3D Spectroscopy3D Spectroscopy

Francisco Müller Sánchez

Instituto de Astrofísica de Canarias

La Laguna, España

Introductory Review and Observational Techniques

Science motivation for 3D Spectroscopy Instrumentation Preparation of Observations and Principles of Data Reduction

Data Analysis

Examples of SINFONI-AO: prototypical merger Examples of SINFONI-AO: prototypical merger NGC6240 NGC6240

velo

city

flux

stars molecular gas ionised gas1”

Analysis of data cubes Analysis of data cubes

Introductory Review and Observational Introductory Review and Observational techniquestechniques

Classical observational techniques Strengths of 3D Data Concepts of Adaptive Optics Instrument techniques used to achieve 3D Spectroscopy

Beckers 1993: ARA&A 31, 13Hardy 1998: Adaptive Optics for Astronomical TelescopesAntichi 2009: ApJ, 695, 1042Kissler-Patig 2005: Science perspectives for 3D spectroscopyalso Sterne & Weltraum articles 1994 (Hippler, Kasper, Davies, Ragazzoni)

Ancient Mayan PhotometryAncient Mayan Photometry

- An eclipse table that predicts times when eclipses may occur.

- A Venus table that predicts the times when Venus appears as morning star and the other apparitions of the planet.

- A Mars table that records the times when Mars goes into retrograde motion. A second Mars table that tracks the planet's motion along the ecliptic has recently been identified.

PhotometryPhotometry

The venerable photographic plate and its more recent version, the CCD, provide objective information in two dimensions concerning the brightness, I(x,y), of an extended object or area of sky.

SpectroscopySpectroscopy

SpectroscopySpectroscopy

Long-slit spectroscopy enables us to split the light that reaches us not just from a point but also from an entire line of points into its constituent colours, thereby providing us with information in two dimensions - position along the slit, x, and colour, lambda:I(x,lambda)

Why not combine them?Why not combine them?

3D spectroscopy attempts to get closer to the fundamental goal of astronomical observing techniques, which is to record the direction, wavelength, polarization state and arrival time for every incoming photon over the largest field of view. In fact using 3D spectroscopy, the wavelength and the incoming direction in a 2D field of view are recorded in a (x,y,λ) data cube, in contrast with standard techniques which either do imaging over a 2D field, or spectroscopy along a 1D slit.

Color

3D spectroscopy yields datacubes3D spectroscopy yields datacubes

Scanning Spectrophotometers (Fabry-Perot Scanning Spectrophotometers (Fabry-Perot interferometer)interferometer)

The FPI can be used to obtain monochromatic images over a full two-dimensional field of view with spectral resolutions comparable to those of grating spectrographs. In a Fabry-Pérot the distance between the plates can be tuned in order to change the wavelengths at which transmission peaks occur in the interferometer.

Imaging Fourier Transform SpectroscopyImaging Fourier Transform Spectroscopy

Imaging SpectroscopyImaging Spectroscopy

Scanning Long-Slit SpectroscopyScanning Long-Slit Spectroscopy

Energy-Resolving DetectorsEnergy-Resolving Detectors

Tantalum superconducting tunnel junctions Peacock et al. 1998

Integral-Field UnitsIntegral-Field Units

Concept of integral-field spectroscopyConcept of integral-field spectroscopy

Don’t confuse IFS with MOS (Multi Object Don’t confuse IFS with MOS (Multi Object Spectroscopy)Spectroscopy)

LUCIFER at the LBT

Three ways of doing IFSThree ways of doing IFS

Lenslets (TIGER Approach)Lenslets (TIGER Approach)

Example of lenslet IFU: SAURON @ WHTExample of lenslet IFU: SAURON @ WHT

Fibers (ARGUS approach)Fibers (ARGUS approach)

Example of fibers IFU: INTEGRAL @ WHTExample of fibers IFU: INTEGRAL @ WHT

SlicersSlicers

SINFONI - made @ MPE

Example of Image slicer IFU: SINFONI @ VLTExample of Image slicer IFU: SINFONI @ VLT

