The Cygnus-X region, as an important star-forming area within the Milky Way, has long been a focus of research concerning the physical conditions and dynamical evolution of its molecular cloud structures. 

In a recent study published in Monthly Notices of the Royal Astronomical Society , Ernar Imanaly, a PhD student from the star formation and evolution research group at the Xinjiang Astronomical Observatory of the Chinese Academy of Sciences, conducted deep observations of the 6-cm formaldehyde (H₂CO) absorption line and H110α recombination line toward the Cygnus-X region (∼9 deg²) using the NanShan 26-meter Radio Telescope. This work has produced the first detailed map of the formaldehyde excitation temperature field, offering fresh perspectives on star formation activities in this region.

The researchers developed an innovative method to estimate excitation temperatures using the 6-cm formaldehyde transition line. This approach not only validated the reliability of previous observational data obtained through hyperfine structure measurements but also enabled the creation of a more comprehensive map of the excitation temperature field.

The observations reveal a distinct north-south differentiation in the formaldehyde excitation temperature distribution across the Cygnus-X region. The northern area exhibits excitation temperatures ranging from 2.40 K to 4.16 K, while the southern region shows temperatures between 2.34 K and 3.88 K. This temperature gradient strongly correlates with the background radiation temperature distribution, suggesting that elevated background temperatures enhance the excitation of formaldehyde absorption transitions. This finding provides an alternative methodology for determing excitation temperatures in future studies. .

Furthermore, the ortho-H₂CO (1₁,₀–1₁,₁) transition demonstrates remarkable sensitivity to the physical environment of molecular clouds, revealing their internal conditions. The researchers determined that the optical depth of this transition ranges from 0.06 to 0.69 (mean 0.19), while the total column density varies from 0.10 × 10¹⁵ cm⁻² to 7.38 × 10¹⁶ cm⁻² (average ∼8.67 × 10¹⁵ cm⁻²). These parameters clearly delineate all star-forming activity regions within the Cygnus-X complex.

This work has produced the first systematic map of the formaldehyde excitation temperature field in the Cygnus-X region,  confirming that formaldehyde absorption lines serve as excellent tracers for identifying both current and future star-forming regions, while H110α emission effectively traces advanced stages. The combination of these tracers provides crucial insights for assessing the intensity and evolutionary stages of star formation processes, significantly advancing our understanding of evolutionary mechanisms in large-scale star-forming regions.

                                                                 The Excitation temperature distribution for two H₂CO velocity components towards the Cygnus X region