<i>JWST</i> PRIMER: a deep <i>JWST</i> study of all ALMA-detected galaxies in PRIMER COSMOS – dust-obscured star formation history back to <i>z</i> ≃ 7

ABSTRACT We use deep NIRCam and MIRI imaging from the James Webb Space Telescope (JWST) PRIMER survey to study the properties of ALMA-detected (sub)mm sources in the COSMOS field, with the aim of defining the cosmic history of dust-enshrouded star formation. The wealth of ALMA data in this field enabled us to isolate a robust sample of 128 (sub)mm sources within the 175 arcmin$^2$ PRIMER COSMOS survey footprint, spanning two decades in (sub)mm flux density. The JWST imaging is deep and red enough to reveal secure galaxy counterparts for all of these sources. This 100 per cent identification completeness is accompanied by a high level of redshift completeness: 52 per cent of the sources have spectroscopic redshifts, and this has enabled us to refine the photometric redshifts for the remaining galaxies. Armed with robust redshift information, we calculate the star formation rates (SFRs) and stellar masses ($M_*$) of all 128 ALMA-detected galaxies, and place them in the context of other galaxies in the field. We find that the vast majority of star formation is dust-enshrouded in all of the ALMA-detected galaxies, with SFR ranging from $\simeq 1000\, {\rm {\rm M}_{\odot }\, yr^{-1}}$ down to $\simeq 20\, {\rm {\rm M}_{\odot }\, yr^{-1}}$. We also find that virtually all (126/128) have high stellar masses, $M_* &amp;gt; 10^{10}\, {\rm {\rm M}_{\odot }}$, independent of redshift. The unusually high quality of our sample enables us to make a robust estimate of the contribution of the ALMA-detected galaxies to cosmic SFR density, $\rho _{\rm SFR}$. The existing ALMA imaging only covers $&amp;lt; 20$ per cent of the PRIMER COSMOS area, but based on our knowledge of all other massive galaxies in the field, we produce a completeness-corrected estimate of dust-enshrouded $\rho _{\rm SFR}$. This confirms that ultraviolet-visible star formation dominates $\rho _{\rm SFR}$ at $z &amp;gt; 4$, but also indicates that dust-enshrouded star formation still makes a contribution of $\simeq 20$ per cent at $z \simeq 8$, and $\simeq 5$ per cent at $z \simeq 10$.