How Did Scientists Miscalculate the Distance of UDFj-39546284?

[bobie]

I have read that when UDFj-39546284 was discovered its z was thought to be 10.3 but now is 11.9.
It was a " blue stars that existed as we see it 13.42 billion years ago, around "380 million years"[2] after the Big Bang (estimated at 13.8 billion years ago)"

I suppose the frequency of the radiation han not changed after 2 years, could you explain
- how a miscalculation of ≈15% was possible, what is the actual frequency detected and the original one, and how you get the value of 11.9
- if a galaxy could exist before the timeline of 400 million years after the BB

Thanks, your help is highly appreciated

 

[jedishrfu]

It would have been based on Hubble's law which means that if the constants value is more accurately determined then the time and distance of the galaxy would change:

http://en.wikipedia.org/wiki/Hubble_law

In the article they show an evolution of accuracy for hubble's constant.

However there may be other sources of error that were fixed that reduced the latest estimate like instrument accuracy in measuring the doppler shift of key spectral lines.

 

[marcus]

Here's the arxiv preprint that proposed (in a rather cautious tentative way) reclassifying the object
http://arxiv.org/pdf/1211.6804v1.pdf

The estimated redshift has not been spectroscopically confirmed.

It is based on images taken thru 3 separate filters, see Figure 1.

The estimate is not presented by the authors (Richard Ellis et al) as definite, but as one possible explanation for an anomalous observation, something that did not add up.

From comment by others quoted in the popular media articles, I detect sentiments like "this is something for the future James Webb telescope". I hope the JWT project goes ahead, and is not delayed by difficulty with funding.
This observation is out at the limit of what the HST can reliably handle. The authors (Richard Ellis et al) do not actually CLAIM Z=11.9. You have to read what they actually say in their professional article. You can't rely on paraphrases in popular media, by journalists. As I read it, they are cautiously proposing one possible explanation which MIGHT or might not be confirmed for something curious or seemingly inconsistent about their observation. I could be wrong though. Maybe some other PF members here know more about this and can say something more definite.
additional info:
http://arxiv.org/abs/1211.6804v1
published January 2013 in APJ Letters vol 763
http://iopscience.iop.org/2041-8205/763/1
http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1211.6804
Here is the article by Ellis et al as actually published in Astrophysical J. Letters
http://iopscience.iop.org/2041-8205/763/1/L7/pdf/2041-8205_763_1_L7.pdf
You can see in figure 1 that the object DID NOT SHOW UP on the Y and the J filters (the way the other objects did) but it appears to show up on the H filter.

Here is what they say on page 3 near the Figure 1:
==quote==
In summary, only one object claimed to be at z > 8.5 from the earlier UDF09 analysis remains and that is the final J-band dropout presented by Bouwens et al. (2011) at z = 10.3, UDFj-39546284 (≡UDF12-3954-6284 in Table 1). However, its non-detection in the UDF12 F140W data indicates a yet higher redshift of z = 11.9 (Figure 2). The most significant advance of our campaign is a significant increase (from 0 to 6) in the number of robustly determined UDF sources in the redshift range 8.5 < z <10.
2.1. Contamination from Strong Emission Line Sources?
A major motivation for the additional F140W filter in our UDF12 strategy was to ensure the robust detection in two filters of potential 8.5 < z < 11.5 candidates since the flux above 1216 Å would be visible in both filters. This is the case for all but one of our UDF12 candidates (Table 1). A major surprise is the non-detection in F140W of UDFj-39546284, implying a redshift of z = 11.90 (Figures 1 and 2).
Single band detections are naturally less convincing, although UDFj-39546284 is confirmed in F160W sub-exposures through UDF09 and UDF12, leaving no doubt that it is a genuine source. However, an alternative solution must also be carefully considered. …
==endquote==

Maybe one should search for later journal articles which CITE this one, and may have commented, or may have resolved the uncertainty that is evident here.
Here's a later one, which happens to be critical:
http://arxiv.org/abs/1304.4594

 

[bobie]

Thanks for your amazingly detailed and exhaustive reply.
Could you comment the second question:

- if a galaxy could exist before the timeline of 400 million years after the BB

is it the ultimate limit or can we expect to find sometime a more distant galaxy?
and also :
- 13.42*10⁹ is 0.972 the age of the universe, how do we get this from 11.9?

