of violent massive star formation, but the population of the young low-mass stars remained very poorly studied until recently. Our aim was to produce a near-infrared survey that is deep enough to detect the full low-mass stellar population (i.e. down to ≃0.1M_☉ and for extinctions up to A_V≃15mag) and wide enough to cover all important parts of the Carina Nebula complex (CNC), including the clusters Tr 14, 15, and 16 as well as the South Pillars region. We used HAWK-I at the ESO VLT to survey the central ≃0.36deg² area of the Carina Nebula. These data reveal more than 600000 individual infrared sources down to magnitudes as faint as J≃23, H≃22, and K_s≃21. The results of a recent deep X-ray survey (which is complete down to stellar masses of ∼0.5-1M_☉) are used to distinguish between young stars in Carina and background contaminants. We analyze color-magnitude diagrams (CMDs) to derive information about the ages and masses of the low-mass stars. The ages of the low-mass stars agree with previous age estimates for the massive stars. The CMD suggests that ≃3200 of the X-ray selected stars have masses of M_*≥1M_☉; this number is in good agreement with extrapolations of the field IMF based on the number of high-mass (M_*≥20M_☉) stars and shows that there is no deficit of low-mass stars in the CNC. The HAWK-I images confirm that about 50% of all young stars in Carina are in a widely distributed, non-clustered spatial configuration. Narrow-band images reveal six molecular hydrogen emission objects (MHOs) that trace jets from embedded protostars. However, none of the optical HH objects shows molecular hydrogen emission, suggesting that the jet-driving protostars are located very close to the edges of the globules in which they are embedded. The near-infrared excess fractions for the stellar population in Carina are lower than typical for other, less massive clusters of similar age, suggesting that the process of circumstellar disk dispersal proceeds on a faster timescale in the CNC than in the more quiescent regions, most likely due to the very high level of massive star feedback in the CNC. The location of all but one of the known jet-driving protostars at the edges of the globules adds strong support to the scenario that their formation was triggered by the advancing ionization fronts.