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Neugebauer, G.

Publications and source records attributed to Neugebauer, G..

At least 55 records · Page 3
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NASA NTRS1989

The near-infrared variability of a sample of optically selected quasars

A complete sample of 108 optically selected quasars, the Palomar-Green quasars, has been studied at near-infrared wavelengths over an average time base of about 6 yr; in some cases the time base extends to 20 yr. The measurements show that about half the quasars have a high probability of having varied, but that half show little evidence of variability, in sharp contrast to published studies indicating that most quasars vary on comparable timescales at optical wavelengths. The maximum amplitude of variation is less than 1 mag and generally near 0.5 mag.

Neugebauer, G.↗
NASA NTRS1989

The optical/infrared counterpart(s) of IRAS 18333-2357

Observations of the potential optical counterparts of the unusual source IRAS 18333-2357 are reported. There are three distinct optical objects located within roughly 2 arcsec of the IR source: a red star, a very blue star, and an extended emission line nebulosity. IRAS 18333-2357 indeed appears to be physically associated with the Galactic globular cluster M22, and while it probably should be considered a PN, its very small nebular mass and extreme abundance anomalies are very unusual among known PNe. IRAS 18333-2357 does not appear to be at an early stage of PN evolution, but instead may be in a late stage. The lack of an associated radio or H-alpha source is the result of abundance anomalies in the source.

Gillett, F. C.↗
NASA NTRS1988

A catalog of IRAS observations of large optical galaxies

A catalog is presented of IRAS observations of 85 galaxies with blue-light isophotal diameters greater than 8 arcmin. The observations, data processing, and data measurement techniques are described, and total IRAS flux densities and integrated infrared emission properties of the sample are reported. Infrared brightness profiles of the detected galaxies and infrared surface brightness contour maps of the galaxies for which structural features were resolved are displayed. A classification scheme based on the degree of central concentration and spatial structure of the 60 micron emission of the best-resolved galaxies is proposed. The 60 micron and blue-light isophotal diameters of the largest galaxies are compared.

Rice, W.↗
NASA NTRS1988

IRAS observations of the globular cluster 47 Tucanae

Integrated and individual-star observations of 47 Tuc obtained at 12, 25, 60, and 100 microns by IRAS are reported. The data are presented in tables and brightness contour maps and analyzed. Features discussed include integrated light dominated by stellar photospheric emission, 12- and 25-micron excesses (associated with red giants in the outer region of the cluster), and a small excess at 100 microns (attributed to integrated-light heating of about 0.0003 solar mass of silicate dust within 6 arcmin of the cluster center). It is pointed out that this is much less dust than predicted by theoretical models of accumulation since the cluster passed through the Galactic plane about 30 Myr ago, and possible dust-removal mechanisms are considered.

Gillett, F. G.↗
NASA NTRS1988

Energy distributions of blazars

This paper presents observations of 162 blazars, over one-half of which were detected with data from the IRAS satellite using a coadded survey and pointed observations. The far-IR data were combined with published data at other wavelengths to complete 93 energy distributions from 10 to the 8th to 10 to the 18th Hz. The IRAS data were used to search for variability on time scales of 3-9 months in 24 objects. The detection rate of variability found for blazars was nearly 40 percent, as compared with a complete absence of detected variability in data sets for quasars and Seyfert galaxies. The range of variability in both spectral index and flux density increases with decreasing wavelength. Half of the blazars with total luminosities less than 10 to the 12th solar luminosity show evidence for thermal IR component. The global energy budget of blazars is dominated by IR emission from 1 to 100 microns.

Impey, C. D.↗
NASA NTRS1988

IRAS observations of radio galaxies

IRAS measurements at 25, 60, and 100 microns have been used to analyze the far-infrared properties of radio galaxies. Fifty-eight of the 131 objects surveyed were detected at the level of better than 300 mJy at 60 microns. The most powerful radio galaxies are strong emitters in the far infrared. Large infrared emission is shown to be correlated with the presence of strong emission lines in the optical spectra. The infrared colors of the strong radio galaxies are similar to those of Markarian Seyferts. The results are shown to be consistent with recent results implying that the host galaxies of radio sources are not normal giant ellipticals and that galaxy-galaxy interactions may power luminous radio sources. Finally, some similarities between powerful radio galaxies and powerful infrared galaxies are noted and briefly discussed.

