Physical and evolutionary status of G1.6–0.025 giant molecular cloud as revealed by 4₋₁-3_OE methanol weak maser

Abstract

G1.6 giant molecular cloud consists of the clumps with sizes varying from 3″ (0,1 pc) to 5′ (10 pc). Column densities of hydrogen and methanol in the large clumps are about (1+4)x10²³ and (1+2)x10¹⁵ cm⁻² correspondingly. Hydrogen densities in the large clumps vary from 10² to 5x10⁴ cm⁻³ and in the small clumps reach the values > 10⁶ cm⁻³. High kinetic temperature in the cloud T_K> 50+100 K partially is a consequence of collisions with individual clumps. Such collision probably occurs nowadays toward (α=17^h46^m12^s,δ=-27^o33′15″), where the 165 km/s clump is observed.

Shocks connected with this collision can lead to enhancement of methanol abundance in some clumps with masses 70+300 M_Θ and sizes about 3″ (4x10¹⁷ cm ), which therefore manifestspikefeatures in 4₋₁-3_OE line. This enhancement is the result of chemical reactions initiated by the methanol evaporation from grain mantles.

A probable protostar cluster is present in the same direction.