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Star Formation Histories of Nearby Elliptical Galaxies. II. Merger Remnant Sample
This work presents high signal-to-noise spectroscopic observations of asample of six suspected merger remnants, selected primarily on the basisof H I tidal debris detections. Single stellar population analysis ofthese galaxies indicates that their ages, metallicities, andα-enhancement ratios are consistent with those of a representativesample of nearby elliptical galaxies. The expected stellar population ofa recent merger remnant, a young age combined with low [α/Fe], isnot seen in any H I-selected galaxy. However, one galaxy (NGC 2534) isfound to deviate from the Z-plane in the sense expected for a mergerremnant. Another galaxy (NGC 7332), selected by other criteria, bestmatches the merger remnant expectations.
| The Second Byurakan Survey. General Catalogue
The Second Byurakan Survey (SBS) General Catalogue is presented. TheSBS, a continuation of the Markarian survey reaching fainter limitingmagnitudes, is the first survey which combines the search of galaxiesand QSOs. A total area of 991OS#square;degrees of the Northern sky wascovered with the use of three objective prisms in combination withSchott filters. The limited magnitude on the best plates reached B ~19.5.The General Catalogue consists of 3563 objects presented in two parts: aCatalogue of galaxies (1863 objects) and one of stellar objects (1700objects). The Catalogue of SBS AGN consists of 761 objects (155 SyG, 596QSOs, and 10 BLLac). Multi-wavelength data are presented for 1438 SBSobjects identified with X-ray, IRAS and FIRST sources.Spectrophotometric observations obtained over 26 years are available for3132 objects. Redshifts were measured for ~ 2100 extragalactic objects.Spectral classification is presented for ~ 2970 objects. The majority ofthe data is presented here for the first time. The Catalogue presentsnew large homogeneous deep representative complete samples of brightQSOs, AGNs, and faint UVX galaxies in the Northern sky. The SBS sampleis found to be complete at 70% for galaxies and ~ 85% for AGN/QSOs withB ≤ 17.5.
| The PDS versus Markarian starburst galaxies: comparing strong and weak IRAS emitter at 12 and 25 μm in the nearby Universe
The characteristics of the starburst galaxies from the Pico dos Diassurvey (PDS) are compared with those of the nearby ultraviolet (UV)bright Markarian starburst galaxies, having the same limit in redshift(vh < 7500 km s-1) and absolute B magnitude(MB < -18). An important difference is found: theMarkarian galaxies are generally undetected at 12 and 25 μm in IRAS.This is consistent with the UV excess shown by these galaxies andsuggests that the youngest star-forming regions dominating thesegalaxies are relatively free of dust.The far-infrared selection criteria for the PDS are shown to introduce astrong bias towards massive (luminous) and large size late-type spiralgalaxies. This is contrary to the Markarian galaxies, which are found tobe remarkably rich in smaller size early-type galaxies. These resultssuggest that only late-type spirals with a large and massive disc arestrong emitters at 12 and 25 μm in IRAS in the nearby Universe.The Markarian and PDS starburst galaxies are shown to share the sameenvironment. This rules out an explanation of the differences observedin terms of external parameters. These differences may be explained byassuming two different levels of evolution, the Markarian being lessevolved than the PDS galaxies. This interpretation is fully consistentwith the disc formation hypothesis proposed by Coziol et al. to explainthe special properties of the Markarian SBNG.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| Accurate optical positions for 2978 objects from the Second Byurakan Survey (SBS) with the Digitized Sky Survey
Optical positions of 2978 objects listed in the Second Byurakan Survey(SBS) were obtained using the Digitized Sky Survey (DSS), and are givenwith an rms uncertainty ~ 1 arcsec in each coordinate. Tables 1 and 2are only available in electronic form at the CDS via anonymous ftp130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| Is the Dust Obscuring Supernovae in Distant Galaxies the Same as Dust in the Milky Way?
