The DESI Legacy Imaging Surveys team is pleased to announce the public release of the Siena Galaxy Atlas 2020 (SGA-2020), a value-added supplemental catalog to imaging Data Release 9 (DR9).
The SGA-2020 is a multiwavelength atlas of 383,620 nearby galaxies selected over the 20,000 square-degree imaging footprint based on their (large) apparent angular diameter. It has been used in Survey Validation and the Main Survey to improve the selection of BGS targets, for improved masking of faint, dark-time (ELG, LRG, QSO) targets, in secondary target programs (e.g., to facilitate studies of the peculiar velocity field in the local volume via the Tully-Fisher and Faber-Jackson relations), and more. Read more about the SGA-2020 on the AAS poster.
For each galaxy in the SGA, we carry out the following measurements:
- We generate custom grz and W1W2 image stacks using all the available imaging (upper-left panel);
- We use The Tractor, in the context of the legacypipe photometric pipeline to build a model of all the sources in the field (middle-left panel);
- We subtract all the sources in the field except the object of interest from the data and measure the surface-brightness profile using nested, fixed-geometry elliptical isophotes (bottom-left panel).
This procedure yields the non-parametric grz surface-brightness profiles, g-r and r-z color-radius profiles, and grz curves of growth shown in the right-hand panels of the figure above, and more.