“Nature and Descendants of Sub-mm and Lyman-break Galaxies in Lambda-CDM ”
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Transcript of “Nature and Descendants of Sub-mm and Lyman-break Galaxies in Lambda-CDM ”
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“Nature and Descendants of Sub-mm and Lyman-break Galaxies in Lambda-CDM”
Juan Esteban González
Obergurgl, 13/12/09
Collaborators: Cedric Lacey, Carlton Baugh, Carlos Frenk, Andrew Benson.
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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.
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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
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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
Galaxy mergers & morphology
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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)
Þ Increase the amount of UV radiation heating the dust.
Þ Higher yield of metals from II SNe=>more dust produced.
The cumulative number counts at 850 µm. Baugh et al. 2005
Durham Galform Model
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Luminosity Function
Baugh et al. 2005
Late type galaxies
Gonzalez et al. 2009
Redshift Distribution
Swinbank et al. 2008
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• The nature of:
–Sub-mm galaxies (SMGs).
– Lyman-break galaxies (LBGs).
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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.
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Galaxy mergers:-> can trigger burst of star formation
In the model, SMGs:- Sv (850um) > 5.0mJy,- Redshift z>1.
Red: SMGs
Galaxy merger tree
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Following the SMGs evolutionCentral Galaxy
Flux Sν (850 µm)
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Following the SMGs evolutionCentral Galaxy
Flux Sν (850 µm)
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Following the SMGs evolutionCentral Galaxy
Flux Sν (850 µm)Stellar Mass
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Examples of Galxy Merger Trees
M*(z=0) = 1011 h-1 M๏
B/T: Bulge to Total Stellar Mass
B/T=1, pure bulge galaxyB/T=0, pure disk galaxy
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Examples of Galxy Merger Trees
M*(z=0) = 1.1 x 1012 h-1 M๏
B/T: Bulge to Total Stellar Mass
B/T=1, pure bulge galaxyB/T=0, pure disk galaxy
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SMG Triggering, Minor or Major Mergers?
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Following the SMGs evolutionCentral Galaxy
Flux Sν (850 µm)
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Duration of Sub-mm phase
Distribution of the time that a galaxy is considered as a SMGSν(850µm) > 5.0 mJy, z > 1
The typical duration of the Sub-mm phase is ~ 0.1 h-1 Gyr
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SMGs evolution
• Stellar mass?
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Stellar mass evolution
Stellar mass
growths with time
First SMGs end up in more massive galaxies
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SMGs descendants
• What are the properties of the descendants of SMGs?
• Find all the SMGs
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SMGs descendants (B/T distribution)
B/T: Bulge to Total Stellar Mass
B/T=1, pure bulge galaxyB/T=0, pure disk galaxy
Mainly bulge dominated descendants. 70% have B/T>0.5
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SMGs descendants (stellar mass distribution)
satellitescentral
M*= 2 x 1011 h-1 M๏ Mhalo = 6 x 1013 h-1 M๏
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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.
Contribution of the SMG phase
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• The nature of:
– Sub-mm galaxies (SMGs).–Lyman-break galaxies (LBGs).
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Lyman-Break Galaxies (LBGs)
Star forming galaxies
Spectral break around 912 Å by absorption by neutral H.
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Characteristic Luminosity L*UV at z=3.
Bright LBGs: LUV > L*UV
Faint LBGs: LUV > 0.1 L*UV
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Examples of Galxy Merger Trees
Bright LBGs (LUV > L*UV)Faint LBGs (LUV > 0.1 L*UV)
redshift
B/T: Bulge to Total Stellar Mass
B/T=1, pure bulge galaxyB/T=0, pure disk galaxy
M*(z=0) = 6.6 x 1010 h-1 M๏ Normal (LUV < 0.1 L*UV)
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Examples of Galxy Merger Trees
redshift
B/T: Bulge to Total Stellar Mass
B/T=1, pure bulge galaxyB/T=0, pure disk galaxy
M*(z=0) = 2.1 x 1011 h-1 M๏ Bright LBGs (LUV > L*UV)Faint LBGs (LUV > 0.1 L*UV)Normal (LUV < 0.1 L*UV)
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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
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Faint LBGs:LUV > 0.1L*UV
Stellar mass distribution, BRIGHT LBGs and their descendants
Faint LBGs at z=3 are more than a order of Magnitude more massive.
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• Different question:– What is the fraction of the total galaxies at z=0
that are descendants of LBGs?
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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.
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0.5% of the Bright-LBGs at z=6 are SMGs
2% of the Bright-LBGs at z=3 are SMGs
Sub-mm flux (850µm). of LBGs, how many are predicted to be SMGs?
z = 6
z = 3
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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.