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

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

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.

POPULATION SYNTHESIS MODELS Initial population with Initial Mass Function: Initial population with Initial Mass Function: IMF(M)  M (M=2-120 M o ) Evolution of stars: Evolution of stars: –Isochrones: evolution of intrinsic properties (T eff, L BOL, etc.) –Libraries: isochrones data  measurable magnitudes (luminsities, colours, etc.) SFR: two types of models 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 SBS: Star Formation Strenght: initial mass of the burst Unless stated: Z o Unless stated: Z o Age < 250 Myr Age < 250 Myr Models used: Models used: –CMHK02 (Cerviño, Mas-Hesse & Kunth) –SB99 (Leitherer et al.)

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

UV EMISSION 1 Direct tracer of star formation But severely affected by extinction L 1500, L 2000 and L 3500 (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 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=

UV EMISSION 2 Metallicity: delay in stellar evolution Metallicity: delay in stellar evolution –IB: MEDIUM dependence, 15-25% higher Z=0.008 for L 1500 and L 2000 –IB: STRONG dependence, 15-65% for L 3500

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

FIR EMISSION 2 Metallicity: delay in stellar evolution 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 (1998): lies within 15% after 100 Myr Kennicutt only appropiate for long-lived (  100 Myr) starbursts

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, dex higher for Z=0.008 – –EB: MEDIUM dependence, 25% higher Z=0.008 EB: attains rapidly the steady state

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

MECHANICAL ENERGY Winds from massive stars and SNe inject mechanical energy into the medium L K : energy injected per unit of time Dominance: – –Early ages: winds – –When massive stars comence to die: SNe Metallicity: 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

EB CALIBRATION MagnitudeEB (30 Myr)EB (250 Myr) L   L   FIR 1.5   N Lyc 4.1  HH 3.0  LKLK 1.1   M o Scaled to SFR=1 M o /yr

IB CALIBRATION MagnitudeIB (4 Myr)IB (6 Myr) L   L   FIR 1.7   N Lyc 6.7   HH 4.9   LKLK 1.1   Scaled to SFS=1 M o

CONCLUSIONS Robust calibrations of SFR and SFS based on several tracers have been obtained using shynthesis models 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 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: Calibrations from literature agree with our models: –Kennicutt (1998) UV: good agreement at all ages > 30 Myr UV: good agreement at all ages > 30 Myr FIR: applies only at ages > 100 Myr FIR: applies only at ages > 100 Myr N Lyc /H  : after correction for prior dust absorption, at ages > 8 Myr N Lyc /H  : after correction for prior dust absorption, at ages > 8 Myr –Salim et al. (2007) UV: it underestimates SFR UV: it underestimates SFR