Most Distant Galaxy: Mysteries Explained

  • Thread starter yuiop
  • Start date
  • Tags
    Galaxy
In summary, the conversation discusses the discovery of one of the earliest galaxies ever observed, with a redshift of 6.96 and an estimated age of 760 million years. The article also mentions the process of recombination, when the universe transitions to being transparent, and the issue of Malquim bias in detecting galaxies at such high redshifts. The conversation also mentions another possible galaxy with a redshift of 7.6 and the need for further confirmation using more advanced telescopes.
  • #1
yuiop
3,962
20
I have been reading this interesting article http://www.subarutelescope.org/Pressrelease/2006/09/13/index.html on one of the earliest galaxies that has ever been observed (z=6.96), that existed when the universe was just 760+/-15 million years old or about 6% of its current age. See also http://www.nature.com/nature/journal/v443/n7108/abs/nature05104.html

The article is very readable and nicely illustrated, but a couple of things puzzle me and I hope someone here can enlighten me. It describes the period of "recombination" when the universe transitions from an opaque period due to scattering of light by ions to a period when the universe becomes transparent when the ions combined to form hydrogen atoms. It then goes on to say that we do not see many galaxies at the early epoch (@760 million years) because neutral hydrogen absorbs the light from the early stars and they only later become visible when the young stars reionize the neutral hydrogen. That seems to contradict the earlier statement but maybe I am missing some important point??

Another issue is that they describe the early universe as being different to later epochs because of the relative rarity of galaxies in the early epoch. That would seem natural if all galaxies did not form simultaneously in the early universe and I would have thought that Malquist bias would be an additional factor at the enormous distances we are talking about here. See http://en.wikipedia.org/wiki/Malmquist_bias . However, they do not mention Malmquist bias anywhere in the article. Have they taken Malmquist bias into account and simply not mentioned it or is it a non issue in this context?
 
Last edited by a moderator:
Space news on Phys.org
  • #2
The recombination is the epoch after which the cosmic radiation background mainly ceases to interact with electrons and allows them to get bounded to protons to form neutral hydrogen. Due to expansion of space most of the photons in the cosmic radiation background will lose energy and will never be able again to ionize hydrogen. However, later on photons are created in stars and quasars that have enough energy to ionize the neutral hydrogen. This process is called reionization.

The point you make with Malquim bias is insightful, but I would expect that they have analyzed it carefully and taken it into account. They are talking about a decrease in the number density for epochs separated 0.4 in redshift. I would expect that similar accuracy in the detection can be expected in that range. However, I do not know their work so I might be wrong.
 
  • #3
I would think that the Malquim bias is to be applied to large surveys where one has a large number of objects and wants to consider the completeness of their survey. For galaxies at these high redshift there aren't large samples, there are a handfull of isolated observations. The bias is extreme and there is no point to go into detailed analysis. However even a single galaxy discovered at these high redshifts, corresponding roughly to the first billion years after the big bang, is interesting. A very active area of research is when the first (population III) stars formed and when they gathered into objects we would call galaxies (and how long the transition to population II stars took and ...). The James Web Telescope is going to make observations of this epoch when it goes up and large radio array telescopes being built now will tell us about the epoch of reionization (when the first luminous objects reionized the neutral Hydrogen)
 
  • #4
An even earlier galaxy: A Lyman Break Galaxy Candidate at z~9
We report the discovery of a z~9 Lyman Break Galaxy (LBG) candidate, selected from the NICMOS Parallel Imaging Survey as a J-dropout with J110 - H160 = 1.7. Spitzer/IRAC photometry reveals that the galaxy has a blue H160 - 3.6 um color, and a spectral break between 3.6 and 4.5 um. We interpret this break as the Balmer break, and derive a best-fit photometric redshift of z~9. We use Monte Carlo simulations to test the significance of this photometric redshift, and show a 96% probability of z>7. We estimate a lower limit to the comoving number density of such galaxies at z~9 of phi > 3.8 x 10^{-6} Mpc^{-3}. If the high redshift of this galaxy is confirmed, this will indicate that the luminous end of the rest-frame UV luminosity function has not evolved substantially from z~ 9 to z~3. Still, some small degeneracy remains between this z~9 model and models at z~2-3; deep optical imaging (reaching I ~ 29 AB) can rule out the lower-z models

Garth
 
  • #5
That is impressive work, but the dropout technique is in a different category then a spectroscopically confirmed galaxy. Note the mention of degeneracy with a z = 2-3 model in the last sentence.
 
  • #6
z = 7.6 ?

kev said:
I have been reading this interesting article http://www.subarutelescope.org/Pressrelease/2006/09/13/index.html on one of the earliest galaxies that has ever been observed (z=6.96), that existed when the universe was just 760+/-15 million years old or about 6% of its current age. See also http://www.nature.com/nature/journal/v443/n7108/abs/nature05104.html
...

If Garth's z = 9 is not confirmed, there is this z = 7.6 candidate
http://www.spitzer.caltech.edu/Media/releases/ssc2008-04/release.shtml[/URL]

the press release is dated 12 February 2008

light from the galaxy would have been emitted when expansion was an estimated 700 million years old.

Ned Wright expresses skepticism ("NASA's budget must be tight") because no lines have been observed. I will see if I can find more about this one.

Here is the article
[url]http://arxiv.org/abs/0802.2506[/url]
it was accepted by Astrophysical Journal for publication and was reported in press as of May 2008
it is another "Lyman break" determination, unless I'm mistaken it will take a more powerful infrared telescope like the James Webb to see lines and be more certain about the redshift.
 
Last edited by a moderator:
  • #7
Obviously the red shift of these galaxies will need to be confirmed once telescopes are sensitive enough to observe spectral lines in the IR but 96% probability that z > 7 is fairly (>3[itex]\sigma[/itex]) convincing.

Garth
 

1. What is the most distant galaxy discovered so far?

The most distant galaxy discovered so far is GN-z11, located approximately 13.4 billion light-years away from Earth.

2. How was the most distant galaxy discovered?

The most distant galaxy was discovered using the Hubble Space Telescope's Wide Field Camera 3, which is able to detect incredibly faint and distant objects.

3. Why is the discovery of the most distant galaxy important?

The discovery of the most distant galaxy is important because it gives us a glimpse into the early universe, allowing us to study the formation and evolution of galaxies and the universe itself.

4. What mysteries about the most distant galaxy have been solved?

The discovery of the most distant galaxy has helped to solve mysteries about the early universe, such as when and how the first galaxies formed and how the universe evolved over time.

5. What new questions have arisen from the discovery of the most distant galaxy?

The discovery of the most distant galaxy has raised new questions about the nature of the early universe and the processes that led to the formation of galaxies. It has also sparked discussions about the possibility of even more distant galaxies waiting to be discovered.

Similar threads

Replies
4
Views
1K
  • Cosmology
Replies
4
Views
1K
Replies
10
Views
2K
Replies
13
Views
2K
Replies
24
Views
5K
  • Astronomy and Astrophysics
Replies
2
Views
2K
Replies
1
Views
2K
Replies
1
Views
1K
  • Science Fiction and Fantasy Media
2
Replies
51
Views
7K
Back
Top