# Rates of galactic evolution (first 3 billion years)

1. May 14, 2006

### kmarinas86

Do the rates of galactic evolution (first 3 billion years) agree in all parts of the observed sky? Or does certain part of evolution vary within the universe by ~1 billion years? Could one part of the sky at redshift z=4 be ~500 million years ahead in evolution than another part of the sky at redshift 4?

Do we know? If not, can this be tested?

If a maximum difference of 1 billion years is observed for the rates of evolution in two particular places in the sky for the first 3 billion years (10.7-13.7 billion years ago), what implication does that have on the Big Bang Theory?

What happens if these deviances line up with large-angle hot and cold spots in WMAP?

2. May 15, 2006

### Garth

For different parts of the sky to evolve at grossly different rates, so the sky is non-isotropic, then this would imply that it was grossly non-homogeneous. Although they are clusters and superclusters of matter these are distributed more or less isotropically across the sky and the CMB is isotropic to the ~ 10-5 level.

So it does not seem to be the case that different parts of the sky have evolved at different rates.

Garth

3. May 15, 2006

### kmarinas86

And this is true for the first 3 billion years? Remember that most observations of the universe do not reach this far and the map of the sky is not complete either, especially that those distances (much less the redshift of those distant galaxies in the first 3 billion years).

4. May 15, 2006

### Garth

Yes this is true, observations go back much further than t ~ 3 Gyrs, the Surface of Last Scattering (the CMB) was at t ~ 400 million years.

Garth

5. May 15, 2006

### kmarinas86

Yes, I know the WMAP is at around 400 million years (actually the surface of the last scattering occurs at around t=400 thousand years). But I'm speaking of galactic evolution which comes after that.

The first 3 billion years is not just WMAP, but also the Hubble Deep Field Views and areas of the sky at that depth that HDF doesn't cover. WMAP doesn't show us galactic evolution. This thread, after all, is a thread about galactic evolution, not WMAP.

Have we made enough observations to discern the galactic evolution rates between 1 billion and 3 billion years at all areas of the sky and are absolutely sure there are no differing rates of galactic evolution among large angle regions (even those that correspond to hot and cold spots in WMAP)?

Last edited: May 15, 2006
6. May 15, 2006

### Garth

Galactic evolution 'begins' with WMAP in that the mass concentrations that form galaxies and their halos condense out of the slightly more dense regions of the Surface of Last Scattering. The standard theory requires condensations of DM to have predated that epoch and continue collapsing to form halos into which the baryonic matter falls.

As the SLS was so isotropic over all the sky there is good reason to believe the subsequent galaxy evolution was also similar over all the sky.

We do observe out to z ~ 6 (i.e. t < 1 Gyr in $\Lambda$CDM model) in select patches of the sky, such as that covered in the HUDF, and galaxy evolution is observed in the sense that on the whole smaller and younger galaxies are observed at increasing z.

There is a question though about whether there is an age problem at these early times or not, as there are some objects (HUDF-JD2 and some high Fe abundance (3 x solar) quasars) that are apparently older than the apparent age of the universe at that red shift.

Of course these observed high-z patches of the sky are very selective so it cannot be categorically stated that there is no difference in galactic evolution at a particular z from area of the sky to another, however, the all-sky isotropy of the CMB would suggest not. Why do you think there could be?

Garth

Last edited: May 15, 2006
7. May 15, 2006

### kmarinas86

Logical possibility: It hasn't been ruled out (as far as I know), so it might turn out to be the case (future information may reveal this).

What would be interesting would the be the discovery of cD galaxies at t<1 billion years.

Last edited: May 15, 2006
8. May 15, 2006

### Garth

Well there is the Hubble ultra deep field object UDF033238.7-274839.8 aka HUDF-JD2 , a 6 x 1011Msolar galaxy at z = 6.5 when the universe was only 860 Myrs old, (age given by Ned Wright's calculator allowing for DE).

Not quite a cD giant elliptical, but if its distance has been interpreted correctly (which is debatable) it presents a problem for the standard hierarchial model of structure formation.

Garth

Last edited: May 16, 2006
9. May 15, 2006

### kmarinas86

Last edited by a moderator: May 2, 2017
10. May 16, 2006

### Chronos

Don't read too much into that, kmarinas86.

11. May 16, 2006

### matt.o

Why is that Chronos?

12. May 17, 2006

### Chronos

It is still a struggle to pin down when reionization was complete. Galactic [as well as stellar] formation models, as I understand it, are very sensitive to this effect.

13. May 17, 2006

### matt.o

Sorry, I'm not sure understand your point. The paper cited uses photometric redshifts for ~1 million luminous red galaxies (these are the best for getting photometric redshifts as they have a strong 4000 angstrom break) to develop a 3-d map of the sky in order to measure the angular power spectra, hence constrain cosmological parameters. The technique used is fairly robust and uses a sophisticated method for deriving redshifts where "artificial neural networks" are used in conjunction with a subset of galaxies with known spectroscopic redshifts to parameterise photometric properties relation to redshift.

The sheer weight of numbers in the sample makes it competitive with current spectroscopic redshift surveys for measuring cosmological parameters.

Besides that, Chris Blake is a friend and collaborator of mine and I hold him in a very high regard!