Chemical e volution of r p rocess e lements in hierarchical g alaxy f ormation models
This presentation is the property of its rightful owner.
Sponsored Links
1 / 30

Chemical E volution of R- p rocess E lements in Hierarchical G alaxy F ormation Models PowerPoint PPT Presentation


  • 53 Views
  • Uploaded on
  • Presentation posted in: General

RIKEN-IPMU-RESCEU Joint Meeting 2014-7-4 理研 , 和光. Chemical E volution of R- p rocess E lements in Hierarchical G alaxy F ormation Models. Yutaka Komiya ( Tokyo Univ., RESCEU ) Collaborators Takuma Suda ( Tokyo Univ., RESCEU ) Shimako Y amada ( Hokkaido Univ. )

Download Presentation

Chemical E volution of R- p rocess E lements in Hierarchical G alaxy F ormation Models

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Chemical e volution of r p rocess e lements in hierarchical g alaxy f ormation models

RIKEN-IPMU-RESCEU Joint Meeting

2014-7-4 理研, 和光

Chemical Evolution of R-process Elements in Hierarchical Galaxy Formation Models

Yutaka Komiya(Tokyo Univ., RESCEU)

Collaborators

Takuma Suda(Tokyo Univ., RESCEU)

ShimakoYamada(Hokkaido Univ.)

Masayuki Y. Fujimoto(Hokkaido Univ.)

Komiya et al. (2014) ApJ, 783, 132


Chemical evolution

Chemical evolution

Big Bang

Galaxy formation

Star formation

Metal-poor stars

Neutron star merger

R-process ?

Stellar evolution

R-process ?

Supernova


Metal poor stars

Metal-poor stars

  • Extremely metal-poor (EMP) stars =Living fossils

    • Galaxy formation, First stars, First supernova

  • Observation :

    • Milky Way halo

      • More than 1000 stars with [Fe/H] < -2.5has been identified

      • Follow-up by high-resolution spectroscopy: >400

    • Database: SAGA (Stellar Abundance for Galactic Archaeology)

    • Globular clustersdSph galaxies (Ishigaki-san)

[Fe/H]=log((nFe/nH)/(nFe/nH)☉)

EMP stars

HMP stars

http://saga.sci.hokudai.ac.jp


Contents

Contents

  • Introduction

    • Observations : r-process elements on EMP stars

    • Previous chemical evolution studies

  • Hierarchical chemical evolution model

    • Merging history of building blocks of MW

      • Pre-enrichment of intergalactic matter

    • Surface pollution of EMP stars

  • Results & Discussion

    • R-process source

      • SN v.s. Neutron star merger

    • Surface pollution : origin of r-deficient EMP stars

    • Light r-process elements (Sr)

      • light-r/heavy-r


Observations ba eu

Observations: Ba, Eu

  • (Ba is also “r-process element”)

  • Large scatter (2-3 dex)

    • (Non-LTE: slightly shifted toward the solar ratio (Andrievski et al. 2009))

    • R-II stars: [Eu/Fe]>1. at [Fe/H]~ -2.8

  • Decreasing trend as metallicity decrease at [Fe/H]< -2.3

  • Abundance pattern of r-process elements heavier than Ba (Z ≥ 56) matches the scaled solar system r-process abundances

Cowan & Sneden(2006)


P revious chemical evolution studies

Previous chemical evolution studies

  • Ishimaru & Wanajo (1999, 2003)

    • Homogeneous ISM + SN shell

    • R-process souce: 8-10 M☉

  • Argast et al.(2004)

    • SNe pollute spherical shell with 5*10^4M☉

    • R-process source: type II SN

      • Neutron star merger is ruled out

  • Cescutti (2008)

    • 100 independent regions

    • R-process source: 10-30 M☉ (stars with 10-15 M☉are dominant)


Observations ba eu1

Observations: Ba, Eu

  • (Ba is also “r-process element”)

  • Large scatter (2-3 dex)

    • (Non-LTE: slightly shifted toward the solar ratio (Andrievski et al. 2009))

  • Decreasing trend as metallicity decrease at [Fe/H]< -2.3

But, Ba is detected for almost all EMP stars. (Roederer 2013)

But, at [Fe/H]<-3, plateau is reached

(Andrievski+ 09)

?

