%0 Generic %1 heintz2021measuring %A Heintz, Kasper E. %A Watson, Darach %A Oesch, Pascal %A Narayanan, Desika %A Madden, Suzanne C. %D 2021 %K library %T Measuring the HI content of individual galaxies out to the epoch of reionization with CII %U http://arxiv.org/abs/2108.13442 %X The HI gas content is a key ingredient in galaxy evolution, the study of which has been limited to moderate cosmological distances for individual galaxies due to the weakness of the hyperfine HI 21-cm transition. Here we present a new approach that allows us to infer the HI gas mass $M_HI$ of individual galaxies up to $z6$, based on a direct measurement of the CII-to-HI conversion factor in star-forming galaxies at $z2$ using $\gamma$-ray burst afterglows. By compiling recent CII-158 $\mu$m emission line measurements we quantify the evolution of the HI content in galaxies through cosmic time. We find that the HI mass starts to exceed the stellar mass $M_\star$ at $z1$, and increases as a function of redshift. The HI fraction of the total baryonic mass increases from around $20\%$ at $z = 0$ to about $60\%$ at $z6$. We further uncover a universal relation between the HI gas fraction $M_HI/M_\star$ and the gas-phase metallicity, which seems to hold from $z6$ to $z=0$. The majority of galaxies at $z>2$ are observed to have HI depletion times, $t_dep,HI = M_HI/SFR$, less than $2$ Gyr, substantially shorter than for $z0$ galaxies. Finally, we use the CII-to-HI conversion factor to determine the cosmic mass density of HI in galaxies, $\rho_HI$, at three distinct epochs: $z\approx 0$, $z2$, and $z4-6$. These measurements are consistent with previous estimates based on 21-cm HI observations in the local Universe and with damped Lyman-$\alpha$ absorbers (DLAs) at $z2$, suggesting an overall decrease by a factor of $5$ in $\rho_HI(z)$ from the end of the reionization epoch to the present.

@misc{heintz2021measuring, abstract = {The HI gas content is a key ingredient in galaxy evolution, the study of which has been limited to moderate cosmological distances for individual galaxies due to the weakness of the hyperfine HI 21-cm transition. Here we present a new approach that allows us to infer the HI gas mass $M_{\rm HI}$ of individual galaxies up to $z\approx 6$, based on a direct measurement of the [CII]-to-HI conversion factor in star-forming galaxies at $z\gtrsim 2$ using $\gamma$-ray burst afterglows. By compiling recent [CII]-158 $\mu$m emission line measurements we quantify the evolution of the HI content in galaxies through cosmic time. We find that the HI mass starts to exceed the stellar mass $M_\star$ at $z\gtrsim 1$, and increases as a function of redshift. The HI fraction of the total baryonic mass increases from around $20\%$ at $z = 0$ to about $60\%$ at $z\sim 6$. We further uncover a universal relation between the HI gas fraction $M_{\rm HI}/M_\star$ and the gas-phase metallicity, which seems to hold from $z\approx 6$ to $z=0$. The majority of galaxies at $z>2$ are observed to have HI depletion times, $t_{\rm dep,HI} = M_{\rm HI}/{\rm SFR}$, less than $\approx 2$ Gyr, substantially shorter than for $z\sim 0$ galaxies. Finally, we use the [CII]-to-HI conversion factor to determine the cosmic mass density of HI in galaxies, $\rho_{\rm HI}$, at three distinct epochs: $z\approx 0$, $z\approx 2$, and $z\sim 4-6$. These measurements are consistent with previous estimates based on 21-cm HI observations in the local Universe and with damped Lyman-$\alpha$ absorbers (DLAs) at $z\gtrsim 2$, suggesting an overall decrease by a factor of $\approx 5$ in $\rho_{\rm HI}(z)$ from the end of the reionization epoch to the present.}, added-at = {2021-09-01T09:53:28.000+0200}, author = {Heintz, Kasper E. and Watson, Darach and Oesch, Pascal and Narayanan, Desika and Madden, Suzanne C.}, biburl = {https://www.bibsonomy.org/bibtex/2585b7675bb05a018ab5ade7a97f2b6b8/gpkulkarni}, description = {Measuring the HI content of individual galaxies out to the epoch of reionization with [CII]}, interhash = {6a6cf4a574f952618af718fa9469ab27}, intrahash = {585b7675bb05a018ab5ade7a97f2b6b8}, keywords = {library}, note = {cite arxiv:2108.13442Comment: Accepted for publication in ApJ}, timestamp = {2021-09-01T09:53:28.000+0200}, title = {Measuring the HI content of individual galaxies out to the epoch of reionization with [CII]}, url = {http://arxiv.org/abs/2108.13442}, year = 2021 }