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大样本巡天中类星体测光红移的确定

大样本巡天中类星体测光红移的确定. 吴学兵 （北京大学天文学系） wuxb@bac.pku.edu.cn. Content. Introduction: quasars in large sky surveys Photometric redshifts of quasars in SDSS How to find high-z quasars Discussion: BATC & LAMOST. 1. Introduction. 类星体（ quasars ）.

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大样本巡天中类星体测光红移的确定

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  1. 大样本巡天中类星体测光红移的确定 吴学兵 （北京大学天文学系） wuxb@bac.pku.edu.cn

  2. Content • Introduction: quasars in large sky surveys • Photometric redshifts of quasars in SDSS • How to find high-z quasars • Discussion: BATC & LAMOST...

  3. 1. Introduction • 类星体（quasars） • Originally discovered in radio survey (3C) in 1950s; first identified as star-like optical sources with emission lines in 1963; Maarten Schmidt (1963) realized the redshift of 3C 273 (z=0.158) • First named simply as “quasi-stellar radio sources”, shorten to “quasars” by H.-Y. Chiu(邱宏义) (1964), accepted by ApJ in 1970 • More than 100,000 discovered; the largest redshift is 6.4 (Fan(樊晓晖), et al. 2003)

  4. 类星体光谱中有强而宽的未知发射线。 1963年Maarten Schmidt证认出它们实际上是红移了的H和其它元素的发射线。 Maarten Schmidt 类星体3C 273的谱线红移量达到0.16

  5. Examples of quasars discovered with the largest optical telescope (2.16m) in China (Wu, Bade & Beckmann 1999, A&A, 347, 63)

  6. Spectra of three most distant quasars (Fan et al. 2003)

  7. Large Optical Sky Quasar Surveys • Palomar-Green (PG) Bright Quasar Survey (BQS): B<16, 10000 deg^2, ~120 Quasars (~7%) • Large Bright Quasar Survey (LBQS): B<17.5, ~10^3 quasars • 2dF: 200 deg^2, U-V<-0.3, ~2.6 10^4 quasars • Sloan Digital Sky Survey(SDSS): eventual 10000 deg^2, ugriz selection, ~10^5 quasars • Data Release 5 (2006): Spectroscopic area: 5740 deg^2. • 79,394 Quasars (redshift <2.3) • 11,217 Quasars (redshift >2.3)

  8. Understanding the distribution and evolution of quasars

  9. The first quasar and the cosmic reionization Detection of A Complete Gunn-Peterson Trough: VLT observation High-redshift quasars probe the end of reionization epoch

  10. Physics Model for the Central Engine of Quasars • Supermassive black hole • Accretion disk • Broad line region • Dusty torus • Narrow line region • Jet

  11. 2. Photometric redshifts of quasars in SDSS • Sloan Digital Sky Survey I • Photometry: ~3 x 108 objects • Limiting magnitudes at the detection limit, S/N 5:1 • Spectroscopy: >106 objects (106 galaxies; 105 quasars) • Galaxies: r <17.77; Quasars: i <19.1 • Only photometric redshifts for fainter objects

  12. Spectroscopy: The best way to determine the redshift of quasars, though not always possible, esp. for fainter quasars

  13. Photometric Systems of SDSS

  14. SDSS composite quasar spectrum (EDR 2200 quasars)

  15. Predicted magnitude and color of quasars • Quasar spectrum f(), SDSS transmission efficiency s() (u,g,r,i,z)

  16. Comparison with the data of 18678 quasars in SDSS DR1

  17. Photometric redshift determinations • Chi^2 minimization • Using 4 colors for z<3.6 and 3 colors for z>3.6 (Ly moves out of u band)

  18. Comparison of photo-z with spectroscopic-z for 18678 SDSS DR1 quasars 68% with |z|<0.2

  19. Examples of wrong photometric redshifts

  20. Improvements on photo-z • More composite quasar spectra • Red quasars, BAL quasars, radio-loud/quiet … • More photometric data in other bands • UV(GALEX), near-IR(JHK), … • VO application

  21. 3. How to find high-z quasars • Separate quasars from stars • Using quasar colors to select hi-z quasar candidates • Spectroscopic identifications, usually with huge ground-based telescopes

  22. Location difference of quasars & stars in color-color diagram quasars stars

  23. Predicted colors of quasars, galaxies and stars in SDSS system, Wu, Zhang & Zhou (2004) Quasars with z>3.5

  24. 4. Discussion • BATC: Beijing-Arizona-Taipei-Connecticut Survey • 60/90 Schmidt telescope • 15 intermediate-band filters covering 3200-10000A • FOV: 1 degree; limiting magnitude V~21 • Surveyed area: >100 degree^2

  25. BATC filter systems

  26. Theoretical color-z relations of quasars in BATC system Wu, Zhang & Zhou (2004)

  27. Theoretical colors of quasars and stars in BATC system, Wu, Zhang & Zhou (2004)

  28. Theoretical colors of quasars, galaxies and stars in BATC system, Wu, Zhang & Zhou (2004)

  29. Selection criteria for quasar candidates with z>3.5 (for BATC)

  30. Possible applications to LAMOST?

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