1. “Nature and Descendants of Sub-mm and Lyman-break Galaxies in Lambda-CDM”
Juan Esteban González
Collaborators: Cedric Lacey, Carlton Baugh, Carlos Frenk, Andrew Benson.
Obergurgl, 13/12/09

2. OUTLINE Semi-analytical modelling: High-redshift populations:
Durham Galform model
Physical processes,
Building Galaxy Merger Trees.
High-redshift populations:
Sub-mm galaxies (SMGs),
Lyman-break galaxies (LBGs), faint and bright criteria.

3. Galform Model: Processes included in the model: gas cooling,
star formation, supernova feedback,
galaxy mergers,
chemical enrichment,
stellar population evolution,
dust extinction and emission.
Cole, Lacey, Baugh & Frenk, 2000, MNRAS, 319, 168

4. Modelling galaxy SEDs with dust
dust in diffuse medium and molecular clouds
stars form in clouds and leak out
radiative transfer of starlight through dust distribution
physical dust grain model
heating of dust grains -> dust temperature distribution
IR/sub-mm emission from grains w distrib of size & T
Important for both type of galaxies.
GRASIL: Silva et al 1998, Granato et al 2000, Vega et al 2005

5. Galaxy mergers & morphology
The model distinguish two type of mergers:
major mergers: stellar disks -> stellar bulge
minor mergers: the disk of the central galaxy is preserved
In all major mergers and in some minor mergers:
-> burst of star formation
bulge can grow new disks

6. Durham Galform Model
Parameters are the same used in Baugh et al. 2005:
- Reproduce the z=3 LF of LBGs
- Reproduce the number of SMGs.
Top-heavy IMF in burst:
in disks:
standard IMF (Kennicut)
Increase the amount of UV radiation heating the dust.
Higher yield of metals from II SNe=>more dust produced.
The cumulative number counts at 850 µm. Baugh et al. 2005

7. Redshift Distribution
Luminosity Function
Redshift Distribution
Swinbank et al. 2008
Late type galaxies
Baugh et al. 2005
Gonzalez et al. 2009

8. Sub-mm galaxies (SMGs).
The nature of:
Sub-mm galaxies (SMGs).
Lyman-break galaxies (LBGs).

9. Submillimetre galaxies (SMGs)
Star-forming galaxies at high z (z ~2-3)
SMGs discovered using SCUBA instrument on the JCMT telescope (850 µm).
Submm:
Galaxies with starburst surrounded by dust, the dust is being heated by UV radiation from young stars,
the UV stellar emission is reradiated by the dust in far-infrared/submm bands,
Observationally selected having fluxes Sν (850µm) > 5.0 mJy.

10. Galaxy merger tree Galaxy mergers:
-> can trigger burst of star formation
In the model, SMGs:
Sv (850um) > 5.0mJy,
Redshift z>1.
Red: SMGs

11. Following the SMGs evolution
Central Galaxy
Flux Sν (850 µm)

12. Following the SMGs evolution
Central Galaxy
Flux Sν (850 µm)

13. Following the SMGs evolution
Central Galaxy
Stellar Mass
Flux Sν (850 µm)

14. B/T: Bulge to Total Stellar Mass
Examples of Galxy Merger Trees
B/T=1, pure bulge galaxy
B/T=0, pure disk galaxy
M*(z=0) = 1011 h-1 M๏

15. B/T: Bulge to Total Stellar Mass
Examples of Galxy Merger Trees
B/T=1, pure bulge galaxy
B/T=0, pure disk galaxy
M*(z=0) = 1.1 x 1012 h-1 M๏

16. SMG Triggering, Minor or Major Mergers?

17. Following the SMGs evolution
Central Galaxy
Flux Sν (850 µm)

18. Duration of Sub-mm phase
Distribution of the time that a galaxy is considered as a SMG
Sν(850µm) > 5.0 mJy, z > 1
The typical duration of the Sub-mm phase is ~ 0.1 h-1 Gyr

