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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Infrared luminosity functions for the young stellar population associated with the L1641 molecular cloud

Results are reported of a deep near-IR imaging survey which samples 0.77 sq deg of the L1641 star-forming complex and reaches 5 sigma limits at J (1.25 micron,), H (1.65 micron), and K (2.2 microns) of 16.8, 15.8, and 14.7 mag, respectively. A population of about 1500 stars spread throughout the cloud, seven small aggregates comprised of 10-50 stars whose typical projected surface densities exceed that of the distributed population by factors of 4-10, and a heretofore unknown, partially embedded dense cluster comprised of about 150 stars are identified. Analysis of the distribution of (J-H), (H-K), and (R-I) colors for these groups suggest that, in all cases, the stellar populations are dominated by solar-type PMS stars which appear to contain a mix of objects analogous to weak-line T Tauri stars. The present observed luminosity functions are based on reddening-corrected J-band magnitude.

Strom, Karen M.↗
NASA NTRS1987

Systematic properties of CO emission from galaxies. I - Luminosity function

A sensitive survey of normal galaxies covering a wide range of luminosities and morphological types is combined with galaxy observations in the literature to provide a sample for statistical study. The global CO emission of these galaxies is extrapolated by modeling the galaxies with an exponential radial profile. The maximum-likelihood distribution functions of CO luminosity and CO/H I flux ratio are similar in behavior. Both have long tails of bright galaxies. However, the typical galaxy has a CO luminosity of about 10 to the 6th Jy km/s Mpc-squared or less and a CO/H I ratio of the order of 10 or less. Averages of the distributions of CO luminosity and CO/H I flux ratio are higher for galaxies of Hubble type Sb-Sbc than for groups of earlier or later types. Quantitative estimates of the possible error sources in the conversion of CO luminosity to molecular mass indicates that the peaking of CO emission at intermediate types is a fairly confident result.

Verter, Frances↗
NASA NTRS1973

The luminosity function of galactic X-ray sources - A cutoff and a 'standard candle'

Analysis of the 2- to 10-kev luminosity distribution of 36 X-ray sources in the Local Group having known or estimated distances, showing that there exists a luminosity cutoff of approximately 10 to the 37.7th ergs/sec in agreement with the theoretical (Eddington) limit for the luminosity of an approximately 1 solar mass star. Furthermore, among the complete sample of high-luminosity sources, there appears to be a statistically significant group of X-ray 'standard candles' at (within less than 0.8 mag) the critical luminosity. This finding (which is in agreement with the self-consistent mass flow accretion models) presents the possibility that X-ray sources may be used as extragalactic distance indicators in the next generation of X-ray astronomy experiments.

Margon, B.↗
NASA NTRS1991

Evidence for evolution of the luminosity function of clusters of galaxies

From an all sky, x-ray flux limited sample of clusters of galaxies evidence for a significant deficit in the number of high luminosity clusters is found in the redshift range z approximately 0.1 to 0.2 compared with numbers of nearby clusters. This indicates that the x-ray luminous clusters are undergoing strong evolution. The strength of the effect is consistent with hierarchical merging models. The implications of such strong evolution for clusters are discussed.

Edge, Alastair C.↗
NASA NTRS1991

Evidence for evolution of the luminosity function of clusters of galaxies

From an all sky, X-ray flux limited sample of clusters of galaxies evidence for a significant deficit in the number of high luminosity clusters is found in the redshift range z approximately 0.1 to 0.2 compared with numbers of nearby clusters. This indicates that the X-ray luminous clusters are undergoing strong evolution. The strength of the effect is consistent with hierarchical merging models. The implications of such strong evolution for clusters are discussed.

Edge, A. C.↗
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

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 NTRS1980

The HEAO A-2 survey of Abell clusters and the X-ray luminosity function

A statistically complete sample of 225 Abell clusters has been examined. Twelve new identifications of clusters with X-ray sources have been made. It is found that (1) Lx is roughly correlated with richness for richness classes 0, 1, and 2; (2) Lx is well correlated with Rood-Sastry type and only loosely correlated with Bautz-Morgan type; and (3) the cluster contribution to the X-ray background is less than or equal to 5% between 2 and 10 keV.

Mckee, J. D.↗
NASA NTRS1985

Studies of the Virgo Cluster. II - A catalog of 2096 galaxies in the Virgo Cluster area. V - Luminosity functions of Virgo Cluster galaxies

The present catalog of 2096 galaxies within an area of about 140 sq deg approximately centered on the Virgo cluster should be an essentially complete listing of all certain and possible cluster members, independent of morphological type. Cluster membership is essentially decided by galaxy morphology; for giants and the rare class of high surface brightness dwarfs, membership rests on velocity data. While 1277 of the catalog entries are considered members of the Virgo cluster, 574 are possible members and 245 appear to be background Zwicky galaxies. Major-to-minor axis ratios are given for all galaxies brighter than B(T) = 18, as well as for many fainter ones.

Binggeli, B.↗
NASA NTRS1986

A study of the discrepant QSO X-ray luminosity function from the HEAO-2 data archive

Sensitive X-ray information for approximately 90 previously uncataloged Quasi-Stellar Objects (QSOs) in the redshift range 1.8 is less than or equal to z which is less than or equal to 3. Even with the longest esixting Einstein Observatory X-ray exposures, only 25% of these objects are positively detected in X-rays. The data were used to investigate the ensemble X-ray properties of high redshift QSOs, and the QSO population in general.

Margon, B.↗
NASA NTRS1992

The hard x ray luminosity function and evolution of AGN

A large number of active galactic nuclei and quasars detected by the HEAO A1 x-ray survey and recently identified using results from the HEAO A3 experiments are described and preliminary results are presented. The sample shows some incompleteness and is not completely identified, so these effects are taken out in the analysis by correcting the effective coverage of the survey. Preliminary analysis indicates that significant evolution can be detected in this data and that the evolution rate appears stronger than that inferred from a sample selected at lower energies.

Marshall, Herman L.↗
NASA NTRS1993

Survey incompleteness and the evolution of the QSO luminosity function

We concentrate on a type of QSO survey which depends on selecting QSO candidates based on combinations of colors. Since QSO's have emission lines and power-law continua, they are expected to yield broadband colors unlike those of stellar photospheres. Previously, the fraction of QSO's expected to be hiding (unselected) within the locus of stellar (U-J, J-F) colors was estimated at about 15 percent. We have now verified that the KK88 survey is at least 11 percent incomplete, but have determined that it may be as much as 34 percent incomplete. The 'missing' QSO's are expected to be predominantly at z less than or = 2.2. We have studied the proper motion and variability properties of all stellar objects with J less than or = 22.5 or F less than or = 21.5 in the SA 57 field which has previously been surveyed with a multicolor QSO search by KK88.

Majewski, Steven R.↗
NASA NTRS1991

Evolution of the X-ray luminosity function of AGN

The HEAO A1 X-ray survey has detected a large number of active galactic nuclei and quasars, as recently identified using results from the HEAO A3 experiment. The sample shows some incompleteness and is not completely identified, so these effects are taken out in the analysis by correcting the effective coverage of the survey. Preliminary analysis indicates that significant evolution can be detected in these data and that the evolution rate appears stronger than that inferred from a sample selected at lower energies.

Marshall, Herman L.↗