Thanks

 

[marcus]

Hi Bobie, I like the questions you sometimes ask at PF, which start interesting/entertaining discussion, on many different topics!
I am not a cosmologist---just an interested amateur who watches the professional research.
therefore I cannot judge with any confidence the future course of research---I cannot guess what more will be found, or not found, in the future. I will be pleasantly surprised if they find protogalaxies at z>12, but I have absolutely no idea whether they will or will not

You should, I think, get some hands-on experience with the relation between the distance stretch ratio z+1
and the estimated look-back time. This depends on what MODEL-PARAMETERS one puts into the standard cosmic model. From time to time as new data comes in, the cosmologists make slight changes in the preferred model parameters. But they don't change them by much so the estimated age of expansion, and the lookback times change very little---it doesn't really matter.

You will see in my signature, where it says "LightCone", a link to a calculator that makes TABLES of the past and future history of cosmos.

The "stretch factor" S = z+1 is the factor by which distances and wavelengths have been increased since the moment when the light was emitted. If z = 2 that means S = 3, which means that distances and wavelengths are 3 times what they were when the light (which we receive today) was emitted.

You should practice with the calculator, I think. At least a little. If you are interested in z = 11.9, that means S = 12.9 and you can set the upper limit "S_upper" to 12.9 and calculate.

The calculator embodies the standard cosmic model (LambdaCDM).

S=1 corresponds to the PRESENT because there is no enlargement of either wavelengths or distances.

You can change the number of steps, so as to get higher time-resolution, or S-resolution.

You can trim the future part of the table so that it does not go as far as S = 0.01 (that is when distances will be 100 times what they are at present, or present wavelengths and distances will be only 1% what they will be at that distant time in future.
You can set S_lower = 0.5 and only go a little ways into future, or even set S_lower = 1 and eliminate the future from the table entirely.

the default S_upper is 1090 which corresponds to the origin of the CMB, the ancient light of the cosmic microwave background. this is not so good if you are only interested in stars and galaxies. You could change it to 12 and not go so far into the past.

I'm interested in your reaction to this table-making calculator. It was built and put on line by Burt Jordaan, "Jorrie", a retired aerospace engineer who got interested in cosmology.

 

[marcus]

Oh, the cosmological model is based on a differential equation governing the scale factor, called Friedman equation, which is a simplification of the 1915 GR equation where you assume approximate uniformity and just look at things large-scale. You may already know of the Friedman equation, or you can easily look it up on wippy or other. If you start out with a certain density and a certain expansion rate, it tells you how those two things evolve, because expansion will reduce the density and density will slow down expansion, so the two things interact the way things in ordinary diffy equations do, and basically generate curves. And the beauty
is that the Friedman equation model gives a really good fit to the data.
So you give it the present-day density and the present-day expansion rate and a couple of other minor numbers and it will calculate their curves back into the past or forward into future.

Jorrie's calculator will also plot curves as an alternative to making tables of past and future stuff, if you so instruct. There is additional useful information in the "column definition and selection" menu. I hope you try it out a bit, and are pleased, Bobie. I think its a valuable resource.

 

[Tanelorn]

What is the shortest time that our theories say a galaxy this size can form?

 

[jedishrfu]

I saw somewhere that it was about 400 million years based primarily on finding a galaxy that was created 480 million years after the big bang.

Many of the theories don't produce the statistical population of galaxies that we see today:

http://en.wikipedia.org/wiki/Galaxy_formation

 

[marcus]

What is the shortest time that our theories say a galaxy this size can form?

I looked up this particular object that the OP is talking about and it was not consistently categorized as a "galaxy". It was sometimes designated as a "protogalaxy".
Sometimes was referred to as a "source"or an "object". Maybe because they didn't know exactly what to call it.

Protogalaxies of that period tend to consist of a comparatively small number of unusually massive stars, which are hotter and more blue than average stars nowadays. I'm not sure why. Maybe you know, or can find out. Let me know if I am wrong about this.

I don't think they can image this very well, just a fuzzy speck that doesn't even show up on all the filter images. So I'm not sure what "galaxy this size" would mean.

These Early Universe stars that I've heard about can form quickly, on the order of a million years. And they have short lifetimes (massive burn very hot)

There were fairly dense clouds in those days and in a patch of high over density you could get a bunch of these stars forming quickly, I would expect. It's not a "galaxy" in the sense we usually think of.

