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Scalar potential model of redshift and discrete redshift
On the galactic scale the universe is inhomogeneous and redshift z isoccasionally less than zero. A scalar potential model (SPM) that linksthe galaxy scale z to the cosmological scale z of the Hubble Law ispostulated. Several differences among galaxy types suggest that spiralgalaxies are Sources and that early type, lenticular, and irregulargalaxies are Sinks of a scalar potential field. The morphology-radiusand the intragalactic medium cluster observations support the movementof matter from Source galaxies to Sink galaxies. A cell structure ofgalaxy groups and clusters is proposed to resolve a paradox concerningthe scalar potential like the Olber’s paradox concerning light.For the sample galaxies, the ratio of the luminosity of Source galaxiesto the luminosity of Sink galaxies approaches 2.7 ± 0.1. Anequation is derived from sample data, which is anisotropic andinhomogeneous, relating z of and the distance D to galaxies. Thecalculated z has a correlation coefficient of 0.88 with the measured zfor a sample of 32 spiral galaxies with D calculated using Cepheidvariable stars. The equation is consistent with z < 0 observations ofclose galaxies. At low cosmological distances, the equation reduces to z≈ exp(KD)‑1 ≈ KD, where K is a constant, positive value. Theequation predicts z from galaxies over 18 Gpc distant approaches aconstant value on the order of 500. The SPM of z provides a physicalbasis for the z of particle photons. Further, the SPM qualitativelysuggests the discrete variations in z, which was reported by Tifft[Tifft, W.G., 1997. Astrophy. J. 485, 465] and confirmed by others, areconsistent with the SPM.

Cepheid Distances to SNe Ia Host Galaxies Based on a Revised Photometric Zero Point of the HST WFPC2 and New PL Relations and Metallicity Corrections
With this paper we continue the preparation for a forthcoming summaryreport of our experiment with the HST to determine the Hubble constantusing Type Ia supernovae as standard candles. Two problems areaddressed. (1) We examine the need for, and determine the value of, thecorrections to the apparent magnitudes of our program Cepheids in the 11previous calibration papers due to sensitivity drifts and chargetransfer effects of the HST WFPC2 camera over the life time of theexperiment from 1992 to 2001. (2) The corrected apparent magnitudes areapplied to all our previous photometric data from which revised distancemoduli are calculated for the eight program galaxies that are parents tothe calibrator Ia supernovae. Two different Cepheid P-L relations areused; one for the Galaxy and one for the LMC. These differ both in slopeand zero point at a fixed period. The procedures for determining theabsorption and reddening corrections for each Cepheid are discussed.Corrections for the effects of metallicity differences between theprogram galaxies and the two adopted P-L relations are derived andapplied. The distance moduli derived here for the eight supernovaeprogram galaxies, and for 29 others, average 0.20 mag fainter (moredistant) than those derived by Gibson et al. and Freedman et al. intheir 2000 and 2001 summary papers for reasons discussed in this paper.The effect on the Hubble constant is the subject of our forthcomingsummary paper.

First Results from SAPAC: Toward a Three-dimensional Picture of the Fornax Cluster Core
A sophisticated surface brightness fluctuation (SBF) analysis packagehas been developed, designed to measure distances of early-type galaxiesby means of SBFs of unresolved stars. This suite of programs, calledSAPAC, is made readily available to the astronomical community forextensive testing, with the long-term goal of providing the necessarytools for systematic distance surveys of early-type galaxies usingmodern optical/near-IR telescopes equipped with wide-field cameras. Wediscuss the technical and scientific concepts of SAPAC and demonstrateits capabilities by analyzing deep B- and R-band CCD images of 10 dwarfelliptical galaxy candidates in the Fornax Cluster obtained with FORS1at the Very Large Telescope. All candidates are confirmed as clustermembers. We then turn our attention to the innermost region of theFornax Cluster. A total of 29 early-type galaxies closer than threecluster core radii (2deg) to the central galaxy NGC 1399 haveradial velocities and SBF distances. Their Hubble diagram exhibits apronounced S-shaped infall pattern, suggesting that Fornax is still inthe process of formation during the present epoch through a generalcollapse and possible accretion of distinct groups of galaxies. Fromfitting a model we estimate the cluster mass within 720 kpc projecteddistance of NGC 1399 to be 2.3+/-0.3×1014Msolar. The associated collapse time istcoll=2.9+1.6-0.9 Gyr. After cleansing our galaxy sample of afew kinematical outliers, the true distance of the Fornax Cluster coreis determined at 20.13+/-0.40 Mpc [(m-M)0=31.51+/-0.04 mag].Applying a bootstrap resampling technique on the distance distributionwith individual distance errors taken into account further reveals asmall intrinsic cluster depth of σint=0.74+0.52-0.74Mpc, in best agreement with the cluster's linear extension in the sky:σR.A.=σdecl.~0.5 Mpc. We conclude thatthe early-type galaxy population in the Fornax Cluster must be spatiallywell constrained, with no evidence of elongation along the line ofsight, in contrast to the Virgo Cluster. Moreover, we find marginalevidence for substructure, a result that is consistent with the youngevolutionary state of the cluster and the overall galaxy infall.Combining the kinematically defined cluster distance with the meancosmological velocity for the central cluster galaxy sample yields aHubble constant of H0=63+/-5 km s-1Mpc-1.Based on observations collected at the ESO Very Large Telescope, underprogram ESO 68.A-0176.

The extragalactic Cepheid bias: a new test using the period-luminosity-color relation
We use the Period-Luminosity-Color relation (PLC) for Cepheids to testfor the existence of a bias in extragalactic distances derived from theclassical Period-Luminosity (PL) relation. We calculate the parametersof the PLC using several galaxies observed with the Hubble SpaceTelescope and show that this calculation must be conducted with a PLCwritten in a form where the parameters are independent. The coefficientsthus obtained are similar to those derived from theoretical models.Calibrating with a few unbiased galaxies, we apply this PLC to allgalaxies of the Hubble Space Telescope Key Program (HSTKP) and comparethe distance moduli with those published by the HSTKP team. The newdistance moduli are larger (more exactly, the larger the distance thelarger the difference), consistent with a bias. Further, the bias trendthat is observed is the same previously obtained from two independentmethods based either on the local Hubble law or on a theoretical modelof the bias. The results are quite stable but when we force the PLCrelation closer to the classical PL relation by using unrealisticparameters, the agreement with HSTKP distance moduli is retrieved. Thisalso suggests that the PL relation leads to biased distance moduli. Thenew distance moduli reduce the scatter in the calibration of theabsolute magnitude of supernovae SNIa at their maximum. This may alsosuggest that the relation between the amplitude at maximum and the decayof the light curve Δ m15 may not be as strong asbelieved.

