Maruša Bradač
 
 
Studying dark matter... One of the most important outstanding quests in cosmology is the understanding of the formation and evolution of galaxies and galaxy clusters. In particular, we seek to answer what the dark matter is and what are its properties, and how it shapes galaxies and galaxy clusters through cosmic time. Whereas the currently accepted paradigm for galaxy formation works well in general, some discrepancies between model predictions and observations (such as the abundance of substructure in halos, and dark matter profile shapes) still remain. The principal objective of my research is to study the dark matter and its properties over a variety of scales and environments. With accurate mass measurements of gravitational lensing by clusters and galaxies I will be able to constrain their dark matter profile and distribution. Following the pioneering example of the ``bullet'' cluster 1E0657-56 I am studying more merging clusters; these are ideal laboratories for distinguishing between CDM and other scenarios (warm dark matter, self-interacting dark matter, modified gravity, etc.) that have been proposed to resolve the CDM crises or to eliminate the need for dark matter altogether. ``Science is a collaborative effort, between us and the universe. We propose ideas, the universe smacks them down -- or occasionally agrees (S. Caroll).''  The color composite of the bullet cluster. The two clusters (their galaxies are predominantly the yellowish ones in this image) have smashed through each other with 15 million kilometers per hour (10 million miles per hour). The dominant mass component (dark matter, blue) has separated from the dominant luminous material (hot gas, red). Credit: NASA Press Release; X-ray NASA/CXC/CfA Optical: NASA/STScI; Magellan/U.Arizona; [Clowe et al 2006, Bradač et al 2006] You can see a cool movie from John Wise and read much more on this at SLAC and NASA webpage. and highest redshift Universe... Galaxy clusters are not only useful to study dar matter. among other fantastic research one can do, clusters also act as gigantic magnifying glasses, again due to the gravitational lensing effect. Therefore we can observe fainter and more distant sources than would otherwise be possible. I use massive clusters as cosmic telescopes to explore the Universe in its infancy, by studying the sources responsible for reionization; an era in which the Universe should go from highly neutral to highly ionized. After that period the universe becomes transparent for visible light and we mark it as the end of Dark Ages. We currently lack a full understanding of the exact properties of the sources responsible for this process, to observe these sources we need to look very far back, at the time when the Universe was only about 400 million years old. I am currently studying these extremely faint sources, a task made possible through magnifying power of massive clusters through gravitational lensing effect. seeing the invisible with gravitational lensing... Selected publications: M. Bradač, D. Clowe, A. H. Gonzalez, P. Marshall, W. Forman, C. Jones, M. Markevitch, S. Randall, T. Schrabback, and D. Zaritsky: Strong and Weak Lensing United III: Measuring the Mass Distribution of the Merging Galaxy Cluster 1E0657-56, Accepted for publication in ApJ [PDF] D. Clowe, M. Bradač, A. H. Gonzalez, M. Markevitch, S. W. Randall, C. Jones, D. Zaritsky: A direct empirical proof of the existence of dark matter, Accepted for publication in ApJL [PDF] M. Bradač, T. Erben, P.Schneider, H. Hildebrand, M. Lombardi, M. Schirmer, J.-M. Miralles, D. Clowe, and S. Schindler: Strong and weak lensing united II: the cluster mass distribution of the most X-ray luminous cluster RX J1347.5-1145, 2005, Astronomy and Astrophysics 437, 49[ PDF ] M. Bradač, P.Schneider, M. Lombardi, and T.Erben: Strong and weak lensing united I: the combined strong and weak lensing cluster mass reconstruction method, 2005, Astronomy and Astrophysics 437, 39[ PDF ] M. Bradač, M. Lombardi, and P.Schneider: Mass-sheet degeneracy: Fundamental limit on the cluster mass reconstruction from statistical (weak) lensing, 2004, Astronomy and Astrophysics, 424, 13 [ PDF ] M. Bradač, P. Schneider, M. Lombardi, M. Steinmetz, L.V.E. Koopmans, and Julio F. Navarro. The signature of CDM substructure on gravitational lensing, 2004, Astronomy and Astrophysics, 423, 797 [ BW PDF ] [ COLOUR PDF ] M. Bradač, P. Schneider, M. Steinmetz, M. Lombardi, L. J. King, and R. Porcas. B1422+231: The influence of mass substructure on strong lensing, 2002, Astronomy and Astrophysics, 388, 373 [ PDF ] Theses M. Bradač: Exploring Dark Matter Properties from the Smallest to the Largest Scales, PhD Thesis, University of Bonn, November 2004 [ PDF ] M. Bradač: Substructure in the Gravitationally lensed system B1422+231. Diploma Thesis, University of Bonn, August 2001 [ TITLE PS.GZ ] http://www.slac.stanford.edu/~marusa/Work/clowe.pdfhttp://www.slac.stanford.edu/~marusa/Work/bradac_strong_weak_III.pdfhttp://www.slac.stanford.edu/~jwise/research/movies/HiResBullet.movhttp://home.slac.stanford.edu/pressreleases/2006/20060821.htmhttp://chandra.harvard.edu/press/06_releases/press_082106.htmlhttp://www.slac.stanford.edu/~marusa/Work/bradac_strong_weak_III.pdfhttp://www.slac.stanford.edu/~marusa/Work/strong_weak_II.pdfhttp://www.slac.stanford.edu/~marusa/Work/strong_weak_II.pdfhttp://www.slac.stanford.edu/~marusa/Work/strong_weak_I.pdfhttp://www.slac.stanford.edu/~marusa/Work/mass_sheet.pdfhttp://www.slac.stanford.edu/~marusa/Work/sstr2_bw.pdfhttp://www.slac.stanford.edu/~marusa/Work/sstr2_c.pdfhttp://www.slac.stanford.edu/~marusa/Work/aah3340.pdfhttp://www.slac.stanford.edu/~marusa/Work/MarusaBradac_PhD.pdfhttp://www.slac.stanford.edu/~marusa/Work/title.pshttp://www.slac.stanford.edu/~marusa/Work/diploma.ps.gzshapeimage_1_link_0shapeimage_1_link_1shapeimage_1_link_2shapeimage_1_link_3shapeimage_1_link_4shapeimage_1_link_5shapeimage_1_link_6shapeimage_1_link_7shapeimage_1_link_8shapeimage_1_link_9shapeimage_1_link_10shapeimage_1_link_11shapeimage_1_link_12shapeimage_1_link_13shapeimage_1_link_14shapeimage_1_link_15
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Department of Physics, University of California Santa Barbara, CA 93106-9530,
U.S.A.
Phone: (805)893-2246 Fax: (805)893-3307
Email: marusa at physics.ucsb.edu