1

A Multiband Imager for Magellan A Multiband Imager for Magellan A Multiband Imager for Magellan A Multiband Imager for Magellan

Christopher StubbsChristopher Stubbs

Department of Physics Department of Physics DepartmeDepartment nt of Astronomyof Astronomy

Harvard UniversityHarvard Universitycstubbs@fas.harvard.educstubbs@fas.harvard.edu

Christopher StubbsChristopher Stubbs

Department of Physics Department of Physics DepartmeDepartment nt of Astronomyof Astronomy

Harvard UniversityHarvard Universitycstubbs@fas.harvard.educstubbs@fas.harvard.edu

                                                 

2

Conceptual DesignConceptual DesignConceptual DesignConceptual Design

Pass Pass > 7000 A> 7000 A

Pass Pass > 5500 A> 5500 A

Pass Pass > 8500 A> 8500 A

ii

zz

rr

gg

Common Common shuttershutter

3

Existing “standard” passbandsExisting “standard” passbandsExisting “standard” passbandsExisting “standard” passbands

U B V R I

4

Pan-Starrs bandsPan-Starrs bandsPan-Starrs bandsPan-Starrs bands

g r i z y

4000 A break at z of 0.2 0.5 0.8 1.0 1.25 1.5

5

CollaboratorsCollaboratorsCollaboratorsCollaborators

• Christopher Stubbs, CfA & Harvard PhysicsChristopher Stubbs, CfA & Harvard Physics• Melissa Franklin, Harvard Physics DeptMelissa Franklin, Harvard Physics Dept• Tony Stark, CfATony Stark, CfA• John Geary, CfAJohn Geary, CfA

• South Pole Telescope/Dark Energy Survey South Pole Telescope/Dark Energy Survey collaboration: J. Carlstrom, J. Mohr...collaboration: J. Carlstrom, J. Mohr...

Alan Uomoto, OCIW, has been very supportiveAlan Uomoto, OCIW, has been very supportive

• Christopher Stubbs, CfA & Harvard PhysicsChristopher Stubbs, CfA & Harvard Physics• Melissa Franklin, Harvard Physics DeptMelissa Franklin, Harvard Physics Dept• Tony Stark, CfATony Stark, CfA• John Geary, CfAJohn Geary, CfA

• South Pole Telescope/Dark Energy Survey South Pole Telescope/Dark Energy Survey collaboration: J. Carlstrom, J. Mohr...collaboration: J. Carlstrom, J. Mohr...

Alan Uomoto, OCIW, has been very supportiveAlan Uomoto, OCIW, has been very supportive

6

Science OpportunitiesScience OpportunitiesScience OpportunitiesScience Opportunities

• Supernova followup observationsSupernova followup observations• Type Ia and type II Sne as cosmological probes• Requires multiband images, multiple epochs

• Photometric redshifts of clustersPhotometric redshifts of clusters• 4 band imaging over modest field

• Transient followupTransient followup• Evolution of SED for GRBs• Microlensing light curves

• Planetary occultationsPlanetary occultations• Multiband data useful for discrimination

• Supernova followup observationsSupernova followup observations• Type Ia and type II Sne as cosmological probes• Requires multiband images, multiple epochs

• Photometric redshifts of clustersPhotometric redshifts of clusters• 4 band imaging over modest field

• Transient followupTransient followup• Evolution of SED for GRBs• Microlensing light curves

• Planetary occultationsPlanetary occultations• Multiband data useful for discrimination

7

Cosmology from SZ ClustersCosmology from SZ ClustersCosmology from SZ ClustersCosmology from SZ Clusters

• Multiple projects now funded and under way to use Multiple projects now funded and under way to use SZ effect to detect galaxy clusters, down to ~2 SZ effect to detect galaxy clusters, down to ~2 xx 10 101414 MMsolarsolar

• Expectation is ~ 7 clusters per sq degreeExpectation is ~ 7 clusters per sq degree• South Pole Telescope will map 4000 sq deg; 29,000 clusters

• SZ signal strength z-independentSZ signal strength z-independent • Optical observations needed for zOptical observations needed for z

