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We present 0\farcs{14}-resolution Atacama Large Millimeter/submillimeterArray (ALMA) CO(2$-$1) observations of the circumnuclear gas disk in UGC 2698,a local compact galaxy. The disk exhibits regular rotation with projectedvelocities rising to 450 km s$^{-1}$ near the galaxy center. We fitgas-dynamical models to the ALMA data cube, assuming the CO emission originatesfrom a dynamically cold, thin disk, and measured the mass of the supermassiveblack hole (BH) in UGC 2698 to be $M_{\mathrm{BH}} = (2.46 \pm{0.07}$[$1\sigma$ stat] $^{+0.70}_{-0.78}$ [sys])$\times 10^9$ $M_\odot$. UGC 2698 ispart of a sample of nearby early-type galaxies that are plausible $z\sim2$ rednugget relics. Previous stellar-dynamical modeling for three galaxies in thesample found BH masses consistent with the BH mass$-$stellar velocitydispersion ($M_{\mathrm{BH}}-\sigma_\star$) relation but over-massive relativeto the BH mass$-$bulge luminosity ($M_{\mathrm{BH}}-L_{\mathrm{bul}}$)correlation, suggesting that BHs may gain the majority of their mass beforetheir host galaxies. However, UGC 2698 is consistent with both$M_{\mathrm{BH}}-\sigma_\star$ and $M_{\mathrm{BH}}-L_{\mathrm{bul}}$. As UGC2698 has the largest stellar mass and effective radius in the local compactgalaxy sample, it may have undergone more recent mergers that brought it inline with the BH scaling relations. Alternatively, given that the threepreviously-measured compact galaxies are outliers from$M_{\mathrm{BH}}-L_{\mathrm{bul}}$, while UGC 2698 is not, there may besignificant scatter at the poorly sampled high-mass end of the relation.Additional gas-dynamical $M_{\mathrm{BH}}$ measurements for the compact galaxysample will improve our understanding of BH$-$galaxy co-evolution.

An ALMA Gas-dynamical Mass Measurement of the Supermassive Black Hole in the Local Compact Galaxy UGC 2698