We report interferometric imaging of CO ( J =3 \to 2 ) emission toward the z =2.846 submillimeter-selected galaxy SMM J04135+10277 , using the Combined Array for Research in Millimeter-wave Astronomy ( CARMA ) .
SMM J04135+10277 was previously thought to be a gas-rich , submillimeter-selected quasar , with the highest molecular gas mass among high- z quasars reported in the literature .
Our maps at \sim 6 \times improved linear resolution relative to earlier observations spatially resolve the emission on \sim 1.7 ^ { \prime \prime } scales , corresponding to a ( lensing-corrected ) source radius of \sim 5.2 kpc .
They also reveal that the molecular gas reservoir , and thus , likely the submillimeter emission , is not associated with the host galaxy of the quasar , but with an optically faint gas-rich galaxy at 5.2 ^ { \prime \prime } , or 41.5 kpc projected distance from the active galactic nucleus ( AGN ) .
The obscured gas-rich galaxy has a dynamical mass of M _ { dyn } { sin } ^ { 2 } i =5.6 \times 10 ^ { 11 } M _ { \odot } , corresponding to a gas mass fraction of \simeq 21 % .
Assuming a typical M _ { BH } / M _ { * } ratio for z \gtrsim 2 quasars , the two galaxies in this system have an approximate mass ratio of \sim 1.9 .
Our findings suggest that this quasar–starburst galaxy pair could represent an early stage of a rare major , gas-rich/gas-poor ( “ wet–dry ” ) merger of two massive galaxies at z =2.8 , rather than a single , gas-rich AGN host galaxy .
Such systems could play an important role in the early buildup of present-day massive galaxies through a submillimeter-luminous starburst phase , and may remain hidden in larger numbers among rest-frame far-infrared-selected quasar samples at low and high redshift .