• Spectroscopy – SALT • Wide field multiband survey – DEC 2009 • Targeted moderate field multiband observations

• Multiple projects now funded and under way to use Multiple projects now funded and under way to use SZ effect to detect galaxy clusters, down to ~2 SZ effect to detect galaxy clusters, down to ~2 xx 10 101414 MMsolarsolar

• Expectation is ~ 7 clusters per sq degreeExpectation is ~ 7 clusters per sq degree• South Pole Telescope will map 4000 sq deg; 29,000 clusters

• SZ signal strength z-independentSZ signal strength z-independent • Optical observations needed for zOptical observations needed for z

• Spectroscopy – SALT • Wide field multiband survey – DEC 2009 • Targeted moderate field multiband observations

8

South Pole Telescope (SPT) SurveySouth Pole Telescope (SPT) SurveySouth Pole Telescope (SPT) SurveySouth Pole Telescope (SPT) Survey

• Bolometric focal plane, 1000 Bolometric focal plane, 1000 elements, and 10m aperture elements, and 10m aperture telescope. telescope.

• Will map Southern Will map Southern extragalactic skyextragalactic sky

• RA from 20 hrs to 7 hrs• DEC from –30 to –75 degrees

• Currently funded by NSF Currently funded by NSF polar programs, under polar programs, under constructionconstruction

• Early 2007 first light. Early 2007 first light.

• Bolometric focal plane, 1000 Bolometric focal plane, 1000 elements, and 10m aperture elements, and 10m aperture telescope. telescope.

• Will map Southern Will map Southern extragalactic skyextragalactic sky

• RA from 20 hrs to 7 hrs• DEC from –30 to –75 degrees

• Currently funded by NSF Currently funded by NSF polar programs, under polar programs, under constructionconstruction

• Early 2007 first light. Early 2007 first light.

9

Anticipated Cluster z-distributionAnticipated Cluster z-distributionAnticipated Cluster z-distributionAnticipated Cluster z-distribution

90% within z<1.290% within z<1.2

50% within z<0.550% within z<0.5

Carlstrom, Holder and ReeseCarlstrom, Holder and ReeseAnn Rev Astron AstrophysAnn Rev Astron Astrophys, 2002, 2002

10

Photometric Redshift for ClustersPhotometric Redshift for ClustersPhotometric Redshift for ClustersPhotometric Redshift for Clusters

• Photo-z’s for individual galaxies tend to Photo-z’s for individual galaxies tend to have scatter of have scatter of zz/(1+z)~0.03, but with a /(1+z)~0.03, but with a few “catastrophic” outliers. few “catastrophic” outliers.

• Combination of morphology, magnitude, Combination of morphology, magnitude, color and location can be used to color and location can be used to establish cluster’s redshift. establish cluster’s redshift.

• Robust statistics can be used to Robust statistics can be used to eliminate “outliers”.eliminate “outliers”.

• Photo-z’s for individual galaxies tend to Photo-z’s for individual galaxies tend to have scatter of have scatter of zz/(1+z)~0.03, but with a /(1+z)~0.03, but with a few “catastrophic” outliers. few “catastrophic” outliers.

• Combination of morphology, magnitude, Combination of morphology, magnitude, color and location can be used to color and location can be used to establish cluster’s redshift. establish cluster’s redshift.

• Robust statistics can be used to Robust statistics can be used to eliminate “outliers”.eliminate “outliers”.

11

Photometric Redshifts in SDSS bandsPhotometric Redshifts in SDSS bandsPhotometric Redshifts in SDSS bandsPhotometric Redshifts in SDSS bands

Blanton et al, astro-ph/0205243Blanton et al, astro-ph/0205243

12

Early-type galaxies in SDSS bandsEarly-type galaxies in SDSS bandsEarly-type galaxies in SDSS bandsEarly-type galaxies in SDSS bands

g-r 0.7g-r 0.7

r-i 0.3r-i 0.3

r-z 0.8r-z 0.8

g-r 0.7g-r 0.7

r-i 0.3r-i 0.3

r-z 0.8r-z 0.8

Bernardi et al, astro-ph/031629Bernardi et al, astro-ph/031629

g 20.7g 20.7r 20.0r 20.0i 19.7i 19.7z 19.2z 19.2

13 Brodwin et al, astro-ph/0310038

Relevant Magnitudes are 18<r<24Relevant Magnitudes are 18<r<24Relevant Magnitudes are 18<r<24Relevant Magnitudes are 18<r<24