Previous attempts to correct type Ia supernovae (SN Ia's) for hostgalaxy extinction have given strange results: increased dispersion onthe Hubble diagram or impossibly low values of the reddening ratio fordust in distant galaxies. The cause is the incorrect assumption that SNIa's have a uniform intrinsic luminosity and color at maximum light. Ourmulticolor light-curve shape (MLCS) method establishes the relationbetween intrinsic luminosity and color for SN Ia's using information inlight-curve shapes. Here we estimate the B - V, V - R, and V - I colorexcess for 20 SN Ia's using MLCS and estimate the reddening ratios ofdust in distant galaxies. The ratios of selective to total absorptionfrom dust in distant galaxies hosting SN Ia's are consistent with thegalactic extinction law. The SN Ia's in late-type galaxies are oftenobscured by dust, while those in early-type galaxies are dust free. Thissuggests that SN Ia extinction is caused by interstellar (notcircumstellar) dust, with similar optical properties as the dust in theMilky Way.
| The reality of anomalous redshifts in the spectra of some QSOs and its implications.
The evidence for the physical association of close pairs involvingbright QSOs with large redshifts and bright nearby galaxies with smallredshifts, is reviewed and, in Table 1, a list of the best cases isgiven. It is shown that in a series of statistical studies usingcatalogs of QSOs and catalogs of galaxies, very strong correlations ofhigh redshift radio QSOs have been found successively with (o) [a.] TheShapley Ames Catalog of the brightest galaxies. Here the correlation iswith powerful radio QSOs with S>=9Jy (0.4GHz). The result issignificant at the 7-10σ level. (o) [b.] The Bright Galaxy Catalog(z<=0.05). Here the QSO sample is dominated by radio emitting QSOs,largely identified from the 3CR, Molonglo, Parkes, and 4C radiocatalogs. (o) [c.] The galaxies in the Lick Catalog (m<~17,z<~0.2). Again the sample of QSOs is a radio sample. (o) [d.] TheIRAS galaxy catalogs, where some fraction of the galaxies may have z upto 0.4, and where a few galaxies may be identical in position with theQSOs, but where the larger fraction have much smaller redshifts than theQSOs. Again the QSO sample is a radio sample. (o) [e.] Finally strongcorrelations on scales <~10' have been found between opticallybright, high redshift radio loud QSOs and the diffuse X-ray emissionseen by ROSAT. Bartelmann et al. (1994) believe that this diffuse X-rayemission is due to galaxy clusters at redshifts significantly less thanthe observed redshifts of the QSOs.
| A multifrequency radio continuum and IRAS faint source survey of markarian galaxies
Results are presented from a multifrequency radio continumm survey ofMarkarian galaxies (MRKs) and are supplemented by IRAS infrared datafrom the Faint Source Survey. Radio data are presented for 899 MRKsobserved at nu = 4.755 GHz with the National Radio Astronomy Observatory(NRAO)-Green Bank 300 foot (91 m) telescope, including nearly 88% ofthose objects in Markarian lists VI-XIV. In addition, 1.415 GHzmeasurements of 258 MRKs, over 30% of the MRKs accessible from theNational Aeronomy and Ionosphere Center (NAIC)-Arecibo, are reported.Radio continuum observations of smaller numbers of MRKs were made at10.63 GHz and at 23.1 GHz and are also presented. Infrared data from theIRAS Faint Source Survey (Ver. 2) are presented for 944 MRKs, withreasonably secure identifications extracted from the NASA/IPACExtragalactic Database. MRKs exhibit the same canonical infraredcharacteristics as those reported for various other galaxy samples, thatis well-known enhancement of the 25 micrometer/60 micrometer color ratioamong Seyfert MRKs, and a clear tendency for MRKs with warmer 60micrometer/100 micrometer colors to also possess cooler 12 micrometer/25micrometer colors. In addition, non-Seyfert are found to obey thewell-documented infrared/radio luminosity correlation, with the tightestcorrelation seen for starburst MRKs.
| Neutral hydrogen observations of elliptical galaxies. II. The IRAS sample.
HI observations are reported for a total of 53 IRAS elliptical galaxies.Nearby confusing sources may be responsible for some of the 33detections. There are 24 isolated detected galaxies, which can be splitinto two groups, one having the same M_HI_/L_B_ ratio as the ellipticalgalaxies from the RSA (M_HI_/L_B_=0.030+/-0.026). A second group is morethan six times richer in HI (M_HI_/L_B_=0.206+/-0.105). The "HI-rich"galaxies have blue colors like spiral galaxies and have a tendencytowards higher average dust temperatures. The large number of ellipticalgalaxies in compact groups (in this sample) suggests that gravitationalinteractions and mergers may be an important source of interstellarmatter for elliptical galaxies.
| The molecular cloud content of early-type galaxies. V. CO in elliptical galaxies.
