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At least 379 records · Page 21
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NASA NTRS1990

Infrared emission from central dominant galaxies in X-ray luminous clusters

IRAS strip scans are used to study the emission properties of 27 dominant galaxies that lie in the center of clusters rich in hot gas. In this sample, 30 percent of the objects were detected at 12/25 microns, while 46 percent were detected at 60/100 microns. The ratio of the IR to optical flux densities is an order of magnitude greater than for elliptical and S0 galaxies. The presence of IR emission is not obviously correlated with z, m(v), Mv, the presence of young stellar populations, emission-line gas, the X-ray luminosity, or the cooling rate of hot gas.

Bregman, Joel N.↗
NASA NTRS1990

Molecular clouds associated with luminous far-infrared sources in the outer Galaxy

The stellar content and physical properties of the molecular clouds associated with 21 bright far-IR sources in the outer Galaxy have been determined through C-12O, C-13O, 6-cm radio continuum, and IRAS observations. The molecular cloud masses range from 200 to about 10,000 solar masses. The far-IR luminosity-to-mass ratio for these clouds has a mean value of 6.8 solar luminosity/solar masses and shows no correlation with the cloud mass, a result similar to that found for more massive clouds in the inner Galaxy. The radio continuum survey of the 21 bright far-IR sources indicates that most of these regions probably have a single, massive star providing most of the ionization. The cloud masses derived from virial and LTE analyses are in agreement, supporting the assumptions commonly made in their calculations, and a tight, near-linear correlation is found between the C-12O luminosity and the cloud mass. The H2 column density and integrated C-12O intensity are also correlated on a point-by-point basis, although the scatter is larger than the C-12O luminosity-cloud mass relation.

Carpenter, John M.↗
NASA NTRS1992

The far-infrared properties of the CfA galaxy sample. I - The catalog

IRAS flux densities are presented for all galaxies in the Center for Astrophysics magnitude-limited sample (mB not greater than 14.5) detected in the IRAS Faint Source Survey (FSS), a total of 1544 galaxies. The detection rate in the FSS is slightly larger than in the PSC for the long-wavelength 60- and 100-micron bands, but improves by a factor of about 3 or more for the short wavelength 12- and 25-micron bands. This optically selected sample consists of galaxies which are, on average, much less IR-active than galaxies in IR-selected samples. It possesses accurate and complete redshift, morphological, and magnitude information, along with observations at other wavelengths.

Thuan, T. X.↗
NASA NTRS1992

Far-infrared luminosity functions of normal galaxies

A volume-limited sample is constructed from the Zwicky catalog and IRAS data base to examine the FIR luminosity functions of normal galaxies, and to investigate possible relationships between FIR emission and galaxy morphology. Quantitative and unbiased treatment is provided by 'survival analysis' statistical methods. It is found that the FIR distributions of normal galaxies are better fit by lognormal than Schechter functions. The total FIR emissivity (8 to 115 microns) of normal galaxies is approximately equal to half their emission in the B plus V optical bands. Normal galaxy FIR emission is uncorrelated with the basic S0-Sm Hubble sequence of spiral galaxy morphology, but appears to be affected by de Vaucouleurs' (1959) revised morphological classifications based on inner rings and S-shaped arms. Spirals with bars and inner rings are systematically fainter than unbarred spirals. It is suggested that bars and rings reduce the amount or spatially confine the dust in spiral disks, resulting in lower efficiency conversion of optical and UV photons into the IR.

Isobe, Takashi↗
NASA NTRS1992

A near-infrared imaging survey of interacting galaxies - The small angular-size Arp systems

Near-IR images of a large sample of interacting galaxies selected from the Atlas of Peculiar Galaxies by Arp (1966) have been obtained. Approximately 180 systems have been imaged in at least two, and usually three of the standard JHK bands. The survey and the observing and data reduction procedures, are described, and contour plots and aperture photometry are presented. Future papers will analyze the imaging data by groupings based on interaction type, stage, and progenitors. The goals of the analysis are to explore the relationships between galaxy interactions, activity, and morphology by studying the structure of the near-IR luminosity distribution, where extinction effects are much reduced relative to the optical and the major stellar mass component of galaxies dominates the observed light.

Bushouse, Howard A.↗
NASA NTRS1992

The origin of the far-infrared luminosity within the spiral galaxy M51

High angular resolution 170 micron and H-alpha maps have been recombined in order to elucidate the origin of the far-IR luminosity within the late-type spiral galaxy M51. New quantitative evidence is presented supporting a common origin for the far-IR and H-alpha luminosities is the striking correspondence, at all locations measured within M51, between the luminosity in the far IR and that expected from the O and B stars which are required to ionize the hydrogen gas. The warm 33 K dust temperature measured for M51 is similar to that measured for galactic and extragalactic star formation regions. It is concluded that O and B stars can easily generate both the far-IR luminosity and the warm dust temperature at all locations within M51. The dust mass required to radiate the IRAS 60 and 100 micron emission measured for M51 represents only a small percentage of the total dust content of M51. Constraints are placed on the mass and temperature of the cold dust.

