evolution of galaxies -...
TRANSCRIPT
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Evolution of Galaxies: Chemical Evolution: The Simple Model
J.Köppen [email protected]
http://astro.u-strasbg.fr/~koppen/JKHome.html
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Assumptions: e.g. solar neighbourhood
• Closed box (no mass exchange): Simple Model
• volume large enough (100 pc) and time interval
long enough (0.1 Gyr) to define average values
• (solar nh’d = solar cylinder: integrate over height
above Galactic plane and azimuth – neglect
vertical kinematics and rotation)
• Gas always well mixed (why not? Makes life easier)
• Constant IMF (why not?)
• Initially 100% gas, metal-free (why not?)
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Gas mass equation
Ejected gas remnant
tMS(m) = lifetime of stars of
initial mass m
≈ time on main sequence
a star:
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Metal mass equation
Ejected unprocessed gas, with ‘old’ metals
Ejected freshly produced metals
Old and new metals locked up in remnant
Ejected fractional stellar mass in the form of element i
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Instantaneous Recycling Approximation
• metals are produced by massive stars (> 10 M
) which live only <10 Myrs
• they also eject most of the gas
• the numerous long-lived stars do not eject metals (O, Ne, Ar, S, …)
• neglect stellar lifetimes in the ejecta
with R = stellar return fraction (simple integral over IMF!!)
Equation for the gas mass
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IRA (continued)
with a = 1-R locked-up mass fraction
y = yield of metal i (another simple integral over IMF!!)
Equation for the metal mass
… and for the metallicity
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IRA Solution The mass s in long-lived stars and remnants
For convenience: the gas fraction f = g/(g+s)
Equation for metallicity is independent of SFR or SF history (SFH)
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IRA Solution: The Simple Model
For a constant yield, the metallicity of the gas depends on
the current gas fraction, independent of SFR or SF history
Z = - y * ln f
Yield:
= average metal production
of the stellar population
• stellar nucleosynthesis
• IMF
Gas fraction:
= current state of galaxy
• galactic gas consumption
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But the age-metallicity relation requires explicit knowledge of SFR:
as well as the history of gas consumption:
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Dependence on SFR = cst. * gn n = 1 2 0.25
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Dependence on SFH
Short sharp starbursts Two long starbursts
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Average stellar metallicity:
The equation
has the solution
… again, independent of SFR or SFH!
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Stellar AbundanceDistributionFunction
• long-lived stars = mixture of old and young
stars … and we don’t need to determine
individual ages … WOW!!!
• Histogram of their metallicities (in IRA):
with
Simple Model:
… once again, independent of SFR or SFH!
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Two Forms of the AbundanceDistributionFunction
ds/dlogZ = Z/y exp(-Z/y) log ds/dZ = const. – Z/y
(- - - with proper Fe synthesis)
theoretician’s pet: observer’s preference:
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G dwarf problem: history I
• Van den Bergh (1962), Schmidt (1963): solar nh’d has
paucity of metal-poor G-dwarfs compared to Simple
Model
• alternative models …
• Pagel & Patchett (1975): 132 stars, photometric [Fe/H]
• … chemical evolution modelers often use infall/inflow of
metal-poor gas into solar nh’d
• Pagel (1989): improved UV excess - [Fe/H] relation
• Sommer-Larsen (1991): correction for different heights
above plane (old stars have higher velocity dispersion
greater scale heights): discrepancy still there!
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Pagel & Patchett 1975
Pagel 1989
Sommer-Larsen 1991
Closed Box with
proper Fe synthesis
Simple Model
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G dwarf problem: history II • Several new data sets …
• … Nordström et al. (2004): 1195 stars with spectroscopic/photometric [Fe/H]: worse than ever!
• Haywood (2006): Closed Box model with scale height correction does the job!
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Nordström 2004
Simple Model
const Fe yield
Closed Box
proper Fe yield
Closed Box,
proper Fe yield,
Sommer-Larsen
scale-height
correction,
d < 40 pc
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0 0.05 0.1 0.15 0.2
0 2 4 6
0 0.5 1 1.5
Stellar ADFs in
Sol.Nh’d Gdwarfs
= Disk
Log(dn/dZ)
Bulge K giants
Halo glob.clusters
slope eff.yield
Fe/H
0.4 Z
1.8 Z
0.025 Z
after Pagel 1989
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Why are the yields different?
• Different nucleosyntheses in
Bulge/Disk/Halo stars?
• Different IMFs?
• Different evolutions/conditions/processes?
• …
• ??
