1. Lecture 11: Age and Metalicity from Observations
“Closed Box” model with constant yield:
Ignores:
IGM--ISM exchanges: IGM falls into galaxy ISM blown out of galaxy
2. SN Ia, stellar winds, PNe, novae, etc.
Initial enrichment by e.g. Pop.III stars prior to galaxy formation?
Faster enrichment (more SNe) in high-density regions of galaxy.
metalicity
yield
gas fraction

2. Ellipticals:
Spirals:

3. Irregulars:

4. Age Estimates Main sequence lifetime: HR diagram L . . Lmax . B-V
giants . . .
Main sequence
Lmax (top of main sequence) gives age t.

5. Abundance Measurements
Star spectra: absorption lines
Gas spectra: emission lines
Galaxy spectra: both
Metal-rich/poor stars: stronger/weaker metal lines relative to H.
HII region spectra
Stellar spectra

6. Lab measurements: Unique line signature for each element.

7. High-Resolution Spectra

8. Abundance Measurements
Spectra Line strengths (equivalent widths) +
Astrophysics Stellar atmosphere models
Physics Laboratory calibrations
(Full details of this process are part of other courses)

9. Bracket Notation
Bracket notation for Fe abundance of a star relative to the Sun:
And similarly for other metals, e.g. relative to Fe:
Star with solar Fe abundance:
Twice solar abundance:
Half solar abundance: .
atoms of Fe
atoms of H

10. [Xi/Fe] vs [Fe/H]

11. Metallicity vs Abundance
Metalicity (by mass):
Abundance (by number): .
(where f = some factor) .
Primordial: Xp = 0.75, Yp = 0.25, Zp = 0.00
Solar: X = 0.70, Y = 0.28, Z = 0.02 . .

12. Key Observational Results
More gas used --> higher metallicity.
More metals near centres of galaxies. Infall of IGM on outskirts + gas migrates to centre. More star generations --> m lower at centre.
Small (low luminosity) galaxies have lower metallicities.
Dwarf irregulars: form later (young galaxies), m high
Dwarf ellipticals: SN ejecta leave the galaxy, m low

13. Less Metals in Small Galaxies
faint > bright

14. More metals near Galaxy Centres
Ellipticals
(NGC 3115)
Spirals
(M100)

15. Review of Course Main events in the evolution of the Universe:
The Big Bang (caused by ???)
Symmetry breaking  matter/anti-matter ratio
Quark + antiquark annihilation  photon/baryon ratio
The quark soup  heavy quark decay
Quark-Hadron phase transition and neutron decay  n/p ratio
Big Bang nucleosynthesis  primordial abundances
Xp = Yp = Zp = 0.0
Matter-Radiation equality
Recombination/decoupling  the Cosmic Microwave Background
Galaxy formation and chemical evolution of galaxies

16. Main events in the chemical evolution of galaxies:
Galaxy formation  Jeans Mass
Ellipticals
Spirals  SFRs, gas fraction m(t)
Irregulars
Star formation  a = efficiency of star formation
The IMF (e.g., Salpeter IMF)
Stellar nucleosynthesis  metals up to Fe  yield r
Black holes, white dwarfs, neutron stars
Supernova (i.e., SN 1987A)  metals beyond Fe
r, p, and s process
Abundances  X = Y = Z = 0.02
(solar abundances)
Planet formation  Life!