Devereux, Nicholas A.↗
NASA NTRS1992

Infrared emission in Seyfert 2 galaxies - Reprocessed radiation from a dusty torus?

New and existing data for a sample of nine Seyfert 2 galaxies with known 'ionization cones' are combined in order to test whether collimation results from shadowing of radiation from a small isotropic nuclear source by a thick dusty torus. The number of ionizing photons emitted by the compact nucleus is calculated from the emission-line ratios measured for gas within the cones. On the assumption that this compact nuclear source radiates isotropically, the optical-UV power incident on the torus, which is expected to be reradiated in the IR, is determined. It is found that the observed IRAS luminosities are consistent with the torus model in eight of the nine objects with sufficient data to perform the calculation. It is concluded that the data are generally consistent with collimation and reradiation by a dusty torus.

Storchi-Bergmann, Thaisa↗
NASA NTRS1993

A physical model of the infrared-to-radio correlation in galaxies

We explore the implications of the IR-radio correlation in star-forming galaxies, using a simple physical model constrained by the constant global ratio q of IR to radio emission and by the radial falloff of this ratio in disks of galaxies. The modeling takes into account the diffusion, radiative decay, and escape of cosmic-ray electrons responsible for the synchrotron emission, and the full range of optical depths to dust-heating photons. We introduce two assumptions: that dust-heating photons and radio-emitting cosmic-ray electrons are created in constant proportion to each other as part of the star formation activity, and that gas and magnetic field are well coupled locally, expressed as B proportional to n exp beta, with beta between 1/3 and 2/3. We conclude that disk galaxies would maintain the observed constant ratio q under these assumptions if the disk scale height h(0) and the escape scale length l(esc) for cosmic-ray electrons followed a relation of the form l(esc) proportional to h(0) exp 1/2; the IR-to-radio ratio will then depend very weakly on interstellar density, and, therefore, on magnetic field strength or mean optical depth.

Helou, G.↗
NASA NTRS1991

Galaxy formation and evolution

The presence of high z quasars and radio galaxies tells us that galaxy formation began at z greater than 5, but leaves unanswered the question of when the bulk of galaxies formed. Recent near infrared number counts of galaxies strongly favor a cosmological geometry with q(sub 0) = 0.5 and lambda = 0. Such a model grossly underpredicts blue galaxy counts. Spectroscopy shows that the excess blue galaxies at B = 24 are dwarfs at z approximately equals 0.4 which are no longer seen at the present time. These dwarfs must contain a large amount of baryonic matter which is not included in current estimates of baryonic omega .

Cowie, Lennox L.↗
NASA NTRS1997

The Contribution of Ionizing Stars to the Far-Infrared and Radio Emission in the Galaxy

This is the first report of a new contract. However, this project represents ongoing work, so there are completed tasks as well as newly started tasks to report. The project involves the completion of the IRAS Galaxy Atlas (IGA), a large image database produced using data from the Infrared Astronomical Satellite (IRAS). In this phase, the project switches from the production and characterization of the IGA to its use in astronomical research studies of massive star formation. The research utilizes the IGA as well as two other large data sets being produced by research partners.

Cao, Yu↗
NASA NTRS1997

Symmetric Parsec-scale OH Megamaser Structures in Arp 220

The parsec-scale OH megamaser emission in the luminous IR galaxy Arp 200 has been imaged in detail using global VLBI array. Four major emission regions are revelaed inthe 1667 MHz line, each with complex spatial and velocity structure showing intriguing symmetries.

parsec-scale galaxies infrared radio lines masers↗
NASA NTRS1996

The Mid-Infrared Color of NGC 6946

We analyze the new mid-infrared maps of NGC 6946 for variations in the color ratio fo the 7-to-15(micro)m emission. Our preliminary findings are that this mid-infrared color is remarkably constant between arms and inter-arm regions, and as a function of radius in the disk, excluding the nuclear region.

Infrared galaxies ISM ngc 6946↗
NASA NTRS1999

Milky Way Unveiled to Reveal a Host of New Galaxies

This census has already discovered nearby galaxies previously hidden behind our Galaxy, and will allow delineation of large-scale structures in the distribution of galaxies across the whole sky.

galaxies infrared unveiled Milky Way↗
NASA NTRS1999

The ISO-IRAS Faint Galaxy Survey: ISOCAM Results

The ISO-IRAS Faint Galaxy Survey (IIFGS) is a program designed to produce one of the largest and deepest samples of luminous galaxies possible with present facilities.

galaxies infrared ISO IRAS↗