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Gerhard Hensler (University of Vienna)

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Cosmic Chemical Evolution

I. Introduction

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WS 2019/20: "Cosmic Chemical Evolution", Lecture Tue 15:00-16:30

Lessons Presentation / Team work

1.10. Organization and introduction

8.,15.,22. cancelled

29.10. I. Introduction

5.11. II. Abundance Determinations in Stars and Gas

12.11. III. Stellar Evolution, Thermonuclear Reactions, and Stellar Nucleosynthesis

19.11. IV. Stellar Mass Loss and Chemical Yields

26.11. V. Primordial Nucleosynthesis Martina Koppitz

3.12. VI. Simple Models of Chemical Galaxy Evolution Sonja Ornella Schobesberger

10.12. VII. Chemical Evolution of the Milky Way Anna Schrenk

17.12. VIII. Element Abundances with Redshift Magdaléna Forusová Alice Schimek

20.12.19 - 6.1.20 Christmas Holidays

7.1.20 IX. Element Abundances in the Intergalactic and Circumgalactic Medium

Stefanie Schönegger Markus Levonyak

14.1. X. Galactic Winds, Gas Infall Carla Nicolin: DGs

21.1. XI. Chemo-dynamical Evolution of Galaxies Matthias Kuehtreiber

28.1. XII. Chemical Abundances with Dust and Molecules

Quality criteria:

For success: >75% presence at lectures, 1+ presentation or adequate contribution to group presentation;

For grade: presentation quality, vital interest, active participation in lessons

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1. The Intern. Year of the Periodic Table

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150 years: from Mendeleev(?) to the modern

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2. Where to see the chemical elements?

Dust consists of metals!

Metals in Astronomy = elements with A>4

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Stellar Spectra

Sun (G2V)

Procyon (F5V)

Stellar spectra contain the

information about their

element abundances. CCE.I WS 2019/20

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e.g. Eu in stellar Spectra

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Metallicity Determination from spectral Indices

Burstein et al. (1984)

Gorgas et al. (1990)

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Emission Nebulae

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Emission lines come on

top of a continuum, if

there is any.

Poor sample within the

optical range, …

but much better in the NIR.

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IR emission of HII regions

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Molecular Cloud Spectra

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Model:

• bipolar outflow;

• the S part towards

observer is unobscured;

• disk inclination known.

X-ray in colors according to hardness (blue: hard, red: soft) overlaid with HI contours (white)

Martin et al. (2002)

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X-ray Spectra

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A1413: z=0.143 (Pratt & Arnaud, 2002)

Abundance determination from X-ray spectra:

cluster gas is metal-enriched up to 40% solar

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Tumlinson et al., 2013, ApJ,

Gaseous halos of 44 z = 0.15–0.35 galaxies

using background QSOs observed with the

Cosmic Origins Spectrograph aboard the HST.

Metal Ions of Circumgalactic Gas

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Differences in metallicities of outflow vs. infall

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Metal content of the cool

(∼104 K) circumgalactic

medium around 28 HI-

selected LLS at z 1

observed in absorption

against background QSOs.

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Signatures as local metal deficiency in high-z galaxies are indicating low-Z/pri-mordial gas infall.

Cre

sci e

t al. (2

01

0) N

atu

re, 4

67

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Chemical Abundance Determination in DLAs

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Observational cosmic sites of chemical evol.

Solar vicinity

The Milky Way components:

disk, bulge, halo, globular clusters

The Milky Way dSphs

Dwarf galaxies:

dEs,

dIrrs

TDGs

Massive galaxies

spirals

gEs

QSOs

DLAs

Intra-cluster medium

Theoretical ingredients

Dynamical effects

SF / Gas-phase transitions

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3. Why a need for chemical evolution models?

obvious

From the Big-Bang nucleosynthesis of light elements

(depending on the baryon-to-photon number ratio η=nb/nγ 3.16·10-10

and the n decay time: τ1/2,n = (889±7) s)

to the present-day abundances!

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neutrons

pro

ton

s

Mass known

Half-life known nothing known

s process

stellar burning

Big Bang

p process

Supernovae

Cosmic Rays H(1)

Fe (26)

Sn (50)

Pb (82)

The Isotopic Range and its Sources

• ~300 Stable and ~2400 radioactive isotopes • Cosmic nucleosynthesis proceeds over much of this range • Knowledge of nuclear physics is incomplete

Figure courtesy Hendrik Schatz

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B2FH + Nucleosynthesis

Burbidge, Burbidge, Fowler and

Hoyle (1957) proposed the elements

were created in 4 ways/environm.s:

– Cosmological nucleosynthesis:

creation in the Big Bang

– Stellar nucleosynthesis: synthesis

of elements by fusion in stars

– Explosive nucleosynthesis:

synthesis of elements by neutron

and proton capture reactions in

supernovae

– Galactic nucleosynthesis:

synthesis of elements by cosmic

ray spallation reactions

Margaret and Geoffrey Burbidge

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B2FH + Nucleosynth.

