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Padova 03 3D Spectrography 3D Spectrography: II - The tracers Morphology: distribution of each component Dynamics: kinematics via the emission or absorption.

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Presentation on theme: "Padova 03 3D Spectrography 3D Spectrography: II - The tracers Morphology: distribution of each component Dynamics: kinematics via the emission or absorption."— Presentation transcript:

1 Padova 03 3D Spectrography 3D Spectrography: II - The tracers Morphology: distribution of each component Dynamics: kinematics via the emission or absorption lines Line strengths: allow to study stellar populations

2 Padova 03 3D Spectrography The different tracers: Gas 90% H, 10% He Neutral, ionized, molecular – – HI HII H2H2 Dust MassCloudT Density Msun (K) cm -3 Orion H He Dust

3 Padova 03 3D Spectrography HI Gas Hyperfine transition line at 21 cm Rare transition, but very abundant gas Aligned poles (higher energy) Opposed poles (lower energy)

4 Padova 03 3D Spectrography HI Gas = Radio astronomy

5 Padova 03 3D Spectrography HI Gas - Cartography

6 Padova 03 3D Spectrography HI Gas Velocity profiles Sofue et al.

7 Padova 03 3D Spectrography HI Gas Position-Velocity diagram

8 Padova 03 3D Spectrography HI Gas - Kinematics NGC 253 – HI Observations Koribalski et al.

9 Padova 03 3D Spectrography Ionized gas: H Ionized gas: H Spectrum in the visible

10 Padova 03 3D Spectrography Ionized gas: H Ionized gas: H Comparison HI / H

11 Padova 03 3D Spectrography Ionized gas: H Ionized gas: H Velocity map Khoruzhii et al.

12 Padova 03 3D Spectrography Stars Absorption lines LOSVD template galaxy Calcium triplet V [km/s] [ang]

13 Padova 03 3D Spectrography Stars Problems due to population differences (template mismatching) Deconvolution: G = i i S i * LOSVD i GS* LOSVD G = i i S i * LOSVD i Different populations = Different kinematics

14 Padova 03 3D Spectrography LOSVDs and kinematics 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)

15 Padova 03 3D Spectrography LOSVDs and kinematics LOSVDs of NGC 5582 Halliday et al., 2001, MNRAS, 326, 473

16 Padova 03 3D Spectrography LOSVDs and kinematics Halliday et al., 2001, MNRAS, 326, 473

17 Padova 03 3D 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

18 Padova 03 3D 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

19 Padova 03 3D Spectrography Stellar population models Vazdekis (1999) models at Lick resolution (~9 Å FWHM) based on Jones (1999) library [MgFe52]=(Mgb x Fe5270)^0.5

20 Padova 03 3D Spectrography Age & metallicity for Fornax galaxies Kuntschner 2000, MNRAS, 315, 184

21 Padova 03 3D Spectrography Aperture spectroscopy Velocity, velocity dispersion …

22 Padova 03 3D Spectrography Long-slit spectroscopy Kinematical profiles

23 Padova 03 3D Spectrography We obtain a spectrum at each position Integral field spectroscopy

24 Padova 03 3D Spectrography And each spectrum gives: IFU spectroscopy Flux VelocityLine StrengthDispersion

25 Padova 03 3D Spectrography H V MgbFe5270 NGC 3384 S0 (cluster)

26 Padova 03 3D Spectrography Line-strength maps – N3384 No H gradient Strong Mgb in centreFe peaks in centre Restricted wavelength range de Zeeuw et al. 2002, MNRAS, 329, 513

27 Padova 03 3D Spectrography 3D Spectrography: Adaptive 2D Binning

28 Padova 03 3D Spectrography Photometry binning NGC4342 WFPC2 Cappellari 2001: Efficient MGE fitting method

29 Padova 03 3D Spectrography Spectroscopy 1D-binning IC1459 Major axis kinematics Cappellari, Verolme et al. 2002

30 Padova 03 3D Spectrography The SAURON test data: NGC 2273 Result of multiple pointings: irregular domain vertical S/N jumps S/N mapReconstructed image Barred Sa galaxy

31 Padova 03 3D Spectrography 2D-binning requirements Topological: partition the plane without holes or overlapping bins Morphological: bins as compact or round as possible Uniformity: minimal S/N scatter

32 Padova 03 3D Spectrography Tiling of the plane Towle 2000 Penrose tiling

33 Padova 03 3D Spectrography 2D-binning by QuadTree decomposition Regular cells but: large S/N scatter border problems 2x Satisfies Topological and Morphological requirements

34 Padova 03 3D Spectrography Voronoi Tessellation Satisfies Topological requirement ONLY Definition: each point in a bin is closer to its generator than to any other point

35 Padova 03 3D Spectrography Taking pixels into account 1D case: growing bins along the slit 2D analog: growing bins around the bin baricenter

36 Padova 03 3D Spectrography Centroidal Voronoi Tessellation All Topological, Morphological and Uniformity requirements satisfied! Cappellari & Copin 2002 It is the perfect solution in the case of Poissonian noise and many pixels.

37 Padova 03 3D Spectrography Voronoi Tesselation 2D-binning for NGC 2273 Small S/N scatter Compact bins No border problems

38 Padova 03 3D Spectrography NGC 2273 stellar mean velocity field 2D-binned velocityNot binned

39 Padova 03 3D Spectrography What 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


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