A Multiband Imager for Magellan

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A Multiband Imager for Magellan

• Christopher Stubbs
• Department of Physics Department of Astronomy
• Harvard University
• cstubbs_at_fas.harvard.edu

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Conceptual Design
r
g
Pass l gt 5500 A
Pass l gt 8500 A
z
Pass l gt 7000 A
Common shutter
i
3
Existing standard passbands
U B V R I
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Pan-Starrs bands
4000 A break at z of 0.2 0.5
0.8 1.0 1.25 1.5
g r i z
y
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Collaborators

• Christopher Stubbs, CfA Harvard Physics
• Melissa Franklin, Harvard Physics Dept
• Tony Stark, CfA
• John Geary, CfA
• South Pole Telescope/Dark Energy Survey
  collaboration J. Carlstrom, J. Mohr...
• Alan Uomoto, OCIW, has been very supportive

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Science Opportunities

• Supernova followup observations
• Type Ia and type II Sne as cosmological probes
• Requires multiband images, multiple epochs
• Photometric redshifts of clusters
• 4 band imaging over modest field
• Transient followup
• Evolution of SED for GRBs
• Microlensing light curves
• Planetary occultations
• Multiband data useful for discrimination

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Cosmology from SZ Clusters

• Multiple projects now funded and under way to use
  SZ effect to detect galaxy clusters, down to 2 x
  1014 Msolar
• Expectation is 7 clusters per sq degree
• South Pole Telescope will map 4000 sq deg 29,000
  clusters
• SZ signal strength z-independent
• Optical observations needed for z
• Spectroscopy SALT
• Wide field multiband survey DEC 2009
• Targeted moderate field multiband observations

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South Pole Telescope (SPT) Survey

• Bolometric focal plane, 1000 elements, and 10m
  aperture telescope.
• Will map Southern extragalactic sky
• RA from 20 hrs to 7 hrs
• DEC from 30 to 75 degrees
• Currently funded by NSF polar programs, under
  construction
• Early 2007 first light.

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Anticipated Cluster z-distribution
90 within zlt1.2 50 within zlt0.5
Carlstrom, Holder and Reese Ann Rev Astron
Astrophys, 2002
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Photometric Redshift for Clusters

• Photo-zs for individual galaxies tend to have
  scatter of sz/(1z)0.03, but with a few
  catastrophic outliers.
• Combination of morphology, magnitude, color and
  location can be used to establish clusters
  redshift.
• Robust statistics can be used to eliminate
  outliers.

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Photometric Redshifts in SDSS bands
Blanton et al, astro-ph/0205243
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Early-type galaxies in SDSS bands
Bernardi et al, astro-ph/031629

• g-r 0.7
• r-i 0.3
• r-z 0.8

g 20.7 r 20.0 i 19.7 z
19.2
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Relevant Magnitudes are 18ltrlt24
Brodwin et al, astro-ph/0310038
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Time (sec) to reach SNR10 Extended source,
ABmag in 2.2 arcsec aperture Dark time, 0.8
arcsec, airmass1.2, scaled to Magellan and
high-r http//rpm.cfht.hawaii.edu/megacam/diet/DI
ET.rpm
Galaxy colors roughly follow contours of constant
integration Shaded boxes are DEC target 10s
magnitudes. We should get ½ the clusters (those
with zlt0.5) in 60 sec
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Clusters per unit telescope time
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Return on Magellan Time Investment

• Could get 200 clusters out to z1, or 100
  clusters out to z of 1.5, in 1 night.
• Fifteen dark nights on Magellan could produce
  photo-zs for 3000 clusters out to z1, about 10
  of the total expected from SPT.

