Nod & Shuffle at Magellan LCIR Survey Update October 18 2002 GDDS Preview.
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Transcript of Nod & Shuffle at Magellan LCIR Survey Update October 18 2002 GDDS Preview.
Nod & Shuffle at Magellan
LCIR Survey Update
October 18 2002
GDDS Preview
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’
Obscured Charge
Storage Area
Obscured Charge Storage Area
First Exposure
Active slit area
“A” position
“B” position
Now nod telescope and shuffle charge
Nod & shuffle the other way
“A” position
“B” position
Repeat N times and then readout
Difference of two positions
Finally shift and add both
LBL High Resistivity CCDs
LBL High Resistivity CCDs
No fringing, but high CR rates
LBL High Resistivity CCDs
Straight average - 2 hours Nod & Shuffle
LBL High Resistivity CCDs
+/- 200 DN rejection
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
Another example
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
GMOS Nod&Shuffle Multislit
GMOS Nod&Shuffle Multislit
Maximum Slit Utilization
Nod & Shuffle on IMACS
Nod & Shuffle on IMACS
2’’ slits
2’’ gaps
Micro-Shuffling on IMACS
2” slits
2” gaps
4000A per
spectrum
Micro-Shuffling on IMACS
Macro-Shuffling on IMACS
High Slit Density or IFU mode
Macro-Shuffling on IMACS
High Slit Density or IFU mode
Macro-Shuffling on IMACS
High Slit Density or IFU mode
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?
Las Campanas IR Survey
McCarthy, Persson, Martini, Koviak (OCIW)
Chen (MIT), Marzke(SFSU), Carlberg, Abraham(UT)
Ellis (Caltech)
Evolved Galaxies at
1 < z < 2
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
Color-Magnitude Diagram
Stars
0.0 < z < 1.0
1.0 < z < 1.5
1.5 < z < 2.0
500 sq. arcmin
Color-Color Diagrams
• Stars form distinct sequence
• Z > 1 galaxies appear at K ~ 19
• Z > 1.5 galaxies at K > 20.5
Color-Color Diagrams
• Stars form distinct sequence
• Z < 1 galaxies well sampled at K ~ 19
Color-Color Diagrams
• Stars form distinct sequence
• Z > 1 galaxies appear at K ~ 19
Color-Color Diagrams
• Stars form distinct sequence
• Z > 1 galaxies appear at K ~ 19
• Z > 1.5 galaxies at K > 20
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
Color-Redshift Diagrams
Photometric Redshifts from LCIR
Photometric Redshifts from LCIR
Clustering of Red Galaxies
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
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
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
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
Gemini + GMOS
GMOS spectrographGemini
GMOSLRISLDSS1
Tel.+instr. efficiency
GMOS represents the best possible option for a red sensitive MOS. Ideal system for nod & shuffle
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):
GDDS mask84 objects 2 tiers with150 l/mm grating
GDDS Spectra77 objects 40,000 secs
GDDS Nod&Shuffle Mask
GDDS Nod&Shuffle Mask
[OII] Redshifts from GDDS
23.7 < I(AB) < 24.2
I=23.8
Example object: raw object+skyOH forest
I=23.8 z=1.07
Example object: N&S subtracted[OII] 3727at 7700Å
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
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
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!
Photometric Redshifts from LCIR
Colors of GDDS galaxies
GDDS
HDF LBGs (Papovich et al. 2001)
z=1.4 E/S0 template
z=1.4 Sbc template
Color-z of GDDS galaxies
At least halfway across the desert!!
Again just the easy ones…
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.
GDDS: seeking old
galaxies at z>1
z=1.4, IK=2.7