Red-shift vs Mass
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by
rudolfbaer
with the quench data I plotted red-shift vs (log) mass. I get an upwards sloping curve. Is there an actual correlation?
Posted
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by
vrooje
admin, scientist
Hi Rudolf,
Sorry for the delay in answering; but that sounds normal to me.
When we observe with a telescope, we're generally limited to seeing things above a certain flux limit, where by "flux" we mean the observed brightness. (Magnitude is a logarithm of the flux.)
Of course, we're more interested in an object's intrinsic properties, i.e., how bright is the light bulb intrinsically, as opposed to how bright it was observed. So we use measures of distance, such as redshift, to convert from observed brightness to intrinsic.
What that means, then, is that a constant observed brightness limit translates to a varying intrinsic brightness limit: as we look farther and farther away, we lose the ability to see the fainter objects. So if you were to plot redshift versus absolute magnitude (or luminosity) you'd see that the luminosity of objects seems to get higher as you go to higher redshift -- but that's purely a result of what the telecsope is able to observe in the first place.
And, of course, because luminosity is related to how many stars there are, and so is mass, you'll see that same limit echo through to mass: we can only detect the lowest-mass stuff if it's nearby.
You can see this in plots here:
http://tools.zooniverse.org/#/dashboards/galaxy_zoo_starburst/52249c01e1e4673995000008Hope that helps!
--BrookePosted
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by
rudolfbaer
in response to vrooje's comment.
Hello Brooke:
Thanks for your reply; I have learned something. Sorry for the late response - I was "off" the internet for some time due to very bad connection (South Pacific (!))
with best regards
RudolfPosted