Survey Observation of CH$_3$NH$_2$ and Its Formation Process

TL;DR

This study observes methylamine and related molecules in high-mass star-forming regions, confirming that grain surface hydrogenation processes are key to methylamine formation, with observed ratios aligning with chemical models.

Contribution

It provides observational evidence supporting grain surface hydrogenation as the formation pathway of methylamine in star-forming regions, validated by chemical modeling.

Findings

Observed methylamine ratios range from 0.11 to 2.2.

Model predictions agree with observed ratios.

One core showed no methylamine detection with a ratio below 0.02.

Abstract

We present the observational result of a glycine precursor, methylamine (CH$_3$NH$_2$), together with methanol (CH$_3$OH) and methanimine (CH$_2$NH) towards high-mass star-forming regions, NGC6334I, G10.47+0.03, G31.41+0.3, and W51~e1/e2 using ALMA. The molecular abundances toward these sources were derived using the rotational diagram method and compared with our state-of-the-art chemical model. We found that the observed ratio of "CH$_3$NH$_2$/CH$_3$OH" is in between 0.11 and 2.2. We also found that the observed "CH$_3$NH$_2$/CH$_3$OH" ratio agrees well with our chemical model by considering the formation of CH$_3$NH$_2$ on the grain surface via hydrogenation process to HCN. This result clearly shows the importance of hydrogenation processes to form CH$_3$NH$_2$. NGC63343I MM3, where CH$_3$NH$_2$ was not detected in this study and showed "CH$_3$NH$_2$/CH$_3$OH" ratio of less than 0.02, is clearly distinguished from the other cores.