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The Star Formation History of Late-Type Galaxies

The Star Formation History of Late-Type Galaxies. Roberto Cid Fernandes UFSC – Florianópolis -Brasil. Flori-where?. Outline. 1- What & Why? Scope & disclaimer Motivations 2 – Who & How? Schools, Ingredients & Methods: - Based on indices - Based on full spectral fits

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The Star Formation History of Late-Type Galaxies

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  1. The Star Formation History of Late-Type Galaxies Roberto Cid Fernandes UFSC – Florianópolis -Brasil

  2. Flori-where?

  3. Outline • 1- What & Why? • Scope & disclaimer • Motivations • 2 – Who & How? • Schools, Ingredients & Methods: • - Based on indices • - Based on full spectral fits • 3 – So what? • Miscelaneous results • Caveats

  4. 1 – What & Why the small print Two of the characteristics we expect of these reviews are the need to present a very balanced overview of the theme, in a manner which informs the audience without burying it in excessive technicalities. We are confident that you will be able to fulfil these criteria • Mission Impossible! • Focus on: • optical spectroscopy • stellar photons (ie, no em. line SFH diagnostics) • late-type (= non-ellipticals) • applications to large samples (= SDSS)

  5. 1 – Why study stellar pops in galaxies?  To learn about galaxy evolution: SFR(t), Z*(t), cosmology... SFH(t) of the Universe Mass assembly history of a late type galaxy Heavens 04 Mathis 06

  6. 1 – Why study stellar pops in galaxies?  To clean starlight pollution from my spectra! Tremonti 04 Li 05

  7. 1 – Why study stellar pops in galaxies?  To clean starlight pollution from my spectra! z ~ 0.7 composite Scattered Broad Hbin a Sey 2 CF 04 Savaglio 05

  8. 2 – How? Spectral synthesis ofintegrated stellar populations:“...a subject with bad reputation. Too much has been claimed, and too few have been persuaded.”(Searle, 1986) • Basic Recipe • (a) Discrete x continuous representations • (b) Observables: Indices x Full spectrum • (c) From observables to SFH: • Methods, methods & methods...

  9. 2 – How? The Fundamental Theorem of Population synthesis: = S’s (+ gas + dust + ...) • Individual Stars • Observed clusters • Model SSPs • Continuous models Fgal(l) = S F*(l) + extinction x 10-0.4 A(l) & kinematics x LOSVD (v*,s*,vrot)

  10. 2a – How? The discrete approach ≈ S SSPj j = 1...N • Empirical Pop. Synthesis: SSP = Observed Clusters • x1 + x2 + x3 + ... : Stellar evol, spectra & IMF given by Mother Nature : Incomplete coverage of (t,Z) space & l-range Bica 88, Schmidt 91, Ahumada 06... + Pelat 97, 98, CF 01 (math)

  11. 2a – How? The discrete approach ≈ S SSPj j = 1...N • SSP = Model “clusters” from evolutionary synthesis • S xj FSSP(l ; tj,Zj ; IMF, tracks, libs...) population vector : Wider coverage of (t,Z) space & l-range : Models are always models... Models: GALAXEV, SED, STABURST99, PEGASE, Maraston, ...

  12. 2a – How? The discrete approach WARNING: Models look great, but there are LOTS of assumptions & tricks in this business! - tracks, - spectral libraries, - interpolation schemes, - ... Models: GALAXEV, SED, STABURST99, PEGASE, Maraston, ...

  13. 2a – How? The continuous approach SFR(t) : More general than S bursts : Need to parametrize SF history & chemical evol. : Models are always models... Fritze-v. Alvensleben 06, Bicker 04, ...

  14. 2b – Observables: Indices x Full Spectrum Compare Index(t,Z,SFH) models to data to constrain SFH parameters. Instantaneous Bursts Continuous SF Kauffmann 03, ...

  15. 2b – Observables: Indices x Full Spectrum Nolan 06 Rectified spectrum (“high pass”) CF 05 Mathis 06

  16. 2b – Observables: Indices x Full Spectrum Reichardt 01 Mayya 06 Walcher 06

  17. Only 1 Z? Z = Z(t)? Al = ? Dust geometry? Al(t,Z)? Kinematics? Which basis? (clusters, models,...) Which parameters? Hypothese space (“priors”) Brute force discrete grid search? Convex-algebra? Markov-Chains? PCA? AI-techniques? Compression on input or output? Comparions to library of models? How to deal with degeneracies? Method 2c – How? From Observables to SFH... WARNING: Impossible to review all combinations! Will browse through a few examples Parameter space Observables space

  18. 2c – How? From Observables to SFH... Pelat 97, 98, Moultaka 00, 04 A very elegant method, yet largely overlooked because (?) of complex math (convex algebra) & few applications. Observables: 2 EWs Parameters: 5 light fractions Reconstructed spectrum Boisson 00

  19. 2c – How? From Observables to SFH... 5 indices: D4000, Hb, Hd+Hg, [MgFe]’ & [Mg2Fe] Bayesian comparison to a large library of models Gallazzi 05 PDF of light weighted mean age

