The half-light radius distribution of LBGs and their stellar mass function

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

1. Motivations 2. Half-light radii of LBGs 3. Stellar mass function of LBGs 4. Summary

Motivations: LBGs are important for the understanding of the galaxy formation and evolution at z~3 Dickinson (98)

The observational properties can be summarized: (1) High SFR: (2) Compact: (3) Strong clustering in space: (4) Metal rich:

(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) ……..

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) …….

Now in general: Shu et al (01), Zhao et al (02), Somerville et al (02) Bullock et al (02), Kauffmann et al (03) ….

Goals for the present work 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; To predict their stellar mass function and other properties; can be tested by IRAC in Spitzer

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

They are almost the same r _ eff in V and I bands

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 Distribution of half-light radii

r _ eff vs R 1. Brighter LBGs are larger; 2. Consist with the predictions of disk-like star forming regions

(1) Based on Shu et al (01); (2) , according to BBN theory, f_b ~ 0.12 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 ? 3. Stellar mass functions of LBGs

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)

The predicted stellar mass function of LBGs:---- which can be tested by Spitzer

--- which can be tested by Spitzer The predicted correlation length for LBGs with different stellar mass:

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 4. Summary

Thanks

The half-light radius distribution of LBGs and their stellar mass function