We describe a new low-frequency wideband radio survey of the southern sky. Observations covering 72-231MHz and Declinations south of +30° have been performed with the Murchison Widefield Array "extended" Phase I I configuration over 2018-2020 and will be processed to form data products including continuum and polarisation images and mosaics, multi-frequency catalogues, transient search data, and ionospheric measurements. From a pilot field described in this work, we publish an initial data release covering 1,447 deg over 4 h≤ RA≤ 13 h, -32.7° ≤ Dec ≤ -20.7°. We process twenty frequency bands sampling 72-231 MHz, with a resolution of 2'-45″, and produce a wideband source-finding image across 170-231MHz with a root-mean-square noise of 1.27 ± 0.15 mJy beam. Source-finding yields 79,124 components, of which 71,320 are fitted spectrally. The catalogue has a completeness of 98% at ~ 50 mJy, and a reliability of 98.2% at 5 rising to 99.7% at 7. A catalogue is available from Vizier; images are made available on the GLEAM-X VO server and SkyView. This is the first in a series of data releases from the GLEAM-X survey.

We illustrate the extraordinary potential of the (far-IR) Origins Survey Spectrometer (OSS) on board the Origins Space Telescope (OST) to address a variety of open issues on the co-evolution of galaxies and AGNs. We present predictions for blind surveys, each of 1000 h, with different mapped areas (a shallow survey covering an area of 10 deg and a deep survey of 1 deg) and two different concepts of the OST/OSS: with a 5.9m telescope (Concept 2, our reference configuration) and with a 9.1 m telescope (Concept 1, previous configuration). In 1000 h, surveys with the reference concept will detect from ~ 1.9 × 10 to ~ 8.7 × 10 lines from ~ 4.8 × 10-2.7 × 10 star-forming galaxies and from ~ 1.4 × 10 to ~ 3.8 × 10 lines from ~ 1.3 × 10-3.5 × 10 AGNs. The shallow survey will detect substantially more sources than the deep one; the advantage of the latter in pushing detections to lower luminosities/higher redshifts turns out to be quite limited. The OST/OSS will reach, in the same observing time, line fluxes more than one order of magnitude fainter than the SPICA/SMI and will cover a much broader redshift range. In particular it will detect tens of thousands of galaxies at ≥ 5, beyond the reach of that instrument. The polycyclic aromatic hydrocarbons lines are potentially bright enough to allow the detection of hundreds of thousands of star-forming galaxies up to ~ 8.5, i.e. all the way through the re-ionization epoch. The proposed surveys will allow us to explore the galaxy-AGN co-evolution up to ~ 5.5 - 6 with very good statistics. OST Concept 1 does not offer significant advantages for the scientific goals presented here.