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Lecture 10: Chemical Evolution of GalaxiesPowerPoint Presentation

Lecture 10: Chemical Evolution of Galaxies

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Lecture 10: Chemical Evolution of Galaxies

- Metalicity evolution Z(t) vs galaxy type:
- Processes that alter the metalicity:
- Type-II SNe enrich the ISM.
- Low-mass stars form from enriched ISM and “lock-up” metals.
- 3. Primordial gas falls in from IGM.
- 4. ISM ejected into IGM. (e.g. SN explosions, galaxy collisions)
- Closed-box model: 1 and 2 only.

Metalicity Evolution: Z(t)

M0 = total mass

MG(t) = mass of gas in ISM

MZ(t) = mass of metals in ISM

MS(t) = mass of the long-lived stars

that lock up metals

We know:

To derive:

Find:

So finally,

As impossible!

But

So, as

The equation above is valid when Z < r, after which Z = r.

Spirals:

The Yield r

First generation: Z=0 later generations Z << ZSN :

From Salpeter IMF and SN 1987A: a = 0.93

From SN 1987A: ZSN = 0.13

However, note that which is larger than the calculated yield, implying ! (remember )

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