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Cosmography of the local Universe
The video "Cosmography of the local Universe" gives a very impressive
view of the positions and peculiar velocities in the neighborhood of the Milky way. See http://vimeo.com/64868713# and http://arxiv.org/abs/1306.0091 In this last document there is the sentence: "Detailed maps of motions are inputs to the translation from redshift space to physical space and constrain the underlying distribution of (mostly dark) matter. " How do they know that most of the matter in our local Universe is dark matter? If someone explain to me the following sentence: "We measure crude three-dimensional (3D) locations from their systematic velocities and sky positions (distorted from true positions by peculiar velocities)" this would be helpful. Next is written: " and we can estimate their baryonic masses from their luminosities. Unfortunately this information degrades with distance and can be lacking in regions of heavy obscuration. In the case of redshift surveys, low luminosity galaxies are mostly lost etc" What this means is that lots of ordinary matter is not observed. Which is true but again does not indicate that there is dark matter involved. Nicolaas Vroom http://users.pandora.be/nicvroom/ |
#2
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Cosmography of the local Universe
In article , Nicolaas Vroom
writes: "Detailed maps of motions are inputs to the translation from redshift space to physical space and constrain the underlying distribution of (mostly dark) matter. " How do they know that most of the matter in our local Universe is dark matter? Probably from the several hundred, if not several thousand, papers on dark matter in the last 40 years or so. If someone explain to me the following sentence: "We measure crude three-dimensional (3D) locations from their systematic velocities and sky positions (distorted from true positions by peculiar velocities)" this would be helpful. Measuring the position on the sky is easy. Measuring a distance is difficult. One can measure the redshift, but that corresponds to a distance only if one knows the cosmological model and if the cosmological redshift is much greater than that due to the peculiar velocity. In the local universe, this is not the case. Lookup " redshift-space distortions". Next is written: " and we can estimate their baryonic masses from their luminosities. Unfortunately this information degrades with distance and can be lacking in regions of heavy obscuration. In the case of redshift surveys, low luminosity galaxies are mostly lost etc" What this means is that lots of ordinary matter is not observed. Which is true but again does not indicate that there is dark matter involved. Again, there are many, many, many papers on dark matter in the local universe. |
#3
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Cosmography of the local Universe
Op dinsdag 17 december 2013 09:21:26 UTC+1 schreef Phillip Helbig:
In article , Nicolaas Vroom writes: How do they know that most of the matter in our local Universe is dark matter? Probably from the several hundred, if not several thousand, papers on dark matter in the last 40 years or so. I agree. But they should demonstrate dark matter based on observations. The issues involved becomes clear by studying the next sentence: The simple question can be asked if the distribution of observed galaxies and the distribution of matter inferred from galaxy motions agree. They should, if galaxies are reasonable tracers of the ensemble of matter, and if our procedures are valid for the interpretation of motions in terms of the matter distribution. The matter inferred from galaxy motions should include both vissible and darkmatter. If there is agreement then there is no dark matter involved. Measuring the position on the sky is easy. Measuring a distance is difficult. One can measure the redshift, but that corresponds to a distance only if one knows the cosmological model and if the cosmological redshift is much greater than that due to the peculiar velocity. In the local universe, this is not the case. Lookup " redshift-space distortions". See: http://astro.berkeley.edu/~mwhite/te...ni_red_mjw.pdf Part of my misunderstanding comes from using the words measuring and calculating. If a certain physical law uses the equation a * b = c than a and b are measured and c is calculated. (of course a could also be calculated) As such I would say: Calculating a distance is difficult. Next is written: " and we can estimate their baryonic masses from their luminosities. Unfortunately this information degrades with distance and can be lacking in regions of heavy obscuration. In the case of redshift surveys, low luminosity galaxies are mostly lost etc" What this means is that lots of ordinary matter is not observed. Which is true but again does not indicate that there is dark matter involved. Again, there are many, many, many papers on dark matter in the local universe. I agree, but in this whole paper the concept of darkmatter is not discussed. The starting sentence of the document reads: "The large scale structure of the universe is a complex web of clusters, filaments, and voids. " This should be: "etc of clusters, filaments, voids and darkmatter." IMO if 85% of matter in the the universe is darkmatter than this should be mentioned or are the authors of this document of the opinion that this amount is much lower? A different opinion is that darkmatter is closely linked within the galaxies and that there is no darkmatter outside the galaxies specific not in the voids. This is just a guess. Nicolaas Vroom http://users.pandora.be/nicvroom/ |
#4
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Cosmography of the local Universe
