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NASA NTRS1984

Observational tests of X-ray heating in the broad-line region of quasars and Seyfert galaxies

Baldwin (1977) has inferred that the Ly-alpha/H-alpha line ratio in quasars was a factor of 10 lower than predicted by case B recombination theory, and direct observations of the Ly-alpha line in low-redshift quasars and Seyfert galaxies and of the Balmer lines in high-redshift quasars have confirmed this discrepancy. The present investigation is concerned with the Ly-alpha/H-alpha and Fe II/H-beta line ratios of a larger sample of quasars and Seyfert galaxies, taking into account the possibility of X-ray heating. Attention is given to details regarding the data set and to tests of X-ray heating in the broad-line region. The significance of the tests for the predictions of a model considered by Kwan and Krolik (1981) is evaluated.

Kriss, G. A.↗
NASA NTRS1976

The redshift of 0938+119

Results are reported for digicon spectrophotometric observations of the radio source 0938+119, which was originally classified as a faint red galaxy. A prism spectrum of the source is presented along with the corresponding sky measurement, and several features of the spectrum are described. It is shown that this source is a QSO with a magnitude of 20.1, a redshift z = 3.19, and a spectrum similar to that of OH 471 or 4C 05.34. The question of whether other faint high-redshift QSOs have been misclassified as galaxies is considered.

Beaver, E. A.↗
NASA NTRS1991

Statistics of gravitational lenses - The uncertainties

The assumptions in the analysis of gravitational lensing statistics are examined. Special emphasis is given to the uncertainties in the theoretical predictions. It is shown that a simple redshift cutoff model, which may result from galaxy evolution, can significantly reduce the lensing probability and explain the large mean separation of images in observed gravitational lenses. This effect may affect the constraint on the contribution of the cosmological constant to producing a flat universe from the number counts of the observed lenses. For the Omega(0) = 1 (filled beam) model, the lensing probability of early-type galaxies with finite core radii is reduced roughly by a factor of 2 for high-redshift quasars as compared with the corresponding singular isothermal sphere model. The finite core radius effect is about 20 percent for a lambda-dominated flat universe. It is also shown that the most recent galaxy luminosity function gives lensing probabilities that are smaller than previously estimated roughly by a factor of 3.

Mao, Shude↗
NASA NTRS1991

Radio properties of extragalactic IRAS sources

The present study identifies extragalactic sources from the IRAS Faint Source Catalog by position coincidence with radio sources stronger than 25 mJy and lying north of +5 deg on the Green Bank 4.85 GHz sky maps. Published VLA maps, new 4.86 GHz VLA maps made with 15-arcsec resolution, and accurate optical positions are used to confirm 122 of these candidate identifications. Normal and starburst spiral galaxies were found to comprise about 97 percent of the FIR flux-limited sample. Radio-loud 'monsters' with q less than 2.25 dominate the radio emission from about 2 percent of the FIR source sample, and radio-quiet monsters are responsible for the FIR emission from less than about 1 percent of the FIR sample. All of the radio-identified sources are optically identified, mostly with relatively bright nearby galaxies. No evidence was found for any new populations of high-redshift FIR sources, nonthermal sources with steep FIR/optical spectra, or dust-shrouded sources visible only at FIR and radio wavelengths.

Condon, J. J.↗
NASA NTRS1983

Paired quasars near NGC 2639 - Evidence for quasars in superclusters

Arp (1979, 1980) has found quasars with similar redshifts which appear to be paired across low-redshift galaxies. Arp concludes that the pairings provide evidence for an association between high-redshift quasars and a small, low-redshift galaxy. Oort et al. (1981) suggested an alternative hypothesis to explain the close redshift pairs. They proposed that the two closest pairs are in superclusters at the cosmological distances implied by the quasars' redshifts. The low-redshift quasar pair U7/U10 (0.303/0.305) is close enough to allow detection of any associated clusters of galaxies on deep red photographs. The present investigation had originally the objective to test the supercluster hypothesis by searching for faint clusters which might comprise a supercluster at z approximately 0.3. Unfortunately, the disappearance of the pairs makes it impossible to test the hypothesis in this field. The search for a supercluster at z = 0.30 revealed a faint rich cluster of galaxies near the quasar U10 (z = 0.305). It was found that U10 is not associated with the cluster.

Ford, H.↗
NASA NTRS1988

Models of the quasar population. II - The effects of dust obscuration

A model for dust obscuration is proposed to account for the apparent lack of high-redshift quasars which are assumed to be obscured by dust in intervening galaxies. The distribution function for the optical depth as a function of redshift is constructed and used to determine the expected properties of quasars. The apparent magnitude distribution at three points is used to fit the model. Optical results are given for the comoving number density, redshift distribution, and mean color excess. If the theory is correct, evidence for dust may be seen in quasar spectra and a correlation between quasar continuum slopes and strength of metal line absorption systems should be observed.

