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We investigate the correlation of HCN 1-0 with dense gas mass in the Galacticcenter. We find that in general (on the ~10 pc size scale of individualmolecular cloud cores) HCN 1-0 is well correlated with the dense molecular gasmass using a standard log-log relationship. However individual clouds in thisenvironment show systematic deviations from this relationship that contributeto around 0.75 dex of scatter. Most notably, Sgr B2, the most massive cloud inthe Galactic center, has an integrated HCN 1-0 intensity of cloud less thanhalf its mass, and several other clouds including GCM-0.02-0.07 show anenhancement of HCN 1-0 by a factor of 2-3 relative to clouds of comparablemass. We also find that HCN 1-0 is more intense for a given mass in thelarge-scale diffuse emission in the central 300 parsecs compared to the compactemission from individual cloud cores. We identify the two primary sources ofscatter in the relationship between HCN 1-0 and dense gas mass to beself-absorption (which reduces the observed HCN 1-0 intensity of Sgr B2) andvariations in HCN abundance, which appear to increase the brightness of HCN 1-0in GCM-0.02-0.07 and other clouds. We find that these sources of scatter wouldonly contribute to an ~10% error in the dense gas mass inferred from the HCN1-0 intensity in the Galactic center. However, the implied order of magnitudeHCN abundance variations between Galactic center clouds, and the systematicnature of these variations warn of potential biases in the use of HCN as densegas mass tracer in more extreme environments, such as AGN and shock-dominatedregions. Finally, we also investigate other tracers having transitions near 3mm, finding that HNCO, HNC and HCO+ largely behave like HCN, while HC3N, andCH3CN are higher fidelity tracers of the amount of gas in clouds like Sgr B2that suffer from strong self-absorption of the HCN 1-0 line. [abridged]

Origins of Scatter in the Relationship Between HCN 1-0 and Dense Gas Mass in the Galactic Center