JWST Imaging of the Closest Globular Clusters—VI. The Lowest‐Mass Objects in M 4 and the Galactic Bulge

ABSTRACT We present James Webb Space Telescope observations of M 4—the closest globular cluster—that probe the lower Main Sequence down to the hydrogen‐burning limit. The unveiled stellar sequence reaches much fainter luminosities than previously possible, revealing a few extremely red objects that are consistent with brown dwarfs as cool as . However, the lack of a second JWST epoch presently prevents us from verifying the cluster membership of these objects. By cross‐matching our data with archival Hubble Space Telescope images, we are able to verify cluster membership for a subset of objects down to . The observed color distribution indicate that the lower Main Sequence of M 4 is likely deficient in oxygen compared to its higher‐mass post‐Main Sequence members by . This feature has now been observed in three different globular clusters (M 4, NGC 6397 and 47 Tuc), suggesting a general trend. Finally, we derive the mass function of the Galactic bulge in the background of M 4. The mass function was found to have the bottom‐heavy slope of and appears to terminate at , although the latter value may be overestimated due to the limited sample size.