Starbursts and metal production

Blue and UV light from stellar populations is dominated by young, massive stars which also contribute the lion s share of the Z-elements ( metals ). Evolutionary synthesis computations show that, between the Lyman limit (912 A) and 2000 A or so, the spectrum expressed as Lv is more or less flat (Fig. 12.3). This leads to some rather simple considerations because Iv retains its value (and flatness) when the light is redshifted (see Eq. 12.1), because the degradation in energy is simply taken up by the factor dv on integration (Lilly Cowie 1987). 

Furthermore, the monochromatic luminosity Lv is related to the total luminosity (approximately) by the simple expression 

When the light is dominated by massive stars, e.g. in starburst galaxies, the luminosity is related in turn to the rate of metal production, since virtually all processed material is ejected in the form of metals (and some helium). Thus there is a relationship between the total co-moving luminosity density, the monochromatic luminosity density (deduced from star-forming galaxy redshift surveys with appropriate corrections for absorption) in a fixed frequency bandwidth (anywhere between 912 and about 2000 A in the rest frame) and the mass going into nucleosynthesis  

Integration over the SFR shown in Fig. 12.4 leads to the present-day stellar density 

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