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4 Report of the Panel on Radio and Submillimeter-Wave Astronomy
Pages 167-220

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From page 167...
... ~ J — Report of the Panel on Radio any Ruby Ammeter- Wave Astronomn
From page 168...
... The ALMA project is far more exciting and capable than originally envisaged and will provide the means to explore the dusty sites of planet and star formation and the hearts of the earliest galaxies. The Panel on Radio and Submillimeter-Wave Astronomy reaffirms the high priority given to ALMA by the 1991 Astronomy and Astrophysics Survey Committee and emphasizes that its construction schedule should be .
From page 169...
... For example, submillimeter studies have shown that a substantial part of the energy release at high redshifts occurs in regions obscured by dust, but the origin of the energy is in question. The EVLA will uniquely distinguish between massive star formation and accretion onto a supermassive black hole as the underlying energy source, allowing researchers to decode the history of star and galaxy formation as well as the role of supermassive black holes in galaxy evolution.
From page 170...
... Observatory is the logical first step toward the long-term goal of space FIIVsubmillimeter interferometry, which could provide high-resolution imaging of star formation sites both locally and at high redshift. Such a capability will provide an excellent FIIVsubmillimeter complement to ALMA, EVLA, and SKA.
From page 171...
... astronomers rely almost entirely on them for telescope access. The NSF needs to provide increased support to operate, maintain, and continually upgrade the radio facilities to keep them at the cutting edge, and it should seize the opportunity to develop subarcsecond imaging capabilities, complementing those of the VLA and the Next Generation Space Telescope (NGST)
From page 172...
... High-resolution radio imaging allows the detailed measurement of the kinematics in galactic microquasars and their more powerful extragalactic counterparts and measurement of the speed of expansion of gamma-ray bursters. Such observations provide compelling evidence of a supermassive black hole in the heart of the nearby galaxy NGC 4258 and suggest the presence of many more massive black holes in galactic cores.
From page 173...
... Before the end of the decade, radio astronomers will provide high-precision determinations of the primary cosmological parameters. Measurements of the polarization of the CMB will determine the contribution to CMB anisotropy from gravitational waves excited by the decaying inflationary potential in the early universe (t = 10-30 s)
From page 174...
... 174 In to .
From page 175...
... In the end, the observations made by these instruments will tell us whether the inflationary model for the origin of the Big Bang is correct or whether our understanding of the origin of the universe must undergo another major revision. The small distortion of the background radiation induced when CMB photons scatter off electrons in the hot gas contained within clusters of galaxies is known as the Sunyaev-Zel'dovich (SZ)
From page 176...
... The large collecting area and high spatial resolution provided by ALMA at 7- to 10-mm wavelengths will allow sensitive detailed imaging of the SZ effect from distant clusters. Radio astronomy also provides its own direct probes of the expansion history of the universe and the allowed values of the cosmological ; 50 1 ~ it.
From page 177...
... Additionally, the gravitational mass, luminous plus dark matter, in the tensing galaxy is measured. Ongoing and future large surveys of tensing in samples of compact radio galaxies and quasars will determine parameters such as the cosmological constant, matter density, and curvature.
From page 178...
... More recently than z ~ 5, the development of the cosmic web of neutral hydrogen and the formation and evolution of galaxy halos should be observable. Calculations of the sensitivity required for these measurements led to the need for a radio telescope with 1 square kilometer of collecting area, giving the SEA its name.
From page 179...
... and most likely represent an early ultraluminous star-formation phase in a forming or merging galaxy. As illustrated in Figure 4.4, high-resolution observations made with the current millimeter arrays demonstrate the likely link between low-redshift, gas-rich, ultraluminous infrared galaxies
From page 180...
... 180 ASTRONOMY AND ASTROPHYSICS IN THE NEW MILLENNIUM: PANEL REPORTS and the high-redshift submillimeter sources; however, the co-moving number density of the distant objects is 100 times higher and their farinfrared luminosities are greater than those of the nearer population. Many of the ultraluminous galaxies appear as faint radio continuum sources, invisible to ground-based optical images and to the Hubble Space Telescope (HST)
From page 181...
... The pilot studies using the VLA at ~ = 4 m are extremely promising, proving that the effects of the ionosphere can be removed. It is well known that radio continuum luminosity correlates tightly with the star formation rate and that radio continuum observations, unlike their optical counterparts, do not suffer from dust extinction.
