Survey Observations of a Possible Glycine Precursor, Methanimine (CH${}_2$NH)

Abstract

We conducted survey observations of a glycine precursor, methanimine or methylenimine (CH${}_2$NH), with the NRO 45 m telescope and the SMT telescope towards 12 high-mass and two low-mass star-forming regions in order to increase number of CH${}_2$NH sources and to better understand the characteristics of CH2NH sources. As a result of our survey, CH${}_2$NH was detected in eight sources, including four new sources. The estimated fractional abundances were ~10${}^8$ in Orion KL and G10.47+0.03, while they were ~10${}^9$ towards the other sources. Our hydrogen recombination line and past studies suggest that CH${}_2$NH-rich sources have less evolved HII regions. The less destruction rates by UV flux from the central star would be contributed to the high CH${}_2$NH abundances towards CH${}_2$NH-rich sources. Our gas-grain chemical simulations suggest that CH${}_2$NH is mostly formed in the gas-phase by neutral-neutral reactions rather than the product of thermal evaporation from the dust surfaces.

49 pages, 12 figures, accepted to ApJ