2017AJ....153..122Z

We present a detailed analysis of the spatial distribution of the stellar population and the present-day mass function (PDMF) of the Westerlund 2 (Wd2) region using the data from our high-resolution multiband survey with the Hubble Space Telescope. We used state-of-the-art artificial star tests to determine spatially resolved completeness maps for each of the broadband filters. We reach a level of completeness of 50% down to F555W=24.8 mag (0.7 M_☉) and F814W=23.3 mag (0.2 M_☉) in the optical and F125W=20.2 mag and F160W=19.4 mag (both 0.12 M_☉) in the infrared throughout the field of view. We had previously reported that the core of Wd2 consists of two clumps: namely the main cluster and the northern clump. From the spatial distribution of the completeness-corrected population, we find that their stellar surface densities are 1114 stars pc^–2 and 555 stars pc^–2, respectively, down to F814W=21.8 mag. We find that the PDMF of Wd2 has a slope of Γ=-1.46±0.06, which translates to a total stellar cluster mass of (3.6±0.3)⋅10⁴ M_☉. The spatial analysis of the PDMF reveals that the cluster population is mass-segregated and most likely primordial. In addition, we report the detection of a stellar population of spatially uniformly distributed low-mass ( 0.15 M_☉) stars, extending into the gas ridges of the surrounding gas and dust cloud, as well as a confined region of reddened stars, likely caused by a foreground CO cloud. We find hints that a cloud-cloud collision might be the origin of the formation of Wd2.