The Large Magellanic Cloud through the lens of the James Webb Space Telescope: Binaries and the mass function in the galaxy's outskirts
Nearby galaxies such as the Large Magellanic Cloud (LMC) offer an ideal laboratory to test the initial mass function under different physical conditions, but previous works have been limited by photometric depth and have therefore poorly constrained the low-mass regime. Here, we analyze ultra-deep James Webb Space Telescope observations of a field in the LMC outskirts, near the intermediate-age and massive star cluster NGC 1846. Using the $m_{\rm F322W2}$ versus $m_{\rm F115W}-m_{\rm F322W2}$ color-magnitude diagram, we derive the mass function (MF) down to unprecedentedly low masses ($M=0.17 M_{\odot}$), explicitly accounting for the contribution of unresolved binaries, whose fraction is constrained directly from the data. For systems with mass ratios $q>0.6$, we measure a binary fraction of $f_{\rm bin}^{q>0.6}=0.15\pm0.01$, implying a total binary fraction of $f_{\rm bin}^{\rm TOT}=0.34\pm0.02$ for a flat mass-ratio distribution. This is consistent with values in the Small Magellanic Cloud (SMC) and in the Milky Way field, suggesting similar binary formation efficiency across low-density environments. We also derive the MF over the mass interval 0.17-0.82 $M_{\odot}$ and fit it with a power law, obtaining a slope of $\alpha = -1.49 \pm 0.16$. This slope is shallower than the canonical Salpeter value ($\alpha=-2.35$) and slightly shallower than that measured in the SMC field, while remaining consistent with determinations for Galactic open clusters and for several clusters in the Magellanic Clouds and the Milky Way. Together, these results support a scenario in which both binary formation efficiency and the shape of the low-mass MF depend only weakly on the environment.