A dominant population of optically invisible massive galaxies in the early Universe

Understand

Our current knowledge of cosmic star-formation history during the first two billion years (corresponding to redshift z >3) is mainly based on galaxies identified in rest-frame ultraviolet light.

• However, this population of galaxies is known to under-represent the most massive galaxies, which have rich dust content and/or old stellar populations.
• This raises the questions of the true abundance of massive galaxies and the star-formation-rate density in the early universe.
• Although several massive galaxies that are invisible in the ultraviolet have recently been confirmed at early epochs, most of them are extreme starbursts with star-formation rates exceeding 1000 solar masses per year, suggesting that they are unlikely to represent the bulk population of massive galaxies.