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WU HONG NAOC

PAH AND MID-IR LUMINOSITIES AS MEASURE OF STAR-FORMATION RATE IN SPITZER FIRST LOOK SURVEY GALAXIES. WU HONG NAOC. Background. polycyclic aromatic hydrocarbons. PAH. The purpose. SFR is the fundamental indicator for galaxy formation and evolution Different SFR indicators

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WU HONG NAOC

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  1. PAH AND MID-IR LUMINOSITIES AS MEASURE OF STAR-FORMATION RATE IN SPITZER FIRST LOOK SURVEY GALAXIES WU HONG NAOC

  2. Background polycyclic aromatic hydrocarbons PAH

  3. The purpose • SFR is the fundamental indicator for galaxy formation and evolution • Different SFR indicators different physics, disadvantages UV Hα Extinction? FIR Cirrus? Submm for high z radio AGN contribution the SFRs, difference of a factor 2

  4. MID-IR indicators advantages: low extinction, less circus contribution Elbaz et al.(2002) relation between LMIR and LIR MIR: ISO 6.75μm 15 μm 6.75μm: PAH(polycyclic aromatic hydrocarbons) 15 μm: VSG continuum(very small grain) polluted by some PAH features (12.7 μm) features

  5. MID-IR in SPITZER 8μm: cover the strongest 7.7μm PAH feature 24μm: VSG, less contribution from PAH expect they can be SFR indicators • TO do THIS: need a sample of star-forming galaxies to build up the relation.

  6. SAMPLE • Based on the main field of Spitzer FLS mid-IR images ( IRAC 3.6, 4.5, 5.6, 8.0μm, MIPS 24 μm) reduced by ourselves The ovelay region is 3.7 degree2 AUTO magnitudes obtained by Sextractor SDSS EDR just cover the FLS region matching the FLS sources with spectra ~400sources: stars, AGNs, galaxies VLA 1.4GHz (Condon et al. 2003) • Removing stars, qsos, galaxies without line emissions and narrow line AGNs (BPT diagram) only keep galaxies with Hαemission (S/N > 5σ)

  7. The sample of star-forming galaxies 91 have Hα and IRAC 4 bands 38 of 91 have 1.4 GHz flux 70 have Hα and MIPS 24 μm 33 of 70 have 1.4 GHz flux all sources z < 0.2 12 dwarf galaxies with MB > -18 mag

  8. RADIO/Hα/ MIR LUMINOSITIES • 1.4GHz luminosities corrected to luminosities at rest frame with power law fluxν-α, α=0.8 • Hαluminosities Extinction correction: Milky Way , Intrinsic from Hα/Hβ Fibre-aperture correction rPetro - rfibre

  9. MIR luminosities ( 8 μm and 24 μm) K-correction, based on M82 template remove the stellar continuum from 8 μm based on the 3.6μm flux => 8 μm (PAH)

  10. MIR --1.4GHz/Hα RELATIONS

  11. Filled circles: sample galaxies Open circles: dwarf galaxies Dotted: linear fit Solid: non-linear Long-dash: Linear fit for radio-quite sources (Appleton et al. 2005) Short-dash: ISO 6.75μm-IR relation (Elbaz et al. 2002)

  12. Dotted: linear fit Solid: non-linear Dot-dash: linear fit between ISO6.75μm—Hα for galactic disks (Roussel et al. 2002)

  13. STAR FORMATION RATES • Based on MIR/1.4GHz relations • Based on MIR/Hα relations

  14. CONCLUSION AND DISCUSSION • MIR are well correlated with radio/ Hα and can be SFR indicators • Even For many low luminosity AGNs, the 24μm emission is dominated by star-formation, not by AGNs. • The relation could not be right for ULIRGs • Dwarf galaxies do not follow the PAH-Hαrelation. (low dust-gas ratio and low metallicity)

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