We present observations of the dense molecular gas tracers \mathrm { HCN } , \mathrm { HNC } , and \mathrm { HCO ^ { + } } in the J = 1 - 0 transition using ALMA .
We supplement our datasets with previous observations of \mathrm { CO } J = 1 - 0 , which traces the total molecular gas content .
We separate the Antennae into 7 bright regions in which we detect emission from all three molecules , including the nuclei of NGC 4038 and NGC 4039 , 5 super giant molecular complexes in the overlap region and 2 additional bright clouds .
We find that the ratio of L _ { \mathrm { HCN } } / L _ { \mathrm { CO } } , which traces the dense molecular gas fraction , is greater in the two nuclei ( L _ { \mathrm { HCN } } / L _ { \mathrm { CO } } \sim 0.07 - 0.08 ) than in the overlap region ( L _ { \mathrm { HCN } } / L _ { \mathrm { CO } } < 0.05 ) .
We attribute this to an increase in pressure due to the stellar potential within the nuclei , similar to what has been seen previously in the Milky Way and nearby spiral galaxies .
Furthermore , the ratio of L _ { \mathrm { HNC } } / L _ { \mathrm { HCN } } \sim 0.3 - 0.4 does not vary by more than a factor of 1.5 between regions .
By comparing our measured ratios to PDR models including mechanical heating , we find that the ratio of L _ { \mathrm { HNC } } / L _ { \mathrm { HCN } } is consistent with mechanical heating contributing \gtrsim 5 \% - 10 \% of the PDR surface heating to the total heating budget .
Finally , the ratio of L _ { \mathrm { HCN } } / L _ { \mathrm { HCO } + } varies from \sim 1 in the nucleus of NGC 4038 down to \sim 0.5 in the overlap region .
The lower ratio in the overlap region may be due to an increase in the cosmic ray rate from the increased supernova rate within this region .