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#21
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Beyond IDCS J1426.5+3508
In article , Eric Flesch
writes: On Sun, 01 Jul 12, Phillip Helbig wrote: How probable is it that the Moon and the Sun have the same angular size? Possibly close to 1, due to the anthropic principle: such a moon may have been needed to give the Earth tectonic and rotational stability across epochs, else we wouldn't have evolved to be discussing it. Isaac Asimov pointed out in an essay called "The Triumph of the Moon" (collected in the book THE TRAGEDY OF THE MOON, which contains an essay by the same name) that the fact that the Moon is large in relation to the Earth (compared to the ratios for other planets and moons) might have an anthropic explanation. However, this cannot explain the nearly perfect coincidence in size. (Also consider that, since the Moon is moving away from the Earth, the coincidence holds only for a relatively short time during the history of the Earth.) |
#22
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Beyond IDCS J1426.5+3508
In article , Phillip
Helbig---undress to reply writes: One needs to interpret such rare objects properly. See recent work by Ian Harrison and Peter Coles on extreme-value statistics in cosmology: http://telescoper.wordpress.com/2011...-the-universe/ Note that Peter Coles criticizes the Gonzalez et al. paper on other grounds: http://telescoper.wordpress.com/2012...d-peer-review/ |
#23
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Beyond IDCS J1426.5+3508
In article ,
Jos Bergervoet writes: OK, in Fig. 1 there, 4 to 5E14 Msun at this redshift seems to be right at the expected largest mass seen. Excellent fit! The paper in question (Harrison and Coles 2012 MNRAS 421, L19) can be located via http://adsabs.harvard.edu/abs/2012MNRAS.421L..19H The worry is that the curve is for the whole sky, while our surveys have so far covered only a small fraction of the sky. We might just have been lucky, but maybe there's something we don't have quite right just yet. Of course tweaking some parameters or attributing unexpected properties to dark matter is a very long way from throwing out the whole Big Bang/lambda-CDM model. And even minor tweaking on this basis is premature at the moment. There is a real problem, however, with the 775 nm magnitude of the lensed source. Even with lensing, it's too bright for the population of known z3 objects. Do we also have statistical expectation curves for this? Like the one above, but for any luminous object at this higher z, and then combined with the probability of it being lensed? A somewhat complicated combination of probability distributions seems to be needed here, apparently shown in Fig. 3 in the preprint: http://arxiv.org/abs/1205.3788 As you say, Fig 3 tells the story. The calculation is complicated because it has to take into account all possible redshifts 1.75 and all possible alignments between the lensing cluster and the background galaxy. The alignment affects the magnification, which means one is looking for a different intrinsic magnitude at each possible alignment and redshift. There is additional uncertainty because the lens mass distribution is poorly known. What Fig 3 says, though, is that _based on known populations_ of z 1.75 objects, the observed 775 nm magnitude of the lensed object is wildly improbable. Either the authors' calculation is wrong (and I haven't checked it) or based on incorrect data, or there is a hitherto unknown population of high-z galaxies, or something is wrong with the cosmology. I wouldn't bet very much on the third of these. (And maybe there are other possibilities I'm missing.) As I wrote earlier, it will be interesting to see how this plays out. The figure seems to show quite some uncertainty (the two curves plotted are quite different) The curves are for two different wavelengths, 1600 and 775 nm. (The notation is somewhat obscure; it refers to HST filters.) The 1600 nm magnitude is a bit surprising but within range of reasonable uncertainties. The 775 nm magnitude is way out of range. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#24
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Beyond IDCS J1426.5+3508
Le 26/06/12 22:11, jacob navia a ecrit :
[snip] That cluster could be "explained away". Tomorrow there is an announcement by NASA that seems to have discovered a new one, even further away! Interesting times... |
#25
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Beyond IDCS J1426.5+3508
On Aug 14, 9:12*pm, jacob navia wrote:
Le 26/06/12 22:11, jacob navia a ecrit : [snip] That cluster could be "explained away". Tomorrow there is an announcement by NASA that seems to have discovered a new one, even further away! Interesting times... Just consider the following question every time you see something really far away, but prior to being so surprised: "At what point should the universe have developed?" Have an open mind. |
#26
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Beyond IDCS J1426.5+3508
Le 15/08/12 04:12, jacob navia a écrit :
Le 26/06/12 22:11, jacob navia a ecrit : [snip] That cluster could be "explained away". Tomorrow there is an announcement by NASA that seems to have discovered a new one, even further away! Interesting times... False alarm,sorry. That announcement was about the Phoenix cluster, "just" 5 Billion years away. |
#27
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Beyond IDCS J1426.5+3508
Le 16/08/12 06:17, Eric Gisse a écrit :
