Download - The formation history of elliptical galaxies
1
The formation history of elliptical galaxiesGabriella De Lucia, Volker Springel, Simon D. M. White,
Darren Croton and Guinevere kauffmann
Libin Fan1st July 2014
2
Authors
Astronomical Observatory of Trieste
Gabriella De Lucia
Galaxies through the cosmic ages The ESO Distance Cluster Survey The VIMOS Public Extragalactic Survey EUCLID
的里雅斯特天文台(意大利东北部港市)
3
Volker Springel
Max-Planck-Institute for Astrophysics
Galaxy formation Numerical Cosmology Dark matter and dark energy Large Projects
• Millennium Simulation• Aquarius Project
Simon D. M. White
Director at the Max-Planck-Institute for Astrophysics
Galactic structure Structure, formation and evolution of galaxies Nature and distribution of dark matter Planck at MPA LOFAR(Low Frequency Array) at MPA
In the spring of 2010, I will move to a professorship in Theoretical Astrophysics at the University of Heidelberg(海德堡市 )
4
Darren Croton
Associate Professor and QEII Research FellowCentre for Astrophysics & SupercomputingSwinburne University of Technology(斯文本科技大学 )
Galaxy formation and evolution, quasars and AGN, cooling flows and "quenching" mechanisms. The red sequence and massive galaxy assembly. Cosmology, large-scale structure and voids, environmental effects.
http://gc2014.csp.escience.cn/dct/page/65580
http://www.meeting.edu.cn/meeting/media/mediaAction!mediaList.action?id=38715
中国学术会议在线
Guinevere Kauffmann
5
Outline
The Millennium simulation used in the study
The semi-analytic model employed for our analysis
Star formation history of model elliptical galaxies depends on the stellar mass of galaxies and environment
The dependence of ages and metallicities on galaxy mass and environment
Summarize and discuss the finding
6
Introduction
a) Monolithic scenario
b) Hierarchical formation scenario
Two problemsα-element enhancement, [α/Fe] ratio
dissimilar evolution of early-type galaxies in different environment
This article concentrates on the analysis of the star formation histories, the ages, and the metallicities of model elliptical galaxies as a function of galaxy mass and of environment.
Fundamental scale relation
Color-magnitude relationFundamental plane
Simulation(ΛCDM) + semi-analytic model
7
The Millennium Simulation
*from 2dFGRS and WMAP
Millennium simulation
Particle 21603
Mass resolution 8.6*108 h-1Ms
Box size 500 h-1Mpc
Spatial resolution 5 h-1kpc
ΛCDM cosmological model
Ωm 0.25
Ωb 0.045
h(100 kms-1Mpc-1) 0.73
Ωᴧ 0.75
n 1
σ8 0.9
8
The Semi-analytic Model
The key difference(De Lucia, 2004a)
explicitly follow dark matter haloes even after they are accreted onto larger systems
Hierarchical merging trees(Springel, 2005)the descendant in the next time slice of each dark matter
(sub)halo is identified as the (sub)halo that contains the largest number of its most tightly bound particles
Star formation
cold crit dyn(M M ) / t /dyn disc virt R V
7 1 21
1.2 10 ( )( )200 10
vircrit
V RM kpc
kms kpc
Bulge formation
Mass ratio > 0.3, we witness a major merger
Take place during merger(De Lucia, 2004b)
Grow from disk instabilities(Croton, 2005)
May be more important for fainter ellipticals
9
Morphology of galaxies(Simien & de Vaucouleurs, 1986)
B-band bulge-to-disk ratio together with the observational relation
Central heating by AGN and suppression of cooling flows(Croton, 2005)
‘ejection slow’ feedback model(De Lucia, 2004b)
reproduce both the observed relation between stellar mass and cold phase metallicity, and the relation between luminosity and cold gas fraction for galaxies in the local universe
ΔM = Mbulge / (Mtotal - Mbulge)Δ M < 0.4 spiral~ lenticularΔ M > 1.56irregular> 4 * 109MΘ 1030149> 1 * 1010M Θ 810486
10
The star formation history of elliptical galaxies
Average star formation
Stellar mass ~1012
Stellar mass ~1011
Stellar mass ~1010
Stellar mass ~109
Cluster elliptical
Field elliptical
Result 1: more massive elliptical galaxies have star formation histories that peak at higher redshift(~5) than lower mass systems
In different bins of stellar mass
11
Bulge formation takes place during merger-induced bursts
Star formation history of randomly selected elliptical galaxies
12
Halo mass ~ 1015
Halo mass ~ 1014
Halo mass ~ 1013
Halo mass ~ 1012
Stellar mass > 4*109
Star formation history in bins of different parent halo mass
Result 2: The faster evolution of proto-cluster regions produces star formation histories that peak at higher redshift for galaxies in more massive haloes.
13
The distribution of ages and metallicity
Formation redshift
As a function of stellar mass and environment
Define the formation redshift as the redshift when 50%(or 80%) of the stars that make up the final elliptical galaxies at redshift zero are already formed
Stellar mass > 1011
Stellar mass > 4 * 109
Result 3: Stars in more massive ellipticals are on average older than stars in their less massive counterparts
14
Assembly redshift
Define the assembly time as the redshift when 50%(or 80%) of the final stellar mass is already contained in a single object
Result 4: A significant fraction of present elliptical galaxies has assembled relatively recently through purely stellar mergers
17
Properties on cluster-centric distance
Haloes M200 > 8 * 1014
Stellar mass > 4 * 109
51
Result 5: Galaxies closer to the center are on average older and more metal rich than galaxies at the outskirts of these clusters
18
Effective number of stellar progenitor
2
,2final
effi i formi
MN
mM
final iiM m
2
02
final
finaleff M
MN
MdM
Single object
= 1
Neff = 2
Neff = 8/3
0.5 M
0.5 M
M
0.5 M
0.25 M
0.25 M
M
19
Median of the distribution in default model galaxy
Median of the distribution in a model where bulge formation through disk instability is switched off
20
1. The dependence of the star formation histories, ages, and metallicities on environment and on galaxy stellar mass
Elliptical galaxies in denser environments are on average older, more metal rich, and redder than the general population of ‘field’ ellipticals
A clear trend for increasing ages and metallicities, and for redder colors, with decreasing cluster-centric distance
2. The properties of model elliptical galaxies change as a function of the stellar mass
Most massive elliptical galaxies have the oldest and most metal rich stellar population
Massive ellipticals are predicted to be assembled later than their lower mass counterparts, and that they have a larger effective number of progenitor systems
Conclusion