# ALMA CO Clouds and Young Star Complexes in the Interacting Galaxies IC 2163 and NGC 2207

## TL;DR

This study uses ALMA CO observations to analyze molecular clouds and star-forming regions in interacting galaxies IC 2163 and NGC 2207, revealing cloud properties, mass functions, and star formation activity related to galactic interactions.

## Contribution

First detailed comparison of molecular cloud properties and star complexes in interacting galaxies using ALMA and HST data, highlighting differences in cloud mass functions and star formation.

## Key findings

- Half of CO mass in 249 clouds >4x10^5 solar masses
- Similar power-law slope of -0.7 for cloud and star complex mass functions in IC 2163
- Maximum age of star complexes in IC 2163's shock front is about 200 Myr

## Abstract

ALMA observations of CO(1-0) emission in the interacting galaxies IC 2163 and NGC 2207 are used to determine the properties of molecular clouds and their association with star-forming regions observed with the Hubble Space Telescope. Half of the CO mass is in 249 clouds each more massive than 4.0x10^5Mo. The mass distribution functions for the CO clouds and star complexes in a galactic-scale shock front in IC 2163 both have a slope on a log-log plot of -0.7, similar to what is observed in Milky Way clouds. The molecular cloud mass function is steeper in NGC 2207. The CO distribution in NGC 2207 also includes a nuclear ring, a mini-bar, and a mini-starburst region that dominates the 24micron, radio, and Halpha emission in both galaxies. The ratio of the sum of the masses of star complexes younger than 30 Myr to the associated molecular cloud masses is ~4%. The maximum age of star complexes in the galactic-scale shock front in IC 2163 is about 200 Myr, the same as the interaction time of the two galaxies, suggesting the destruction of older complexes in the eyelids.