The Brightest Galaxies in the Dark Ages: Galaxies’ Dust Continuum Emission during the Reionization Era

Abstract

Though half of cosmic starlight is absorbed by dust and reradiated at long wavelengths (3µm-3 mm), constraints on the infrared through millimeter galaxy luminosity function (the 'IRLF') are poor in comparison to the rest-frame ultraviolet and optical galaxy luminosity function, particularly at z > ∼ 2.5. Here we present a backward evolution model for interpreting number counts, redshift distributions, and cross-band flux density correlations in the infrared and submillimeter sky, from 70µm-2 mm, using a model for the IRLF out to the epoch of reionization. Mock submillimeter maps are generated by injecting sources according to the prescribed IRLF and flux densities drawn from model spectral energy distributions that mirror the distribution of SEDs observed in 0 < z < 5 dusty star-forming galaxies (DSFGs). We explore two extreme hypothetical case-studies: a dust-poor early Universe model, where DSFGs contribute negligibly (<10%) to the integrated star-formation rate density at z > 4, and an alternate dust-rich early Universe model, where DSFGs dominate ∼90% of z > 4 star-formation. We find that current submm/mm datasets do not clearly rule out either of these extreme models. We suggest that future surveys at 2 mm will be crucial to measuring the IRLF beyond z ∼ 4. The model framework developed in this paper serves as a unique tool for the interpretation of multiwavelength IR/submm extragalactic datasets and will enable more refined constraints on the IRLF than can be made from direct measurements of individual galaxies' integrated dust emission.

The East Asian Observatory SCUBA-2 Survey of the COSMOS Field: Unveiling 1147 Bright Sub-millimeter Sources across 2.6 Square Degrees

“…Thus, to firstorder redshift evolution in the peak wavelength for massselected sources is consistent with the well-established L FIR -λ peak relation and redshift evolution in average farinfrared luminosity of galaxies selected at a fixed stellar mass (see Figure 9), and should not be interpreted in terms of a global λ peak (T dust )-z relation. Casey et al (2018b) recently presented a best-fit L FIRλ peak relation for a heterogeneous sample of far-infraredto-millimeter-selected galaxies at z = 0-6, which was subsequently employed in a phenomenological model of galaxy evolution designed to estimate the number counts and redshift distribution of sub-mm / mm sources (Casey et al 2018a). The L FIR -λ peak relation presented by Casey et al (2018b) lies systematically above our results by ∼ 5-10 µm, at a fixed far-infrared luminosity, with the offset increasing to ∼ 15-20 µm for the most luminous systems (see Figure 10; equivalent to ∆ T d ∼ 3-7 K).…”

“…Open symbols represent our stacking results for "active" galaxies in the COSMOS field at z < 1.5 that were selected based on the N U V -r and r-J colors. For comparison we show a sample of infrared-bright sources at z = 0-1 (Symeonidis et al 2013; typical uncertainty is shown in the lower left) and the best-fit relation to a heterogeneous sample of far-infrared-selected systems at z = 0-6 (Casey et al 2018b). We construct a simple model for the expected trend between λp and L FIR , which shown for galaxies at log 10 M = 10.0-10.5 (dot-dash), 10.5-11.0 (solid), and 11.0-12.0 (dashed).…”

“…This simple model provides a reasonable representation of the relation between far-infrared luminosity and rest-frame peak wavelength of our stacked subsets, including the dependence on stellar mass, although we caution that there is a large uncertainty associated with each track (shaded region; log 10 M = 10.5-11.0). Casey et al (2018b) is dominated by 1.4 mm-selected sources, which may introduce a bias towards lower dust temperature (see Blain et al 2002;Swinbank et al 2014). Investigating this discrepancy further is beyond the scope of this work but we highlight that a systematic reduction in the normalization in the L FIR -λ peak relation presented by (Casey et al 2018a) would decrease the estimated surface density of sub-mm / mm sources predicted by their model, although the magnitude of the change is sensitive to the redshift evolution of the assumed farinfrared luminosity and stellar mass functions, and the relative mapping between the two.…”

SCUBA-2 Ultra Deep Imaging EAO Survey (Studies). III. Multiwavelength Properties, Luminosity Functions, and Preliminary Source Catalog of 450 μm Selected Galaxies

“…The LFs from Béthermin et al (2017) and Aoyama et al (2019) are shown in orange and light green, respectively. The results of the dust-poor model are shown in cyan and the dust-rich model in red Casey et al (2018). feedback. Dust is generated by supernovae and AGB stars and can grow by accretion.…”

First Detection of the [O i] 63 μm Emission from a Redshift 6 Dusty Galaxy

“…At z ≥ 6.8, the [O I] 63 shifts outside the Band 9, and is only redshifted into Band 8 at z ≥ 8.5, when the required on-source time increases into hours. In contrast to G09.83808-like sources, detecting the [O I] 63 emission from normal star-forming galaxies such as the population from the Olsen et al The modest expense of ALMA time required to detect the [O I] 63 emission from G09.83808-like DSFGs will allow an efficient follow-up of z 6 DSFGs which will be delivered by the on-going and planned mm-wave surveys (e.g., Casey et al 2018;Zavala et al 2018a;Magnelli et al 2019 line is in agreement with radiative transfer models of star-forming galaxies (e.g., Kaufman et al 1999Kaufman et al , 2006Narayanan & Krumholz 2017;Olsen et al 2017 145 observations are necessary to distinguish between the two scenarios.…”