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NASA NTRS1988

Small grains and IRAS colors

The paper studies how infrared colors of dust emission from the interstellar medium vary with the energy density of the radiation field on the basis of IRAS observation of the California Nebula. The data suggest that color variations result from a combinatin of equilibrium emission from large grains, and nonequilibrium emission from small grains, with destruction of the small grains emitting at 12 microns at high energy density; it is estimated that 80 percent of these small particles are destroyed for an energy density in ultraviolet photons larger than 50 times that of the average interstellar radiation field in the solar neighborhood. In a color-color diagram, I(v)(60 microns)/I(v)(100 microns) versus I(v)(12 microns)/I(v)(25 microns), the California Nebula measurements at various distances to the ionizing star Zeta Per follow a sequence similar to that of galaxies. This result shows that the position of a galaxy along this sequence is a measure of the intensity of the radiation field in the regions responsible for the infrared emission.

Boulanger, F.↗

NASA NTRS1988

Infrared astronomical satellite (IRAS) catalogs and atlases. Volume 4: The point source catalog declination range 0 deg greater than delta greater than -30 deg

The Infrared Astronomical Satellite (IRAS) was launched 26 January 1983. During its 300-day mission, it surveyed over 96 pct of the celestial sphere at four infrared wavelengths, centered approximately at 12, 25, 60, and 100 microns. This is Volume 4, The Point Source Catalog Declination Range 0 deg greater than delta greater than -30 deg.

Source record↗

NASA NTRS1988

Infrared astronomical satellite (IRAS) catalogs and atlases. Volume 6: The point source catalog declination range -50 deg greater than delta greater than -90 deg

The Infrared Astronomical Satellite (IRAS) was launched January 26, 1983. During its 300-day mission, it surveyed over 96 pct of the celestial sphere at four infrared wavelengths, centered approximately at 12, 25, 60, and 100 microns. This is Volume 6, The Point Source Catalog Declination Range -50 deg greater than delta greater than -90 deg.

Source record↗

NASA NTRS1988

IRAS observations of extended zodiacal structures

In 1983, the Infrared Astronomical Satellite discovered two pairs of dust bands, straddling the ecliptic plane and located in the asteroid belt. New analysis of the IRAS data has resulted in the detection of as many as eight additional bands, spread over more than 40 deg of ecliptic latitude. Dust band morphology is found to vary between different band pairs, having a typical apparent width of a few degrees. This limits the total number of bands which can be distinguished to near the number observed. The Tempel 2 and Encke dust trails are observed to extend over much more of their orbits than had been previously reported, and a new type of dust trail is found which has a relatively large angular width and no imbedded cometary source.

Sykes, Mark V.↗

NASA NTRS1988

IRAS observations of an optically selected sample of interacting galaxies

IRAS observations of a large, morphologically selected sample of strongly interacting disk-type galaxies have demonstrated that galaxy-galaxy collisions can lead to enhanced infrared emission, but not in all cases. Infrared luminosities of the interacting galaxies span a large range, but are about a factor of 2 higher, on average, than those of isolated disk galaxies. The data suggest the existence of a cutoff in blue luminosity, below which no galaxies show markedly enhanced infrared emission. Only the most strongly interacting systems in the sample show extreme values of infrared excess, suggesting that deep, interpenetrating collisions are necessary to drive infrared emission to extreme levels. Comparisons with optical indicators of star formation show that infrared excess and color temperatures correlate with the level of star-formation activity in the interacting galaxies. All interacting galaxies in our sample that exhibit an infrared excess and have higher than normal color temperatures also have optical indicators of high levels of star formation. It is not necessary to invoke processes other than star formation to account for the enhanced infrared luminosity in this sample of interacting galaxies.

Bushouse, Howard A.↗

NASA NTRS1988

The link between IRAS spectra and near-infrared emission features in external galaxies

The relationship in external galaxies between the presence of the near-infrared (NIR) emission features attributed to polycyclic aromatic hydrocarbon (PAH) molecules, and the far-infrared (FIR) properties as observed by IRAS, is investigated. It is found that whenever the NIR features are absent in a galaxy, the FIR spectrum displays an enhancement at shorter wavelengths relative to normal galaxies. This enhancement is always associated with a strong activity in the galactic nucleus. Some Seyfert galaxies do not exhibit such an infrared signature and therefore they are probably energetically dominated by star-formation processes. Finally, the importance of hard UV photons and of the hot medium in the narrow line region of active nuclei is emphasized in relation to the survival of the PAH molecules. In this frame, the absence of PAHs in the galactic center could be taken as evidence for the presence of an active nucleus.

