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Astrophysics Research With astronomical data arriving at essentially every wavelength of the electromagnetic spectrum, this is a fascinating time for astronomy and astrophysics worldwide. Johns Hopkins astrophysicists lead research across the entire range of the discipline, from cosmology to galactic structure to planets, using observational, numerical and theoretical methods. JHU astronomers along with members of the Space Telescope Science Institute just across the street from our building jointly form one of the largest astrophysics communities in the country. The past two years have brought many exciting developments for the astrophysics researchers in our department. Professor Adam Riess received the 2011 Nobel Prize in physics for the discovery of the accelerated expansion of the Universe. The department continued its commitment to leadership in large-scale astronomical surveys and joined the Prime Focus Spectrograph project. Several new astrophysics faculty joined our department: professor Marc Kamionkowski, assistant professors Tobias Marriage, Nadia Zakamska and Brice Menard, and Homewood Professor Joseph Silk in a shared appointment. Below we briefly summarize research interests of our faculty and research staff members, arranged roughly in the following order: Cosmology, Extragalactic Astronomy, Galactic Astronomy, Numerical Simulations, Large Datasets, Instrumentation, Group activities.
Cosmology A false color image of the intensity of the CMB; typical fluctuation scales Delta T/T are ~10^{-5} Graduate students J.Eimer and L.Zeng and Prof. Bennett (in the middle) photographed through the largest wire polarizer ever built -- Cosmology Large Angular Scale Surveyor. Arguably the biggest cosmological surprise we have ever encountered is the very large contribution to the expansion of the Universe due to the mysterious "Dark Energy". Through his use of high-redshift supernovae to measure the cosmological distance scale, Prof. Adam Riess has contributed more to this discovery than perhaps any other single person. Prof. Marc Kamionkowski works on a variety of subjects in cosmology and particle astrophysics. Much of his recent research has aimed to develop new ways to use cosmic microwave background data to constrain fundamental physics and to probe the early Universe. He has also been pursuing the development of analogous tests that can be carried out with large-scale-structure data and, more recently, what ultimately may be learned from 21-centimeter probes of atomic hydrogen. Prof. Kamionkowski has a longstanding interest in exploring ideas for particle dark matter and methods for its detection. He is also interested in exploring questions involving dark energy, galaxy formation and the physics of galaxy clusters, neutrino physics and astrophysics, and a bit in stellar astrophysics. Six different types of distortions to an otherwise isotropic two-point correlation function. Such distortions may be imprinted on the cosmological mass distribution if the inflaton responsible for primordial perturbations couples to some new tensor (left two columns), scalar (middle two columns), or vector field (right two columns). Prof. Brice Menard is analyzing massive datasets from the SDSS-I, II and III surveys to learn about formation and evolution of galaxies, to map out the dark matter distribution with gravitational lensing and to study the distribution of tenuous matter filling the space between cosmic structures. "Adolescent" galaxies (galaxies only a few Gyr old) have a propensity for dramatic behavior. Just about all good-sized galaxies acquire super-massive black holes at their centers, and when they are young, so much matter is accreted onto these black holes that the power output can easily be 100 times as great as that of all the stars in the host galaxy. Both Prof. Timothy Heckman and Prof. Julian Krolik are widely-recognized experts in the study of these strange objects (called "quasars" or "active galactic nuclei"), with Prof. Heckman approaching the issue from an observational point of view and Prof. Krolik concentrating on theoretical aspects. Using the Chandra X-ray Observatory to obtain some of the deepest images of the X-ray sky ever made, University Professor (and Nobel Laureate) Riccardo Giacconi and Prof. Colin Norman showed that the diffuse X-ray background is in fact made by huge numbers of these active galaxies. Data from the Chandra spacecraft and other X-ray telescopes is also the basis for Principal Research Scientist Dr. Tahir Yaqoob's work on supermassive black holes in galactic nuclei. Chandra Deep Field South color-coded based on the objects' spectral energy distribution: bluer sources have "harder" X-ray spectra Prof. Nadia Zakamska's research spans topics in observational and theoretical astrophysics. Highlights from her recent work include the discovery of galaxy-wide winds