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Each Science Goal in an ALMA project consists of Group ObsUnitSets (GOUS) which themselves consist of Member ObsUnitSets (MOUS). A GOUS contains all datasets (MOUS) that are foreseen to be combined to achieve the science objective intended by the PI. Each MOUS contains observations corresponding to a single array configuration.

It is likely that in the wideband sensitivity upgrade (WSU) era ALMA will also provide data-products at the GOUS level, i.e. combined products from different array configurations in a GOUS. Currently, there is a discussion if ALMA should ONLY provide data products on the GOUS level or also still on the MOUS level. 

W2246-0526 is a hot dust-obscured galaxy (Hot DOG) at z=4.6, and the most luminous obscured quasar known to date. In a recent A&A paper, Román Fernández Aranda and collaborators presented ALMA observations in seven bands, including Bands 9 and 10, of the brightest far-IR fine-structure emission lines of this galaxy: [OI]63 μm (the first detection ever with ALMA), [OIII]88 μm, [NII]122 μm, [OI]145 μm, [CII]158 μm, [NII]205 μm, [CI]370 μm, and [CI]609 μm. Comparing these observations with a large grid of radiative transfer models reveals that the conditions of the interstellar medium of the galaxy need to be extreme: high hydrogen density and extinction, together with extreme ionization and high X-ray to UV ratio, among the largest found in the literature. Moreover, in this work they also hypothesize that the X-ray emission must not only be very large but also confined to the galaxy core, since large amounts of cold molecular gas have been detected before, but far away from the central quasar, where it can survive.

This work sheds light on the extreme conditions that galaxies can experience during the early stages of the Universe, a piece of information that is critical to our understanding of how distant and young galaxies evolve. ALMA's multi-band observations, including the hard-to-observe Bands 9 and 10, were essential to the study of this faraway galaxy.

This is the first of the new series of updates on the ALMA Wideband Sensitivity Upgrade (WSU), an exciting and comprehensive program to keep ALMA at the scientific and technological forefront. The WSU aims at increasing the simultaneous bandwidth of ALMA by a factor of up to four while offering full spectral resolution over the entire bandwidth. Hence, the WSU will offer much improved continuum and spectral-line sensitivity to ALMA users, as well as an increase of the spectral scan speed up to a factor of ~50. All of this will be done to make one of the most productive astronomical facilities of our age even more sensitive and more efficient, offering unprecedented science capabilities.

Each ALMA partner - ESO in Europe, NAOJ in Japan, and NRAO in North America - manages their own development projects in the respective regions, and together these projects constitute the WSU. Obviously, this can only happen through a tight collaboration and coordination between the partners and a planning responsibility for the observatory in Chile. The individual WSU development projects include new receivers with increased bandwidth and improved receiver temperatures, new digitizers and data transmission system, a new correlator with improved efficiency, and improved data processing and archiving capabilities.

In Europe, ALMA development projects are carried out with essential contributions from institutes in the ESO member states. The main hardware responsibilities for Europe during the first phase of WSU are to deliver a new receiver band, a high-speed system to digitize analog receiver outputs, process and format the resulting data stream, and a new fibre-optics connection between the 5000m site and the 3000m site, where the new correlator will be based.  The Band 2 receiver project, which will observe in the frequency range 67 to 116 GHz with an IF bandwidth of 2 to 18 GHz, is now in the production phase and receivers are expected to be installed in ALMA antennas sequentially over the next two years. This project, which is a collaboration between ESO and NOVA, GARD, INAF and NAOJ, is a very substantial component of the WSU, as the Band 2 receivers will be the first ones to exploit the new bandwidth. They will also play a key role in the WSU commissioning over the next few years.

In addition to the hardware side of the WSU, there is currently a lot of activity around the world focused on the planning of the assembly, integration and verification phase, the data processing and quality assurance, the deployment concept, the science observing strategies, definition of standards and risks, the technical requirements etc. Many ALMA staff in Europe are heavily involved in the preparation of an external review that will happen this summer, during which these aspects will be assessed and recommendations and feedback on the WSU plans will be solicited. The preparations for this review (and passing it!) will be a momentous step towards making the WSU happen.

In the upcoming issues of the European ARC Newsletter, we will focus in more detail on the different WSU components, with a special emphasis on the European contributions, the technology behind the WSU, and will keep the reader updated on the progress made.

Pascal Keller

Pascal joined the Allegro ARC node in Leiden in May 2024. He will support the Dutch ALMA user community as a contact scientist for PIs with ALMA time and offering general services including face-to-face support in proposal preparation and data handling.

Pascal just submitted his thesis (Title: "Investigating the Epoch of Reionisation with Radio Interferometers") at Cambridge. In his thesis he explores a non-standard analysis method that uses the interferometric closure phase to search for the redshifted 21 cm signal of neutral hydrogen during the Epoch of Reionisation. He further applies the "closure phase method" to data from the Hydrogen Epoch of Reionization Array (HERA). Another chapter of his thesis investigates the L-band radio emissions of optically selected quasars at redshifts greater than 6 using data from the JVLA. The aim was to better understand the population of reionisation-era quasars and identify potential candidates that could be used to detect the 21 cm line in absorption to their bright radio emissions.

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