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NASA NTRS1987

Star formation in active galaxies and quasars

The observational evidence for a causal or statistical link between star formation and active galactic nuclei are reviewed. The chief difficulty is in quantitatively ascertaining the star formation rate in active galaxies: most of the readily observable manifestations of star formation superficially resemble those of an active nucleus. Careful multi-wavelength spatially-resolved observations demonstrate that many Seyfert galaxies are undergoing star formation. A survey of CO emission from Seyferts (interpreted in conjunction with IRAS data) suggests that type 2 Seyferts have unusually high rates of star formation, but type 1 Seyferts do not. Recent work also suggests that many powerful radio galaxies may be actively forming stars: radio galaxies with strong emission-lines often have blue colors and strong far-infrared emission. Determining the star formation rate in the host galaxies of quasars is especially difficult. Multicolor imaging and long-slit spectroscopy suggests that many of the host galaxies of radio-loud quasars are blue, and a cold interstellar medium has been detected in some quasar hosts.

Heckman, Timothy M.↗
NASA NTRS1988

Second epoch of simultaneous lambda 3.6 and lambda 13 cm observations of the pair of quasars 1038+528 A,B

It is found that the quasar 1038+528 B is a good reference for studying the internal motions in quasar 1038+528 A. The apparent superluminal motion of a feature in quasar A takes place with respect to a neary stationary core; its proper motion is bounded from above by about 40 micro-as/yr. The wavelength dependence of the location of the core brightness peak of A is confirmed.

Marcaide, J. M.↗
NASA NTRS1989

A spiral galaxy at z = 0.366 which overlaps the image of the quasar 4C 39.47

Direct CCD images in broad-band R and I were obtained of the radio quasar 1632+391 (4C 39.46). A faint galaxy which overlaps the quasar's image was identified. The galaxy is centered 4.2 arcsecs east of the quasar, corresponding to 28 kpc at the galaxy's redshift. It is found that the galaxy is a disk-dominated late-type spiral with an absolute B magnitue of -21.6. Low-dispersion spectroscopy yielded a redshift of 0.3662 for the galaxy based on Ca II, H, and K absorption and weak forbidden line O II 3727 emission. It is suggested that appreciable interstellar gas is present in the galaxy.

Hintzen, Paul↗
NASA NTRS1989

Detection of CO(1 to 0) emission from infrared quasars and luminous Seyfert galaxies

CO(1 to 0) emission has been detected from the infrared quasar IRAS 07598+6508 and the luminous Seyfert galaxies IRAS 08572+3915 and Markarian 463 with the IRAM 30-m telescope. These objects were selected from a complete list of warm ultraluminous IRAS sources. The maximum redshift observed was 0.149 (cz = 44.621 km/s , IRAS 07598+6508). Assuming the same empirical relationship between CO brightness and H2 surface mass density as has been found for giant molecular clouds in the Milky Way, the mass of H2 gas in these objects is in the range 0.7 - 6 x 10 to the 10th solar masses, more than 2 - 20 times the H2 content of the Galaxy. The infrared and molecular gas properties of these galaxies are similar to other 'warm' ultraluminous infrared galaxies such as Mrk 231, and the UV-excess quasar Mrk 1014. It is suggested that objects such as these represent an important link in the evolution of ultraluminous infrared galaxies into UV-excess quasars.

Sanders, D. B.↗
NASA NTRS1990

Radio continuum observations of the quasar-galaxy pair 3C 232-NGC 3067

The quasar-galaxy pair 3C 232-NGC 3067 is well known to show absorption by gas associated with the foreground galaxy against the background quasar (see Stocke et al. this volume). Observations by Carilli, van Gorkom, and Stocke (Nature 338, 134, 1989) found that the absorbing gas is located in a long tail of gas which extends from the galaxy toward the quasar and beyond (in projection). Though the HI observations of NGC 3067 indicate that the galaxy has been severely disturbed, there is no obvious candidate in the field which could cause such a disturbance, leading to the conclusion that the system has undergone a recent merger. The radio continuum observations of this system were designed to study the nature of this highly disturbed galaxy. New continuum observations confirm the notion that NGC 3067 is a highly disturbed system, and, in particular, the notion that the western half of the galaxy extends only 1/2 as far in radius as the eastern half. This disturbance must have occurred recently, since the galactic rotation would smooth out the observed asymmetry in about 10(exp 8) years. Researchers are left with the problem that there are no obvious candidates which could have caused such a disturbance.

Haxthausen, Eric↗
NASA NTRS1990

Are extremely luminous far-infrared galaxies the result of merging quasar cores

Extremely Luminous far-infrared galaxies (ELFs) are a class of galaxy discovered independently by several groups. The class is characterized by a quasar-like total luminosity (10(exp 11) to 10(exp 13) solar luminosity) which is radiated almost entirely in the far-infrared. It has been suggested that obscured quasar cores may be responsible for generating this luminosity. Here the author demonstrates that ELFs appear in several guises which can be characterized by the number of quasar cores they contain (zero, one or two). The author develops a unified model to account for these differences.

