2025/08/04 by Ivana F. van Leeuwen, van Leeuwen, I. F., R. J. Bouwens +37
Physics and Astronomy · #Galaxies: Formation, Evolution, Phenomena #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies
paper · pdf · doi:10.48550/arxiv.2508.02390
We present the [OIII]88μm spectral scan results from the ALMA Large Program REBELS (Reionization Era Bright Emission Line Survey). The generally high luminosity of [OIII]88μm and ALMA's Band 7 efficiency motivated its use for line scans of REBELS targets at z>8. Spectral scans of four sources covered 326.4-373.0 GHz (z=8.10-9.39), reaching [OIII]88μm luminosities of \mathrm∼7.6×108 L\odot (5σ) for a FWHM of 400 km s-1. No credible lines are detected for the four targets. For REBELS-04, the non-detection is unexpected given the ≥92% coverage of the redshift likelihood distribution and its estimated SFR of 40 M\odot yr-1. Possible explanations for the faint [OIII]88μm emission (assuming a FWHM of 100 km s-1) include high ISM densities (>ncrit ≈ 510 cm-3) and low ionization parameters (\mathrmlog10 Uion\lesssim -2.5). For REBELS-37, a subsequent detection of [CII]158μm (z=7.643) confirmed it lay outside our scan range. For REBELS-11 and REBELS-13, it remains unclear if the non-detection is due to the depth of the line scan or redshift coverage. REBELS-04 and REBELS-37 show significant (≥3.8σ) dust continuum emission in Band 7. If the photometric redshift of REBELS-04 is accurate, i.e., zphot=8.57+0.10-0.09 or zphot=8.43+0.10-0.10 accounting for additional neutral hydrogen in the circumgalactic medium, REBELS-04 would constitute the most distant dust-detected galaxy identified with ALMA to date. Additional Band 6 dust observations of REBELS-37 constrain the shape of the far-IR SED, ruling out cold dust temperatures (\lesssim28 K) at 3σ. Further insight into these galaxies will require spectroscopic redshifts and deeper multi-band dust observations.