How to convert between different mass measurements for CDM H

Click For Summary

Discussion Overview

The discussion revolves around the conversion of cluster mass measurements from M_500c to M_200c, particularly in the context of relating these masses to velocity dispersion. The conversation includes theoretical considerations and practical implications of using different mass definitions based on the NFW profile.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant seeks to convert cluster mass from M_500c to M_200c to relate it to velocity dispersion, noting that the existing relation is defined in terms of M_200c.
  • Other participants question the need for conversion and seek clarification on the purpose of the conversion.
  • Some participants provide insights into the definitions of M_500 and M_200, indicating that M_500 is the mass within R_500 and M_200 is the mass within R_200, with R_500 being approximately 0.7 times R_200.
  • There is a suggestion that it might be simpler to convert the relation between mass and dispersion to M_500 instead of M_200.
  • One participant expresses a desire to follow a specific methodology from a paper, indicating a preference for replicating established results.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best approach to the conversion or the necessity of it. Multiple viewpoints regarding the conversion process and its implications remain present.

Contextual Notes

The discussion highlights the dependence on the NFW profile and the specific definitions of mass within different radii, which may affect the conversion process. There are unresolved aspects regarding the methodology and the implications of using different mass definitions.

floyd0117
Messages
6
Reaction score
0
If I have a cluster with a mass measured in M_500c, then how do I go about converting that mass to M_200c given some concentration and an NFW profile?
 
Space news on Phys.org
What do you mean converting the mass? What are you converting? Why?
 
Chalnoth said:
What do you mean converting the mass? What are you converting? Why?

I have a dataset of cluster masses, expressed in units of M_500c, which I need to relate to a velocity dispersion. But the relation between cluster mass and velocity dispersion is in terms of M_200c, so I need to convert the masses in the dataset before I can find the equivalent dispersions.
 
floyd0117 said:
I have a dataset of cluster masses, expressed in units of M_500c, which I need to relate to a velocity dispersion. But the relation between cluster mass and velocity dispersion is in terms of M_200c, so I need to convert the masses in the dataset before I can find the equivalent dispersions.
Ahh, okay. I'm honestly not sure. I did find this resource, which describes these measures a bit:
https://www.princeton.edu/astro/undergraduate/astro-jps-senior-theses-a/bilhudathesis-2.pdf

It looks like M_{500} is the mass within R_{500}, while M_{200} is the mass within R_{200}, where R_{500} \approx 0.7 R_{200}. If you've got a good understanding of the NFW profile, you might be able to use that to do the conversion.

That said, my guess is it'd be even better to convert the relation between mass and dispersion to be in terms of M_{500} instead of M_{200}, as that's most likely a far simpler operation.
 
Last edited by a moderator:
Chalnoth said:
Ahh, okay. I'm honestly not sure. I did find this resource, which describes these measures a bit:
https://www.princeton.edu/astro/undergraduate/astro-jps-senior-theses-a/bilhudathesis-2.pdf

It looks like M_{500} is the mass within R_{500}, while M_{200} is the mass within R_{200}, where R_{500} \approx 0.7 R_{200}. If you've got a good understanding of the NFW profile, you might be able to use that to do the conversion.

That said, my guess is it'd be even better to convert the relation between mass and dispersion to be in terms of M_{500} instead of M_{200}, as that's most likely a far simpler operation.

Perhaps, but I'm trying to follow the methodology presented in a specific paper and replicate their results. Thanks anyway
 
Last edited by a moderator:
floyd0117 said:
Perhaps, but I'm trying to follow the methodology presented in a specific paper and replicate their results. Thanks anyway
Makes sense. Sorry I can't be of more help.
 

Similar threads

Graduate Is there a way to convert distance modulus to get H(z) values
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad New Hubble Paper On Lensing In Galactic Clusters
  • · Replies 2 ·
Replies
2
Views
3K
Convert to Center of Mass Reference Frame
  • · Replies 9 ·
Replies
9
Views
1K
Graduate Convert from Magnitude Density to Mass
  • · Replies 1 ·
Replies
1
Views
1K
Graduate How do you convert the Pound–Rebka redshift into time variation?
  • · Replies 6 ·
Replies
6
Views
982
Undergrad How is the mass of the Earth or the Sun measured?
  • · Replies 7 ·
Replies
7
Views
2K
Undergrad The Latest Higgs Boson Mass Measurement
  • · Replies 13 ·
Replies
13
Views
5K
Graduate Why should the Bullet Cluster focus light?
  • · Replies 35 ·
2
Replies
35
Views
4K
Graduate Gas Mass Calcuation in Galaxy Cluster
  • · Replies 3 ·
Replies
3
Views
2K
Measurements Calculation Problem
  • · Replies 3 ·
Replies
3
Views
1K