ALMA-JELLY I: High Resolution CO(2-1) Observations of Ongoing Ram Pressure Stripping in NGC 4858 Reveal Asymmetrical Gas Tail Formation and Fallback

TL;DR

This study uses high-resolution ALMA CO(2-1) observations combined with optical data to analyze ram pressure stripping effects in galaxy NGC 4858, revealing asymmetrical gas tails, fallback gas, and the influence of torques in inclined interactions.

Contribution

It provides detailed observational evidence of inclined ram pressure stripping effects, including gas fallback and asymmetric tail formation, supported by comparison with advanced simulations.

Findings

Detection of asymmetric inner gas tail.

Identification of gas fallback phenomena.

Evidence of torques driving inward gas movement.

Abstract

We present new CO(2-1) observations (resolution $\sim1" = 460$pc) of the Coma cluster jellyfish galaxy NGC 4858 obtained from the ALMA-JELLY large program. Analyzing this data alongside complimentary Subaru H$\alpha$ and HST (F600LP / F350LP) observations, we find numerous structural and kinematic features indicative of the effects from strong, inclined ram pressure, including an asymmetric inner gas tail. We estimate a highly-inclined disk-wind angle of $\phi_{DW} = 75^{+10}_{-27}$. By subtracting a simple circular velocity model, we find (1): gas clumps that are being accelerated by ram pressure, and (2): signatures of gas clumps that had been previously pushed out of the disk but are now falling inwards. We also discuss head-tail morphologies in star complexes within the stellar disk that appear to be RPS-influenced. Lastly, we compare this galaxy to state-of-the-art galaxy ``wind tunnel'' simulations. We find that this galaxy is one of the best nearby examples of strong and inclined ram pressure gas stripping, and of gas that is perturbed by ram pressure but not fully stripped and falls back. We emphasize the importance of torques due to ram pressure in highly-inclined interactions, which help drive gas inwards on the side rotating against the wind, contributing to the formation of asymmetric inner RPS tails.