Recently, international PhD student Serikbek Sailanbek from the Star Formation and Evolution Group at the Xinjiang Astronomical Observatory, Chinese Academy of Sciences, studied a large sample of dense clumps found in the Bolocam Galactic Plane Survey（BGPS）sources using ammonia data obtained from the NanShan 26-m Radio Telescope (NSRT).

The results were published in the Monthly Notices of the Royal Astronomical Society (2025, MNRAS, 539, 2987–3012).

They selected 217 dense clumps from the BGPS v1.0 catalog with a 1.1 mm flux greater than 5 Jy that were observable by the NSRT, and performed NH₃(1,1) and (2,2) inversion transitions survey.

A remarkable detection rate of 86.6% was achieved, with 188 sources showing clear ammonia emission. These sources span a broad range of galactic longitudes (1.2°to 192.6°), covering major spiral arms—including the Perseus, Sagittarius-Carina, Scutum-Centaurus, and Norma arms, at distances between 0.16 to 17.23 kiloparsecs. The ammonia emission lines reveal linewidths of 0.91–6.98 km/s and rotational temperatures between 9.7 and 50.2 K, indicating a dynamic range of physical conditions.

A key finding of this research is the positive correlation between turbulence and temperature, suggesting that stellar feedback influences the internal dynamics of these clumps. In contrast, some clumps with broad lines and low temperatures may represent early, prestellar phases. The study also highlights the strong correlation between gas and dust temperatures, validating temperature estimation methods used in molecular clouds studies, especially in high-temperature regions.

The study revealed widespread star formation activities, with three key findings : 1) 82% of the sources are associated with 22 GHz water masers, a hallmark of active star formation. 2) 52% qualify as High-Mass Star-Forming Regions (HMSFRs), identified through detections of 6.7 GHz class II methanol masers. 3) 72% of these HMSFRs show signs of being in late evolutionary stages, indicated by the presence of OH or 12 GHz methanol masers.

Through statistical analyses, the researchers demonstrated that maser detected sources have significantly higher kinetic temperatures and ammonia column densities with results reaching 3σ statistical significance, confirming the diagnostic power of maser emission in identifying active, evolving star-forming regions.

Furthermore, the study reveals a weak negative correlation between ammonia column density and Galactocentric distance (in the 2–8 kpc range), potentially linked to Galactic chemical or density gradients. However, local conditions such as turbulence and spiral arm structure appear to dominate these large-scale trends.

This study significantly advances our understanding of the physical conditions and star formation activities within the Galaxy, and lays a foundation for future investigations of Galactic structure and the role of masers in tracing star formation.

Figure 1. Face-on view of the Milky Way (from the north Galactic pole) showing the distribution of ammonia-observed sources matched with the Hi-GAL 360 catalog. Spiral arms are adapted from Reid et al. (2019). Marker sizes reflect ammonia column densities; arm associations are indicated by color. Red dashed circles mark the 2–8 kpc distance-limited sample.

Figure 2. Face-on view of the Milky Way (from the north Galactic pole) showing the distribution of ammonia-observed sources matched with the Hi-GAL 360 catalog. Spiral arms are adapted from Reid et al. (2019). Marker sizes reflect ammonia column densities; arm associations are indicated by color. Red dashed circles mark the 2–8 kpc distance-limited sample.Correlations between Galactocentric distance and ammonia properties for sources within 2–8 kpc: (left) log of total NH₃ column density, (rigth) gas kinetic temperature. Points are colored by spiral arm association. Best-fit lines and correlation coefficients are indicated in each panel.