Cadence studies N. Regnault, P. Gris et al (many thanks to D. - - PowerPoint PPT Presentation

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Cadence studies N. Regnault, P. Gris et al (many thanks to D. - - PowerPoint PPT Presentation

Jan 28, 2023 340 likes •723 views

Cadence studies N. Regnault, P. Gris et al (many thanks to D. Rothchild and P. Yoachim, E. Rykoff, C. Stubbs and many others for past and future helpful discussions) Metrics SN cosmology Survey uniformity Cosmology metrics Light pipeline

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Cadence studies

  • N. Regnault, P. Gris et al

(many thanks to D. Rothchild and P. Yoachim, E. Rykoff, C. Stubbs and many others for past and future helpful discussions)

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SLIDE 2

Metrics

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SN cosmology

  • Cosmology metrics

○ DETF figure of merit ○ Using SNe to probe LSS

⇓

  • How many well sampled SNe ?

○ Sampling quality requirements from Photo-id & distance measurements

  • Redshift limit of SN survey

○ z above which measurement error > SN intrinsic dispersion Survey uniformity Light pipeline & ubercal toy model, to evaluate

  • If we can fit a ubercal solution

○ After 1, 2... 3+ year(s)

  • The quality of the ubercal

solution ○ Fisher matrix studies ○ Multiple fits

  • How cadence can be tweaked

○ To improve ubercal errors

GAIA may help ! (PCWG pop-up session on Thursday)

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SLIDE 3

Three cadence families

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White paper call

  • Baseline 2018a
  • Kraken 2026 (new baseline)
  • Colossus 2665
  • Pontus 2002 (very wide WFD)
  • Colossus 2664
  • Colossus 2667 (1 visit / night)
  • Pontus 2489
  • Kraken 2035
  • Mothra 2045
  • Pontus 2502
  • Kraken 2036

Jan 2018 simulations (Tests of the feature scheduler)

  • Minion
  • Feature baseline
  • Feature rolling ½
  • Feature rolling ⅔

AltSched

  • AltSched
  • AltSched rolling

No ditherings in released files (added after the fact with MAF) Released files come with ditherings AltSched’s own dithering scheme

http://astro-lsst-01.astro.washington.edu:8080/?runId=1 http://www.rothchild.me:8080

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Three cadence families

  • All give very similar metrics

○ Number of visits per filter per healpix superpixel ○ Total survey depth ○ Average image quality ○ …

  • … but cadences differ very significantly w.r.t

○ Median interval between visits for a given field ○ Filter allocation strategy ○ Integrated depth in a ~ 45 days time window ○ ...

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This is what matters for SN science

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SLIDE 5

Example

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Example

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Different filter allocation strategies

AltSched rolling

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Minion 1016

Guarantees that each field observed in At least 2 bands during a given night Keep observing in a given filter over long durations

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SLIDE 8

SN metrics

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SN and cadence

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  • Cosmological impact of SNe is primarily a function of cadence (and

calibration) ○ Indeed, cadence determines the number and redshift distribution of well measured SNe

Using SNe Ia to constrain the growth of structure (Howlett, et al, 2017) DESC SRD DETF FoM

Provided enough well measured SNe (several 105)

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SLIDE 10

Method

1. Superpixellize the sphere (nside=64) 2. Build a focal plane model 3. Play the cadence : for each exposure a. Project the focal plane on the sky b. Determine the healpixs observed (= center in the focal plane) c. Build an observing log for each pixel

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Global metrics (depth, seeing, effective cadence, per pixel) SN specific metrics Use SN light curves as a “probe” to determine cadence quality

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SLIDE 11

Choice of a fiducial SN

  • Sample of SNe with

a. “Good LC sampling” to allow ■ photo-ID ■ good distance measurement b. Redshift-limited (i.e. all SNe Ia up to the redshift limit pass criterion (a) ⇒ size of SN redshift-limited cosmology sample is a good metric for LSST cadence

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Region of interest in (X1, Color) parameter space Median SN

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Method (II)

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  • Use the LC of a fiducial SN as a probe of the cadence
  • Method

○ For each MJD, for each healpix pixel, in a given redshift bin ■ Generate a fiducial SN that peaks at MJD ■ Demand

  • At least 1 visit every 4 days, in either g,r,i or z
  • > 1 visit in [-20, -10] days (restframe, g,r,i or z)
  • > 1 visit in [+35, +45] days (restframe, g,r,i or z)
  • σ(color) < 0.04

■ If pass, mark the pixel, ■

  • therwise, go to the next lower z-bin
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SLIDE 13

Can be summarized as a movie

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SN peak date

Instantaenous Integrated

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SLIDE 14

Examples

Minion

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http://supernovae.in2p3.fr/~nrl/lsst_sn_cadence/

Baseline 2018 AltSched AltSched rolling

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SLIDE 15

Examples

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http://supernovae.in2p3.fr/~nrl/lsst_sn_cadence/

