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Nod & Shuffle at Magellan
LCIR Survey Update
October 18 2002
GDDS Preview
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Conventional Slit Spectroscopy
• Sky subtraction is primary limitation– Slit irregularities– Flat-field errors– Residual Fringing– Geometric distortions– Low slit density on sky
• Beam switching ?– Variable sky spectrum– Read noise penalty– High read-out overhead
• The solution: ‘nod & shuffle’
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Obscured Charge
Storage Area
Obscured Charge Storage Area
First Exposure
Active slit area
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“A” position
“B” position
Now nod telescope and shuffle charge
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Nod & shuffle the other way
“A” position
“B” position
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Repeat N times and then readout
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Difference of two positions
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Finally shift and add both
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LBL High Resistivity CCDs
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LBL High Resistivity CCDs
No fringing, but high CR rates
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LBL High Resistivity CCDs
Straight average - 2 hours Nod & Shuffle
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LBL High Resistivity CCDs
+/- 200 DN rejection
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Sky cancellation: ‘nod and shuffle’Storage of ‘sky’ image next to object image via ‘charge shuffling’Zero extra noise introduced, rapid switching (60s)
A
B
AB
Typically A=60s/15 cy: 1800s exposure10 subtraction
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Another example
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GMOS N&S Sky residualsSUMMED along long slit (1.8 arcmin)
Raw Sky/20
Subtracted sky
(i.e. ~10 level is enough for 200,000 sec pointed obs.)
Cycle:A=60sB=60s
+ 25s o/head
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GMOS Nod&Shuffle Multislit
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GMOS Nod&Shuffle Multislit
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Maximum Slit Utilization
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Nod & Shuffle on IMACS
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Nod & Shuffle on IMACS
2’’ slits
2’’ gaps
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Micro-Shuffling on IMACS
2” slits
2” gaps
4000A per
spectrum
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Micro-Shuffling on IMACS
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Macro-Shuffling on IMACS
High Slit Density or IFU mode
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Macro-Shuffling on IMACS
High Slit Density or IFU mode
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Macro-Shuffling on IMACS
High Slit Density or IFU mode
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Technical and Practical Considerations• Telescope, Guider and CCD controller must be
well synchronized
• Active Optics must work with short dwell time
• Overheads must be minimized
• Mask making software needs special capabilities• Reduction software (done! - Abraham & Glazebrook)
• Order blocking filters?
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Las Campanas IR Survey
McCarthy, Persson, Martini, Koviak (OCIW)
Chen (MIT), Marzke(SFSU), Carlberg, Abraham(UT)
Ellis (Caltech)
Evolved Galaxies at
1 < z < 2
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Las Campanas IR Survey
• Goal: Empirical understanding of early galaxy evolution
• Target: 1 square degree to K = 21
• Pilot survey in 2000/2001: VRIH to H=20.5
• Six fields around the equator (2 in south!)
• 1 square degree in BVRIz’H
• 0.5 square degrees in J & K to K = 20.8
• 200+ redshifts with LDSS2
• ~ 50 redshifts with GMOS & LRIS
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Color-Magnitude Diagram
Stars
0.0 < z < 1.0
1.0 < z < 1.5
1.5 < z < 2.0
500 sq. arcmin
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Color-Color Diagrams
• Stars form distinct sequence
• Z > 1 galaxies appear at K ~ 19
• Z > 1.5 galaxies at K > 20.5
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Color-Color Diagrams
• Stars form distinct sequence
• Z < 1 galaxies well sampled at K ~ 19
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Color-Color Diagrams
• Stars form distinct sequence
• Z > 1 galaxies appear at K ~ 19
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Color-Color Diagrams
• Stars form distinct sequence
• Z > 1 galaxies appear at K ~ 19
• Z > 1.5 galaxies at K > 20
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Color-Color Diagrams
• Stars form distinct sequence
• Z > 1 galaxies appear at K ~ 19
• Z > 1.5 galaxies at K > 20
• Reddest galaxies follow minimal evolution track
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Color-Redshift Diagrams
