Our research revolves around X-ray astronomy and observational cosmology,
concentrating on the overlap between these two. The group is led by
Prof. Steve Allen
(publication list).
Galaxy clusters and cosmology
Galaxy clusters are the largest objects in the Universe, spanning 10
million light years across and containing as much mass as a million,
billion suns. Our research examines the physics of these remarkable
systems using the best available multi-wavelength data, and uses the
observed properties of clusters to probe the nature of dark
matter, the weakly interacting yet dominant matter component of
the Universe, and dark energy, the driving force behind
cosmic acceleration.
Most of the normal, baryonic matter in the Universe is in gaseous
form. Within galaxy clusters, the enormous gravity squeezes this gas,
heating it to 100 million degrees and causing it to shine brightly at
X-ray wavelengths. The X-ray brightness at a given radius reflects the
gas density; the temperature, measured by X-ray spectroscopy, reflects
the total mass (dark-plus-normal matter). Thus, as well as enabling us
to observe clusters out to high redshifts, X-ray observations, made
with satellite observatories
like Chandra and
XMM-Newton allow us to measure
the masses of both the baryonic and dark, non-baryonic matter within
them.
For an introduction to this work, see e.g.:
-
Feedback under the microscope: thermodynamic structure and AGN driven shocks in M87
Million, E. T.; Werner, N.; Simionescu, A.; Allen, S. W.; Nulsen, P. E. J.; Fabian, A. C.; Bohringer, H.; Sanders, J. S.
Accepted to MNRAS.
6/2010.
1006.5484.
-
The observed growth of massive galaxy clusters - I. Statistical methods and cosmological constraints
Mantz, A.; Allen, S. W.; Rapetti, D.; Ebeling, H.
Monthly Notices of the Royal Astronomical Society, Volume 406, Issue 3, pp. 1759-1772.
8/2010.
ADS,
0909.3098.
-
The observed growth of massive galaxy clusters - III. Testing general relativity on cosmological scales
Rapetti, David; Allen, Steven W.; Mantz, Adam; Ebeling, Harald
Monthly Notices of the Royal Astronomical Society, Volume 406, Issue 3, pp. 1796-1804.
8/2010.
ADS,
0911.1787.
-
Revealing the Properties of Dark Matter in the Merging Cluster MACS J0025.4-1222
Bradac, Marusa; Allen, Steven W.; Treu, Tommaso; Ebeling, Harald; Massey, Richard; Morris, R. Glenn; von der Linden, Anja; Applegate, Douglas
The Astrophysical Journal, Volume 687, Issue 2, pp. 959-967.
11/2008.
ADS,
0806.2320.
-
Improved constraints on dark energy from Chandra X-ray observations of the largest relaxed galaxy clusters
Allen, S. W.; Rapetti, D. A.; Schmidt, R. W.; Ebeling, H.; Morris, R. G.; Fabian, A. C.
Monthly Notices of the Royal Astronomical Society, Volume 383, Issue 3, pp. 879-896.
1/2008.
ADS
-
The relation between accretion rate and jet power in X-ray luminous elliptical galaxies
Allen, S. W.; Dunn, R. J. H.; Fabian, A. C.; Taylor, G. B.; Reynolds, C. S.
Monthly Notices of the Royal Astronomical Society, Volume 372, Issue 1, pp. 21-30.
10/2006.
ADS,
astro-ph/0602549.
Black holes, jets and galaxy formation
Classical models for galaxy formation predict that the largest
galaxies should be much brighter than we observe. A large power source
must be preventing gas from cooling and forming vast numbers of new
stars. We were part of one of the first teams to show that
supermassive black holes are likely to be responsible for the
suppression of star formation, pumping out huge amounts of energy from
the hearts of galaxies in the form of relativistic jets. These jets
inflate giant cavities in the X-ray emitting gas and generate enormous
sound waves. Recently, we have also shown that this `feedback' occurs
with a high and near-universal efficiency, potentially sufficient to
solve the galaxy formation problem. However, significant questions
relating to the `duty-cycle' of black hole heating, the accretion
process, jet formation and black hole growth remain.
