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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.

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Lecture 10: Chemical Evolution of Galaxies

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  1. 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.

  2. 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:

  3. ISM Recycling

  4. The Yield r

  5. Metalicity Evolution Z(t) Differentiate: But, Thus:

  6. Definition of yield: Conserve mass: Integrate (with r = constant ) : At Z = 0, MG = M0 :

  7. But, So finally, As impossible! But So, as The equation above is valid when Z < r, after which Z = r.

  8. Ellipticals: Spirals:

  9. Irregulars:

  10. . 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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