Norris, R. P.↗
NASA NTRS1991

Moderate resolution spectrophotometry of high redshift quasars

A uniform set of photometry and high signal-to-noise moderate resolution spectroscopy of 33 quasars with redshifts larger than 3.1 is presented. The sample consists of 17 newly discovered quasars (two with redshifts in excess of 4.4) and 16 sources drawn from the literature. The objects in this sample have r magnitudes between 17.4 and 21.4; their luminosities range from -28.8 to -24.9. Three of the 33 objects are broad absorption line quasars. A number of possible high redshift damped Ly-alpha systems were found.

Schneider, Donald P.↗
NASA NTRS1992

Probability distributions for the magnification of quasars due to microlensing

Gravitational microlensing can magnify the flux of a lensed quasar considerably and therefore possibly influence quasar source counts or the observed quasar luminosity function. A large number of distributions of magnification probabilities due to gravitational microlensing for finite sources are presented, with a reasonable coverage of microlensing parameter space (i.e., surface mass density, external shear, mass spectrum of lensing objects). These probability distributions were obtained from smoothing two-dimensional magnification patterns with Gaussian source profiles. Different source sizes ranging from 10 exp 14 cm to 5 x 10 exp 16 cm were explored. The probability distributions show a large variety of shapes. Coefficients of fitted slopes for large magnifications are presented.

Wambsganss, Joachim↗
NASA NTRS1992

The infrared properties of quasars and radio galaxies - Testing the unification schemes

The IRAS data base is used to compare the mid-FIR properties of two classes of radio-loud AGN whose LF radio emission arises in large-scale radio lobes. The two primary samples consist of 42 quasars and 75 narrow-line radio galaxies selected on the basis of their 178 MHz radio flux density from the 3 CR catalog and having redshifts of not less than 0.3 and Galactic latitudes of not less than 20 deg. The mid-FIR emission was found to be about four times stronger on average in the quasars than in the radio galaxies. Even though the radio galaxies are systematically weaker mid-FIR sources than the quasars, they are still exceptionally luminous (about 10 exp 12 solar luminosities) in the mid-FIR. These powerful radio galaxies contain potent sources of radiation that are either hidden or energetically unimportant at shorter wavelengths.

Heckman, Timothy M.↗
NASA NTRS1992

Gravitational lensing of quasars as seen by the Hubble Space Telescope Snapshot Survey

Results from the ongoing HST Snapshot Survey are presented, with emphasis on 152 high-luminosity, z greater than 1 quasars. One quasar among those observed, 1208 + 1011, is a candidate lens system with subarcsecond image separation. Six other quasars have point sources within 6 arcsec. Ground-based observations of five of these cases show that the companion point sources are foreground Galactic stars. The predicted lensing frequency of the sample is calculated for a variety of cosmological models. The effect of uncertainties in some of the observational parameters upon the predictions is discussed. No correlation of the drift rate with time, right ascension, declination, or point error is found.

Maoz, D.↗
NASA NTRS1992

The discovery of an X-ray selected, radio-loud quasar at z = 3.9

About 600 weak X-ray sources from a data base of about 100,000 2-4sigma fluctuations derived from Einstein Observatory imaging proportional counter X-ray images are selected on the basis of a flux-limited catalog of radio sources in the northern sky. Optical spectroscopy of only six of these sources resulted in the discovery of a quasar with an emission-line redshift of 3.87. Subsequent VLA observations reveal the source to have a flat-spectrum radio core plus an unresolved radio lobe 2.5 arcsec away with a spectral index of 1.45. The lobe is connected to the core by a weak jet. The integrated flux density of the source at 20 cm is 0.66 Jy. The v magnitude of the quasar is 19.5, and the tentative X-ray sources has a very soft spectrum. The properties of this object are discussed in the context of known high-redshift radio sources and existing X-ray selected quasar samples, and the potential of the present discovery technique for examining the properties of very distant active galaxies is explored.

Becker, R. H.↗
NASA NTRS1992

Quasar evolution and the growth of black holes

A 'minimalist' model of AGN evolution is analyzed that links the measured luminosity function to an elementary description of black hole accretion. The observed luminosity function of bright AGN is extrapolated and simple prescriptions for the growth and luminosity of black holes are introduced to infer quasar birth rates, mean fueling rates, and relict black hole distribution functions. It is deduced that the mean accretion rate scales as (M exp -1./5)(t exp -6.7) and that, for the most conservative model used, the number of relict black holes per decade declines only as M exp -0.4 for black hole masses between 3 x 10 exp 7 and 3 x 10 exp 9 solar masses. If all sufficiently massive galaxies pass through a quasar phase with asymptotic black hole mass a monotonic function of the galaxy mass, then it is possible to compare the space density of galaxies with estimated central masses to that of distant quasars.

