The cosmic distance scale

Summary The status of the cosmic distance scale problem in early 1989 is reviewed. Internally consistent distances to Local Group galaxies are given in Tables 5 and 6. Within the Local Group the distance scale is found to be 11±5% smaller than that previously adopted by Sandage and Tammann. Distances to nearby galaxies are used as stepping stones to the Virgo cluster. The interpretation of the Tully-Fisher observations of Virgo spirals is found to be ambiguous because it is not yet clear which spirals are cluster members and which are background objects. Distance estimates of the Virgo cluster obtained by different techniques are listed in Table 11. The distance modulus of the Virgo cluster is found to be 31.5±0.2, corresponding to a distance of 20±2 Mpc. The elliptical galaxies in the core of the Virgo cluster haveV ₀=1200±46 kms^–1, which corresponds toV _LG=1082±48 km s^–1. With an infall velocity of 250±50 km s^–1 this yields a cosmological redshiftV=1332±69 km s^–1, from which a Hubble parameter H₀=67±8 km s^–1 Mpc^–1 is obtained. Space Telescope observations of distant Cepheids, Tully-Fisher observations of spirals in the Hercules eluster, and interference filter observations of Virgo planetary nebulae in the light of [O_III], should soon result in a major improvement in the accuracy with which H₀ is known.     

Surveying the Local Supercluster Plane

We investigate the distribution and velocity field of galaxies situated in a band of 100 by 20 degrees centered on M87 and oriented along the Local supercluster plane. Our sample amounts 2158 galaxies with radial velocities less than 2000 km s^?1. Of them, 1119 galaxies (52%) have distance and peculiar velocity estimates. About 3/4 of early-type galaxies are concentrated within the Virgo cluster core, most of the late-type galaxies in the band locate outside the virial radius. Distribution of gas-rich dwarfs with M_HI >M_* looks to be insensitive to the Virgo cluster presence. Among 50 galaxy groups in the equatorial supercluster band 6 groups have peculiar velocities about 500–1000 km s^?1 comparable with virial motions in rich clusters. The most cryptic case is a flock of nearly 30 galaxies around NGC4278 (Coma I cloud), moving to us with the mean peculiar velocity of ?840 km s^?1. This cloud (or filament?) resides at a distance of 16.1 Mpc from us and approximately 5 Mpc away from the Virgo center. Galaxies around Virgo cluster exhibit Virgocentric infall with an amplitude of about 500 km s^?1. Assuming the spherically symmetric radial infall, we estimate the radius of the zero-velocity surface to be R₀ = (7.0±0.3) Mpc that yields the total mass of Virgo cluster to be (7.4 ± 0.9)× 10¹⁴M_⊙ in tight agreement with its virial mass estimates. We conclude that the Virgo outskirts does not contain significant amounts of dark mater beyond its virial core.     

Concerning the errors arising through the use of Tully-Fisher relation for estimation of the Virgo cluster distance

The distance modulus of the Virgo cluster has been reexamined based on the Tully-Fisher relation between fully corrected B. ₁ ⁰ values and 21 cm velocity width derived from RC3 catalogue for spiral galaxies of Sbc-Sdm types, belonging to the “low-velocity” Virgo subcluster, singled out according to the statistical method proposed by Anosova, and led to the value μ = 31.15 ± 0.57 mag. A strong dependence of the intrinsic scatter in the Tully-Fisher relation on the apparent axes ratio of galaxies has been found, with a value of 0.4 mag for strongly flattened, highly inclined galaxies and galaxies with small inclinations and a value of 0.72 mag for objects with intermediate values of axes ratio. The restriction to samples only with galaxies with photoelectric observations does not lead to a considerable change of amplitude of scatter and decreases the value the of distance modulus. Published in Astrofizika, Vol. 42, No. 1, pp. 37–46, January–March, 1999.     

