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:
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
Padova 03 3D Spectrography The different tracers: Gas 90% H, 10% He Neutral, ionized, molecular 5 10 9 0.1 – 10100 - 1000 10 3 - 10 4 10 000 1 – 5 10 9 10 5 - 10 6 10 3 - 10 5 10 5 10 7 40 HI HII H2H2 Dust MassCloudT Density Msun (K) cm -3 Orion H He Dust
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)
Padova 03 3D Spectrography HI Gas = Radio astronomy
Padova 03 3D Spectrography HI Gas Velocity profiles Sofue et al.
Padova 03 3D Spectrography HI Gas Position-Velocity diagram
Padova 03 3D Spectrography HI Gas - Kinematics NGC 253 – HI Observations Koribalski et al.
Padova 03 3D Spectrography Ionized gas: H Ionized gas: H Spectrum in the visible
Padova 03 3D Spectrography Ionized gas: H Ionized gas: H Comparison HI / H
Padova 03 3D Spectrography Ionized gas: H Ionized gas: H Velocity map Khoruzhii et al.
Padova 03 3D Spectrography Stars Absorption lines LOSVD template galaxy Calcium triplet V [km/s] [ang]
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
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)
Padova 03 3D Spectrography LOSVDs and kinematics LOSVDs of NGC 5582 Halliday et al., 2001, MNRAS, 326, 473
Padova 03 3D Spectrography LOSVDs and kinematics Halliday et al., 2001, MNRAS, 326, 473
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
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
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
Padova 03 3D Spectrography Age & metallicity for Fornax galaxies Kuntschner 2000, MNRAS, 315, 184
Padova 03 3D Spectrography Spectroscopy 1D-binning IC1459 Major axis kinematics Cappellari, Verolme et al. 2002
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
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
Padova 03 3D Spectrography Tiling of the plane Towle 2000 Penrose tiling
Padova 03 3D Spectrography 2D-binning by QuadTree decomposition Regular cells but: large S/N scatter border problems 2x Satisfies Topological and Morphological requirements
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
Padova 03 3D Spectrography Taking pixels into account 1D case: growing bins along the slit 2D analog: growing bins around the bin baricenter
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.
Padova 03 3D Spectrography Voronoi Tesselation 2D-binning for NGC 2273 Small S/N scatter Compact bins No border problems
Padova 03 3D Spectrography NGC 2273 stellar mean velocity field 2D-binned velocityNot binned
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