Transcript 1_Gonzalezx

“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
OUTLINE
• Semi-analytical modelling:
– Durham Galform model
– Physical processes,
– Building Galaxy Merger Trees.
• High-redshift populations:
– Sub-mm galaxies (SMGs),
– Lyman-break galaxies (LBGs), faint and bright
criteria.
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
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
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
Luminosity Function
Redshift Distribution
Swinbank et al. 2008
Late type galaxies
Baugh et al. 2005
Gonzalez et al. 2009
• The nature of:
–Sub-mm galaxies (SMGs).
– Lyman-break galaxies (LBGs).
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 farinfrared/submm bands,
– Observationally selected having fluxes Sν (850µm) > 5.0 mJy.
Galaxy merger tree
Galaxy mergers:
-> can trigger burst
of star formation
In the model, SMGs:
-Sv (850um) > 5.0mJy,
-Redshift z>1.
Red: SMGs
Following the SMGs evolution
Central Galaxy
Flux Sν (850 µm)
Following the SMGs evolution
Central Galaxy
Flux Sν (850 µm)
Following the SMGs evolution
Central Galaxy
Stellar Mass
Flux Sν (850 µm)
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๏
Examples of
Galxy Merger
Trees
B/T: Bulge to Total
Stellar Mass
B/T=1, pure bulge galaxy
B/T=0, pure disk galaxy
M*(z=0) = 1.1 x 1012 h-1 M๏
SMG Triggering, Minor or Major Mergers?
Following the SMGs evolution
Central Galaxy
Flux Sν (850 µm)
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
SMGs evolution
• Stellar mass?
Stellar mass evolution
Stellar
mass
growths
with time
First
SMGs
end up
in more
massive
galaxies
SMGs descendants
• What are the
properties of the
descendants of
SMGs?
• Find all the SMGs
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
SMGs descendants (stellar mass distribution)
M*= 2 x 1011 h-1 M๏
satellites
central
Mhalo = 6 x 1013 h-1 M๏
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.
• The nature of:
– Sub-mm galaxies (SMGs).
–Lyman-break galaxies (LBGs).
Lyman-Break Galaxies (LBGs)
Star forming
galaxies
Spectral break
around 912 Å by
absorption by
neutral H.
Characteristic
Luminosity L*UV at z=3.
Bright LBGs:
LUV > L*UV
Faint LBGs:
LUV > 0.1 L*UV
Examples of
Galxy Merger
Trees
B/T: Bulge to Total
Stellar Mass
B/T=1, pure bulge galaxy
B/T=0, pure disk galaxy
Bright LBGs (LUV > L*UV)
Faint LBGs (LUV > 0.1 L*UV)
Normal (LUV < 0.1 L*UV)
redshift
M*(z=0) = 6.6 x 1010 h-1 M๏
Examples of
Galxy Merger
Trees
B/T: Bulge to Total
Stellar Mass
B/T=1, pure bulge galaxy
B/T=0, pure disk galaxy
Bright LBGs (LUV > L*UV)
Faint LBGs (LUV > 0.1 L*UV)
Normal (LUV < 0.1 L*UV)
redshift
M*(z=0) = 2.1 x 1011 h-1 M๏
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
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.
• Different question:
– What is the fraction of the total galaxies at z=0
that are descendants of LBGs?
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.
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
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.