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Abundance ratios …
If the yield of element i depends
on metallicity of an element with
constant yield (‘primary production’):
in IRA one gets this equation
and the solution
The exponent k (= slope in a log-log plot) of the
abundance ratio as a function of metallicity indicates
the metallicity-dependence of the yield, and thus tells
about the nucleosynthesis of the element i
k = 0 primary
k = 1 secondary
k = 2 tertiary …
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Abundance ratios: O,Ne,S,Ar
Henry & Worthey 2000
Slope = 0 constant yield
« primary production »
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Abundance ratios: N/O
Slope = 0
Slope = 1 yield linear with Z
« secondary production »
???
Henry, Edmunds, Köppen 2001
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Abundance ratios: C/O
Slope = 0
Slope = 0.5
Slope = 1
???
Henry, Edmunds, Köppen 2001
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C-N-O is a longer story …(see later)
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Fe
• Some comes from core-collapse SN (‘type
II SN’): about < 0.15 M
… depends on
the mass of the remnant
• From C-deflagration SN (‘type Ia SN’):
about 0.6 M
per event (Model 7 of
Nomoto et al.)
• Need fraction of stars that evolve as
binaries: about 0.035 (but free parameter)
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SN Ia
SN II
SN
rate
(arb
itra
ry)
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SSP yield for iron
.. but most comes out
after abt 1Gyr, from SN Ia
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O/Fe (or a/Fe) ratio measures
SFR time-scale (illustrative model)
SFR = C * g
C [Gyr-1]
high a/Fe fast formation
low a/Fe slow formation
SN II
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O/Fe (or a/Fe) ratio measures
SFR time-scale (real nucleosynth. data)
Nucleo:
HG, WW95
IMF: Salpeter
SFR = C*g
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Abundance ratios: O/Fe, Mg/Fe, …
Pagel & Tautvaišienė 1995
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Properties of the Simple Model
Independent of SFR and SFH:
primary metallicity (yp=const.) Zp = - yp ln f
Z-depend. metallicity y Znp Z/Zp Znp
stellar ADF log dn/dZ = -Z/y + const.
peak of ADF (dn/dlogZ) Zpeak = yp
mean stellar metallicity: < y
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Beyond the Simple Model
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The G-dwarf problem lead to think about
• The initial metallicity was NOT zero:
Prompt Initial Enrichment, Hypernovae
• The box is NOT closed: gas inflow/outflow
• The yield is NOT constant
• Metallicity-enhanced star formation
• …
• and all these ideas did give better fits …
Deviations from the Simple Model:
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Deviations from the Simple Model:
• Gas outflows
• (Enriched outflows = loss of stellar ejecta)
• Gas accretion: inflows/infall
• (Gas throughflow)
• Imperfect mixing of the gas
• Multiple components
• Sudden events
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Outflows of interstellar gas Arbitrary outflow rate: W(t) general function w(t) = W/aY > 0
Same as Simple Model!
Solution with constant w > 0
= Simple Model with reduced yield!
and the G-dwarfs:
= Simple Model with reduced yield!
It can be shown (by num.eperiments) and also proven that there is
no function w(t) that would explain the observed G-dwarf distribution
+
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Enriched outflows
• SN explosion carries out of the galaxy part
or all of the freshly produced metals
(‘blow-out’, ‘blow-away’)
• reduces the yield by some factor averaged
over the stellar population …
• factor depends on the gravitational field of
the galaxy, the position where the SN
explodes (requires detailed
hydrodynamical calculation of the SN
explosion and its effect on the ISM)
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Enriched outflows
• one could also introduce a certain time
evolution of the reduction factor of the
yield … and play with that …
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Accretion of (primordial) gas Arbitrary accretion rate: A(t) accretion factor a(t) = A/aY > 0
yield: p = y Köppen & Edmunds 1999
Linear Accretion Models (a=const.) give the clue:
consider the streamlines in the f-Z diagram
critical points: f = 1 – 1/a (as long as 0 < f < 1)
Z = p/a = y/a
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Accretion: 2 equilibrium modes
a > 1: both critical conditions are met:
an attracting node =
• gas consumption = gas accretion
• metal production = metal ‘dilution’
• but close to Simple Model
a < 1: only condition on Z is met:
an attracting funnel (=partial equilibrium):
• continuous gas consumption
• metal production = metal ‘dilution’
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Behaviour of arbitrary accretion
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Accretion: secondary elements
Streamlines:
Equilibrium = attr.Node
Zs/Z = R = Z * ys/y
close to Simple Model
factor 2
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Accretion: summary
• Accretion of metal-poor gas always reduces the effective yield
• Models with monotonically decreasing a(t) evolve close to the Simple Model
• Rapid and massive accretion onto a gas-poor system can give strong deviations ()
• Accretion of metal-rich gas (through-flow models) can push up the yield a bit (but you have to make the metals elsewhere…)
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Accretion helps G dwarfs:
Closed Box
Exponential infall
timescale:
5 Gyrs, 10 Gyrs
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One could also deduce infall history
AC
CR
Köppen 2006 (unpubl.)