The extragalactic Cepheid bias: significant influence on the cosmic distance scale
The unique measurements with the Hubble Space Telescope of Cepheidvariable stars in nearby galaxies led to extragalactic distances thatmade the HST Key Project conclude that the Hubble constant isH0 = 72 km s-1 Mpc-1. The idea thatH0 is now known is widely spread among the astronomicalcommunity. Some time ago, we suggested that a strong selection effectmay still exist in the Cepheid method, resulting in too short distances.Using a model similar to traditional bias corrections, we deduce herenew estimates of distances from HST and previous ground-basedobservations which are both affected by this effect, showing the sametrend which starts at different distances. The recent measurement of M83 with the VLT is unbiased. Revisiting the calibration of HSTKP's withour new scale, makes long-range distance criteria more concordant andreduces the value of H0 to ≈60 km s-1Mpc-1. Locally, the corrected Cepheid distances giveHlocal=56 km s-1 Mpc-1 and reduce thevelocity dispersion in the Hubble flow. These numbers are indicative ofthe influence of the suggested Cepheid bias in the context of the HSTKPstudies and are not final values.

Dwarf and Normal Spiral Galaxies: are they Self-Similar?
The investigation presented here was focused on clarifying the existenceof dwarf spiral galaxies as a separate group from classical spirals.First, a list of spiral galaxies with small sizes was obtained.Information on colors, luminosities, morphologies and chemical contentwas searched for in the literature for these galaxies. Using thisinformation, it can be concluded that dwarf spirals are not likely to bethe tail of the distribution of classical galaxies. On the contrary,significant differences in some of the most important properties ofspiral galaxies, such as the metallicity gradient and the bar frecuency,were found. In any case, further and more accurate observations areneeded for a definitive answer.

The dispersion in the Cepheid period-luminosity relation and the consequences for the extragalactic distance scale
Using published Hubble Space Telescope (HST) Cepheid data from 25galaxies, we have found a correlation between the dispersion in theCepheid period-luminosity (P-L) relation and host galaxy metallicity,which is significant at the ~3σ level in the V band. In the I bandthe correlation is less significant, although the tighter intrinsicdispersion of the P-L relation in I may make it harder to detect such acorrelation in the HST sample. One possibility is that low metallicitygalaxies have smaller metallicity gradients than high metallicitygalaxies; if the Cepheid P-L relation has a significant dependence onmetallicity then this might explain the higher P-L dispersion in thehigher metallicity galaxies. A second possibility is that the increasedP-L dispersion is driven by metallicity dispersion but now due to arelation between metallicity and Cepheid colour rather than luminosity.A third possibility is that the increased P-L dispersion is caused by anincrease in the width of the instability strip with metallicity.Whatever the explanation, the high observed dispersions in the HSTCepheid P-L relations have the important consequence that the bias dueto incompleteness in the P-L relation at faint magnitudes is moresignificant than previously thought. Using a maximum likelihoodtechnique which takes into account the effect on the P-L relations oftruncation by consistently defined magnitude completeness limits, werederive the Cepheid distances to the 25 galaxies. In the case of thegalaxies with the highest P-L dispersion at the largest distances, wefind that the published distance modulus underestimates the truedistance modulus by up to ~0.5 mag.When both metallicity and magnitude incompleteness corrections are made,a scale error in the published Cepheid distances is seen in the sensethat the published distance moduli are increasingly underestimated atlarger distances. This results in the average distance modulus to thefour galaxies in the Virgo cluster core increasing from(m-M)0= 31.2 +/- 0.19 to (m-M)0= 31.4 +/- 0.19 ifthe γVI=-0.24 mag dex-1 metallicitycorrection of Kennicutt et al. is assumed. For the 18 HST galaxies withgood Tully-Fisher (TF) distances and (m-M)0 > 29.5 theCepheid-TF distance modulus average residual increases from 0.44 +/-0.09 to 0.63 +/- 0.1 mag with γVI=-0.24. This indicatesa significant scale error in TF distances, which reduces the previousPierce & Tully TF estimate of H0= 85 +/- 10 kms-1 Mpc-1 to H0= 63 +/- 7 kms-1 Mpc-1, assuming γVI=-0.24 anda still uncertain Virgo infall model. Finally, for the eight HSTgalaxies with Type Ia supernovae (SNIa), the metallicity andincompleteness corrected Cepheid distances marginally suggest there maybe a metallicity dependence of SNIa peak luminosity in the sense thatmetal-poor hosts have lower luminosity SNIa. Thus, SNIa Hubble diagramestimates of both H0 and q0 may therefore alsorequire significant corrections for metallicity, once the exact sizes ofthe Cepheid metallicity corrections become better established.

Classical Cepheids and the Distances of HST Program Galaxies
The distances of HST program galaxies are revised using the PL-relationswe have obtained previously along with a different method from thatemployed by Freedman et al. On the average, the resulting distances tothese galaxies have higher internal accuracies than those obtainedbefore by others. In addition, we have used no corrections formetallicity or for the incompleteness of the samples of classicalcepheids in deriving these distances. Despite this, our distance moduli,with a dispersion of ±0m.395, agree with those of Freedman et al.This indicates that these two effects have little or even no effect forthe samples of classical cepheids in the HST program galaxies.