For an introduction to this work, see e.g.:
-
Feedback under the microscope II: heating, gas uplift, and mixing in the nearest cluster core
Werner, N.; Simionescu, A.; Million, E. T.; Allen, S. W.; Nulsen, P. E. J.; von der Linden, A.; Hansen, S. M.; Boehringer, H.; Churazov, E.; Fabian, A. C.; Forman, W. R.; Jones, C.; Sanders, J. S.; Taylor, G. B.
3/2010.
1003.5334.
-
The radio properties of a complete, X-ray selected sample of nearby, massive elliptical galaxies
Dunn, R. J. H.; Allen, S. W.; Taylor, G. B.; Shurkin, K. F.; Gentile, G.; Fabian, A. C.; Reynolds, C. S.
Monthly Notices of the Royal Astronomical Society, Volume 404, Issue 1, pp. 180-197.
5/2010.
ADS,
1001.1630.
-
Constraints on turbulent pressure in the X-ray haloes of giant elliptical galaxies from resonant scattering
Werner, N.; Zhuravleva, I.; Churazov, E.; Simionescu, A.; Allen, S. W.; Forman, W.; Jones, C.; Kaastra, J. S.
Monthly Notices of the Royal Astronomical Society, Volume 398, Issue 1, pp. 23-32.
9/2009.
ADS,
0904.0254.
-
The relation between accretion rate and jet power in X-ray luminous elliptical galaxies
Allen, S. W.; Dunn, R. J. H.; Fabian, A. C.; Taylor, G. B.; Reynolds, C. S.
Monthly Notices of the Royal Astronomical Society, Volume 372, Issue 1, pp. 21-30.
10/2006.
ADS,
astro-ph/0602549.
Cluster Surveys and Multi-wavelength Follow-up
We have been involved in the construction and/or utilization of some
of the most powerful galaxy cluster catalogs ever made, including the
ROSAT
Brightest Cluster Sample, the
Extended
Brightest Cluster Sample and the
Massive
Cluster Survey. We are currently carrying out detailed
multi-wavelength follow-up of these sources, including
deep gravitational lensing studies, optical imaging and spectroscopy,
infrared studies and radio observations. For this, we use instruments
such as the Hubble Space
Telescope, Subaru
Telescope, Herschel Space
Observatory, and the Very Large
Array.
-
Herschel photometry of brightest cluster galaxies in cooling flow clusters
Edge, A. C.; Oonk, J. B. R.; Mittal, R.; Allen, S. W.; Baum, S. A.; Böhringer, H.; Bregman, J. N.; Bremer, M. N.; Combes, F.; Crawford, C. S.; Donahue, M.; Egami, E.; Fabian, A. C.; Ferland, G. J.; Hamer, S. L.; Hatch, N. A.; Jaffe, W.; Johnstone, R. M.; McNamara, B. R.; O'Dea, C. P.; Popesso, P.; Quillen, A. C.; Salomé, P.; Sarazin, C. L.; Voit, G. M.; Wilman, R. J.; Wise, M. W.
Astronomy and Astrophysics, Volume 518, id.L47
7/2010.
ADS,
1005.1211.
-
Revealing the magnetic field in a distant galaxy cluster: discovery of the complex radio emission from MACS J0717.5 +3745
Bonafede, A.; Feretti, L.; Giovannini, G.; Govoni, F.; Murgia, M.; Taylor, G. B.; Ebeling, H.; Allen, S.; Gentile, G.; Pihlström, Y.
Astronomy and Astrophysics, Volume 503, Issue 3, 2009, pp.707-720
9/2009.
ADS,
0905.3552.
-
Revealing the Properties of Dark Matter in the Merging Cluster MACS J0025.4-1222
Bradac, Marusa; Allen, Steven W.; Treu, Tommaso; Ebeling, Harald; Massey, Richard; Morris, R. Glenn; von der Linden, Anja; Applegate, Douglas
The Astrophysical Journal, Volume 687, Issue 2, pp. 959-967.
11/2008.
ADS,
0806.2320.
Gravitational lensing
General Relativity predicts that the gravity associated with a mass
concentration will bend light rays passing near to it in a phenomenon
known as gravitational lensing. This can both magnify and distort the
apparent images of background galaxies. The effects of lensing can be
clearly detected in the statistical appearance of background objects
seen through clusters (weak lensing). Occasionally, lensing can also
lead to large distortions (strong lensing). Our group is using deep,
wide-field, multi-band optical observations of clusters to measure the
gravitational lensing signal of galaxy clusters and constrain their
masses. In contrast to other methods, lensing offers a way of
measuring the (projected) masses of clusters that is free of
assumptions regarding the dynamical state of the gravitating matter.