19. SMGs evolution
Stellar mass?

20. Stellar mass evolution
Stellar mass growths with time
First SMGs end up in more massive galaxies

21. SMGs descendants What are the properties of the descendants of SMGs?
Find all the SMGs

22. SMGs descendants (B/T distribution)
B/T: Bulge to Total Stellar Mass
B/T=1, pure bulge galaxy
B/T=0, pure disk galaxy
Mainly bulge dominated descendants. 70% have B/T>0.5

23. SMGs descendants (stellar mass distribution)
M*= 2 x 1011 h-1 M๏
Mhalo = 6 x 1013 h-1 M๏
satellites
central

24. Contribution of the SMG phase
Evolution of the cosmic star formation rate
SMGs
The star formation produced in the z>1 SMG phase contribute only 0.06% of the total present-day stellar mass density.

25. Lyman-break galaxies (LBGs).
The nature of:
Sub-mm galaxies (SMGs).
Lyman-break galaxies (LBGs).

26. Lyman-Break Galaxies (LBGs)
Star forming galaxies
Spectral break around 912 Å by absorption by neutral H.

27. Bright LBGs: LUV > L*UV
Characteristic Luminosity L*UV at z=3.
Bright LBGs: LUV > L*UV
Faint LBGs:
LUV > 0.1 L*UV

28. B/T: Bulge to Total Stellar Mass
Examples of Galxy Merger Trees
B/T=1, pure bulge galaxy
B/T=0, pure disk galaxy
redshift
Bright LBGs (LUV > L*UV)
M*(z=0) = 6.6 x 1010 h-1 M๏
Faint LBGs (LUV > 0.1 L*UV)
Normal (LUV < 0.1 L*UV)

29. B/T: Bulge to Total Stellar Mass
Examples of Galxy Merger Trees
B/T=1, pure bulge galaxy
B/T=0, pure disk galaxy
Bright LBGs (LUV > L*UV)
redshift
M*(z=0) = 2.1 x 1011 h-1 M๏
Faint LBGs (LUV > 0.1 L*UV)
Normal (LUV < 0.1 L*UV)

30. Stellar mass distribution, BRIGHT LBGs and their descendants
Bright LBGs: LUV > L*UV
Bright LBGs at z=3 are five times more massive than LBGs at z=6

31. Stellar mass distribution, BRIGHT LBGs and their descendants
Faint LBGs: LUV > 0.1L*UV
Faint LBGs at z=3 are more than a order of Magnitude more massive.

32. Different question:
What is the fraction of the total galaxies at z=0 that are descendants of LBGs?

33. z = 3 z = 6 Fraction of the total galaxies at z=0 with LBG progenitors
BRIGHT LBGs
FAINT LBGs
z = 3
z = 6
A Milky Way mass galaxy is predicted to have a 50% of prob. of having a faint LBG progenitor.
& to have a 6% (at z=3) and a 2% (at z=6) of probability of having a bright LBG progenitor.

34. Sub-mm flux (850µm). of LBGs, how many are predicted to be SMGs?
z = 6
0.5% of the Bright-LBGs at z=6 are SMGs
z = 3
2% of the Bright-LBGs at z=3 are SMGs

35. Conclusions The model make predictions in a unified way,
For SMGs brighter than 5.0 mJy we find the following:
Duration of the sub-mm phase is typically 0.1/h Gyr,
Median stellar mass of their descendants is 2 x 1011h-1M⊙,
70% of the SMGs end up as bulge-dominated galaxies,
however, the stellar mass produced in the sub-mm phase in these bright SMGs is only a tiny fraction (0.06%) of the total present day stellar mass density.
For LBGs:
Median stellar mass of the descendants is 4 x 1010h-1M⊙ (of bright z=3 LBGs) and 1011h-1M⊙ (of bright z=6 LBGs),
Median stellar mass of the descendants is 8 x 109h-1M⊙ (of both faint z=3 LBGs and faint z=6 LBGs),
One every 10 and one every 50 Milky Way mass galaxy is predicted to be descendants of z=3 and z=6 LBGs.
2% and 0.5% of the LBGs at z=6 and z=3 are found to be SMGs.