Time-averaged chemical evolution of the studied species across all second stage models, as defined in Tab. 2. Line styles and shading follow those in Fig. 1. Only gas-phase abundances above the detectable threshold (X > 10−14) are considered. Changes in abundance, including both enhancement and depletion, generally follow the timescales seen in the average temperature profiles (see Fig. 1). In models of protostellar objects, the species that most frequently dominates over the others is HCN, whereas in shocks, CH3OH is the most dominant during the shock phase, while SiO takes over in the post-shock phase. — astro-ph.GA
(Abridged) The Central Molecular Zone (CMZ) of the Milky Way exhibits extreme conditions, including high gas densities, elevated temperatures, enhanced cosmic-ray ionization rates, and large-scale dynamics. Large-scale molecular surveys reveal increasing chemical and physical complexity in the CMZ.
A key step to interpreting the molecular richness found in the CMZ is to build chemical templates tailored to its diverse conditions. The combined impact of high ionization, elevated temperatures, and dense gas remains insufficiently explored for observable tracers.
In this study, we utilized UCLCHEM, a gas-grain time-dependent chemical model, to link physical conditions with their corresponding molecular signatures and identify key tracers of temperature, density, ionization, and shock activity.
We ran a grid of models of shocks and protostellar objects representative of typical CMZ conditions, focusing on twenty-four species, including complex organic molecules. Shocked and protostellar environments show distinct evolutionary timescales (≲104 vs. ≳104 years), with 300 K emerging as a key temperature threshold for chemical differentiation.
We find that cosmic-ray ionization and temperature are the main drivers of chemical trends. HCO+, H2CO, and CH3SH trace ionization, while HCO, HCO+, CH3SH, CH3NCO, and HCOOCH3 show consistent abundance contrasts between shocks and protostellar regions over similar temperature ranges.
While our models underpredict some complex organics in shocks, they reproduce observed trends for most species, supporting scenarios involving recurring shocks in Galactic Center clouds and enhanced ionization towards Sgr B2(N2). Future work should assess the role of shock recurrence and metallicity in shaping chemistry.
Katarzyna M. Dutkowska, Gijs Vermariën, Serena Viti, Izaskun Jiménez-Serra, Laura Colzi, Laura A. Busch, Víctor M. Rivilla, Elisabeth A.C. Mills, Sergio Martín, Christian Henkel, Pablo García, Xing Lu, Miriam G. Santa-Maria, Jairo Armijos-Abendaño, Yue Hu, Jürgen Ott, Kai Smith, Fengwei Xu, Shaoshan Zeng, Álvaro Sánchez-Monge, Anika Schmiedeke, Jaime E. Pineda, Steven N. Longmore, Thanja Lamberts
Comments: Accepted for publication in A&A. 23 pages, 12 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2508.10759 [astro-ph.GA) (or arXiv:2508.10759v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2508.10759
Focus to learn more
Submission history
From: Katarzyna M. Dutkowska
[v1] Thu, 14 Aug 2025 15:43:37 UTC (1,226 KB)
https://arxiv.org/abs/2508.10759
Astrobiology, Astrochemistry,