Re: A direct empirical proof of the existence of dark matter


Sam Wormley wrote:
Astrophysics, abstract
http://arxiv.org/abs/astro-ph/0608407

From: Marusa Bradac [view email]
Date: Sat, 19 Aug 2006 17:51:03 GMT (119kb)

A direct empirical proof of the existence of dark matter

Authors: Douglas Clowe (1), Marusa Bradac (2), Anthony H. Gonzalez (3),
Maxim Markevitch (4), Scott W. Randall (4), Christine Jones (4), Dennis
Zaritsky (1) ((1) Steward Observatory, Tucson, (2) KIPAC, Stanford, (3)
Department of Astronomy, Gainesville, (4) CfA, Cambridge)

Comments: Accepted for publication in ApJL

We present new weak lensing observations of 1E0657-558 (z=0.296), a
unique cluster merger, that enable a direct detection of dark matter,
independent of assumptions regarding the nature of the gravitational
force law. Due to the collision of two clusters, the dissipationless
stellar component and the fluid-like X-ray emitting plasma are
spatially segregated. By using both wide-field ground based images and
HST/ACS images of the cluster cores, we create gravitational lensing
maps which show that the gravitational potential does not trace the
plasma distribution, the dominant baryonic mass component, but rather
approximately traces the distribution of galaxies. An 8-sigma
significance spatial offset of the center of the total mass from the
center of the baryonic mass peaks cannot be explained with an
alteration of the gravitational force law, and thus proves that the
majority of the matter in the system is unseen.

___________________________________


Astrophysics, abstract
http://arxiv.org/abs/astro-ph/0608408

From: Marusa Bradac [view email]
Date: Fri, 18 Aug 2006 20:06:48 GMT (373kb)

Strong and weak lensing united III: Measuring the mass distribution of
the merging galaxy cluster 1E0657-56

Authors: Marusa Bradac (1,2), Douglas Clowe (3), Anthony H. Gonzalez
(4), Phil Marshall (1), William Forman (5), Christine Jones (5), Maxim
Markevitch (5), Scott Randall (5), Tim Schrabback (2), Dennis Zaritsky
(3) ((1) KIPAC, Stanford, (2) AIfA, Bonn, (3) Steward Observatory,
Tucson, (4) Department of Astronomy, Gainesville, (5) CfA, Cambridge)

Comments: Accepted for publication in ApJ; Version with full-resolution
figures available at this http URL

The galaxy cluster 1E0657-56 (z = 0.296) is remarkably well-suited
for addressing outstanding issues in both galaxy evolution and
fundamental physics. We present a reconstruction of the mass
distribution from both strong and weak gravitational lensing data.
Multi-color, high-resolution HST ACS images allow detection of many
more arc candidates than were previously known, especially around the
subcluster. Using the known redshift of one of the multiply imaged
systems, we determine the remaining source redshifts using the
predictive power of the strong lens model. Combining this information
with shape measurements of "weakly" lensed sources, we derive a
high-resolution, absolutely-calibrated mass map, using no assumptions
regarding the physical properties of the underlying cluster potential.
This map provides the best available quantification of the total mass
of the central part of the cluster. We also confirm the result from
Clowe et al. (2004,2006a).
All they have proven (once again)
is that our theory of gravity fails to explain galaxies.
Bin dere dun dat.
John

.

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