The project

In the first 5 cycles of ALMA operations, data for more than 1800 projects have been calibrated and manually imaged for quality assurance purposes before being delivered to the PI and being added to the ASA. However, imaging is a time-consuming process and therefore for each project the quality assessors only imaged small portions of the data to verify that the PI requirements were achieved. As a consequence, images generated with manual imaging are highly inhomogeneous and incomplete. The recently developed imaging pipeline has improved this rate, but its usage as Quality Assurance (QA) tool has been implemented only during cycle 4 and applied only since then.

The Additional Representative Images for Legacy (ARI-L, Massardi et al. 2021) in the ALMA Science Archive is an ALMA Development project approved by JAO in December 2018 for execution and based on the results of a feasibility study approved by ESO and reported in Massardi et al. (2019). The project aim is to increase the legacy value of the ASA by bringing the reduction level of ALMA data from Cycles 2-4 close to the level of the more recent Cycles processed with the ALMA Imaging Pipeline.

Currently, an archive miner can choose to download for each MOUS only the products and/or the raw data. To complement or re-produce the product images, once all the data are downloaded, calibration scripts must be run with the same CASA version that the analyst used to generate them. This might become an issue for datasets of the earliest cycles. Nevertheless, the archive is considered a precious resource and is broadly used (Fig. 1 and Stoehr, 2017), so that more than 30% of the publications with ALMA data exploited the ASA resources.

The ARI-L complete set of imaging products will be highly relevant for all science-cases and enhance the possibilities of exploitation of archival data. Indeed, images for all the datasets will:

• facilitate the archive access and the data usage for science purposes also to non-expert data-miners,

• provide a homogeneous view of all data to compare datasets and to do a more conscious download selection,

• allow to more profitably link the archive to several tools of visualization and analysis (e.g. VO, CARTA, ADMIT, KAFE, ...)

• allow to generate previews similar to those planned for the following cycles.

The project aimed to produce and ingest into the ASA a uniform set of full data cubes and continuum images covering at least 70% of the data from Cycles 2-4.

The project was officially expected to finish in June 2022. The main goal was reached in January 2022 ahead of schedule and, on the consideration of its success, a six-months no-cost extension was accorded to increase the fraction of delivered datasets to even higher rates.

ARI-L produced and ingested into the ASA a uniform set of full data cubes and continuum images covering at 86% of the data from Cycles 2-4 processable with the ALMA pipeline. These cubes complement the more limited QA2-generated image products which cover only a small fraction (< 10%) of the observed data for those cycles.

The project was leaded by the Italian node of the European ALMA Regional Centre (ARC) in collaboration with staff from the ESO and UK European ARC nodes.

The ARI-L images were generated, certified for quality and ingested into the archive as external products. The workflow and rocessing and quality assurance procedures are described in the ARI-L project website and papers (Massardi et al. 2021, and Massardi et al. 2022).

ARI-L image, README and Weblog files can be queried in the ALMA Science Archive through the “ari_l” label in the “Collection” column, visualised in a dedicated preview and downloaded as single file among the "Externally delivered products" in the Request Handler system.

The calibrated Measurement Sets for all the ARI-L delivered MOUS are stored at the Italian Astronomical Archive (INAF-IA2) facilities and are publicly available.They can be requested via e-mail to help-desk@alma.inaf.it .

Comprehensive reviews of science cases that could benefit from similar images in the archive are in the ARI study report (Massardi et et al., 2019), in the KAFE paper (Burkutean et al., 2018), in the ALMACAL papers (Bonato et al., 2018) and in the ARI-L collaboration papers (Massardi et al. 2021).

For more information on the ARI-L activities please see the ARI-L documents.