Reconstructing a Cepheid Light Curve with Fourier Techniques. I. The Fourier Expansion and Interrelations
Fourier decomposition is a well-established technique used in the studyof stellar pulsation. However, the quality of reconstructed light curvesusing this method is reduced when the observed data have uneven phasecoverage. We use simulated annealing techniques together with Fourierdecomposition to improve the quality of the Fourier decomposition formany Optical Gravitational Lensing Experiment LMC fundamental-modeCepheids. This method restricts the range that Fourier amplitudes cantake. The ranges are specified by well-sampled Cepheids in the Galaxyand Magellanic Clouds. We also apply this method to reconstructingCepheid light curves observed by the Hubble Space Telescope (HST). Thesetypically consist of 12 V-band and four I-band points. We employ adirect Fourier fit to the 12 V-band points using the simulated annealingmethod mentioned above and explicitly derive and use Fourierinterrelations to reconstruct the I-band light curve. We discussadvantages and drawbacks of this method when applied to HST Cepheid dataover existing template methods. Application of this method toreconstruct the light curves of Cepheids observed in NGC 4258 shows thatthe derived Cepheid distance (μ0=29.38+/-0.06 mag, randomerror) is consistent with its geometrical distance(μ0=29.28+/-0.09 mag) derived from observations of itswater maser.

Companions of Bright Barred Shapley-Ames Galaxies
Companion galaxy environment for a subset of 78 bright and nearby barredgalaxies from the Shapley-Ames Catalog is presented. Among the spiralbarred galaxies, there are Seyfert galaxies, galaxies with circumnuclearstructures, galaxies not associated with any large-scale galaxy cloudstructure, galaxies with peculiar disk morphology (crooked arms), andgalaxies with normal disk morphology; the list includes all Hubbletypes. The companion galaxy list includes the number of companiongalaxies within 20 diameters, their Hubble type, and projectedseparation distance. In addition, the companion environment was searchedfor four known active spiral galaxies, three of them are Seyfertgalaxies, namely, NGC 1068, NGC 1097, and NGC 5548, and one is astarburst galaxy, M82. Among the results obtained, it is noted that theonly spiral barred galaxy classified as Seyfert 1 in our list has nocompanions within a projected distance of 20 diameters; six out of 10Seyfert 2 bar galaxies have no companions within 10 diameters, six outof 10 Seyfert 2 galaxies have one or more companions at projectedseparation distances between 10 and 20 diameters; six out of 12 galaxieswith circumnuclear structures have two or more companions within 20diameters.

The extra-galactic Cepheid distance scale from LMC and Galactic period-luminosity relations
In this paper, we recalibrate the Cepheid distance to some nearbygalaxies observed by the HST Key Project and the Sandage-Tammann-Sahagroup. We use much of the Key Project methodology in our analysis butapply new techniques, based on Fourier methods to estimate the mean of asparsely sampled Cepheid light curve, to published extra-galacticCepheid data. We also apply different calibrating PL relations toestimate Cepheid distances, and investigate the sensitivity of thedistance moduli to the adopted calibrating PL relation. We re-determinethe OGLE LMC PL relations using a more conservative approach and alsostudy the effect of using Galactic PL relations on the distance scale.For the Key Project galaxies after accounting for charge transfereffects, we find good agreement with an average discrepancy of -0.002and 0.075 mag when using the LMC and Galaxy, respectively, as acalibrating PL relation. For NGC 4258 which has a geometric distance of29.28 mag, we find a distance modulus of 29.44+/-0.06(random) mag, aftercorrecting for metallicity. In addition we have calculated the Cepheiddistance to 8 galaxies observed by the Sandage-Tammann-Saha group andfind shorter distance moduli by -0.178 mag (mainly due to the use ofdifferent LMC PL relations) and -0.108 mag on average again when usingthe LMC and Galaxy, respectively, as a calibrating PL relation. Howevercare must be taken to extrapolate these changed distances to changes inthe resulting values of the Hubble constant because STS also usedistances to NGC 3368 and 4414 and because STS calibration of SN Ia isoften decoupled from the distance to the host galaxy through their useof differential extinction arguments. We also calculate the distance toall these galaxies using PL relations at maximum light and find verygood agreement with mean light PL distances.However, after correcting for metallicity effects, the differencebetween the distance moduli obtained using the two sets of calibratingPL relations becomes negligible. This suggests that Cepheids in the LMCand Galaxy do follow different PL relations and constrains the sign forthe coefficient of the metallicity correction, gamma , to be negative,at least at the median period log (P) ~ 1.4, of the target galaxies.Full Table 1 is available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/411/361

Surface brightness fluctuation distances for dwarf elliptical galaxies in the Fornax cluster
We have obtained deep B and R-band CCD images of eight dwarf elliptical(dE) galaxies in the Fornax cluster using the FORS1 instrument at theVLT in service mode under excellent atmospheric conditions. A total of92 fields distributed over the central regions of the galaxies have beenanalysed to measure local (B-R)0 colours and R-band surfacebrightness fluctuation (SBF) magnitudes /line{m}R. Within agalaxy the observed correlation of (B-R)0 with/line{m}R0 follows closely the predicted slope ofthe colour-fluctuation luminosity relation for composite single-burst,mainly old, metal-poor stellar populations. This allows to determine thedistances of the dEs from simple offset measurements to a typically 9%accuracy. The distance distribution of these genuine cluster dwarfscenters at a mean distance of (m-M)0=31.54+/-0.07 mag, or20.3 +/- 0.7 Mpc, a value that is in best agreement with previous SBFwork on Fornax early-type giants and thus represents a robust estimateof the distance to the Fornax cluster core. The application of thebootstrap resampling technique on the distance data further reveals acluster depth of sigmaint = 1.4{+0.5 atop -0.8} Mpc. We takethis preliminary result as a confirmation of the compact appearance ofFornax in the projection on the sky although the cluster might beslightly more elongated along the line of sight. Combining the newlyderived cluster distance with the cosmological velocity of Fornax of1324+/-41 km s-1 gives a Hubble constant of H0 =65 +/- 4 km s-1 Mpc-1. This value is consistent atthe 95% confidence level with both the most recent result from the teamthat favours a long distance scale and the final value adopted by theHST ``Key Project'' team in their work for the Hubble constant. Finally,we explore the possibility to determine rough metallicities of ourcluster dEs from their (B-R)0 colours via Worthey's stellarpopulation synthesis models. The median metallicities are found in therange from -1.5 to -1 with a concentration around [Fe/H] =-1. Acomparison with spectral line indices results available for threegalaxies shows good agreement. Moreover, the derived metallicities placethe bright Fornax dEs on the extension of the metallicity-luminosityrelation defined by the low luminous Local Group dEs which providesadditional support for the (B-R)0 colour as a usefulmetallicity estimator. The data further suggest an age range between 10and 12 Gyr for the Fornax dwarfs.Based on observations collected at the European Southern Observatory(ESO 68.A-0176).