From jump in observed ADF: artifact?
![Page 46: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/46.jpg)
Possibilities to alter the ADF? Take general chemical model (but in IRA):
• metallicity-dependent yield y(Z)
• accretion of gas a(t) = acc.rate/SFR
• metallicity of accreted gas Za(t)
• outflow of gas w(t) = flow.rate/SFR
• escape of stellar ejecta h(t) = fraction that escapes
To solve G dwarf
problem, need
dD/dZ > 0
Accretion (Infall, Inflow)
Low yield or strong metal loss at high Z
Outflows? NO!
D
Z
![Page 47: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/47.jpg)
Imperfect mixing …
![Page 48: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/48.jpg)
after 1st time step
![Page 49: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/49.jpg)
after 2nd time step
![Page 50: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/50.jpg)
after 3rd time step
![Page 51: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/51.jpg)
Imperfect mixing: results
= closed box slope = 1.0
slope = 0.4
slope = 0.25
.. but everything else is like the Simple Model:
mean metallicities, G dwarfs Wilmes & Köppen 1995
![Page 52: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/52.jpg)
Argast et al. 2000
Imperfect mixing:
halo stars
• gives dispersion of
abundances in
halo stars
• model dispersions:
• in O/Fe greater
• in Ni/Fe smaller
than observed
nucleosynthesis of
massive stars??
![Page 53: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/53.jpg)
Multiple components: bulge+disk
Stars
Gas
Bulge
Stars
Gas
Disk
ADF of K giants ADF of G dwarfs
Köppen & Arimoto 1990
SN driven wind
terminates
bulge evolution
![Page 54: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/54.jpg)
Diffuse gas
Remnants,
low mass
stars
Massive
stars
Cloud gas
Halo
Diffuse gas
Remnants,
low mass
stars
Massive
stars
Cloud gas
Thick Disk
and other models …
Diffuse gas
Remnants,
low mass
stars
Massive
stars
Cloud gas
Thin Disk
Multiple components: Shore/Ferrini
![Page 55: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/55.jpg)
ADF of halo, thick, thin disk:
![Page 56: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/56.jpg)
Sudden events: Starbursts Simple Model is insensitive to SFH () but it does matter when
time-delayed
production
is involved! Starburst
AGB stars eject
N slowly
![Page 57: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/57.jpg)
Sudden events: gas removal,
outflows
• Galactic winds: accumulated thermal energy (heated by SN) in ISM exceeds gravitational binding energy
• Ram pressure stripping: passage through dense intracluster gas removes ISM
• Gas + metals escape
• Star formation stops (truncated ADF)
• Gas could be built up from returns by stars, gas metallicity decreases as the older, metal-poorer stars die …
![Page 58: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/58.jpg)
Sudden events: Infall events
IRA
pure secondary N
At 5 Gyrs, massive
infall starts with
100 Mgal/Gyr
‘dilution’
![Page 59: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/59.jpg)
Infall events: same model with stellar lifetimes
and ‘proper’ nucleosynth. (incl. primary production)
![Page 60: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/60.jpg)
Collisions with High Velocity Clouds …
Köppen &
Hensle
r 2005
![Page 61: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/61.jpg)
The yield
![Page 62: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/62.jpg)
Yield = metal production
of a stellar generation « yield »
« integrated yield »
« IMF weighted yield » IMF (Salpeter: 1.35)
« stellar yield »
= Fraction of stellar mass
ejected in form of newly
produced element i
« fresh stellar yield »
« net stellar yield »
… !!!
max (IMF lower mass limit, turn-off mass)
locked-up mass fraction
i i
![Page 63: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/63.jpg)
Stellar yields: what stars produce:
0
0.2
0.4
0.6
Mass fraction
1 2 4 8 10 20 40 M stellar mass
MS lifetime 10 0.7 0.1 0.01 0.003 Gyr
Spec.Type G2 A0 B5 B0 05
White dwarf
Neutron star
H,He N
Si … Fe
Supernova PN Type I PN
![Page 64: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/64.jpg)
Accuracy of stellar yields
and the yield ?
