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Astronomy Research at Rutgers 

Astrophysics research at Rutgers ranges from late stages of stellar evolution to the early universe, and includes both observational studies at many wavelengths and theoretical work. Current research interests include:

  • Cosmic Microwave Background
  • Cosmological Parameters
  • Distant Galaxies
  • Galaxy Clusters
  • Dark Matter in Stellar and Galactic Systems
  • Gravitational Lensing (Strong & Weak)
  • The Milky Way
  • Theoretical Galaxy Dynamics
  • Dwarf Spheroidal Galaxies
  • Black Holes & Active Galactic Nuclei
  • Globular Clusters
  • Supernovae
  • Interstellar Medium

In addition, several members of the faculty are involved in the development of state-of-the-art instruments for both ground- and space-based telescopes. An outline of this research is given below, and more detailed information is available on other web pages.

Cosmic Microwave Background

The detailed pattern of temperature and polarization fluctuations expected in the microwave background has now been worked out for specific cosmological models.

Two Rutgers astronomers (Hughes and Williams) are CoIs of the Atacama Cosmology Telescope under construction in the northern Chilean desert. The telescope will observe the CMB at millimeter wavelengths to produce a deeper and more complete catalog of galaxy clusters than any so far available; this information will constrain the equation of state of the mysterious dark energy and place a tighter bound on the mass of the neutrino. The galaxy clusters detected through the Sunyaev-Zel'dovich effect will be observed using SALT.

Cosmological Parameters

Gawiser, Hughes, Jha and Keeton contribute to diverse efforts to determine the expansion rate and density of the universe.

Hughes is a member of the Chandra GTO team using that telescope to study the X-ray emission of galaxy clusters and to obtain direct measurements (i.e., independent of the distance ladder) of the Hubble constant using the Sunyaev-Zel'dovich effect of the hot plasma in galaxy clusters.

As a member of the High-Z Supernovae Search team, Jha uses ground- and space-based telescopes to study exploding stars in galaxies near and far. These Type Ia supernovae have proven to be exquisite tools with which to survey the expansion history of the Universe, and they played the central role in the discovery that the cosmic expansion is accelerating. Precise distances from these supernovae have a number of important cosmological applications, and provide a better understanding of the mysterious dark energy that drives the accelerating Universe.

Gawiser is a member of the LSST collaboration, which will determine the baryon acoustic oscillation scale from the clustering of galaxies and dark matter, with the goal to measure the equation-of-state of the dark energy.

Keeton is a member of the CASTLES project using the Hubble Space Telescope to obtain precise data on strong gravitational lens systems. He studies how well gravitational lens models can be used to obtain direct measurements of the Hubble constant, and how well the statistics of lens populations can constrain the density of the universe.

Distant Galaxies

Gawiser is PI of the MUSYC collaboration, which is determining the star formation rates, stellar masses, ages, dark matter masses, and low-redshift descendants of high-redshift galaxies.

Baker studies the evolution of galaxies, both as individuals and as populations, using observations of the nearby and distant universe. He makes regular use of data acquired at multiple wavelengths from the ultraviolet through the radio, but focuses on the (sub)millimeter bands where we can observe continuum emission from dust grains and rotational line emission from small molecules. These tracers allow us to study the most optically obscured (and often the most interesting!) regions of the galaxies. Some current questions of interest: How do extreme environmental conditions affect the process of star formation? What are the demographics, properties, and evolutionary states of dusty, high-redshift "submillimeter galaxies"? How can we use observations to test the assumptions and predictions of galaxy evolution models that are based on the cold dark matter paradigm for structure formation?

Galaxy Clusters

The origin, evolution, and nature of large galaxy clusters are still not well understood. Hughes's research in this area includes: (1) X-ray observations of high-redshift galaxy clusters; (2) weak lensing studies of X-ray/SZE galaxy clusters; and (3) studies of rich, nearby galaxy clusters in X-rays with the aim of constraining the merger histories of clusters and measuring their temperature structure.

Dark matter in Stellar and Galactic Systems

It is a matter of some controversy whether the dark matter in normal galaxies dominates all the way to their centers. Evidence on this question assembled by our group suggests that dark matter halos have low central densities and large core radii, possibly inconsistent with the predictions of CDM.