?


Observations sr ba

Observations: Sr/Ba

But, at [Fe/H]<-3.5, no light element enhanced stars. (Aoki+ 2013)

  • Light-element primary process (LEPP) (weak r-process)

    • Enhancements of lighter r-process elements (Z<56; Sr, Y, Zr…) relative to heavier elements (Ba, Eu, Pb…)

    • Anti correlation between [Sr/Ba] – [Ba/Fe]

But, stars withvery low [Ba/Fe] and [Sr/Ba]~0.(Qian+ 2008, 3rd source origin stars)

?

?

[Sr/Ba]

[Ba/Fe]

(Aoki+ 2013)


2 the hierarchical chemical evolution model

2. The Hierarchical chemical evolution model


Hierarchical model for chemical evolution

Hierarchical model for chemical evolution

First star

First supernova

Mini-halo~106M☉

Milky Way

Proto-galaxy

  • Chemical evolution along a merger tree

  • All the individual EMP stars are registered

    • Yield from each individual SN

  • Metal pre-enrichment of intergalactic medium (IGM)

  • Surface pollution of EMP starsby accretion of interstellar medium (ISM)


Model galaxy formation

Model: Galaxy formation

  • Merger tree:

    • Extended Press-SchechterMethod Somerville & Kollat (1999)

    • MMW=1012 M☉, Mmin=M(Tvir=103K)

  • Proto-galaxy

    • Gassinfall: ⊿Mh×Ωb/ΩM

    • At the beginning, stars are formed in mini-halo with Tvir > 103K (Tegmark+ 1997, Yoshida+ 2003)

    • At z< 20, by Lyman-Werner photon, stars are not formed in newly formed mini-halos with Tvir< 104K

    • Reionization: At z < 10 gas do not accrete to mini-halos with Tvir< 104K

    • Proto galaxies are chemically homogeneous


Model chemical evolution

Model: Chemical evolution

  • Star formation

    • All the individual EMP stars are registered in computations

    • Star Formation Rate: ψ = Mgas×10-10/yr

    • Lognormal IMF:

      • Pop.III stars (Z<10-6Z☉) Pop. III.1: Mmd= 200 M☉, Pop.III.2 : Mmd= 40 M☉

      • EMP (Pop.II) stars: Mmd= 10 M☉(Komiya et al. 2007)

    • Binary fraction: 50%

      • Mass ratio distribution: n(q) = 1

    • Massive Pop.III.1 stars suppress star formation in their host halos.

  • Metal enrichment

    • Stellar lifetime : Schaerer et al. (2002)

    • Instantaneous mixing inside mini-halos.

    • Yield : (He-Zn) Kobayashi et al.(2006, Type II SN)Nomoto et al. (1984, Type Ia SN)

      Umeda & Nomoto (2002, Pair-instability SN; PISN)


Model accretion of interstellar matter ism

Model: Accretion of interstellar matter (ISM)

  • Surface abundances of EMP stars can be changed by accretion of ISM.

    • Trace the changes of the surface abundance of EMP stars along the evolution of galaxies

    • Accretion rate in mini-halos are much higher than in the MW halodue to small relative velocity between stars and ISM.

  • Accretion rate

    • Bondi accretion

    • In the mini-halos in which stars are formed, v = cs(T), ρ=ρav×(Tvir/T)T = 200K for primordial clouds, T = max(10K, TCMB) for Z > 10-6Z☉

    • After their host halos merge with larger halo, stars moves with circular velocity v = vcir, ρav(average density of virialized halo)

  • Accreted matter is mixed in surface convective zone of EMP stars.

