A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Research
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Is higher mass-density at higher Z detectable with current probes?



 
 
Thread Tools Display Modes
  #1  
Old November 19th 18, 06:11 PM posted to sci.astro.research
stargene
external usenet poster
 
Posts: 43
Default Is higher mass-density at higher Z detectable with current probes?

A question regarding the expansion of the universe:
As the Hyperphysics page @ http://hyperphysics.phy-astr.gsu.
edu/hbase/Astro/redshf.html shows, the mass density rho(M@z)
= rho(Mz=0)x(1+z)^3, for the universe at any value of z.
Eg: At a z = 4, the mass density of the universe at that point in its
expansion (at about 13.8 Gly (z=0) - 12.77 Gly (z=4) = ~1.03 Gly),
would be roughly 5^3 or 125 times its current mass density. So--

Would any of the deep galactic survey programs, like the Hubble
Ultra-Deep Field, actually be capable of detecting such an increase
in both the average mass density, and perhaps even the number-
density of galaxies, possibly correlating with such a higher mass
density?

[[Mod. note -- I doubt it. It's already rather difficult to measure
the mean mass density of the local universe (z=0), and such a measurement
would be vastly harder at high redshift where we can only observe the
high-luminosity tail of the luminosity function. (That is, at high
redshift we can only observe objects (e.g., galaxies) which are
intrinsically much more luminous highly luminous than the average
object at that redshift.) Measuring the number density is even harder,
because it's more affected by intrinsically-faint objects (galaxies).
-- jt]]
  #2  
Old November 20th 18, 08:35 AM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
external usenet poster
 
Posts: 273
Default Is higher mass-density at higher Z detectable with current probes?

In article ,
stargene writes:

rho(M@z)= rho(Mz=0)x(1+z)^3, for the universe at any value of z.
Eg: At a z = 4, the mass density of the universe at that point in its
expansion (at about 13.8 Gly (z=0) - 12.77 Gly (z=4) = ~1.03 Gly),
would be roughly 5^3 or 125 times its current mass density.


Not "roughly"; pretty much exactly. Of course, this is the average
density.

Would any of the deep galactic survey programs, like the Hubble
Ultra-Deep Field, actually be capable of detecting such an increase
in both the average mass density, and perhaps even the number-
density of galaxies, possibly correlating with such a higher mass
density?

[[Mod. note -- I doubt it. It's already rather difficult to measure
the mean mass density of the local universe (z=0),


The radiation density goes like (1+z)^4 (photons are diluted by (1+z)^3
like non-relativistic particles, and additionally they are redshifted by
(1+z)). This CAN be detected.
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
What if(on higher life in higher dimension) G=EMC^2 Glazier[_1_] Misc 8 February 5th 09 05:56 PM
Higher Intelligence John Harshman Misc 0 January 9th 06 02:32 AM
Higher Intelligence nightbat Misc 0 January 8th 06 10:55 PM
Getting Mars higher in the sky Mike Murphy UK Astronomy 2 July 17th 03 02:39 PM


All times are GMT +1. The time now is 09:40 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.