An Improved Measurement of the Hubble Constant from the Sunyaev-Zeldovich Effect

We present a determination of the Hubble constant from measurements of the Sunyaev-Zeldovich Effect (SZE) in an orientation-unbiased sample of 7 z < 0.1 galaxy clusters. With improved X-ray models and a more accurate 32-GHz calibration, we obtain H_O = 64+14-11 +/- 14_sys km/s/Mpc. for a standard CDM cosmology, or 66+14-11 +/- 15_sys km/s/Mpc for a flat LambdaCDM cosmology. In combination with X-ray cluster measurements and the BBN value for Omega_B, we find Omega_M = 0.32 +/- 0.05.Comment: 5 pp., Accepted for publication in ApJ

Coherent Receiver Arrays for Astronomy and Remote Sensing

Monolithic Millimeter-wave Integrated Circuits (MMICs) provide a level of integration that makes possible the construction of large focal plane arrays of radio-frequency detectors—effectively the first “Radio Cameras”—and these will revolutionize radio-frequency observations with single dishes, interferometers, spectrometers, and spacecraft over the next two decades. The key technological advances have been made at the Jet Propulsion Laboratory (JPL) in collaboration with the Northrop Grumman Corporation (NGC). Although dramatic progress has been made in the last decade in several important areas, including (i) packaging that enables large coherent detector arrays, (ii) extending the performance of amplifiers to much higher frequencies, and (iii) reducing room-temperature noise at high frequencies, funding to develop MMIC performance at cryo-temperatures and at frequencies below 150GHz has dropped nearly to zero over the last five years. This has severely hampered the advance of the field. Moreover, because of the high visibility of < 150GHz cryogenic detectors in astrophysics and cosmology, lack of progress in this area has probably had a disproportionate impact on perceptions of the potential of coherent detectors in general. One of the prime objectives of the Keck Institute for Space Studies (KISS) is to select crucial areas of technological development in their embryonic stages, when relatively modest funding can have a highly significant impact by catalyzing collaborations between key institutions world-wide, supporting in-depth studies of the current state and potential of emerging technologies, and prototyping development of key components—all potentially leading to strong agency follow-on funding. The KISS large program “Coherent Instrumentation for Cosmic Microwave Background Observations” was initiated in order to investigate the scientific potential and technical feasibility of these “Radio Cameras.” This opens up the possibility of bringing support to this embryonic area of detector development at a critical phase during which KISS can catalyze and launch a coherent, coordinated, worldwide effort on the development of MMIC Arrays. A number of key questions, regarding (i) the importance and breadth of the scientific drivers, (ii) realistic limits on sensitivity, (iii) the potential of miniaturization into receiver “modules,” and (iv) digital signal processing, needed to be studied carefully before embarking on a major MMIC Array development effort led by Caltech/JPL/NGC and supported by KISS, in the hope of attracting adequate subsequent government funding. For this purpose a large study was undertaken under the sponsorship and aegis of KISS. The study began with a workshop in Pasadena on “MMIC Array Receivers and Spectrographs” (July 21–25, 2008)1, immediately after an international conference “CMB Component Separation and the Physics of Foregrounds” (July 14–18, 2008)2 that was organized in conjunction with the MMIC workshop. There was then an eight-month study period, culminating in a final “MMIC 2Workshop” (March 23–27, 2009).3 These workshops were very well attended, and brought together the major international groups and scientists in the field of coherent radio-frequency detector arrays. A notable aspect of the workshops is that they were well attended by young scientists—there are many graduate students and post-doctoral fellows coming into this area. The two workshops focused both on detailed discussions of key areas of interest and on the writing of this report. They were conducted in a spirit of full and impartial scrutiny of the pros and cons of MMICs, in order to make an objective assessment of their potential. It serves no useful purpose to pursue lines of technology development based on unrealistic and over-optimistic projections. This is crucially important for KISS, Caltech, and JPL which can only have real impact if they deliver on the promise of the technologies they develop. A broad range of opinions was evident at the start of the first workshop, but in the end a strong consensus was achieved on the most important questions that had emerged. This report reflects the workshop deliberations and that consensus. The key scientific drivers for the development of the MMIC technology are: (i) large angular-scale Bmode polarization observations of the cosmic microwave background—here MMICs are one of two key technologies under development at JPL, both of which are primary detectors on the recently-launched Planck mission; (ii) large-field spectroscopic surveys of the Galaxy and nearby galaxies at high spectral resolution, and of galaxy clusters at low resolution; (iii) wide-field imaging via deployment as focal plane arrays on interferometers; (iv) remote sensing of the atmosphere and Earth; and (v) wide-field imaging in planetary missions. These science drivers are discussed in the report. The most important single outcome of the workshops, and a sine qua non of this whole program, is that consensus was reached that it should be possible to reduce the noise of individual HEMTs or MMICs operating at cryogenic temperatures to less than three times the quantum limit at frequencies up to 150 GHz, by working closely with a foundry (in this case NGC) and providing rapid feedback on the performance of the devices they are fabricating, thus enabling tests of the effects of small changes in the design of these transistors. This kind of partnership has been very successful in the past, but can now be focused more intensively on cryogenic performance by carrying out tests of MMIC wafers, including tests on a cryogenic probe station. It was felt that a properly outfitted university laboratory dedicated to this testing and optimization would be an important element in this program, which would include MMIC designs, wafer runs, and a wide variety of tests of MMIC performance at cryogenic temperatures. This Study identified eight primary areas of technology development, including the one singled out above, which must be actively pursued in order to exploit the full potential of MMIC Arrays in a timely fashion: 1. Reduce the noise levels of individual transistors and MMICs to three times the quantum limit or lower at cryogenic temperatures at frequencies up to 150 GHz. 2. Integrate high-performing MMICs into the building blocks of large arrays without loss of performance. Currently factors of two in both noise and bandwidth are lost at this step. 3. Develop high performance, low mass, inexpensive feed arrays. 4. Develop robust interconnects and wiring that allow easy fabrication and integration of large arrays. 5. Develop mass production techniques suitable for arrays of differing sizes. 6. Reduce mass and power. (Requirements will differ widely with application. In the realm of planetary instruments, this is often the most important single requirement.) 7. Develop planar orthomode transducers with low crosstalk and broad bandwidth. 8. Develop high power and high efficiency MMIC amplifiers for LO chains, etc. Another important outcome of the two workshops was that a number of new collaborations were forged between leading groups worldwide with the object of focusing on the development of MMIC arrays

