• 1 Introduction
• 2 Galaxy clustering with the Rubin LSST
• 3 Maximising the Science Return of Major Survey Facilities
• 4 LSST:UK sessions at NAM2023
• 5 Recent LSST:UK Science Centre outputs
• 6 Forthcoming meetings of interest
• 7 Announcements

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Introduction

The undoubted highlight of July for LSST:UK was our three-part session at NAM2023 (summarised below). We were fortunate to secure three authoritative speakers from the US - Bob Blum (Director of Rubin Observatory Operations), Christina Williams (from the Rubin Community Science Team) and Ashley Villar (co-chair of the Informatics and Statistics Science Collaboration) - for our introductory/background session, and it was particularly good to see so many Early Career Researchers presenting preparatory science talks, to complement presentations outlining a number of the UK’s in-kind contributions.

The programme for the 2023 Project and Community Workshop has now been released. In-person registration has now closed (although it is possible to join a waiting list), but registration for remote participation is still possible.

As mentioned last month, (self-)nominations are being sought for membership of the Rubin Science Advisory Council (SAC), with a deadline of July 31st to complete the nomination form. While SAC members serve in a personal capacity, rather than representing any scientific or national/institutional constituency, it is expected that at least one member of the SAC will be from the UK, so LSST:UK members (at any career stage and with any scientific interest) are strongly encouraged to consider nominating themselves: @Stephen Smartt can provide further details of what the role entails, as he and @Meg Schwamb are amongst those now leaving the SAC at the end of their terms.

The second piece written by EPCC staff working in the LSST:UK Science Centre has appeared, with @James Perry's account of introducing GPU acceleration into the GalSim code to help speed up DESC simulations.

Those with ideas for future newsletter items should contact the LSST:UK Project Managers (@George Beckett and @Terry Sloanlusc_pm@mlist.is.ed.ac.uk), while everyone is encouraged to subscribe to the Rubin Observatory Digest for more general news from the US observatory team.

Galaxy clustering with the Rubin LSST

As part of the Phase C of the LSST:UK Science Centre (LUSC) programme, a new contribution will focus on providing infrastructure for the accurate estimation of the clustering of galaxies, which is of central importance to the cosmological science to be carried out by the Dark Energy Science Collaboration, as well as galaxy evolution studies targeted by the Galaxies Science Collaboration. The work will be carried out between the University of Oxford and Imperial College (PIs: Alonso & Leistedt) and will aim to model the non-cosmological modulation of galaxy density caused by Galactic and observational sky contaminants (e.g., dust extinction, stars, PSF fluctuations). This will involve a combination of well-established techniques (e.g. foreground templates fitting and deprojection) as well as new ones based on Source Injections (SI), where mock objects are added to images which are reprocessed in order to characterise system responses and sensitivity to foregrounds. SI are promising but require the development of new algorithms and new infrastructure to be embedded in the DESC and GSC software ecosystems. This contribution will tackle this challenge and validate the associated software on early Rubin data to model the survey’s transfer function in detail.

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Figure 7 of https://iopscience.iop.org/article/10.3847/1538-3881/acb213, illustrating how a foreground (here, dust) can extremely affect the detection of a particular type of galaxy (here, ELGs).

Maximising the Science Return of Major Survey Facilities

The white paper can be found in full on arXiv:

LSST:UK sessions at NAM2023

We had three LSST-related sessions at the 2023 National Astronomy Meeting in Cardiff, with talks divided into three categories.

The first session started with a brief scene-setting introduction from @Bob Mann , followed by a wide-ranging update on Rubin construction and operations plans from Bob Blum, the Rubin Director for Operations, who noted that 2023 is a key year: testing of the Telescope Mount Assembly continues, while LSSTCam is undergoing final testing at SLAC, prior to being shipped to Chile in the autumn. He also summarised the current understanding of the likely impact of satellite constellations on the LSST - i.e., a nuisance (<1% of pixels affected), rather than a catastrophe (>10% affected), but with a realisation that no combination of mitigations will remove the impact entirely - and also outlined the Observatory’s sustainability plans, which have the goal of making operations on Cerro Pachon carbon-neutral. In the next talk, Christina Williams from the Rubin Community Science Team introduced the Rubin Science Platform (RSP) - the integrated set of web applications that Rubin is developing to support analysis of LSST data - and described how the Data Preview programme is helping users learn to use the RSP tools through manipulation of simulated and, soon, commissioning data. The final introductory talk came from Ashley Villar, co-chair of the Informatics and Statistics Science Collaboration, who introduced the eight LSST Science Collaborations, which now comprise more than 2000 people from 33 countries. Villar summarised the scope of each Science Collaboration and their role in advising the Observatory, as well as coordinating the future scientific exploitation of LSST data. She emphasised that they aspire to providing an inclusive and supportive environment within which LSST science can take place and that, in particular, they provide Early Career Researchers with an excellent way to secure a place in the LSST community.