The large-scale distribution of neutral hydrogen in the Fornax region
Using data from the HI Parkes All Sky Survey (HIPASS), we have searchedfor neutral hydrogen in galaxies in a region ~25 × 25deg2 centred on NGC 1399, the nominal centre of the Fornaxcluster. Within a velocity search range of 300-3700 km s-1and to a 3σ lower flux limit of ~40 mJy, 110 galaxies with HIemission were detected, one of which is previously uncatalogued. None ofthe detections has early-type morphology. Previously unknown velocitiesfor 14 galaxies have been determined, with a further four velocitymeasurements being significantly dissimilar to published values.Identification of an optical counterpart is relatively unambiguous formore than ~90 per cent of our HI galaxies. The galaxies appear to beembedded in a sheet at the cluster velocity which extends for more than30° across the search area. At the nominal cluster distance of ~20Mpc, this corresponds to an elongated structure more than 10 Mpc inextent. A velocity gradient across the structure is detected, withradial velocities increasing by ~500 km s-1 from south-eastto north-west. The clustering of galaxies evident in optical surveys isonly weakly suggested in the spatial distribution of our HI detections.Of 62 HI detections within a 10° projected radius of the clustercentre, only two are within the core region (projected radius<1°) and less than 30 per cent are within 3.5°, suggesting aconsiderable deficit of HI-rich galaxies in the centre of the cluster.However, relative to the field, there is a 3(+/-1)-fold excess ofHI-rich galaxies in the outer parts of the cluster where galaxies may beinfalling towards the cluster for the first time.

Surface Brightness Fluctuations of Fornax Cluster Galaxies: Calibration of Infrared Surface Brightness Fluctuations and Evidence for Recent Star Formation
We have measured KS-band (2.0-2.3 μm) surface brightnessfluctuations (SBFs) of 19 early-type galaxies in the Fornax Cluster.Fornax is ideally suited both for calibrating SBFs as distanceindicators and for using SBFs to probe the unresolved stellar content ofearly-type galaxies. Combining our results with published data for othernearby clusters, we calibrate KS-band SBFs using Hubble SpaceTelescope (HST) Cepheid cluster distances and I-band SBF distances toindividual galaxies. With the latter, the resulting calibrationisMKS=(-5.84+/-0.04)+(3.6+/-0.8)[(V-Ic)0-1.15],valid for1.05<(V-Ic)0<1.25 and not including anysystematic errors in the HST Cepheid distance scale. The fit accountsfor the covariance between V-Ic and MKSwhen calibrated in this fashion. The intrinsic cosmic scatter ofMKS appears to be larger than that of I-band SBFs.S0 galaxies may follow a different relation, although the data areinconclusive. The discovery of correlation between KS-bandfluctuation magnitudes and colors with V-Ic is a new clueinto the star formation histories of early-type galaxies. This relationnaturally accounts for galaxies previously claimed to have anomalouslybright K-band SBFs, namely, M32 and NGC 4489. Models indicate that thestellar populations dominating the SBF signal have a significant rangein age; some scatter in metallicity may also be present. The youngestages imply some galaxies have very luminous giant branches, akin tothose in intermediate-age (few Gyr) Magellanic Cloud clusters. Theinferred metallicities are roughly solar, although this depends on thechoice of theoretical models. A few Fornax galaxies have unusuallybright KS-band SBFs, perhaps originating from ahigh-metallicity burst of star formation in the last few Gyr. Theincreased spread and brightening of the KS-band SBFs withbluer V-Ic suggest that the lower mass cluster galaxies(<~0.1L*) may have had more extended and more heterogeneous starformation histories than those of the more massive galaxies.

Calibration of the distance scale from galactic Cepheids. II. Use of the HIPPARCOS calibration
New estimates of the distances of 36 nearby galaxies is presented. Theseare based on the calibration of the V- and I-band Period-Luminosityrelations for galactic Cepheids measured by the HIPPARCOS mission. Thedistance moduli are obtained in a classical way. The statistical biasdue to the incompleteness of the sample is corrected according to theprecepts introduced by Teerikorpi (\cite{Tee87}). We adopt a constantslope (the one obtained with LMC Cepheids). The correction forincompleteness bias introduces an uncertainty that depends on eachgalaxy. On average, this uncertainty is small (0.04 mag) but it mayreach 0.3 mag. We show that the uncertainty due to the correction of theextinction is small (propably less than 0.05 mag). The correlationbetween the metallicity and the morphological type of the host galaxysuggests that we should reduce the application to spiral galaxies inorder to bypass the problem of metallicity. We suspect that the adoptedPL slopes are not valid for all morphological types of galaxies. Thismay induce a mean systematic shift of 0.1 mag on distance moduli. Acomparison with the distance moduli recently published by Freedman etal. (\cite{Fre01}) shows there is a reasonably good agreement with ourdistance moduli. The compilation of raw data is only available inelectronic form at CDS via anonymous ftp to\ cdsarc.u-strasbg.fr( or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/389/19 and on ouranonymous ftp-server www-obs.univ-lyon1.fr (pub/base/CEPHEIDES.tar.gz).