The Hubble relation: Differences between galaxy types Sb and Sc

The most accurate data on galaxy types, corrected apparent magnitudes and redshifts as given in the Sandage-TammanRevised Shapley-Ames catalog are analyzed. It is shown that Sb galaxies of the same luminosity class as M31 and M81 define a narrow Hubble relation withH ₀=65 _–6 ⁺¹⁵ km s^–1 Mpc^–1.In contrast, Sc galaxies deviate strongly towars higher redshift from a linear, log redshift—apparent magnitude relation. Not all this deviation can be selection effect due to increasing volume sampled at increasing redshift (Malmquist bias). Physical associations of groups of galaxies in theRSA Catalog are used to establish the existence of various amounts of excess (non-velocity) redshifts among Sc and allied types of galaxies.Independent distances fromHi line width — luminosity criterion (Tully-Fisher) are analyzed. It is shown that this criterion gives much smaller distances than redshifts do for galaxies which deviate above the Hubble line. Unless the Tully-Fisher relation gives too small distances for more luminous galaxies, this confirms the excess redshift to be intrinsic to the Galaxy. But it is next demonstrated, that for low redshift galaxies, there is no discrepancy between redshift and Tully-Fisher distance even though there is a wide range of absolute magnitudes.If Tully-Fisher distances are accepted, the onlly alternative to having a Hubble constant which increases strongly with distance is to have a component of the higher redshift Sc's contributed by a non-recessional redshift. Streaming motions would have to be large, increase with distance and be always in the receding sence. It is shown here that the Sc's which deviate most from the Hubble relation and have the largest discrepancies with Tully-Filsher distances lie predominantly in the sky toward very nearby groups of galaxies. If they were at these closer distances the discordant galaxies, mostly ScI's, would have dwarfish physical properties but not so unprecedented as the large sizes which result from redshift distances.Finally the interaction of specific high redshift ScI's with nearby galaxies is presented as an independent proof that ScI's are generally small, low luminosity galaxies. This result furnishes insight into the long standing puzzle of how apparently distant ScI's can interact with nearby galaxies such as in Stephan's Quintet, Seyfert's Sextet and NGC 4151/4156.     

Luminosity-HI velocity width relation for spirals

Multicolour and multiaperture photometry of 22 late-type Virgo cluster galaxies in a newV (5500 Å),r (6738 Å),IV (10500 Å) system confirm the previously known correlations between the luminosity and H₁ velocity width, and show them to be strongly wavelength dependent with the slope of the relation reaching a maximum value of ～ ? 10 at 10500 Å and remaining constant at longer wavelengths. The scatter in the luminosity-H₁ width relation is nearly the same, whether we use (V)^c _?0.5, (r)^c _?0.5, (IV)^c _-0.5, or (H)^c _-0.5 magnitudes. The error in the determination of the corrected magnitudes is much less than the scatter in the luminosity-H₁ width relations as evidenced by the fact that the residuals of individual galaxies inV, r, IV, andH are correlated with one another. An attempt to use a ‘kinematic magnitude’ instead of an isophotal magnitude shows the slope of the luminosity-H₁ width relations to be reduced substantially. Observations in theV, r, andIV system for fifteen field galaxies and three galaxies in the Cancer and Zw 74-23 clusters have been obtained and combined with the H₁ velocity width to derive their differences in distance modulus, between the galaxy and the Virgo cluster, through the luminosity-H₁ width relations of the Virgo cluster galaxies. The three independent differences in the distance modulus of each galaxy agree with one another indicating that the relations usingV, r andIV magnitudes have the same zero point in absolute magnitude, independent of the wavelength of observations. The distance modulus difference from the Virgo cluster to the three galaxies U 4334, U 8942 and U 8944, which are outside the Local Supercluster, are +1·50, +3·45 and +2·81 mag respectively and are in agreement with those of +1·75, +3·23 and +2·46 mag derived for the same galaxies by Aaronsonet al. (1980) throughH magnitudes. The scatter in the velocity distance relation of the field galaxies compares well with the mean error derived in the luminosity-H_I width relations and hence is intrinsic.     