14

m ABm AB gg rr ii zz Median redshiftMedian redshift

(r mag)(r mag)

2323 3535 8686 320320 870870 0.52 to 230.52 to 23rdrd

23.523.5 7878 210210 800800 22002200 0.730.73

2424 180180 500500 19001900 55005500 0.850.85

24.524.5 450450 12001200 49004900 1300013000 1.011.01

Time (sec) to reach SNR=10 Time (sec) to reach SNR=10 Extended source, ABmag in 2.2 arcsec apertureExtended source, ABmag in 2.2 arcsec apertureDark time, 0.8 arcsec, airmass=1.2, scaled to Magellan and high-Dark time, 0.8 arcsec, airmass=1.2, scaled to Magellan and high-http://rpm.cfht.hawaii.edu/~megacam/diet/DIET.rpm

Galaxy colors roughly follow contours of constant integration Galaxy colors roughly follow contours of constant integration

Shaded boxes are DEC target 10Shaded boxes are DEC target 10 magnitudes. magnitudes.

We should get ½ the clusters (those with z<0.5) in 60 secWe should get ½ the clusters (those with z<0.5) in 60 sec

15

Clusters per unit telescope timeClusters per unit telescope timeClusters per unit telescope timeClusters per unit telescope timeZ rangeZ range NN Time (seconds)Time (seconds)

0 – 0.20 – 0.2 1515 15*60 = 90015*60 = 900

0.2 – 0.40.2 – 0.4 30 30 30*60 = 180030*60 = 1800

0.4 – 0.60.4 – 0.6 30 30 30*60 = 180030*60 = 1800

0.6 – 0.80.6 – 0.8 1515 15*200 = 300015*200 = 3000

0.8 – 1.00.8 – 1.0 1010 10*600 = 600010*600 = 6000

1.0 – 1.21.0 – 1.2 99

1.2 – 1.41.2 – 1.4 44 15*1000= 1500015*1000= 15000

1.4 – 1.61.4 – 1.6 22

totalstotals 115115 ~4 hrs for 100, z<1~4 hrs for 100, z<1

4.2 hours for 15 more, z>14.2 hours for 15 more, z>1

16

Return on Magellan Time InvestmentReturn on Magellan Time InvestmentReturn on Magellan Time InvestmentReturn on Magellan Time Investment

Could get 200 clusters out to z~1, or 100 Could get 200 clusters out to z~1, or 100 clusters out to z of 1.5, in 1 night.clusters out to z of 1.5, in 1 night.

Fifteen dark nights on Magellan could Fifteen dark nights on Magellan could produce photo-z’s for 3000 clusters out produce photo-z’s for 3000 clusters out to z=1, about 10% of the total expected to z=1, about 10% of the total expected from SPT. from SPT.

Could get 200 clusters out to z~1, or 100 Could get 200 clusters out to z~1, or 100 clusters out to z of 1.5, in 1 night.clusters out to z of 1.5, in 1 night.

Fifteen dark nights on Magellan could Fifteen dark nights on Magellan could produce photo-z’s for 3000 clusters out produce photo-z’s for 3000 clusters out to z=1, about 10% of the total expected to z=1, about 10% of the total expected from SPT. from SPT.

