Mapping the Universe in hydrogen deuteride

Hydrogen deuteride (HD) is prevalent in a wide variety of astrophysical environments, and measuring its large-scale distribution at different epochs can, in principle, provide information about the properties of these environments. In this paper we explore the prospects for accessing this distribution using line-intensity mapping of emission from the lowest rotational transition in HD, focusing on observations of the epoch of reionization (z similar to 6-10) and earlier. We find the signal from the epoch of reionization to be most promising, through cross correlations within existing [CII] intensity mapping surveys. While the signal we predict is out of reach for current-generation projects, planned future improvements should be able to detect reionization-era HD without any additional observations, and would help to constrain the properties of the star-forming galaxies thought to play a key role in reionization. We also investigate several avenues for measuring HD during cosmic dawn (z similar to 10-30), a period in which HD could provide one of the only complementary observables to 21 cm intensity maps. We conclude that existing and planned facilities are poorly matched to the specifications desirable for a significant detection, though such a measurement may be achievable with sustained future effort. Finally, we explain why HD intensity mapping of the intergalactic medium during the cosmic dark ages (z greater than or similar to 30) appears to be out of reach of any conceivable experiment.

Automated summary

This paper explores the prospects of accessing the distribution of hydrogen deuteride (HD) using line-intensity mapping and discusses its observations during the epoch of reionization and cosmic dawn. The findings suggest that the signal from the epoch of reionization is the most promising but currently out of reach for existing projects. However, future improvements could detect reionization-era HD. The measurement of HD during cosmic dawn is challenging due to poorly matched facilities, but sustained future effort may achieve significant detection.