launched by accreting black holes -- quasars -- which may limit the maximal mass of galaxies. Her active research focuses on the cosmic evolution of supermassive black holes in the Universe and on starburst galaxies, and she is also interested in topics in theoretical astrophysics such as relativistic outflows and planetary dynamics. Kinematic map of quasar winds obtained by JHU postdoctoral researcher Dr. Guilin Liu and Prof. Zakamska using the Gemini telescope. From left to right, the figure shows intensity, radial velocity and a measure of velocity dispersion of ionized gas encompassing the entire quasar host galaxy. How and why galaxies undergo dramatic bursts of star-formation, and the connection this may have to their initial construction as well as to the fuelling of central black holes is another area of rapid advance, one in which Prof. Heckman has been especially prominent. As the following figures show, this is one of the many problems in astrophysics for which the truly multi-wavelength approach favored by many JHU astronomers is especially valuable. NGC 5135 at different wavelengths. From left to right, a ground-based optical image, Hubble Space Telescope optical and ultraviolet view and an X-ray image by Chandra. The development of individual galaxies is yet another area which has attracted widespread attention. Prof. Rosemary Wyse carefully examines the structure of our own Galaxy as a template for how galaxies in general were built. Prof. Luciana Bianchi characterizes elusive components of the Milky Way stellar populations using optical and ultra-violet observations, including those by NASA's GALEX satellite. Her census of hot white dwarf stars, with over an order of magnitude increase from previous catalogs, provided new insight on their progenitors and their contribution to the chemical enrichment of the Milky Way Galaxy. Using optical and ultra-violet spectroscopic data, Prof. Bianchi derived new diagnostics of the surface chemistry of evolved stars. She also studies hot massive stars, which are the main driver of the dynamical and chemical evolution of galaxies. She used the Hubble Space Telescope as well as data from JHU-built FUSE satellite to measure physical parameters of such stars, finding that they were less hot and less luminous than previously thought. She also uses Hubble Space Telescope and GALEX to study star formation in external galaxies. This work is revealing star formation in sites where it was never expected or seen before, as well as providing insight into how young stellar populations form and evolve in different environments and conditions. Our nearest big neighbor, the Andromeda Galaxy (M31), seen here in ultra-violet light as detected by the GALEX satellite Closer to home, we find that the interstellar medium of galaxies is often rich with molecular gas. In some circumstances, naturally-occurring masers can form, producing extremely bright and collimated beams of radiation. Prof. David Neufeld is an expert in all aspects of molecular astrophysics, and uses molecular diagnostics to elucidate the properties of astronomical systems from planets and comets to stellar atmospheres to molecular clouds. His research using SOFIA and Herschel observatories has recently resulted in discoveries of several new interstellar molecules which provide key information about the interstellar medium. Characterizing diffuse UV emission has long been a goal of Prof. Richard Henry's work. The last decade has seen an explosion of interest in the formation of planetary systems, now that we can detect dozens of extra-Solar planets as well as conduct detailed studies of many of our own Solar System's planets through a variety of space experiments. A number of Hopkins astrophysicists are deeply involved in these efforts, developing new techniques for detecting extra-Solar Planets (Prof. Holland Ford), studying the atmospheres and magnetospheres of other planets in our Solar System (Prof. Warren Moos), and analyzing cometary spectra (Prof. Paul Feldman). Following up on these exciting developments, Prof. Colin Norman has organized an interdisciplinary program in astrobiology. A fundamental problem in the physics of astrophysics is the role of magneto-hydrodynamic processes in accretion (for example, onto black holes) and in the generation of relativistic jets. Professors Krolik and Norman are both pursuing this problem, using techniques ranging from large-scale general relativistic MHD simulations to analytic models. Prof. Krolik has numerous ongoing research programs in this area: exploring the interaction between MHD turbulence and radiation forces in accretion flows; using data generated by 3-d general relativistic MHD simulations to predict the emitted spectrum and polarization of light radiated by accreting black holes; unraveling the dynamics of tilted and precessing disks; and predicting photon signatures of merging supermassive