3 D Spectrography II The tracers Morphology distribution

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

The different tracers: Gas l 90% H, 10% He H He l Dust Neutral, ionized, molecular Mass Orion HI 5 109 HII H 2 Dust 1 – 5 109 Density T 0. 1 – 10 100 - 1000 103 - 104 10 000 105 - 106 103 - 105 107 Msun 3 D Spectrography Cloud 40 Msun cm-3 (K) Padova 03

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

HI Gas = Radio astronomy 3 D Spectrography Padova 03

HI Gas - Cartography 3 D Spectrography Padova 03

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

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

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

Ionized gas: Ha l Spectrum in the visible 3 D Spectrography Padova 03

Ionized gas: Ha l Comparison HI / Ha 3 D Spectrography Padova 03

Ionized gas: Ha l Velocity map Khoruzhii et al. 3 D Spectrography Padova 03

Stars l galaxy Absorption lines template Calcium triplet l Deconvolution: l [ang] G = S* LOSVD : Line Of Sight Velocity Distribution V [km/s] 3 D Spectrography Padova 03

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

LOSVDs and kinematics l Many different methods for deconvolving: – Direct pixel fitting – Fourier fitting – Cross-correlation techniques – Fourier Quotient Correlation method – Others… l Fittings LOSVD moments: – Gauss-Hermite moments (van der Marel & Franx 93, Ap. J 407, 525 Gerhard 93, MNRAS 265, 213) 3 D Spectrography Padova 03

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

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

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 3 D Spectrography Padova 03

Determining age and metallicity in practice The Lick System of Indices • Determine strengths of absorption features • Correct them for velocity broadening of the galaxy • Compare them with theoretical line strengths 3 D Spectrography Padova 03

Stellar population models Vazdekis (1999) models at Lick resolution (~9 Å FWHM) based on Jones (1999) library [Mg. Fe 52]=(Mgb x Fe 5270)^0. 5 3 D Spectrography Padova 03

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

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

Long-slit spectroscopy Kinematical profiles 3 D Spectrography Padova 03

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

IFU spectroscopy And each spectrum gives: Flux Line Dispersion Velocity Strength 3 D Spectrography Padova 03

NGC 3384 S 0 V H 3 D Spectrography Mgb (cluster) s Fe 5270 Padova 03

Line-strength maps – N 3384 No H gradient Strong Mgb in centre Fe peaks in centre Restricted wavelength range de Zeeuw et al. 2002, MNRAS, 329, 513 3 D Spectrography Padova 03

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

Photometry binning NGC 4342 WFPC 2 Cappellari 2001: Efficient MGE fitting method 3 D Spectrography Padova 03

Spectroscopy 1 D-binning IC 1459 Major axis kinematics Cappellari, Verolme et al. 2002 3 D Spectrography Padova 03

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

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

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

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

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

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

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

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

NGC 2273 stellar mean velocity field 2 D-binned velocity 3 D Spectrography Not binned Padova 03

What to keep in mind l l l 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 3 D Spectrography Padova 03