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Population Synthesis at the Crossroads Claus Leitherer (STScI) and Sylvia Ekström (Geneva Obs.). Cosmology. Galaxy Evolution. Stellar Populations. Stellar Astrophysics. Nuclear and Atomic Physics. Errors • Information Flow. Popularity • Mobility • Front Page News.

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population synthesis at the crossroads claus leitherer stsci and sylvia ekstr m geneva obs

Population Synthesis at the CrossroadsClaus Leitherer (STScI)andSylvia Ekström (Geneva Obs.)

Claus Leitherer: Population Synthesis

slide2

Cosmology

Galaxy Evolution

Stellar Populations

Stellar Astrophysics

Nuclear and Atomic Physics

Errors • Information Flow

Popularity • Mobility • Front Page News

Claus Leitherer: Population Synthesis

evol utio nary population synthesis basics
Evolutionary Population Synthesis: Basics
  • Goal: model SEDs of nearby and distant galaxies
  • Star formation law (IMF, SF history, clustering…)
  • Stellar evolution models (conversion of mass into luminosity and introduction of the time-scale)
  • Spectral libraries (empirical and theoretical)
  • Other (dust, geometry…)

Claus Leitherer: Population Synthesis

most widely used public model packages
Most widely used, public model packages:
  • GALEV (Schulz et al. 2002; Kotulla et al. 2009)
  • GALEXEV(Bruzual & Charlot 1993; 2003)
  • PEGASE (Fioc & Rocca-Volmerange 1997; Le Borgne et al. 2004)
  • STARBURST99 (Leitherer et al. 1999; Leitherer & Chen 2009)

 generally good agreement

Claus Leitherer: Population Synthesis

broadened scope beyond stellar populations
Broadened scope beyond stellar populations:
  • Panchromatic SEDs including stellar and gaseous contributions (Dopita et al. 2005; 2006a; 2006b; 2008)
  • SEDs with self-consistent inclusion of dust (Dwek & Scalo 1980; Dwek 2009)
  • Chemical evolution due to stars and galactic outflows and infall (Matteucci 2009; 2010)

Claus Leitherer: Population Synthesis

new developments the new normal
New Developments: the New Normal
  • Stochasticity
  • Rapid eruptive evolutionary phases
  • Stellar multiplicity
  • Convective overshooting
  • Stellar rotation

Claus Leitherer: Population Synthesis

stochasticity
Stochasticity
  • Bruzual (2002):
  • Cluster simulations of sparsely populated evolutionary phases due to stochastic fluctuations of the IMF
  • Cerviño et al. (2002):
  • Relevant for clusters with M < 105 M⊙, depending on wavelength

Claus Leitherer: Population Synthesis

da silva et al 2011 slug stochastically light up galaxies
Da Silva et al. (2011): SLUG – Stochastically Light Up Galaxies
  • SLUG synthesizes stellar populations using a Monte Carlo technique with stochastic sampling, including the effects of clustering, the stellar IMF, star formation history, stellar evolution, and cluster disruption

Claus Leitherer: Population Synthesis

eldridge 2011 bpass binary population and spectral synthesis
Eldridge (2011): BPASS – Binary population and spectral synthesis
  • Application: comparison with sample of 300 star-forming galaxies within 11 Mpc (Lee et al. 2009)
  • SFR(H)/SFR(UV) declines for small SFR(UV)
  • Photon leakage?
  • Eldridge (2011): can also be accounted for by stochastic effects

Claus Leitherer: Population Synthesis

crowther et al 2010 the most massive stars in r136 lmc
Crowther et al. (2010): the most massive stars in R136 (LMC)
  • Four stars have masses between 150 and 300 M⊙
  • These stars account for ~50% of the ionizing photon output of R136
  • Correspondingly, they account for ~10% of the ionizing luminosity of the entire LMC

Claus Leitherer: Population Synthesis

rapid eruptive evolutionary phases
Rapid Eruptive Evolutionary Phases
  • Maraston (2011)
  • Contribution to LBol of SSP by TP-AGB stars
  • Evolution/atmospheres still poorly understood

Claus Leitherer: Population Synthesis

conroy gunn 2010 fsps flexible stellar population synthesis
Conroy & Gunn (2010): FSPS – flexible stellar population synthesis
  • SPS code combines stellar evolution calculations with stellar spectral libraries to produce simple stellar populations
  • Manually adjust stellar phases and estimate errors
  • Allows estimate of uncertainties of, e.g., the AGB phase