In the final presentation of the first session, @George Beckett delivered the first of a set of talks describing the UK’s in-kind contributions to Rubin operations, covering the development of the UK’s Independent Data Access Centre (IDAC). Beckett emphasised that, while there are a dozen IDACs planned, it is likely that the one in the UK will be only “full IDAC”, holding all the LSST Data Release products and running an instance of the RSP (in the IRIS cloud environment), as well as hosting the UK’s Lasair broker and datasets from a number of UK in-kind contributions. The second session started with @James Mullaney describing another the UK’s major in-kind contributions, namely its 25% share of the workload for Data Release Processing (DRP). Mullaney explained the various steps in the DRP, the variety of data products that it will produce and the international (French-UK-US) team that will undertake it. The same pipeline software being used for the DRP will also be used in another UK in-kind contribution, to produce an LSST-VISTA optical/near-infrared dataset, and @Manda Banerji summarised how this has been tested, by performing the fusion of HyperSuprimeCam and VISTA data. This work has been complicated by the continuing development of modules in the pipeline, but the Southampton team have recently passed a major milestone in producing catalogues from the full areal overlap of the HSC and VISTA surveys. In the next talk @Tom J Wilson described an in-kind contribution that will perform catalogue-level data fusion, with particular attention to the modelling of the Astrometric Uncertainty Function, which will be crucial for the estimation of accurate cross-match probabilities, given how crowded the sky seen by LSST will be. Next up was @Christopher Frohmaier , who described TiDES, the Time-Domain Extragalatic Survey, which will perform spectroscopic follow-up of LSST transients with 4MOST. TiDES has three scientific objectives: (i) to map the diversity of the transient universe (which it will do by obtaining spectra for >40,000 LSST transients); (ii) to constrain dark energy models through the Hubble diagram for >50,000 Type Ia supernovae; and (iii) perform reverberation mapping of >1000 AGN to z~2.5. A more technical in-kind contribution was described by @Aaron Watkins , who has been studying how to optimise the DRP pipeline for low-surface-brightness science. After investigating a number of alternative sky-subtraction algorithms, it appears that the best approach - as well as the simplest - will be to omit one of the steps in the sky correction procedure currently being applied to HSC data.

The remaining nine talks, spanning the remainder of the second session and all of the third, comprised a series of talks on scientific preparations for LSST data. In the first of these, @Naomi Robertson discussed the range of modelling choices that face DESC as it prepares for the cosmic shear analysis of the LSST Year 1 dataset. These range from methodological (e.g., which statistics to measure) to technical (e.g., which sampler to use) to scientific choices (e.g., how best to correct for the intrinsic alignments of galaxies) and careful studies of their interplay are needed before DESC decides the best way to analyse the Year 1 data. Studies of stellar streams in the Milky Way have provided information about the gravitational potential of the Galaxy, and Madison Walder discussed how these methods can be extended to external galaxies with the advent of data from Euclid, LSST and, later, the Nancy Grace Roman Space Telescope, which, together, are expected to detect thousands of extragalactic streams, albeit with much less known about each than is the case for Galactic stream. Nonetheless, Walder showed that the radial profile of a galaxy can be determined with only the track of the stream on the sky, provided it is long enough, while the addition of at least one radial velocity measurement is needed to yield an estimate of the galactic halo mass. Mike Walmsley started the final session with a description of how the Zooniverse platform has been used for a range of galaxy morphology studies and how the methodology used to date may be scaled up for LSST and Euclid. A second Zooniverse project was then outlined by Adam McMaster, who has been using citizen scientists to identify potential black hole microlensing events; to date that has used SuperWASP data, but the intention is to apply the same approach to data from TESS, ZTF and, eventually, LSST. Francesco Petri showed how the depth of LSST data will allow the selection of many millions of Lyman-break galaxies in the interval 3 < z < 5, whose clustering, cross-correlated with CMB lensing, will probe the universe before it became dominated by dark energy. @Sugata Kaviraj explained how existing surveys have presented a biased view of the dwarf galaxy population and showed that initial HSC results imply that LSST data will reveal large numbers of red (i.e., quenched) dwarf galaxies out to cosmologically-significant redshifts for the first time, thereby allowing the determination of the evolution of this numerically-predominant component of the galaxy population. The next two talks described novel cosmological analyses that will be possible with LSST data: Isabelle Yi explained that the Doppler magnification dipole should be detectable by LSST, while Sebastian von Hausegger described three DESC projects to probe the isotropy and homogeneity of the Universe. A poor wifi connection prevented Suhail Dhawan from delivering the final talk, which would have covered the use of strongly-lensed supernovae as cosmological probes, with the goal of an independent estimate of the Hubble constant to ~1% from LSST.

Taken together, the talks in these three sessions presented a welcome update on the status of Rubin construction and operations planning, as well as a good impression of the UK contributions to Rubin operations that will earn data rights for UK researchers and the wide range of ways that they intend to exploit those data rights for science. Particularly impressive and encouraging was the fact that so many of the sciece preparation talks were given by Early Career Researchers, which bodes well for the long-term scientific return on STFC’s investment in UK involvement in LSST. @James Mullaney concluded the session by offering tutorials on accessing data through the Rubin Data Previews, which give users an early look at the Rubin Science Platform and tools to interrogate and interpret the data. James' has built up substantial experience and is happy to offer advice and help to the UK community.

Recent LSST:UK Science Centre outputs

The LSST:UK Science Centre has recently produced the following technical reports.

Forthcoming meetings of interest

The online registration for the Rubin Project and Community Workshop 2023 remains open.

Other meetings of potential interest for the coming months include:

Members of the Consortium (not in receipt of travel funding through one of the Science Centre grants) may apply for travel support for meetings of this kind via the the LSST:UK Pool Travel Fund. Details are available at Forthcoming LSST-related Meetings .

Note that the current list of forthcoming meeting is always available on the Relevant Meetings page. You may also wish to check information held on the LSST organisation website LSST-organised events and the LSST Corporation website.

Announcements

If you have significant announcements that are directly relevant to LSST:UK and would like to share the announcement in a future newsletter, please contact the LSST:UK project managers.