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Chemical Abundances

Anders & Grevesse (1989)

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Cosmic Abundances

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Definitions

Stellar ‘abundances’ are number density calculations with respect to H and the solar value On a scale where H is 12.0: This quantity is the output of all model atmospheres!

log(X) log10 NX /NH 12for element X

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sun

H

Festar

H

Fesun

H

Ostar

H

O

N

N

N

N

N

N

N

N

HFeHOFeO

)(log)(log)(log)(log

]/[]/[]/[

BAHBHA /// for elements A and B

How to calculate chemical abundances?

• Need a spectrum => measure equivalent width of absorption lines (=integrated line strength)

• Need atomic data (excitation potential+log gf values) => feed both into “model atmosphere”

• Get: calculated abundance (number density) log (X) • Calculate [Fe/H] with solar abundances

• Example: • log (Mg)star = 5.96; log (Fe)star = 5.50 • log (Mg)sun = 7.60; log (Fe)sun = 7.50 • [Mg/H] = log (Mg)star - log (Mg)sun = -1.64 • [Mg/Fe] = [Mg/H] - [Fe/H] = -1.64 - (-2.0) = 0.36

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Solar abundances Photospheric (=‘stellar’ abundance) • Anders, Grevesse & Sauval ‘89

• Grevesse & Sauval ‘98

• Asplund, Grevesse &Sauval ‘05

• Grevesse, Asplund & Sauval ‘07

• Asplund, Grevesse, Sauval & Scott ‘09

• reference element: H

• calculation

Meteoritic (=‘star dust’ grain nalysis) • Lodders 03

• Lodders, Palme & Gail 09

• reference element: Si

• measurement

• Volatile elements depleted, incl. the most abundant elements: H, He, C, N, O, Ne cannot rely on meteorites to determine the primordial Solar System abundances for such elements

For each application, the most similarly obtained solar abundances should be use to minimize systematic uncertainties!

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Abundance tables

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4. Mass-Z relation

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Skillman 1989

[O/H] -0.4 LB

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Skillman 1989

Kunth & Östlin 2000

For galaxies a wide but significant

correlation exists between MB and

O abundance

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5. The early metal enrichment of

galaxies

High-z galaxy spectra

also reveal the chemical

evolution of the early

universe.

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The Mstar − Z relation at z ∼ 2. Shapley (2011) ARAA, 49

Evolution of the Mass-Z relation

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Evolution of the Mstar−Z

relation with time.

Maiolino et al. (2008) A&A, 488

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Shapley et al. (2005)

Galaxies at z 1.0 (upper)

and z 1.5 (lower);

O abundance determination

with different methods:

O3N2 (top), N2 (bottom) CCE.I WS 2019/20

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Size-relation

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6. Chemical enrichment of the Milky Way

Components

Freeman & Bland-Hawthorn (2002)

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Twarog (1985)

Garnett & Kobulnicky (2000)

Age-metallicity Relation

Def.: [Fe/H] = log(Fe/H)

– log(Fe/H)

Conclusion: The older the stars the lower

their metallicity! Remark: for the disk [Fe/H] -1.0 appears as the threshold.

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Assumptions:

closed box

constant Yields yi (m)

Z y

ln (1/μ)

7. Simple Chemical Evolution

Effect:

Zi(t) = Zi(0) – yi · ln[Mg(t)/Mg(0)]

= Zi(0) – yi · ln[1/μ]

i.e. y determines the slope in the

Z-1/μ diagram.

ln μ =

- ln *

- y

f = Z/Z WS 2019/20 CCE.I

Assumptions:

closed box,

constant Yields yi

O+Fe from SNeII

of massive stars,

Fe by SN Ia from

WD-WD or

WD-RG

slow evolution fast gas consumption

Effects:

The ratio of element abundances from particular precursor stars allow

the age dating of their lifetimes and the derivation of the gas

consumption.

8. SF timescale from element abundances

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SNeII produce an aömost constant ratio [O/Fe]0.5, while Fe

increases continuously. After the typical formation timescale of SN

Ia Fe is further enriched independently on O. Thus, O/Fe decreases.

From the SN Ia timescale with respect to the gas consumption

timescale the turn-down is determined.

Tolstoy & Venn, 2003

The star-formation timescale

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The most metal-poor star in the Milky

Way that has been recently detected

is the

Halo giant HE 0107-5240:

Teff 5140 K

log g = 2.2

[Fe/H] –5.3

What are its abundance patterns?

Christlieb et al. (2002)

9. The most metal-poor Stars

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How metal-poor? A rough estimate.

classical example:

early universe: primordial gas

how metal-poor is the next-generation star?

canonical SN Fe yield: 0.1 Msun

available gas mass: 106 Msun

Observation:

Calculation:

log(Fe)sun log(NFe /NH )sun 12 7.50

log(NFe /NH )sun 7.5012 4.50

NH Mtot

mH

106Msun

mH

NFe M tot

mFe0.1Msun

56mH

NFe

NH0.1Msun

56mH

mH

106Msun

107

56

[Fe /H] log(107

56) (4.50) 4.2

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10. The N/O Problem

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Why are dIrrs as metal-poor (O/H) as DLAs?

Not young and pristine!

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et al., 2009,

ApJ, 695

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11. Abundance

Curiosities = outliers