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Conceptual Optical Design Exists
Identical triplets (all spherical)
Doublet field flattener (2 aspheric surfaces)
Field stop
T. Stark, CfA
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Optical Performance

• Plate scale is 0.062 arcsec per 15 mm pixel
• FOV is 4.1 x 4.1 arcminutes ( 700 kpc at z0.3)
• 80 encircled energy in 0.15 arcsec

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Tightly coupled software/observing
Take Image 1 30 sec
Analyze Image flatten, WCS, sextractor
Galactic reddening corr. Produce z, sz OK?
Offset Take Image 2 30 sec
Offset if appropriate More images
Slew to next target
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Rapid Readout and High Efficiency

• Integrated SW reduces wasted time
• Binning 2x2 gives
• 0.124 arcsec/pix,
• Single amplifier output per 2K x 4K chip
• 8 sec readout _at_ 250Kpix/sec
• Effective telescope time multiplier
• For balanced exposures, sequential images take
• Tseries 4(texptreadout)x Nframes
• Parallel imager takes (with 0.8 throughput
  degradation)
• Tparallel (texp/0.8 treadout) x
  Nframes
• For texpgtgttreadout total time is reduced by a
  factor of 3

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Controlling Systematics

• Our design is readily baffled
• Can use both field stop and pupil stop
• Suppresses stray and scattered light
• Better flatfielding
• Single common shutter near pupil
• Reduced shutter artifacts
• Flux ratios with a single pointing and 2-3
  exposures, under all conditions!
• Even with patchy cloud cover, get Poisson-limited
  colors.

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Complementarity with Dark Energy Camera

• Multiband Camera 16 arcmin2, 6.5m aperture
• - Get 100 clusters to z1 in 4 hours.
• - Can be on the sky at start of SPT survey
• Dark Energy Camera 3 sq deg, single band, 4m
  aperture
• - Survey approach on CTIO 4m gets 3 sq deg
  x 7 clusters/sq deg 21 clusters per hour, or 84
  clusters in 4 hours.
• - Delivers other science as well weak
  lensing, SN detection...
• Multiband imagers cluster hunting advantage is
  100/84 1.2
• Does not take into account seeing advantage on
  Magellan
• Does not take into account cloud-immunity of
  multiband imager
• If SPT survey falls short of flux goals,
  multiband advantage increases
• Multiband camera better suited to chasing zgt1
  clusters.

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Two-stage plan

• 2007 2009
• SPT in operation
• Use multiband camera to image 2000 clusters
• Initial cluster count vs. z results
• Use camera for SN followup as well...
• Post-2009
• Dark Energy Camera on Blanco 4m (if )
• Deep wide DEC survey will find SNe
• Follow SN light curves with multiband camera
• Chase higher-z clusters with multiband camera

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Status

• Rough conceptual design done
• Proof-of-concept optical design done
• Detectors are in hand
• Lincoln labs 2K x 4K, 15 mm pixels
• Some epitaxial, some high-resistivity
• Readout electronics require replication
• MegaCam architecture and board set
• Machine shop capacity available

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Task list

• Modeling
• Slew vs. expose tradeoffs vs. redshift and
  richness
• Photo-z determination
• Hardware
• Finish design work, order optics
• Mechanical design, fabrication
• Electronics and detector optimization
• System integration, testing...
• Software
• Scripts that connect Sextractor to photoz codes
• Test with SDSS and IMACS data
• Integrate with instrument
• Proposals
• Plan is to submit NSF ATI proposal Nov 1.

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Summary

• A multiband imager for Magellan makes sense
• Multiple science drivers
• Unique capability
• Quality photometry
• Conceptual design completed
• Detectors on hand, optics straightforward
• Design needs to be refined, and optimal observing
  strategy devised
• Software is a key aspect.
• Your comments participation welcome!

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Backup Slides and residual clutter
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Cluster luminosity function

• DM 38.2 implies L 17.1 AB r mag at z 0.1

F(M)
Christlein and Zabludoff, astro-ph/0304031
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Solid w - 1 Dotted w -
0.6 Shortdash w - 0.2 Longdash open CDM
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Limiting Magnitude

• ½ L cluster galaxies at redshift 4000A break
  leaving blue filter
• g,r,i,z 22.8,23.4,24.0,23.3
• Complete cluster catalog
• Galaxy catalog completeness
• g,r,i,z 22.8,23.4,24.0,23.6
• Simple selection function
• Blue galaxy photo-z at faint mags
• g,r,i,z 24.0,24.0,24.0,23.6
• Photo-z for angular power spectra and weak
  lensing

AB Mag of ½ L