leveraging LSST

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leveraging LSST
Tony Tyson Director, LSST Project University of
California, Davis
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DSS digitized photographic plates
7.5 arcminutes
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Sloan Digital Sky Survey
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LSST -- almost
2800 galaxies ilt25 mag
200 for one DESpec FOV
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LSST Observing Cadence

• Pairs of 15 second exposures (to 24.5 mag) per
  visit to a given position in the sky.
• Visit this position again within the hour with
  another pair of exposures.
• Number of 9.6 sq.deg FOV visits per night 900
• Deep-Drilling 1 hour per night on a selected
  field. Continuous 15 sec exposures

Detection of transients announced within 60
seconds. Expect 1 million per night
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Number of visits per field in Deep Wide Survey
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Two planned LSST surveys
MAIN SURVEY Deep Wide Survey 20,000 square
degrees to a uniform depth of
u 26.7 g 27.4 r 27.7 i 26.9
z 26.1 y 24.9 DEEP DRILLING 10 of time
30 selected fields. 300 square degrees
Continuous 15 sec
exposures. 1hour/night
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LSST Wide-Fast-Deep survey

• 4 billion galaxies with photometric redshifts
• 20 trillion photometric measurements of 20
  billion objects
• 70PB database
• Immediate transient alerts

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LSST Science Book v2.0 written by LSST
Collaboration

• 245 authors
• 598 pages
• Living document
• (on lsst.org)

http//www.lsst.org/lsst/scibook
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LSST Science Charts New Territory
Probing Dark Matter And Dark Energy
Mapping the Milky Way
opens the time window!
Finding Near Earth Asteroids
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Three classes of useful LSST spectroscopy

1. Calibration samples for quantities that can be
   derived from photometric data photometric
   redshifts for galaxies, photometric metallicity
   for stars
2. Supplemental data that cannot be obtained from
   LSST data radial velocity, emission and
   absorption line strengths
3. Identification spectra for transient, weird and
   unusual objects (SNe, GRB followup, high-z
   quasars, brown dwarfs)

These differ by the needed sample size, sample
depth, required spectral resolution, and the
time delay relative to imaging data.
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The vast majority of LSST science uses LSST
multi-band time domain photometry data alone

• Some exceptions
• 1. Photo-z needs spec for rlt24 mag over 10
  sq.deg -gt 10meter
• 2. TRANSIENTS
• Rare bright needs 2-4meter
• Faint (22-24mag) needs 10-30meter
• 3. Strong lensing magnified source
  spectroscopy
• 4. SNe zlt1.2 needs 10meter
• 5. Stellar mostly hi-res

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190 sq deg
DESpec on Blanco
to 24.5
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Alert Rate

• In ten minutes time the LSST transient pipeline
  is likely to issue 10,000 alerts at 5s.
• While most of these will be moving objects,
  perhaps several thousand will be flaring objects
  or bursts. Possibly new kinds of objects!
• Clearly any feasible spectroscopic followup at 23
  mag will lag behind 1 hour per hour. What is
  needed then is highly trusted event
  classification. FAST

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DESpec coverage of LSST surveys

• ¼ of main 20,000 sq.deg to 22.5 mag at S/N5
• 0.7 of gold sample of ilt25 mag
  galaxies
• useful for correlation calibration of
  photo-z
• deep spectroscopy of deep drilling fields
• 20 fields, 20 hours each, 50 nights
• 24 mag _at_ S/N10 per 10Å bin
• transient host spectra
• co-observing spectroscopy of deep drilling
  fields
• 1 hour / night
• 22 mag _at_ S/N5 per 1Å bin
• transient spectra

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DATA PRODUCTS
CLASSIFICATION
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Science at the Limit

• Much of the breakthrough science using surveys
  (imaging or spectroscopy) occurs at the limits of
  the surveys
• Noise, Sample incompleteness
• Subtle systematic errors

Statistical studies must be corrected for these
errors
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large spectroscopic samples are useful

• Example even an incomplete spectroscopic
  sample can help photo-z in two ways
• angular cross correlation with faint photometric
  sample will calibrate photo-z statistically
  (Newman)
• large spectroscopic samples can improve
  knowledge of evolution of galaxy SEDs.

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There are currently 20 telescopes larger than 3m
with spectrographs that can reach the LSST survey
area. Even in the ELT era, wide field
multi-object spectroscopy on 4-10m class
telescopes will be useful Statistics matters.
Calibration of the 70PB LSST database, and
massively parallel follow-up of a million
transients will be complementary to selected
faint object spectroscopy
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LSST science deliverables do not require followup
spectroscopy
But we can and should pursue a range of followup
programs, from co-observing highly parallel
spectroscopy, to individual object followup.
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QA
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Assuring accurate classification

• Characterize the known clustering)
• Assign the new (classification)
• Discover the unknown (outlier detection)

Tom Vestrand

• Benefits of very large data sets
• best statistical analysis of typical events
• automated search for rare events

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The dimension reduction problem

• Finding correlations and fundamental planes of
  parameters

• The Curse of High Dimensionality !
• Are there combinations (linear or non-linear
  functions) of observational parameters that
  correlate strongly with one another?
• Are there basis sets that represent the full set
  of properties?