B S E R V I 1992 Statistics S M M A
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NATIONAL RADIO o B S S u E M R M V A I R N Y G ASTRONOMY OBSERVATORY 1992 STATISTICS Cover: An image of neutral atomic hydrogen in the triple galaxy system M81 • M82 - NGC 3077. These three galaxies are gravitationally bound to one another; the mutual tidal forces are stripping the hydrogen gas out of each galaxy. Darker red in this radio image indicates an increasing concentration of hydrogen gas. The image seen here is a mosaic of twelve separate images made with the NRAO Very Large Array. VLA observers: Min Su Yun, Paul Ho and K. Y. Lo. NATIONAL RADIO ASTRONOMY OBSERVATORY Observing Summary 1992 Statistics February 1993 SOME HIGHLIGHTS OF THE 1992 RESEARCH PROGRAM • The 12 Meter Telescope has been used to detect CO in the damped Lyman-alpha absorption systems at redshifts greater than 2. Such systems are thought to be the evolutionary precursors of galactic disks. The CO observations confirm this hypothesis and further demonstrate that the mass of gas involved with these systems, 1012 solar masses, is a more than sufficient reservoir of material for galaxy formation. Since the damped Lyman-alpha absorption systems emit little or no visible light, the CO observations provide the only direct way to observe these early "proto-galaxies" and to measure their properties. A critical question is when in the history of the universe the heavy elements carbon and oxygen were produced and how this material is spatially distributed. Millimeter-wave CO observations of high angular resolution have the potential to answer these questions and to provide us with a detailed view of galaxy formation. • A recent volume-limited sample of compact dwarf (HQ) galaxies-systems experiencing outbursts of starbirth-has been studied in the 21 cm HI line with the VLA and reveals that many have "midwife" companions that do not have ongoing starbursts themselves but are likely to be causing the starbursts in the HE galaxies. HI emission was detected from companions near 19 of 28 compact dwarfs studied. The compact dwarf galaxies appear to be too small for their starbursts to be triggered by density waves, so the gravitation of the newly discovered companions is the most likely triggering mechanism. This discovery provides new information to constrain theories of both galaxy formation and of star formation within galaxies. • The 140 Foot Telescope has been used to detect HI absorption at a redshift of 0.684 towards the smallest Einstein ring, 0218+357. Comparison with optical spectra show that the HI is associated with the lensing galaxy rather than the background quasar. Very high optical extinction is implied by both the large HI column density and the extremely red optical colors. This detection is important in providing a very accurate value for the lens redshift, which is essential in modeling the mass distribution through the lens, and in providing a check on the inferred lens mass through the width of the HI absorption. The detection also demonstrates a new approach to searching for and characterizing lens systems, and suggests that unusually red systems are the most likely ones to be detected. • The VLBA has recently been involved in the mapping of a very distant quasar, 0014+813, at 18 cm wavelength. This object has a redshift of 3.41, corresponding to a distance of more than 9 billion light-years. This is one of the first VLBI maps to achieve a sensitivity essentially at the thermal noise level It shows a long straight jet, about 6 kpc long, and much more regular than had been expected of quasars at this distance, seen as they were when the universe was young. For unknown reasons, this jet stops abruptly at a level considerably above the noise level • A new interstellar molecule, SO*, has been detected in the shocked molecular clump IC443G, which is undergoing impact from the blast wave of the supernova remnant IC 443. Analysis shows that the SO+ cannot have formed by either ion-molecule chemistry or by non-dissociative shock chemistry, but that the reaction involved, that of S+ with OH, requires a dissociative shock. SO+ is the only known interstellar molecule requiring such shocks for its formation. It has subsequently been detected in 17 massive star-forming regions out of 20 searched, thus indicating that massive stars may require strong (dissociating) shocks for their formation, and confirming the long-held belief that shocks of some sort are necessary to initiate the gravitational collapse of the large molecular clumps involved in massive star formation. • The VLA has detected counter-rotating gaseous disks in the "Evil-Eye Galaxy" (the Sab spiral NGC 4826) by means of high spatial and velocity resolution observations of the 21 cm HI line. The HI map reveals two