Cross-matching Rubin and VISTA surveys
Project information
Project leads: Raphael Shirley (Southampton), Manda Banerji (Southampton), Richard McMahon (Cambridge).
This work package is part of the LSST:UK in-kind contribution, with the Galaxies SC as a secondary recipient (the primary recipient is NOIRLab).
Project point of contact: Raphael Shirley (r.a.b.shirley@soton.ac.uk)
Rubin project code: UKD-UKD-S5
Relevant working groups: SED-fitting and Photometric Redshifts
Project status: Active
Rationale
Combining optical photometry from Rubin with other wavelengths will be crucial to harnessing the power of the data. Near infrared imaging from the VIRCAM camera on VISTA will extend coverage to the ZYJHKs bands. These will provide additional information for spectral energy distribution modelling and the calculation of photometric redshifts.
A simple positional cross match can be used to combine multiple bands but conducting forced photometry has a number of advantages. A key challenge with combining the wide area Vista Hemisphere Survey (VHS) which covers the entire Wide Fast Deep (WFD) LSST survey to be conducted by Rubin is the disparity in depths. VHS typically goes to Ks AB five sigma point source depths of 20.0. The ten year WFD depths will however go to as high as 27 mag in the r band.
We therefore are working on using the LSST Science Pipelines to conduct band merged photometry between Rubin and VISTA. This allows a 'detected in any band measured in every band' pipeline such that low signal to noise near infrared measurements can still contribute to a given object effectively increasing the possible depths that can be probed in the near infrared. It will also allow us to determine upper limits for non detections which also contribute information.
Results
A key part of the project involves quality control on the test data reductions. There are various decisions involved in developing the pipeline and calibrating the photometry. We automatically produce diagnostic plots as we continue development. These are available in the public database repository:
https://github.com/lsst-uk/lsst-ir-fusion
We have made all code required to repeat these reductions public. The code required for using VISTA VIRCAM data with the LSST science pipelines is available here:
Talks and presentations
Talk at LSST Galaxies SC telecon, 1 Apr 2021
Outputs
We are currently serving the first prototype band merged catalogues on the Vista Science Archives (VSA). Please contact us for help with writing queries. A very simply example to get started is:
SELECT TOP 10 * FROM VIDEO_VISTA_Ks_Forced
We can also supply raw files in the 'second generation Butler' format used by the LSST Science Pipelines. We are currently working on a rerun using the third generation Butler and the latest pipelines. Eventually we also plan to move to the LSST data management 'Qserv' table publishing format in addition to other means to serve the data in the same manner as the Rubin data itself.