Download Evolutionary Population Synthesis models

Advanced Lectures on Galaxies (2008 INAOE): Chapter 4
Evolutionary Population
Synthesis models
Divakara Mayya
INAOE
http://www.inaoep.mx/~ydm
What do we try to synthesize?
Observed quantities (spectrum,
colors, Luminosity etc.) from a
region of a galaxy which consists of
Stars: emit light
Dust : absorb and re-radiate
Gas : ionize and re-radiate
In general the three components
are mixed even for parsec size
regions such as the Super Star
Cluster R136.
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What do we try to synthesize?
The aim is to obtain the ages and masses of all important
stellar groups the in a given region, by comparing the observed
quantities with the theoretically computed quantities.
The region in study may be as simple as an old
globular cluster (GC) or as complex as a starburst
in 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
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The Simplest model
Simple Stellar Populations (SSP)
or Instantaneous Bursts (IB)
Stars:
Total Stellar Flux = Number of living stars * Flux of each star
- all the living stars have the same age and metallicity
- mass distribution is power-law (Salpeter IMF)
Dust: Correct the observed fluxes using a derived extinction assuming
foreground dust model and an extinction curve (Cardelli et al. 1989)
Gas: Add the fluxes calculated from photo-ionization models
for an HII region to the synthesized stellar fluxes (Osterbrock’s text)
SSP: Basic equations and Ingredients
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SSP: Basic equations and Ingredients
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SSP: Basic equations and Ingredients
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SSP: Basic equations and Ingredients
Stellar Evolutionary tracks (Isochrones)
- Geneva
- Padova
Stellar Atmospheric models
- Kurucz (LTE) models
- Observed stellar spectra
Uncertainties:
-Mass-loss rates?
-Rotation?
Uncertainties:
-non-LTE effects?
-Hot star models
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SSP: The method
Isochrone Interpolation schemes
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SSP: The method
Effect of rotation: rotating (_____)
non-rotating (---)
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SSP: The output
1. Nebular Lines
2. Continuum band luminosity
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SSP: The output
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
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(Class II) SSP: Results
Discussion of the paper Sec. 3: Dependence of SSP evolution
with input parameter, comparison with observations etc.
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(Class III) SSP: observable phases
1. Nebular ( < 6 Myr)
: Emission lines
2. Wolf-Rayet (3-5 Myr)
: HeII 4686 broad spectral feature
3. Red Supergiant (7-20 Myr): Calcium Triplet in absorption
4. A-star (50-500 Myr)
: Balmer lines in absorption
5. Intermediate (0.5-2 Gyr) : Balmer and CaII H and K line ratios
6. Old population (>2 Gyr): 4000 Ang break and other Lick indices
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SSP: spectral evolution
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Continuous Star formation (CSF) vs IB:
Ionizing photons
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CSF vs IB: Magnitude
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CSF vs IB: colors
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CSF vs IB: SED
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Deriving Age and Mass: diagnostic diagrams
1. Color vs Color
: age/extinction
2. Magnitude vs Color: age/extinction and mass
3. EW(Ha) vs Color : age and extinction
4. Spectral fitting
: age and extinction
5. Lick Indices
: age/metallicity
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CSF vs IB: RSG features
Mayya 1997
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The real case:star formation history of
starburst nuclei
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The real case: star formation history of
starburst nuclei
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Star formation history of M82 disk
Mayya et al. (2006)
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Other applications: SFR
Kennicutt 1998
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Other applications: Galaxy
formation and evolution
1. Fossil analysis (MOPED)
2. Integrated approach (GRASIL)
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