Searching Far and Long I: Pilot ALMA 2mm Follow-up of Bright Dusty Galaxies as a Redshift Filter

Olivia R. Cooper; Caitlin M. Casey; Jorge A. Zavala; Jaclyn B. Champagne; Elisabete da Cunha; Arianna S. Long; Justin S. Spilker; Johannes Staguhn

doi:10.3847/1538-4357/ac616d

paper

Searching Far and Long I: Pilot ALMA 2mm Follow-up of Bright Dusty Galaxies as a Redshift Filter

arXiv:2203.14973 · doi:10.3847/1538-4357/ac616d

Abstract

A complete census of dusty star-forming galaxies (DSFGs) at early epochs is necessary to constrain the obscured contribution to the cosmic star formation rate density (CSFRD), however DSFGs beyond $z \sim 4$ are both rare and hard to identify from photometric data alone due to degeneracies in submillimeter photometry with redshift. Here, we present a pilot study obtaining follow-up Atacama Large Millimeter Array (ALMA) $2$ mm observations of a complete sample of 39 $850 μ m$ -bright dusty galaxies in the SSA22 field. Empirical modeling suggests $2$ mm imaging of existing samples of DSFGs selected at $850 μ m - 1$ mm can quickly and easily isolate the "needle in a haystack" DSFGs that sit at $z > 4$ or beyond. Combining archival submillimeter imaging with our measured ALMA $2$ mm photometry ( $1 σ \sim 0.08$ mJybeam $^{- 1}$ rms), we characterize the galaxies' IR SEDs and use them to constrain redshifts. With available redshift constraints fit via the combination of six submillimeter bands, we identify 6/39 high- $z$ candidates each with $> 50%$ likelihood to sit at $z > 4$ , and find a positive correlation between redshift and $2$ mm flux density. Specifically, our models suggest the addition of $2$ mm to a moderately constrained IR SED will improve the accuracy of a millimeter-derived redshift from $Δ z / (1 + z) = 0.3$ to $Δ z / (1 + z) = 0.2$ . Our IR SED characterizations provide evidence for relatively high emissivity spectral indices ( $⟨ β ⟩ = 2.4 \pm 0.3$ ) in the sample. We measure that especially bright ( $S_{850 μ m} > 5.55$ mJy) DSFGs contribute $\sim 10$ % to the cosmic-averaged CSFRD from $2 < z < 5$ , confirming findings from previous work with similar samples.

arXiv comment22 pages, 7 figures, accepted for publication in ApJ

References in corpus (118)

Cited by in corpus (1)

COSMOS2020: The Galaxy Stellar Mass Function: the assembly and star formation cessation of galaxies at $0.2 < z \leq 7.5$