Spatially Resolved Comparison of SFRs from UV and Hα in GASP Gas-stripped Galaxies

Abstract Star formation rates (SFRs) in galaxies offer a view of various physical processes across them, and are measured using various tracers, such as H α and ultraviolet (UV). Different physical mechanisms can affect H α and UV emission, resulting in a discrepancy in the corresponding SFR estimates (ΔSFR). We investigate the effects of ram pressure on the SFR measurements and ΔSFR across five galaxies from the GASP survey caught in the late stages of gas stripping due to ram pressure. We probe spatially resolved ΔSFR at pixel scales of 0.5 kpc, and compare disks to tails and regions dominated by the dense gas to diffuse ionized gas (DIG) regions. The regions dominated by dense gas show similar SFR values for UV and H α tracers, while the regions dominated by the DIG show up to 0.5 dex higher SFR(UV). There is a large galaxy-by-galaxy variation in ΔSFR, with no difference between the disks and the tails. We discuss the potential causes of variations in ΔSFR between the dense gas and DIG areas. We conclude that the dominant cause of discrepancy are recent variations in star formation histories, where star formation recently dropped in the DIG-dominated regions leading to changes in ΔSFR. The areal coverage of the tracers shows areas with H α and no UV emission; these areas have LINER-like emission (excess in [O i λ 6300]/H α line ratio), indicating that they are ionized by processes other than star formation.