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We use a suite of high-resolution cosmological dwarf galaxy simulations totest the accuracy of commonly-used mass estimators from Walker et al.(2009) andWolf et al.(2010), both of which depend on the observed line-of-sight velocitydispersion and the 2D half-light radius of the galaxy, $Re$. The simulationsare part of the the Feedback in Realistic Environments (FIRE) project andinclude twelve systems with stellar masses spanning $10^{5} - 10^{7} M_{\odot}$that have structural and kinematic properties similar to those of observeddispersion-supported dwarfs. Both estimators are found to be quite accurate:$M_{Wolf}/M_{true} = 0.98^{+0.19}_{-0.12}$ and $M_{Walker}/M_{true}=1.07^{+0.21}_{-0.15}$, with errors reflecting the 68% range over allsimulations. The excellent performance of these estimators is remarkable giventhat they each assume spherical symmetry, a supposition that is broken in oursimulated galaxies. Though our dwarfs have negligible rotation support, their3D stellar distributions are flattened, with short-to-long axis ratios $ c/a\simeq 0.4-0.7$. The accuracy of the estimators shows no trend withasphericity. Our simulated galaxies have sphericalized stellar profiles in 3Dthat follow a nearly universal form, one that transitions from a core at smallradius to a steep fall-off $\propto r^{-4.2}$ at large $r$, they are well fitby S\'ersic profiles in projection. We find that the most important empiricalquantity affecting mass estimator accuracy is $Re$ . Determining $Re$ by ananalytic fit to the surface density profile produces a better estimated massthan if the half-light radius is determined via direct summation.

Dwarf Galaxy Mass Estimators vs. Cosmological Simulations