Cluster-scale magnetic fields

The search for non thermal radio emission from clusters of galaxies is a powerful tool to investigate the existence of magnetic fields on such large scale. Unfortunately, such observations are scarce thus far, mainly because of the very faint large scale radio emission expected in clusters of galaxies. In the present contribution we will first review the status of the radio observations of clusters of galaxies, carried out with the aim of detecting large scale radio emission.We will then focus on the large scale radio emission detected at 327 MHz and 610 MHz in the Coma cluster of galaxies. The features of the detected radio emission suggest that a magnetic field with an intensity of the order of ~ 10^–7 Gauss must be present on a scale of about 2 Mpc (forH _o = 100km s ^–1 Mpc ^–1). The morphology of the radio emission is similar to that of the most recent X-ray images derived with ROSAT, and follows the distribution of the galaxies in the cluster. All these pieces of information will be taken into account in the discussion on the possible origin of this large scale magnetic field.     

The peaks and gaps in the redshift distributions of active galactic nuclei and quasars

The distributionsf(z) of the redshifts for active galaxies (Seyfert galaxies, radio galaxies, and quasars) have been studied. Some statistically-significant maxima and minima are observed in the distributionsf(z) for these objects. The significance of peaks and gaps increases for the brighter objects, for which the samples are more complete. The clustering of the Seyfert galaxies is significantly different from that of the nearby normal galaxies. The distributionf(z) for the radio galaxies is similar to the analogous distribution for the galaxy clusters. Three of the five peaks in the distributionf(z) for the radio quasars may be caused by the selection effects. Two peaks within the intervalsz (0.5, 0.7) and (1.0, 1.1) are probably real. The corresponding scales of the QSO clustering along the line-of-sight are about 100h ^–1 Mpc (h is the Hubble constant in the units of 75 km s^–1 Mpc^–1). The possibility of some global quasi-periodical cycles for the processes of activity is discussed. The period of a cycle for the Seyfert and radio galaxies is about 1×10⁸ years that corresponds to the distances of about 30h ^–1 Mpc between the shells.     

Nearby galaxies. IV. The global Hubble parameter and the dispersion of the Hubble relation

Using a spherically symmetric model of the Virgo flow the global Hubble parameter has been estimated from the observed radial velocities and the photometrically measured distances of nearby galaxies. Adopting the observed recession velocity of the Virgo Cluster to about 1000 km s⁻¹ and the infall velocity of the Local Group to 350 km s⁻¹ the global Hubble constant results to 73 ± 10 km s⁻¹ Mpc⁻¹. This value corresponds with the distance of the Virgo Cluster of 18 ± 2 Mpc. The cosmic dispersion of the galaxies around the Hubble relation is of order of 35 km s⁻¹.     

Blueshifted galaxies in the virgo cluster

We examine a sample of 65 galaxies in the Virgo cluster with negative radial velocities relative to the Local Group. Some features of this sample are pointed out. All of these objects are positioned compactly within a virial zone of radius 6o in the cluster, but their centroid is displaced relative to the dynamic center of the cluster, M87, by 1o.1 to the northwest. The dwarf galaxies in this sample are clumped on a scale of ∼10' (50 kpc). The observed asymmetry in the distribution of the blueshifted galaxies may be caused by infall of a group of galaxies around M86 onto the main body of the cluster. We offer another attempt to explain this phenomenon, assuming a mutual tangential velocity of ∼300 km/s^-1 between the Local Group and the Virgo cluster owing to their being repelled from the local cosmological void.     

Structures in the large-scale distribution of galaxies with different luminosities

The large-scale structures of volume-limites subsample sorted out from the CfA catalog have been analysed by percolation method. The result shows that the features in the distribution of galaxies with different luminosities are significantly different. Especially, the most luminous galaxies are likely to exhibit hierarchical clustering on a scale about 50h ₅₀ ^–1 Mpc, and the least luminous galaxies in our subsamples show string-like or sheet-like character in their distribution. These results suggest that the large-scale distribution of galaxies consists of clusters or cluster cores of most luminous galaxies and the less luminous galaxies spread out from these cores with a string-like or sheet-like structure. This picture of the large-scale distribution consists with previous results from two-point correlation analysis and fractal analysis. The implication of these results has been discussed.     

