# Molecular Gas Dominated 50 kpc Ram Pressure Stripped Tail of the Coma Galaxy D100

## TL;DR

This study reports the discovery of a 50 kpc molecular gas tail in galaxy D100 within the Coma cluster, revealing that molecular gas can dominate ram pressure stripped tails and highlighting phase separation and dynamic effects.

## Contribution

It provides the first detailed measurement of molecular gas in a long ram pressure stripped tail, suggesting molecularization is common in cluster environments.

## Key findings

- Molecular gas mass in the tail is about 10^9 solar masses.
- A velocity gradient indicates phase separation due to ram pressure.
- Molecular gas correlates with H-alpha brightness in stripped tails.

## Abstract

We have discovered large amounts of molecular gas, as traced by CO emission, in the ram pressure stripped gas tail of the Coma cluster galaxy D100 (GMP 2910), out to large distances of about 50 kpc. D100 has a 60 kpc long, strikingly narrow tail which is bright in X-rays and H{\alpha}. Our observations with the IRAM 30m telescope reveal in total ~ 10^9 M_sun of H_2 (assuming the standard CO-to-H_2 conversion) in several regions along the tail, thus indicating that molecular gas may dominate its mass. Along the tail we measure a smooth gradient in the radial velocity of the CO emission that is offset to lower values from the more diffuse H{\alpha} gas velocities. Such a dynamic separation of phases may be due to their differential acceleration by ram pressure. D100 is likely being stripped at a high orbital velocity >2200 km/s by (nearly) peak ram pressure. Combined effects of ICM viscosity and magnetic fields may be important for the evolution of the stripped ISM. We propose D100 has reached a continuous mode of stripping of dense gas remaining in its nuclear region. D100 is the second known case of an abundant molecular stripped-gas tail, suggesting that conditions in the ICM at the centers of galaxy clusters may be favorable for molecularization. From comparison with other galaxies, we find there is a good correlation between the CO flux and the H{\alpha} surface brightness in ram pressure stripped gas tails, over about 2 dex.