Simultaneous Radio to (Sub-) mm-Monitoring of Variability and Spectral Shape Evolution of potential GLAST Blazars

The Large Area Telescope (LAT) instrument onboard GLAST offers a tremendous opportunity for future blazar studies. In order to fully benefit from its capabilities and to maximize the scientific return from the LAT, it is of great importance to conduct dedicated multi-frequency monitoring campaigns that will result comprehensive observations. Consequently, we initiated an effort to conduct a GLAST-dedicated, quasi-simultaneous, broad-band flux-density (and polarization) monitoring of potential GLAST blazars with the Effelsberg and OVRO radio telescopes (11cm to 7mm wavelength). Here, we present a short overview of these activities which will complement the multi-wavelengths activities of the GLAST/LAT collaboration towards the 'low-energy' radio bands. Further we will give a brief outlook including the extension of this coordinated campaign towards higher frequencies and future scientific aims.Comment: 3 pages, to appear in the Proceedings of the First GLAST Symposium, Stanford University, February 200

A New Component in the Radio Continua of PNe

A byproduct of experiments designed to map the CMB is the recent detection of a new component of foreground galactic emission. The anomalous foreground at 10–30 GHz, unexplained by traditional emission mechanisms, correlates with 100 mum dust emission, and is thus presumably due to dust.Is the anomalous foreground ubiquitous in the Galaxy? I will present evidence obtained with the CBI and SIMBA+SEST supporting the existence of the new component in the ISM at large, and in specific objects, in the form of a 31 GHz excess over free-free emission in PNe

Polarization Observations with the Cosmic Background Imager

We describe polarization observations of the CMBR with the Cosmic Background Imager, a 13 element interferometer which operates in the 26-36 GHz band from Llano de Chajnantour in northern Chile. The array consists of 90-cm Cassegrain antennas mounted on a steerable platform which can be rotated about the optical axis to facilitate polarization observations. The CBI employs single mode circularly polarized receivers which sample multipoles from ℓ~400 to ℓ~4250. The instrumental polarization of the CBI was calibrated with 3C279, a bright polarized point source which was monitored with the VLA

VLBI Mapping of the Nuclei of Radio Galaxies and Quasars

It is now possible, by means of VLBI hybrid mapping, to make maps of radio sources with a resolution of ~ 1 milliarcsecond. This enables us for the first time to compare the morphologies of the small- and large-scale structures of extragalactic radio sources, and they are strikingly different

Mass along the Line of Sight to the Gravitational Lens B1608+656: Galaxy Groups and Implications for H_0

We report the discovery of four groups of galaxies along the line of sight to the B1608+656 gravitational lens system. One group is at the redshift of the primary lensing galaxy (z = 0.631) and appears to have a low mass, with eight spectroscopically confirmed members and an estimated velocity dispersion of 150 ± 60 km s^(-1). The three other groups are in the foreground of the lens. These groups contain ~10 confirmed members each and are located at redshifts of 0.265, 0.426, and 0.52. Two of the three additional groups are centered roughly on the lens system, while the third is centered ~1' south of the lens. We investigate the effect of each of the four groups on the gravitational lensing potential of the B1608+656 system, with a particular focus on the implications for the value of H_0 derived from this system. We find that each group provides an external convergence of ~0.005-0.060, depending on the assumptions made in the calculation. For the B1608+656 system, the stellar velocity dispersion of the lensing galaxy has been measured, thus breaking the mass sheet degeneracy due to the group that is physically associated with the lens. The effect of the other groups along the line of sight can be folded into the overall uncertainties due to large-scale structure (LSS) along the line of sight. Because B1608+656 appears to lie along an overdense line of sight, the LSS will cause the measurement of H_0 to be biased high for this system. This effect could be 5% or greater