Editorial Dwarf-GalaxyCosmologydownloads.hindawi.com/journals/aa/2010/930426.pdfpreionization...
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Hindawi Publishing Corporation Advances in Astronomy Volume 2010, Article ID 930426, 2 pages doi:10.1155/2010/930426 Editorial Dwarf-Galaxy Cosmology Regina Schulte-Ladbeck, 1 Ulrich Hopp, 2, 3 Elias Brinks, 4 and Andrey Kravtsov 5 1 Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, USA 2 Universit¨ ats-Sternwarte, Ludwig-Maximilians-Universit¨ at M¨ unchen, 81679 M¨ unchen, Germany 3 Max-Planck Institut f¨ ur Extraterrestrische Physik, 85748 Garching, Germany 4 Centre for Astrophysics Research, University of Hertfordshire, Hatfield AL10 9AB, UK 5 Kavli Institute for Cosmological Physics, The Department of Astronomy and Astrophysics, The University of Chicago, Chicago, IL 60637, USA Correspondence should be addressed to Regina Schulte-Ladbeck, [email protected] Received 3 February 2010; Accepted 3 February 2010 Copyright © 2010 Regina Schulte-Ladbeck et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Dwarf galaxies provide opportunities for drawing inferences about the processes in the early universe by observing our “cosmological backyard”—the Local Group and its vicinity. This special issue of the open-access journal Advances in Astronomy is a snapshot of the current state of the art of dwarf-galaxy cosmology. The issue contains fourteen review papers, and one original research article. All papers were peer-reviewed by a minimum of two referees. Dwarf galaxies continue to challenge our cosmological models and models of galaxy formation. Two well-known problems are the “missing satellites problem” and the “cores versus cusps problem.” The dilemma posed by the fact that observations seem to indicate an approximately constant dark matter density in the inner parts of galaxies, while cosmological simulations prefer a steep, power-law-like behavior that is assessed by W. J. G. de Blok in the paper “The core-cusp problem.” A. Kravtsov reviews the quandary that predicted subhalos outnumber observed dwarf galaxies of the Local Group. In his paper “Dark matter substructure and dwarf galactic satellites,” he emphasizes insights that have been gained from cosmological simulations and their tension with observa- tional data. The observer’s viewpoint of the missing satellites prob- lem is provided by B. Willman in the review “In pursuit of the least luminous galaxies.” Her paper focuses on the progress made with the help of the Sloan Digital Sky Survey data and gives perspectives on the potential for contributions to this research by future surveys and new telescopes. Her paper is complemented by H. Jerjen’s review “Dwarf cosmology with the Stromlo missing satellites survey.” He makes the case that the southern hemisphere has been largely unexplored to faint magnitude levels with modern digital imaging data and discusses the prospects for a complete census of the Milky Way satellite population. An approach to finding missing dwarf galaxies that is independent of their luminous stellar content is through detecting their gravitational lensing signal. E. Zackrisson and T. Riehm examine the many ways through which lensing by subhalos can manifest itself in their paper titled “Gravitational lensing as a probe of cold dark matter subhalos.” Early cosmological simulations also predict large num- bers of dwarf galaxies in voids, which, since this is not confirmed by observations either, is another face of the missing dwarfs issue. It is currently hoped that a better understanding of the physics that controls star formation might resolve the discrepancies between the simulated and observed dwarf galaxies in both environments. Work has therefore focused on how gas is accreted and retained in dwarf-galaxy-sized halos to form stars. In “The first galaxies and the likely discovery of their fossils in the local group,” M. Ricotti reviews simulations of the formation and fate of preionization dwarfs. M. Hoeft and S. Gottl¨ ober describe what progress has been made with high-resolution simula- tions to tackle the issue of “Dwarf galaxies in voids: dark matter halos and gas cooling.” K. Nagamine adds his views
Transcript of Editorial Dwarf-GalaxyCosmologydownloads.hindawi.com/journals/aa/2010/930426.pdfpreionization...
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Hindawi Publishing CorporationAdvances in AstronomyVolume 2010, Article ID 930426, 2 pagesdoi:10.1155/2010/930426
Editorial
Dwarf-Galaxy Cosmology
Regina Schulte-Ladbeck,1 Ulrich Hopp,2, 3 Elias Brinks,4 and Andrey Kravtsov5
1 Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, USA2 Universitäts-Sternwarte, Ludwig-Maximilians-Universität München, 81679 München, Germany3 Max-Planck Institut für Extraterrestrische Physik, 85748 Garching, Germany4 Centre for Astrophysics Research, University of Hertfordshire, Hatfield AL10 9AB, UK5 Kavli Institute for Cosmological Physics, The Department of Astronomy and Astrophysics, The University of Chicago,Chicago, IL 60637, USA
Correspondence should be addressed to Regina Schulte-Ladbeck, [email protected]
Received 3 February 2010; Accepted 3 February 2010
Copyright © 2010 Regina Schulte-Ladbeck et al. This is an open access article distributed under the Creative CommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.
Dwarf galaxies provide opportunities for drawing inferencesabout the processes in the early universe by observing our“cosmological backyard”—the Local Group and its vicinity.This special issue of the open-access journal Advances inAstronomy is a snapshot of the current state of the art ofdwarf-galaxy cosmology. The issue contains fourteen reviewpapers, and one original research article. All papers werepeer-reviewed by a minimum of two referees.