From page 182...
... related to a massive central engine. Molecular gas, as traced particularly by carbon monoxide but also by other species, represents the star-forming component of the interstellar medium in galaxies.
From page 183...
... The study of the neutral hydrogen 21-cm line emission has been a staple of observational cosmology, providing diverse clues to the structure of galaxy disks, the circumstances of star formation within them, and the history of galaxy interactions. The molecular, atomic, and continuum studies of galaxies provide the foundation on which detailed galaxy formation models will be built, while the information extracted from the velocity fields via spectroscopic imaging of atomic and molecular species reveals the history of encounter dynamics.
From page 184...
... Extension of such studies to the more distant universe awaits improvements in spectral resolution and coverage through the VLA correlator enhancement and in lowfrequency-array sensitivity through LOFAR and, later, the SKA. With these advances, the otherwise invisible network of lower-density, largescale structure bridging the clusters, superclusters, and galaxy groups will be delineated by HI line emission and/or absorption.
From page 185...
... It is widely speculated that this energy originates in a supermassive black hole accreting material from its surroundings. FIGURE 4.6 Spectroscopic studies of disturbed gas disks bear the spatial and kinematic signatures of the dynamics of galaxy encounters.
From page 186...
... The central mass contained within 0.1 parsec exceeds 3 x 107 solar masses, with a mass density exceeding 10~° solar masses per cubic parsec; such a high density provides compelling evidence that the central object is a supermassive black hole. In the new decade, similar observations will be extended to much higher sensitivity with the large, ground-based radio telescopes and arrays and to unprecedented angular resolution with ARISE.
From page 187...
... , the jet appears to narrow toward its base. Bottom left panel: A cartoon of a supermassive black hole, surrounding accretion disk, and jet like the one in the center of M87.
From page 188...
... The wire grid diagram depicts the accretion disk determined from the positions, velocities, and accelerations ofthe maser spots. The continuum emission near the dynamical center ofthe system appears to be the innermost portion of a jet.
From page 189...
... itself indicates that the subastronomical-unit-scale radio source is more massive than 103 solar masses and that it anchors the dynamical center of the Galaxy. Coupled with proper motions of stars in the central cluster, the case for a black hole of a few million solar masses in the center of the Galaxy is very strong.
From page 190...
... As a result, radio observations of star formation have been most intensely pursued at millimeter and submillimeter wavelengths, revealing the rich complexity of molecular clouds. Such observations have only just begun to unveil the details of the accretion disks that feed the stars and eventually form planets.
From page 191...
... Studies of star formation in clustered environments will also address questions about the origin of the stellar initial mass function (IMF)
From page 192...
... The polarization of continuum and line emission has also been detected with current arrays in a few cases, although the interesting structures in these objects are somewhat blurred by the limited spatial resolution of the arrays; CARMA and ALMA will allow systematic study of the role of magnetic fields in star formation. From the red-giant phase to their final state, stars eject dust grains and molecules back to the interstellar medium (ISM)
From page 193...
... . Right: A sequence of VLBA images of the evolving x-ray nova Cl Cam taken 75 (top)
From page 194...
... All the theoretical mechanisms for inducing the migration of large planets during star formation require the presence of a massive gas and dust disk that can exchange angular momentum with the Jovian protoplanet. The gas densities required of such massive disks imply large optical depths in the optical and infrared.
From page 196...
... Does the migration process in such systems differ dramatically from that which operates in the disks around single low-mass stars? Radio and submillimeter instruments will also make possible the first detailed studies of the chemical composition of circumstellar accretion disk analogues of the solar nebula.
From page 197...
... The subarcsecond imaging capability envisioned for CARMA, ALMA, and the EVLA will enable observations of solar system objects at radio and submillimeter wavelengths with resolution similar to that of HST and NGST. In continuum mode, such observations can be used to examine the properties of the surface and subsurface layers of terrestrial bodies, while spectroscopic tracers at radio wavelengths directly probe the atmospheric circulation and composition.
From page 198...
... In nearby molecular clouds, these same instruments will trace the evolution of chemical complexity in the dense cores that will form stars. It is already clear that molecules accrete onto dust grains in cold regions, are sublimated when those grains are heated by forming stars, and trigger further increases in complexity when ejected back into the gas phase.