    • Mscz= 0.2M☉ for giant

    • = 0.0035M☉ for main sequence

EMP star


Result chemical evolution

Result: Chemical evolution

Metallicity distribution function (MDF)

Metallicityditribution of EMP stars is well reproduced

HES survsy (Sch¨orck et al.2009)

SAGA database

formation redshift

Histograms: observvations

Red: Predicted MDF (after ISM accretion)


3 results discussion

3. Results & discussion


Chemical e volution of r p rocess e lements in hierarchical g alaxy f ormation models

  • R-process sources

    • Main-r: SN? Neutron star binary?

  • Abundance distribution @ [Fe/H]<-3

  • Why Ba is detected in almost all EMP stars

  • LEPP (light element primary process) source

  • Origin of vey Ba-poor and Sr-poor stars


3 1 r process site

3.1 R-process site

  • Core-collapse SN (e.g. Burbidge+ 1957)

    • Neutrino driven wind

      • >20M☉(Woosley & Hoffman 1992)

      • Very high entropy is required to synthesize heavy r-process elements

    • Electron-capture (O-Ne-Mg) SN (8-12M☉) (e.g. Wheeler et al. 1998)

      • Artificial enhancement of the explosion energy (Wanajo et al. 2003)

      • n + νe→ p+ + e- :not so n rich

    • (Light r-process elements can be synthesized)

  • Neutron star merger (e.g. Lattimer+ 1974, Rosswog+ 1999)

    • Abundance pattern : ○ (e.g. Wanajo & Janka 2011)

    • Chemical evolution: ×(Argast et al. 2004)

      • Event rate: ~1/1000 of SN

      • Long delay time ( ~ Gyr )


Core collase sn mass range of r process source

Core-collase SNMass range of r-process source

9-10 M☉

9-40 M☉

30-40 M☉

Main R-process site is ~10% of SNe with progenitor stars at low-mass end of the SN mass range.

Color : predicted distribution

Blue lines: 95, 75, 50, 25, 5 percentile curves of predicted distributions

Black symbols: SAGA sample


Results 9 m 10m

Results: [9 M☉,10M☉]

Color : predicted distribution

Blue lines: 95, 75, 50, 25, 5 percentile curves of predicted distributions

Black symbols: SAGA sample

(S-process)

R-process yield:

Ba: 6.55×10-6Mʘ/event

Eu: 8.62 ×10-7 Mʘ/event

9-10 M☉ model well reproduce the abundance distributions of heavy r-process elements.

R-II stars:

7%(4-10%) of EMP stars ([Fe/H]<-2.5) (SAGA sample: 5.6% )

average metallicity: [Fe/H] ~ -2.8

  • 7.5% of EMP stars shows [Ba/H] < -5.5


Neutron star ns merger scenario

Neutron star (NS) merger scenario

  • tc: Timescale to coalesce NS binary

    • ~109yr (e.g. Fryer+ 1999)

    • ~106yr (Belczynski+ 2002)

  • pNSM: number fraction of r-process source among massive star binary

    • Event rate

    • Galactic event rate: 40 – 660 /Myr

      • pNSM =0.01 for the high-mass IMF and ψ = 10M☉/yr


Ns merger scenario

NS merger scenario

tc=1Myr

tc=10Myr

tc=100Myr

ψ = 10-10Mgas/yr

pNSM = 1.0

ENSM = 1050erg

tc=10Myr ψ = 10-11Mgas

tc=10MyrpNSM = 0.1

tc=10MyrENSM = 1051erg

SN with 9-10M☉progenitor

lifetime: 2×10^7yr

event rate: 0.1×ψSN

  • delay time: tc~ 107yr

  • coalescence probability : pNSM = 100%

  • Ba: 5.7×10-6Mʘ/event

But, consider the dynamics of very high velocity (~ 0.2c ) ejecta (Shigeyama-san)


Chemical e volution of r p rocess e lements in hierarchical g alaxy f ormation models

  • R-process sources

    • Main-r: SN? Neutron star binary?

