Introduction
Pool travel - meetings and travel
News digest - https://www.lsst.org/news/digest
Report on Joint Technical Meeting (tbc)
New paper on the merits and pitfalls of sky subtraction techniques
MNRAS has recently published an article by Aaron Watkins and collaborators (including Sugata Kaviraj and Chris Collins) discussing the merits and pitfalls of different kinds of sky subtraction techniques. The paper, Strategies for optimal sky subtraction in the low surface brightness regime, describes experiments using fully synthetic images to investigate three different techniques, two commonly used in low surface brightness surveys, another experimental.
The study's results quantify the impact of undetected flux on sky models, which tends to bias estimated sky brightnesses high, risking over-subtraction of flux. If the sky is modelled with a complex function (for example, a high-order polynomial, or a spline interpolation), that over-subtraction can occur locally, leading to artificial divots surrounding extended objects like galaxies, or even objects which are simply located close together on the sky. However, the results demonstrate that when a simple model is used, and when proper care is taken to mask detected astronomical objects to low surface brightness levels, this bias can be reduced to negligible amounts.
Even for a survey as deep as LSST, any sky subtraction technique traditionally used in low surface brightness surveys can still be applied safely, so long as empirical corrections are made for scattered light and undetected faint sources.
The paper justifies the recommendations Watkins and collaborators have proposed to LSST's data management (DM) team regarding the survey's pipeline sky subtraction. Working alongside DM, Watkins et al. found that the existing algorithm suffers from two problems: insufficient masking of low surface brightness flux, and too complex a sky model. Following the paper's results, the team found that adjusting the algorithm to use a much simpler model, even without an improvement to the masking, proves very successful at minimizing the impact of the sky subtraction on the flux of extended or clustered objects. In fact, a preliminary investigation suggests that the proposed revised algorithm might benefit more than just low surface brightness science: a number of DM's photometric quality metrics appear to improve slightly when the revised algorithm is used, compared to the default pipeline. However, the full impact of the proposed change is still being investigated.
Examples of the synthetic images used to conduct the tests on sky subtraction routines, showcasing the kinds of model sources injected for four different experiment types.
The top-left panel shows a sparsely populated control field.
The top-right panel shows that same image, but convolved with an extended scattered light model derived from the Subaru Telescope's Hyper Suprime-Cam imager, to investigate the impact of that scattered light on sky models.
The bottom-left panel shows an image simulating data processed through a typical low surface brightness--optimised data reduction routine, in which that scattered light is subtracted from the stars (but not the galaxies).
Finally, the bottom-right panel shows an image which includes models of many faint, high-redshift sources drawn from the New Horizon simulation, to investigate the impact of undetected faint objects on sky models (also known as extragalactic background light).
The paper is available under an open access license:
https://academic.oup.com/mnras/article/528/3/4289/7603727
Both the code used to generate and process synthetic images, as well as a tutorial Jupyter Notebook demonstrating two of the sky subtraction algorithms tested, are available on GitHub:
https://github.com/lsst-uk/sky-estimation-WP3.7
Report on Cosmic Streams Conference December 2023 (Chris Frohmaier TBC)
Inspiring a new era in space missions – latest Rubin science release
Forthcoming meetings of interest
Since the previous newsletter, a number of further meetings have been announced, plus we have more details for some others.
Dates | Meeting Title / Event | Meeting Website/ Contact | Meeting venue/ location |
---|---|---|---|
22/Jul/24—26/Jul/24 | Rubin Community Workshop | Further details about the meeting will be available once the meeting website is set up and registration opens. In the meantime, if you have questions about the meeting please send an email to pmo.rubin@noirlab.edu. | SLAC, California (hybrid) |
08/Jul/24—12/Jul/24 | DESC Collaboration Meeting | ETZ Zurich, Switzerland | |
20/May/24—23/May/24 | Rare Gems in Big Data. The discovery potential of large astrophysical surveys: science opportunities, tools, and techniques | https://mailchi.mp/d8d4daa3ed0a/first-announcement-rare-gems-in-big-data?e=5176cbbd93 | Tucson, AZ, USA |
15/Apr/24—19/Apr/24 | KAVLI-IAU (IAUS 387) Symposium, “(Toward) Discovery of Life Beyond Earth and its Impact,” | Durham University, UK | |
18/Mar/24—20/Mar/24 | Rubin ToO 2024: Envisioning the Vera C. Rubin Observatory LSST Target of Opportunity program | Berkeley, California (or virtual) | |
12/Mar/24—15/Mar/24 | Preparing for the Statistical Age of Strong Gravitational Lens Science with the Rubin Observatory Legacy Survey of Space and Time (LSST) | Oxford, UK | |
26/Feb/24—01/Mar/24 | DESC Collaboration Meeting | Virtual |
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 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.
News in brief
LSST:UK in the media / Aprajita in the Guardian
Announcements
The Challenging the Standard Cosmological Model workshop takes place at the Royal Society in London on 15 and 16 April 2024. Both in person and online attendance are available but advance registration (now open) is essential.
(Requested by Subir Sarkar)
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 Eleanor O'Kane (email eokane@roe.ac.uk)