Intrinsic Anisotropy of the Cosmic Microwave Background Radiation
Observations of the microwave background radiation (MBR) have led to precision determinations of the geometry of the universe, the fractions of matter in baryonic matter and in non-baryonic cold dark matter, and the dark energy content of the universe, along with several other fundamental cosmological parameters, such as the slope of the mass-distribution spectrum. They also provide a solid foundation upon which to build theories of the formation of structure in the universe.
Observations carried out by our group on the Owens Valley Radio Observatory (OVRO) 40 M Telescope of fields near the North Celestial Pole (NCP) in the 1980s provided the most stringent limits in the pre-COBE era on intrinsic anisotropy on angular scales of a few arc minutes (DT/T<1.7x10-5) , thereby ruling out theories of galaxy formation based on baryonic matter, and providing compelling evidence for a dominant non-baryonic matter component. Observations in the 1990s on the OVRO 5.5 M and 40 M Telescopes at 32 GHz and 14.5 GHz, respectively, revealed an anomalous galactic foreground which has a spectral index alpha ~0. After removal of this foreground, the remaining fluctuations, attributed to the MBR, have DT/T~2.5x10^-5 at the spherical harmonic l~600, indicating, in combination with COBE, NCP and TOCO results, a flat geometry, and consistent with standard CDM models.
The Cosmic Background Imager; (CBI)
The Caltech group designed and constructed the Cosmic Background Imager (CBI) on the Caltech campus during 1995-1999 and moved it to Chile in August 1999. The instrument was re-assembled at the Chajnantor Test Facility at an altitude of 5080 m in September/October 1999, and was fully operational until June 2008. It was upgraded to polarization capability in 2002. The CBI was a radio interferometric array of 13 90-cm cassegrain antennas mounted on a 6.1 meter platform. The instrument had 10 1-GHz frequency channels spanning 26 GHz to 36 GHz, and low-noise HEMT amplifiers cooled to 6 Kelvin. It had an altazimuth mount, and a third rotation axis about the optical axis. The third rotation axis was used to discriminate between astronomical signals and very low-level signals which originated in the instrument itself, and also to facilitate polarization observations.
Observations with the CBI provided the first detection of intrinsic anisotropy on mass scales ranging from a few times the mass of the local group up to the most massive superclusters of galaxies; and also provided the first detectrion of the "Silk Damping" tail due to photon viscosity at the surface of last scattering. The total intensity observations with the CBI extend up to multipoles ~3500. Polarization observations with the CBI provided the most sensitive detection (11-sigma) of the E-mode polarization fluctuations for four years, from 2004 to 2008 and, in addition, provided compelling evidence that the E-mode spectrum is out of phase with the T-mode spectrum, thereby confirming one of the major assumptions in the interpretation or these spectra, namely, that the features in these spectra are produced by acoustic waves in a photon-baryon fluid.
In 2005 we began working on the QU Imaging ExperimenT (QUIET). The first receiver, a 19-element Q-band system, was installed in July 2008, and observed until June 2009, when it was replaced by a 91-element W-band system.
Sunyaev-Zel'dovich Effect Observations
In collaborations with Oxford, NRAO and CITA, our group is studying the Sunyaev-Zel'dovich Effect (SZE) in a series of programs. Thus far we have observed the SZE with high sensitivity in over 30 clusters
The Caltech 40 M Telescope Fermi-GST Program
In collaboration with Fermi-GST and the MPIfR(Bonn), our group has carried out an upgrade of the 40M Telescope and 15 GHz receiver for an intensive program to monitor 1200 GLAST Blazars twice per week. It is vital that the most active objects being observed by Fermi-GST be studied over a wide frequency range. This program is part of a large multi-frequency collaboration, with colleagues at Stanford, the University of New Mexico, Oxford, Manchester and Torun, in which the 1200 brightest blazars north of declination -20 degrees are being monitored and imaged at radio wavelengths, using the OVRO 40m, Effelsberg 100m and Torun 32m telescopes, and the VLBA; and studied at optical wavelengths on the Palomar, Keck, Hobby-Eberly, SALT and VLT telescopes.
The Cosmic Lens All Sky Survey (CLASS)
In a large-scale collaboration we have carried out a radio survey with the VLA to identify gravitational lenses, and follow-up observations on the Palomar and Keck telescopes. Alltold, combining CLASS and JVAS, 21 new gravitational lenses were discovered. This program is now being continued with observations of CLASS lenses on the Keck telescopes.