Local Field of Galaxy Velocities

A sample of 145 galaxies having radial velocities relative to the centroid of the Local Group V _LG < 500 km/sec and estimated photometric distances D < 8 Mpc is considered. The field of peculiar velocities of these galaxies is estimated using the tensor of the local value of the Hubble constant H _ij , with principal values of 81:62:48 in km/sec·Mpc, which have a standard error of 4 km/sec·Mpc. The minor axis of the Hubble ellipsoid is oriented almost along the polar axis of the Local Supercluster, while the major axis forms an angle = (29 ± 5)° with the direction toward the center of the Virgo Cluster. Such a configuration of the peculiar-velocity field shows unsatisfactory agreement with the model of a spherically symmetric flow of galaxies toward the Virgo Cluster. Rotation of the Local Supercluster may be one reason for this difference. The peculiar velocities of galaxies within a volume with D < 8 Mpc are characterized by a dispersion _V = 74 km/sec, a considerable part of which is due to the virial motions of galaxies in groups and to distance errors. For field galaxies, located in a layer of 1 < D < 3 Mpc around the Local Group, the radial-velocity dispersion does not exceed 25 km/sec. The velocity—distance relation, constructed from the 20 closest galaxies around the Local Group with D < 3 Mpc and with errors (D) < 0.2 Mpc, exhibits the expected effect of gravitational deceleration. Using the estimate of R ₀ = (0.96 ± 0.05) Mpc for the observed radius of the zero-velocity sphere, we determined the total mass of the Local Group to be (1.2 ± 0.2)·10¹² M , which agrees well with the sum of the virial masses of the subgroups of galaxies around the Local Group and M31. The ratio of the Local Group's total mass (within R ₀) to its luminosity is M/L = (23 ± 4) M /L , which does not require the existence of supermassive dark halos around our Galaxy and M31.     

Galaxy populations in the Fornax and Virgo clusters

In these first results from a photographic survey of nearby clusters and groups of galaxies, we compare the luminosity functions of galaxies of various Hubble types in the core of the Formax cluster to luminosity functions in the core of the Virgo cluster from Sandageet al. (1985). The galaxy classifications for the two clusters are based on identical plate material, and are hence directly comparable. The properties (galaxy density, velocity dispersion, X-ray luminosity) of the two clusters are quite different, yet we find few significant differences in the luminosity functions, or in the morphological mix of galaxies between the two clusters. In particular, while there is some indication that the ratios of giants to dwarfs and early to late-type galaxies in the two clusters differ, we cannot exclude the possibility that the ratios are identical. We discuss the selection limits of our survey and the completeness corrections that must be applied to the faint end of the luminosity function. The effective surface brightness of early-type galaxies in our sample decreases with decreasing luminosity. We show that this correlation is not an artifact of our selection criteria for dwarf spheroidal galaxies and use it to determine the relative distances to the Fornax and Virgo clusters. We also present evidence for a radial variation in the luminosity function of dwarf ellipticals within the two clusters in the sense that the faint end of the luminosity distribution is enhanced at the centre of each cluster.     

HI imaging the low red-shift cosmic web

Only in recent years has the realization emerged that galaxies do not dominate the universal baryon budget but are merely the brightest pearls of an underlying cosmic web. Although the gas in these inter-galactic filaments is moderately to highly ionized, QSO absorption lines have shown that the surface area increases dramatically in going down to lower HI column densities. The first image of the cosmic web in HI emission has just been made of the Local Group filament connecting M31 and M33. The corresponding HI distribution function is in very good agreement with that of the QSO absorption lines, confirming the 30-fold increase in surface area expected between 10¹⁹ and 10¹⁷ cm⁻². The critical observational challenge is crossing the “HI desert”, the range of log(N_HI) from about 19.5 down to 18, over which photo-ionization by the intergalactic radiation field produces an exponential decline in the neutral fraction from essentially unity down to a few percent. Nature is kinder again to the HI observer below log(N_HI) = 18, where the neutral fraction decreases only very slowly with log(N_HI). With the SKA, we can begin the systematic study of the cosmic web beyond the Local Group. With moderate integration times, the necessary resolution and sensitivity can be achieved out to distances beyond the Virgo cluster. When combined with targeted optical and UV absorption line observations, the total baryonic masses and enrichment histories of the cosmic web will be determined over the complete range of environmental over-densities.     

