Temperature Evolution of Molecular Clouds in the Central Molecular Zone

TL;DR

This study tracks how the gas temperature in molecular clouds near the Galactic Center evolves over time, supporting the idea that pericenter passage triggers gravitational collapse, based on ammonia temperature maps and dynamical models.

Contribution

It provides the first detailed time-dependent analysis of gas temperature evolution in CMZ molecular clouds using ammonia maps and dynamical modeling.

Findings

Gas temperatures increase with time before and after pericenter passage.

Pericenter passage likely triggers gravitational collapse.

Other cloud properties show no clear time dependence.

Abstract

We infer the absolute time dependence of kinematic gas temperature along a proposed orbit of molecular clouds in the Central Molecular Zone (CMZ) of the Galactic Center (GC). Ammonia gas temperature maps are one of the results of the "Survey of Water and Ammonia in the Galactic Center" (SWAG, PI: J. Ott); the dynamical model of molecular clouds in the CMZ was taken from Kruijssen et al. (2015). We find that gas temperatures increase as a function of time in both regimes before and after the cloud passes pericenter on its orbit in the GC potential. This is consistent with the recent proposal that pericenter passage triggers gravitational collapse. Other investigated quantities (line width, column density, opacity) show no strong sign of time dependence but are likely dominated by cloud-to-cloud variations.