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We use Atacama Large Millimeter/submillimeter Array (ALMA) observations ofH30$\alpha$ (231.90 GHz) emission from the low metallicity dwarf galaxy NGC5253 to measure the star formation rate (SFR) within the galaxy and to test thereliability of SFRs derived from other commonly-used metrics. The H30$\alpha$emission, which originates mainly from the central starburst, yields aphotoionizing photon production rate of (1.9$\pm$0.3)$\times$10$^{52}$ s$^{-1}$and an SFR of 0.087$\pm$0.013 M$_\odot$ yr$^{-1}$ based on conversions thataccount for the low metallicity of the galaxy and for stellar rotation. Amongthe other star formation metrics we examined, the SFR calculated from the totalinfrared flux was statistically equivalent to the values from the H30$\alpha$data. The SFR based on previously-published versions of the H$\alpha$ flux thatwere extinction corrected using Pa$\alpha$ and Pa$\beta$ lines were lower thanbut also statistically similar to the H30$\alpha$ value. The mid-infrared (22$\mu$m) flux density and the composite star formation tracer based on H$\alpha$and mid-infrared emission give SFRs that were significantly higher because thedust emission appears unusually hot compared to typical spiral galaxies.Conversely, the 70 and 160 $\mu$m flux densities yielded SFR lower than theH30$\alpha$ value, although the SFRs from the 70 $\mu$m and H30$\alpha$ datawere within 1-2$\sigma$ of each other. While further analysis on a broaderrange of galaxies are needed, these results are instructive of the best andworst methods to use when measuring SFR in low metallicity dwarf galaxies likeNGC 5253.

Tests of star formation metrics in the low metallicity galaxy NGC 5253 using ALMA observations of H30$\alpha$ line emission