1. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics The half-light radius distribution of LBGs and their stellar mass function Chenggang Shu Joint Center for Astrophysics Shanghai Normal University Collaborated with J. Huang, B. Zhou & X. Liu et al

2. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics 1. Motivations 2. Half-light radii of LBGs 3. Stellar mass function of LBGs 4. Summary

3. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics 1.Motivations: LBGs are important for the understanding of the galaxy formation and evolution at z~3 Dickinson (98)

4. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics The observational properties can be summarized: (1) High SFR: (2) Compact: (3) Strong clustering in space: (4) Metal rich:

5. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics (5) Stellar velocity dispersion: (6) Large scale motions of gas bulks: …….. Steidel et al (99), Adelbergerg & Steidel (00), Adelberger et al (98), Lowenthal et al (97), Giavalisco & Dickinson (01), Giavalisco et al (96), Pettini et al (01), Huang et al (05) ……..

6. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics Theoretical work Early: 1. Massive galaxies: Steidel et al (96), Mo & Fukugita (96), Jing (98), Baugh et al (98), Kauffmann et al (99), Mo et al (99), Shu (00) …… 2. Interacting small galaxies: Kolatt et al (99), Somerville et al (00), Wechsler et al (00) …….

7. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics Now in general: Shu et al (01), Zhao et al (02), Somerville et al (02) Bullock et al (02), Kauffmann et al (03) ….

8. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics Goals for the present work (1)To investigate the distribution of their half-light radii in rest-frame UV; previous 45 LBGs available; which is a strong constraint on galaxy formation and evolution model; (2)To predict their stellar mass function and other properties; can be tested by IRAC in Spitzer

9. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics 2. The half-light radii of LBGs Sample Steidel et al 2003 As an example in Westphel total 207 with 114 have confirmed redshifts; 87 have unknown redshifts; 3 QSOs; 3 AGNs; All have R, G-R and U-G; r _ eff are measured in V and I bands

10. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics r _ eff in V and I bands They are almost the same

11. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics Distribution of half-light radii 1. similar for V and I bands; 2. can be well-fitted by log-normal functions, star forming regions seems to be disk-like is a log-normal distribution 3. they are compact objects with median value ~ 1.3 h^{-1} kpc a bit smaller than previous ones

12. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics r _ eff vs R 1. Brighter LBGs are larger; 2. Consist with the predictions of disk-like star forming regions

13. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics 3. Stellar mass functions of LBGs (1) Based on Shu et al (01); (2), according to BBN theory, f_b ~ 0.12 (3)By Monte Carlo simulations, comparing with the prediction of PS formalism Baryons within individual LBG halos seems to cool down ---- fast accretion phase? ---- bulge formation ?

14. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics Star formation timescales max time scale Duty cycle The properties of an observed LBG can be assumed to be at time t_* statistically, which is randomly selected between (0, t_s)

15. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics The predicted stellar mass function of LBGs: ---- which can be tested by Spitzer

16. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics The predicted correlation length for LBGs with different stellar mass: --- which can be tested by Spitzer

17. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics 4. Summary The half-light radius of LBGs have been measured; Their distribution can be well fitted by log-normal, There exists an correlation between r_ff and SFR --- imply that the star forming regions are disk-like; Star formation timescale is about 0.3Gyr Duty cycle effect is important for LBGs ---- there should exist non-LBG population with massive stellar mass at z~ 3 which can be detected by Spitzer; The predicted stellar mass function of LBGs is obtained; The predicted correlation length of LBGs, which can be tested by Spitzer, is also obtained

18. 联 合 天 体 物 理 中 心 Joint Center for Astrophysics Thanks