Golombek, D.↗
NASA NTRS1987

The IRAS bright galaxy sample. II - The sample and luminosity function

A statistically complete sample of 324 of the brightest infrared galaxies discovered at 60 microns in the IRAS all-sky survey is described. The results show that far-infrared emission is a significant luminosity component in the local universe, representing 25 percent of the luminosity emitted by stars in the same volume. Above 10 to the 11th solar luminosities, the infrared luminous galaxies are the dominant population of objects in the universe, being as numerous as the Seyfert galaxies and more numerous than quasars at higher luminosities. The infrared luminosity appears to be independent of the optical luminosity of galaxies. Most infrared bright galaxies appear to require much of the interstellar matter to be contributing to the observed infrared luminosity. Approximately 60-80 percent of the far-infrared luminosity of the local universe can be attributed, directly or indirectly, to recent or ongoing star formation.

Soifer, B. T.↗
NASA NTRS1987

Ultraluminous infrared galaxies

The IRAS survey of the local universe has revealed the existence of a class of ultraluminous infrared galaxies with L(8 to 1000 micrometer) greater than 10 to the 12th L sub 0 that are slightly more numerous, and as luminous as optically selected quasars at similar redshift. Optical CCD images of these infrared galaxies show that nearly all are advanced mergers. Millimeter wave CO observations indicate that these interacting systems are extremely rich in molecular gas with total H2 masses 1 to 3 x 10 to the 10th power M sub 0. Nearly all of the ultraluminous infrared galaxies show some evidence in their optical spectra for nonthermal nuclear activity. It is proposed that their infrared luminosity is powered by an embedded active nucleus and a nuclear starburst both of which are fueled by the tremendous reservoir of molecular gas. Once these merger nuclei shed their obscuring dust, allowing the AGN to visually dominate the decaying starburst, they become the optically selected quasars.

Sanders, D. B.↗
NASA NTRS1987

The luminosity function of the brightest galaxies in the IRAS survey

Results from a study of the far infrared properties of the brightest galaxies in the IRAS survey are described. There is a correlation between the infrared luminosity and the infrared to optical luminosity ratio and between the infrared luminosity and the far infrared color temperature in these galaxies. The infrared bright galaxies represent a significant component of extragalactic objects in the local universe, being comparable in space density to the Seyferts, optically identified starburst galaxies, and more numerous than quasars at the same bolometric luminosity. The far infrared luminosity in the local universe is approximately 25% of the starlight output in the same volume.

Soifer, B. T.↗
NASA NTRS1987

Near-infrared observations of IRAS minisurvey galaxies

Near infrared photometry at J, H, and K was obtained for 82 galaxies from the IRAS minisurvey. The near infrared colors of these galaxies cover a larger range in J-H and H-K than do normal field spiral galaxies, and evidence is presented of a tighter correlation between the near and far infrared emission in far infrared bright galaxies than exists between the far infrared and the visible emission. These results suggest the presence of dust in the far infrared bright galaxies, with hot dust emission contributing to the 2.2 micron emission, and extinction by dust affecting both the near infrared colors and the visible luminosities. In addition, there is some indication that the infrared emission in many of the minisurvey galaxies is coming from a strong nuclear component.

Carico, David P.↗
NASA NTRS1987

IRAS observations of BL Lac objects

IRAS data was analyzed for 35 BL Lac objects selected from a complete 5 GHz radio sample, using the coadded survey database. The detection rate is 50% with more than 40% detected in more than one band. This compares with only 15% of these sources that are included in the IRAS Point Source Catalog. High luminosity BL Lac objects generally have smooth energy spectra over four or five decades in frequency, consistent with incoherent synchrotron emission from 1 cm to 1 micron. However, many low luminosity BL Lac objects have discontinuous spectra, with a large range in the spectral index at IRAS wavelengths. For BL Lacs with a total luminosity of less than 10 to the 44th power ergs/-s, most of the far infrared energy probably originates from dust heated near the galaxy nucleus. The energy budget shows that the majority of the power per unit bandwidth emerges in the infrared (1 to 100 microns).

