# Extreme CO Isotopic Abundances in the ULIRG IRAS 13120-5453: An Extremely Young Starburst or Top-Heavy Initial Mass Function

## TL;DR

This study uses ALMA observations of multiple CO isotopologues in the ULIRG IRAS 13120-5453 to investigate its extreme isotopic abundances, suggesting a very young starburst or a top-heavy initial mass function as possible causes.

## Contribution

It provides detailed isotopic abundance measurements in IRAS 13120-5453, revealing unusual ratios that imply recent starburst activity or a top-heavy initial mass function.

## Key findings

- High $^{12}$CO/$^{13}$CO ratios exceeding 200 in the center.
- C$^{18}$O more abundant than $^{13}$CO in some regions.
- ISM enrichment consistent with a young starburst or top-heavy IMF.

## Abstract

We present ALMA $^{12}$CO (J=1-0, 3-2 and 6-5), $^{13}$CO (J=1-0) and C$^{18}$O (J=1-0) observations of the local Ultra Luminous Infrared Galaxy, IRAS 13120-5453 (dubbed "The Yo-yo"). The morphologies of the three isotopic species differ, where $^{13}$CO shows a hole in emission towards the center. We measure integrated brightness temperature line ratios of $^{12}$CO/$^{13}$CO $\geq$ 60 (exceeding 200) and $^{13}$CO/C$^{18}$O $\leq$ 1 in the central region. Assuming optical thin emission, C$^{18}$O is more abundant than $^{13}$CO in several regions. The abundances within the central 500 pc are consistent with enrichment of the ISM via a young starburst ($<$7Myr), a top-heavy initial mass function or a combination of both.