I'm not sure I understand how to correctly scale flux density with redshift. That is, if I observe say 10 Jy at my observing frequency coming from a source at z = 0.3, how can I estimate the flux density I would expect from the same source at z=2? From what I understand, the final scaling is given by(adsbygoogle = window.adsbygoogle || []).push({});

$$S \propto \frac{1}{(1+z)}$$,

but I'm not sure I understand how that comes about. I believe there are two factors of1/(1+z)due to the photon energy and time dilation, but I'm not sure what other factors to take into account, such that it reduces to only one factor of(1+z)in the denominator.

Furthermore, it seems strange to me that in the example I give, a 10 Jy source at z=0.3 is only dimmed to a flux density of 4.3 Jy at z=2. Doesn't this suggest that one could in principle see this source to very extreme redshifts (pending the sensitivity of the instrument, of course). Or have I made a mistake in the scaling?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# I How does flux density scale with redshift?

Have something to add?

Draft saved
Draft deleted

**Physics Forums | Science Articles, Homework Help, Discussion**