In article ,
Nicolaas Vroom writes: But they should demonstrate dark matter based on observations. The video http://vimeo.com/64868713# described at http://arxiv.org/abs/1306.0091 is an _illustration_ of current knowledge of galaxy positions, masses, and motions. It isn't meant to demonstrate dark matter, though as far as I can tell, the results are consistent with the standard dark matter picture. In particular, galaxies exist preferentially where dark matter is densest. The matter inferred from galaxy motions should include both vissible and darkmatter. If there is agreement then there is no dark matter involved. That second sentence seems to have an extra "no" in it, but the first sentence is a misunderstanding. The video shows the _observed_ motions based on observations and with statistical corrections for galaxies that cannot be observed because they are too faint or are in the zone of avoidance. I didn't see a direct comparison with the expected motions based on dark matter models, but there seems to be at least qualitative agreement. Observed flows towards the Great Attractor, for example, are larger than can be accounted for by visible matter in that direction. (That statement doesn't come from the video but rather from previous work.) Part of my misunderstanding comes from using the words measuring and calculating. There's no real difference in practice. Be aware that the video makes use of velocity-independent distances in order to measure (or calculate, if you like) the peculiar velocities. The starting sentence of the document reads: "The large scale structure of the universe is a complex web of clusters, filaments, and voids. " This should be: "etc of clusters, filaments, voids and darkmatter." Or perhaps "...observed large scale structure...." -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#5
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Cosmography of the local Universe
In article , Nicolaas Vroom
writes: Op dinsdag 17 december 2013 09:21:26 UTC+1 schreef Phillip Helbig: In article , Nicolaas Vroom writes: How do they know that most of the matter in our local Universe is dark matter? Probably from the several hundred, if not several thousand, papers on dark matter in the last 40 years or so. I agree. But they should demonstrate dark matter based on observations. The issues involved becomes clear by studying the next sentence: The simple question can be asked if the distribution of observed galaxies and the distribution of matter inferred from galaxy motions agree. They should, if galaxies are reasonable tracers of the ensemble of matter, and if our procedures are valid for the interpretation of motions in terms of the matter distribution. The matter inferred from galaxy motions should include both vissible and darkmatter. If there is agreement then there is no dark matter involved. Yes. But I don't see any contradiction. By definition, dark matter is not "observed" and historically it was the fact that the observation of the motions of (parts of) galaxies don't correspond to the matter which can be directly inferred from the luminous stuff observed which led to the dark-matter idea. If a certain physical law uses the equation a * b = c than a and b are measured and c is calculated. (of course a could also be calculated) As such I would say: Calculating a distance is difficult. Well, in some sense, all one really measures are counts from a CCD as a function of position. Everything else is calculation. The starting sentence of the document reads: "The large scale structure of the universe is a complex web of clusters, filaments, and voids. " This should be: "etc of clusters, filaments, voids and darkmatter." Dark matter is presumably included in the clusters and filaments. |
#6
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Cosmography of the local Universe
Op donderdag 19 december 2013 09:58:11 UTC+1 schreef Phillip Helbig:
In article , Nicolaas Vroom writes: The matter inferred from galaxy motions should include both vissible and darkmatter. If there is agreement then there is no dark matter involved. This last sentence should be: If there is agreement between the distribution of observed galaxies and the distribution of matter inferred from galaxy motions then there is no dark matter involved. Yes. But I don't see any contradiction. By definition, dark matter is not "observed" directly but could be inferred indirectly via observed motions. and historically it was the fact that the observation of the motions of (parts of) galaxies don't correspond to the matter which can be directly inferred from the luminous stuff observed which led to the dark-matter idea. Corect. But you have to be carefull to first include all low intensity luminous matter and all invisible baryonic matter. It is even possible inpriciple that there is enough baryonic matter in galaxies to explain flat galaxy rotation curve and that no darkmatter is required. 85% of all matter in the Universe is darkmatter. I expect that the amount of darkmatter in galaxies is lower. If that is the case than the amount of darkmatter outside galaxies is even higher than 85% This huge amount should be discussed because it influences the galaxy motions and galaxy clusters. |
#7
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Cosmography of the local Universe
Op donderdag 19 december 2013 09:57:12 UTC+1 schreef Steve Willner:
