The Bluedisk survey: thickness of HI layers in gas rich spiral galaxies

Abstract: We use an empirical relation to measure the HI scale height of relatively HI rich galaxies using 21-cm observations. The galaxies were selected from the BLUEDISK, THINGS and VIVA surveys. We aim to compare the thickness of the HI layer of unusually HI rich with normal spiral galaxies and find any correlation between the HI scale height with other galaxies properties. We found that on average the unusually HI rich galaxies have similar HI disk thickness to the control sample and the galaxies selected from the THINGS and VIVA surveys within their uncertainties. Our result also show that the average thickness of the neutral hydrogen inside the optical disk is correlated with the atomic gas fraction inside the optical disk with a scatter of ~ 0.22 dex. A correlation is also found between the HI scale height with the atomic-to-molecular gas ratio which indicates the link between star formation and the vertical distribution of HI which is consistent with previous studies. This new scaling relation between the HI scale height and atomic gas fraction will allow us to predict the HI scale height of a large number of galaxies but a larger sample is needed to decrease the scatter.