distinct disks of gas, with one in the central 2 kiloparsecs counter-rotating relative to the rest of the galaxy. The inner disk, inclined 45 degrees to the outer disk, contains about half the galaxy's total gas mass. This is the first galaxy known to contain counter-rotating gaseous disks, and probably indicates a galactic merger. The structure seems quite consistent with supercomputer simulations of mergers, and raises interesting questions about the frequencies of mergers, the extent to which mergers may be responsible for shaping the Hubble sequence of galaxy types, and the lifetimes of the observable signatures of such mergers. • VLBA observations at 43 GHz have revealed new details of drcumstellar SiO masers surrounding cool red stars. U Herculis shows a clear ring of SiO maser emission with a diameter of 16 milliarcseconds, or 7.4 AU. The maser is very close to, or within outer layers of the star itself, whose size is estimated at 10 to 20 milliarcseconds. VY Canis Majoris, which has a more complex shell (with OH, H20, and SiO masers), reveals three apparent concentrations of SiO maser activity very near the star and raises the possibility that it may be a previously unresolved multiple star system SiO masers have also been observed around five other stars. OBSERVING HOURS 1980 81828384858687888990 9192 93 9495 Calendar Year 1 40-Foot 12-Meter VLA Fig. 1 This figure shows the hours scheduled for observing on each telescope during the last decade. Includes astronomical observing, testing, and calibration. DISTRIBUTION OF SCHEDULED OBSERVING TIME 12-Meter 140-Foot VLA o X o3 X 1983 84 85 86 87 88 89 90 91 92 1983 84 85 86 87 88 89 90 91 92 1983 84 85 86 87 88 89 90 91 92 Calendar Year Calendar Year Calendar Year NRAO Staff Wisitors I Testing and Calibration Fig. 2. These graphs show the number of hours scheduled for testing and calibration, and for observing by the NRAO staff and by visitors on each telescope system during the last decade. 12-METER RADIO TELESCOPE SUMMARY 100 s* - \ JL. -i- -^ \ -^ ^ "V ./r "\ s e— n A ^ A \ A 80 L ^^ r r r s \ / •\ 1 j - 60 . \ A A \ A \ / \ (\ L I r r A 1 f A r A if h 1 h 1 a> \ —, j , j ■ Q- 40 ■t \ 1 r- ' I 5 1 \ V V V V »•_. V \ V \ V \ \ 20 1 ^SI , T y y '"' \ I /— "^ y ^ >r J t > •^ =>< V V V > ►^ J ^ ^ ^\ S' i y '-- s t »••' *s N j. I 0 t 1 ^ -.' Calendar Year Observing Installation, Maintenance and Calibration Equipment Failure, Weather and Interference Figi 3. This summary for each quarter of the calendar year shows the percentage of time the telescope was scheduled for observing; for routine calibration, maintenance, and installation of new experiments; and the percentage of time lost due to equipment failure, bad weather, and radio interference. The telescope is removed from service for a period of four to six weeks each summer during the wet season. This period is used for maintenance and upgrading of the instrument. For most of 1983 the telescope was out of service for the replacement of the reflecting surface and its backup structure. 140-FOOT RADIO TELESCOPE SUMMARY 100 -s - ^\ A ^ ^s Z^ s* NX 'S ^V k , r ' % j S r V j \ 80 V -/ > X V^' >y V V sx S Z \ 1 V - ^ 60 \lV - - ^ 40 A - A A - \ /•s ^- > L 20 TT—J / s */ V ^ y V »•- ^" < <x ^ ^ >* ^ s ^ * ^^ »-•» — ^ •— *~-->. ^^ —• ^ .^ *«•• ... • • 0 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 Calendar Year Observing Installation, Maintenance and Calibration Equipment Failure, Weather and Interference Fig.4 This summary for each quarter of the calendar year shows the percentage of time the telescope was scheduled for observing; for routine calibration, maintenance, and installation of new experiments; and the percentage of time lost due to equipment failure, bad weather, and radio interference. Major improvements to the telescope system indude holographic surface tests and panel readjustments in 1987. VERY LARGE ARRAY TELESCOPE SUMMARY IUU - - 80 ^ ^ A .— —' * "^ ^s ^ s^ "*- — —** ^N ^ — /" ^. - ^ S. V ^ * 60 - - & 40 "^ —. __ ^-. — /" N - 20 ^/ *k s\ s*. ^x ^ "•* .» ^. — ^ •>« — —. .- — — ... ■ .— "^*''^. — rC ™** -- — ^.. — .^«. —- ».^« , — ^1 — .—* *"*" k^_ —- — = 0 Calendar Year Observing Testing, Maintenance and Calibration Downtime Fig. 5 This summary for each quarter of the calendar year shows the percentage of time the telescope was scheduled for observing; for routine system testing, maintenance, and calibration; and the percentage of time lost due to hardware or software failure, power failure, or bad weather. FULLrTIME EMPLOYEES ttBBft CVXAQ 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 Calendar Year V77XVLA Construction Research and Operations I I VLBA Construction E-iggl 6BT Construction Rg. 6 This figure shows the total number of NRAO full-time employees at the end of each year, projected into the future.