Near-identical star formation rate densities from H$\hat{I}\pm$ and FUV at redshift zero

Abstract

For the first time both H$\hat{I}\pm$ and far-ultraviolet (FUV) observations from an HI-selected sample are used to determine the dust-corrected star formation rate density (SFRD: $\dot{\ddot{I}}$) in the local Universe. Applying the two star formation rate indicators on 294 local galaxies we determine log($\dot{\ddot{I}}$${}_{H\hat{I}\pm })=-1.68{}_{-0.05}^{+0.13}$ [M${}_{\odot }$ yr${}^{-1}$ Mpc${}^{-3}]$ and log($\dot{\ddot{I}}{}_{FUV}$) $=-1.71{}_{-0.13}^{+0.12}$ [M${}_{\odot }$ yr${}^{-1}$ Mpc${}^{-3}]$. These values are derived from scaling H$\hat{I}\pm$ and FUV observations to the HI mass function. Galaxies were selected to uniformly sample the full HI mass (M${}_{HI}$) range of the HI Parkes All-Sky Survey (M${}_{HI}\sim 10^7$ to $\sim 10^{10.7}$ M${}_{\odot }$). The approach leads to relatively larger sampling of dwarf galaxies compared to optically-selected surveys. The low HI mass, low luminosity and low surface brightness galaxy populations have, on average, lower H$\hat{I}\pm$/FUV flux ratios than the remaining galaxy populations, consistent with the earlier results of Meurer. The near-identical H$\hat{I}\pm$- and FUV-derived SFRD values arise with the low H$\hat{I}\pm$/FUV flux ratios of some galaxies being offset by enhanced H$\hat{I}\pm$ from the brightest and high mass galaxy populations. Our findings confirm the necessity to fully sample the HI mass range for a complete census of local star formation to include lower stellar mass galaxies which dominate the local Universe.

17 pages, 7 figures