1. 吴学兵 （北京大学天文学系） wuxb@bac.pku.edu.cn
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）

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. 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。
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

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

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

8. Large Optical Sky Quasar Surveys
Palomar-Green (PG) Bright Quasar Survey (BQS): B<16, 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 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)

9. Understanding the distribution and evolution of quasars

10. 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

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

12. 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

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

14. Photometric Systems of SDSS

15. SDSS composite quasar spectrum (EDR 2200 quasars)

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

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

18. 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)

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

20. Examples of wrong photometric redshifts

21. 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

22. 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

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

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

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

26. BATC filter systems

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

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

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

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

31. Possible applications to LAMOST?