Heisler, Julia↗
NASA NTRS1977

On possible associations of quasi-stellar objects and radio galaxies with rich clusters of galaxies

A comparison of the cataloged coordinates of QSOs and of 3CR galaxies with those of Abell's rich clusters of galaxies yields the following results: (1) There is no statistically significant evidence that high-redshift QSOs lie preferentially close to Abell clusters. (2) There is no statistically significant evidence that low-redshift QSOs lie preferentially close to Abell clusters. (3) There is (as is well known) highly significant evidence that 3CR galaxies lie preferentially close to Abell clusters. (4) The distributions of angular separations between QSOs and clusters and between 3CR galaxies and clusters differ at statistically significant (but not highly significant) levels. In view of these results, a generic relationship between low-redshift QSOs and radio galaxies seems questionable. This result for the QSOs is also entirely consistent with the idea that they are 'local' objects with redshifts of noncosmological origin.

Roberts, D. H.↗
NASA NTRS1987

Four-shooter - A large format charge-coupled device camera for the Hale telescope

The Hale telescope has employed an astronomical camera using four 800x800 CCDs in an optical arrangement that allows the imaging of a contiguous 1600-pixel-square region of the sky; reimaging optics are then used to yield a scale of 0.33 arcsec/pixel. Optical coatings are incorporated to yield a throughput at peak efficiency of nearly 50 percent, including telescope losses. This camera can be used in a scanning mode, in which the telescope tracking rate is offset and the charge is clocked in the chips in such a way that the charge image remains aligned with the optical image. Attention is given to the results of a survey for high-redshift quasars using this equipment, which has produced images for the most distant galaxy clusters yet discovered.

Gunn, James E.↗
NASA NTRS1991

An ultraviolet atlas of quasar and blazar spectra

An atlas is presented which provides a uniformly extracted and calibrated set of over 1000 UV spectra of the highest possible SNR for quasars and blazars observed with the IUE. The spectra show that quasars and blazars vary more in the UV than in the optical, and show increasing variability toward shorter wavelengths. The low-redshift quasars have Ly-alpha emission lines dominated by strong, narrow components, while high-redshift quasars seem to lack such narrow components. Absorption by gas in the Galaxy is ubiquitous in strong interstellar lines of C II, O I, Si II, Mg II, and Fe II. Of special note is the detection of Fe II and Mg II absorption due to gas associated with NGC3067 in the quasar 3C 232. Over 20 percent of the combined quasar and Seyfert 1 sample show either associated absorption or absorption just shortward of the emission redshift.

Kinney, A. L.↗
NASA NTRS1991

The complete sample of 1 Jansky BL Lacertae objects. I - Summary properties

The first well-defined, homogeneous radio sample of 34 BL Lac objects selected from a large-area survey of sources brighter than 1 Jy at 5 GHz is presented. Extensive optical spectroscopy reveals weak emission lines in roughly 3/4 of the 34 BL Lac objects in the sample. Optical imaging reveals that the nearby BL Lac objects are not stellar, and that the surface brightness distribution of the surrounding fuzz is consistent with the host galaxies being bright ellipticals. The results suggest that gravitational lensing may affect three of the 17 high-redshift BL Lac objects in the sample. The observations do not support a microlensing scenario for the low-redshift objects.

Stickel, M.↗
NASA NTRS1990

The kinematics of Abell clusters

Velocity histograms, galaxy positions, and velocity dispersions are presented for 69 nearby Abell clusters. The shape of the cumulative distribution for R = 1 or more clusters does not match the predictions of standard CDM models for any biasing parameter b. The only models consistent with the median and maximum dispersions of the sample are those of b about 1.6-2.0 and in which clusters are identified in three dimensions. Velocity dispersions of high-redshift systems appear fundamentally different from those of nearby clusters. The median dispersion of the subset of 25 cD clusters is similar to that of non-cD systems. A substantial fraction of the cD galaxies have velocities significantly different from the mean of their parent clusters. Three of these have 4 s or more measured redshifts. These last two results suggest that the formation of cD galaxies is dominated by the local, rather than global, cluster environment.

Zabludoff, Ann I.↗
NASA NTRS1981

SC 2059-247 - An unusual radio/X-ray source in a distant cluster of galaxies

The X-ray, optical and radio properties of a high redshift, Bautz-Morgan type I cluster of galaxies, namely SC 2059-247, are examined. This cluster is optically dominated by a cD galaxy with a powerful flat-spectrum radio source coincident with the possibly stellar nucleus. Two possible interpretations are suggested for the apparently soft X-ray spectrum of the extremely luminous cluster. Either the intracluster gas is much cooler in high-redshift clusters because they are less relaxed, or the X-ray and radio emissions from SC 2059-247 are the result of a nonthermal QSO/BL Lac type object in the nucleus of the cD. If the latter, it would be the first time that an X-ray source similar to a quasar or BL Lac object has been discovered in a previously identified galaxy.

