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Gravitational Lensing and the search for Dark Matter



 
 
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  #1  
Old April 29th 14, 09:20 PM posted to sci.astro.research
AM[_3_]
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Posts: 1
Default Gravitational Lensing and the search for Dark Matter

Can someone point me to a good explanation of this method ? I.e. by
analysing lensing effects in a galaxy cluster, it is possible to map
the distribution of DM within the cluster, and presumably also to
estimate the amount of DM present in the cluster.

Thanks,
AM

[Mod. note: there are many reviews of this topic that you can find
with a search engine or by searching ADS. For a recent one try
http://arxiv.org/abs/1303.3274 -- mjh]
  #2  
Old May 1st 14, 01:11 PM posted to sci.astro.research
Phillip Helbig---undress to reply
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Posts: 629
Default Gravitational Lensing and the search for Dark Matter

In article , AM
writes:

Can someone point me to a good explanation of this method ? I.e. by
analysing lensing effects in a galaxy cluster, it is possible to map
the distribution of DM within the cluster, and presumably also to
estimate the amount of DM present in the cluster.

Thanks,
AM

[Mod. note: there are many reviews of this topic that you can find
with a search engine or by searching ADS. For a recent one try
http://arxiv.org/abs/1303.3274 -- mjh]


Apart from Martin's suggestion, you might want to search for "weak
lensing", in order to filter out other gravitational-lens stuff which is
not related to what you are looking for. (In gravitational lensing,
"weak lensing" generally refers to (a) resolved (i.e. not point) sources
(b) which are not multiply imaged. So, usually, distorted and
magnified images of background galaxies as a result of the gravitational
field of the foreground lens (galaxy cluster).
  #3  
Old May 4th 14, 08:02 AM posted to sci.astro.research
Jonathan Thornburg [remove -animal to reply][_3_]
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Posts: 137
Default Gravitational Lensing and the search for Dark Matter

In article , AM
asked:
Can someone point me to a good explanation of this method ? I.e. by
analysing lensing effects in a galaxy cluster, it is possible to map
the distribution of DM within the cluster, and presumably also to
estimate the amount of DM present in the cluster.


A nice black-marks-on-dead-trees review is

Peter Schneider, Christopher S. Kochanek, and Joachim Wambsganss,
"Gravitational Lensing: Strong, Weak and Micro"
(Saas-Fee Advanced Course 33)
Springer-Verlag, 2006, ISBN 978-3-540-30309-1

--
-- "Jonathan Thornburg [remove -animal to reply]"
Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA
"There was of course no way of knowing whether you were being watched
at any given moment. How often, or on what system, the Thought Police
plugged in on any individual wire was guesswork. It was even conceivable
that they watched everybody all the time." -- George Orwell, "1984"
  #4  
Old May 5th 14, 06:54 AM posted to sci.astro.research
Phillip Helbig---undress to reply
external usenet poster
 
Posts: 629
Default Gravitational Lensing and the search for Dark Matter

In article , "Jonathan
Thornburg [remove -animal to reply]"
writes:

Can someone point me to a good explanation of this method ? I.e. by
analysing lensing effects in a galaxy cluster, it is possible to map
the distribution of DM within the cluster, and presumably also to
estimate the amount of DM present in the cluster.


A nice black-marks-on-dead-trees review is

Peter Schneider, Christopher S. Kochanek, and Joachim Wambsganss,
"Gravitational Lensing: Strong, Weak and Micro"
(Saas-Fee Advanced Course 33)
Springer-Verlag, 2006, ISBN 978-3-540-30309-1


This covers essentially all of gravitational lensing, though, not just
what the OP was looking for. Still, no reason not to read it.
  #5  
Old May 5th 14, 06:57 AM posted to sci.astro.research
Richard D. Saam
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Posts: 240
Default Gravitational Lensing and the search for Dark Matter

On 4/29/14, 3:20 PM, AM wrote:
Can someone point me to a good explanation of this method ? I.e. by
analysing lensing effects in a galaxy cluster, it is possible to map
the distribution of DM within the cluster, and presumably also to
estimate the amount of DM present in the cluster.

Thanks,
AM

[Mod. note: there are many reviews of this topic that you can find
with a search engine or by searching ADS. For a recent one try
http://arxiv.org/abs/1303.3274 -- mjh]

IGM Emission Observations with the Cosmic Web Imager:
I. The Circum-QSO Medium of QSO 1549+19,
and Evidence for a Filamentary Gas Inflow
http://arxiv.org/abs/1402.4816

IGM Emission Observations with the Cosmic Web Imager:
II. Discovery of Extended, Kinematically-Linked Emission
around SSA22 Lyα Blob 2
http://arxiv.org/abs/1402.4809

These two studies are at the nexus
of gravitationally observed dark matter and gaseous neutral
and ionized hydrogen observed by Lyman alpha.

It is difficult to measure the described parameters
but the most difficult is ideal gas temperature (good old PV=nRT).
A finite Lyman alpha emission 121.60 nm
indicates a temperature equivalent Planck*c/(Boltzmann*121.6)=118,320 K
that is not energy equi-partitioned
or in thermodynamic equilibrium with the hydrogen gas temperature.
The gas temperature is linked
to Maxwell Lyman alpha distribution and related velocity distribution
The papers say temperatures on the order of 10,000 K,
but I do not see the calculations.

Hydrogen temperature and related velocity distribution
would be on the order of:

T (K) v (km/sec)
10,000 12.85
1,000 4.06
500 2.87
100 1.28
50 0.91
10 0.41
5 0.29

where v= SQRT(2*Boltzmann*T/hydrogen_mass)

It is difficult to segregate this derived Maxwell distribution
from all other velocities
(in-out- rotational flows 300 - 1200 km/sec).

These relatively small temperature related velocity distributions
would be overwhelmed by the other kinetic velocity distributions.

And then there are neutral and ionized hydrogen gases
that may not be in thermodynamic equilibrium with each other.
What are the temperatures of each?

Hydrogen temperature may be an important issue in galactic formation
but how is it (PV=nRT) measured in this extremely dynamic context?
Within the limits of current observation,
it could be cold(T near zero K) or hot(T in thousands of K)?
and still be congruent with gravitational lensing observations.
 




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