3Outline 1- What & Why? 2 – Who & How? 3 – So what? Scope & disclaimer Motivations2 – Who & How?Schools, Ingredients & Methods:- Based on indices- Based on full spectral fits3 – So what?Miscelaneous resultsCaveats
41 – What & Why Mission Impossible! optical spectroscopy the small printTwo 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 criteriaMission Impossible!Focus on:optical spectroscopystellar photons (ie, no em. line SFH diagnostics)late-type (= non-ellipticals)applications to large samples (= SDSS)
51 – Why study stellar pops in galaxies? To learn about galaxy evolution: SFR(t), Z*(t), cosmology...SFH(t) of the UniverseMass assembly history of a late type galaxyHeavens 04Mathis 06
61 – Why study stellar pops in galaxies? To clean starlight pollution from my spectra!Tremonti 04Li 05
71 – Why study stellar pops in galaxies? To clean starlight pollution from my spectra!z ~ 0.7 compositeScattered Broad Hb in a Sey 2Savaglio 05CF 04
82 – How?Spectral synthesis of integrated 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= S ’s (+ gas + dust + ...) Fgal(l) = S F*(l) 2 – How? The Fundamental Theorem of Population synthesis:= S ’s (+ gas + dust + ...)Individual StarsObserved clustersModel SSPsContinuous modelsFgal(l) = S F*(l)+ extinction x A(l)& kinematics x LOSVD (v*,s*,vrot)
102a – How? The discrete approach ≈ S SSPj j = 1...NEmpirical Pop. Synthesis: SSP = Observed Clustersx x x: Stellar evol, spectra & IMF given by Mother Nature: Incomplete coverage of (t,Z) space & l-rangeBica 88, Schmidt 91, Ahumada Pelat 97, 98, CF 01 (math)
112a – How? The discrete approach ≈ S SSPj j = 1...NSSP = Model “clusters” from evolutionary synthesisS 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, ...
122a – 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, ...
132a – 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, ...
142b – Observables: Indices x Full Spectrum Compare Index(t,Z,SFH) models to data to constrain SFH parameters.Instantaneous BurstsContinuous SFKauffmann 03, ...
152b – Observables: Indices x Full Spectrum Nolan 06Rectified spectrum (“high pass”)Mathis 06CF 05
162b – Observables: Indices x Full Spectrum Reichardt 01Walcher 06Mayya 06
172c – How? From Observables to SFH... Hypothese space(“priors”)Only 1 Z? Z = Z(t)?Al = ? Dust geometry? Al(t,Z)?Kinematics?Which basis? (clusters, models,...)Which parameters?WARNING:Impossible to review all combinations!Will browse through a few examplesObservables spaceParameter spaceMethodBrute 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?
182c – How? From Observables to SFH... Pelat 97, 98, Moultaka 00, 04A very elegant method, yet largely overlooked because (?) of complex math (convex algebra) & few applications.Observables: 2 EWsParameters:5 light fractionsReconstructed spectrumBoisson 00
192c – How? From Observables to SFH... 5 indices: D4000, Hb, Hd+Hg, [MgFe]’ & [Mg2Fe]Bayesian comparison to a large library of modelsGallazzi 05PDF of light weighted mean age
202c – How? From Observables to SFH... F(l) fitting with MOPEDMultiple Optimized Parameter Estimation & Dta cmpsnMass & Z in N ~ 10 time-binsM*Mass assembly histories: M(t)Panter 03Mathis 06
212c – How? From Observables to SFH... F(l) fitting with STARLIGHT- Light (Mass) in N ~ 100 time & Z SSPs- Compress outputDownsizingM*M(t) & Z(t) of Star-Forming galaxiesPop. vector=SFHCF , 06, Mateus 06, Asari 07
222c – How? From Observables to SFH... UCBD galaxiesCorbin 06
232c – How? From Observables to SFH... Many other methods!STEllar Content via Maximum A Posteriori – Ocvirk 05 + Koleva + ...Active Instance-Based Machine Learning – Solorio 05Bayesian Latent Variable modelling – Nolan 06Principal Component Analysis – Li 05, WildDirect fitting – Tadhunter 05, Holt 06, Moustakas MacArthur...Brute Force – Bush 01, 02, 03, 04, 05, 06, 07, 08...Diversity in:Math / elegance / speed1000 “Technicalities” (masks, kinematics, extinction, ...)Physical ingredientsInput & Output...
243 – 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 checksCaveats(d) Closing words
25<Z> & <t> x Mass 3a – Global relationsZ(gas) x Mass<Z> x Z(gas)<t> x Z(gas)<t> x Z(gas)<Z> x Z(gas)<Z> & <t> x MassM*Tremonti 04, Gallazzi 05CF 05, Mateus 06, Asari 07
263b – Going one step further: Evolution AGNSFZ(gas)Idea: Dissect the SFH = SFR(t) & Z*(t)along the left wing of the Seagull(normal SF galaxies)
273b – Going one step further: Evolution ResultLow Z(gas) galaxies are much slower in their mass assembly and chemical evolution
293c – Sanity checks: good news Different ingreedients yield ~ similar result !!Panter 06SFR(Synt) ~ SFR(Ha)Asari 07
303c – Sanity checks: good news Ha/HbNebular exctinction – NaD ISM
313c – Sanity checks: good news Ha/HbAV (Balmer) ~ 2 AV (Stellar)
32a–enhancement is not only an E-gal problem... 3c – Warning: Ellipticalsa–enhancement is not only an E-gal problem...SF-galaxiesaAsari 07Sodre 05
33AZD still present in full spectral fits 3c – Warning: AZD still present in full spectral fitsCF 05, Gomes 05
343c – Residuals: ~ Within errors, but ... EllipticalsSF-galaxiesHb–troff: Low amplitude, but systematic. ~ 100 Myr pops. STELIB?
353 – 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 & Futurea/Fe issueRealistict dust models...
36Spectral synthesis of integrated stellar populations: “ Spectral synthesis of integrated stellar populations: “...a subject with bad reputation. Too much has been claimed, and too few have been persuaded.” (Searle, 1986)
37(At least we managed to fool Scott!) 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)
38Public version of STARLIGHT + results for SDSS galaxies &