Spatially resolved comparison of SFRs from UV and H$\alpha$ in GASP gas-stripped galaxies

TL;DR

This study compares star-formation rate measurements from UV and Hα tracers in gas-stripped galaxies, revealing spatial variations and the influence of recent star formation history and ionization processes.

Contribution

It provides a spatially resolved analysis of SFR discrepancies in ram pressure stripped galaxies, highlighting the role of recent star formation changes and ionization mechanisms.

Findings

Dense gas regions show consistent SFR from UV and Hα.

DIG regions exhibit higher SFR(UV) compared to Hα.

Variations in ΔSFR are galaxy-dependent and linked to recent star formation history.

Abstract

Star-formation rates (SFR) in galaxies offer a view of various physical processes across them and are measured using various tracers, such as H$\alpha$ and UV. Different physical mechanisms can affect H$\alpha$ and UV emission, resulting in a discrepancy in the corresponding SFR estimates ($\Delta SFR$). We investigate the effects of ram pressure on the SFR measurements and $\Delta SFR$ across 5 galaxies from the GASP survey caught in the late stages of gas stripping due to ram pressure. We probe spatially resolved $\Delta SFR$ 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$\alpha$ 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 $\Delta SFR$, with no difference between the disks and the tails. We discuss the potential causes of variations in $\Delta SFR$ between the dense gas and DIG areas. We conclude that the dominant cause of discrepancy is recent variations in star formation histories, where star formation recently dropped in the DIG-dominated regions leading to changes in $\Delta SFR$. The areal coverage of the tracers shows areas with H$\alpha$ and no UV emission; these areas have LINER-like emission (excess in $[OI\lambda\,6300]/H\alpha$ line ratio), indicating that they are ionized by processes other than star-formation.