David Helfand

Professor of Astronomy

Research Interests:

- Large-scale structure and AGN in radio surveys 
- The origin and evolution of neutron stars and supernova remnants 
- Active galactic nuclei and the X-ray background

Professor Helfand recently completed a radio survey of the Galactic Plane that is 30 times more sensitive and has 30 times the angular resolution of the best existing Plane surveys. MAGPIS (the Multi-Array Galactic Plane Imaging Survey) was designed to complement the GLIMPSE infrared Plane survey withe the Spitzer Space telescope. Earlier, he was involved in another radio survey project, also using the Very Large Array, to construct the equivalent of the Palomar Sky Survey for the radio Universe. His FIRST Survey, begun in 1993, has produced over 34,000 two-million pixel images covering 9200 square degrees of the sky at 20 cm. The survey is complete for point sources to 1.0 mJy, and each of the ~850,000 radio sources catalogued has a position accurate to better than 1". This unprecedented astrometric accuracy has allowed us to increase the number of optically identified radio sources by more than a factor of 100. His team is using the survey to map large scale structure by computing the radio source angular correlation functions, detecting the weak-lensing shear produced by the foreground mass distribution on the distant radio sources, calculating the angular diameter-redshift relation for classical double radio sources, and identifying rich clusters at high redshift using bent-double radio galaxies as tracers of high density environments. They are also conducting a FIRST Bright Quasar Survey which has already led to the discovery of over 1000 new quasars with R<18, the first radio-loud BAL objects, and a high incidence of gravitational lenses. Several other projects using this unique new resource are also underway, including a search for highly obscured quasars. In addition, he continues to pursue a long-standing interest in the evolution of neutron stars and the supernova remnants in which the youngest ones are found. They have several programs approved for observations of synchrotron nebulae their neutron stars with Chandra and Newton. Recent results on the pulsars inVela and 3C58 were of particular interest. In order to increase the number of young remnants known, they have begun a major survey of the Galactic plane with the VLA and XMM Newton, complemented by the MSX mid-IR survey. He also expects to use the new generation of X-ray observatories to address the issue of the contribution of starburst galaxies and AGN to the cosmic X-ray background, and to study the high-redshift clusters we are finding with FIRST.