1、大樣本巡天中類星體測光紅移的確定,吳學兵 （北京大學天文學系） ,Content,Introduction: quasars in large sky surveys Photometric redshifts of quasars in SDSS How to find high-z quasars Discussion: BATC first identified as star-like optical sources with emission lines in 1963; Maarten Schmidt (1963) realized the redshift of 3C 273 (

2、z=0.158) First named simply as “quasi-stellar radio sources”, shorten to “quasars” by H.-Y. Chiu(邱宏義) (1964), accepted by ApJ in 1970 More than 100,000 discovered; the largest redshift is 6.4 (Fan(樊曉暉), et al. 2003),Maarten Schmidt,類星體3C 273的譜線紅移量達到0.16,類星體光譜中有強而寬的未知發(fā)射線。 1963年Maarten Schmidt證認出它們實際上

3、是紅移了的H和其它元素的發(fā)射線。,Examples of quasars discovered with the largest optical telescope (2.16m) in China (Wu, Bade 105 quasars) Galaxies: r 17.77; Quasars: i 19.1 Only photometric redshifts for fainter objects,Spectroscopy: The best way to determine the redshift of quasars, though not always possible, es

4、p. for fainter quasars,Photometric Systems of SDSS,SDSS composite quasar spectrum (EDR 2200 quasars),Predicted magnitude and color of quasars,Quasar spectrum f(), SDSS transmission efficiency s() (u,g,r,i,z),Comparison with the data of 18678 quasars in SDSS DR1,Photometric redshift determinations,Ch

5、i2 minimization Using 4 colors for z3.6 (Ly moves out of u band),Comparison of photo-z with spectroscopic-z for 18678 SDSS DR1 quasars,68% with |z|0.2,Examples of wrong photometric redshifts,Improvements on photo-z,More composite quasar spectra Red quasars, BAL quasars, radio-loud/quiet More photome

6、tric data in other bands UV(GALEX), near-IR(JHK), VO application,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,Location difference of quasars limiting magnitude V21 Surveyed area: 100 degree2,BATC filter systems,Theoretical color-z relations of quasars in BATC system Wu, Zhang & Zhou (2004),Theoretical colors of quasars and stars in BATC system, Wu, Zhang & Zhou (2004),Theoretical colors of quasars, galaxies and stars in BATC system, Wu, Zhang