Final Results from the Hubble Space Telescope Key Project to Measure the Hubble Constant
We present here the final results of the Hubble Space Telescope (HST)Key Project to measure the Hubble constant. We summarize our method, theresults, and the uncertainties, tabulate our revised distances, and givethe implications of these results for cosmology. Our results are basedon a Cepheid calibration of several secondary distance methods appliedover the range of about 60-400 Mpc. The analysis presented here benefitsfrom a number of recent improvements and refinements, including (1) alarger LMC Cepheid sample to define the fiducial period-luminosity (PL)relations, (2) a more recent HST Wide Field and Planetary Camera 2(WFPC2) photometric calibration, (3) a correction for Cepheidmetallicity, and (4) a correction for incompleteness bias in theobserved Cepheid PL samples. We adopt a distance modulus to the LMC(relative to which the more distant galaxies are measured) ofμ0(LMC)=18.50+/-0.10 mag, or 50 kpc. New, reviseddistances are given for the 18 spiral galaxies for which Cepheids havebeen discovered as part of the Key Project, as well as for 13 additionalgalaxies with published Cepheid data. The new calibration results in aCepheid distance to NGC 4258 in better agreement with the maser distanceto this galaxy. Based on these revised Cepheid distances, we find values(in km s-1 Mpc-1) of H0=71+/-2(random)+/-6 (systematic) (Type Ia supernovae), H0=71+/-3+/-7(Tully-Fisher relation), H0=70+/-5+/-6 (surface brightnessfluctuations), H0=72+/-9+/-7 (Type II supernovae), andH0=82+/-6+/-9 (fundamental plane). We combine these resultsfor the different methods with three different weighting schemes, andfind good agreement and consistency with H0=72+/-8 kms-1 Mpc-1. Finally, we compare these results withother, global methods for measuring H0. Based on observationswith the NASA/ESA Hubble Space Telescope, obtained at the SpaceTelescope Science Institute, which is operated by AURA, Inc., under NASAcontract NAS5-26555.

Substructure and Dynamics of the Fornax Cluster
We present the first dynamical analysis of a galaxy cluster to include alarge fraction of dwarf galaxies. Our sample of 108 Fornax Clustermembers measured with the UK Schmidt Telescope FLAIR-II spectrographcontains 55 dwarf galaxies (15.5>bJ>18.0 or-16>MB>-13.5). Hα emission shows that 36%+/-8% ofthe dwarfs are star forming, twice the fraction implied by morphologicalclassifications. The total sample has a mean velocity of 1493+/-36 kms-1 and a velocity dispersion of 374+/-26 km s-1.The dwarf galaxies form a distinct population: their velocity dispersion(429+/-41 km s-1) is larger than that of the giants (308+/-30km s-1) at the 98% confidence level. This suggests that thedwarf population is dominated by infalling objects whereas the giantsare virialized. The Fornax system has two components, the main FornaxCluster centered on NGC 1399 with cz=1478 km s-1 andσcz=370 km s-1 and a subcluster centered3° to the southwest including NGC 1316 with cz=1583 kms-1 and σcz=377 km s-1. Thispartition is preferred over a single cluster at the 99% confidencelevel. The subcluster, a site of intense star formation, is bound toFornax and probably infalling toward the cluster core for the firsttime. We discuss the implications of this substructure for distanceestimates of the Fornax Cluster. We determine the cluster mass profileusing the method of Diaferio, which does not assume a virialized sample.The mass within a projected radius of 1.4 Mpc is(7+/-2)×1013 Msolar, and the mass-to-lightratio is 300+/-100 Msolar/Lsolar. The mass isconsistent with values derived from the projected mass virial estimatorand X-ray measurements at smaller radii.

A Determination of the Hubble Constant from Cepheid Distances and a Model of the Local Peculiar Velocity Field
We present a measurement of the Hubble constant based on Cepheiddistances to 27 galaxies within 20 Mpc. We take the Cepheid data frompublished measurements by the Hubble Telescope Key Project on theDistance Scale (H0KP). We calibrate the Cepheidperiod-luminosity (PL) relation with data from over 700 Cepheids in theLMC obtained by the OGLE collaboration; we assume an LMC distancemodulus of 18.50 mag (dLMC=50.1 kpc). Using this PLcalibration, we obtain new distances to the H0KP galaxies. Wecorrect the redshifts of these galaxies for peculiar velocities usingtwo distinct velocity field models: the phenomenological model of Tonryet al. and a model based on the IRAS density field and lineargravitational instability theory. We combine the Cepheid distances withthe corrected redshifts for the 27 galaxies to derive H0, theHubble constant. The results are H0=85+/-5 km s-1Mpc-1 (random error) at 95% confidence when the IRAS model isused, and 92+/-5 km s-1 Mpc-1 when thephenomenological model is used. The IRAS model is a better fit to thedata, and the Hubble constant it returns is more reliable. Systematicerror stems mainly from LMC distance uncertainty, which is not directlyaddressed by this paper. Our value of H0 is significantlylarger than that quoted by the H0KP, H0=71+/-6 kms-1 Mpc-1. Cepheid recalibration explains ~30% ofthis difference, and velocity field analysis accounts for ~70%. Wediscuss in detail possible reasons for this discrepancy and futurestudies needed to resolve it.

The neutral hydrogen content of Fornax cluster galaxies
We present a new set of deep H I observations of member galaxies of theFornax cluster. We detected 35 cluster galaxies in HI. The resulting sample, the most comprehensive to date, is used toinvestigate the distribution of neutral hydrogen in the clustergalaxies. We compare the H I content of the detected cluster galaxieswith that of field galaxies by measuring H I mass-to-light ratios andthe H I deficiency parameter of Solanes et al. (\cite{Sol96}). The meanH I mass-to-light ratio of the cluster galaxies is 0.68+/- 0.15,significantly lower than for a sample of H I-selected field galaxies(1.15+/- 0.10), although not as low as in the Virgocluster (0.45+/- 0.03). In addition, the H I content of twocluster galaxies (NGC 1316C and NGC1326B) appears to have been affected by interactions. The meanH I deficiency for the cluster is 0.38+/-0.09 (for galaxy types T=1-6),significantly greater than for the field sample (0.05+/-0.03). Boththese tests show that Fornax cluster galaxies are HI-deficient compared to field galaxies. The kinematics of the clustergalaxies suggests that the H I deficiency may be caused by ram-pressurestripping of galaxies on orbits that pass close to the cluster core. Wealso derive the most complete B-band Tully - Fisher relation of inclinedspiral galaxies in Fornax. A subcluster in theSouth-West of the main cluster contributes considerably to the scatter.The scatter for galaxies in the main cluster alone is 0.50 mag, which isslightly larger than the intrinsic scatter of 0.4 mag. We use the Tully- Fisher relation to derive a distance modulus ofFornax relative to the Virgocluster of -0.38+/- 0.14 mag. The galaxies in the subclusterare (1.0+/-0.5) mag brighter than the galaxies of the main cluster,indicating that they are situated in the foreground. With their meanvelocity 95 km s-1 higher than that of the main cluster weconclude that the subcluster is falling into the main Fornaxcluster.