  • Abundance distribution @ [Fe/H]<-3

  • Why Ba is detected in almost all EMP stars

  • LEPP source

  • Origin of Sr-poor & Ba-poor stars

SN with progenitor mass with 9-10M☉


Chemical evolution process

Chemical evolution process

One r-process source event ⇒

[Ba/H]=-2.5~-3

First stars (Population III)

First SN eject Fe but no r-process elements


Ism accretion

ISM accretion

Before surface pollution

no ISM accretion

Majority of stars with [Fe/H]<-3 was [Ba/H] = -∞.

For stars with [Ba/H] ≲ -3.5, accretion of ISM is the dominate source of heavier r-process elements on their surface.

After surface pollution

with ISM accretion

Accretion dominant

  • All EMP stars have Ba

  • Plateau at [Fe/H] < -3


Chemical e volution of r p rocess e lements in hierarchical g alaxy f ormation models

  • R-process sources

    • Main-r: SN? Neutron star binary?

  • Abundance distribution @ [Fe/H]<-3

  • Why Ba is detected in almost all EMP stars

  • LEPP sites

  • Origin of Sr-poor & Ba-poor stars

SN with progenitor mass with 9-10M☉

Surface pollution by ISM accretion

→ [Ba/H] ~ - 4


Observation sr

Observation: Sr

  • Many stars with large [Sr/Ba] Light Element Primary Process (LEPP)

  • At [Fe/H] < -3.6, [Sr/Ba] ≦ 0

  • Very Ba-poor stars with [Sr/Ba] ~ 0

Aoki+ (2013)

R-II stars

[Sr/Ba]

[Ba/Fe]


Result

Result

MLEPP = 10-12 M☉

[Sr/Fe]

Main-r source: 9 -10 M☉

[Sr/Ba] = - 0.5

LEPP source: 10 – 12 M☉

YBa = 0YSr is set to be <Sr/Ba> = solar r-process

[Ba/Fe]

-5 -4 -3 -2 -1

[Fe/H]


Result sr ba

Result: [Sr/Ba]

LEPP (10-12Mʘ)

Main-r(9-10Mʘ)

Polluted stars formed with [Ba/Fe] = −∞ [Sr/Fe] = −∞


Chemical e volution of r p rocess e lements in hierarchical g alaxy f ormation models

  • R-process sources

    • Main-r: SN? Neutron star binary?

  • Abundance distribution @ [Fe/H]<-3

  • Why Ba is detected in almost all EMP stars

  • LEPP source

  • Origin of Sr-poor & Ba-poor stars

SN with progenitor mass with 9-10M☉

Surface pollution by ISM accretion

→ [Ba/H] ~ - 4

SN with progenitor mass with 10-12M☉

Surface pollution by ISM accretion

→ [Sr/Ba] ~ 0

29


Summary

Summary

  • Hierarchical chemical evolution

    • Evolution along the merger tree

      • Inhomogeneous model of IGM metal pre-enrichment

      • Surface pollution by ISM accretion

        Results

  • Sources of Main r-process elements

    • 9 – 10M☉ (Electron-capture SN)

      • SNe with progenitors at low-mass end of the SN mass range

      • The abundance distribution is well reproduced

    • Neutron star merger

      • Not plausible if most (~100%) massive star binary coalesce in short timescale (~10^7 yr)…

  • R-deficient EMP stars

    • Surface pollution is dominant for stars with [Ba/H] < -3.5

    • All EMP stars have Ba on their surfaces

  • Light elements (Sr)

    • ~10-12 M☉ (core-collapse supernovae)(9-10M☉ also elect light elements, [Sr/Ba] ~ -0.5)

    • 3rdsource origin stars: Surface pollution


  • Login