Ultra-Violet Imaging Telescope view of ram-pressure stripping in action: Star formation in the stripped gas of the GASP jellyfish galaxy JO201 in Abell 85

Abstract

Jellyfish are cluster galaxies that experience strong ram-pressure effects that strip their gas. Their H$\alpha$ images reveal ionized gas tails up to 100 kpc, which could be hosting ongoing star formation. Here we report the ultraviolet (UV) imaging observation of the jellyfish galaxy JO201 obtained at a spatial resolution $\sim$ 1.3 kpc. The intense burst of star formation happening in the tentacles is the focus of the present study. JO201 is the "UV-brightest cluster galaxy" in Abell 85 ($z \sim$ 0.056) with knots and streams of star formation in the ultraviolet. We identify star forming knots both in the stripped gas and in the galaxy disk and compare the UV features with the ones traced by H$\alpha$ emission. Overall, the two emissions remarkably correlate, both in the main body and along the tentacles. Similarly, also the star formation rates of individual knots derived from the extinction-corrected FUV emission agree with those derived from the H$\alpha$ emission and range from $\sim$ 0.01 -to- 2.07 $M_{\odot} \, yr^{-1}$. The integrated star formation rate from FUV flux is $\sim$ 15 $M_{\odot} \, yr^{-1}$. The unprecedented deep UV imaging study of the jellyfish galaxy JO201 shows clear signs of extraplanar star-formation activity due to a recent/ongoing gas stripping event.