2 mm Observations and the Search for High-redshift Dusty Star-forming Galaxies

Abstract

Finding high-redshift (z ≫ 4) dusty star-forming galaxies is extremely challenging. It has recently been suggested that millimeter selections may be the best approach since the negative K-correction makes galaxies at a given far-infrared luminosity brighter at z ≳ 4 than those at z = 2–3. Here we analyze this issue using a deep Atacama Large Millimeter/submillimeter Array (ALMA) 2 mm sample obtained by targeting ALMA 870 μm priors (these priors were the result of targeting SCUBA-2 850 μm sources) in the GOODS-S. We construct prior-based 2 mm galaxy number counts and compare them with published blank field-based 2 mm counts, finding good agreement down to 0.2 mJy. Only a fraction of the current 2 mm extragalactic background light is resolved, and we estimate what observational depths may be needed to resolve it fully. By complementing the 2 mm ALMA data with a deep SCUBA-2 450 μm sample, we exploit the steep gradient with a redshift of the 2 mm–450 μm flux density ratio to estimate redshifts for those galaxies without spectroscopic or robust optical/near-infrared photometric redshifts. Our observations measure galaxies with star formation rates in excess of 250 M ⊙ yr−1. For these galaxies, the star formation rate densities fall by a factor of 9 from z = 2–3 to z = 5–6.

Comparing SCUBA-2 and ALMA Selections of Faint Dusty Star-forming Galaxies in A2744

“…Other authors have compared submillimeter/millimeter flux ratios to published speczs and photzs (Casey et al 2013;Lim et al 2020;Barger et al 2022;Cowie et al 2023) or used them to make rough redshift estimates for sources whose optical/ near-infrared (NIR) counterparts are faint or not identified (e.g., Wang et al 2019). These estimates rely on the fact that the submillimeter bands lie closer to the peak of the dust emission in the FIR and therefore have flux ratios that change substantially as the spectral energy distribution (SED) is redshifted.…”

A Full Resolution of the 450 μm Extragalactic Background Light

“…The advent of space-based telescopes, like the Herschel Space Observatory, and ground-based facilities, like the Atacama Large Millimeter/submillimeter Array (ALMA), has revolutionized our ability to perform either wide-field or deep FIR surveys, enabling unprecedented studies of galaxy number counts (Oliver et al 2010;Berta et al 2011;Gómez-Guijarro et al 2022;Chen et al 2023;Cowie et al 2023). These observations, coupled with theoretical models, provide a comprehensive view of the FIR Universe and its connection to other astrophysical phenomena (e.g., Lacey et al 2016;Lagos et al 2019;Hayward et al 2021).…”