2026A&A...706A.149R

Context. The shape of the initial mass function (IMF) remains a fundamental yet contentious topic in the study of stellar formation and evolution. It is imperative to understand the potential variability of the IMF across different young regions. This study examines the IMF within the young massive cluster RCW 36 situated in the Vela Molecular Ridge, comparable with the Orion Nebula Cluster in terms of stellar surface density.
Aims. The primary objective of this research is to construct the most comprehensive census of the stellar population in RCW 36 to date and determine the first ever IMF and star to brown dwarf (BD) ratio for the cluster.
Methods. We used state-of-the art observational techniques, drawing on new GLAO observations conducted with HAWK-I/VLT in addition to archival data from 2MASS, SOFI/NTT, and new kinematics from Gaia DR3. To enhance photometric accuracy and source extraction, we employed DENEB, an advanced deep learning algorithm capable of removing the complex filamentary nebula in our images. Statistical comparisons of color-magnitude diagrams were performed between RCW 36 and a control field, also obtained using HAWK-I under the same mode, to assign membership weights for the sources in our field. Mass estimates to individual sources were also derived through comparison with model isochrones in order to determine the IMF using the membership weights.
Results. We found a new distance of 954 ± 40 pc. We determined the IMF for RCW 36 down to ∼0.03 M_⊙, characterized by a broken power law (dN/d M ∝ M^-α^) with α = 1.62 ± 0.03 (0.20 M_⊙ -20 M_⊙) and α = 0.46 ± 0.14 (0.03 M_⊙-0.20 M_⊙). We also determined the star-BD ratio to be 2-5, in agreement with other Galactic clusters. Lastly, through a study of the differences in the IMF within and outside 0.2 pc and the cumulative mass distributions for low-mass and intermediate to high-mass sources, we also detected signs of possible mass segregation within RCW 36, which should be primordial.
Conclusions. RCW 36 shares many characteristics with other young massive clusters, such as a shallower than Salpeter high-mass slope and the possibility of mass segregation. The flatter lower-mass regime of the IMF is similar to most Galactic clusters. The star-BD ratio is also in line with the observed values in other clusters, independent of their inherent properties.