White, R. A.↗
NASA NTRS1980

The photometric properties of brightest cluster galaxies. I - Absolute magnitudes in 116 nearby Abell clusters

Two-color aperture photometry of the brightest galaxies in a complete sample of nearby Abell clusters is presented. The results are used to anchor the bright end of the Hubble diagram; essentially the entire formal error for this method is then due to the sample of distant clusters used. New determinations of the systematic trend of galaxy absolute magnitude with the cluster properties of richness and Bautz-Morgan type are derived. When these new results are combined with the Gunn and Oke (1975) data on high-redshift clusters, a formal value (without accounting for any evolution) of q sub 0 = -0.55 + or - 0.45 (1 standard deviations) is found.

Hoessel, J. G.↗
NASA NTRS1987

Bimodal star formation - Constraints from galaxy colors at high redshift

The possibility that at early epochs the light from elliptical galaxies is dominated by stars with an initial mass function (IMF) which is deficient in low-mass stars, relative to the solar neighborhood is investigated. V-R colors for the optical counterparts of 3CR radio sources offer the most severe constraints on the models. Reasonable fits are obtained to both the blue, high-redshift colors and the redder, low-redshift colors with a model galaxy which forms with initially equal star formation rates in each of two IMF modes: one lacking low-mass stars, and one with stars of all masses. The net effect is that the time-integrated IMF has twice as many high-mass stars as the solar neighborhood IMF, relative to low mass stars. A conventional solar neighborhood IMF does not simultaneously account for both the range in colors at high redshift and the redness of nearby ellipticals, with any single star formation epoch. Models with a standard IMF require half the stellar population to be formed in a burst at low redshift z of about 1.

Wyse, Rosemary F. G.↗
NASA NTRS1987

X-ray selected high redshift clusters of galaxies

Studies of the evolution of X-ray emission from clusters of galaxies have so far used distant clusters discovered optically and then observed at X-ray wavelengths (Henry et al., 1982; Henry and Lavery, 1984). A different approach to the study of cluster evolution is to use clusters selected directly by their X-ray emission, since X-ray selection is extremely successful at discovering high-redshift clusters (up to z = 0.5). The Extension of the Medium Sensitivity Survey, a study of serendipitous X-ray sources discovered with the Einstein Imaging Proportional Counter, has so far provided a sample of more than 60 clusters with relatively high redshifts. Upon completion of the identification programs the sample will include over 100 clusters. Here the data currently available are presented, and the basic properties of this new sample of clusters of galaxies are discussed. A preliminary number-counts distribution is also derived.

Gioia, Isabella M.↗
NASA NTRS1981

Quasar number density evolution

A simple model of quasar number density evolution is presented based on the occurrence of quasar-like radio galaxies (i.e., strong optical emission lines and type 2 radio morphology) exclusively in regions of low galaxy and intergalactic medium (IGM) density. This suggests a limit for the IGM density of 10 to the -4th (+ or - 1) per cu cm below which quasars are allowed to form and above which they are not allowed. In the recent past (z not greater than 1), the inferred quasar environments are the outskirts of clusters and near the centers of groups of galaxies. However, models of rich cluster evolution consistent with current X-ray observations predict gas densities of less than 10 to the -4th per cu cm in cluster cores in the more distant past (z between 1 and 5). This suggests that quasars were allowed to form in the cores of rich clusters at those epochs, which explains both the rich absorption spectra of high-redshift quasars and the absence of clusters surrounding quasars at lower redshift.

Stocke, J. T.↗
NASA NTRS1978

A study of the absorption-line spectra of six high-redshift quasi-stellar objects

High-resolution spectrograms of six QSOs with apparent visual magnitudes of 17.0 to 18.5 and redshifts greater than 2 are studied for absorption lines. Accurate wavelengths are measured for all the absorption lines that could be detected, attempts are made to identify redshift systems, and the redshifts in each object are examined. Analysis of the absorption-line spectra shows that: (1) a large number of redshifts covering a wide range of values are present in five of the QSOs; (2) about two-thirds of the absorption lines remain unidentified, cannot be of Galactic origin, and are not associated with existing redshift systems; (3) many comparatively small absorption redshifts exist which, if they are due to intervening galaxies, must be produced by very large halos; and (4) in one QSO there is a possible redshift system containing five lines with an absorption redshift that is significantly greater than the emission redshift.

Roberts, D. H.↗
NASA NTRS1991

Discovery of an apparent companion galaxy to Q1548 + 0917 with z = 2.758

The discovery of a resolved companion to the QSO Q1548 + 0917 (redshift 2.749) is reported. The possible nature of the companion, designated C1548 + 0917, is discussed, and new spectroscopic observations of the prototypical case of a Lyman alpha emitting companion to a high-redshift QSO, PKS 1614 + 0508 A, are presented for comparison. C1548 + 0917 appears to be the first case of a radio-quiet continuum object discovered in the vicinity of what must be considered a radio-quiet QSO at high redshift. Evidence is also found for extended Lyman alpha emission associated with the QSO itself.

Steidel, Charles C.↗