  20. 2c – How? From Observables to SFH... F(l) fitting with MOPED Multiple Optimized Parameter Estimation & Dta cmpsn Mass & Z in N ~ 10 time-bins M* Mass assembly histories: M(t) Panter 03 Mathis 06

  21. 2c – How? From Observables to SFH... F(l) fitting with STARLIGHT - Light (Mass) in N ~ 100 time & Z SSPs - Compress output Downsizing M* M(t) & Z(t) of Star-Forming galaxies Pop. vector = SFH CF 04. 05, 06, Mateus 06, Asari 07

  22. 2c – How? From Observables to SFH... UCBD galaxies Corbin 06

  23. 2c – How? From Observables to SFH... • Many other methods! • STEllar Content via Maximum A Posteriori – Ocvirk 05 + Koleva + ... • Active Instance-Based Machine Learning – Solorio 05 • Bayesian Latent Variable modelling – Nolan 06 • Principal Component Analysis – Li 05, Wild • Direct fitting – Tadhunter 05, Holt 06, Moustakas 06 ... + MacArthur... • Brute Force – Bush 01, 02, 03, 04, 05, 06, 07, 08 • ... Diversity in: Math / elegance / speed 1000 “Technicalities” (masks, kinematics, extinction, ...) Physical ingredients Input & Output ...

  24. 3 – So What? A few miscelaneous results • (a) Global relations: • Synthesis parameters X other things: • <t>, <Z>, <SFR>, <SSFR>, ... • Zgas, M*, Mdyn, environment, ... • (b) Daring one step further: SFH(t)! • (c) Sanity checks • Caveats • (d) Closing words

  25. 3a – Global relations Z(gas) x Mass <Z> x Z(gas) <t> x Z(gas) <t> x Z(gas) <Z> x Z(gas) <Z> & <t> x Mass M* Tremonti 04, Gallazzi 05 CF 05, Mateus 06, Asari 07

  26. 3b – Going one step further: Evolution AGN SF Z(gas) Idea: Dissect the SFH = SFR(t) & Z*(t) along the left wing of the Seagull (normal SF galaxies)

  27. 3b – Going one step further: Evolution Result Low Z(gas) galaxies are much slower in their mass assembly and chemical evolution

  28. M* Mass assembly histories: M(t) 3b – Going one step further: Evolution M* SFR(t)/Vol Panter 06 Downsizing Mathis 06

  29. 3c – Sanity checks: good news  Different ingreedients yield ~ similar result !! Panter 06 SFR(Synt) ~ SFR(Ha) Asari 07

  30. 3c – Sanity checks: good news  Ha/Hb Nebular exctinction – NaD ISM

  31. 3c – Sanity checks: good news  Ha/Hb AV (Balmer) ~ 2 AV (Stellar)

  32. 3c – Warning:  Ellipticals a–enhancement is not only an E-gal problem... SF-galaxies a Asari 07 Sodre 05

  33. 3c – Warning:  AZD still present in full spectral fits CF 05, Gomes 05

  34. 3c – Residuals: ~ Within errors, but ... Ellipticals SF-galaxies Hb–troff: Low amplitude, but systematic. ~ 100 Myr pops. STELIB?

  35. 3 – So What? Conclusions • (a) Ingreedients & methods have matured a lot! • (b) Global properties • <t>, <Z>, SFR, SSFR, ... • in very good shape  • (b) Evolution ... Looking good! • (c) Caveats & Future • a/Fe issue • Realistict dust models • ...

  36. Spectral synthesis ofintegrated stellar populations:“...a subject with bad reputation. Too much has been claimed, and too few have been persuaded.”(Searle, 1986)

  37. Spectral synthesis of integrated stellar populations:“...a subject with a not so bad reputation anymore. By not claiming too much, we’re now able to convince quite a few people.” (At least we managed to fool Scott!) (A bunch of us, 2006)

  38. Public version of STARLIGHT + results for 572581 SDSS galaxies soon @ www.starlight.ufsc.br & www.inaoep.mx

  39. M*, m*, t* & Z* x nebular Z ... etc, etc & etc!

  40. STARLIGHT & its many applications HE0450-2958 – The “homeless” QSO CaII Triplet velocity dispersions Merritt et al 2006 Vega 2004, Garcia-Rissman et al 2005

  41. 2 – The SF-History of Sey 2 nuclei CF, Gu, Melnick, Terlevich2, Kunth, Rodrigues Lacerda, Joguet 2004, MNRAS Strong FC in this Sey 1  • 79 galaxies • 65 Sey 2s • ~ 200 pc • Base = BC03 + FC

  42. 6 – Synthesis of 582k SDSS galaxies N Asari, J Gomes, W Schoenell, J P Papaqui (UFSC) A Mateus (IAG), L Sodré (IAG) & G Stasinska (Meudon) The SEAGal Collaboration: Semi-Empirical Analysis of Galaxies

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