New HI scaling relations to probe the HI content of galaxies via global HI-deficiency maps

We present new multiwavelength scaling relations between the neutral hydrogen content (H I) and the stellar properties of nearby galaxies selected from the HI Parkes All-Sky Survey (HIPASS). We use these new scaling relations to investigate the environmental dependence of the HI content of galaxies. We find that galaxies in high-density environments tend to have on average less HI than galaxies with the same stellar mass in low-density environments. Our new HI scaling relations allow us to identify individual galaxies, as well as group/cluster environments, that have an 'anomalous' HI content. We map the global distribution of HI-deficient and HI-excess galaxies on the sky and compare it to the large-scale structure of galaxies. We find galaxy clusters to be HI deficient, and we identify that the regions surrounding clusters tend to beHI excess. Finally, we demonstrate the potential of using HI scaling relations to predict future HI surveys based on an optical redshift survey. We apply our scaling relations to 16 709 galaxies in the 6dF Galaxy Survey that lie in the HIPASS volume and compare our predictions to the measurements. We find that scaling relations are a good method to estimate the outcome of HI surveys.