Timeline for Hydrostatic Equilibrium in Galaxy Clusters
Current License: CC BY-SA 3.0
18 events
| when toggle format | what | by | license | comment | |
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| Nov 26, 2015 at 9:16 | history | edited | ProfRob | CC BY-SA 3.0 |
recent literature
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| Nov 9, 2015 at 7:46 | history | edited | ProfRob | CC BY-SA 3.0 |
Added new work plus reference.
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| Oct 22, 2015 at 16:21 | comment | added | user32023 | You asked why would gas rotate differently than the galaxies. Here's a quote from the Hwang and Lee document: "According to off-axis merging models, the global rotation of “collisional” ICM originated by merging survives longer than that of “collisionless” galaxies in clusters (Roettiger & Flores 2000). Therefore, it is expected that it is more difficult to detect the global rotation of galaxies than that of ICM". FWIW. | |
| Oct 20, 2015 at 12:26 | comment | added | user32023 | I want to make sure I'm interpreting these results correctly. When you say 'almost 1', we're talking about a disagreement between $M_{x}$ and $M_{wl}$ between 55% and 172%. And there's the assumption of dark matter, so we're talking about 55% to 172% of roughly $1 \times 10^{15} M_{⊙}$? Is that right? | |
| Oct 20, 2015 at 6:40 | comment | added | ProfRob | @DonaldRoyAirey There is a scatter and an uncertainty (mainly I think) in the X-ray masses. The average ratio is almost 1, indicating no huge systematic effects. Individual clusters can be discrepant, or is this just underestimated uncertainties? Hydrostatic inequilibrium should only push it one way, but there are discrepancies either way. I don't dismiss Peng's result. But it is one result. | |
| Oct 20, 2015 at 0:34 | comment | added | user32023 | @RobJefferies I read through Molnar et al (2010) again and you seem to dismiss it for reasons I don't understand. He performs modeling and then tests his model on A1689. How is this process any less valid than the method of Zhang when it comes to establishing whether Hydrostatic Equilibrium is a valid assumption for Galaxy Clusters? | |
| Oct 19, 2015 at 22:27 | comment | added | user32023 | I just got through reading Zhang. I'm not sure I understand from where your earlier statistic of 10% comes. The $M_{x}/M_{wl}$ ratio of 0.55 to 1.72 is, to my eye, a lot. If a hydrostatic equilibrium calculates a mass of $1 \times 10^{15}$, then a weak lens can calculate a mass of $5.5 \times 10^{14}$ to $1.72 \times 10^{15}$? What am I missing? | |
| Oct 19, 2015 at 21:46 | comment | added | user32023 | @RobJeffereis What makes you think this is a contest? I'm exchanging information. That's my point. | |
| Oct 19, 2015 at 21:43 | comment | added | ProfRob | @DonaldRoyAirey The result is from Peng et al. (2009), Molnar did some modelling. Zhang et al. (2010) studied a large sample, finding $M_{lens}/M_{x}$ varied from about 0.5-1.5. Not sure what your point is. | |
| Oct 19, 2015 at 20:59 | comment | added | user32023 | Molnar et al (2013) arxiv.org/pdf/1002.4691.pdf have found significant differences between the gravitational lensing and the mass derived hydrostatic equilibrium assumptions in A1689. | |
| Oct 15, 2015 at 17:23 | comment | added | ProfRob | @DonaldRoyAirey If so, there would be a clear discrepancy between total masses derived from the gas profile, gravitational lensing or the galaxy velocity dispersions. This is part of my answer. | |
| Oct 15, 2015 at 15:48 | comment | added | user32023 | I'm not (even close to) an expert on hierarchical evolution, that's why I'm asking the question. I guess the one idea I had is that a couple of core galaxies form the gravitational well, the gas is drawn into the well, additional proto-galaxies are drawn in, repeat until the present time. The gas would have the average angular velocity where the galaxies with have a random trajectory. | |
| Oct 15, 2015 at 14:13 | comment | added | ProfRob | @DonaldRoyAirey The galaxies formed from/in the gas. Why would they rotate differently? Or to put it another way, what torques do you think act on the gas? Again - the comparison between virial masses from the galaxies and total lensing mass is excellent. | |
| Oct 15, 2015 at 14:08 | comment | added | user32023 | "Instead of directly looking at the gas we could look to the galaxies in clusters for evidence of rotation." Is there any rule that says the galaxies must follow the gas? We're talking about densities that are still close to a vacuum (~$10^{-27} cm^{-3}$). | |
| Oct 15, 2015 at 13:47 | comment | added | user32023 | "The agreement was within 10%" - I can't remember where I read it, but wasn't there a problem with the weak lensing contours in that they were far to concentrated in the center to match up with a NFW Dark Matter halo? That is, the total numbers were in good agreement, but the contours were way off. | |
| Oct 14, 2015 at 10:19 | vote | accept | CommunityBot | ||
| Oct 14, 2015 at 10:11 | history | edited | ProfRob | CC BY-SA 3.0 |
Much more detail and references
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| Oct 14, 2015 at 6:47 | history | answered | ProfRob | CC BY-SA 3.0 |