“Nature and Descendants of Sub-mm and Lyman-break Galaxies in Lambda-CDM ”

“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.

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

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

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

Luminosity Function

Baugh et al. 2005

Late type galaxies

Gonzalez et al. 2009

Redshift Distribution

Swinbank et al. 2008

• 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

far-infrared/submm bands,– Observationally selected having fluxes Sν (850µm) > 5.0 mJy.

Galaxy mergers:-> can trigger burst of star formation

In the model, SMGs:- Sv (850um) > 5.0mJy,- Redshift z>1.

Red: SMGs

Galaxy merger tree

Following the SMGs evolutionCentral Galaxy

Flux Sν (850 µm)

Following the SMGs evolutionCentral Galaxy

Flux Sν (850 µm)

Following the SMGs evolutionCentral Galaxy

Flux Sν (850 µm)Stellar Mass

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

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

SMG Triggering, Minor or Major Mergers?

Following the SMGs evolutionCentral Galaxy

Flux Sν (850 µm)

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

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 galaxyB/T=0, pure disk galaxy

Mainly bulge dominated descendants. 70% have B/T>0.5

SMGs descendants (stellar mass distribution)

satellitescentral

M*= 2 x 1011 h-1 M๏ Mhalo = 6 x 1013 h-1 M๏

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

• 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

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)

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)

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

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.

• 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.

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

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.