A Database of Cepheid Distance Moduli and Tip of the Red Giant Branch, Globular Cluster Luminosity Function, Planetary Nebula Luminosity Function, and Surface Brightness Fluctuation Data Useful for Distance Determinations
We present a compilation of Cepheid distance moduli and data for foursecondary distance indicators that employ stars in the old stellarpopulations: the planetary nebula luminosity function (PNLF), theglobular cluster luminosity function (GCLF), the tip of the red giantbranch (TRGB), and the surface brightness fluctuation (SBF) method. Thedatabase includes all data published as of 1999 July 15. The mainstrength of this compilation resides in the fact that all data are on aconsistent and homogeneous system: all Cepheid distances are derivedusing the same calibration of the period-luminosity relation, thetreatment of errors is consistent for all indicators, and measurementsthat are not considered reliable are excluded. As such, the database isideal for comparing any of the distance indicators considered, or forderiving a Cepheid calibration to any secondary distance indicator, suchas the Tully-Fisher relation, the Type Ia supernovae, or the fundamentalplane for elliptical galaxies. This task has already been undertaken byFerrarese et al., Sakai et al., Kelson et al., and Gibson et al.Specifically, the database includes (1) Cepheid distances, extinctions,and metallicities; (2) reddened apparent λ5007 Å magnitudesof the PNLF cutoff; (3) reddened apparent magnitudes and colors of theturnover of the GCLF (in both the V and B bands); (4) reddened apparentmagnitudes of the TRGB (in the I band) and V-I colors at 0.5 mag fainterthan the TRGB; and (5) reddened apparent surface brightness fluctuationmagnitudes measured in Kron-Cousin I, K', andKshort, and using the F814W filter with the Hubble SpaceTelescope (HST) WFPC2. In addition, for every galaxy in the database wegive reddening estimates from IRAS/DIRBE as well as H I maps, J2000coordinates, Hubble and T-type morphological classification, apparenttotal magnitude in B, and systemic velocity.

The Globular Cluster Systems in the Coma Ellipticals. I. The Luminosity Function in NGC 4874 and Implications for Hubble's Constant
We have used deep Hubble Space Telescope WFPC2 images in V (F606W) and I(F814W) to measure the luminosity distribution of the globular clustersin NGC 4874, the central cD galaxy of the Coma cluster. We find the``turnover'' point of the globular cluster luminosity function (GCLF) tolie at V=27.88+/-0.12, while the overall GCLF shape matches the standardGaussian-like form with dispersion σV=1.49+/-0.12. Weuse the GCLF as a standard candle by matching the turnover points in NGC4874 and another Coma elliptical, IC 4051, with those of the giantellipticals in the Virgo cluster (M87 and five others). The result isΔ(m-M) (Coma-Virgo)=4.06+/-0.11 mag, which converts to a Comadistance d=102 Mpc if the Virgo distance modulus is(m-M)0=30.99+/-0.04. The Hubble constant which emerges fromour GCLF measurement is then H0=(69+/-9) km s-1Mpc-1. We confirm this H0 value with a novelpresentation of the ``Hubble diagram'' for GCLFs in giant E galaxies.Measurements of additional GCLFs in the Coma ellipticals, as well ascalibrating galaxies in Virgo and Fornax, have excellent potential torefine this result in the near future. Based on observations obtainedwith the NASA/ESA Hubble Space Telescope, obtained at the SpaceTelescope Science Institute, which is operated by the Association ofUniversities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

The Surface Brightness Fluctuation Survey of Galaxy Distances. II. Local and Large-Scale Flows
We present results from the Surface Brightness Fluctuation (SBF) Surveyfor the distances to 300 early-type galaxies, of which approximatelyhalf are ellipticals. A modest change in the zero point of the SBFrelation, derived by using Cepheid distances to spirals with SBFmeasurements, yields a Hubble constant H0=77+/-4+/-7 kms-1 Mpc-1, somewhat larger than the HST KeyProject result. We discuss how this difference arises from a differentchoice of zero point, a larger sample of galaxies, and a different modelfor large-scale flows. Our result is 4% larger than found in a recentcomparison of the SBF Survey peculiar velocities with predictionsderived from the galaxy density field measured by redshift surveys(Blakeslee et al. 1999b). The zero point of the SBF relation is thelargest source of uncertainty, and our value for H0 issubject to all the systematic uncertainties of the Key Project zeropoint, including a 5% decrease if a metallicity correction for theCepheids is adopted. To analyze local and large-scale flows-departuresfrom smooth Hubble flow-we use a parametric model for the distributionfunction of mean velocity and velocity dispersion at each point inspace. These models include a uniform thermal velocity dispersion andspherical attractors whose position, amplitude, and radial shape arefree to vary. Our modeling procedure performs a maximum likelihood fitof the model to the observations. Our models rule out a uniform Hubbleflow as an acceptable fit to the data. Inclusion of two attractors, oneof which having a best-fit location coincident with the Virgo clusterand the other having a fit location slightly beyond the Centaurusclusters (which we refer to by convention as the Great Attractor),reduces χ2/N from 2.1 to 1.1. The fits to theseattractors both have radial profiles such that v~r-1 (i.e.,isothermal) over a range of overdensity between about 10 and 1, but falloff more steeply at larger radius. The best-fit value for thesmall-scale, cosmic thermal velocity is 180+/-14 km s-1. Thequality of the fit can be further improved by the addition of aquadrupole correction to the Hubble flow. The dipole velocity offsetfrom the CMB frame for the volume we survey (amplitude ~150 kms-1) and the quadrupole may be genuine (though weak)manifestations of more distant density fluctuations, but we findevidence that they are more likely due to the inadequacy of sphericalmodels to describe the density profile of the attractors. The residualdipole we find is comparable to the systematic error in these simple,parametrized models; in other words, our survey volume of R<3000 kms-1 is, in a mass averaged sense, essentially at rest withrespect to the CMB. This contradicts claims of large amplitude flows inmuch larger volumes that include our sample. Our best-fitting model,which uses attenuated power-law mass distributions for the twoattractors, has enclosed mass overdensities at the Local Group of7x1014 Msolar for the Virgo Attractor and9x1015 Msolar for the Great Attractor. Withoutrecourse to information about the overdensities of these attractors withrespect to the cosmic mean we cannot provide a good constraint onΩM, but our data do give us accurate measurements interms of δ, the overdensities of the enclosed masses with respectto the background: δ Ω2/3M=0.33 forthe Virgo Attractor and δ Ω2/3M=0.27for the Great Attractor. Observations in part from theMichigan-Dartmouth-MIT (MDM) Observatory.