Observational efforts to identify and characterize the properties of dark matter in galaxies include the study of H-alpha emitting gas in spiral galaxies by Williams and Sellwood using the Rutgers Fabry-Perot spectrometer. When combined with optical photometry and 21 cm radio maps, these observations provide powerful constraints on the overall mass distribution. Pryor is carrying out dynamical studies of dwarf spheriodal galaxies using high-precision radial velocities of red giant stars obtained with a variety of ground-based optical telescopes. The large-scale distribution of dark matter in spiral and elliptical galaxies is being studied by Williams using radial velocities for both globular clusters, dwarf galaxies and planetary nebulae. Keeton is studying the distribution of mass in distant early-type galaxies using strong gravitational lensing.

Sellwood and former Rutgers graduate student Debattista have shown that the dynamical friction expected when a bar in a disk galaxy rotates in a dense halo leads to rotation rates for bars much lower than observed. Further work to buttress this result is in hand.

Gravitational Lensing

Observational signatures of gravitational lensing include multiple and/or highly-distorted images of distant galaxies or quasars (strong lensing), and small but correlated distortions in the shapes of distant galaxies (weak lensing). Lensing is directly sensitive to all mass (both luminous and dark), which makes it a powerful astrophysical tool. Around 100 examples of strong lensing by galaxies and clusters are known. Mass models of these systems can be used to study dark matter in galaxies and clusters and test the CDM paradigm, to probe the environments and evolution of early-type galaxies out to redshift z~1, to study massive black holes in the centers of distant galaxies, and to constrain cosmological parameters, among other things. Lens modeling software by Keeton has been used by a number of researchers to analyze observed strong lens systems. Gravitational lensing can also be used as a "natural telescope" to study fainter or smaller objects than could normally be observed.

The Milky Way

The distribution of mass within the Milky Way is still highly uncertain, particularly the contribution of dark matter. Properties of the gas flow in the bar, and other kinematic data can be used to provide additional constraints on the distribution of mass. Sellwood, with former student Weiner, has modeled the gas flow in the inner Galaxy in barred galaxy potentials. Using numerical simulations, Pryor and coworkers have explored the effect of tides on the evolution of the satellites of the Milky Way.

Williams and Sellwood are using the Rutgers Fabry-Perot to measure the velocities of a large sample of stars in several OGLE fields in the Galactic Bulge to help to determine structural parameters of the bar.

Theoretical Galaxy Dynamics

The present-day distribution of mass and angular momentum in galaxies is partly determined by initial conditions and partly by evolutionary changes. Studies by Sellwood and coworkers, in this area include: (1) lop-sided and bending instabilities; (2) bending modes of stellar systems with random motion; (3) the determination of linear instabilities of equilibrium stellar systems using high precision from N-body simulations; (4) instabilities in oblate galaxy models.

Dwarf Spheroidal Galaxies

Some of the dwarf spheroidal (dSph) galaxy companions of the Milky Way have mass-to-light ratios approaching M/LV ~ 100, even in their cores. The density of dark matter implied by these measurements is surprisingly high: 0.1-1 solar masses per cubic parsecs. These galaxies are clearly excellent laboratories for studying the properties of the dark matter and the evolution of dwarf galaxies. Pryor is carrying out various projects to study their stellar populations, binary fraction, star formation histories, internal kinematics and chemical evolution. With the aid of large ground-based telescopes, these studies are now being extended far beyond the dSph galaxies of the Milky Way, to other Local Group galaxies.

Black Holes (BHs) and Active Galactic Nuclei (AGN)

The study of BHs and Active Galactic nuclei by Joseph and Keeton is making use of the premier astronomical facilties, such as the Hubble Space telescope and various 4-10m class ground-based telescopes. Techniques to measure BH masses include stellar velocity dispersion measurements, kinematical studies of nuclear gas disks, reverberation mapping, and gravitational lensing. It has recently become clear that the formation and evolution of large central BHs in galaxies is closely related to that of their host galaxies. The processes that cause BHs to grow may be truncated by the destruction of bars and triaxality as the BHs grow in size, e.g., by the effect of central mass concentrations on the evolution of galactic bars (Sellwood).

