An, F.XZheng, X.ZCai, Z2021-06-032021-06-032021An, F.X. et al. (2021). MAMMOTH: Confirmation of two massive galaxy overdensities at z = 2.24 with Hα emitters. Monthly Notices of the Royal Astronomical Society, 500(4), 4354-43640035871110.1093/mnras/staa2882http://hdl.handle.net/10566/6255Massive galaxy overdensities at the peak epoch of cosmic star formation provide ideal testbeds for the formation theories of galaxies and large-scale structure. We report the confirmation of two massive galaxy overdensities at z = 2.24, BOSS1244 and BOSS1542, selected from the Mapping the Most Massive Overdensities Through Hydrogen (MAMMOTH) project using Lyα absorption from the intergalactic medium over the scales of 15-30 h-1 Mpc imprinted on the quasar spectra. We use Hα emitters (HAEs) as the density tracer and identify them using deep narrow-band H2S(1) and broad-band Ks imaging data obtained with the wide-field infrared camera (WIRCam) at the Canada-France-Hawaii Telescope. In total, 244 and 223 line emitters are detected in these two fields, and 196 ± 2 and 175 ± 2 are expected to be HAEs with an Hα flux of >2.5 × 10-17 erg s-1 cm-2 (corresponding to a star formation rate of >5 M· yr-1). The detection rate of HAE candidates suggests an overdensity factor of δgal = 5.6 ± 0.3 and 4.9 ± 0.3 over the volume of 54 × 32 × 32 co-moving Mpc3.enGalaxies: clustersGalaxies: star formationGalaxies: high-redshiftQuasars: absorption linesBOSS1244Article