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Is this (Nature 469, 504-407 (2011)) graph wrong?
Hello, Can anyone help me understand this graph? The graph appears
to be incorrect to me, what am I missing? http://www.nature.com/nature/journal...e09717_F4.html The Y axis on left and right have two different sets of units. On the left, there is log_10 (M_sun / (yr * Mpc^3)) On the right axis, there is: log_10 (erg / (s * Mpc^3)) Seconds and years are both just units of time, so those plots are different by a constant value of seconds per year. Since everything is all the same, I should be able to cancel out all of the units... Log_10 and time and volume, so that the plot is asserting that star formation *rate* within a region and at some time is the same as the value of ergs within the region of the universe at a specific time considered. I understand that as the number of stars goes up, the value for ergs ought to go up. But if the star formation rate went to zero, there would still be all of the previously formed stars, so, the erg value would not go to zero just because the universe stopped forming stars. So, it doesn't seem right to me that these two Y axis' can be placed on this graph????? Isn't the left Y axis a completely different thing from the right Y axis? What am I missing. rt |
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Is this (Nature 469, 504-407 (2011)) graph wrong?
On Saturday, November 26, 2016 at 8:58:26 PM UTC-5, wro=
te:=20 The Y axis on left and right have two different sets of units. On the left, there is log_10 (M_sun / (yr * Mpc^3)) =20 On the right axis, there is: log_10 (erg / (s * Mpc^3)) .... I understand that as the number of stars goes up, the value for ergs ought to go up. But if the star formation rate went to zero, there would still be all of the previously formed stars, so, the erg value would not go to zero just because the universe stopped forming stars. Stellar UV emission is dominated by O an B type stars, whose lifetime is short (10s to few 100s million years) compared to galactic evolutionary timescales. So in effect, no, in UV one do not see "all" of the previously formed stars, just the very recently formed, short-lived, massive stars. Check out this review for more info https://ned.ipac.caltech.edu/level5/..._contents.html CM |
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