Although sensitive to the effects of triaxiality for individual
systems, statistical samples of weak lensing measurements are expected
to provide essentially unbiased mass results.
For an introduction to this work, see e.g.:
-
Weighing the giants: X-ray and weak lensing studies measurements of the most massive clusters
von der Linden, Anja; Applegate, Doug; Kelly, Pat; Allen, Mark; Allen, Steve; Ebeling, Harald; Mantz, Adam
Chandra's First Decade of Discovery, Proceedings of the conference held 22-25 September, 2009 in Boston, MA. Edited by Scott Wolk, Antonella Fruscione, and Douglas Swartz, abstract #28
9/2009.
ADS.
-
Revealing the Properties of Dark Matter in the Merging Cluster MACS J0025.4-1222
Bradac, Marusa; Allen, Steven W.; Treu, Tommaso; Ebeling, Harald; Massey, Richard; Morris, R. Glenn; von der Linden, Anja; Applegate, Douglas
The Astrophysical Journal, Volume 687, Issue 2, pp. 959-967.
11/2008.
ADS,
0806.2320.
-
Dark Matter and Baryons in the X-Ray Luminous Merging Galaxy Cluster RX J1347.5-1145
Bradac, Marusa; Schrabback, Tim; Erben, Thomas; McCourt, Michael; Million, Evan; Mantz, Adam; Allen, Steve; Blandford, Roger; Halkola, Aleksi; Hildebrandt, Hendrik; Lombardi, Marco; Marshall, Phil; Schneider, Peter; Treu, Tommaso; Kneib, Jean-Paul
The Astrophysical Journal, Volume 681, Issue 1, pp. 187-196.
7/2008.
ADS,
0711.4850.
Future missions
We are involved in the development of new X-ray satellite
observatories such as
The International X-ray Observatory
(IXO) and
The Wide-Field X-ray Telescope
(WFXT), and ground-based optical telescopes such as
the Large Synoptic Survey Telescope,
which aim to push back the boundaries of our understanding of the Universe:
-
Cosmological studies with a large-area X-ray telescope
Vikhlinin, A.; Allen, S.W.; Arnaud, M.; Bautz, M.; Böringer, H.; Bonamente, M.; Burns, J.; Evrard, A.; Henry, J.P.; Jones, C.; McNamara, B.R.; Nagai, D.; Rapetti, D.; Reiprich, T.
Astro2010: The Astronomy and Astrophysics Decadal Survey, Science White Papers, no. 304
1/2009.
ADS,
0903.2297.
-
X-ray Cluster Cosmology
Vikhlinin, A.; Murray, S.; Gilli, R.; Tozzi, P.; Paolillo, M.; Brandt, N.; Tagliaferri, G.; Bautz, M.; Allen, S.; Donahue, M.; Evrad, A.; Flanagan, K.; Rosati, P.; Borgani, S.; Giacconi, R.; Weisskopf, M.; Ptak, A.; Alexander, D.; Pareschi, G.; Forman, W.; Jones, C.
Astro2010: The Astronomy and Astrophysics Decadal Survey, Science White Papers, no. 305
1/2009.
ADS,
0903.5320.
-
The growth and evolution of super massive black holes
Murray, S.; Gilli, R.; Tozzi, P.; Paolillo, M.; Brandt, N.; Tagliaferri, G.; Vikhlinin, A.; Bautz, M.; Allen, S.; Donahue, M.; Flanagan, K.; Rosati, P.; Borgani, S.; Giacconi, R.; Weisskopf, M.; Ptak, A.; Gezari, S.; Alexander, D.; Pareschi, G.; Forman, W.; Jones, C.; Hickox, R.
Astro2010: The Astronomy and Astrophysics Decadal Survey, Science White Papers, no. 217
1/2009.
ADS,
0903.5272.
-
The prospects for constraining dark energy with future X-ray cluster gas mass fraction measurements
Rapetti, David; Allen, Steven W.; Mantz, Adam
Monthly Notices of the Royal Astronomical Society, Volume 388, Issue 3, pp. 1265-1278.
8/2008.
ADS,
0710.0440.
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