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

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 AstrophysicsShanghai 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


1. 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

(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


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


r _ eff in V and I bands

They are almost the same


Distribution of half-light radii1. 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 distribution3. they are compact objects with median value ~ 1.3 h^{-1} kpc a bit smaller than previous ones


r _ eff vs R

1. Brighter LBGs are larger;

2. Consist with the predictions of disk-like star forming regions


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 ?


• 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


The predicted correlation length for LBGs with different stellar mass:

--- which can be tested by Spitzer


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 stella

r 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


Thanks

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