MUSE sneaks a peek at extreme ram-pressure stripping events. II. The physical properties of the gas tail of ESO137-001

TL;DR

This study uses spatially-resolved spectroscopy to analyze the physical properties of the gas tail of ESO137-001, revealing shock signatures, photoionized regions, and in situ star formation within the ram-pressure stripped tail.

Contribution

It provides detailed spectroscopic analysis of the gas tail of ESO137-001, highlighting the presence of shocks, photoionized gas, and in situ star formation, which advances understanding of ram-pressure stripping effects.

Findings

Detection of shock-like emission line ratios suggesting turbulent gas

Identification of HII regions with typical properties within the tail

Evidence for in situ formation of star-forming regions in the stripped gas

Abstract

We present a study of the physical properties of the disc and tail of ESO137-001, a galaxy suffering from extreme ram-pressure stripping during its infall into the Norma cluster. With sensitive and spatially-resolved MUSE spectroscopy, we analyse the emission line diagnostics in the tail of ESO137-001, finding high values of [NII]/H$\alpha$ and [OI]/H$\alpha$ that are suggestive of the presence of shocks in turbulent gas. However, the observed line ratios are not as strong as commonly seen in pure shock heating models, suggesting that other emission mechanisms may contribute to the observed emission. Indeed, part of the observed emission, particularly at close separations from the galaxy disc, may originate from recombination of photoionised gas stripped from the main body of ESO137-001. We also identify a large number of bright compact knots within in the tail, with line ratios characteristic of HII regions. These HII regions, despite residing in a stripped gas tail, have quite typical line ratios, densities, temperatures, and metallicity ($\sim0.7$ solar). The majority of these HII regions are embedded within diffuse gas from the tail, which is dynamically cool ($\sigma \sim 25-50\ \rm{km\ s^{-1}}$ ). This fact, together with a lack of appreciable gradients in age and metallicity, suggests that these HII regions formed in situ. While our analysis represents a first attempt to characterise the rich physics of the ESO137-001 tail, future work is needed to address the importance of other mechanisms, such as thermal conduction and magneto hydrodynamic waves, in powering the emission in the tail.