Upper limits to the rotation measure and magnetism of the Great Attractor supercluster

A substantial concentration of galaxies towardl ⁱⁱ =320°,b ⁱⁱ =+7°, with a mean radial velocity of 4000 km s^–1, has earlier been nicknamed the Great Attractor — it is a nearby supercluster of galaxies. Here, an attempt is made to detect an excess Faraday rotation measure that could be attributed to the magnetic field and thermal gas in the space between the galaxies inside the Great Attractor supercluster. Only an upper limit to the rotation measure, of at most 8 rad m^–2, could be placed on the Great Attractor supercluster, implying in turn an upper limit on the supercluster magnetic field, of at most 0.1 microgauss (ordered component only).     

Quantized redshifts: A status report

The current status of a continuing programme of tests for redshift periodicity or ‘quantization’ of nearby bright galaxies is described. So far the redshifts of over 250 galaxies with high-precision HI profiles have been used in the study. In consistently selected sub-samples of the datasets of sufficient precision examined so far, the redshift distribution has been found to be strongly quantized in the galactocentric frame of reference. The phenomenon is easily seen by eye and apparently cannot be ascribed to statistical artefacts, selection procedures or flawed reduction techniques. Two galactocentric periodicities have so far been detected, ∼ 71 .5km s^-1 in the Virgo cluster, and ∼37. 5km s^-1 for all other spiral galaxies within ∼ 2600km s^-1. The formal confidence levels associated with these results are extremely high.     

A hypothesis to explain the virial discrepancy in clusters of galaxies

On the basis of numerical experiments onn-body binding energies we tentatively consider the following hypothesis: If the distance between two galaxies forming a binary system isa _g, and a cluster of galaxies that is substructured in a hierarchical fashion onall scales froma _g upwards has a total massM, then the total gravitational binding energy of the cluster is _TH = –GM ²/2a _g . As an explanation for missing masses up to order 100 we test this hypothesis in three different ways, finding remarkable agreement with observation, with no need for physical missing mass.     

On the relation between radius,luminosity, surface brightness,and surface density in elliptical galaxies

We have analyzed luminosity profiles of E galaxies studied by Strom and Strom in six clusters of galaxies. We have found a relationship between radius, luminosity, and surface brightness for galaxies in each of the clusters. A dependence of the zero point of the relation with the local projected density of galaxies is likewise found:r _{e proj} ^–0.14 L ^0.445 I _e ^–0.413 . This relationship implies (i) that there is not a universal luminosity profile for elliptical galaxies, (ii) the environmental variation of radius is larger than that produced by mergers of galaxies, (iii) distance to a galaxy can be estimated from apparent magnitude, surface brightness, angular size, and apparent local projected density of galaxies.     

Photographicuvby photometry of the open cluster M52

Photographicuvby photometry of 15 stars in the open cluster M52 (NGC 7654) has been obtained. The distance modulusV _o–M _v=11.3±0.1 and mean cluster reddeningE(B–V)=0.57 are determined. Some basic physical characteristics of 30 stars with observeduvby values are obtained as well as a numerical estimation of the open cluster age 9.6×10⁷ yr is made.     

Barred spirals and dwarf galaxies in the virgo cluster

Using the extensive catalog of Binggelli, Sandage, and Tammann it is shown that dwarf galaxies in the Virgo cluster are more tightly connected with barred rather than with normal spirals. The number of dwarfs is higher, the greater the number of barreds in the given field. There is no preferential direction in the distribution of dwarfs around barred galaxies.Published in Astrofizika, Vol. 38, No. 4, pp. 630–635, October–December, 1995.     

An estimation of the oblateness of Sun from the motion of Icarus

From astrometric observations of minor planet (1566) Icarus from 1949 to 1987 were made solutions for improved orbital elements of Icarus and the quadrupole moment of the Sun. The formal result was J₂ = -0.6±5.8 &d 10^–6. From this we can conclude that J ₂ is very probably less than 2 · 10^–-5.