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Spitzer Observations of the Dusty Warped Disk of Centaurus A
Spitzer mid-infrared images of the dusty warped disk in the galaxyCentaurus A show a parallelogram-shaped structure. We successfully modelthe observed mid-infrared morphology by integrating the light from anemitting, thin, and warped disk, similar to that inferred from previouskinematic studies. The models with the best match to the morphology lackdust emission within the inner 0.1-0.8 kpc, suggesting that energeticprocesses near the nucleus have disturbed the inner molecular disk,creating a gap in the molecular gas distribution.
| Why Are Radio Galaxies Prolific Producers of Type Ia Supernovae?
An analysis of SN Ia events in early-type galaxies from the database ofCappellaro and coworkers provides conclusive evidence that the rate ofSNe Ia in radio-loud galaxies is about 4 times higher than the ratemeasured in radio-quiet galaxies, i.e., SN Ia rate(radio-loudgalaxies)=0.43+0.19-0.14h275 SNu as compared to SN Ia rate(radio-quietgalaxies)=0.11+0.06-0.03h275 SNu. The actual value of the enhancement islikely to be in the range ~2-7 (P~10-4). This finding puts onrobust empirical grounds the results obtained by Della Valle &Panagia on the basis of a smaller sample of SNe. We analyze the possiblecauses of this result and conclude that the enhancement of the SN Iaexplosion rate in radio-loud galaxies has the same origin as their beingstrong radio sources, but there is no causal link between the twophenomena. We argue that repeated episodes of interaction and/or mergersof early-type galaxies with dwarf companions, on timescales of about 1Gyr, are responsible for both inducing strong radio activity observed in~14% of early-type galaxies and supplying an adequate number of SN Iaprogenitors to the stellar population of elliptical galaxies.
| Reddening, Absorption, and Decline Rate Corrections for a Complete Sample of Type Ia Supernovae Leading to a Fully Corrected Hubble Diagram to v < 30,000 km s-1
Photometric (BVI) and redshift data corrected for streaming motions arecompiled for 111 ``Branch-normal,'' four 1991T-like, seven 1991bg-like,and two unusual supernovae of Type Ia (SNe Ia). Color excessesE(B-V)host of normal SNe Ia, due to the absorption of thehost galaxy, are derived by three independent methods, giving excellentagreement leading to the intrinsic colors at maximum of(B-V)00=-0.024+/-0.010 and (V-I)00=-0.265+/-0.016if normalized to a common decline rate of Δm15=1.1. Thestrong correlation between redshift absolute magnitudes (based on anarbitrary Hubble constant of H0=60 km s-1Mpc-1), corrected only for the extrinsic Galactic absorption,and the derived E(B-V)host color excesses leads to thewell-determined yet abnormal absorption-to-reddening ratios ofRBVI=3.65+/-0.16, 2.65+/-0.15, and 1.35+/-0.21.Comparison with the canonical Galactic values of 4.1, 3.1, and 1.8forces the conclusion that the law of interstellar absorption in thepath length to the SN in the host galaxy is different from the localGalactic law, a result consistent with earlier conclusions by others.Improved correlations of the fully corrected absolute magnitudes (on thesame arbitrary Hubble constant zero point) with host galaxymorphological type, decline rate, and intrinsic color are derived. Werecover the result that SNe Ia in E/S0 galaxies are ~0.3 mag fainterthan in spiral galaxies for possible reasons discussed in the text. Thenew decline rate corrections to absolute magnitudes are smaller thanthose by some authors for reasons explained in the text. The fourspectroscopically peculiar 1991T-type SNe are significantly overluminousas compared to Branch-normal SNe Ia. The overluminosity of the seven1999aa-like SNe is less pronounced. The seven 1991bg types in the sampleconstitute a separate class of SNe Ia, averaging in B 2 mag fainter thanthe normal Ia. New Hubble diagrams in B, V, and I are derived out to~30,000 km s-1 using the fully corrected magnitudes andvelocities, corrected for streaming motions. Nine solutions for theintercept magnitudes in these diagrams show extreme stability at the0.02 mag level using various subsamples of the data for both low andhigh extinctions in the sample, proving the validity of the correctionsfor host galaxy absorption. We shall use the same precepts for fullycorrecting SN magnitudes for the luminosity recalibration of SNe Ia inthe forthcoming final review of our Hubble Space Telescope Cepheid-SNexperiment for the Hubble constant.
