Evolutionary Population Evolutionary Population Synthesis modelsSynthesis models

Divakara MayyaDivakara Mayya

INAOEINAOE

http://www.inaoep.mx/~ydmhttp://www.inaoep.mx/~ydm

Advanced Lectures on Galaxies (2008 INAOE): Chapter 4

What do we try to synthesize?What do we try to synthesize?

Mayya

Observed quantities (spectrum, colors, Luminosity etc.) from a region of a galaxy which consists of

Stars: emit lightDust : absorb and re-radiateGas : ionize and re-radiate

In general the three componentsare mixed even for parsec size regions such as the Super Star Cluster R136.

What do we try to synthesize?What do we try to synthesize?

Mayya

The aim is to obtain the ages and masses of all important stellar groups the in a given region, by comparing the observedquantities with the theoretically computed quantities.

The region in study may be as simple as an old globular cluster (GC) or as complex as a starburstin an interacting galaxy such as the Antennae.

GCs are relatively simple --- all the stars are of the same age, hardly any gas and dust

Starburst systems are complex --- - Age spread - Metallicity spread - In-homogenous dust distribution - Underlying background

The Simplest modelThe Simplest modelSimple Stellar Populations (SSP)Simple Stellar Populations (SSP)

or or Instantaneous Bursts (IB)Instantaneous Bursts (IB)

Stars:Stars:Total Stellar Flux = Number of living stars * Flux of each starTotal Stellar Flux = Number of living stars * Flux of each star - all the living stars have the same age and metallicity- all the living stars have the same age and metallicity - mass distribution is power-law (Salpeter IMF)- mass distribution is power-law (Salpeter IMF)

Dust: Correct the observed fluxes using a derived extinction assuming Dust: Correct the observed fluxes using a derived extinction assuming foreground dust model and an extinction curve (Cardelli et al. 1989)foreground dust model and an extinction curve (Cardelli et al. 1989)

Gas: Add the fluxes calculated from photo-ionization modelsGas: Add the fluxes calculated from photo-ionization models for an HII region to the synthesized stellar fluxes (Osterbrock’s text)for an HII region to the synthesized stellar fluxes (Osterbrock’s text)

SSP: SSP: Basic equations and IngredientsBasic equations and Ingredients

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SSP: SSP: Basic equations and IngredientsBasic equations and Ingredients

Mayya

SSP: SSP: Basic equations and IngredientsBasic equations and Ingredients

Mayya

SSP: SSP: Basic equations and IngredientsBasic equations and Ingredients

Mayya

Stellar Evolutionary tracks (Isochrones) - Geneva - Padova

Uncertainties:-Mass-loss rates?-Rotation?

Stellar Atmospheric models - Kurucz (LTE) models - Observed stellar spectra

Uncertainties:-non-LTE effects?-Hot star models

SSP: SSP: The methodThe method

MayyaIsochrone Interpolation schemes

SSP: SSP: The methodThe method

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Effect of rotation: rotating (_____) non-rotating (---)

SSP: SSP: The outputThe output

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1. Nebular Lines

2. Continuum band luminosity

SSP: SSP: The outputThe output

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3. Colors and equivalent widths - U-B, B-V, V-K etc. - EW(Ha), EW(Hb) etc.

4. Selected spectral features - CaT from RSGs - Broad 4686 from Wolf-Rayet

5. Radio continuum - Thermal flux from HII region - Non-thermal flux from SNRs

6. Far-infrared continuum in dusty galaxies - Bolometric luminosity

7. Mechanical energy - Power from stellar winds and SN explosions

(Class II) SSP: Results(Class II) SSP: Results

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Discussion of the paper Sec. 3: Dependence of SSP evolution with input parameter, comparison with observations etc.

(Class III) SSP: observable phases(Class III) SSP: observable phases

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1. Nebular ( < 6 Myr) : Emission lines2. Wolf-Rayet (3-5 Myr) : HeII 4686 broad spectral feature3. Red Supergiant (7-20 Myr): Calcium Triplet in absorption4. A-star (50-500 Myr) : Balmer lines in absorption5. Intermediate (0.5-2 Gyr) : Balmer and CaII H and K line ratios6. Old population (>2 Gyr): 4000 Ang break and other Lick indices

SSP: spectral evolutionSSP: spectral evolution

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Continuous Star formation (CSF) vs IB:Continuous Star formation (CSF) vs IB:Ionizing photonsIonizing photons

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CSF vs IB: MagnitudeCSF vs IB: Magnitude

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CSF vs IB: colorsCSF vs IB: colors

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CSF vs IB: SEDCSF vs IB: SED

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Deriving Age and Mass: diagnostic diagramsDeriving Age and Mass: diagnostic diagrams

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1. Color vs Color : age/extinction2. Magnitude vs Color: age/extinction and mass3. EW(Ha) vs Color : age and extinction4. Spectral fitting : age and extinction5. Lick Indices : age/metallicity

CSF vs IB: RSG featuresCSF vs IB: RSG features

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Mayya 1997

The real case:The real case:star formation history of star formation history of starburst nucleistarburst nuclei

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The real case:The real case: star formation history of star formation history of starburst nucleistarburst nuclei

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Star formation history of M82 diskStar formation history of M82 disk

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Mayya et al. (2006)

Other applications: SFROther applications: SFR

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Kennicutt 1998

Other applications: Other applications: Galaxy formation and evolution

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1. Fossil analysis (MOPED)2. Integrated approach (GRASIL)