2026ApJ...999...74M

We use deep Hubble Space Telescope imaging to study stellar populations in the outer halo of the spiral galaxy M96, located in the dynamically active Leo I galaxy group. Our imaging targets two fields at a projected distance of 50 kpc from the galaxy's center, with a 50% photometric completeness limit of F814W = 28.0-nearly 2 magnitudes below the tip of the red giant branch (RGB). In both fields, we clearly detect red giant stars in M96's halo, with a space density that corresponds to an equivalent broadband surface brightness of μ_V ≈ 31.7 mag arcsec^–2. We find little evidence for any differences in the spatial density or color of the RGB stars in the two fields. Using isochrone matching, we derive a median metallicity for the red giants of [M/H] = -1.36, with an interquartile spread of ± 0.75 dex. Adopting a power-law radial density profile, we also derive a total halo mass of ${M}_{h}=7.{8}_{-4.9}^{+17.4}\times 1{0}^{9}$M_⊙, implying a stellar halo mass fraction of ${M}_{* ,\mathrm{halo}}/{M}_{* ,\mathrm{tot}}\approx 1{5}_{-9}^{+33}$%-on the high end for spiral galaxies, but with significant uncertainty. Finally, we find that M96 appears offset from the stellar halo mass-metallicity relationship for spirals, with a halo that is distinctly metal-poor for its halo mass. While a variety of systematic effects could have conspired to drive M96 off this relationship, if confirmed our results may argue for a markedly different accretion history for M96 compared to other spirals in the nearby Universe.