Dwarf galaxies continue to challenge our cosmologicalmodels and models of galaxy formation. Two well-knownproblems are the “missing satellites problem” and the “coresversus cusps problem.”
The dilemma posed by the fact that observations seemto indicate an approximately constant dark matter density inthe inner parts of galaxies, while cosmological simulationsprefer a steep, power-law-like behavior that is assessed byW. J. G. de Blok in the paper “The core-cusp problem.”A. Kravtsov reviews the quandary that predicted subhalosoutnumber observed dwarf galaxies of the Local Group.In his paper “Dark matter substructure and dwarf galacticsatellites,” he emphasizes insights that have been gained fromcosmological simulations and their tension with observa-tional data.
The observer’s viewpoint of the missing satellites prob-lem is provided by B. Willman in the review “In pursuit of theleast luminous galaxies.” Her paper focuses on the progressmade with the help of the Sloan Digital Sky Survey data andgives perspectives on the potential for contributions to this
research by future surveys and new telescopes. Her paperis complemented by H. Jerjen’s review “Dwarf cosmologywith the Stromlo missing satellites survey.” He makes the casethat the southern hemisphere has been largely unexploredto faint magnitude levels with modern digital imaging dataand discusses the prospects for a complete census of theMilky Way satellite population. An approach to findingmissing dwarf galaxies that is independent of their luminousstellar content is through detecting their gravitational lensingsignal. E. Zackrisson and T. Riehm examine the many waysthrough which lensing by subhalos can manifest itself in theirpaper titled “Gravitational lensing as a probe of cold darkmatter subhalos.”
Early cosmological simulations also predict large num-bers of dwarf galaxies in voids, which, since this is notconfirmed by observations either, is another face of themissing dwarfs issue. It is currently hoped that a betterunderstanding of the physics that controls star formationmight resolve the discrepancies between the simulated andobserved dwarf galaxies in both environments. Work hastherefore focused on how gas is accreted and retained indwarf-galaxy-sized halos to form stars. In “The first galaxiesand the likely discovery of their fossils in the local group,”M. Ricotti reviews simulations of the formation and fate ofpreionization dwarfs. M. Hoeft and S. Gottlöber describewhat progress has been made with high-resolution simula-tions to tackle the issue of “Dwarf galaxies in voids: darkmatter halos and gas cooling.” K. Nagamine adds his views
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2 Advances in Astronomy
on how to include star formation processes in cosmologicalsimulations in “Star formation history of dwarf galaxies incosmological hydrodynamic simulations.”
These papers are accompanied by a review of the currentknowledge of the star-formation histories of dwarf galaxiesthat has been gained from observations. M. Cignoni andM. Tosi describe experimental approaches and results in“Star formation histories of dwarf galaxies from the colour-magnitude diagrams of their resolved stellar populations.”
Several papers address how dynamical interactions influ-ence the evolution of dwarf galaxies. In “Environmentalmechanisms shaping the nature of dwarf galaxies: the viewof computer simulations,” L. Mayer describes a mechanismfor transforming disky dwarfs into dwarf spheroidals, anddiscusses implications for the substructure problem. L. V.Sales et al. consider “The effect of tidal stripping on compositestellar populations in dwarf spheroidal galaxies.” Their dwarfgalaxy model follows the evolution of two kinematicallyand spatially segregated stellar components. They ask howthese can be distinguished after having interacted withthe potential of a massive galaxy. F. Bournaud, in “Tidaldwarf galaxies and missing baryons,” discusses a tensionthat exists between model predictions that tidal dwarfsshould not contain a significant mass fraction from the darkmatter halos of their progenitor spiral galaxies, and existingobservations which do suggest the presence of an unseencomponent.
Dwarf spheroidal galaxies are considered to providegood astronomical sites for the study of the nature of darkmatter. In “Kinematics of Milky Way satellites: mass estimates,rotation limits, and proper motions,” L. Strigari reviews theevidence for the presence of dark matter in dwarf spheroidalcompanions of the Milky Way. M. Kuhlen portrays prospectsfor the detection of the hypothetical dark matter particle.His paper is titled “The dark matter annihilation signal fromdwarf galaxies and subhalos.” A. Kosowsky makes the casethat dwarf spheroidals are not only important for testing thedark matter hypothesis, but also the competing, modifiedNewtonian gravity hypothesis. His paper critically analyzes“Dwarf galaxies, MOND, and relativistic gravitation.”
A. Kosowsky aptly summarizes what we consider thespirit of this special issue: “Until the predominant picture ofdark matter cosmology can explain all of the observations,other competing ideas should be pursued, either as a way ofsharpening the case for dark matter cosmology, or, perhaps,uncovering an eventual replacement. . . . We should not allowthe successes of our leading theories to blind us to otherpossibilities.”
There is much opportunity for theoretical and obser-vational innovation in the area of dwarf-galaxy cosmology.We asked the authors of our review papers to write themin the style of a tutorial and at a level suitable forbeginning graduate students. We hope our special issue willreach a wide audience of graduate students and beginningresearchers, in particular since all of the papers, under theopen-access model, are accessible free of charge to anyonewith a computer and an internet connection.
We would like to thank the members of the editorialboard of Advances in Astronomy, the authors and referees
of articles submitted to the special issue, and the staff ofHindawi publisher. Without their support and hard work,this special issue would not have come into being.
We hope you will enjoy reading “Dwarf-galaxy cosmol-ogy.”
Regina Schulte-LadbeckUlrich HoppElias Brinks
Andrey Kravtsov
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