On Aug 14, 9:12 pm, jacob navia wrote: Le 26/06/12 22:11, jacob navia a ecrit : [snip] That cluster could be "explained away". Tomorrow there is an announcement by NASA that seems to have discovered a new one, even further away! Interesting times... Just consider the following question every time you see something really far away, but prior to being so surprised: "At what point should the universe have developed?" Have an open mind. I do not understand your point. What does it mean "At what point should the universe have developed" makes no sense to me. Personally I doubt that a half animal species, that has never went beyond the cradle of his little planet can say something about "the universe". We have always had a "theory of the universe" since we left the caves we used to live in. And it was always wrong, as we learned when we observed a little bit more of it. This time is no different. But in any case the announcement of NASA didn't concern cosmology but astronomy, two separate fields. The Phoenix cluster looks special, its central black hole can't keep matter falling into its center and is building stars at a prodigious rate. So, I was jumping to conclusions, something I should avoid because I do want to keep an open mind. |
#28
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Beyond IDCS J1426.5+3508
On 7/1/12 3:00 AM, Phillip Helbig---undress to reply wrote:
In article , "Richard D. Saam" writes: How about framing the question in terms of a more defined Supernovae Type 1a standard candle condition. Use the distance modulus equation: m-M = 5 log(d) - 5 then d = 10^((m-M)/5 - 1) From Supernovae compilation http://supernova.lbl.gov/Union/figur....1_mu_vs_z.txt the current maximum Type 1A redshift 2003dy z = 1.34 m-M = 45.0675055813 d = 10^((m-M)/5 - 1) = 1.03E+08 parsec or 3.18E+26 cm I haven't checked the actual numbers, but OK so far. This is about 2.5 percent of the present universe First, note that the distance involved is the luminosity distance. There is little point in expressing this in terms of the radius of the universe. luminosity distance is a distance measured by luminosity but a distance is a distance and a function of z. It is understood that universe radius is subject to the particular model used and can be expressed as a function of z A model can be used wherein the Hubble sphere expands at c assuming expansion from the Big Bang at the speed of light c/H = 1.30E+28 cm Not sure what you mean here. The speed of light is not a limiting factor for the expansion of the universe. The speed of light is not in the general view a limiting factor for the expansion of the universe but this view does not negate the possibility that it is. If z=1.34, then the universe is 2.34 times larger now than when the light was emitted. This is independent of the cosmological model. In the limited view, one could consider that 2.34 larger based on speed of light So why does type 1A 2003dy standard candle redshift (z=1.34) represent a condition within ~2.5% of the Big Bang with its z in the thousands and probably much greater? I do not understand this. What does the "z in the thousands" mean? "z in the thousands" in the context that the first light was at z~1000 |
#29
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Beyond IDCS J1426.5+3508
In article , "Richard D. Saam"
writes: From Supernovae compilation http://supernova.lbl.gov/Union/figur....1_mu_vs_z.txt the current maximum Type 1A redshift 2003dy z = 1.34 m-M = 45.0675055813 d = 10^((m-M)/5 - 1) = 1.03E+08 parsec or 3.18E+26 cm I haven't checked the actual numbers, but OK so far. This is about 2.5 percent of the present universe First, note that the distance involved is the luminosity distance. There is little point in expressing this in terms of the radius of the universe. luminosity distance is a distance measured by luminosity but a distance is a distance and a function of z. Right. However, what does it mean that it is 2.5 percent of the present universe? What is the luminosity distance to z=infinity? (Hint: much larger than the speed of light times the age of the universe.) Yes, one can express it as a percentage, but the question is whether this is useful. It is understood that universe radius is subject to the particular model used and can be expressed as a function of z OK. A model can be used wherein the Hubble sphere expands at c Yes, although this doesn't correspond to our universe. So why does type 1A 2003dy standard candle redshift (z=1.34) represent a condition within ~2.5% of the Big Bang with its z in the thousands and probably much greater? Because you are confusing different types of distance and because distance is a non-linear function of redshift. |
#30
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Beyond IDCS J1426.5+3508
On 9/10/12 7:18 PM, Phillip Helbig---undress to reply wrote:
Right. However, what does it mean that it is 2.5 percent of the present universe? What is the luminosity distance to z=infinity? (Hint: much larger than the speed of light times the age of the universe.) Yes, one can express it as a percentage, but the question is whether this is useful. Yes in the conventional view, luminosity distance to z=infinity is much larger than speed of light times the age of the universe. This points to an error in concept. What is a non linear distance function of redshift such that distance approaches speed of light times the age of the universe as redshift approaches infinity? [Mod. note: quoted text trimmed -- mjh] |
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