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Calibración de trazadores de formación estelar mediante modelos de síntesis

Calibración de trazadores de formación estelar mediante modelos de síntesis. LAEFF-INTA Laboratorio de Astrofísica Espacial y Física Fundamental. Héctor Otí-Floranes, J. M. Mas-Hesse & M. Cerviño SEA, Santander, 11 de julio de 2008. STARBURSTS. Regions of intense stellar formation

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Calibración de trazadores de formación estelar mediante modelos de síntesis

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  1. Calibración de trazadores de formación estelar mediante modelos de síntesis LAEFF-INTA Laboratorio de Astrofísica Espacial y Física Fundamental Héctor Otí-Floranes, J. M. Mas-Hesse & M. Cerviño SEA, Santander, 11 de julio de 2008

  2. STARBURSTS • Regions of intense stellar formation • Galaxies  Starburst galaxies, ULIRGs • Star formation measured by • SFR: Star Formation Rate (Mo/yr) • SFS: Star Formation Strength (Mo) • We are interested in the youngest population  Massive stars • Different SFR tracers: • UV • H: ionized gas • FIR: heated dust • Mechanical energy  X-rays • [OII]3727

  3. GOALS • Using synthesis models, study the evolution of magnitudes: • FIR • NLyc • UV • Mechanical Energy • Others • Obtain SFR & SFS calibrations for each of them • Calibrate the tracers: metallicity, age, etc.

  4. POPULATION SYNTHESIS MODELS • Initial population with Initial Mass Function: IMF(M) M-2.35 (M=2-120 Mo) • Evolution of stars: • Isochrones: evolution of intrinsic properties (Teff, LBOL, etc.) • Libraries: isochrones data  measurable magnitudes (luminsities, colours, etc.) • SFR: two types of models • EB (extended models, SFR): constant star formation • IB (instantaneous bursts, SFS): no further formation (usual age 4-6 Myr) • SBS: Star Formation Strenght: initial mass of the burst • Unless stated: Zo • Age < 250 Myr • Models used: • CMHK02 (Cerviño, Mas-Hesse & Kunth) • SB99 (Leitherer et al.)

  5. IMF CORRECTION • Compare our calibrations with those from: • Kennicutt (1998) • Salim et al. (2007) • But they consider M=0.1-100 Mo (us M=2-120 Mo) • Two-fold correction: • SFR(0.1-100) = 3.4135 * SFR(2-120) • We include more massive stars. With SB99 calculate the ratio when steady state is attained (<30 Myr): • L1500/L’1500=1.04 • FIR/FIR’=1.16 • NLyc/N’Lyc=1.16

  6. UV EMISSION 1 • Good agreement with Kennicutt within 12% after 30 Myr: useful for ages > 20 Myr • Disagreement with Salim: 30% with respect to Kennicutt • Intrinsic difference between models: 15% • Variety of SFHs of sources of sample: 10% • Z=0.016: 5% • Z of sample  Salim value was expected to be between predictions of models with Z=0.008-0.020 • Direct tracer of star formation • But severely affected by extinction • L1500, L2000 and L3500 (U-band) • EB evolution • steep increase: 0.7 dex in 4-5 Myr • slower raise: 0.3 dex in 250 Myr • Metallicity: delay in stellar evolution • EB: VERY LOW dependence, <10% Z=0.008

  7. UV EMISSION 2 • Metallicity: delay in stellar evolution • IB: MEDIUM dependence, 15-25% higher Z=0.008 for L1500 and L2000 • IB: STRONG dependence, 15-65% for L3500

  8. FIR EMISSION 1 • We assume thermal equilibrium of dust  All energy absorbed is reemitted • Parameters: • Cardelli et al. (1989) extinction law (RV=3.1) + 30% ionizing photons + 100% Ly • E(B-V): colour excess E(B-V)=0.1-1 • Similar behaviour to UV radiation Saturation for E(B-V)>0.5  E(B-V)=1

  9. FIR EMISSION 2 • Metallicity: delay in stellar evolution • IB: MEDIUM dependence, 25% higher Z=0.008 • EB: VERY LOW dependence, <11% Z=0.008 • Kennicutt (1998): lies within 15% after 100 Myr Kennicutt only appropiate for long-lived (100 Myr) starbursts

  10. IONIZING PHOTONS 1 • Photons with<912 Å can ionize H atoms  Balmer lines (among others) • Assume a fraction 1-f=0.3 is absorbed by dust before ionization • Metallicity: delay in stellar evolution • IB: HIGH dependence, 0.2-0.4 dex higher for Z=0.008 • EB: MEDIUM dependence, 25% higher Z=0.008 EB: attains rapidly the steady state

  11. IONIZING PHOTONS 2 When considering 1-f=0.3 in Kennicutt • Kennicutt value without correction 50% higher than models • After correction Models & expressions agree for ages > 8 Myr

  12. MECHANICAL ENERGY • Winds from massive stars and SNe inject mechanical energy into the medium • LK: energy injected per unit of time • Dominance: • Early ages: winds • When massive stars comence to die: SNe • Metallicity: • When Z  power of winds , number of WR stars  • IB: HIGH dependence, 60% discrepancies with Z=0.008 • EB: EXTREMELY LOW dependence in the stationary state (>40 Myr) when compared to Z=0.008

  13. EB CALIBRATION Scaled to SFR=1 Mo/yr

  14. IB CALIBRATION Scaled to SFS=1 Mo

  15. CONCLUSIONS Robust calibrations of SFR and SFS based on several tracers have been obtained using shynthesis models Appropriate calibrations should be used depending on the burst properties Star formation regime: EB or IB VERY IMPORTANT Age VERY IMPORTANT, especially in IB models Metallicity: negligible in EB models for UV and FIR E(B-V), etc. Calibrations from literature agree with our models: Kennicutt (1998) UV: good agreement at all ages > 30 Myr FIR: applies only at ages > 100 Myr NLyc/H: after correction for prior dust absorption, at ages > 8 Myr Salim et al. (2007) UV: it underestimates SFR

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