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We present a new metric that uses the spectral curvature (SC) above 10 keV toidentify Compton-thick AGN in low-quality Swift BAT X-ray data. Using NuSTAR,we observe nine high SC-selected AGN. We find that high-sensitivity spectrashow the majority are Compton-thick (78% or 7/9) and the remaining two arenearly Compton-thick (NH~5-8x10^23 cm^-2). We find the SC_bat and SC_nustarmeasurements are consistent, suggesting this technique can be applied to futuretelescopes. We tested the SC method on well-known Compton-thick AGN and find itis much more effective than broad band ratios (e.g. 100% using SC vs. 20% using8-24/3-8 keV). Our results suggest that using the >10 keV emission may be theonly way to identify this population since only two sources show Compton-thicklevels of excess in the OIII to X-ray emission ratio (F_OIII/F_2-10 keV>1) andWISE colors do not identify most of them as AGN. Based on this small sample, wefind that a higher fraction of these AGN are in the final merger stage thantypical BAT AGN. Additionally, these nine obscured AGN have, on average, fourtimes higher accretion rates than other BAT-detected AGN (Edd ratio=0.068compared to 0.016). The robustness of SC at identifying Compton-thick AGNimplies a higher fraction of nearby AGN may be Compton-thick (~22%) and the sumof black hole growth in Compton-thick AGN (Eddington ratio times populationpercentage), is nearly as large as mildly obscured and unobscured AGN.

A New Population of Compton-Thick AGN Identified Using the Spectral Curvature Above 10 keV