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

TL;DR

This study measures the thickness of HI layers in gas-rich spiral galaxies using 21-cm observations, finding correlations with gas fractions and star formation indicators, and introduces a new scaling relation for predicting HI scale height.

Contribution

It presents an empirical relation linking HI scale height with atomic gas fraction and star formation indicators, enabling predictions for large galaxy samples.

Findings

HI disk thickness is similar in HI-rich and normal galaxies within uncertainties.

HI scale height correlates with atomic gas fraction inside the optical disk.

A link exists between HI scale height and the atomic-to-molecular gas ratio.

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.