Padova 03 3D Spectrography 3D Spectrography: II - The tracers Morphology: distribution of each...

Padova 033D Spectrography

3D Spectrography:3D Spectrography:

II - The tracersII - The tracers

Morphology: distribution of each component

Dynamics: kinematics via the emission or absorption lines

Line strengths: allow to study stellar populations

Padova 033D Spectrography

The different tracers: The different tracers: GasGas

90% H, 10% He

Neutral, ionized, molecular

H

He

Poussière

5 109 0.1 – 10 100 - 1000

100 - 1000 103 - 104 10 000

1 – 5 109 105 - 106 103 - 105 10

5 107 40

HI

HII

H2

Dust

Mass Cloud TDensity

Msun Msun (K)cm-3

Orion

H

He

Dust

Padova 033D Spectrography

HI GasHI Gas

Hyperfine transition line at 21 cm

Rare transition, but very abundant gas

Aligned poles(higher energy)

Opposed poles (lower energy)

Padova 033D Spectrography

HI Gas = Radio astronomyHI Gas = Radio astronomy

Padova 033D Spectrography

HI Gas - CartographyHI Gas - Cartography

Padova 033D Spectrography

HI GasHI Gas

Velocity profiles

Sofue et al.

Padova 033D Spectrography

HI GasHI Gas Position-Velocity diagram

Padova 033D Spectrography

HI Gas - KinematicsHI Gas - Kinematics

NGC 253 – HI Observations

Koribalski et al.

Padova 033D Spectrography

Ionized gas: HIonized gas: H

Spectrum in the visible

Padova 033D Spectrography

Ionized gas: HIonized gas: H Comparison HI / H

Padova 033D Spectrography

Ionized gas: HIonized gas: H

Velocity map

Khoruzhii et al.

Padova 033D Spectrography

StarsStars

Absorption lines

Deconvolution:

G = S* LOSVD GG = S*S* LOSVDLOSVD

LOSVD :

Line Of Sight

Velocity Distribution

Deconvolution:

G = S* LOSVD GG = S*S* LOSVDLOSVD

LOSVD :

Line Of Sight

Velocity Distribution

LOSVD

template

galaxy

Calcium triplet

V [km/s]

[ang]

Padova 033D Spectrography

StarsStars Problems due to population differences

(template mismatching)

Deconvolution: G = ii Si* LOSVDi

GG = ii SSi* * LOSVDLOSVDi

Different populations=

Different kinematics

Padova 033D Spectrography

LOSVDs and LOSVDs and kinematicskinematics

Many different methods for deconvolving:– Direct pixel fitting– Fourier fitting– Cross-correlation techniques– Fourier Quotient Correlation method– Others…

Fittings LOSVD moments:– Gauss-Hermite moments

(van der Marel & Franx 93, ApJ 407, 525

Gerhard 93, MNRAS 265, 213)

Padova 033D Spectrography

LOSVDs and LOSVDs and kinematicskinematics

LOSVDs of NGC 5582

Halliday et al., 2001, MNRAS, 326, 473

Padova 033D Spectrography

LOSVDs and LOSVDs and kinematicskinematics

Halliday et al., 2001, MNRAS, 326, 473

Padova 033D Spectrography

How to determine the age and composition of a galaxy?

• Assume 1 age and uniform composition.

• Assume same laws of physics as in a globular cluster.

• Stellar evolution: artificial HR diagram

• Find matching spectra

• Add these spectra composite galaxy spectrum

• Repeat previous steps for different ages/metallicities

• Determine best fit

Padova 033D Spectrography

The Lick System of Indices

Determining age and metallicity in practice

• Determine strengths of absorption features• Correct them for velocity broadening of the galaxy• Compare them with theoretical line strengths

Padova 033D Spectrography

Stellar population modelsStellar population models

Vazdekis (1999) models atLick resolution (~9 Å FWHM) based on Jones (1999) library

[MgFe52]=(Mgb x Fe5270)^0.5

Padova 033D Spectrography

Age & metallicity Age & metallicity for Fornax galaxiesfor Fornax galaxies

Kuntschner 2000, MNRAS, 315, 184

Padova 033D Spectrography

Aperture spectroscopy

Velocity, velocity dispersion …

Padova 033D Spectrography

Long-slit spectroscopyLong-slit spectroscopy

Kinematical profiles

Padova 033D Spectrography

We obtain a spectrum at each position

Integral field spectroscopyIntegral field spectroscopy

Padova 033D Spectrography

And each spectrum gives:

IFU spectroscopyIFU spectroscopy

FluxVelocityLine StrengthDispersion

Padova 033D Spectrography

H

V

Mgb Fe5270

NGC 3384 S0 NGC 3384 S0 (cluster)(cluster)

Padova 033D Spectrography

Line-strength maps – N3384Line-strength maps – N3384

No H gradient Strong Mgb in centre Fe peaks in centre

Restricted wavelength range

de Zeeuw et al. 2002, MNRAS, 329, 513

Padova 033D Spectrography

3D Spectrography:3D Spectrography:

Adaptive 2D BinningAdaptive 2D Binning

Padova 033D Spectrography

Photometry binningPhotometry binning

NGC4342WFPC2

Cappellari 2001: Efficient MGE fitting method

Padova 033D Spectrography

Spectroscopy 1D-binningSpectroscopy 1D-binning

IC1459

Major axis kinematics

Cappellari, Verolme et al. 2002

Padova 033D Spectrography

The SAURON test data:The SAURON test data:NGC 2273NGC 2273

Result of multiple pointings:• irregular domain• vertical S/N jumps

S/N mapReconstructed image

Barred Sa galaxy

Padova 033D Spectrography

2D-binning requirements2D-binning requirements Topological: partition the plane without holes or

overlapping bins Morphological: bins as compact or “round” as

possible Uniformity: minimal S/N scatter

Padova 033D Spectrography

Tiling of the planeTiling of the plane

20 10 0 10 20

20

10

0

10

20

10 0 10

10

0

10

10 0 10

10

0

10

Towle 2000

Penrose tiling

Padova 033D Spectrography

2D-binning by QuadTree 2D-binning by QuadTree decompositiondecomposition

Regular cells but: • large S/N scatter • border problems

2x

Satisfies Topological and Morphological requirements

Padova 033D Spectrography

Voronoi TessellationVoronoi Tessellation

Satisfies Topological requirement ONLY

Definition: each point in a bin is closer to its generator than to any other point

Padova 033D Spectrography

Taking pixels into accountTaking pixels into account

1D case: growing bins along the slit

2D analog: growing bins around the bin baricenter

Padova 033D Spectrography

Centroidal Voronoi Centroidal Voronoi TessellationTessellation

All Topological, Morphological and Uniformity requirements satisfied!Cappellari & Copin 2002

It is the perfect solution in the case of Poissonian noise and many pixels.

Padova 033D Spectrography

Voronoi TesselationVoronoi Tesselation2D-binning for2D-binning for

NGC 2273NGC 2273

• Small S/N scatter• Compact bins• No border problems

Padova 033D Spectrography

NGC 2273 NGC 2273 stellar mean velocity field stellar mean velocity field

2D-binned velocity Not binned

Padova 033D Spectrography

What to keep in mindWhat to keep in mind

Ionized gas and stars are (easily?) traceable via emission and absorption line spectra.

Derivation of the distribution, kinematics and line strengths.

Again, a two-dimensional spatial coverage is often critical for the scientific interpretation

More importantly: it is the link between all these tracers which allows us to really understand the physical status of these objects, leading to a theory of their formation and evolution.

Further readings:– Galactic Astronomy, Binney & Merrifield,

Cambridge University Press