Small, Todd A.↗
NASA NTRS1993

Consistency of spherical, gravity-dominated dynamics with quasar high-ionization emission-line profiles

Line profile data are used to test a simple kinematic model - spherically symmetric gravitational free fall - in which the number of free parameters is limited by requiring physical self-consistency. The predictions of this model are fitted to high-resolution spectra of the stronger rest-frame UV emission lines in 12 quasars with z of about 2. It is found that if all the lines are radiated predominantly from the illuminated faces of the emission-line clouds, the profiles of Ly-alpha, N V 1240 A, and C IV 1549 A can be simultaneously well fitted with very similar parameters for all 12 quasars. It is concluded that spherically symmetric gravitational free fall does not correctly describe the dynamics of quasar broad emission-line regions.

Kallman, T. R.↗
NASA NTRS1991

The faint quasar luminosity function

Preliminary results of an expanded program to determine the faint-quasar luminosity function are described. Quasars have been selected in four fields totaling 1.2 sq deg from four-band photometry. Out of a total of 130 quasars with good spectroscopy, 37 have J greater than 21.5 and 46 have F greater than 21.0. The spectroscopic sample is representative of all of the color-selected candidates. An estimate of the luminosity function as a function of redshift is derived.

Kron, Richard G.↗
NASA NTRS1991

Cosmic evolution of Quasar radio structure

We discuss the results of a survey of Quasar radio structures over redshifts from 0.6 to 3.7. There are clear evolutionary trends in size and luminosity, which suggest that the duty cycle of individual Quasars has increased over cosmic time. This affects source count statistics and gives clues on the evolution of Quasar environments.

Hutchings, J. B.↗
NASA NTRS1993

The ultraviolet absorption spectrum of the quasar PKS 0405-12 and the local density of Lyman-alpha absorption systems

A sample of 32 absorption lines has been identified in the ultraviolet spectrum of the z = 0.57 quasar PKS 0405-12. Data cover the wavelength range 1190-3260 A. There are 10 extragalactic Ly-alpha absorption lines in the complete sample, all with observed equivalent widths greater than or equal to 0.40 A; three of the Ly-alpha lines have Ly-beta counterparts. The number of Ly-alpha lines observed in the spectrum of PKS 0405-12 is within 1 sigma of the number predicted on the basis of previous HST observations of 3C 273 and of H1821 + 643. Combining the HST observations of 3C 273, H1821 + 643, and PKS 0405-12, we estimate the local number density of Ly-alpha systems with rest equivalent widths larger than 0.32 A to be about 15 +/- 4 Ly-alpha lines per unit redshift. Ground-based images reveal a rich field of galaxies in the direction of PKS 0405-12, including many galaxies with the brightnesses and sizes expected if they belong to a cluster associated with the quasar. The quasar spectrum does not show any evidence for absorption at the redshift of the emission lines, indicating a covering factor of less than unity for the halos of galaxies in the cluster around PKS 0405 - 12.

Bahcall, John N.↗
NASA NTRS1993

The Hubble Space Telescope quasar absorption line key project. I - First observational results, including Lyman-alpha and Lyman-limit systems

Spectra are presented for 37 quasars with small and moderate redshifts; the quasars were observed with the Faint Object Spectrograph of the HST. New higher resolution measurements of the absorption lines in the UV spectra of 11 quasars with emission-line redshifts that lie between 0.3 and 1.0 are reported. Calibrated spectra and continuum fits are shown for each object. A total of 104 extragalactic Ly-alpha systems are identified, nine of which are found at the same redshifts as metal-line systems. The local number density of Ly-alpha systems with rest equivalent widths larger than 0.32 A and without detected metal lines is about 15.1 +/- 4.3 Ly-alpha systems per unit redshift with gamma = 0.30 +/- 0.62 and W* = 0.22 +/- 0.02 A. A total of 10 Lyman-limit systems with an optical depth greater than 0.4 are identified. The paucity of damped Ly-alpha lines at small and moderate redshifts shows that the number density of damped absorption systems decreases with decreasing redshift.

Bahcall, John N.↗
NASA NTRS1993

The ROSAT spectrum of 3C 351 - A warm absorber in an X-ray-'quiet' quasar?

3C 351 is one of the most X-ray-quiet radio quasars (alpha(ox) about 1.6). We have observed 3C 351 with the ROSAT position sensitive proportional counter (PSPC) and find a complex X-ray spectrum which is not well reproduced by a power law plus low-energy cut-off model. Soft excess, partial covering, and 'warm absorber' models can all produce acceptable fits, although only the warm absorber model gives typical values for the high-energy continuum slope. The alpha(ox) measured by using quasi-simultaneous ROSAT, MMT, and HST observations is in the range 1.5-1.6, significantly above the average of 1.37 for a complete sample of 33 3CR quasars. If the soft excess or partial covering models are correct, 3C 351 appears X-ray-quiet in the PSPC band because it has an extremely steep or flat intrinsic high-energy spectral slope. However, if the warm absorber model is correct, the quasar is intrinsically X-ray-quiet; the normalization of the intrinsic (unabsorbed) X-ray emission is unusually low relative to the optical luminosity. We investigate the properties of our warm absorber model in some detail. The apparently complicated behavior of the fit parameters may be understood by considering the effects of changing absorbing column and ionization parameter on intrinsic power-law-spectra of different slopes.

Fiore, Fabrizio↗