Desert, F. X.↗

NASA NTRS1989

IRAS observations of a large sample of normal irregular galaxies

IRAS 12, 25, 60, and 100 micron data are presented for a sample of Irr galaxies which span a large range in star-formation activity. It is found that the dwarf, giant, and amorphous Irr's generally have similar IR properties. The typical L(IR)/L(H-alpha) ratios of most classes of Irr's, except for many of the luminous blue galaxies, are low compared with those of spiral galaxies and are consistent with the Irr's being relatively transparent systems without large amounts of optically hidden star formation. Compared with spiral galaxies, the Irr's have similar L(IR)/L(B) ratios, warmer S(100)/S(60) ratios, cooler S(25)/S(12) ratios, and lower dust-to-H I gas mass ratios. The temperature, dust-to-H I gas mass ratios, and L(IR)/L(B) ratios do not correlate with the metallicity of the ionized gas of the Irr's. A correlation between the IR fluxes and both the H-alpha and the blue stellar fluxes is found for the Irr's.

Hunter, Deidre A.↗

NASA NTRS1989

IRAS observations of dust heating and energy balance in the Rho Ophiuchi dark cloud

The equilibrium process dust emission in the Rho Ophiuchi dark cloud is studied. The luminosity of the cloud is found to closely match the luminosity of the clouds's known embedded and external radiation sources. There is no evidence for a large population of undetected low-luminosity sources within the cloud and unknown external heating is also only a minor source of energy. Most of the cloud's luminosity is emitted in the mid-to-far-IR. Dust temperature maps indicate that the dust is not hot enough to heat the gas to observed temperatures. A simple cloud model with a radiation field composed of flux HD 147889, S1, and Sco OB2 associations predicts the observed IRAS 60 to 100 micron in-band flux ratios for a mean cloud density n(H2) = 1400. Flattened 12 and 25 micron observations show much extended emission in these bands, suggesting stochastic heating of very small grains or large molecules.

Greene, Thomas P.↗

NASA NTRS1989

Blue compact dwarf galaxies in the Virgo Cluster - H I and IRAS data and upper limits on proto-dwarf galaxies

Correlations between various properties of blue compact dwarf (BCD) galaxies in the Virgo Cluster were studied. It was found that, at constant mass, BCD galaxies are comparable to non-BCD irregulars in both blue luminosity and H I flux. About one-third of the BCDs were detected by IRAS at 60 or 100 microns, mostly at intensities just above the threshold sensitivity.

Hoffman, G. Lyle↗

NASA NTRS1989

IRAS observations of the Rho Ophiuchi infrared cluster - Spectral energy distributions and luminosity function

High-sensitivity IRAS coadded survey data, coupled with new high-sensitivity near-IR observations, are used to investigate the nature of embedded objects over an 4.3-sq-pc area comprising the central star-forming cloud of the Ophiuchi molecular complex; the area encompasses the central cloud of the Rho Ophiuchi complex and includes the core region. Seventy-eight members of the embedded cluster were identified; spectral energy distributions were constructed for 53 objects and were compared with theoretical models to gain insight into their evolutionary status. Bolometric luminosities could be estimated for nearly all of the association members, leading to a revised luminosity function for this dust-embedded cluster.

Wilking, Bruce A.↗

NASA NTRS1989

IRAS observations of optically selected galaxies. I - The properties of the UGC redshift sample

The FIR properties of more than 2400 optically selected galaxies in the Uppsala General Catalog are examined. The galaxies were detected by IRAS at 60 and 100 microns and have measured redshifts. A simple radiative transfer model is presented to study the nature of dust-heating sources. It is shown that for many normal disk galaxies, dust heated by old disk stars competes with dust heated by UV photons from newly formed stars. It is found that the 60-micron/100-micron flux density ratio may be used as an indicator of the dominant dust-heating source. Scaling relations with galaxy size and mass are presented which make it possible to estimate the contributions of any cirrus-like component to the total FIR luminosity.

Bothun, Gregory D.↗

NASA NTRS1989

The infrared emission bands. III - Southern IRAS sources

Airborne 5-8-micron spectra of southern IRAS sources are presented which display the strong PAH emission features. The sources studied include those in a previous paper (Cohen et al, 1986) and NGC 6302, HR 4049, and CPD -56 deg 8032. A good correlation is found between the intensity ratio of the 7.7-micron feature relative to the FIR dust continuum and nebular C/O ratio, supporting a carbonaceous carrier for these emission features. In addition, a weak PAH band is detected near 5.2 microns in several sources.

