Characterization of Two 2mm-detected Optically-Obscured Dusty Star-Forming Galaxies

TL;DR

This study characterizes two high-redshift, optically-obscured dusty star-forming galaxies from the MORA survey, revealing their physical properties and suggesting they are progenitors of massive quiescent galaxies at lower redshifts.

Contribution

The paper provides detailed analysis of two high-redshift OIR-dark DSFGs, including their physical properties and implications for galaxy evolution, which is a novel contribution to understanding obscured star formation in the early universe.

Findings

MORA-5 is a highly active starburst galaxy with SFR ~830 M_sun/yr.

MORA-9 has a more modest SFR of ~200 M_sun/yr.

Both galaxies are likely progenitors of massive quiescent galaxies at z~3-4.

Abstract

The 2mm Mapping Obscuration to Reionization with ALMA (MORA) Survey was designed to detect high redshift ($z\gtrsim4$), massive, dusty star-forming galaxies (DSFGs). Here we present two, likely high redshift sources, identified in the survey whose physical characteristics are consistent with a class of optical/near-infrared (OIR) invisible DSFGs found elsewhere in the literature. We first perform a rigorous analysis of all available photometric data to fit spectral energy distributions and estimate redshifts before deriving physical properties based on our findings. Our results suggest the two galaxies, called MORA-5 and MORA-9, represent two extremes of the "OIR-dark" class of DSFGs. MORA-5 ($z_{\rm phot}=4.3^{+1.5}_{-1.3}$) is a significantly more active starburst with a star-formation rate of 830$^{+340}_{-190}$M$_\odot$yr$^{-1}$ compared to MORA-9 ($z_{\rm phot}=4.3^{+1.3}_{-1.0}$) whose star-formation rate is a modest 200$^{+250}_{-60}$M$_\odot$yr$^{-1}$. Based on the stellar masses (M$_{\star}\approx10^{10-11}$M$_\odot$), space density ($n\sim(5\pm2)\times10^{-6}$Mpc$^{-3}$, which incorporates two other spectroscopically confirmed OIR-dark DSFGs in the MORA sample at $z=4.6$ and $z=5.9$), and gas depletion timescales ($<1$Gyr) of these sources, we find evidence supporting the theory that OIR-dark DSFGs are the progenitors of recently discovered $3<z<4$ massive quiescent galaxies.