Impey, C.↗
NASA NTRS1987

The IRAS view of the extragalactic sky

The IR-observable characteristics of the extragalactic sky are reviewed, summarizing the results of recent studies based on the IRAS survey, which covers over 96 percent of the sky to about 500 mJy at 12, 25, and 60 microns and to about 1.5 Jy at 100 microns. The numerical and morphological data are described; possible mechanisms for the IR emission are discussed; and the object classes are considered separately. Consideration is given to spiral and disk galaxies, barred and ring galaxies, irregular and dwarf galaxies, blue compact galaxies, elliptical and S0 galaxies, AGN observations (BL Lacs and OVV quasars, Seyfert galaxies, and quasars), highly luminous IR galaxies, and the cosmological implications of the IRAS findings. Diagrams, graphs, and tables are provided.

Soifer, B. T.↗
NASA NTRS1986

IRAS observations of R Coronae Borealis - Detection and study of a fossil shell

IRAS observations of the extreme hydrogen-deficient supergiant R CrB are presented and discussed. The star is surrounded by an enormous cool dust cloud which is tentatively identified as a fossil remnant of the hydrogen-rich envelope of the star. The angular extent of the emission corresponds to a linear extent of 8 pc, 20 times larger than the largest previously known shell around a late-type star. The radiating material is distributed very symmetrically over a wide range of radial distances from the star. The dust temperature is nearly constant throughout the extended shell. The total mass in the shell is about 0.3 solar mass. The ejection process appears to have occurred in a spherically symmetric fashion with a nearly constant mass loss rate and expansion velocity over a period of about 150,000 yr, terminating about 26,000 yr ago.

Gillett, F. C.↗
NASA NTRS1986

X-ray spectra of PG quasars. I - The continuum from X-rays to infrared

Einstein IPC X-ray spectra for a sample of eight optically selected quasars from the Palomar Bright Quasar survey are presented. The quasars have a mean power law energy slope which in five individual cases is inconsistent with the value found in hard X-ray selection criterion rather than luminosity, redshift, or U-B color. New IUE and optical continuum spectra and infrared photometry are presented for these quasars. The data are combined into log vf(v) and log v distributions which support the decomposition of the overall quasar spectrum into a power law plus a superposed optical-UV 'big bump' which may be due to an accretion disk. At least six of the quasars have vf(v)s which are roughly constant between their infrared and X-ray power laws, suggesting a strong link between the two regions.

Elvis, Martin↗
NASA NTRS1986

Discovery of an infrared-loud quasar

The IRAS source 13349 + 2438 is a quasar with a redshift of z = 0.107, broad (15,000 km/s) emission lines and a luminosity of 2.7 x 10 to the 12th solar luminosity, emitted mostly between 4.8 and 12 microns. The object, a weak radio source, is the first previously unidentified quasar selected through its infrared emission and is the prototype radio-quiet, infrared-bright quasar. A dusty interstellar medium may be responsible for the infrared emission as well as for quenching the visual emission and attenuating the radio emission from the central energy source.

Beichman, C. A.↗
NASA NTRS1986

The luminosity function and space density of the most luminous galaxies in the IRAS survey

The local luminosity function for galaxies with vLv (60 microns) of 10 to the 10th solar luminosities or more is derived from a sample of bright galaxies detected in the IRAS survey. It is found that within several hundred megaparsecs the infrared luminous galaxies comprise a significant fraction of high-luminosity objects, and the infrared luminosity emitted by galaxies is a substantial fraction of that emitted in the visible portion of the spectrum. The far-infrared energy density in the local universe is close to that in visible light.

Soifer, B. T.↗
NASA NTRS1986

Multifrequency observations of the superluminal quasar 3C 345

Attention is given to the continuum properties of the superluminal quasar 3C 345, on the basis of radio, optical, IR, and X-ray frequency monitorings, as well as by means of simultaneous multifrequency spectra extending from the radio through the X-ray bands. Radio outbursts, which appear to follow IR-optical outbursts by about one year, first occur at the highest frequencies, as expected from optical depth effects; the peak flux is nevertheless often reached at several frequencies at once. The beginning of outbursts, as defined by mm-measurements, corresponds to the appearance of the three known 'superluminal' components. An increase in the X-ray flux during 1979-1980 corresponds to increased radio flux, while the IR flux changes in the opposite sense.

Bregman, J. N.↗