Ammonia mapping observations toward the Galactic massive star-forming region Sh 2-255 and Sh 2-257

Abstract

We performed NH$_3\ (J,K)=(1,1),(2,2),$ and $(3,3)$ mapping observations toward the Galactic massive star-forming region Sh 2-255 and Sh 2-257 using the Nobeyama 45-m telescope as a part of the KAGONMA (KAgoshima Galactic Object survey with the Nobeyama 45-metre telescope by Mapping in Ammonia lines) project. NH$_3$ (1,1) has an intensity peak at the cluster S255 N, is distributed over 3 pc $\times$ 2 pc and is located between two HII regions. The kinetic temperature derived from the NH$_3 (2,2)/(1,1)$ ratio was $\sim 35$ K near the massive cluster S255 IR. These clusters also show emission with a large line width of $\sim$ 3-4 km s$^{-1}$. Based on the reported data we suggest that NH$_3$ gas in these regions is affected by stellar feedback from embedded YSO clusters in S255 IR and S255 N. We also detected NH$_3$ (1,1) emission in a region west of the main gas clump at the location of a concentration of Class II YSOs adjacent to the HII regions Sh 2-254. The presence of Class II YSOs implies $\sim$ 2 Myr of star formation, younger than Sh 2-254 ($\sim 5$ Myr), thus we suggest that star formation in the western region could be influenced by the older HII region Sh 2-254.