Evolutionary Population Synthesis models Divakara Mayya INAOEhttp:// Advanced Lectures on Galaxies (2008 INAOE): Chapter 4

What do we try to synthesize? Mayya 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.

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 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

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 - 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 foreground dust model and an extinction curve (Cardelli et al. 1989) 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 Gas: 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: Basic equations and Ingredients Mayya

SSP: Basic equations and Ingredients Mayya

SSP: Basic equations and Ingredients Mayya

SSP: Basic 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: The method Mayya Isochrone Interpolation schemes

SSP: The method Mayya Effect of rotation: rotating (_____) non-rotating (---)

SSP: The output Mayya 1. Nebular Lines 2. Continuum band luminosity

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

(Class III) SSP: observable phases Mayya 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 ( 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

SSP: spectral evolution Mayya

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

CSF vs IB: Magnitude Mayya

CSF vs IB: colors Mayya

CSF vs IB: SED Mayya

Deriving Age and Mass: diagnostic diagrams Mayya 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

CSF vs IB: RSG features Mayya Mayya 1997

The real case: star formation history of starburst nuclei Mayya

The real case: star formation history of starburst nuclei Mayya

Star formation history of M82 disk Mayya Mayya et al. (2006)

Other applications: SFR Mayya Kennicutt 1998

Other applications: Other applications: Galaxy formation and evolution Mayya 1.Fossil analysis (MOPED) 2.Integrated approach (GRASIL)