ALMA and the First Galaxies

SH16_almaFirstGalaxies.pngThe Reionization Era Bright Emission Line Survey (REBELS) is a Cycle 7 Atacama Large Millimeter/submillimeter Array (ALMA) Large Program (LP) that is identifying and performing a first characterization of many of the most luminous star-forming galaxies known in the z>6.5 universe. REBELS is providing this probe by systematically scanning 40 of the brightest UV-selected galaxies identified over a seven square degree area for bright 158-micron [CII] and 88-micron [OIII] lines and dust-continuum emission. Selection of the 40 REBELS targets was done by combining 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, the authors are increasing the number of massive interstellar medium (ISM) reservoirs known at z > 6.5 by ~4-5x to > 30. The authors 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] lines have already been discovered, the bulk of which (13/18) also show  ≳ 3.3σ 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 ~79% efficiency in scanning for [CII] when the SFR(UV+IR) is in excess of 28 M⊙/yr. These new LP results further demonstrate ALMA's efficiency as a "redshift machine", particularly in the Epoch of Reionization.

Image Caption: ALMA spectra of [CII] 158 micron emission from the REBELS sample at z = 6.5 to 7.7.

Publication: Rychard J. Bouwens (Leiden University) et al., Reionization Era Bright Emission Line Survey: Selection and Characterization of Luminous Interstellar Medium Reservoirs in the z>6.5 Universe, Astrophysical Journal (accepted), arXiv:2106:13719.

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