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

Sinclaire M Manning ,D L Clements ,J A Hodge ,Ezequiel Treister ,M Talia ,Jaclyn B Champagne ,Christopher C Hayward ,Jorge A Zavala ,Patrick Drew ,K K Knudsen ,Jeyhan S Kartaltepe ,G Magdis ,D B Sanders ,Seiji Fujimoto ,Justin Spilker ,Johannes Staguhn ,Anton M Koekemoer ,Allison Man ,Steven L Finkelstein ,M Aravena ,Kartik Sheth ,O Ilbert ,Caitlin M Casey ,M Béthermin ,Min S Yun

doi:10.3847/1538-4357/ac366a

Abstract

Abstract The 2 mm Mapping Obscuration to Reionization with ALMA (MORA) Survey was designed to detect high-redshift (z ≳ 4), 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 phot = 4.3 − 1.3 + 1.5 ) is a significantly more active starburst with a star formation rate (SFR) of 830 − 190 + 340 M ⊙ yr−1 compared to MORA-9 ( z phot = 4.3 − 1.0 + 1.3 ), whose SFR is a modest 200 − 60 + 250 M ⊙ yr−1. Based on the stellar masses (M ⋆ ≈ 1010−11 M ⊙), space density (n ∼ (5 ± 2) × 10−6 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.

Highlights

Our current understanding of star formation and galaxy evolution within the first two billion years after the Big Bang is severely limited by a lack of infrared (IR) constraints and associated sample incompleteness at z > 4 (Gruppioni et al 2013; Casey, Narayanan, & Cooray 2014; Madau & Dickinson 2014; Casey et al 2018b)
The available Atacama Large Millimeter/submillimeter Array (ALMA) observations only offer a few narrow frequency ranges for molecular lines to be detected and a detection at these frequencies would be indicative of a z < 4 redshift solution, providing some evidence for our adopted estimates
We present photometric redshifts and physical characterization of Mapping Obscuration to Reionization with ALMA (MORA)-5 and MORA-9, two OIR-dark dusty star-forming galaxies (DSFGs) detected in the 2 mm MORA survey

Summary

Introduction

Our current understanding of star formation and galaxy evolution within the first two billion years after the Big Bang is severely limited by a lack of infrared (IR) constraints and associated sample incompleteness at z > 4 (Gruppioni et al 2013; Casey, Narayanan, & Cooray 2014; Madau & Dickinson 2014; Casey et al 2018b). The census of cosmic star formation out to the highest redshifts is biased towards unobscured star formation tracers, relying on rest-frame ultraviolet (UV) continuum measurements to seek out Lyman-break selected galaxies (LBGs). Knowing the prevalence of dust-obscured star formation is important at z > 4 (within the first 1.5 billion years of the Universe) when cosmic time becomes a significant constraint on the physical processes which produce the dust, metals, and stars observed in galaxies

Results

Discussion

Conclusion