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