Reionization Era Bright Emission Line Survey: Selection and Characterization of Luminous Interstellar Medium Reservoirs in the z>6.5 Universe

Abstract

The Reionization Era Bright Emission Line Survey (REBELS) is a cycle-7 ALMA Large Program (LP) that is identifying and performing a first characterization of many of the most luminous starforming galaxies known in the z > 6.5 universe. REBELS is providing this probe by systematically scanning 40 of the brightest U V -selected (−23.0 < M U V,AB < −21.3) galaxies identified over a 7-deg 2 area (including the wide-area COSMOS/UltraVISTA, VIDEO/XMM-LSS, and UKIDSS/UDS fields) for bright [CII] 158µm and [OIII] 88µm lines and dust-continuum emission. Selection of the 40 REBELS targets was done by combining our own and other photometric selections, each of which is subject to extensive vetting using three completely independent sets of photometry and template-fitting codes. Building on the observational strategy deployed in two pilot programs, we are increasing the number of massive interstellar medium (ISM) reservoirs known at z > 6.5 by ∼4-5× to >30. In this manuscript, we motivate the observational strategy deployed in the REBELS program and present initial results. Based on the 60.6 hours of ALMA observations taken in the first year of the program (November 2019 to January 2020), 18 highly significant ≥ 7σ [CII] 158µm lines have already been discovered, the bulk of which (13/18) also show ≥3σ dust-continuum emission. These newly discovered lines more than triple the number of bright ISM-cooling lines known in the z > 6.5 universe, such that the number of ALMA-derived redshifts at z > 6.5 already rival Lyα redshift discoveries. An analysis of the completeness of our search results vs. star formation rate (SFR) suggests an ∼81% efficiency in scanning for [CII] 158µm when the SFR U V +IR is in excess of 20 M /yr. These new LP results further demonstrate ALMA's efficiency as a "redshift machine," particularly in the epoch of reionization.

The ALMA REBELS survey: the dust content of z ∼ 7 Lyman break galaxies

“…Firstly, the observationally inferred dust masses for z ∼ 7 galaxies seem to be essentially independent of the underlying stellar mass. This somewhat flat trend is consistent with the data points from REBELS (Bouwens et al 2021a), using either the fiducial stellar masses from Stefanon et al (2022, in prep. ) or those inferred by Topping et al 2022 (in prep.…”

“…Including astration and dust destruction leaves the slope unchanged whilst leading to a decrease in the normalisation (by about 0.3 dex) resulting in the dust-to-stellar mass ratio decreasing to about 0.17%. Adding ejection leads to a steepening of this relation as low-mass halos (M * < ∼ 10 9 M ) lose a larger fraction of their gas (and dust) via outflows as compared to (Bouwens et al 2021a, Stefanon et al 2022 where the stellar and dust masses have been re-scaled to a Salpeter IMF between 0.1 − 100M . The other points show observational data for A1689-zD1 (empty star) from Watson et al (2015) and Bakx et al (2021), for B14-65666 (empty circle) from Hashimoto et al (2019) and for SPT0311-58 (empty triangle) from Reuter et al (2020).…”

“…In order to build a larger sample of dusty star forming galaxies at high-z, an ALMA large program (the Reionization Era Bright Emission Line Survey; REBELS; PI: Bouwens) is underway. REBELS focuses on studying 40 of the brightest galaxies at z > ∼ 6.5 over a 7 deg 2 area which are being scanned for both bright ISM cooling lines (such as those from [CII] 158 µm and [OIII] 88 µm) and dust continuum emission, as detailed in Bouwens et al (2021a). This survey has already serendipitously revealed two dusty star forming galaxies at z ∼ 7 (Fudamoto et al 2021) in addition to yielding a sample of 13 (continuum and CII detected) z ∼ 7 LBGs (Inami et al 2022, in prep;Schouws et al 2022, in prep.…”

The THESAN project: properties of the intergalactic medium and its connection to Reionization-era galaxies

“…Nevertheless, the formation of primeval galaxies above redshift z 6 is rapidly becoming the new frontier in the study of both cosmic reionization and galaxy formation, as evidenced by recent observational campaigns that have started to constrain the population of galaxies at the end of the EoR, e.g. REBELS (Bouwens et al 2021) and ALPINE (Le Fèvre et al 2020). These are (or will soon be) flanked by many instruments providing us with a multi-faceted picture of the emergence of primeval galaxies in the context of the EoR.…”

Are the Newly-Discovered $z \sim 13$ Drop-out Sources Starburst Galaxies or Quasars?

“…We note that this "first-order" calculation ignores the impact of feedback (both from supernovae and reionization) that is crucial in determining the properties of low-mass galaxies (Sobacchi & Mesinger 2013;Dayal et al 2014;Hutter et al 2021), as well as the impact of dust attenuation, which is important in determining the visibility of high-mass galaxies (e.g. Dayal et al 2010;Bowler et al 2015;Bouwens et al 2021a).…”