We report the detection at 850 \mu m of the central source in SSA22-LAB1 , the archetypal ‘ Lyman- \alpha Blob ’ ( LAB ) , a 100 kpc-scale radio-quiet emission-line nebula at z = 3.1 .
The flux density of the source , S _ { 850 } = 4.6 \pm 1.1 mJy implies the presence of a galaxy , or group of galaxies , with a total luminosity of L _ { IR } \approx 10 ^ { 12 } { L _ { \odot } } .
The position of an active source at the center of a \sim 50 kpc-radius ring of linearly polarized Ly \alpha emission detected by Hayes et al .
( 2011 ) suggests that the central source is leaking Ly \alpha photons preferentially in the plane of the sky , which undergo scattering in H i clouds at large galactocentric radius .
The Ly \alpha morphology around the submillimeter detection is reminiscent of biconical outflow , and the average Ly \alpha line profiles of the two ‘ lobes ’ are dominated by a red peak , expected for a resonant line emerging from a medium with a bulk velocity gradient that is outflowing relative to the line center .
Taken together , these observations provide compelling evidence that the central active galaxy ( or galaxies ) is responsible for a large fraction of the extended Ly \alpha emission and morphology .
Less clear is the history of the cold gas in the circumgalactic medium being traced by Ly \alpha : is it mainly pristine material accreting into the halo that has not yet been processed through an interstellar medium ( ISM ) , now being blown back as it encounters an outflow , or does it mainly comprise gas that has been swept-up within the ISM and expelled from the galaxy ?