A survey of CO emission in 29 far-IR selected elliptical galaxiesresulted in 16 detections, of which 3 remain tentative. The moleculargas masses range from 2x10^6^Msun_ to1x10^9^Msun_, and appear to be unrelated to the underlyingstellar population. This suggests an external origin of the gas. Most ofthe elliptical galaxies with a molecular gas component have agas-to-dust mass ratio of ~700, where dust masses are derived from theIRAS fluxes, but some appear to have a ratio as low as 50. A smallapparent gas-to-dust mass ratio is also found for some late-typegalaxies, and is correlated with a low dust temperature. We suggest thata large part of the far-infrared emission from these galaxies (bothearly- and late-types) comes from dust associated with the atomic gascomponent rather than star forming regions associated with the moleculargas, and that they contain a cold dust component. Low excitationtemperatures for CO transitions in galaxies with cold dust could lead toan underestimate of the molecular gas mass by a factor of 5. The averageM_H_2__/M_HI_ ratio for the elliptical galaxies is 2-5 times lower thanfor normal spiral galaxies. Field ellipticals appear more likely tocontain an observable molecular gas component than those ellipticalsresiding in groups and clusters.
| The Hubble Space Telescope Snapshot Survey. IV - A summary of the search for gravitationally lensed quasars
We report the concluding results of the HST Snapshot Survey forgravitationally lensed quasars. New observations of 153 high-luminosityz above 1 quasars are presented, bringing to 498 the total number ofquasars observed in the survey. The new observations do not reveal newcandidates for gravitational lensing. We present tables summarizing allof the snapshot observations, with measured V-magnitudes, accurate to0.1 mag, for each of the quasars successfully observed. The observedfrequency of lensing of quasars into multiple images is 3-6 out of 502,depending on whether one counts candidates that are not yet securelyconfirmed and cases in which clusters play a role. This frequency is inthe range predicted by calculations with a vanishing cosmologicalconstant, assuming galaxies can be modeled by unevolving isothermalspheres dominated in their centers by dark matter. The observedfrequency is an order of magnitude lower than expected in such modelswhen the universe is strongly dominated by a cosmological constant. Thisconclusion is, however, sensitive to the model assumptions and to theprecise number of actual lensed quasars.
| Accurate positions and finding charts for 528 high-redshift, luminous quasars
Finding charts and J2000 positions accurate to about 1 arcsec arepresented for the 528 high-redshift (z is greater than 1), luminous (MVis less than -25.5) quasars investigated in the HST Snapshot Survey. Ahistogram showing the distribution of the differences between thepositions determined by the Space Telescope Science InstituteAstrometric Support Program and the catalog positions is provided.
| Molecular gas in elliptical galaxies with dust lanes
We have searched for CO(1-0) line emission in eight dust lane ellipticaland lenticular galaxies using the Nobeyama 45 m telescope. Five of theeight galaxies, including the well-studied elliptical NGC 1052, have COemission at above the 5-sigma level, with inferred molecular gas massesranging from 10 exp 8 to a few times 10 exp 9 solar masses. Ourselection criterion differs from previous surveys in that it does notdepend on the FIR fluxes, and thus is less sensitive to the sizes anddistances of the host galaxies or to the degree to which dust is heated.The relatively high detection rate of CO in these ellipticals suggests aclose correlation between molecular mass and cold dust. Compared withpreviously studied samples of FIR selected early-type galaxies, oursample has on average four times more CO emission per unit FIR (40-120microns) luminosity. If the intrinsic gas-to-dust ratio of thesegalaxies as similar to that of the Milky Way, then only about 5 percentof the dust mass in dust lane ellipticals radiates substantially at 60and 100 microns, and the remaining dust must be colder than about 30 K.
| Pairing properties of Markarian starburst Galaxies
The environmental parameters of 516 non-Seyfert Markarian galaxies werestudied in a redshift-bounded sample, supplemented by new spectra andredshift measures for possible companions, in order to evaluate theiroccurrence in galaxy pairs, defined through quantitative criteria. Itwas found that one-third of these galaxies occur in pairs (while only 6to 10 percent of optically-selected galaxies are known to be paired). Acomparison of various optical and IR properties of paired and nonpairedMarkarian galaxies showed no differences in the shape of the optical,far-IR, or H-alpha luminosity functions. It was found, however, that theMarkarian component is brighter than the other galaxy in each pair by0.66 magnitude in the mean at B.
