Program: GS-2022B-Q-312

We propose to use NIRI for a pilot project to probe the structure of two protocluster candidates centered on the brightest high-redshift dusty star-forming galaxies at redshift 2.1 to 2.3 through an estimate of unobscured star-formation (Halpha, down to 5Msun/yr). Our proposed observations exploit the most efficient large-area (500x500 kpc) mapping technique for targeting spectral lines over a narrow redshift slice, contrasting narrow-band filters against broad-band continuum (Ks). Simultaneous Flamingos 2 Ks band observations on these (+ 4 extra sources) will provide futher wide-area interpretation, and test the potential for future MOS observations. From our large (~300) master sample, 28 targets fall within the narrow-bands of NIRI, large enough to conclusively test the current picture of protocluster evolution. Our two (+ four) targets are representative in observed properties to the master sample, and thus are excellent targets to test our selection criteria. This proven method will reveal the wider environment around galaxies undergoing massive stellar build-up during the important evolutionary period for protoclusters at z=2 through direct observations of Halpha and stellar emission. The final sample will, for the first time, test whether the observed diversity of scaling relations in protoclusters is due to observational biases or because of intrinsic variations.