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
• Black Holes & Active Galactic Nuclei
• Supernovae

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.

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, Hughes, Jha and Keeton are members of the Large Synoptic Survey Telescope (LSST) Dark Energy Science Collaboration, which will measure the equation-of-state of dark energy using weak and strong gravitational lensing, the baryon acoustic oscillation scale from galaxy clustering, the abundance of galaxy clusters, and the brightness of Type Ia supernovae.

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, Jha, and Somerville are members of CANDELS, which has conducted the largest-ever survey using the Hubble Space Telescope. Ongoing research includes the high-redshift Type Ia supernova rate, reconstruction of galaxy star formation histories, evolution of the normalization and intrinsic scatter of the galaxy Star Formation Rate-Stellar Mass correlation, and the creation of highly realistic mock CANDELS catalogs.

Through the Hobby Eberly Telescope Dark Energy Experiment (HETDEX), Gawiser and his research group are studying the clustering of nearly a million distant Lyman Alpha Emitting galaxies to probe the dark energy equation-of-state and the properties of dark matter.

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 has carried 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. Keeton is studying the distribution of mass in distant early-type galaxies using strong gravitational lensing.

Gravitational Lensing

Gravity's ability to bend light leads to a rich array of astrophysical applications. Keeton uses strong gravitational lensing to study the distribution of matter in and around galaxies, to understand the lensing mass in its cosmological context, to probe quasars and galaxies at high redshift, and to investigate black holes as both astrophysical and relativistic objects. His team recently joined the Hubble Frontier Fields program ( http://www.stsci.edu/hst/campaigns/frontier-fields/) to use galaxy clusters as "cosmic telescopes" to study high-redshift galaxies.

The Milky Way

Pryor is using images taken with the Hubble Space Telescope to measure proper motions for dwarf satellite galaxies of our Milky Way Galaxy. These yield space velocities and orbits for the galaxies. Obtaining the correct numbers and properties for the Milky Way satellites has been a problem for models of galaxy formation. Thus, the long-term goal of this work is to provide orbits for a sample of satellites that can be used to test these models. He is currently leading the effort to analyze the data from a 110-orbit program studying low-luminosity satellites.

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).

Supernovae

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.

Instrumentation

Robert Stobie Spectrograph (PFIS)

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

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.

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.