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.

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Lecture 10: Chemical Evolution of Galaxies

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Lecture 10 chemical evolution of galaxies

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

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:


Ism recycling

ISM Recycling


The yield r

The Yield r


Metalicity evolution z t1

Metalicity Evolution Z(t)

Differentiate:

But,

Thus:


Lecture 10 chemical evolution of galaxies

Definition of yield:

Conserve mass:

Integrate (with r = constant ) :

At Z = 0, MG = M0 :


Lecture 10 chemical evolution of galaxies

But,

So finally,

As impossible!

But

So, as

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


Lecture 10 chemical evolution of galaxies

Ellipticals:

Spirals:


Lecture 10 chemical evolution of galaxies

Irregulars:


The yield r1

.

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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