Timeline for Gas Mass Calculation in Galaxy Cluster
Current License: CC BY-SA 3.0
14 events
| when toggle format | what | by | license | comment | |
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| Oct 15, 2015 at 11:47 | vote | accept | CommunityBot | ||
| Oct 12, 2015 at 21:00 | comment | added | user32023 | You have indeed given me all the ingredients. It took a little while to pound them into shape with a spreadsheet. The critical thing was the stupid Hubble scaling factors. Once I got a handle on that the numbers started falling into place. Thank you! | |
| Oct 12, 2015 at 13:22 | comment | added | Pulsar | @DonaldRoyAirey No, I don't mean 5.44 Mpc, I don't know where you got that number from. And Briel et al give the total mass and the gas fraction in the abstract of their paper, in terms of $h_{50}$. I've given you all the ingredients, so I'm going to stop the conversation at this point. | |
| Oct 12, 2015 at 13:03 | comment | added | user32023 | At the edges of this galaxy cluster, we have a roughly 50/50 mix of baryons and DM. Doesn't that fly in the face of the ΛCDM where the mix is supposed to be something like 1/6? | |
| Oct 12, 2015 at 12:52 | comment | added | user32023 | Did you mean 5.44 Mpc? | |
| Oct 12, 2015 at 12:45 | history | edited | Pulsar | CC BY-SA 3.0 |
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| Oct 12, 2015 at 12:31 | comment | added | Pulsar | @DonaldRoyAirey The virial radius is the radius at which the total density drops below $200\rho_c$, not just the gas density; the cluster extends far beyond this radius. Anyway, $\rho_c = 4.69\times 10^{-33}h_{50}^2\,\text{kg}\,\text{cm}^{-3}$. You'll find that, if $h_{50}=1$, $n_e(r)$ is equal to $200\rho_c$ at $r=0.82\,\text{Mpc}$. | |
| Oct 12, 2015 at 11:47 | comment | added | user32023 | It's the density that determines the boundary of the cluster. We define the boundary of the cluster when the density has dropped below 200 times the critical density of the universe. According to this function, it never gets to this point and extends forever like a solid. I was hoping you could answer my question: what kind of a gas acts like this? | |
| Oct 12, 2015 at 9:49 | comment | added | Pulsar | @DonaldRoyAirey The density profile is only valid within a certain radius, where the gas is isothermal and in thermal equilibrium. At the outer edges of the cluster, this will no longer be the case, and the density will drop off rapidly. So you cannot extrapolate this density profile to larger radii, beyond what has been observed. | |
| Oct 12, 2015 at 9:43 | comment | added | Pulsar | @DonaldRoyAirey The value 0.42 Mpc is given in the first paragraph on page L33 in Briel et al. I've added an explicit calculation to my post. | |
| Oct 12, 2015 at 9:42 | history | edited | Pulsar | CC BY-SA 3.0 |
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| Oct 12, 2015 at 1:42 | comment | added | user32023 | Actually, no, we don't agree on the numbers. How did you get 0.42 Mpc for a core radius? At 99 Mpc, that number should be about 0.22 Mpc (for 10.5 arcmin). Would you mind showing me how you calculated this value? | |
| Oct 12, 2015 at 1:02 | comment | added | user32023 | Thank you very much for the derivation. It's far more detailed than the papers I found which seemed to take these steps as implicit. Anyway, we agree on the formula for mass and, approximately, the number for the density. My point is that this formula describes a solid. If you double the radius (10 Mpc) you triple the mass (6.8 e14 M⊙). What kind of a gas works like that? | |
| Oct 11, 2015 at 22:06 | history | answered | Pulsar | CC BY-SA 3.0 |