The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XXVII. A Derivation of the Hubble Constant Using the Fundamental Plane and Dn-σ Relations in Leo I, Virgo, and Fornax
Using published photometry and spectroscopy, we construct thefundamental plane and Dn-σ relations in Leo I, Virgo,and Fornax. The published Cepheid period-luminosity (PL) relations tospirals in these clusters fixes the relation between angular size andmetric distance for both the fundamental plane and Dn-σrelations. Using the locally calibrated fundamental plane, we inferdistances to a sample of clusters with a mean redshift of cz~6000 kms-1, and derive a value of H0=78+/-5+/-9 kms-1 Mpc-1 (random and systematic errors,respectively) for the local expansion rate. This value includes acorrection for depth effects in the Cepheid distances to the nearbyclusters, which decreased the deduced value of the expansion rate by5%+/-5%. If one further adopts the metallicity correction to the CepheidPL relation as derived by the Key Project, the value of the Hubbleconstant would decrease by a further 6%+/-4%. These two sources ofsystematic error, when combined with a +/-6% error due to theuncertainty in the distance to the Large Magellanic Cloud, a +/-4% errordue to uncertainties in the WFPC2 calibration, and several small sourcesof uncertainty in the fundamental plane analysis, yield a totalsystematic uncertainty of +/-11%. We find that the values obtained usingeither the cosmic microwave background (CMB) or a flow-field model, forthe reference frame of the distant clusters, agree to within 1%. TheDn-σ relation also produces similar results, asexpected from the correlated nature of the two scaling relations. Acomplete discussion of the sources of random and systematic error inthis determination of the Hubble constant is also given, in order tofacilitate comparison with the other secondary indicators being used bythe Key Project.

The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XXVI. The Calibration of Population II Secondary Distance Indicators and the Value of the Hubble Constant
A Cepheid-based calibration is derived for four distance indicators thatutilize stars in old stellar populations: the tip of the red giantbranch (TRGB), the planetary nebula luminosity function (PNLF), theglobular cluster luminosity function (GCLF), and the surface brightnessfluctuation method (SBF). The calibration is largely based on theCepheid distances to 18 spiral galaxies within cz=1500 km s-1obtained as part of the Hubble Space Telescope (HST) Key Project on theExtragalactic Distance Scale, but relies also on Cepheid distances fromseparate HST and ground-based efforts. The newly derived calibration ofthe SBF method is applied to obtain distances to four Abell clusters inthe velocity range 3800-5000 km s-1. Combined with clustervelocities corrected for a cosmological flow model, these distancesimply a value of the Hubble constant of H0=69+/-4(random)+/-6 (systematic) km s-1 Mpc-1. Thisresult assumes that the Cepheid PL relation is independent of themetallicity of the variable stars; adopting a metallicity correction asin Kennicutt et al. would produce a 5%+/-3% decrease in H0.Finally, the newly derived calibration allows us to investigatesystematics in the Cepheid, PNLF, SBF, GCLF, and TRGB distance scales.

The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XXV. A Recalibration of Cepheid Distances to Type IA Supernovae and the Value of the Hubble Constant
Cepheid-based distances to seven Type Ia supernovae (SNe) host galaxieshave been derived using the standard Hubble Space Telescope (HST) KeyProject on the Extragalactic Distance Scale pipeline. For the firsttime, this allows for a transparent comparison of data accumulated aspart of three different HST projects: the Key Project, the Sandage etal. Type Ia supernovae (SNe) program, and the Tanvir et al. Leo I Groupstudy. Reanalyzing the Tanvir et al. galaxy and six Sandage et al.galaxies, we find a mean (weighted) offset in true distance moduli of0.12+/-0.07 mag; i.e., 6% in linear distance, in the sense of reducingthe distance scale or increasing H0. Adopting thereddening-corrected Hubble relations of Suntzeff et al. tied to a zeropoint based on SNe 1990N, 1981B, 1998bu, 1989B, 1972E, and 1960F and thephotometric calibration of Hill et al. leads to a Hubble constant ofH0=68+/-2(random)+/-5(systematic) km s-1Mpc-1. Adopting the Kennicutt et al. Cepheidperiod-luminosity-metallicity dependency decreases the inferredH0 by 4%. The H0 result from Type Ia SNe is now ingood agreement, to within their respective uncertainties, with that fromthe Tully-Fisher and surface brightness fluctuation relations. Based onobservations with the NASA/ESA Hubble Space Telescope, obtained at theSpace Telescope Science Institute, which is operated by AURA, Inc.,under NASA contract NAS 5-26555.

The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XXI. The Cepheid Distance to NGC 1425
The distance to NGC 1425 has been derived from Cepheid variables, aspart of the Hubble Space Telescope Key Project on the ExtragalacticDistance Scale. Thirteen F555W (V) and eight F814W (I) epochs ofcosmic-ray-split Wide Field Planetary Camera 2 observations wereobtained. Twenty-nine Cepheids were discovered, with periods rangingfrom 16 to 63 days. Adopting a Large Magellanic Cloud distance modulusand extinction of 18.50+/-0.10 mag and E(V-I)=0.13 mag, respectively, atrue reddening-corrected distance modulus (based on an analysisemploying the ALLFRAME software package) of 31.73+/-0.16 (random)+/-0.17(systematic) mag was determined for NGC 1425. The corresponding distanceof 22.2+/-1.0 (random)+/-1.0 (systematic) Mpc is in satisfactoryagreement with that found with an independent analysis based on theDoPHOT photometry package.