AltSched very wide AltSched rolling Kraken 2026 Pontus 2002

New baseline candidate Very wide WFD Very wide WFD Altsched experiment By P. Gris, with guidance and help from D. Rothchild

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SLIDE 16

Size of WFD SN sample

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Fiducial SN = median SN Bug in the weather files (now corrected)

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SLIDE 17

Size of WFD SN sample

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Fiducial SN = median SN

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SLIDE 18

Size of WFD SN sample

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Fiducial SN = median SN

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SLIDE 19

Size and redshift lever arm (WFD)

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Fiducial SN = median SN

Sample redshift limit Number of well sampled SNe

Good ! “Under-optimal”

Fiducial SN = median SN

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SLIDE 20

Size and redshift lever arm (WFD)

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Fiducial SN = median SN

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SLIDE 21

Size and redshift lever arm (WFD)

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Fiducial SN = median SN

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SLIDE 22

Ongoing experiments with SLAIR

  • Tune the feature-based scheduler (a.k.a. SLAIR), to get an

“Altsched-like” behavior

  • Experiments carried out by P. Yoachim (thanks a lot !)
  • Key points are:

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○ Observe near the meridian ○ Observe fields in blocks that are repeated twice a night ○ Second visit in a different filter (use the filter changer!) ○ Make sure that any revisit occurs at least 2 days later

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SLIDE 23

Size and redshift lever arm (WFD)

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Fiducial SN = median SN

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SLIDE 24

Conclusions for SN metrics

  • LSST can yield ~ 4 105 well sampled SN in the WFD

○ New SN Ia science (?) beyond the HD ○ All types of fast transients !

  • Ongoing effort to tune OpSim/SLAIR to obtain a AltSched-like

behavior

  • Ongoing effort to explore how we can improve on best cadences

identified so far ○ Wider survey ? ○ 80%-20% rolling ? ○ shallow survey to increase size of very low-z sample ? ○ More g & r-band, in order to go deeper ?

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Work for Tucson a& New York workshop

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SLIDE 25

Size and redshift lever arm (WFD)

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Fiducial SN = median SN Help from P. Yoachim and Project very much appreciated Lots of help from

  • D. Rothchild
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SLIDE 26

Survey uniformity

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Survey uniformity

  • Why do we (DESC) care about survey uniformity ?
  • Flux calibration

○ Primary flux reference(s) in specific locations on the sky ○ Flux scale must be transported on the full survey footprint ○ Essential for SN cosmology, target accuracy ~ 1 mmag

  • Specific calibration error modes on the sky ?

○ may affect PZ determinations ○ at specific scales that are relevant for cosmology ?

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SLIDE 28

Questions

  • Main question is

○ How well can we transport the flux scale carried by a handful of flux reference on the entire sky ?

  • Technical questions are

○ For a given cadence, can we solve the ubercal problem ? ○ Does interlacing DDF obs help improving the calibration ? ○ Are some dithering patterns significantly better than others ? ○ What is the impact of non-photometric sequences on solution ? ○ Are there specific error modes, at specific scales that have an impact on the analyses ? ○ Will adding GAIA help ?

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SLIDE 29

Ubercal toy model

  • Fitting simultaneously:

○ Calibrated magnitudes ○ Calibration parameters (ZP + uniformity maps)

  • With constraints from

○ Primary references ○ Future uniform star catalog (GAIA ?)

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Measurement Calibrated mag Exposure ZP Uniformity map ~ 1 / month ? ~ 1 / week ? ~ / day ?

Padmanabhan 2008 Schlafly et al, 2015 Burke & Rykoff, 2017

PCWG GAIA pop-up session Thursday@8 am

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SLIDE 30

Fast ubercal simulator

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Ubercal simulator

Cadence Observing conditions Ubercal model External constraints (Primary standards, GAIA) Uncertainty budget (Fisher matrix) Ubercal fit Power spectrum Two simulators available so far:

  • Using healpixs (NR)
  • Using stars

(F. Feinstein et al)

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SLIDE 31

Example

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(with 2 years of survey) Error power spectrum ℓ Jan 2018 cadences (dithering applied) New cadences (no dithering applied yet) ℓ ~ 150 Many cadences not connected

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SLIDE 32

Conclusion & work ahead

  • Transform fast ubercal simulator into a MAF metrics

○ Systematics checks of all cadences available

  • Add ditherings to the white paper call metrics

○ No white paper cadence allows us to constrain the ubercal model without the dithers

  • Open questions

○ How can we make sure that the cadence allow to constrain an ubercal model with 1 yr of data only ? ○ Understand how DDF observations help rigidifying solution ○ Location of fundamental flux standards ? In the DDFs ? ○ Calibration specific minisurvey ? ■ Additional dithered observations ? ■ Specific observations to transport CALSPEC -> DDF ?

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SLIDE 33

Backup slides

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SLIDE 34

Different mean observing conditions

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SLIDE 35

Different mean observing conditions

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SLIDE 36

Global filter allocation

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SLIDE 37

Size of WFD SN sample

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Fiducial SN = median SN Pontus 2489 AltSched very wide (P. Gris)