From page 199...
... N AT ~ O NAT C E N TE RS Through cooperative agreements, the NSF supports two national centers for radio astronomy: the National Radio Astronomy Observatory (NRAO) , operated by Associated Universities, Inc., and the National Astronomy and Ionosphere Center (NAIC)
From page 200...
... In addition to supporting their respective scientific programs, both NRAO and NAIC maintain effective education and outreach programs. U NIVERSITY RADIO FACILITIES Until ALMA begins operation, the university radio facilities will provide the only U.S.
From page 201...
... Support for university radio facilities provides the astronomy community access to unique observational capabilities and maintains a strong university involvement in scientific and technological development. The NSF-supported university radio facilities all provide substantial community access, typically 30 to 50 percent, through their guest observer programs.
From page 202...
... 50 (NSF) As illustrated in Figure 4.11, the proposed facilities will contribute wide-ranging new capabilities, among them increased angular resolution and wavelength coverage, thus opening up large areas of discovery space.
From page 203...
... . The radio and submillimeter programs recommended in this chapter will add wide-ranging new capabilities, amongthem increased angular resolution and wavelength coverage, thus opening up large areas of discovery space.
From page 204...
... Of particular interest will be the study of protogalaxies as well as protostars and protostellar disks that are often optically thick or obscured by dust at shorter wavelengths. With the greatly increased sensitivity and resolution of the VLA at centimeter wavelengths, it will be possible to study star formation at the earliest epochs, to distinguish starburst from AGN phenomena even for z > 5, and within our Galaxy, to see into the regions corresponding to planetary formation on scales of 10 AU and less.
From page 205...
... S Q HARE K L0 M ETER ARRAY The SKA is a proposed centimeter-wave radio telescope with 106 me of collecting area.
From page 206...
... Molecular Zeeman studies will trace how magnetic fields control cloud collapse. The effects of weak gravitational tensing will map the dark matter on the largest scales.
From page 207...
... Together with Earth-based radio telescopes, ARISE will allow radio imaging with a sixfold improvement in angular resolution compared with the VLBA. In combination with the large ground-based telescopes such as the VLBA, GET, and LMT, the 25-m space antenna, equipped with state-of-the-art receivers, will be more than an order of magnitude more sensitive than the 8-m Japanese HALCA antenna.
From page 208...
... The panel recommends that NASA continue to support the development and operation of large apertures in Earth orbit for VLBI in order to achieve angular resolution of ~ 10 ,uarcsec. An instrument such as that on the ARISE mission will allow mapping of the emission from the inner accretion disks and the masers in the outer accretion disks in AGN as well as the x-ray- and gamma-ray-emitting regions from the jets of blazers.
From page 209...
... Among the several promising areas identified by the panel for smaller-scale investment are the following, which are neither exhaustive nor ranked: construction of LOFAR, a ground-based array for long-wavelength (2- to 20-m) astronomy; studies of CMB polarization and the SZ effect; development of far-infrared/submillimeterwave interferometry in space; laboratory astrophysics; and solar radio astronomy.
From page 210...
... COSMIC MICROWAVE BACKGROUND EXPERIMENTS Because of the large number of imminent observations and the likelihood of surprises, the panel elects not to specify in detail future CMB missions and projects. Clearly, however, further study of the CMB radiation will produce unique and fundamental clues to the processes and evolution of the earliest epochs.
From page 211...
... A suitable dedicated instrument such as the proposed Frequency Agile Solar Radio telescope (FASR) discussed by the Panel on Solar Astronomy appears to be feasible and would be ideal for the continued investigation of these areas.
From page 212...
... allocated for commercial and other purposes. Radio astronomers, accordingly, must develop ways to characterize and excise man-made signals in order to recognize and study cosmic ones.
From page 213...
... However, the panel is concerned about how future cost-sharing arrangements may affect this policy. Traditionally, some foreign radio facilities have provided comparable open access.
From page 214...
... AGENCY FUNDING AND MANAGEMENT POLICIES The NSF needs to provide adequate support for operating, maintaining, and continually upgrading federally funded radio facilities (both the national centers and the university radio facilities) to keep them at the cutting edge.
From page 215...
... , R Ekers (Australia Telescope National Facility)
From page 216...
