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  • 1
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    Northern dwarf and low surface brightness galaxies. II - The Green Bank neutral hydrogen survey (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The paper reports neutral hydrogen observations of a large sample of dwarf and other low surface brightness galaxies. A detailed discussion and error analysis of the observations are presented, and spectra are displayed for 329 galaxies detected for the first time, or detected with substantially better signal-to-noise ratios than achieved previously. The positions on the sky of 667 galaxies meeting the present selection criteria north of delta = 38 deg are shown. The distribution of the redshifts of galaxies detected at Green Bank is illustrated. The Green Bank detections tapered off strongly below the median H I flux of 3.7 Jy km/s detected at Arecibo: only 12 percent of the Green Bank sample was detected with smaller fluxes.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 81; 1 Ju
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  • 2
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    Gravitational lensing of quasars as seen by the Hubble Space Telescope Snapshot Survey (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Results from the ongoing HST Snapshot Survey are presented, with emphasis on 152 high-luminosity, z greater than 1 quasars. One quasar among those observed, 1208 + 1011, is a candidate lens system with subarcsecond image separation. Six other quasars have point sources within 6 arcsec. Ground-based observations of five of these cases show that the companion point sources are foreground Galactic stars. The predicted lensing frequency of the sample is calculated for a variety of cosmological models. The effect of uncertainties in some of the observational parameters upon the predictions is discussed. No correlation of the drift rate with time, right ascension, declination, or point error is found.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 394; 1 Ju; 51-60
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  • 3
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    A gravitational lens candidate with an unusually red optical counterpart (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The properties of the strong radio source MG0414 + 0534 are described. It is found to display many of the properties expected in a gravitational lens system. At radio wavelengths and 0.5-arcsec resolution, MG0414 + 0534 is made up of four compact components whose unusual configuration and relative flux densities are similar to those found in confirmed four-image gravitational lens systems. At optical wavelengths three objects are detected, consistent with there being optical objects at the positions of the radio components, given the lower optical resolution. The radio and optical centroid positions agree within the astrometric errors, and the relative ordering of the fluxes is the same. The colors and radiooptical spectral indices are similar, but there are differences larger than the photometric errors and the measured variability (about 30 percent). Extinction by dust might simultaneously explain the unusually red color and the absence of light from a lens.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 104; 3 Se; 968-979
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  • 4
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    Radio properties of optically selected high-redshift quasars. I - VLA observations of 22 quasars at 6 cm (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A total of 22 optically selected high-redshift QSOs were obseved at 5 GHz with the VLA. The measured radio properties of low-redshift optically selected quasars indicate that radio emission should have been detected from 5-10 objects in this sample of high-redshift QSOs, but only one QSO was found to have a radio flux above the 5 sigma limit of roughly 0.2 mJy. Possible explanations of this finding are considered.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 103; 5 Ma
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  • 5
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    Hubble Space Telescope imaging of the large-redshift gravitational lens candidate 1208 + 1011 (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Four-color photometry obtained with the HST is consistent with the hypothesis that the light from the quasar 1208 + 1011 (z = 3.8) is gravitationally lensed. Guided exposures taken with the HST Planetary Camera resolve the quasar image into two point-source components separated by 0.476 +/- 0.004 arcsec. The intensity ratio of the components is approximately 4:1 in each of four broadband HST filters with mean wavelengths of 4352, 5416, 6898, and 8922 A. The HST photometry, when combined with high-resolution ground-based spectroscopy, rules out the possibility that the secondary component is a Galactic star. The limit on additional point sources is 3 percent of the brighter image for separations greater than 0.5 arcsec from the primary component and 5 percent of the brighter component for separations between 0.1 and 0.5 arcsec. If the gravitational lens is an ordinary galaxy, it would not have been detected on the HST images.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 392; 1 Ju; L1-L4
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  • 6
