GASP. XXII The molecular gas content of the JW100 jellyfish galaxy at z~0.05: does ram pressure promote molecular gas formation?

TL;DR

This study investigates the molecular gas content in the jellyfish galaxy JW100, revealing large amounts of molecular gas in the tail likely formed from stripped HI gas, and examines how ram pressure influences molecular gas formation.

Contribution

It provides detailed ALMA observations of JW100, showing that a significant fraction of molecular gas is newly formed in the tail due to ram-pressure stripping, a novel insight into galaxy evolution.

Findings

Large molecular gas mass (~2.5×10^10 M☉) in JW100, with 30% in the tail.

Molecular gas in the tail likely formed from stripped HI or condensed from diffuse gas.

Depletion time of 5-10 Gyr indicates low star formation efficiency.

Abstract

Within the GASP survey, aimed at studying the effect of the ram-pressure stripping on the star formation quenching in cluster galaxies, we analyze here ALMA observations of the jellyfish galaxy JW100. We find an unexpected large amount of molecular gas ($\sim 2.5 \times 10^{10} M_{\odot}$), 30\% of which is located in the stripped gas tail out to $\sim$35 kpc from the galaxy center. The overall kinematics of molecular gas is similar to the one shown by the ionized gas, but for clear signatures of double components along the stripping direction detected only out to 2 kpc from the disk. The line ratio $r_{21}$ has a clumpy distribution and in the tail can reach large values ($\geq 1$), while its average value is low (0.58 with a 0.15 dispersion). All these evidence strongly suggest that the molecular gas in the tail is newly born from stripped HI gas or newly condensed from stripped diffuse molecular gas. The analysis of interferometric data at different scales reveals that a significant fraction ($\sim 40\%$) of the molecular gas is extended over large scales ($\geq 8$ kpc) in the disk, and this fraction becomes predominant in the tail ($\sim 70\%$). By comparing the molecular gas surface density with the star formation rate surface density derived from the \Ha emission from MUSE data, we find that the depletion time on 1 kpc scale is particularly large ($5-10$ Gyr) both within the ram-pressure disturbed region in the stellar disk, and in the complexes along the tail.