... 216 ASTRONOMY AND ASTROPHYSICS IN THE NEW MILLENNIUM: PANEL REPORTS AGN active galactic nuclei ALMA Atacama Large Millimeter Array ARISE Advanced Radio Interferometry between Space and Earth, an orbiting antenna that will be used in concert with the ground-based VLBA AU astronomical unit. A basic unit of distance equal to the separation between Earth and the Sun, about 150 million km BEAST Background-Emission-Anisotropy Scanning Telescope; a longduration, balloon-borne cosmic microwave background experiment BIMA Array Berkeley-Illinois-Maryland Association Array BOOMERANG—Balloon Observations of Millimetric Extragalactic Radiation and Geophysics; a balloon-borne telescope that circumnavigated Antarctica CARMA Combined Array for Research in Millimeter-wave Astronomy, a millimeter-wave array in the Northern Hemisphere CBI Cosmic Background Imager, a 13-element interferometer located in northern Chile CMB cosmic microwave background CMVA Coordinated Millimeter VLBI Array COBE Cosmic Background Explorer, a NASA mission launched in 1989 to study the cosmic background radiation from the Big Bang CSO Caltech Submillimeter Observatory, a 10-m telescope operating on Mauna Kea, Hawaii, used for observations of millimeter and submillimeter wavelength radiation D/H deuterium/hydrogen ratio DASI Degree-Angular-Scale Interferometer for imaging anisotropy in the cosmic microwave background EVLA Expanded Very Large Array FASR Frequency-Agile Solar Radio telescope FCRAO Five College Radio Astronomy Observatory FIR far infrared FIRST European Far Infrared Space Telescope GET Green Bank Telescope ORB gamma-ray burst HALCA Highly Advanced Laboratory for Communications and Astronomy, the Japanese VSOP satellite launched in February of 1997 HI atomic hydrogen HII ionized hydrogen
From page 217...
... initiative to make observations at radio wavelengths longer than 2 m MAP Microwave Anisotropy Probe mission MAXIMA Millimeter Anisotropy Experiment Imaging Array; a balloonborne millimeter-wave telescope designed to measure the cosmic microwave background NAIC National Astronomy and Ionosphere Center, Arecibo, Puerto Rico NASA National Aeronautics and Space Administration NFRA Netherlands Foundation for Research in Astronomy NGST Next Generation Space Telescope, an 8-m infrared space telescope NICMOS Near Infrared Camera and Multi-Object Spectrometer, an instrument on the Hubble Space Telescope NRAO National Radio Astronomy Observatory NRL Naval Research Laboratory NSF National Science Foundation NVSS NRAO VLA Sky Survey OVRO Owens Valley Radio Observatory POLAR Polarization Observations of Large Angular Regions, an instrument designed to measure the polarization of the cosmic microwave background Planck Surveyor A European-led space mission to image anisotropies in the CMB. Polatron a bolometric receiver with polarization capability designed for use at the Owens Valley 5.5-m radio telescope 217
From page 218...
... SKA Square Kilometer Array, an international centimeter-wave radio telescope SMA Submillimeter Array SOFIA Stratospheric Observatory for Infrared Astronomy, a 2.5-m telescope flown above most of the Earth's water vapor in a modified Boeing 747 aircraft to study infrared and Submillimeter radiation SPST South Pole Submillimeter Telescope STScI Space Telescope Science Institute SZ effect Sunyaev-Zel'dovich effect, the small distortion of the CMB radiation induced when CMB photons scatter off electrons in the hot gas contained within clusters of galaxies TopHat A NASA-sponsored experiment in which a telescope was placed on top of a balloon to measure cosmic microwave background .
From page 219...
... PANEL ON RADIO AND SUBMILLIMETER-WAVE ASTRONOMY VSA Very Small Array, a project to make images of the CMB radiation on angular scales of around 1 deg VSOP VLBI Space Observatory Program, a mission led by the Institute of Space and Astronautical Science in collaboration with the National Astronomical Observatory of Japan WFPC Wide-Field Planetary Camera, an instrument on the Hubble Space Telescope 219
From page 220...
... cost of maintaining the National astronomy data resources, which includes the individual surveys and data archives. The NVO will be built on four layers: standards, archive services, basic analysis tools, and advanced analysis tools.


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