| Bar-induced perturbation strengths of the galaxies in the Ohio State University Bright Galaxy Survey - I
Bar-induced perturbation strengths are calculated for a well-definedmagnitude-limited sample of 180 spiral galaxies, based on the Ohio StateUniversity Bright Galaxy Survey. We use a gravitational torque method,the ratio of the maximal tangential force to the mean axisymmetricradial force, as a quantitative measure of the bar strength. Thegravitational potential is inferred from an H-band light distribution byassuming that the M/L ratio is constant throughout the disc. Galaxiesare deprojected using orientation parameters based on B-band images. Inorder to eliminate artificial stretching of the bulge, two-dimensionalbar-bulge-disc decomposition has been used to derive a reliable bulgemodel. This bulge model is subtracted from an image, the disc isdeprojected assuming it is thin, and then the bulge is added back byassuming that its mass distribution is spherically symmetric. We findthat removing the artificial bulge stretch is important especially forgalaxies having bars inside large bulges. We also find that the massesof the bulges can be significantly overestimated if bars are not takeninto account in the decomposition.Bars are identified using Fourier methods by requiring that the phasesof the main modes (m= 2, m= 4) are maintained nearly constant in the barregion. With such methods, bars are found in 65 per cent of the galaxiesin our sample, most of them being classified as SB-type systems in thenear-infrared by Eskridge and co-workers. We also suggest that as muchas ~70 per cent of the galaxies classified as SAB-types in thenear-infrared might actually be non-barred systems, many of them havingcentral ovals. It is also possible that a small fraction of the SAB-typegalaxies have weak non-classical bars with spiral-like morphologies.
| Dynamical friction in flattened systems: a numerical test of Binney's approach
We carry out a set of self-consistent N-body calculations to investigatehow important the velocity anisotropy in non-spherical dark matterhaloes is for dynamical friction. For this purpose, we allow satellitegalaxies to orbit within flattened and live dark matter haloes (DMHs)and compare the resulting orbit evolution with a semi-analytic code.This code solves the equation of motion of the same satellite orbitswith mass loss and assumes the same DMH, but either employsChandrasekhar's dynamical friction formula, which does not incorporatethe velocity anisotropy, or Binney's description of dynamical frictionin anisotropic systems. In the numerical and the two semi-analyticmodels, the satellites are given different initial orbital inclinationsand orbital eccentricities, whereas the parent galaxy is composed of aDMH with aspect ratio qh= 0.6.We find that Binney's approach successfully describes the overallsatellite decay and orbital inclination decrease for the whole set oforbits, with an averaged discrepancy of less than 4 per cent in orbitalradius during the first three orbits. If Chandrasekhar's expression isused instead, the discrepancy increases to 20 per cent. Binney'streatment therefore appears to provide a significantly improvedtreatment of dynamical friction in anisotropic systems.The velocity anisotropy of the DMH velocity distribution function leadsto a significant decrease with time of the inclination of non-polarsatellite orbits. But, at the same time, it reduces the difference indecay times between polar and coplanar orbits evident in a flattened DMHwhen the anisotropic DMH velocity distribution function is not takeninto account explicitly. Our N-body calculations furthermore indicatethat polar orbits survive about 1.6 times longer than coplanar orbitsand that the orbital eccentricity e remains close to its initial valueif satellites decay slowly towards the galaxy centre. However, orbits ofrapidly decaying satellites modelled with the semi-analytic code show astrong orbital circularization () not present in the N-bodycomputations.
| Stellar Velocity Dispersion and Mass Estimation for Galactic Disks
Available velocity dispersion estimates for the old stellar populationof galactic disks at galactocentric distances r=2L (where L is thephotometric radial scale length of the disk) are used to determine thethreshold local surface density of disks that are stable againstgravitational perturbations. The mass of the disk Mdcalculated under the assumption of its marginal stability is comparedwith the total mass Mt and luminosity LB of thegalaxy within r=4L. We corroborate the conclusion that a substantialfraction of the mass in galaxies is probably located in their darkhalos. The ratio of the radial velocity dispersion to the circularvelocity increases along the sequence of galactic color indices anddecreases from the early to late morphological types. For most of thegalaxies with large color indices (B-V)0 > 0.75, whichmainly belong to the S0 type, the velocity dispersion exceedssignificantly the threshold value required for the disk to be stable.The reverse situation is true for spiral galaxies: the ratiosMd/LB for these agree well with those expected forevolving stellar systems with the observed color indices. This suggeststhat the disks of spiral galaxies underwent no significant dynamicalheating after they reached a quasi-equilibrium stable state.