black holes. Magnetic fieldline structure in both the accretion disk surrounding a black hole and its outflow, superimposed on logarithmic color contours of gas density. JHU astrophysicists are also among the world's leading developers of new astronomical tools. Our department is a full member of the Sloan Digital Sky Survey, which mapped a quarter of the sky and obtained spectra of a million galaxies, 100,000 quasars, and sundry stars and other interesting objects in its first and second phase. SDSS is continuing to acquire data for a range of novel projects in Galactic and extragalactic astronomy. Prof. Paul Feldman and Dr. Alan Uomoto built the spectrograph for the SDSS, while Prof. Alex Szalay designed the data archive, which is hosted here in our department. Based on that experience, Prof. Szalay became a Co-Principal Investigator of the National Virtual Observatory, a project merging the electronic databases of a large number of astronomical surveys. He is also involved in a number of other programs to make use of extremely large scientific databases, in medicine, earth sciences, and other disciplines. Furthermore, JHU is one of only three US university members of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) which repeatedly scans 75% of the sky in search of time-varying astronomical objects. It is a pre-cursor to the highest-ranked astronomical project of the next decade -- the Large Synoptic Survey Telescope, of which our department is also a full institutional member. Our plans for the next decade include leadership in the next generation of the spectroscopic surveys, and we recently joined the international collaboration designing the Prime Focus Spectrograph on Subaru Telescope. Profs. Bennett, Heckman, Menard and Zakamska are involved in the infrastructure and software development for this project, which leads in the new generation of the spectroscopic surveys. Discoveries made using the wealth of proprietary data on our survey facilities are often followed up using our time share of the 3.5 m telescope at the Apache Point Observatory. The Department of Physics and Astronomy at JHU has long been one of the principal centers for developing instrumentation for space and ground-based astronomy. The department’s instrumental roots can be traced to JHU’s first Professor of Physics Henry A. Rowland, who developed the precision ruling engine that enabled routine production of high quality diffraction gratings, which ushered in a new era of quantitative spectroscopy as applied in both laboratory and astronomical settings. Profs. A. Herman Pfund, Robert W. Wood, John Strong and colleagues built on these efforts, a tradition we continue to this day. This section describes the department's ground-based and space-based instrumentation efforts, which are in addition to the microwave background instrumentation development described above. Graduate students Keith Redwine and Brian Fleming are shown here assembling a sounding rocket payload. Low Earth Orbit and Beyond The Astrophysics community at Johns Hopkins University is dynamic, active and offers many avenues for collaboration and for meeting scientists from all over the world in any area of astrophysics research. Both our department and the Space Telescope Science Institute across the street host many visitors every week, either as speakers at various colloquia and seminars or as collaborators visiting one of the working groups. Roughly a third of all colloquia in the Physics and Astronomy Department (Thursday) are focused on Astronomy. Many members of our deparment also attend the Astronomy Colloquia at STScI on Wednesday afternoons. The Center for Astrophysical Sciences hosts a weekly seminar on Tuesday afternoons, and postdoctoral researchers present their research at the bi-weekly Monday Wine-and-Cheese seminar. There are journal clubs which focus on more specific subjects and which meet weekly or bi-weekly to discuss the current literature on astrobiology, star formation, galaxies, active nuclei, cosmology, or instrument engineering, while on Tuesday mornings members of CAS and their visitors enjoy coffee and cookies in the lobby of the 5th floor. The main colloquia and seminars are listed on the Events Page, and other meetings are managed through mailing lists; students and postdocs are highly encouraged to attend and participate. Theoretical Interdisciplinary Physics and Astrophysics Center's function is to support theoretical work within all three subgroups (astrophysics, condensed matter physics, and particle physics) of the Physics and Astronomy Department, especially on topics that bridge these subgroups. It sponsors visits by researchers from other universities, hosts seminars, and organizes workshops. An informal weekly lunch (on Thursdays) brings together theorists interested in astrophysics and cosmology both from the Department and from the Space Telescope Science Institute. |
