Calibraci

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

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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

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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.

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POPULATION SYNTHESIS MODELS

• Initial population with Initial Mass Function
• IMF(M)?? M-2.35 (M2-120 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 lt 250 Myr
• Models used
• CMHK02 (Cerviño, Mas-Hesse Kunth)
• SB99 (Leitherer et al.)

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IMF CORRECTION

• Compare our calibrations with those from
• Kennicutt (1998)
• Salim et al. (2007)
• But they consider M0.1-100 Mo (us M2-120 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
  (lt30 Myr)
• L1500/L15001.04
• FIR/FIR1.16
• NLyc/NLyc1.16

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UV EMISSION 1

• 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, lt10 Z0.008

• Good agreement with Kennicutt within 12 after 30
  Myr useful for ages gt 20 Myr
• Disagreement with Salim 30 with respect to
  Kennicutt
• Intrinsic difference between models 15
• Variety of SFHs of sources of sample 10
• Z0.016 5
• Z of sample ? Salim value was expected to be
  between predictions of models with Z0.008-0.020

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UV EMISSION 2

• Metallicity delay in stellar evolution
• IB MEDIUM dependence, 15-25 higher Z0.008 for
  L1500 and L2000
• IB STRONG dependence, 15-65 for L3500

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FIR EMISSION 1

• We assume thermal equilibrium of dust
• ? All energy absorbed is reemitted
• Parameters
• Cardelli et al. (1989) extinction law (RV3.1)
• 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)gt0.5 ? E(B-V)1
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FIR EMISSION 2

• Metallicity delay in stellar evolution
• IB MEDIUM dependence, 25 higher Z0.008
• EB VERY LOW dependence, lt11 Z0.008
• Kennicutt (1998) lies within 15 after 100 Myr

Kennicutt only appropiate for long-lived (?100
Myr) starbursts
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IONIZING PHOTONS 1

• Photons with??lt912 Å can ionize H atoms
• ? Balmer lines (among others)
• Assume a fraction 1-f0.3 is absorbed by dust
  before ionization
• Metallicity delay in stellar evolution
• IB HIGH dependence, 0.2-0.4 dex higher for
  Z0.008
• EB MEDIUM dependence, 25 higher Z0.008

EB attains rapidly the steady state
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IONIZING PHOTONS 2
When considering 1-f0.3 in Kennicutt

• Kennicutt value without correction
• 50 higher than models
• After correction
• Models expressions agree
• for ages gt 8 Myr

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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
  Z0.008
• EB EXTREMELY LOW dependence in the stationary
  state (gt40 Myr) when compared to Z0.008

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EB CALIBRATION
Scaled to SFR1 Mo/yr
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IB CALIBRATION
Scaled to SFS1 Mo
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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 gt 30 Myr
• FIR applies only at ages gt 100 Myr
• NLyc/H? after correction for prior dust
  absorption, at ages gt 8 Myr
• Salim et al. (2007)
• UV it underestimates SFR