Strengths of 3D data 1Strengths of 3D data 1

- No slit losses: high system efficiency

- Less time consuming

- More accurate radial velocity determination

- Background estimate can be obtained simultaneously

- Kinematics of crowded regions

- It doesn’t suffer from changes of several exposures

Strengths of 3D data 2. Einstein’s cross sectionStrengths of 3D data 2. Einstein’s cross section

Atmospheric TurbulenceAtmospheric Turbulence

2)'()'()( rrfrfrD

for Kolmogorov statistics, the refractive index structure function is

van Karman model includes inner (~1cm) & outer (~30m) scales

3/22)( rCrD Nn

0

23/52

sec2

91.2)( dhCrrD N

for a wavefront propagating through the atmosphere, the phase structure function is

quantified using the structure function

CN2 at Mt Graham

(LBT site)

Atmospheric TurbulenceAtmospheric Turbulence

CN2 is refractive index

structure constant.

Turbulence limits the resolution of a telescope to λ/r0 instead of λ/D.

5/3

0

20

dhCr N

The integral of CN2 is

Fried’s parameter

and variance of wavefront aberrations is just

3/5

0

2 030.1

r

D

Everything depends on CEverything depends on CNN22

5/3

0

25/35/60 sec185.0

dhCr N

coherence length 0r

where

windVr00 314.0

5/3

0

2

0

3/52

dhCdhvCV NNwind

coherence timescale

where

assumes Taylor’s frozen flow hypothesis

Hr /314.0 00 5/3

0

2

0

3/52sec

dhCdhhCH NNwhere

isoplanatic angle

Impact of a Perturbed WavefrontImpact of a Perturbed Wavefront

blurPoint focus

parallel light rays can be focussed

light rays affected by turbulence

how well spatial frequencies are transferred through the optical system

resulting shape of a point source

coma & trefoil

Modal DecompositionModal Decomposition

Most common & simplest for a circular aperture are Zernike modes.

For an annular aperture, Karhunen-Loève modes are better.

A simple adaptive optics systemA simple adaptive optics system

open & closed loop images

Neptune (Keck, NGS)

star (Calar Alto, LGS)

Shack Hartmann SensorShack Hartmann Sensor

Measures first derivative of wavefront (gradients)

Displacement of spots is proportional to the wavefront tilt

Many algorithms possible for centroiding

Easy to extend to very high order systems

Divides pupil into subapertures

(developed in 1900 by J.Hartmann)

Shack Hartmann SensorShack Hartmann Sensor

Piezo Actuator MirrorsPiezo Actuator Mirrors

349 actuator DM

wiring on back sidereference block

thin flexible (glass) mirror

piezo actuators which contract & lengthen when voltages are applied

incoming wavefront will be flat when it reflects off the mirror

Curvature SensorCurvature Sensor (developed in 1994 by F.Roddier)

A few things to bear in mindA few things to bear in mind

- AO works better at longer wavelengths (dependence of r0 on λ6/5)e.g. consider a phase change of 250nm with respect to 500nm optical light and 2.2μm near infrared light. So at longer wavelengths, coherence length is greater & timescales are longer

- One can measure in optical & correct in infrared (absolute phase change is same)- AO systems have to run fast (bandwidth ~1/10 of the frame rate)

prediction would be great…

time

ampl

itude

of a

berr

atio

n

Residual Wavefront Variance & Strehl RatioResidual Wavefront Variance & Strehl Ratio

coherence length

isoplanatic angle

3/50

232 2944.0~ rDjfitting

3/50

2 angle

total wavefront variance ...22222 noisetimedelayanglefittingtotal

for large j (number of Zernike modes)

Strehl ratio 2exp~ SR ratio of peak intensity to that for a perfect optical system

coherence timescale 3/50

2 timedelay

Sodium & Rayleigh Laser Guide StarsSodium & Rayleigh Laser Guide Stars

MMT

VLT

Keck

sky coverage few % with NGS but ~50% with LGS(most coverage in galactic plane; almost none at galactic pole)

Starfire Optical Range, Calar Alto, Lick, MMT, Keck, VLT, Subaru, Gemini North, WHT, Palomar 200”, Mt Wilson 100”, (LBT, Gemini South)