Claus Leitherer: Population Synthesis

smith et al 2011 transient eruptive phases in the upper hrd
Smith et al. (2011): transient, eruptive phases in the upper HRD
  • Continuum in M(peak) from novae to SNe
  • AGB in the red, vs. LBV in the blue
  • AGB important for mass loss and luminosity
  • LBV only important for mass loss
  • LBVs are critical predecessors of WR stars

Claus Leitherer: Population Synthesis

stellar multiplicity
Stellar Multiplicity
  • Sana & Evans 2011: >50% of all massive stars in binaries; significant fraction in close binaries

Claus Leitherer: Population Synthesis

de mink 2010 evolution of a massive close binary
de Mink (2010): evolution of a massive close binary

On the main-sequence: spin-up and higher rotation; mixing and evolution to higher L and Teff.

Post-main-sequence: Roche-lobe overflow and mass transfer to secondary: “rejuvenation”.

Claus Leitherer: Population Synthesis

eldridge stanway 2009 rejuvenation effect in ssp
Eldridge & Stanway (2009): rejuvenation effect in SSP
  • Evolution of Hβ equivalent width with time in SF galaxy
  • Solid: single stars with different Z; dashed: binaries with different Z
  • Hot, ionizing population appears after ~10 Myr
  • Relevance: age spread of star formation? LINERs?

Claus Leitherer: Population Synthesis

convective overshooting
Convective Overshooting

Energy production of massive stars in convective core

Claus Leitherer: Population Synthesis

stellar rotation
Stellar Rotation
  • Hunter et al. (2009): N/H and v sin i in LMC OB stars
  • Significant N enrichment on the main sequence

Claus Leitherer: Population Synthesis

how to reproduce the n enhancement
How to reproduce the N enhancement
  • Stellar winds to remove outer, stellar layers
  • Mass loss and mass transfer in close binaries
  • Enhanced convective overshooting
  • Correlates with rotation rotationally induced mixing

Claus Leitherer: Population Synthesis

brott et al 2011 evolutionary models with rotation
Brott et al. (2011): evolutionary models with rotation

M < 2 M⊙: rotation negligible because of magnetic braking

2 M⊙ < M < 15 M⊙: Teff decrease caused by centrifugal forces

M > 15 M⊙: larger convective core with higher Teff and L

Claus Leitherer: Population Synthesis

ekstr m et al 2012 full set of evolution models with rotation
Ekström et al. (2012): full set of evolution models with rotation
  • 0.8 M⊙ < M < 120 M⊙
  • Z = Z⊙ (other Z in preparation)
  • vrot = 0.4 vbreakup on ZAMS
  • Calibrated extensively via local stars and star clusters
  • Implemented in Starburst99

Claus Leitherer: Population Synthesis

m bol vs time ssp 10 6 m z kroupa imf
MBol vs. time (SSP, 106 M⊙, Z⊙, Kroupa IMF)
  • Models with rotation are more luminous by ~0.4 magbecause of the higher L/M and Teff of individual stars

Claus Leitherer: Population Synthesis

lyman photons vs time ssp 10 6 m z kroupa imf
Lyman photons vs. time (SSP, 106 M⊙, Z⊙, Kroupa IMF)
  • The number ionizing photons increases by a factor of ~4 when hot, massive stars are present

Claus Leitherer: Population Synthesis

h equivalent width vs time continuous sf z kroupa imf
H equivalent width vs. time (continuous SF, Z⊙, Kroupa IMF)
  • W(H) increases by ~0.2 dex. If used as an IMF indicator in late-type galaxies, the new models change the IMF exponent from, e.g, 2.3 to 2.6

Claus Leitherer: Population Synthesis

br luminosity vs time sfr 100 m yr 1 z kroupa imf
Br luminosity vs. time (SFR = 100 M⊙ yr-1, Z⊙, Kroupa IMF)
  • Applied to IR-luminous galaxies: models with rotation lead to, e.g., SFR = 100 M⊙yr-1, whereas models without give SFR = 175 M⊙yr-1.

Claus Leitherer: Population Synthesis

take away points
Take-Away Points
  • Replacemement of traditional population synthesis models by a new generation of models
  • Ready for quantitative testing, beyond mere concept studies
  • Stochastic effects, stellar multiplicity, rotation
  • Significant decrease of M/L, and therefore revision of IMF and SF rates
  • The new models need to be tested by comparison with galaxy properties

Claus Leitherer: Population Synthesis

slide27

Cosmology

Galaxy Evolution

Stellar Populations

Stellar Astrophysics

Nuclear and Atomic Physics

Information Flow

Claus Leitherer: Population Synthesis

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