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We report ALMA observations with resolution $\approx0.5$" at 3 mm of theextended Sgr B2 cloud in the Central Molecular Zone (CMZ). We detect 271compact sources, most of which are smaller than 5000 AU. By ruling outalternative possibilities, we conclude that these sources consist of a mix ofhypercompact HII regions and young stellar objects (YSOs). Most of thenewly-detected sources are YSOs with gas envelopes which, based on theirluminosities, must contain objects with stellar masses $M_*\gtrsim8$ M$_\odot$.Their spatial distribution spread over a $\sim12\times3$ pc region demonstratesthat Sgr B2 is experiencing an extended star formation event, not just anisolated `starburst' within the protocluster regions. Using this new sample, weexamine star formation thresholds and surface density relations in Sgr B2.While all of the YSOs reside in regions of high column density($N(H_2)\gtrsim2\times10^{23}$ cm$^{-2}$), not all regions of high columndensity contain YSOs. The observed column density threshold for star formationis substantially higher than that in solar vicinity clouds, implying eitherthat high-mass star formation requires a higher column density or that any starformation threshold in the CMZ must be higher than in nearby clouds. Therelation between the surface density of gas and stars is incompatible withextrapolations from local clouds, and instead stellar densities in Sgr B2follow a linear $\Sigma_*-\Sigma_{gas}$ relation, shallower than that observedin local clouds. Together, these points suggest that a higher volume densitythreshold is required to explain star formation in CMZ clouds.

Distributed star formation throughout the Galactic Center cloud Sgr B2