Illuminating the Dark Side of Cosmic Star Formation II. A second date with RS-NIRdark galaxies in COSMOS

TL;DR

This study investigates the role of dust-rich, radio-selected NIR-dark galaxies in the early universe's star formation history, expanding the sample size and refining photometric methods to better understand their contribution to cosmic star formation.

Contribution

It extends the sample of RS-NIRdark galaxies in COSMOS and develops improved photometric procedures for contaminated sources, enhancing understanding of their impact on cosmic star formation.

Findings

RS-NIRdark galaxies contribute 10-25% to the cosmic SFRD at 3<z<5.

Expanded sample from 197 to 272 objects in COSMOS.

Refined photometric methods for contaminated sources.

Abstract

About 12 billion years ago, the Universe was first experiencing light again after the dark ages, and galaxies filled the environment with stars, metals and dust. How efficient was this process? How fast did these primordial galaxies form stars and dust? We can answer these questions by tracing the Star Formation Rate Density (SFRD) back to its widely unknown high redshift tail, traditionally observed in the Near-InfraRed (NIR), Optical and UV bands. Thus, the objects with a high amount of dust were missing. We aim to fill this knowledge gap by studying Radio Selected NIR-dark (\textit{RS-NIRdark}) sources, i.e. sources not having a counterpart at UV-to-NIR wavelengths. We widen the sample by Talia et al. (2021) from 197 to 272 objects in the COSMic evolution Survey (COSMOS) field, including also photometrically contaminated sources, previously excluded. Another important step forward consists in the visual inspection of each source in the bands from u* to MIPS-24$\mu$m. According to their "environment" in the different bands, we are able to highlight different cases of study and calibrate an appropriate photometric procedure for the objects affected by confusion issues. We estimate that the contribution of RS-NIRdark to the Cosmic SFRD at 3$<$z$<$5 is $\sim$10--25$\%$ of that based on UV-selected galaxies.