ALMA reveals optically thin, highly excited CO gas in the jet-driven winds of the galaxy IC5063

TL;DR

ALMA observations show that molecular gas in the galaxy IC5063's jet-driven winds is highly excited and optically thin, indicating that such winds may be less massive but more detectable at high redshift than previously believed.

Contribution

This study provides the first evidence of highly excited, optically thin CO gas in galaxy winds, challenging previous assumptions about their mass and detectability.

Findings

Molecular gas in winds has CO(4-3)/CO(2-1) ratios between 5 and 11.

Excitation temperatures of 30-100 K are common in wind regions.

Mass of outflowing molecular gas is at least 2 million solar masses, lower than previous estimates.

Abstract

Using CO (4-3) and (2-1) Atacama Large Millimeter Array (ALMA) data, we prove that the molecular gas in the jet-driven winds of the galaxy IC5063 is more highly excited than the rest of the molecular gas in the disk of the same galaxy. On average, the CO(4-3)/CO(2-1) flux ratio is 1 for the disk and 5 for the jet accelerated or impacted gas. Spatially-resolved maps reveal that in regions associated with winds, the CO(4-3)/CO(2-1) flux ratio significantly exceeds the upper limit of 4 for optically thick gas. It frequently takes values between 5 and 11, and it occasionally further approaches the upper limit of 16 for optically thin gas. Excitation temperatures of 30-100 K are common for the molecules in these regions. If all of the outflowing molecular gas is optically thin, at 30-50 K, then its mass is 2*10^6 M_sun. This lower mass limit is an order of magnitude below the mass derived from the CO(2-1) flux in the case of optically thick gas. Molecular winds can thus be less massive, but more easily detectable at high z than they were previously thought to be.