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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
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
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Joint Center for Astrophysics
1. Motivations:
LBGs are important
for the understanding
of the galaxy formation
and evolution at z~3
Dickinson (98)
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The observational properties can be summarized:
(1) High SFR:
(2) Compact:
(3) Strong clustering in space:
(4) Metal rich:
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(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) ……..
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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) …….
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Now in general:
Shu et al (01), Zhao et al (02), Somerville et al (02)
Bullock et al (02), Kauffmann et al (03) ….
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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
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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
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r _ eff in V and I bands
They are almost
the same
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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
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r _ eff vs R
1. Brighter LBGs are larger;
2. Consist with the predictions
of disk-like star forming
regions
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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 ?
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• 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)
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The predicted stellar mass function of LBGs:
---- which can be tested by Spitzer
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The predicted correlation length for LBGs with different
stellar mass:
--- which can be tested by Spitzer
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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
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Joint Center for Astrophysics
Thanks