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Photometric Redshifts from LCIR
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Photometric Redshifts from LCIR
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Clustering of Red Galaxies
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Evolving Luminosity Functions• LFs derived from photo-
z’s with modified likelihood approach
• LF at intermediate z agrees well with CNOC2
• Very little apparent evolution in L* to z ~ 1.2
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Gemini Deep Deep Survey
GDDS Team: Karl Glazebrook (JHU), Bob Abraham (Toronto), Pat McCarthy (OCIW), Rick Murowinski (DAO), Ray Carlberg (Toronto), Ron Marzke (SDSU), Sandra Savaglio (JHU), H-W Chen (OCIW) David Crampton (DAO), Isobel Hook (Oxford), Inger Jørgensen & Kathy Roth (Gemini)
Goal: Deep 100,000 sec MOS exposures on Las Campanas IR Survey fields to get redshifts of a complete K<22.4 I<25 sample covering 1<z<2
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Goals:• First Complete sample 1<z<2
– use photo-z’s to weed out low-z galaxies (BVRIzJHK)
• Determine luminosity and mass functions– Can we see the assembly of mass? – Massive galaxies at z=2 would severely trouble CDM– Mass(z) more robust than SFR(z)
• Relate to galaxy morphology (ACS)– Identify Ell/Sp/Irr over 1<z<2– Track low-z behavior to high-z
• E.g. can we see mass assembly of giant Ellipticals?• Can we track the dynamical evolution of spiral disks
• Track SFH over 1<z<2: – Age of galaxies, metallicities of population
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GDDS history• Sep 2001: start of GDDS evil planning• Jan 2002: team approached Gemini observatory with nod
& shuffle proposal• Feb 2002, obtained Gemini go-ahead.• Feb-May 2002. Implementation of N&S at DAO (~$10K
cost)• May 2002: first N&S engineering observations on 8m• July 2002: N&S commissioned on sky• Aug 2002: First 4 nights of GDDS Science Verification
for N&S success!!• Sep-Dec 2002: Band I queue time, 50 hrs
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Gemini + GMOS
GMOS spectrographGemini
GMOSLRISLDSS1
Tel.+instr. efficiency
GMOS represents the best possible option for a red sensitive MOS. Ideal system for nod & shuffle
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GDDS sample LCIRS
4 fields BVRIzJHKs
2626Limits:B<26.0 V<26.5R<26.8 I<25.8z<24.7 J<22.5H<22.5 Ks<22.4
Use photo-z’s to weed out z<0.7 foreground
I<25 typical model n(z):
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GDDS mask84 objects 2 tiers with150 l/mm grating
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GDDS Spectra77 objects 40,000 secs
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GDDS Nod&Shuffle Mask
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GDDS Nod&Shuffle Mask
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[OII] Redshifts from GDDS
23.7 < I(AB) < 24.2
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I=23.8
Example object: raw object+skyOH forest
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I=23.8 z=1.07
Example object: N&S subtracted[OII] 3727at 7700Å
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GDDS: Oct 2002 snapshot• GDDS SV Aug 2002 + Band I Queue time
(Sep/Oct 2002) Up to 100 ksec on first field (SA22)First 40 ksec now reduced and very preliminary redshifts
• TO COME 2002-2003 (total time awarded 50 hrs in Band I):Complete 3 GDDS fields, secure 100 z>1 redshifts
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GDDS: ultra-super-preliminary results
These are just the‘easy’ ones so far!~ 40 ksec
Working on CCF
Data on this field is still coming in.
Full 100,000 secswill pound on z=1.5old red galaxies
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High Redshift Elliptical Galaxies?
FeIIMgII
53W091 at z=1.393VI=2.2 IK=2.94
Model: 4 Gyr old stellar populationat z=1.4, age of Universe = 4.5Gyr
z(form) ≈10
Obj # 398 from GDDS SA22VI=1.7 IK=2.7
Wavelength / Angstroms
f
Rest-frame UV absorption line redshifts!
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Photometric Redshifts from LCIR
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Colors of GDDS galaxies
GDDS
HDF LBGs (Papovich et al. 2001)
z=1.4 E/S0 template
z=1.4 Sbc template
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Color-z of GDDS galaxies
At least halfway across the desert!!
Again just the easy ones…
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GDDS: summary• GDDS hits complete sample at z>1
– Photo-z selection z>1 ~works
• Gets spectra via ‘nod & shuffle’ sky cancellation– Successfully commissioned July-Aug 2002, have data
on first (half) field
• Are we seeing a dearth of high mass galaxies at z>1 ? Possible epoch of mass assembly?
• TO COME 2002-2003:Complete 3 GDDS fields, secure 100 redshifts Apply for HST/ACS imaging for morphologies
Mass function vs Morphology vs z.
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GDDS: seeking old
galaxies at z>1
z=1.4, IK=2.7