In article , Nicolaas Vroom writes: But they should demonstrate dark matter based on observations. The video etc isn't meant to demonstrate dark matter, They should include a discussion about darkmatter because 85% of all matter is darkmatter The matter inferred from galaxy motions should include both vissible and darkmatter. If there is agreement then there is no dark matter involved. The last sentence should be: If there is agreement between the distribution of observed galaxies and the distribution of matter inferred from galaxy motions, then there is no dark matter involved. The issue is that both visible matter and darkmatter influence the motion of galaxies. If visible matter agrees with the motions than there is no darkmatter in the universe. This result should be discussed in the document, because it is remarkable. In fact you can go two paths: 1 Based on the observed_motions you can calculate the mass responsible for these motions and compare this calculated mass with the observed_mass 2 Based on the observed_matter in the universe you can calculate the motions and compare them with the observed_motions. This is a very difficult exercise. I tried to do discuss this in the newsgroup sci.physics.research. (#1 is also not easy because the distribution of this mass has to be calculated. Ofcourse you can assume that the distribution of all mass is identical as the distribution of visible matter, but that solution is too simple) That second sentence seems to have an extra "no" in it, but the first sentence is a misunderstanding. The video shows the _observed_ motions based on observations and with statistical corrections for galaxies that cannot be observed because they are too faint or are in the zone of avoidance. That is correct but I think what you mean are calculated motions. And IMO these calulations should include darkmatter. Observed flows towards the Great Attractor, for example, are larger than can be accounted for by visible matter in that direction. This demonstrates my point. To explain this you need more baryonic or nonbaryonic matter (or both) Nicolaas Vroom http://users.pandora.be/nicvroom/ |
#8
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Cosmography of the local Universe
Op vrijdag 20 december 2013 20:37:41 UTC+1 schreef Nicolaas Vroom:
Op donderdag 19 december 2013 09:57:12 UTC+1 schreef Steve Willner: Observed flows towards the Great Attractor, for example, are larger than can be accounted for by visible matter in that direction. This demonstrates my point. To explain this you need more baryonic or nonbaryonic matter (or both) In order to investigate what other authors had to say specific about nonbaryonic in our local universe I read the following documents: 1) Formation and rotation of disc galaxies with halos (1980) http://articles.adsabs.harvard.edu/f...NRAS.193..189F 2) a revised model for the formation of disk galaxies: Low spin and dark halo expansion. (2007) http://iopscience.iop.org/0004-637X/...X_654_1_27.pdf 3) The Extragalactic Distance Database: all digital Hi profile catalog http://iopscience.iop.org/1538-3881/...138_6_1938.pdf 4) Cosmic Flows surveys and CLUES simulations http://arxiv.org/pdf/1205.4627.pdf 5) The mid-infrared Tully-Fisher Relation: calibration of the SNIa scale and H0 http://arxiv.org/pdf/1208.3311.pdf 6) Anatomy of Ursa Majoris http://arxiv.org/pdf/1211.5975.pdf 7) http://arxiv.org/abs/1303.5328 by Igor Karachentsev, 8) http://arxiv.org/abs/1306.0091 Cosmography of the Local Universe For a detailed evalution see the following document: http://users.telenet.be/nicvroom/fri...20age.htm#Ref1 My conclusion is that the scientists who study the local universe and the evolution of galaxies dark matter in the form of nonbaryonic matter is not mentioned. Specific nowhere you can read that 85% of the matter in any galaxy should be nonbaryonic. That does not mean that the issue of dark matter related towards the evolution of galaxies is not discussed, but this dark matter is always considered invisible baryonic matter in the form of gas, A different situation arises if you study WMAP date. Only in these studies related to CMB radiation the concept of non-baryonic matter is considered. Their conclusion is that 85% of all matter in the universe should be nonbaryonic. This number is very high specific if you want to explain flat galaxy rotation curves. Nicolaas Vroom |
#9
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Cosmography of the local Universe
Op zondag 2 februari 2014 08:49:41 UTC+1 schreef Nicolaas Vroom:
Op vrijdag 20 december 2013 20:37:41 UTC+1 schreef Nicolaas Vroom: Op donderdag 19 december 2013 09:57:12 UTC+1 schreef Steve Willner: Observed flows towards the Great Attractor, for example, are larger than can be accounted for by visible matter in that direction. This demonstrates my point. To explain this you need more baryonic or nonbaryonic matter (or both) In order to investigate what other authors had to say specific about nonbaryonic in our local universe I read the following documents: 8) http://arxiv.org/abs/1306.0091 Cosmography of the Local Universe For a detailed evalution see the following document: http://users.telenet.be/nicvroom/fri...20age.htm#Ref1 In Scientific American of March 2014 there is an article about the same subject. For a review select: http://users.telenet.be/nicvroom/Sci...rch%202014.htm Two more documents are interesting: 1) http://arxiv.org/abs/1307.6210 23 July 2013 2) http://arxiv.org/abs/1309.1159 4 Sept 2013 Specific the second one is interesting which claims that it is very difficult to simulate the dwarf galaxies of the Milky way in the way they actual are (aligned in a plane) What makes such a simulation difficult is non-baryonic dark matter in the halo of the Milky way galaxy. Such a halo is required to solve the missing matter problem or better: the flat galaxy rotation curve issue. IMO this leaves only one solution possible: to allow for more invisible baryonic matter in the disc. Nicolaas Vroom. |
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