Dithering and Large-Scale Structure: LSST Wide Fast Deep Survey - - PowerPoint PPT Presentation

Dithering and Large-Scale Structure: LSST Wide Fast Deep Survey

Humna Awan, Eric Gawiser, for the DESC-LSS Working Group

LSST PCW 2018 August 14, 2018

LSS Studies

Want a wide, uniform survey.

• Why wide?

○ Systematics ~ 1/area

• Why uniform?

○ Need to correct for artificial structure induced by the observing strategy: uncertainties in our corrections are a limiting factor in reducing systematic uncertainties (Awan+2016)

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LSS Studies: Dithers

Want a wide, uniform survey.

• Uniformity is achieved by implementing frequent, large translational

dithers (on the scale of FOV) ○ Awan+2016 ○ LSST Community Observing Strategy White Paper

• Here: random offsets (in baseline WFD pointings) after every visit

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LSS Studies: Survey Footprint

Want a wide, uniform survey.

• For LSS (and any other extragalactic science):

○ Need to account for Milky Way extinction ○ For good photo-zs, focus on footprint covered in all bands ○ Implement depth cuts to ensure S/N in extended sources (galaxies) ○ Science is carried out on the final survey footprint ■ Want to maximize this usable area

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WP Call: Included OpSim Outputs

https://docushare.lsst.org/docushare/dsweb/Get/Document-28716

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Wide-Fast-Deep (WFD): Current

Includes high-extinction galactic anti-center Example: i-band coadded depth

(after accounting for MW extinction)

Total area:19,127 deg2

(all-band footprint; no depth cut)

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Wide-Fast-Deep (WFD): Current

In some regions, extinction is high enough to disallow extragalactic science: depth cuts to discard “bad” area DESC SRD: i>26.0 for 10 yr

(after accounting for MW extinction)

Total area: 14,668 deg2

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Wide-Fast-Deep (WFD): Current

~23% area is discarded → effectively smaller WFD to work with Similar results for Year 1: ~24% area is discarded

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Goal here: Define WFD to consist of useable footprint

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Included OpSim Outputs

https://docushare.lsst.org/docushare/dsweb/Get/Document-28716

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https://docushare.lsst.org/docushare/dsweb/Get/Document-28716

Wider WFD Footprint

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Work with pontus_2002 to find the optimal footprint for WFD

• Minimize coverage loss following depth cuts

https://docushare.lsst.org/docushare/dsweb/Get/Document-28716

Wider WFD Footprint

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Work with pontus_2002 to find the optimal footprint for WFD 26,912 to 19,227 deg2 for i>26.0 -- plenty of usable remaining area

( discarded area: ~28% of original)

Wider WFD Footprint

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Comparison

Remaining area: 14,668 vs 19,227 deg2 (~24% increase)

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Extragalactic-Optimal WFD

Current WFD contains high-extinction areas that should be discarded for extragalactic science

• Design has used stellar density to define MW exclusion - not enough
• MW dust sets stricter requirements

Goal: design WFD to not include high-extinction regions, which would give more effective, usable footprint for extragalactic science. Further work:

• Run OpSim WFD cadence in optimized WFD footprint

○ Deeper, more realistic sense of depth

• Propagate through for FoM for LSS, WL and other probes.

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Questions?

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kraken_2026

https://docushare.lsst.org/docushare/dsweb/Get/Document-28715

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Year 1 WFD: Current

DESC SRD: i>24.5 for Year 1 → ~24% area is discarded

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Year 1 Wider WFD Footprint

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i>24.5: 24,511 to 15,426 deg2

( discarded area: ~37% of original)

Year 1: Comparison

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Remaining area: 13,984 vs 15,426 deg2 (~10% increase)