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Analyzing Star Formation Rates in Nearby Field Galaxies: A Comprehensive Study

This study investigates the star formation rates (SFRs) of nearby field galaxies, utilizing observations from the Nearby Field Galaxy Survey (NFGS). By analyzing integrated spectra and infrared (IR) data, this research addresses the discrepancies between various SFR measurements derived from H-alpha, IR, and radio emissions. The findings indicate that young star formation dominates across different environments and highlight the relationships between SFRs derived from [OII] lines and galaxy abundances, enriching our understanding of galaxy evolution and star formation history.

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Analyzing Star Formation Rates in Nearby Field Galaxies: A Comprehensive Study

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  1. Star Formation Rates In the Nearby Field Galaxies Survey Lisa Kewley (CfA) Margaret Geller (CfA) Rolf Jansen (ASU) Mike Dopita (RSAA)

  2. Summary • Introduction • NFGS Sample • IR & Ha SFRs • Radio SFRs • [OII] SFRs • Abundances • Conclusions • Future Directions

  3. Why are SFRs important? • Galaxy evolution • Star formation history of the universe Problem?SFRs do not agree

  4. Galaxy Evolution Starburst99 (Leitherer et al. 1999) Stellar population age prediction

  5. Cosmic Star Formation History Madau 1998

  6. Assumptions: solar abundance no dust total re-emission of ionizing photons Saltpeter IMF SFR from Ha SFR(Ha) = 7.9 x 10-42 L(Ha) (Kennicutt 1998)

  7. SFR(IR) = 4.5 x 10-44 L(IR) 7.9 x 10-44 L(FIR) ~ ~ Assumptions: young stars dominate emission large optical depth continuous burst model Saltpeter IMF Infrared SFR (Kennicutt 1998, Calzetti et al. 2000)

  8. SFR(IR) & SFR(Ha)in interacting starburst galaxies No reddening correction Disagreement Dopita, Pereira, Kewley & Capaccioli (2002) Sample: Kewley et al. (2001)

  9. SFR(IR) & SFR(Ha)in starburst galaxies Reddening correction better agreement Dopita, Pereira, Kewley & Capaccioli (2002) Also: Charlot et al. 2002 Rosa-Gonzalez et al. 2002

  10. Nearby Field Galaxy Survey Sample selection: • 198 galaxies objectively selected from the CfA galaxy survey • (Davis & Peebles 1983, Huchra et al. 1983) • full range in Hubble type • full range of absolute magnitudes in CfA survey • Jansen et al. (2000) • http://cfa-www.harvard.edu/~jansen/nfgs/nfgssample.html

  11. extinction corrected using Balmer Decrement • corrected for stellar absorption F(Ha) : Integrated spectra

  12. Ha & IR SFRs SFR(IR) = (2.7+/- 0.3) SFR(Ha)1.30 +/- 0.06 Ha uncorrected for reddening Kewley et al. (2002)

  13. Ha & IR SFRs Ha uncorrected for reddening Kewley et al. (2002)

  14. L(FIR) log = (0.62 +/- 0.08) log {E(B-V)} + 2.66 +/- 0.06 L( Ha ) Reddening vs. FIR/Ha Kewley et al. (2002)

  15. SFR(Ha) & SFR(IR) agree to within 10% Ha corrected for reddening SFR(IR) = (0.91+/- 0.04) SFR(Ha)1.07+/- 0.03 Kewley et al. (2002)

  16. Ha & IR SFRs Ha corrected for reddening Kewley et al. (2002)

  17. K98 SFR constants L(FIR) / L(Ha) => Empirical test L(FIR) / L(Ha) x k(FIR)/k(Ha) = 0.96 +/- 0.04 estimate the relationship between L(FIR) / L(Ha) and SFR (FIR) / SFR (Ha)

  18. Implications for NFGS galaxies • Young star formation responsible for Ha & FIR • Dust heated close to the active SF regions • global dust & gas relationship universal

  19. Infrared Emission dust heated by young OB stars photospheres of evolved stars infrared “cirrus” More IR cirrus in early-type spirals? Sauvage & Thuan (1992)

  20. Stellar populations in early-type spirals Early-types deficient in young stars Kennicutt & Kent (1983) Sauvage & Thuan (1994)

  21. IR detections

  22. Implications for early-type spirals Either: 1. Compensation effect? Inoue 2002, Bell 2003 or 2. Young star formation dominates radio-FIR correlation: Gavazzi et al. 1986 12mm-FIR correlation: Shapley et al. 2001

  23. Assumptions: Galactic relation between LN & nSN no dust nonthermal spectral index ~ 0.8 IMF slope ~ 2.5 for M > 5 Mo Saltpeter IMF for M < 5 Mo . . Radio SFRs SFR(1.4 GHz) = 1.2 x 10-21 L(1.4 GHz) (Condon, Cotton, & Broderick 2002, Condon 1992)

  24. Radio & Ha SFRs SFR(20cm) = (0.54+/- 0.04) SFR(Ha)0.90 +/- 0.03 Constant offset Kewley, Geller, & Jansen (2003, in prep)

  25. Radio & IR SFRs SFR(IR) = (0.54+/- 0.04) SFR(20cm)0.88 +/- 0.03 Constant offset Kewley, Geller, & Jansen (2003, in prep)

  26. Radio & Ha SFR constants L(20cm) / L(Ha) => Empirical test L(20cm) / L(Ha) x C02/K98 constants ~ 2.4 +/- 0.2 do notagree with the empirical relationship between L(20cm) / L(Ha) possible causes: IMF differences, SN rate, ...

  27. Assumptions: solar abundance no dust Saltpeter IMF [OII] SFRs SFR([OII]) = (1.4 +/- 0.4) x 10-41 L([OII]) (Kennicutt 1998)

  28. [OII] & Ha SFRs SFR([OII]) = (1.51+/- 0.07) SFR(Ha)0.92 +/- 0.02 Kewley, Geller, & Jansen (2003, in prep)

  29. [OII], Ha and magnitude Jansen et al. (2001)

  30. Abundances Derived using Kewley & Dopita (2002, ApJS, 142, 35)

  31. [OII] SFR & abundance Kewley, Geller & Jansen (2003, in prep) also Moustakas, 2002, AAS, 200, 43

  32. Conclusions • Reddening & stellar absorption correction SFR(IR) & SFR(Ha) agree to within 10% • Systematic offset between Condon 2002 20cm constant and K98 constants • SFR[OII] depends on abundance (low metallicities) • FIR/Ha & FIR/radio relations All IR NFGS star-forming galaxies are dominated by young SF in the FIR, Ha, and radio.

  33. Future Directions • NFGS J, H, K, L imaging survey (UKIRT) old stellar populations & hot dust • Ha images young stellar populations • Differences between K98 and C02 SFR constants: Stellar population synthesis models => IMF Radio measurements => SN rate

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