# Cold Molecular Gas Along the Merger Sequence in Local Luminous Infrared Galaxies

## TL;DR

This study systematically investigates the distribution and size of molecular gas in local luminous infrared galaxies at different merger stages, revealing gas inflow toward the center during mergers.

## Contribution

It introduces a new method to estimate CO gas distribution sizes and applies it to a large sample, providing insights into gas dynamics during galaxy mergers.

## Key findings

- CO size decreases from early to late merger stages
- Molecular gas mass remains constant in central regions during mergers
- Gas inflows replenish central gas, supporting starburst activity

## Abstract

We present an initial result from the 12CO (J=1-0) survey of 79 galaxies in 62 local luminous and ultra-luminous infrared galaxy (LIRG and ULIRG) systems obtained using the 45 m telescope at the Nobeyama Radio Observatory. This is the systematic 12CO (J=1-0) survey of the Great Observatories All-sky LIRGs Survey (GOALS) sample. The molecular gas mass of the sample ranges 2.2 x 10^8 - 7.0 x 10^9 Msun within the central several kiloparsecs subtending 15" beam. A method to estimate a size of a CO gas distribution is introduced, which is combined with the total CO flux in the literature. The method is applied to a part of our sample and we find that the median CO radius is 1-4 kpc. From the early stage to the late stage of mergers, we find that the CO size decreases while the median value of the molecular gas mass in the central several kpc region is constant. Our results statistically support a scenario where molecular gas inflows towards the central region from the outer disk, to replenish gas consumed by starburst, and that such a process is common in merging LIRGs.