Evolutionary Population Synthesis models

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Evolutionary Population Synthesis models
Advanced Lectures on Galaxies (2008 INAOE)
Chapter 4

• Divakara Mayya
• INAOE
• http//www.inaoep.mx/ydm

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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 modelSimple 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 (Osterbrocks text)

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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
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SSP Basic equations and Ingredients
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

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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

• Nebular (
• Wolf-Rayet (3-5 Myr) HeII 4686 broad
  spectral feature
• Red Supergiant (7-20 Myr) Calcium Triplet in
  absorption
• A-star (50-500 Myr) Balmer lines in
  absorption
• Intermediate (0.5-2 Gyr) Balmer and CaII H and
  K line ratios
• 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 IBIonizing
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 casestar 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

• Fossil analysis (MOPED)
• Integrated approach (GRASIL)

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