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The formation history of elliptical galaxiesGabriella De Lucia, Volker Springel, Simon D. M. White,

Darren Croton and Guinevere kauffmann

Libin Fan1st July 2014

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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）

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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 )

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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

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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

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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

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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

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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

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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

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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

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Bulge formation takes place during merger-induced bursts

Star formation history of randomly selected elliptical galaxies

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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.

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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

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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

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The age, the metallicity and the B-V color Depend on the galaxy stellar

mass

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Depend on the virial mass of the halo

The age, the metallicity and the B-V color

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Properties on cluster-centric distance

Haloes M200 > 8 * 1014

Stellar mass > 4 * 109

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Result 5: Galaxies closer to the center are on average older and more metal rich than galaxies at the outskirts of these clusters

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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

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Median of the distribution in default model galaxy

Median of the distribution in a model where bulge formation through disk instability is switched off

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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

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• The most massive ellipticals have the most extend star formation histories

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Default model

Model without AGN feedback and without any cooling cutoff

Model without AGN feedback but with a cooling cutoff