Rethinking Habitability using Biogenic Precursors: Formaldehyde in Millimeter Molecular Clouds of the Inner Galaxy

We present a comprehensive study of formaldehyde (H₂CO) absorption and radio recombination line (H110a) emission in 215 molecular clouds from the Bolocam Galactic Plane Survey (BGPS), observed using the Nanshan 25-m radio telescope.

H₂CO was detected in 88 sources (40.93 percent) with 59 being new detections, while H110a emission was found in only 11 sources (5.12 percent), 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-CMB 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 x 10^11 to 6.69 x 10^14 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.

Location of BGPS-H₂CO sources in the Milky Way based on cross-matching with MD17. The yellow spot denotes the location of the Sun, while the green annuli shows the traditional GHZ between 7 and 9 kpc from the Galactic Center. Credit (Milky Way Background): NASA/JPL-Caltech/R. Hurt (SSC/Caltech). — astro-ph.GA

Our results underscore the importance of incorporating chemical tracers like H₂CO, alongside physical constraints, to refine the boundaries of the GHZ and advance the research of prebiotic chemistry in the Milky Way.

Nursyazela Badrina Baharin, Affan Adly Nazri, Zulfazli Rosli, Zamri Zainal Abidin, Hairul Anuar Tajuddin, Jarken Esimbek, Dalei Li, Xiaoke Tang

Comments: Accepted to The Astrophysical Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2505.15027 [astro-ph.GA] (or arXiv:2505.15027v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2505.15027
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Related DOI:
https://doi.org/10.3847/1538-4357/add691
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Submission history
From: Nursyazela Badrina
[v1] Wed, 21 May 2025 02:20:02 UTC (6,913 KB)
https://arxiv.org/abs/2505.15027
Astrobiology, Astrochemistry,