A survey of large molecules of biological interest toward selected high-mass star-forming regions

We have surveyed the high-mass Galactic star-forming regions G19.61-0.23, G45.47+0.05, and W75N for interstellar methanol (CH3OH), formic acid (HCOOH), acetic acid (CH3COOH), methyl formate (HCOOCH3), methyl cyanide (CH3CN), and ethyl cyanide (CH3CH2CN) with the Berkeley-Illinois-Maryland Association Array. From our observations, we have detected two new sources of interstellar HCOOH toward the hot core regions G19.61-0.23 and W75N. We have also made the first detections of CH3CH2CN and HCOOCH3 toward G19.61-0.23. The relative HCOOH/HCOOCH3 abundance ratio toward G19.61-0.23 is 0.18, which is comparable to the abundance ratios found by Liu and colleagues toward Sgr B2(N-LMH), Orion, and W51 (similar to0.10). We have made the first detection of HCOOCH3 toward W75N. The relative HCOOH/HCOOCH3 abundance ratio toward W75N is 0.26, which is more than twice as large as the abundance ratios found by Liu and colleagues. Furthermore, the hot core regions around W75N show a chemical differentiation between the O and N cores similar to what is seen toward the Orion Hot Core and Compact Ridge and W3(OH) and W3(H2O). It is also apparent from our observations that the high-mass star-forming region G45.47+0.05 does not contain any compact hot molecular core (HMC), and as a consequence its chemistry may be similar to that of cold dark clouds. Finally, the formation of CH3COOH appears to favor HMCs with well-mixed N and O, despite the fact that CH3COOH does not contain a N atom. If proved to be true, this is an important constraint on CH3COOH formation and possibly other structurally similar biomolecules.