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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


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


Cosmology

Galaxy Evolution

Stellar Populations

Stellar Astrophysics

Nuclear and Atomic Physics

Information Flow

Claus Leitherer: Population Synthesis


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