Globular Clusters

The Hubble Space Telescope is now providing photometry of globular cluster (GC) stars with unprecedented depth and angular resolution. Similarly unprecedented are velocities for samples of hundreds to thousands of stars in individual GCs made possible by fiber-fed spectrographs and the Rutgers Fabry Perot. Together, these data can test our models for GC dynamical evolutionand better define the Pop II mass function. Fabry-Perot data taken by Pryor and Williams at CTIO, CFHT and Palomar has produced radial velocities for thousands of stars belonging to severl different Galactic globular clusters. Dynamical modelling of the radial velocities is being used to understand the internal dynamics of these objects.

Pryor is part of a group using HST to measure proper motions for a large sample of stars in several Galactic globular clusters. When combined with radial velocities measurements, many obtained using the Rutgers Fabry-Perot spectrometer, it will be possible to obtain the first reliable measurements of the distribution function in these clusters.


Chemically enriched material ejected by supernovae (SN) contains a detailed picture of stellar nucleosynthesis during both the evolution of the progenitor star and during its explosive death. X-ray emission from the fast moving shocks propagating through the ejecta and the surrounding medium provide an important probe of the material's composition. Hughes is using Chandra GTO and GO observations to study the X-ray emission from young SN remnants to learn about nucleosynthesis and to shed light on SN explosion mechanisms. Questions of basic physics, e.g., the extent of electron heating and the efficiency of cosmic ray acceleration, at high Mach number SN shock fronts is also under investigation. He is also carrying out X-ray imaging-spectroscopy of older supernova remnants with the aim of investigating their evolution, measuring the amount of energy they input to the ISM, and determining gas phase abundances of the ISM. Programs to identify new compact objects in remnants are also underway.

Interstellar Matter

Joseph is using high-precision measurements of element abundances in the instellar medium (ISM) to identify variations in the chemical composition of the diffuse gas. Other projects include the study of dust grain stability in the diffuse ISM, the susceptibility of grains to shock destruction and the search for Mg II absorbers in the direction of low-z, bright QSO spectra.


Primary Focus Imaging Spectrograph (PFIS)

Williams and Joseph, jointly with a team at Wisconsin, have built the PFIS instrument for use on SALT. The Rutgers component of the effort included the instrument structure and a Fabry-Perot Imaging Spectrophotometer.

The Ultraviolet Detector Lab

The Ultraviolet Detector Lab at Rutgers, operated by Joseph, provides a unique national facility for the development and testing of space image sensors. This facility, which is funded by NASA, assists researchers from around the country who are developing ultraviolet detectors. The laboratory currently has 3 UV development programs in 1)wide-band-gap solid-state detectors, 2) electron-bombarded CCDs, and 3) large (2-m x 2-m) focal-plane image tubes for NASA's envisaged OWL mission.

Rutgers Fabry-Perot Imaging Spectrophotometer

Williams built the initial Rutgers Fabry-Perot Imaging Spectrophotometer which was installed as a highly successful user instrument at CTIO between 1986 and 1999. A National Science Foundation grant to Williams supports the construction of a new Fabry-Perot Imaging Spectrophotometer at Rutgers. This instrument is expected to see widespread use on telescopes at CTIO, on the SOAR telescope, and on the Gemini-South 8m telescope.

X-ray Instrumentation

Hughes, a member of the Chandra design team, is also a member of the Science Team for NASA's Constellation-X Facility, which is a high throughput X-ray spectroscopy follow-on mission to the Chandra X-ray Observatory.

The men of experiment are like the ant, they only collect and use; the reasoners resemble spiders, who make cobwebs out of their own substance. But the bee takes the middle course: it gathers its material from the flowers of the garden and field, but transforms and digests it by a power of its own. Not unlike this is the true business of science; for it neither relies solely or chiefly on the powers of the mind, nor does it take the matter which it gathers from natural history and mechanical experiments and lay up in the memory whole, as it finds it, but lays it up in the understanding altered and disgested. Therefore, from a closer and purer league between these two faculties, the experimental and the rational...  much may be hoped.

- Francis Bacon, Novum Organum

    This page last updated on September 26, 2007, but fooled around with in 2009 by C. Joseph.
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