 

[bobie]

I'm interested in your reaction to this table-making calculator..

Thanks for your nice words, marcus.
The calculator is really great, on the level or even better than Hyperphysics, congrats!

I started practicing with a simple scenario (12.9, 1 and step=1)
T = 372 billion years after BB, less than 400 since it is a protogalaxy, right; but:
R = .56 Gly, D_then = 2.53 Gly, how do I get this value, why is it 5 times greater than R?
then I get D_now = 2.53*12.9 = 32.65 Gly, right?

I have read the tutorial and the user guide, but found no clue to V_{now /then} (the values for S=12.9 are now: 2.27, then: 4.52 c).

As to UDFJ:
I don't know if I overlooked it, but I was asking what is the frequency/wavelength detected (I discovered only that it is in the infrared region [10¹³ hv*12.9?]), and how you conclude that the emitted frequency was 12.9 greater.

Since you followed some of my threads, I suppose you are fully aware that I'll use up all your expertise and patience!

 

[Bill_K]

Protogalaxies of that period tend to consist of a comparatively small number of unusually massive stars, which are hotter and more blue than average stars nowadays. I'm not sure why. Maybe you know, or can find out. Let me know if I am wrong about this.

This article explains in detail why the first stars are thought to have been more massive.

 

[bobie]

and up at the top click "WMAP inputs (2013)". By good fortune the calculator already has that 14.0 figure as one of the two options, so there is nothing you need to type in.

I have updated the calculator, according to marcus's latest instructions, could anyone answer a few questions?

These are the new figures for z=11.9

a=1/S...S ...T (Gy)...R (Gly)...Dnow (Gly).Dthen (Gly)...DHor (Gly) Vnow (c) Vthen (c)
0.078..12.900 0.3786 ..0.5696...32.820...2.544....3.770...2.34...4.47
1.000 1.000 13.7533 13.9999 0.000 0.000......15.792

- 380 million year after BB, the radius of the universe was R = .57 Gly, how can the distance D_then be greater than its diameter: 2.5 > .57*2 D =1.4 Gly?

- the horizon now is 15.8 Gly, how can the radius of the observable universe be set at 46 Gly?
D_hor
"The cosmic event horizon, which is the largest distance (at time of emission) between an emitter and receiver that light can ever bridge. At larger distances, accelerating expansion prevents light from reaching the receiver."

(the comoving distance ..., is about 14.0 billion parsecs (about 45.7 billion light years), while the comoving distance to the edge of the observable universe is about 14.3 billion parsecs (about 46.6 billion light years)
If light cannot reach us beyond 15.8 Gly, is an object at 16 Gly or 46.6 Gly observable?

Thanks

-

 

[Chronos]

You are dealing with two different issues here. The CMB photons we currently observed were emitted 380,000 years after the big bang at z=1090 from what is called the surface of last scattering. Those photons required about 14 billion years to reach earth, even though the surface of last scattering was only about 42 million light years distant at the instant those photon were emitted. If that surface were to emit photons 'now', it would be from a distance of 46 billion light years and they would never reach us. It has receded beyond our horizon. The article by Davis & Lineweaver, Expanding Confusion, explains all of this. The long and short of it is anything with a redshift greater than about 1.7 has receded beyond our cosmological horizon and any photons emitted 'now' will never reach us.

 

[marcus]

If light cannot reach us beyond 15.8 Gly, is an object at 16 Gly or 46.6 Gly observable?
...

Whatever objects we observe are always seen as they were in past. Whatever MATTER we can observe is seen today as it was in the past.
So 46 Gly is the radius of the observable region. It is the distance today of the most distant matter which we are able to observe today (as it was, of course, a long time ago.)

The figure of 15 or 16 Gly is something entirely different from that. It is called cosmological event horizon. it is the distance today of the farthest galaxy which TODAY could send us a message (which would eventually get here) telling us about how it is TODAY.
It is, reciprocally of course, the farthest galaxy which we could reach by sending a message today, a flash of light, say, which would eventually get there.

Oh, I see Chronos already answered! Probably I am just duplicating his response, but I'll leave it anyway in case it adds a little clarity.

 

[marcus]

This article explains in detail why the first stars are thought to have been more massive.