A few issues with Laser Guide StarsA few issues with Laser Guide Stars

sodium density

heig

ht (

km)

time (min)

on-axis LGS spot

off-axis LGS spot

1. laser technology2. elongation of spot due to finite thickness of layer 3. variations in height of sodium layer 4. need for tip-tilt star

MultiConjugate Adaptive OpticsMultiConjugate Adaptive Optics

1 star & 1 DM

3 stars & 2 DMs

MAD strehl maps reference stars

high turbulence layer

low turbulence layer

telescope

one wavefront sensor per star

DM1

DM2

WFSs

MultiConjugate Adaptive OpticsMultiConjugate Adaptive Optics

This is computationally complex

Classical MCAO needs multiple guide stars (e.g. Gemini South MCAO needs 5 LGS & 3 NGS).

Instead, one can use the layer oriented approach, with LGS or NGS.

reference stars

high turbulence layer

low turbulence layer

telescope

one wavefront sensor per deformable mirror

DM1

DM2

WFS1

WFS1

LINC-NIRVANA on the LBT uses pyramid sensors to co-add the light from many faint stars on the detector;but note that the strehl ratio is expected to be limited & vary a bit over the field

Examples of LGS-AO: interacting galaxies IRAS 09061-Examples of LGS-AO: interacting galaxies IRAS 09061-12481248

NACO-LGS/VLTUKIRT (archive)

K-band image of these interacting galaxies shows the vast amount more detail that LGS-AO can reveal

Examples of LGS-AO: prototypical merger NGC6240 Examples of LGS-AO: prototypical merger NGC6240

Komossa et al. 2003 Tecza et al. 2000

2µm continuum

1”

Examples of LGS-AO: prototypical merger NGC6240 Examples of LGS-AO: prototypical merger NGC6240 ve

loci

tyflu

x

stars molecular gas ionised gas1”

Examples of LGS-AO: high redshift galaxiesExamples of LGS-AO: high redshift galaxies

Future perspectives: FRIDA @ GTCFuture perspectives: FRIDA @ GTC

Future perspectives: SERPIL @ LBTFuture perspectives: SERPIL @ LBT

Multiple IFS: KMOS @ VLTMultiple IFS: KMOS @ VLT

Multiple IFS: KMOS @ VLTMultiple IFS: KMOS @ VLT

IFS @ ELTIFS @ ELT

Outlook for tomorrow’s lectureOutlook for tomorrow’s lecture

Science perspectives for IFS

Galactic astronomy

The Galactic Center

Nearby AGN Quasars and high-z galaxies

Bimorph MirrorsBimorph Mirrors

bimorph mirror for Gemini, showing the zones

2 layer piezo ceramic which bends when a voltage is applied

continuous electrode

control electrodes

thin glass mirror

incoming wavefront will be flat when it reflects off the mirror

Realistic ExpectationsRealistic ExpectationsExtreme AO (e.g. “planet finders”) aims for >90% strehl at K… but with bright stars

AGN are not particularly bright (fainter than typical limit of R~15mag), and tend to be fuzzy with a relatively bright background.Off-axis correction is usually not an option.LGS performance can vary from 0.1” resolution to ~20% Strehl at K.

One can do much better than the seeing limit, but don’t expect perfect performance every time; and beware of spatial & temporal

variations

5”

600nm2.2µm

5”

Circinus Galaxy

no bright point source for AO reference; and bright background.

with an IR-WFS (i.e. NACO)

adapted from Rigaut 2000

Multiple Layers of TurbulenceMultiple Layers of Turbulence

Turbulence Layers

with 2 turbulent layers, on- and off-axis wavefronts are different

adapted from Rigaut 2000

Deformable mirror

Turbulence Layers

Multiple Layers of TurbulenceMultiple Layers of Turbulence

with 2 turbulent layers, on- and off-axis wavefronts are different

and cannot be corrected with a single DM

Multiple Layers of TurbulenceMultiple Layers of Turbulence

adapted from Rigaut 2000

with 2 turbulent layers, on- and off-axis wavefronts are different

Deformable mirrors

Turbulence Layers

but they can be corrected with multi-conjugate DMs

and cannot be corrected with a single DM