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

Abstract

We present a study of the physical properties of the disc and tail of\nESO137-001, a galaxy suffering from extreme ram-pressure stripping during its\ninfall into the Norma cluster. With sensitive and spatially-resolved MUSE\nspectroscopy, we analyse the emission line diagnostics in the tail of\nESO137-001, finding high values of [NII]/H$\\alpha$ and [OI]/H$\\alpha$ that are\nsuggestive of the presence of shocks in turbulent gas. However, the observed\nline ratios are not as strong as commonly seen in pure shock heating models,\nsuggesting that other emission mechanisms may contribute to the observed\nemission. Indeed, part of the observed emission, particularly at close\nseparations from the galaxy disc, may originate from recombination of\nphotoionised gas stripped from the main body of ESO137-001. We also identify a\nlarge number of bright compact knots within in the tail, with line ratios\ncharacteristic of HII regions. These HII regions, despite residing in a\nstripped gas tail, have quite typical line ratios, densities, temperatures, and\nmetallicity ($\\sim0.7$ solar). The majority of these HII regions are embedded\nwithin diffuse gas from the tail, which is dynamically cool ($\\sigma \\sim\n25-50\\ \\rm{km\\ s^{-1}}$ ). This fact, together with a lack of appreciable\ngradients in age and metallicity, suggests that these HII regions formed in\nsitu. While our analysis represents a first attempt to characterise the rich\nphysics of the ESO137-001 tail, future work is needed to address the importance\nof other mechanisms, such as thermal conduction and magneto hydrodynamic waves,\nin powering the emission in the tail.\n