| On the external origin for dust in elliptical galaxies
Large samples of elliptical galaxies, observed at high signal-to-noiseratio with CCDs, are used with ADDSCAN 100 micron fluxes from IRAS toexamine evidence for the external origin of dust in these galaxies. Foursmall sets of galaxies are picked which show features stronglyindicative of a merger, that is, infalling H I gas, extensive dustlanes, and kinematically peculiar cores and shells. Though somecounterexamples exist, it is shown that the dust and isophotalproperties are consistent with the current merger model for thesegalaxies.
| Galaxy alignments
Large areas of the sky around the brightest apparent magnitude galaxieshave been examined. In almost every case where they are not crowded byother right galaxies, clearly marked lines of higher red shift galaxieshave been going through, or originating from, the positions of thesebright apparent magnitude galaxies. It is shown that galaxies of about3000 to 5000 km/s red shift define narrow filaments of from 10 to 50 degin length. It is found that galaxies of very bright apparent magnitudetend to occur at the center or ends of these alignments. The 20brightest galaxies in apparent magnitude north of delta = 0 deg areinvestigated here. Of the 14 which are uncrowded by nearby brightgalaxies, a total of 13 have well marked-lines and concentrations offainter, higher red shift galaxies.
| Associations between quasi-stellar objects and galaxies
A table is presented here listing all close pairs of QSOs and galaxiesthat were found in a computer-aided search of catalogs of QSOs andbright galaxies and an extensive search of the literature. There is alarge excess of pairs with separations of 2 arcmin lor less, or about 60kpc, over the numbers expected if the configurations were accidental.The angular separation for 392 pairs adds to the evidence for physicalassociation, and it is shown that selection effects are not important. Ageneral rule is stated that QSOs tend to lie in the vicinity of normalgalaxies much more often than is expected by chance whether or not thegalaxies and the QSOs have the same redshifts. It is emphasized thatthis rule cannot be explained in terms of gravitational microlensing,and it is concluded that some part of the redshift of all classes ofactive nuclei is not associated with the expansion of the universe.
| Optical and far-IR luminosity functions of Markarian galaxies
A new optical luminosity function of Markarian galaxies is presentedwhich improves on earlier determinations. The importance of clusteringof Markarian galaxies is checked by applying an alternative methodproposed by Turner (1979) which allows the shape of the luminosityfunction to be derived for an arbitrary space distribution provided thatthe shape is the same in clusters and in the field. A fractionalbivariate function is constructed using IRAS data, and survival analysistechniques are used to exploit the information content of IR upperlimits. The resulting far-IR luminosity function is presented andcompared with previous estimates.
| Properties of elliptical galaxies with dust lanes
The new galactic class of elliptical galaxies with dust lanes ischaracterized by an elliptical stellar body crossed along the minor axisby a dust lane. Ninety objects are presently listed as dust laneellipticals. In this paper, the morphological, statistical, kinematical,and photometric properties of these galaxies are described. The natureof the warps seen in the dust lanes in some of the galaxies isaddressed.
| A catalog of Markarian galaxies
A catalog of Markarian galaxies is presented which tabulates redshifts,spectral and morphological classifications, magnitudes, infrared andradio flux densities, and over 600 references to available datapublished before January 1, 1986. Redshifts are now available for 1228objects with strong ultraviolet continua, and follow-up spectroscopicand photometric observations of Markarian galaxies have providedclassifications of 115 Seyfert 1, 43 Seyfert 2, and 137 starburst and HII-type galaxies. After a description of the Markarian survey and thecurrent catalog, a summary of the general results obtained from the datais presented. A preliminary study of the infrared properties ofMarkarian galaxies as measured by IRAS reveals a number of interestingresults, including the existence of a sample of elliptical andlenticular galaxies with appreciable infrared emission.
| A Deficiency of Normal Elliptical Galaxies among Markarian Galaxies
Not Available
| On the relation of Markarian galaxies with Zwicky clusters. I - Data
In the area covered by the survey of Markarian et al. (1967-1981) andthe CGCG of Zwicky et al. (1961-1968) there are 1344 Markarian galaxies,of which 597 are positioned inside the contours of Zwicky clusters. Dataon these galaxies and respective clusters are presented in differenttables, according to whether they are galaxies which are members ofclusters, or probable or possible members; projection cases areconsidered separately.