Theoretical models for classical Cepheids. VII. Metallicity effects on the Cepheid distance scale
We use theoretical Period-Luminosity and Period-Luminosity-Colorrelations in the VI passbands, as based on nonlinear, nonlocal andtime-dependent convective pulsating models, to predict the reddening andtrue distance modulus of distant Cepheids observed with the Hubble SpaceTelescope. By relying on the pulsating models with metal contentZ=0.008, we find that the theoretical predictions agree to the valuesobtained by the Extragalactic Distance Scale Key Project on the basis ofempirical Period-Luminosity relations referenced to LMC variables. Inthe meantime, from the theoretical relations with Z=0.004 and 0.02 wefind that the predicted E(B-V) and mu_0 decrease as the adopted metalcontent increases. This suggests a metallicity correction to LMC-baseddistances as given by Delta mu_0 /Delta log Z ~ -0.27 magdex-1, where Delta log Z is the difference between themetallicity of the Cepheids whose distance we are estimating and the LMCvalue Z=0.008. Such a theoretical correction appears supported by anexisting, although weak, correlation between the Cepheid distance andthe [O/H] metallicity of galaxies within a given group or cluster, aswell as by a similar correlation between the H_0 estimate and the [O/H]metallicity of the galaxies which calibrate the SNIa luminosity. On thecontrary, the metallicity corrections earlier suggested on empiricalgrounds seem to be excluded. Eventually we suggest that the averagevalue < H_0> ~ 67 km s-1 Mpc-1 provided bythe Key Project team should increase at least up to ~ 69 kms-1 Mpc-1. Further observational evidences insupport of the predicted scenario are finally presented.

The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XXII. The Discovery of Cepheids in NGC 1326A
We report on the detection of Cepheids and the first distancemeasurement to the spiral galaxy NGC 1326A, a member of the FornaxCluster of galaxies. We have employed data obtained with the Wide Fieldand Planetary Camera 2 on board the Hubble Space Telescope. Over a 49day interval, a total of 12 V-band (F555W) and eight I-band (F814W)epochs of observation were obtained. Two photometric reduction packages,ALLFRAME and DoPHOT, have been employed to obtain photometry measuresfrom the three Wide Field CCDs. Variability analysis yields a total of17 Cepheids in common with both photometry data sets, with periodsranging between 10 and 50 days. Of these, 14 Cepheids with high-qualitylight curves are used to fit the V and I period-luminosity relations andderive apparent distance moduli, assuming a Large Magellanic Clouddistance modulus μLMC=18.50+/-0.10 mag and color excessE(B-V)=0.10 mag. Assuming A(V)/E(V-I)=2.45, the DoPHOT data yield a truedistance modulus to NGC 1326A ofμ0=31.36+/-0.17(random)+/-0.13(systematic) mag,corresponding to a distance of 18.7+/-1.5(random)+/-1.2(systematic) Mpc.The derived distance to NGC 1326A is in good agreement with the distancederived previously to NGC 1365, another spiral galaxy member of theFornax Cluster. However, the distances to both galaxies aresignificantly lower than that to NGC 1425, a third Cepheid calibrator inthe outer parts of the cluster.

The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XV. A Cepheid Distance to the Fornax Cluster and Its Implications
Using the Hubble Space Telescope, 37 long-period Cepheid variables havebeen discovered in the Fornax Cluster spiral galaxy NGC 1365. Theresulting V and I period-luminosity relations yield a true distancemodulus of mu_0=31.35+/-0.07 mag, which corresponds to a distance of18.6+/-0.6 Mpc. This measurement provides several routes for estimatingthe Hubble constant. (1) Assuming this distance for the Fornax Clusteras a whole yields a local Hubble constant of 70+/-18 (random) +/-7(systematic) km s^-1 Mpc^-1. (2) Nine Cepheid-based distances to groupsof galaxies out to and including the Fornax and Virgo Clusters yieldH_0=73+/-16 (random) +/-7 (systematic) km s^-1 Mpc^-1. (3) Recalibratingthe I-band Tully-Fisher relation using NGC 1365 and six nearby spiralgalaxies, and applying it to 15 galaxy clusters out to 100 Mpc, giveH_0=76+/-3 (random) +/-8 (systematic) km s^-1 Mpc^-1. (4) Using abroad-based set of differential cluster distance moduli ranging fromFornax to Abell 2147 gives H_0=72+/-3 (random) +/-6 (systematic) km s^-1Mpc^-1. Finally, (5) assuming the NGC 1365 distance for the twoadditional Type Ia supernovae in Fornax and adding them to the SN Iacalibration (correcting for light-curve shape) gives H_0=67+/-6 (random)+/-7 (systematic) km s^-1 Mpc^-1 out to a distance in excess of 500 Mpc.All five of these H_0 determinations agree to within their statisticalerrors. The resulting estimate of the Hubble constant, combining all ofthese determinations, is H_0=72+/-5 (random) +/-7 (systematic) km s^-1Mpc^-1. An extensive tabulation of identified systematic and statisticalerrors, and their propagation, is given.

The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XIV. The Cepheids in NGC 1365
We report the detection of Cepheid variable stars in the barred spiralgalaxy NGC 1365, located in the Fornax cluster, using the Hubble SpaceTelescope (HST) Wide Field and Planetary Camera 2 (WFPC2). Twelve V(F555W) and four I (F814W) epochs of observation were obtained. The twophotometry packages ALLFRAME and DoPHOT were separately used to obtainprofile-fitting photometry of all the stars in the HST field. The searchfor Cepheid variable stars resulted in a sample of 52 variables, withperiods between 14 and 60 days, common to both data sets. ALLFRAMEphotometry and light curves of the Cepheids are presented. A subset of34 Cepheids were selected on the basis of period, light curve shape,similar ALLFRAME and DoPHOT periods, color, and relative crowding, tofit the Cepheid period-luminosity relations in V and I for both ALLFRAMEand DoPHOT. The measured distance modulus to NGC 1365 from the ALLFRAMEphotometry is 31.31+/-0.20 (random)+/-0.18 (systematic) mag,corresponding to a distance of 18.3+/-1.7 (random)+/-1.6 (systematic)Mpc. The reddening is measured to be E(V-I)=0.16+/-0.08 mag. Thesevalues are in excellent agreement with those obtained using the DoPHOTphotometry, namely a distance modulus of 31.26+/-0.10 mag and areddening of 0.15+/-0.10 mag (internal errors only).

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Right ascension:03h25m08.20s
Aparent dimensions:1.905′ × 1.259′

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