17

Conceptual Optical Design ExistsConceptual Optical Design ExistsConceptual Optical Design ExistsConceptual Optical Design Exists

Doublet field flattenerDoublet field flattener(2 aspheric surfaces)(2 aspheric surfaces)

Field stopField stop

Identical tripletsIdentical triplets(all spherical)(all spherical)

T. Stark, CfA

18

Optical PerformanceOptical PerformanceOptical PerformanceOptical PerformancePlate scale is 0.062 arcsec per 15 Plate scale is 0.062 arcsec per 15 m pixelm pixel

FOV is 4.1 x 4.1 arcminutes (~ 700 kpc at z=0.3)FOV is 4.1 x 4.1 arcminutes (~ 700 kpc at z=0.3)

80% encircled energy in ~0.15 arcsec:80% encircled energy in ~0.15 arcsec:

Plate scale is 0.062 arcsec per 15 Plate scale is 0.062 arcsec per 15 m pixelm pixel

FOV is 4.1 x 4.1 arcminutes (~ 700 kpc at z=0.3)FOV is 4.1 x 4.1 arcminutes (~ 700 kpc at z=0.3)

80% encircled energy in ~0.15 arcsec:80% encircled energy in ~0.15 arcsec:

19

Tightly coupled software/observingTightly coupled software/observingTightly coupled software/observingTightly coupled software/observing

Take Image 1Take Image 130 sec 30 sec

Analyze Image: Analyze Image: flatten, WCS, sextractor flatten, WCS, sextractor Galactic reddening corr.Galactic reddening corr.

Produce z, Produce z, zz

OK? OK?

OffsetOffsetTake Image 2Take Image 2

30 sec 30 sec

Slew to next targetSlew to next target

Offset if appropriateOffset if appropriate

More imagesMore images

20

Rapid Readout and High EfficiencyRapid Readout and High EfficiencyRapid Readout and High EfficiencyRapid Readout and High EfficiencyIntegrated SW reduces wasted timeIntegrated SW reduces wasted timeBinning 2x2 gives Binning 2x2 gives

• 0.124 arcsec/pix, • Single amplifier output per 2K x 4K chip

8 sec readout @ 250Kpix/sec

Effective telescope time multiplier:Effective telescope time multiplier:• For “balanced” exposures, sequential images take

Tseries = 4(texp+treadout)x Nframes • Parallel imager takes (with 0.8 throughput degradation)

Tparallel = (texp/0.8 + treadout) x Nframes

For texp>>treadout total time is reduced by a factor of ~3

Integrated SW reduces wasted timeIntegrated SW reduces wasted timeBinning 2x2 gives Binning 2x2 gives

• 0.124 arcsec/pix, • Single amplifier output per 2K x 4K chip

8 sec readout @ 250Kpix/sec

Effective telescope time multiplier:Effective telescope time multiplier:• For “balanced” exposures, sequential images take

Tseries = 4(texp+treadout)x Nframes • Parallel imager takes (with 0.8 throughput degradation)

Tparallel = (texp/0.8 + treadout) x Nframes

For texp>>treadout total time is reduced by a factor of ~3

21

Controlling SystematicsControlling SystematicsControlling SystematicsControlling Systematics

• Our design is readily baffledOur design is readily baffled• Can use both field stop and pupil stop• Suppresses stray and scattered light• Better flatfielding

• Single common shutter near pupilSingle common shutter near pupil• Reduced shutter artifacts

• Flux ratios with a single pointing and 2-3 Flux ratios with a single pointing and 2-3 exposures, under all conditions!exposures, under all conditions!

• Even with patchy cloud cover, get Poisson-limited colors.

• Our design is readily baffledOur design is readily baffled• Can use both field stop and pupil stop• Suppresses stray and scattered light• Better flatfielding

• Single common shutter near pupilSingle common shutter near pupil• Reduced shutter artifacts

• Flux ratios with a single pointing and 2-3 Flux ratios with a single pointing and 2-3 exposures, under all conditions!exposures, under all conditions!

• Even with patchy cloud cover, get Poisson-limited colors.

22

Complementarity Complementarity with Dark Energy Camerawith Dark Energy Camera

Complementarity Complementarity with Dark Energy Camerawith Dark Energy Camera

Multiband Camera:Multiband Camera: 16 arcmin 16 arcmin22, 6.5m aperture:, 6.5m aperture:

- Get 100 clusters to z~1 in 4 hours. - Get 100 clusters to z~1 in 4 hours.