| Recognition and classification of galaxies with optical jets
Deep images and spectra are presented for galaxies reported in variouscatalogs to have jets, as well as in a search of the SRC J survey platesin a region near the south galactic pole. Most of these are shown to besuperpositions, polar rings, tidal features, or artifacts of theoriginal plate material. Examples are shown of ten ways that false jetscan be produced, with more detailed case studies for several systems.Based on this experience, several criteria for the brightness, location,and symmetry of genuine optical jets are suggested, which should yieldsurvey samples much less contaminated by 'false alarms' than existingones. Among the objects that remain as optical-jet candidates, ESO0610-23 shows a linear, radial chain of H II regions on the outskirts ofan amorphous system with complex internal structure, UGC 3995 is a closepair of spirals, one of which has a type 2 Seyfert nucleus and apparentknotty jet, and NGC 1598 has the radial features previously reported,but considerable chaotic outer structure as well. Several systems (suchas AM 0207-49 and ESO 2330-38) illustrate the intrinsic difficulty ofseparating jets and tidal tails on morphological grounds alone incertain cases.
| The statistical distribution of the neutral-hydrogen content of elliptical galaxies
An examination has been conducted of the form of the distributionfunction for the relative H I content, MH I/LB, of elliptical galaxies,using a data set derived from all recent H I observations of ellipticalsin the literature. The characteristics of this combined data set arepoorly defined, but upon examination it appears to be reassuringly freeof built-in biases and correlations. The data set contains 152 galaxies;23 of these have been detected in the H I line. The detected galaxiesare shown to be more H I rich on average than the galaxies in the wholesample. A method for recovering the intrinsic distribution of MH I/LB,using both detection and upper-limit data, is described, and the dataare shown to be consistent with a shallow power-law differentialdistribution N approximately (MH I/LB) to the -1.5th. This distributionis quite different from that for spirals, where N(MH I/LB) has awell-defined mean value and a small dispersion. This result stronglysuggests that the gas and star contents of ellipticals are decoupled,i.e., the gas has an external origin.
| A catalog of dusty elliptical galaxies
A catalog of about 100 dusty elliptical galaxies and some relatedobjects is presented. A morphological classification system is proposed,and the observed dust lane characteristics of some of the individualgalaxies are described. The properties of the galaxies are discussed,including the distribution of morphological types, their radioproperties, radio source orientation, neutral hydrogen, kinematics anddynamics, and relationship to other types of peculiar galaxies.
| Early-type /discless/ galaxies with dust lanes
A comprehensive, homogeneous sample of 40 optically selected dust-lanegalaxies, which exhibit no obvious associated luminous disks, ispresented along with a preliminary discussion of its properties. Adearth of such galaxies in the north is attributed to the poorerresolution of the Palomar Sky Survey relative to the Southern SkySurvey, which is the source materiaal in the south. It is inferred thatthere may not be a comparably large population of galaxies with dustlanes closely confined to their central regions. The orientation of thedust lanes is varied, but the majority occurs impartially on the majoror minor axes of the light distribution, with a substantial minority ofskew cases with the dust at an intermediate angle. Observed propertiesof the galaxies are summarized, and it is suggested that the propertiesare best attributed to the accretion of cool material at a fairly recentepoch (less than a few x 10 to the 9th yr ago), and that subsequentevolution of this material can explain the observed distribution of dustlane orientation. It is thought that a significant number of early-typegalaxies are prolate in form.
| Quasars near companion galaxies
Twenty-two new quasars close to galaxies are reported. All nonellipticalgalaxies brighter than 12.8 with apparent companion galaxies areexamined, and 13 of the 34 candidate companion galaxies are found to bequasars with an accidental probability of less than 0.01. In the RAregion between NGC 5055 and NGC 7448, the confirmation is at the 10 tothe -8th to 10 to the -16th level, and in the NGC 2441 to NGC 3184region, the association is confirmed at the 10 to the -17th to the 10 tothe -19th level. It is concluded that to avoid the association of thesequasars with the low redshift companions, the average background densityof distant quasars must be somewhere around 20 times what it iscurrently measured to be.
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