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    Hubble Space Telescope Wide Field Camera imaging of the gravitational lens 2237 + 0305 (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Images of the gravitational lens system 2237 + 0305, taken with the HST Wide Field Camera, are analyzed. Positions for the four quasar images, accurate to +/-0.015 arcsec, and relative magnitudes in U and R, accurate to +/-0.06 and 0.04 mag, respectively, are determined. The upper limits on the observed brightness of the fifth image are found to be less than or approximately equal to 7 percent of the brightest quasar image. The mass of the lens inside 0.9 arcsec is found to be 1.08 +/-0.02 x 10 exp 10 solar masses/h100 corresponding to a mass-to-light ratio in B of 12.3h100. This solar mass/solar luminosity estimate agrees with values obtained from stellar dynamics for other elliptical galaxies. A comparison of predictions from this mass model with the measured central velocity dispersion yields a distance-independent agreement to within 10 percent, assuming isotropic velocity dispersions.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 104; 3 Se; 959-967
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  • 7
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    Accurate positions and finding charts for 528 high-redshift, luminous quasars (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Finding charts and J2000 positions accurate to about 1 arcsec are presented for the 528 high-redshift (z is greater than 1), luminous (MV is less than -25.5) quasars investigated in the HST Snapshot Survey. A histogram showing the distribution of the differences between the positions determined by the Space Telescope Science Institute Astrometric Support Program and the catalog positions is provided.
    Keywords: ASTRONOMY
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 104; 678
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  • 8
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    The cluster of galaxies associated with the low-redshift quasar H1821 + 643 (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Low resolution spectra have been obtained of eight R is approximately equal to 19 mag galaxies located within 1 arcmin of the low-redshift, high luminosity quasar H1821 + 643. Six of the eight galaxies belong to a cluster that has the same redshift, within the observational errors, as the quasar. Five of the six cluster members have the spectra of early type galaxies; the spectrum of the sixth cluster member contains H-alpha, semiforbidden O III, and possibly O II emission lines. The other two objects are an emission line foreground galaxy and a background galaxy. The cluster has a Galactocentric redshift of 0.299 +/- 0.002 and a radial velocity dispersion of 1050 +/- 320 km/s. The photometric and spectroscopic data suggest that H1821 + 643 is associated with a rich cluster of galaxies.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 103; 1047-105
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  • 9
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    The snapshot survey - A search for gravitationally lensed quasars with the Hubble Space Telescope (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The first results from the HST Non-Proprietary Snapshot Survey are presented in order to investigate new examples of multiply imaged quasars that are the result of gravitational lensing. None of the approximately 30 quasars observed at high spatial resolution show evidence of multiple imaging by gravitational lensing. These results are compared with lower resolution ground-based surveys and current theoretical predictions. Several engineering problems in the observatory's performance are addressed. It particular, the large telescope pointing errors and drift rates are found to be primarily the result of the lack of correction for stellar aberration when pointing and tracking are performed solely with gyroscopes. The implications for the possibly low intrinsic gyro drift rate on future observations are discussed.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 387; 56-68
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  • 10
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    The relation of dust and atomic gas properties of galaxies (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The way in which the neutral atomic hydrogen and far-IR emission from galaxies relate to their environments is shown. It is found that isolated and interacting galaxies display a fairly narrow range of a temperature-adjusted 'H I/100-micron index', suggesting that atomic gas-to-dust ratios are relatively constant among most galaxies. Isolated normal galaxies are used to develop a fiducial standard for the H I/100-micron index, against which galaxies in other environments are compared. Galaxies undergoing tidal interactions prove to have the same value for the index once the proper temperature adjustment is applied according to their FIR color. Applied to clusters, the H I/100-micron index shows a clear discrimination between galaxies whose H I is 'stripped' or 'unstripped', implying that there is about 6 times less H I in stripped galaxies relative to the 100-micron-emitting dust. The stripped galaxies also appear to have a slightly lower mean dust temperature, which is surprising since the stripping process might be expected to remove preferentially cooler than average dust from the outer disk.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 393; 1 Ju
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