A New Method For Measuring Extragalactic Distances

1. A New Method For Measuring Extragalactic Distances Authors: Yuzuru Yoshii et al. Speaker: Zheng Xuechen 2014.03.25

2. Outline • Introduction • New Method • Data Analysis • Results and discussion

3. Introduction

4. Why? • Estimate expansion rate • Hubble constant H0 • Distances

5. Methods • Empirical • Cepheid variable stars • Tulley-Fisher • Faber-Jackson • Ia supernovae • et al. • Accurate • Physical model • SZ effect • Gravitational lensing • Parameters uncertainties -> not accurate

6. New Method

7. Base • Sublimation radius • Dust reverberation • Time delay  

8. Light curves example

9. Time delay correction • 1、Time dilation effect • 2、K-band shift and T gradient •  higher z, shorter Δt •  empirically correction • Correction <1%

10. Calibration factor g g is from equation below Q: absorption coefficient Td: ~1700K from NIR a: dust grain mean radius

11. Extinction and K-correction • Av :Galactic extinction • Kv: K-correction • assuming power law spectrum • 

12. DATA aNALYSIS

14. Procedures • 1、K-band subtraction • From V-band and power low • 2、cross-correlating V, K band • Use bidirectional interpolation scheme • 49 incidents to measure time lag

15. Results and discusssion

16. Results • Compare with Cepheid variable stars

17. Compare • Our results: • H0 =73 ±3 km s-1 Mpc-1 • No empirical calibration • Extends 10 times distance • Cepheid variables: • H0 =75 ±10 km s-1 Mpc-1

18. Systematic error • Index : • : • Dust grain radius a  •  • Largest systematic error • How to reduce? • Individually measuring • Determine UV-optical spectrum • Empirical method constrain

19. Two other reverberation methods • 1、reverberation mapping of BLR • BLR size-L relation • Continuum – broad lines time delay • Need empirical calibration • 2、UV-optical continuum time lag • Physical method • H0 =42-44 km s-1 Mpc-1 • Model difficuties

20. Thanks!