- Can be on the sky at start of SPT survey- Can be on the sky at start of SPT survey

Dark Energy CameraDark Energy Camera: 3 sq deg, single band, 4m: 3 sq deg, single band, 4m aperture:aperture:

- Survey approach on CTIO 4m gets 3 sq deg x 7 clusters/sq deg = 21 - Survey approach on CTIO 4m gets 3 sq deg x 7 clusters/sq deg = 21 clusters per hour, or 84 clusters in 4 hours.clusters per hour, or 84 clusters in 4 hours.

- Delivers other science as well: weak lensing, SN detection... - Delivers other science as well: weak lensing, SN detection...

Multiband imager’s cluster hunting advantage is 100/84 = 1.2 Multiband imager’s 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 z>1 clusters. Multiband camera better suited to chasing z>1 clusters.

Multiband Camera:Multiband Camera: 16 arcmin 16 arcmin22, 6.5m aperture:, 6.5m aperture:

- Get 100 clusters to z~1 in 4 hours. - Get 100 clusters to z~1 in 4 hours.

- Can be on the sky at start of SPT survey- Can be on the sky at start of SPT survey

Dark Energy CameraDark Energy Camera: 3 sq deg, single band, 4m: 3 sq deg, single band, 4m aperture:aperture:

- Survey approach on CTIO 4m gets 3 sq deg x 7 clusters/sq deg = 21 - Survey approach on CTIO 4m gets 3 sq deg x 7 clusters/sq deg = 21 clusters per hour, or 84 clusters in 4 hours.clusters per hour, or 84 clusters in 4 hours.

- Delivers other science as well: weak lensing, SN detection... - Delivers other science as well: weak lensing, SN detection...

Multiband imager’s cluster hunting advantage is 100/84 = 1.2 Multiband imager’s 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 z>1 clusters. Multiband camera better suited to chasing z>1 clusters.

23

Two-stage planTwo-stage planTwo-stage planTwo-stage plan• 2007 – 20092007 – 2009: : SPT in operationSPT in operation Use multiband camera to image ~2000 clustersUse multiband camera to image ~2000 clusters

Initial cluster count vs. z resultsInitial cluster count vs. z results Use camera for SN followup as well...Use camera for SN followup as well...• Post-2009:Post-2009: Dark Energy Camera on Blanco 4m (if $)Dark Energy Camera on Blanco 4m (if $) Deep wide DEC survey will find SNe Deep wide DEC survey will find SNe Follow SN light curves with multiband cameraFollow SN light curves with multiband camera Chase higher-z clusters with multiband cameraChase higher-z clusters with multiband camera

• 2007 – 20092007 – 2009: : SPT in operationSPT in operation Use multiband camera to image ~2000 clustersUse multiband camera to image ~2000 clusters

Initial cluster count vs. z resultsInitial cluster count vs. z results Use camera for SN followup as well...Use camera for SN followup as well...• Post-2009:Post-2009: Dark Energy Camera on Blanco 4m (if $)Dark Energy Camera on Blanco 4m (if $) Deep wide DEC survey will find SNe Deep wide DEC survey will find SNe Follow SN light curves with multiband cameraFollow SN light curves with multiband camera Chase higher-z clusters with multiband cameraChase higher-z clusters with multiband camera

24

StatusStatusStatusStatus

• Rough conceptual design doneRough conceptual design done

• Proof-of-concept optical design doneProof-of-concept optical design done

• Detectors are in handDetectors are in hand• Lincoln labs 2K x 4K, 15 m pixels• Some epitaxial, some high-resistivity

• Readout electronics require replicationReadout electronics require replication• MegaCam architecture and board set

• Machine shop capacity availableMachine shop capacity available

• Rough conceptual design doneRough conceptual design done

• Proof-of-concept optical design doneProof-of-concept optical design done

• Detectors are in handDetectors are in hand• Lincoln labs 2K x 4K, 15 m pixels• Some epitaxial, some high-resistivity

• Readout electronics require replicationReadout electronics require replication• MegaCam architecture and board set

• Machine shop capacity availableMachine shop capacity available

25

Task listTask listTask listTask list• ModelingModeling

• Slew vs. expose tradeoffs vs. redshift and richness

• Photo-z determination

• HardwareHardware• Finish design work, order optics

• Mechanical design, fabrication

• Electronics and detector optimization

• System integration, testing...

