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Using SDSS database to study metallicities of star-forming galaxies

Using SDSS database to study metallicities of star-forming galaxies. 梁艳春，国家天文台 2006.10.29 ， 上海. Outline. SDSS: hot topic Methods to estimate metallicities of star-forming galaxies (12+log(O/H)) SDSS samples: metal-rich, metal-poor

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Using SDSS database to study metallicities of star-forming galaxies

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  1. Using SDSS database to study metallicities of star-forming galaxies 梁艳春，国家天文台 2006.10.29， 上海

  2. Outline • SDSS: hot topic • Methods to estimate metallicities of star-forming galaxies (12+log(O/H)) • SDSS samples: metal-rich, metal-poor • Interests to our LAMOST: about the metallicities of large sample of galaxies • N/O abundances

  3. 1. SDSS: hot topic ADS--- search by “SDSS”: “Abstract” -- 2964 , “Title” — 1227 Xi’An AGN meeting：1) sdss samples themselves, 2) selecting objects, multi-wavelength studies –- large sample, or strange objects e.g. Hao L.: Mid-IR spectra of SDSS AGNs Yuan W.M.: NLS1, then X-ray etc. Li C. : clustering of NL AGNs Wang T.G: Type 2 QSO Nagao N.: metallicity evolution of AGNs Groves B.: low-metallicity AGNs

  4. The SDSS-DR5 SDSS DR5 Imaging Sky Coverage (Aitoff projection of Equatorial coordinates) SDSS DR5 Spectral Sky Coverage (Aitoff projection of Equatorial coordinates) 8000 sq. deg. 5740 sq. deg.

  5. The SDSS-DR5 Imaging

  6. The SDSS-DR5 Spectroscopy

  7. Star-forming galaxies from SDSS (from Tremonti et al. 2004)

  8. 2. Methods to estimate metallicities of star-forming galaxies • Te-method： the most accurate method • 2) R23-method ((I[OII]+I[OIII])/Hb) • 3) P-method (R23,P) • 4) Other strong-line ratio methods:[NII]/Ha, • [OIII]/[NII],[NII]/[OII],[NII]/[SII], • [SII]/Ha,[OIII]/Hb, S23,S234 • 5) Photoionization model fitting • (梁艳春等，天文学进展，2006，第四期)

  9. 1) Te-method：the most accurate method ( Izotov et al. 2005) (Garnett 1992)

  10. 2) R23-method：empirical strong-line ratio (Pagel et al. 1979 for metal-rich galaxies) (Skillman 1989 for metal-poor galaxies)

  11. 3) P-method (Pilyugin 2000,2001,2005) • From the sample galaxies with Te,R23,P, they derive calibrations for O/H=f(R23,P)(P=logR3/R23,R3=[OIII]/Hb) • 7.1<12+log(O/H)Te<7.95: • 8.2<12+log(O/H)Te<8.7:

  12. 4) Other strong-line ratio methods: N2=log([NII]/Ha), O3N2=log(([OIII]/Hb)/([NII]/Ha))[NII]/[OII], [NII]/[SII][SII]/Ha, [OIII]/Hb Use the large sample of SDSS galaxies to get calibration relations There are photoionization model calculations published (Kewley & Dopita 2000)

  13. 3. Sample selection (Groves, B. et al. 2006,astro-ph/0608058)

  14. Metal-rich galaxies: (i) SDSS-DR2 (261,054), 14.5<r<17.77 mag (193,890 left); (ii) 12+log(O/H)(SDSS) > 0 (50,385 left) (SDSS: Tremonti et al. 2004); (iii) 0.04<z<0.25 (40,693 left); (iv) emission lines [OII], H\beta, [OIII], H\alpha, [NII] were detected (40,239 left, this number will be reduced to 39,919 if the [SII]6717,6731 are considered as well); (v) fluxes of emission lines H\beta, H\alpha, and [NII]6583 were detected at greater than 5\sigma (39,029 left); (vi) 8.4<12+log(O/H)<10 (39,006 left); (vii) the discrepancy between 12+log(O/H) values of Tremonti et al. (2004) and our estimates is less than 0.15 dex (38,478 left finally).

  15. Calibrations:N2=log([NII]6583/Ha) O3N2=log[([OIII]/Hb)/ ([NII]6583/Ha)] (Liang et al. 2006, ApJ astro-ph/0607074; Pettini & Pagel 2004; Denicolo et al. 2002;Kewley & Dopita 2002)

  16. Metal-poor galaxies We summarize consequently the selection criteria : (i) SDSS-DR4 (567,486) (ii) star-forming galaxies (141,317) (iii) 0.04<z<0.25 (123,994) (iv) emission lines [OII], Hb, [OIII]4363,5007, Ha, [NII]6583, [SII]6717,6731 were detected (53,469) (v) Fluxes of emission lines Hb, Ha, [NII] , [SII]6717,6731, [OIII]4363 was detected at greater than 5σ (531) In addition, there are 164 extremely metal-poor galaxies with [OIII]4363detected from literature. (Yin et al. 2006, A&A, astro-ph/0610068)

  17. N2 O3N2 log{([OIII]/Hb)/([NII]/Ha)} log([NII]/Ha) Re-deriving calibrations on N2, O3N2, S2 S2 N2, P

  18. Comparisons with models, full metallicity range: O3N2 [NII]/[OII] N2 [NII]/[SII] [SII]/Ha [OIII]/Hb

  19. R23 • (1) [NII]/[OII] is the best for the metal-rich region, • but it needs careful dust correction • N2, O3N2, S2 correlate with O/H in metal-poor • R23 is a good calibration for 12+log(O/H)<7.9 • [NII]/Ha is very useful since the two lines are • close, and can be obtained from the NIR • observations for inter.-, high-z galaxies. • However, it relates to the enrichment history • of N element, must be kept in mind.

  20. 4. Hints to our LAMOST: estimating the metallicities of large sample of galaxies Flux-calibrated spectra, Te method, R23 method, P method, other strong-line ratios (N2, O3N2, S2 etc.) Un-Flux-calibrated spectra, EW (N2，O3N2， N2S2), EW R23 method(?)

  21. 5. Estimating N abundances tII=10-4T[NII] x=logR23

  22. N/O the combination of ``primary" and ``secondary“ components of nitrogen, but the ``secondary" one dominates. It is the first such large sample. They do not show large scatter in the log(N/O) vs.12+log(O/H) relations. (R23)

  23. (SDSS)

  24. (12+log(O/H) -0.25dex to fit solar N/O value) GCE models from Molla et al. 2006, MN, 372,1069

  25. Summary • The large sample of SDSS galaxies are very efficient to derive metallicity calibrations of galaxies; samples selections for metal-rich and metal-poor • Methods to estimate metallicities of star-forming galaxies (12+log(O/H)) • Interests to our LAMOST: about the metallicities of large sample of galaxies e.g. O/H, N/O abundances

  26. Thank you!

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