Cohen, Martin↗

NASA NTRS1989

The warp of the Galactic stellar disk detected in IRAS source counts

About 90,000 IRAS point sources have been used as disk tracers in order to explore the possibility of warp in the Galactic stellar disk. The results imply that the Galactic stellar disk is warped at large radii in a way similar to the H-I layer, and that the warp is an important characteristic of the Galaxy as a whole. It is suggested that the warp may be a long-lasting phenomenon, possibly caused by asymmetries of the mass distribution in the outer regions of the Galactic dark halo.

Djorgovski, S.↗

NASA NTRS1989

The Wasilewski sample of emission-line galaxies - Follow-up CCD imaging and spectroscopic and IRAS observations

The results of an extensive imaging and spectroscopic follow-up of the objective prism-selected emission line galaxy (ELG) sample of Wasilewski (1982) are presented. Fluxes at 12, 25, 60, and 100 microns were also obtained from the coadded IRAS survey data. ELGs found by objective prism surveys are found to be generally small and underluminous galaxies which usually have higher than average optical surface brightness. The Seyfert detection rate in objective prism surveys is roughly 10 percent and the ratio of the space densities of Seyfert 2 to Seyfert 1 galaxies is significantly larger than unity. Most of the galaxies selected by objective prism surveys are star-forming, late-type spirals which often show disturbed morphology. About 25 percent of the galaxies detected by the surveys are faint, high-excitation metal-poor compact H II regions.

Bothun, Gregory D.↗

NASA NTRS1989

IRAS LRS spectra of extended objects: The Crab nebula

The spectra of extended sources from the raw Infrared Astronomy Satellite (IRAS) Low Resolution Spectrometer (LRS) data, is recovered by means of a nonlinear deconvolution technique built around a maximum entropy algorithm. The results are applied to the Crab Nebula. The deconvolved spectrum of the Crab shows significant departures from a blackbody spectrum, with emission features present at 10.2, 11.3, 12.3 and 12.8 microns.

Lynch, D. K.↗

NASA NTRS1989

Observations of 40-70 micron bands of ice in IRAS 09371+1212 and other stars

The observations of the M giant star, IRAS 09371+1212, in the 40 to 70 microns emission bands, are reported. This star has a circumstellar CO envelope, and a unique infrared color, attributed to ice emission bands. The observations performed in February 1988, using grating spectrometer, showed that the far infrared bands of ice are the strongest known in the sky, and that its dust temperature (50K) is the lowest known for a circumstellar envelope. The 43 microns band of ice is also detected in several very cold circumstellar envelopes.

Omont, A.↗

NASA NTRS1990

Implications of the IRAS data for galactic gamma ray astronomy and EGRET

Using the results of gamma-ray, millimeter wave and far surveys of the galaxy, logically consistent picture of the large scale distribution of galactic gas and cosmic rays was derived, tied to the overall processes of stellar birth and destruction on a galactic scale. Using the results of the IRAS far-infrared survey of te galaxy, the large scale radial distributions of galactic far-infrared emission independently was obtained for both the Northern and Southern Hemisphere sides of the Galaxy. The dominant feature in these distributions was found to be a broad peak coincident with the 5 kpc molecular gas cloud ring. Evidence was found for spiral arm features. Strong correlations are evident between the large scale galactic distributions of far-infrared emission, gamma-ray emission and total CO emission. There is particularly tight correlation between the distribution of warm molecular clouds and far-infrared emission on a galactic scale. The 5 kpc ring was evident in existing galactic gamma-ray data. The extent to which the more detailed spiral arm features are evident in the more resolved EGRET (Energetic Gamma-Ray Experimental Telescope) data will help to determine more precisely the propagation characteristics of cosmic rays.

Stecker, Floyd W.↗

NASA NTRS1990

Implications of the IRAS data for galactic gamma-ray astronomy and EGRET

Using the results of gamma-ray, millimeter wave and far infrared surveys of the galaxy, one can derive a logically consistent picture of the large scale distribution of galactic gas and cosmic rays, one tied to the overall processes of stellar birth and destruction on a galactic scale. Using the results of the IRAS far-infrared survey of the galaxy, the large scale radial distribution of galactic far-infrared emission were obtained independently for both the Northern and Southern Hemisphere sides of the Galaxy. It was found that the dominant feature in these distributions to be a broad peak coincident with the 5 kpc molecular gas cloud ring. Also found was evidence of spiral arm features. Strong correlations are evident between the large scale galactic distributions of far infrared emission, gamma-ray emission and total CO emission. There is a particularly tight correlation between the distribution of warm molecular clouds and far-infrared emission on a galactic scale.

Stecker, F. W.↗