>>>>> "s" == sean <jaymoseley@xxxxxxxxxxx> writes:
s> I was wondering if anyone could clarify my following question about
s> filter band redshift calculations for me. From other sources I am
s> informed that redshift interpretations from simultaneous optical
s> observations in different filter bands can be made by working out
s> which filters the source is visible and which it isnt and then
s> calculating a redshift approximately from that data.
Yes, the term is "photometric redshift." It of course is not as
accurate as a spectroscopic redshift, in which one observes specific
spectral lines, but photometric redshifts can still be useful
particularly when one is considering large numbers of sources.
s> So for example... If filters U,B and V are used to observe a light
s> source known seperately to be at z=3 am I correct in assuming that
s> due to lyman alpha cutoff no detection could be made in the U band
s> filter as the lyman break prevents this ie..121nm*3(+1)=484nm. So
s> anything blueward of 484 nm isnt visible.? Or in other words am I
s> correct in thinking that if one were viewing in U, B and V filters
s> one would get no detection in U (area curve 300-400nm), a possible
s> detection in B ( area curve is 380-490nm) and a definite detection
s> in V band (area curve 500-590)?
I haven't checked your math, but, yes, this is the general idea. In
general, the source can be present in all bands, and the relative
brightnesses in the bands is still an indication of its redshift.
Also, as you might guess, the larger the number of bands used, the
more accurate this method becomes.
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