We present 1 \arcsec ( < 100 pc ) resolution maps of millimeter emission from five molecules–CN , HCN , HCO ^ { + } , CH _ { 3 } OH , and HNCO–obtained towards NGC 4038 , which is the northern galaxy of the mid-stage merger , Antennae galaxies , with the Atacama Large Millimeter/submillimeter Array .
Three molecules ( CN , CH _ { 3 } OH , and HNCO ) were detected for the first time in the nuclear region of NGC 4038 .
High-resolution mapping reveals a systematic difference in distributions of different molecular species and continuum emission .
Active star forming regions identified by the 3 mm and 850 \mu m continuum emission are offset from the gas-rich region associated with the HCN ( 1–0 ) and CO ( 3–2 ) peaks .
The CN ( 1–0 ) /HCN ( 1–0 ) line ratios are enhanced ( CN/HCN \simeq 0.8–1.2 ) in the star forming regions , suggesting that the regions are photon dominated .
The large molecular gas mass ( 10 ^ { 8 } ~ { } M _ { \solar } ) within a 0 \farcs 6 ( \sim 60 pc ) radius of the CO ( 3–2 ) peak and a high dense gas fraction ( > 20 % ) suggested by the HCN ( 1–0 ) /CO ( 3–2 ) line ratio may signify a future burst of intense star formation there .
The shocked gas traced in the CH _ { 3 } OH and HNCO emission indicates sub-kpc scale molecular shocks .
We suggest that the molecular shocks may be driven by collisions between inflowing gas and the central massive molecular complex .