Generally not better than a factor of 2 …
![Page 65: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/65.jpg)
Slope of IMF is very important:
• Need a plot Salpeter IMF
![Page 66: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/66.jpg)
Effective yields
• We may use the Simple Model relations to
define « effective yields »:
• Gas metallicity: yeff = -Z/ln f
• Stellar ADF
– slope yeff = -1/(Dln(dn/dZ)/DZ)
– peak in plot as dn/dlogZ
![Page 67: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/67.jpg)
E.g. oxygen
H He C O CNO cycle triple a a addition
Main sequence post-main sequence
(H-burning) (He-burning)
From H to O in one stellar generation
yield independent of metallicity: H >> O
‘primary’ production
![Page 68: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/68.jpg)
Single Stellar Population Yield
For a Salpeter IMF all the oxygen
comes from the most massive stars
![Page 69: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/69.jpg)
How to make nitrogen …
1) H He C CNO cycle triple a
Main sequence post-main sequence
Takes two stellar generations
yield metallicity
‘secondary’ production
2) C N
CNO cycle
Main sequence
ISM
![Page 70: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/70.jpg)
… but it also works this way …
H He C CNO cycle triple a
Main sequence post_main sequence
All in the same star
yield independent of metallicity
‘primary’ production
C N
CNO cycle (hot-bottom burning)
AGB
3rd dredge-up on AGB
![Page 71: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/71.jpg)
Intermediate mass stars
• mass range: 3 … 9 M
• produce He, C, N
• complex evolution: • convection + ‘overshooting’ (no exact theory, but
can be scaled from numerical HD simulations)
• internal mixing by dredge-ups on RGB, AGB
• thermal pulses (AGB) full models very scarce
• mass-loss (RGB, AGB, no theory)
• details of final phases, ejection of PN
![Page 72: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/72.jpg)
Ejected Nitrogen = fresh + thru
Z = Solar
Z = Solar / 20
thru thru
fresh secondary
fresh
primary
van den Hoek & Groenewegen Woosley & Weaver 1995
![Page 73: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/73.jpg)
SSP yield for nitrogen
Most nitrogen comes out
after about 100 Myr:
primary N from AGBs
Z = solar / 20
![Page 74: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/74.jpg)
Maeder 1992:
Lower O-yields
from metal-rich
massive stars
due to higher
mass loss
from stellar wind
Oxygen is
NOT « primary »
![Page 75: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/75.jpg)
Reduction of O yield by
stellar winds (Maeder 92)
can explain the increase
of both C/O and N/O
Henry, Edmunds, Köppen 2000
SFR
![Page 76: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/76.jpg)
Illustrative closed box models
RV
= R
enzin
i&V
oli
1981
HG
= v
an d
en H
oek&
Gro
enew
ege
n 1
994
WW
95 =
Woosle
y&
Weaver
199
5
M92 =
Maeder
1992
![Page 77: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/77.jpg)
The observed NO-OH
relation can well be matched
by different assumptions on
the O and N yields’
metallicity dependence …
N: purely primary
N: purely secondary
O: purely primary
N/O
N/O
N/O
O/H
O/H
O/H
N yield O yield
O yield
Z
Z Z
![Page 78: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/78.jpg)
The last word on N/O so far …
• * * * Spite² (2005) find
high N/O and C/O ratios in
very metal poor stars
• Implies large N-production
before AGB stars die
massive stars must
produce large C+N
• Hirschi (2007) rapidly
rotating massive stars
produce substantial C+N
• Chiappini (2006)
chem.ev. models - - - -
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Usefulness of the Simple Model
• Simple Model is the most efficient way to
make metals while consuming as little gas
as possible
• Inflow of gas, outflows of gas or ejecta
only decrease the effective yield
• Gives an upper limit for metallicity and
hence the true yield
• Zp = -yp ln f and Zs/Zp= ys/2yp * Zp are
insensitive to SFR, SFH, (infall) …
![Page 80: Evolution of Galaxies - portia.astrophysik.uni-kiel.deportia.astrophysik.uni-kiel.de/~koeppen/ue7b/docs/EoG_7simpleModel.pdfG dwarf problem: history I • Van den Bergh (1962), Schmidt](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd10240d6be591ccb63c6ad/html5/thumbnails/80.jpg)
Multiple components: Mergers
M = M1 + M2
f = (f1M1+ f2M2)/M
Z = (Z1f1M1 + Z2f2M2)/(f1M1+ f2M2)
M2, fgas2, Z2
M1, fgas1, Z1
Example: M1 = M2, f1 = 0.1,f2 = 0.9 Z1/y = 2.3, Z2/y = 0.1
f = 0.5, Z/y = 0.32 but -ln(0.5) = 0.69
merged system is only a factor 2 off the Simple Model prediction
Z = -y ln f