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Semi-analytic modelling in the era of
wide, deep and multiwavelenght
surveys
Gabriella De Lucia
Max-Planck Institut für Astrophysik
Bologna – May 25, 2006
Outline:
Semi-analytic models
-- substructures & galaxies
-- hybrid models – methods, limits & aims
Applications
-- the formation history of elliptical galaxies
-- the hierarchical formation of BCGs (with J. Blaizot)
-- some other prelimilary results…
Cooling
Star formation
(metallicity,structure,
conductivity)
(threshold, efficiency,
initial mass function)
Galaxy interactions
Dust
(formation, distribution,
heating and cooling)
galaxy
formation
Winds
(IGM heating,
IGM enrichment)
AGN
(BH growth, feedback)
(morphological
transformations,
induced star
formation)
Stellar evolution
(spectro-photometric
evolution, yields,feedback)
The SAM – the classical models:
Extended Press & Schechter
“Planting” the merger trees
Lacey & Cole (1993)
These might provide a not
adequate description of the
merger rates (Benson et al.,
2005)
The SAM – the hybrid models :
CDM
Central galaxy
CDM
Halo galaxy
Satellite
galaxy
Springel
(2001)
Mathis H.et
et al.
al., 2002
De Lucia et al., 2004
About 800 million
subhaloes
The Millennium Simulation (Springel et al. 2005)
64 time slices stored
Group catalogues and
information about their
embedded substructures
used to construct merger
trees
About 20 million
galaxies
Individual trees are
stored separately so that
the SAM can be run for
each tree sequentially
The SAM – the physics :
re-incorporation
Croton et al. 2006
- AGN heating
Cold Gas
Hot Gas
cooling
star formation
feedback
recycling
Ejected Gas
DLG, Kauffmann & White, 2004
Stars
Colour-magnitude
Tully-Fisher
DLG, Kauffmann & White, 2004
Luminosity
function
Metallicitymass
Gas fractionluminosity
Observational signature of different
feedback models #1:
DLG, Kauffmann & White, 2004
David, Forman, Jones
1995
ejection fast
wind fast
ejection slow
wind slow
A slow ejection feedback scheme:
David, Forman,
Jones 1995
(M/L)V  190 – 230 (M/L) 
(M/L)B  240 – 290 (M/L) 
IMLR  0.015 – 0.020 M/L
DLG, Kauffmann & White, 2004
Ellipicals: an old controversy
Toomre &
Toomre 1972
Barnes 1992
Visvanathan &
Sandage (1977)
Kauffmann & Charlot (1998)
Bender 1992
Gladders et al. (1998)
Ellipicals: the [/Fe] problem
Thomas et al. did not use a selfconsistent approach
SNIa Thomas et al. 2001
Previous SAM work based on
extended PS theory
Most previous SAM work not in
a CDM Universe
SNII
[/Fe]V
Observations are still plagued by systematic uncertainties
(template bias)
observation
s
superwind
superwind
/Kennicutt
Nagashima et al. (2005) Log [/km s-1]
conduction
Ellipticals in a hierarchical model :
AGN model for suppression of the cooling-flows (Croton et al., 2006)
Three channels to make bulges:
In a ‘minor’ merger the stellar mass of the merged galaxy is
transferred to the bulge of the central galaxies + burst of a
fraction of the combined cold gas
A ‘major’ merger completely destroys the disc of the
central galaxy + burst of a fraction of the remaining gas
Disk instability (Mo, Mao & White 1998)
De Lucia et al., 2006
1,031,049 (810,486 ) Es with Mstar > 4x109 (1x1010) Msun
16% Es / 66% Sp / 18 % S0 (MV < -18)
(13%, 67%, 20% Loveday et al., 1996)
The star formation histories:
redshift
cluster
cluster
1010M
clusters
ellipticals
1011M
1212

Mstar 10
= 10M
Msun
Mstar = 109 Msun
field
field
field
ellipticals
Elliptical galaxies also have a
shorter formation timescale!
This is “anti-hierarchical”!!!
Lookback time (Gyr)
Lookback time (Gyr)
De Lucia et al., 2006
Ellipticals: formation & assembly:
50 %
stars
formed
50 % stars
in a single
object
80 %
80 %
redshift
redshift
De Lucia et al., 2006
Comparison with previous work:
Kauffmann & Charlot (1998)
most massive ellipticals younger than their less massive
counter-parts!
Comparison with previous work:
No AGN feedback
No cooling cutoff
AGN feedback
reversal due to a combination
of the change in the physical
model and in the cosmology
Kauffmann & Charlot:
Cooling cutoff
Vcrit = 350 km/s
-- critical matter density
-- cutoff 500 km/s
The Brighest Cluster Galaxies :
The most luminous and most massive
objects in the Universe at the present
epoch
NGC4889 - z ~ 0
CL1232.5-1250 z ~ 0.5
The formation of BCGs:
De Lucia & Blaizot, in prep.
The formation of BCGs:
0.5
Time of last major
50 BCGs selected
merger
@z=0
“Assembly vs formation”
history
De Lucia & Blaizot, in prep.
The formation of BCGs:
Mass in the main branch
Fraction of mass gained
through accretion
>1010Msun
<1010Msun
Most of the stars of this
BCG were not formed in
the MB, but were instead
accreted over time
De Lucia & Blaizot, in prep.
The formation of BCGs:
Mass in the main branch
quiescent
starburst
the stars formed in
separate entities in a
quiescent mode.
stars formed during
Starbursts contribute
only for about 10%.
De Lucia & Blaizot, in prep.
The formation of BCGs:
“Progenitors”
more massive
than 1010 Msun
De Lucia & Blaizot, in prep.
The formation of BCGs:
Burke, Collins & Mann 2000
De Lucia & Blaizot, in prep.
Ellipticals: the evolution of the CM
A well
defined
CM up to z~2
A clear bimodal
distribution up
to z~2
De Lucia et al.,
in preparation
V
The evolution of the stellar MF
Fontana et al. 2004
Drory et al. 2005
~ good
agreement
up to
z~2
for massive
gxs.
The origin of the colour-magnitude:
Gallazzi et al., 2006
Log [Mstars]
Log [Mstars]
De Lucia et al., in preparation
Tools to observe ideas :
Mock 2dF
75 x 4 deg2
BAB < 19.5
Blaizot et al. 2005: MoMaF
Tools to observe ideas :
Mock SDSS
19 < r < 20
H
18 < r < 19
20 < r < 21
21 < r < 22
D4000
with Jérémy Blaizot
The colour-magnitude bimodality:
oTail of blue
bright objects
o Transition
region not well
populated
o Excess of faint
red satellites
u-r
Quantitatively the CM bimodality is not well reproduced
The D4000 distribution:
Same problems are visible in the distribution of D4000
Conclusions:
Semi-analytic models are a technique for studying galaxy
formation - they are not meant to be definitive!
The observed down-sizing is not in contradiction with the
hierarchical paradigm
More massive systems assemble later than their less massive
counter-parts (this does not seem to be in contradiction with
observational data but more detailed comparisons nedeed here)
The ever more detailed picture of our Universe also requires a
more complex modelling and the development of new tools for a
more straightforward comparison with observational data