Thanks again! This article makes it very clear why the first stars had to be so massive. A contracting cloud has to radiate away excess energy as heat. Hydrogen molecules are not as efficient as, say CO or CO2. So only the really massive clouds had strong enough gravity to contract down to stars. they had to fight their own tendency to heat up, given their less efficient means of shedding excess energy. I like the writing, so I'll quote an excerpt
==quote Sci Am http://www.scientificamerican.com/article/the-first-stars-in-the-un/ ==
The simulations show that the primordial gas clouds would typically form at the nodes of a small-scale filamentary network and then begin to contract because of their gravity. Compression would heat the gas to temperatures above 1,000 kelvins. Some hydrogen atoms would pair up in the dense, hot gas, creating trace amounts of molecular hydrogen. The hydrogen molecules would then start to cool the densest parts of the gas by emitting infrared radiation after they collide with hydrogen atoms. The temperature in the densest parts would drop to about 200 to 300 kelvins, reducing the gas pressure in these regions and hence allowing them to contract into gravitationally bound clumps.

This cooling plays an essential role in allowing the ordinary matter in the primordial system to separate from the dark matter. The cooling hydrogen settles into a flattened rotating configuration that is clumpy and filamentary and possibly shaped like a disk. But because the darkmatter particles would not emit radiation or lose energy, they would remain scattered in the primordial cloud. Thus, the star-forming system would come to resemble a miniature galaxy, with a disk of ordinary matter and a halo of dark matter. Inside the disk, the densest clumps of gas would continue to contract, and eventually some of them would undergo a runaway collapse and become stars.

The first star-forming clumps were much warmer than the molecular gas clouds in which most stars currently form. Dust grains and molecules containing heavy elements cool the present-day clouds much more efficiently to temperatures of only about 10 kelvins. The minimum mass that a clump of gas must have to collapse under its gravity is called the Jeans mass, which is proportional to the square of the gas temperature and inversely proportional to the square root of the gas pressure. The first star-forming systems would have had pressures similar to those of present-day molecular clouds. But because the temperatures of the first collapsing gas clumps were almost 30 times higher than those of molecular clouds, their Jeans mass would have been almost 1,000 times larger.

In molecular clouds in the nearby part of the Milky Way, the Jeans mass is roughly equal to the mass of the sun, and the masses of the prestellar clumps observed in these clouds are about the same. If we scale up by a factor of almost 1,000, we can estimate that the masses of the first star-forming clumps would have been about 500 to 1,000 solar masses. In agreement with this prediction, all the computer simulations mentioned above showed the formation of clumps with masses of several hundred solar masses or more...
==endquote==

There's more good stuff there, this is just a sample.

 

[bobie]

These are the new figures for z=11.9

a=1/S...S ...T (Gy)...R (Gly)...Dnow (Gly).Dthen (Gly)...DHor (Gly) Vnow (c) Vthen (c)
0.078..12.900 0.3786 ..0.5696...32.820...2.544....3.770...2.34...4.47

- 380 million year after BB, the radius of the universe was R = .57 Gly, how can the distance D_then be greater than its diameter: 2.5 > .57*2 D =1.4 Gly?-

You are dealing with two different issues here. .

Thanks Chronos,
In the case of UDFJ the light was sent at 0.3786 Gy after BB, when the radius of the universe was 0.5696 Gly, the maximum distance between two object at that time could be 2*.57 = 1.14 Gly
The calculator says the distance then was 2.5 Gly. What does that mean?

 

[marcus]

Thanks Chronos,
In the case of UDFJ the light was sent at 0.3786 Gy after BB, when the radius of the universe was 0.5696 Gly, the maximum distance between two object at that time could be 2*.57 = 1.14 Gly
The calculator says the distance then was 2.5 Gly. What does that mean?

In the calculator output there is a column labeled R which gives the Hubble radius.
This is not the radius of the universe!
R is the distance which at that time is growing at the speed of light.

Hi Bobie! I'm glad to see you tried out the calculator. Sorry that you got puzzled by not understanding what R is.

You found that at time .3786 Gy the distance R was 0.57 Gly.

that distance was growing at speed c

the distance 1.14 Gly was growing at speed 2c

the distance 1.71 Gly was growing at speed 3c

When you go to the calculator you can see these blue dots around on it, next to things. Move the mouse so as to put the cursor over one of the blue dots and you get some information.

there is also a button that says "column selection and definition". If you click that, you get a menu for selecting other columns to put in the table and there are more blue dots that can give information about what the columns mean.