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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 - PowerPoint PPT Presentation
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1
The Star Formation History
of Late-Type Galaxies
Roberto Cid FernandesUFSC – Florianópolis -Brasil
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Flori-where?
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Outline1- 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
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1 – What & Why
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)
the small print
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1 – Why study stellar pops in galaxies?
To learn about galaxy evolution: SFR(t), Z*(t), cosmology...
Mathis 06
Heavens 04
Mass assembly history of a late type galaxy
SFH(t) of the Universe
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1 – Why study stellar pops in galaxies?
To clean starlight pollution from my spectra!
Tremonti 04 Li 05
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1 – Why study stellar pops in galaxies?
CF 04Savaglio 05
Scattered Broad H in a Sey 2
To clean starlight pollution from my spectra!
z ~ 0.7 composite
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Basic Recipe
• (a) Discrete x continuous representations
• (b) Observables: Indices x Full spectrum
• (c) From observables to SFH: Methods, methods & methods...
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)
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2 – How?
’s (+ gas + dust
+ ...)
Fgal()F*()
The Fundamental Theorem of Population synthesis:
+ extinction x 10-0.4 A()
& kinematics x LOSVD (v*,*,vrot)
• Individual Stars• Observed clusters• Model SSPs• Continuous models
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2a – How? The discrete approach
x1 + x2 + x3 + ...
• Empirical Pop. Synthesis: SSP = Observed Clusters
≈ SSPj j = 1...N
: Stellar evol, spectra & IMF given by Mother Nature: Incomplete coverage of (t,Z) space & -range
Bica 88, Schmidt 91, Ahumada 06... + Pelat 97, 98, CF 01 (math)
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2a – How? The discrete approach
xj FSSP( ; tj,Zj ; IMF, tracks, libs...)
• SSP = Model “clusters” from evolutionary synthesis
≈ SSPj j = 1...N
: Wider coverage of (t,Z) space & -range: Models are always models...
Models: GALAXEV, SED, STABURST99, PEGASE, Maraston, ...
population vector
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2a – How? The discrete approach
Models: GALAXEV, SED, STABURST99, PEGASE, Maraston, ...
WARNING:
Models look great, but there are LOTS of assumptions & tricks in this business!
- tracks, - spectral libraries,- interpolation schemes,- ...
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2a – How? The continuous approach
: More general than bursts: Need to parametrize SF history & chemical evol.: Models are always models...
Fritze-v. Alvensleben 06, Bicker 04, ...
SFR(t)
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2b – Observables: Indices x Full Spectrum
Kauffmann 03, ...
Instantaneous Bursts
Continuous SF
Compare Index(t,Z,SFH) models to data to constrain SFH parameters.
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2b – Observables: Indices x Full Spectrum
Mathis 06 CF 05
Rectified spectrum (“high pass”)
Nolan 06
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2b – Observables: Indices x Full Spectrum
Mayya 06Walcher 06
Reichardt 01
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2c – How? From Observables to SFH...
Observables space Parameter space
Hypothese space (“priors”)
Only 1 Z? Z = Z(t)? A = ? Dust geometry? A(t,Z)?Kinematics?Which basis? (clusters, models,...)Which parameters?
Method
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?
WARNING:
Impossible to review all combinations!Will browse through a few examples
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2c – How? From Observables to SFH...
A very elegant method, yet largely overlooked because (?) of complex math (convex algebra) & few applications.
Pelat 97, 98, Moultaka 00, 04
Observables: 2 EWs
Parameters: 5 light fractions Reconstructed spectrum
Boisson 00
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2c – How? From Observables to SFH...5 indices: D4000, H, H+H, [MgFe]’ & [Mg2Fe]Bayesian comparison to a large library of models
Gallazzi 05
PDF of light
weighted mean age
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2c – How? From Observables to SFH...
Panter 03
F() fitting with MOPED Multiple Optimized Parameter Estimation & Dta cmpsn
Mass & Z in N ~ 10 time-bins
Mathis 06
M*Mass
assembly
histories: M(t)
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2c – How? From Observables to SFH...F() fitting with STARLIGHT- Light (Mass) in N ~ 100 time & Z SSPs- Compress output
CF 04. 05, 06, Mateus 06, Asari 07
M*M(t) & Z(t) of Star-Forming
galaxiesPop.
vector=
SFH
Downsizing
22 Corbin 06
2c – How? From Observables to SFH...
UCBD galaxies
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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 / speed1000 “Technicalities” (masks, kinematics, extinction, ...)
Physical ingredientsInput & Output...
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• (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
3 – So What? A few miscelaneous results
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3a – Global relations
Tremonti 04, Gallazzi 05 CF 05, Mateus 06, Asari 07M*
<t> x Z(gas)
<Z> x Z(gas)
<t> x Z(gas) Z(gas) x Mass <Z> x
Z(gas)
<Z> & <t> x Mass
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3b – Going one step further: Evolution
Idea: Dissect the SFH = SFR(t) & Z*(t)along the left wing of the Seagull
(normal SF galaxies)
Z(gas)
AG
NSF
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3b – Going one step further: Evolution
Result
Low Z(gas) galaxies are much
slower in their mass assembly and chemical
evolution
28
3b – Going one step further: Evolution
M*Mass
assembly
histories: M(t)Downsizing
SFR(t)/Vol
Panter 06
Mathis 06
M*
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3c – Sanity checks: good news
Different ingreedients
yield ~ similar result !!
SFR(Synt) ~ SFR(H)
Panter 06
Asari 07
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3c – Sanity checks: good news
Nebular exctinction – NaD ISM
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3c – Sanity checks: good news
AV (Balmer) ~ 2 AV (Stellar)
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3c – Warning:
–enhancement is not only an E-gal problem...
Asari 07Sodre 05
Ellipticals
SF-galaxies
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3c – Warning: AZD still present in full
spectral fits
CF 05, Gomes 05
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3c – Residuals: ~ Within errors, but ...
H–troff: Low amplitude, but systematic. ~ 100 Myr pops. STELIB?
Ellipticals SF-galaxies
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• (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• /Fe issue• Realistict dust models• ...
3 – So What? Conclusions
36
Spectral synthesis ofintegrated stellar
populations:
“...a subject with bad reputation. Too much has been claimed, and too few
have been persuaded.”
(Searle, 1986)
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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)
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Public version of STARLIGHT + results for 572581 SDSS galaxies soon @ www.starlight.ufsc.br & www.inaoep.mx
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M*, *, t* & Z* x nebular Z
... etc, etc & etc!
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STARLIGHT & its many applications
HE0450-2958 – The “homeless” QSO
CaII Triplet velocity dispersions
Vega 2004, Garcia-Rissman et al 2005
Merritt et al 2006
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CF, Gu, Melnick, Terlevich2, Kunth, Rodrigues Lacerda, Joguet 2004, MNRAS
2 – The SF-History of Sey 2 nuclei
• 79 galaxies 65 Sey 2s
• ~ 200 pc
• Base = BC03 + FC
Strong FC in this Sey
1
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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