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 multi-band 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 broad-band filters .
We reach a level of completeness of 50 % down to F 555 W = 24.8 mag ( 0.7 ~ { } M _ { \odot } ) and F 814 W = 23.3 mag ( 0.2 ~ { } M _ { \odot } ) in the optical and F 125 W = 20.2 mag and F 160 W = 19.4 mag ( both 0.12 ~ { } M _ { \odot } ) 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 ( MC ) and the northern clump ( NC ) .
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 F 814 W = 21.8 mag .
We find that the present-day mass function ( PDMF ) of Wd2 has a slope of \Gamma = -1.46 \pm 0.06 , which translates to a total stellar cluster mass of ( 3.6 \pm 0.3 ) \cdot 10 ^ { 4 } ~ { } M _ { \odot } .
The spatial analysis of the PDMF reveals that the cluster population is mass-segregated , most likely primordial .
In addition , we report the detection of a stellar population of spatially uniformly distributed low-mass ( < 0.15 ~ { } M _ { \odot } ) 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 .