2025ApJ...988...36B

We present a comprehensive study of formaldehyde (H₂CO) absorption and radio recombination line (H_110α) emission in 215 molecular clouds from the Bolocam Galactic Plane Survey, observed using the Nanshan 25 m radio telescope. H₂CO was detected in 88 sources (40.93%) with 59 being new detections, while H_110α emission was found in only 11 sources (5.12%), all coincident with H₂CO absorption. There exists a correlation of H₂CO fluxes with millimeter fluxes below a 3 Jy threshold and an increased dispersion above it, suggesting the sub-cosmic microwave background cooling of H₂CO. Cross-matching with kinematic distance catalogs revealed H₂CO spanning galactocentric distances from 0.216 to 10.769 kpc, with column densities ranging from 7.82 × 10¹¹ to 6.69 × 10¹⁴ cm^–2. A significant inverse correlation was observed between H₂CO detection fraction and galactocentric distance, suggesting enhanced star-forming activity closer to the Galactic Center. These findings challenge traditional Galactic Habitable Zone (GHZ) models by demonstrating the presence of biogenic precursors in the inner Galaxy, shielded within dense molecular clouds. Our results underscore the importance of incorporating chemical tracers such as H₂CO, alongside physical constraints to refine the boundaries of the GHZ and advance the research of prebiotic chemistry in the Milky Way.