We study galaxies undergoing ram pressure stripping in the Virgo cluster to examine whether we can identify any discernible trend in their star formation activity. We first use 48 galaxies undergoing different stages of stripping based on Hi morphology, Hi deficiency, and relative extent to the stellar disk, from the VIVA survey. We then employ a new scheme for galaxy classification which combines Hi mass fractions and locations in projected phase space, resulting in a new sample of 365 galaxies. We utilize a variety of star formation tracers, which include g - r, WISE [3.4]-[12] colors, and starburstiness that are defined by stellar mass and star formation rates to compare the star formation activity of galaxies at different stripping stages. We find no clear evidence for enhancement in the integrated star formation activity of galaxies undergoing early to active stripping. We are instead able to capture the overall quenching of star formation activity with increasing degree of ram pressure stripping, in agreement with previous studies. Our results suggest that if there is any ram pressure stripping induced enhancement, it is at best locally modest, and galaxies undergoing enhancement make up a small fraction of the total sample. Our results also indicate that it is possible to trace galaxies at different stages of stripping with the combination of Hi gas content and location in projected phase space, which can be extended to other galaxy clusters that lack high-resolution Hi imaging.

We performed systematic observations of the Hi Brα line (4.05 μm) in 51 nearby (z<0.3) ultraluminous infrared galaxies (ULIRGs), using AKARI near-infrared spectroscopy. The Brα line is predicted to be the brightest among the Hi recombination lines in ULIRGs with visual extinction higher than 15 mag. We detected the Brα line in 33 ULIRGs. In these galaxies, the relative contribution of starburst to the total infrared luminosity (LIR) is estimated on the basis of the ratio of the Brα line luminosity (LBrα) to LIR. The mean LBrα/LIR ratio in LINERs or Seyferts is significantly lower (~50%) than that in Hii galaxies. This result indicates that active galactic nuclei contribute signicantly (~50%) to LIR in LINERs, as well as Seyferts. We also estimate the absolute contribution of starburst to LIR using the ratio of star formation rates (SFRs) derived from LBrα (SFRBrα) and those needed to explain LIR (SFRIR). The mean SFRBrα/SFRIR ratio is only 0.33 even in Hii galaxies, where starburst is supposed to dominate the luminosity. We attribute this apparently low SFRBrα/SFRIR ratio to the absorption of ionizing photons by dust within Hii regions.