• SoftwareSoftware• Scripts that connect Sextractor to photoz codes

• Test with SDSS and IMACS data

• Integrate with instrument

• ProposalsProposals• Plan is to submit NSF ATI proposal Nov 1.

• ModelingModeling• Slew vs. expose tradeoffs vs. redshift and richness

• Photo-z determination

• HardwareHardware• Finish design work, order optics

• Mechanical design, fabrication

• Electronics and detector optimization

• System integration, testing...

• SoftwareSoftware• Scripts that connect Sextractor to photoz codes

• Test with SDSS and IMACS data

• Integrate with instrument

• ProposalsProposals• Plan is to submit NSF ATI proposal Nov 1.

26

SummarySummarySummarySummary• A multiband imager for Magellan makes A multiband imager for Magellan makes

sense:sense:• Multiple science drivers• Unique capability• Quality photometry

• Conceptual design completedConceptual design completed• Detectors on hand, optics straightforwardDetectors on hand, optics straightforward• Design needs to be refined, and optimal Design needs to be refined, and optimal

observing strategy devisedobserving strategy devised• Software is a key aspect. Software is a key aspect. • Your comments & participation welcome!Your comments & participation welcome!

• A multiband imager for Magellan makes A multiband imager for Magellan makes sense:sense:

• Multiple science drivers• Unique capability• Quality photometry

• Conceptual design completedConceptual design completed• Detectors on hand, optics straightforwardDetectors on hand, optics straightforward• Design needs to be refined, and optimal Design needs to be refined, and optimal

observing strategy devisedobserving strategy devised• Software is a key aspect. Software is a key aspect. • Your comments & participation welcome!Your comments & participation welcome!

27

Backup Slides and residual clutterBackup Slides and residual clutterBackup Slides and residual clutterBackup Slides and residual clutter

28

Cluster luminosity functionCluster luminosity functionCluster luminosity functionCluster luminosity function

DM= 38.2 implies L* ~ 17.1 AB r mag at z = 0.1DM= 38.2 implies L* ~ 17.1 AB r mag at z = 0.1DM= 38.2 implies L* ~ 17.1 AB r mag at z = 0.1DM= 38.2 implies L* ~ 17.1 AB r mag at z = 0.1

(M)(M)

Christlein and Zabludoff, astro-ph/0304031Christlein and Zabludoff, astro-ph/0304031

29

Solid: w= Solid: w= 11Dotted: w= Dotted: w= 0.60.6Shortdash: w= Shortdash: w= 0.20.2Longdash: open CDMLongdash: open CDM

30

Limiting MagnitudeLimiting Magnitude Limiting MagnitudeLimiting Magnitude

• ½ L* cluster galaxies at redshift ½ L* cluster galaxies at redshift 4000A break leaving blue filter4000A break leaving blue filter g,r,i,z = 22.8,23.4,24.0,23.3 Complete cluster catalog

• Galaxy catalog completenessGalaxy catalog completeness g,r,i,z = 22.8,23.4,24.0,23.6 Simple selection function

• Blue galaxy photo-z at faint Blue galaxy photo-z at faint magsmags g,r,i,z = 24.0,24.0,24.0,23.6 Photo-z for angular power spectra

and weak lensing

• ½ L* cluster galaxies at redshift ½ L* cluster galaxies at redshift 4000A break leaving blue filter4000A break leaving blue filter g,r,i,z = 22.8,23.4,24.0,23.3 Complete cluster catalog

• Galaxy catalog completenessGalaxy catalog completeness g,r,i,z = 22.8,23.4,24.0,23.6 Simple selection function

• Blue galaxy photo-z at faint Blue galaxy photo-z at faint magsmags g,r,i,z = 24.0,24.0,24.0,23.6 Photo-z for angular power spectra

and weak lensing

AB

Ma

g

of

½ L

*