We report the results of 1 ^ { \prime } .5 \times 3 ^ { \prime } mapping at 1.1 mm with the Atacama Large Millimeter/submillimeter Array ( ALMA ) toward the central region of the z = 3.09 SSA22 protocluster .
By combining our source catalog with archival spectroscopic redshifts , we find that eight submillimeter galaxies ( SMGs ) with flux densities , S _ { 1.1 ~ { } mm } = 0.7 - 6.4 mJy ( L _ { IR } \sim 10 ^ { 12.1 } -10 ^ { 13.1 } L _ { \odot } ) are at z = 3.08 - 3.10 .
Not only are these SMGs members of the protocluster but they in fact reside within the node at the junction of the 50 Mpc-scale filamentary three-dimensional structure traced by Lyman- \alpha emitters ( LAEs ) in this field .
The eight SMGs account for a star formation rate density ( SFRD ) \sim 10 M _ { \odot } yr ^ { -1 } Mpc ^ { -3 } in the node , which is two orders of magnitudes higher than the global SFRD at this redshift .
We find that four of the eight SMGs host a X-ray luminous active galactic nuclei ( AGN ) .
Our results suggest that the vigorous star formation activity and the growth of super massive black holes ( SMBHs ) occurred simultaneously in the densest regions at z \sim 3 , which may correspond to the most active historical phase of the massive galaxy population found in the core of the clusters in the present universe .
Two SMGs are associated with Lyman- \alpha blobs ( LABs ) , implying that the two populations coexist in high density environments for a few cases .