| Properties of isolated disk galaxies
We present a new sample of northern isolated galaxies, which are definedby the physical criterion that they were not affected by other galaxiesin their evolution during the last few Gyr. To find them we used thelogarithmic ratio, f, between inner and tidal forces acting upon thecandidate galaxy by a possible perturber. The analysis of thedistribution of the f-values for the galaxies in the Coma cluster leadus to adopt the criterion f ≤ -4.5 for isolated galaxies. Thecandidates were chosen from the CfA catalog of galaxies within thevolume defined by cz ≤5000 km s-1, galactic latitudehigher than 40o and declination ≥-2.5o. Theselection of the sample, based on redshift values (when available),magnitudes and sizes of the candidate galaxies and possible perturberspresent in the same field is discussed. The final list of selectedisolated galaxies includes 203 objects from the initial 1706. The listcontains only truly isolated galaxies in the sense defined, but it is byno means complete, since all the galaxies with possible companions underthe f-criterion but with unknown redshift were discarded. We alsoselected a sample of perturbed galaxies comprised of all the diskgalaxies from the initial list with companions (with known redshift)satisfying f ≥ -2 and \Delta(cz) ≤500 km s-1; a totalof 130 objects. The statistical comparison of both samples showssignificant differences in morphology, sizes, masses, luminosities andcolor indices. Confirming previous results, we found that late spiral,Sc-type galaxies are, in particular, more frequent among isolatedgalaxies, whereas Lenticular galaxies are more abundant among perturbedgalaxies. Isolated systems appear to be smaller, less luminous and bluerthan interacting objects. We also found that bars are twice as frequentamong perturbed galaxies compared to isolated galaxies, in particularfor early Spirals and Lenticulars. The perturbed galaxies have higherLFIR/LB and Mmol/LB ratios,but the atomic gas content is similar for the two samples. The analysisof the luminosity-size and mass-luminosity relations shows similartrends for both families, the main difference being the almost totalabsence of big, bright and massive galaxies among the family of isolatedsystems, together with the almost total absence of small, faint and lowmass galaxies among the perturbed systems. All these aspects indicatethat the evolution induced by interactions with neighbors would proceedfrom late, small, faint and low mass Spirals to earlier, bigger, moreluminous and more massive spiral and lenticular galaxies, producing atthe same time a larger fraction of barred galaxies but preserving thesame relations between global parameters. The properties we found forour sample of isolated galaxies appear similar to those of high redshiftgalaxies, suggesting that the present-day isolated galaxies could bequietly evolved, unused building blocks surviving in low densityenvironments.Tables \ref{t1} and \ref{t2} are only available in electronic form athttp://www.edpsciences.org
| The Rate and the Origin of Type Ia Supernovae in Radio Galaxies
An analysis of Type Ia supernova (SN Ia) events in early-type galaxiesfrom the Evans et al. database provides strong evidence that the rate ofSNe Ia in radio-loud galaxies is about 6 times higher than the ratemeasured in radio-quiet galaxies, i.e., SN Ia rate (radio-loudgalaxies)=0.47+0.23-0.15h250 SNe per century and per 1010LBsolar (SNU) as compared to SN Ia rate(radio-quiet galaxies)<~0.080 h250 SNU. Theexact value of the enhancement is still rather uncertain, but it islikely to be in the range ~4-15. We discuss the possible causes of thisresult, and we conclude that the enhancement of the SN Ia explosion ratein radio-loud galaxies has the same common origin as their being strongradio sources but that there is no causality link between the twophenomena. We argue that repeated episodes of interaction and/or mergersof early-type galaxies with dwarf companions are responsible forinducing both strong radio activity in ~14% of early-type galaxies andthe ~1 Gyr old stellar population needed to supply an adequate number ofSN Ia progenitors. Within this scenario, we predict that the probabilityof detecting a core-collapse SN event in radio-loud elliptical galaxiesamounts to about 4% of their SN Ia events.
| Ultraviolet-Optical Pixel Maps of Face-on Spiral Galaxies: Clues for Dynamics and Star Formation Histories
Ultraviolet and optical images of the face-on spiral galaxies NGC 6753and NGC 6782 reveal regions of strong ongoing star formation that areassociated with structures traced by the old stellar populations. We usethese images to construct NUV-(NUV-I814) pixelcolor-magnitude diagrams (pCMDs) that reveal plumes of pixels withstrongly varying near-ultraviolet (NUV) surface brightness and nearlyconstant I814 surface brightness. The plumes correspond tosharply bounded radial ranges, with (NUV-I814) at a given NUVsurface brightness being bluer at larger radii. The plumes are parallelto both the reddening vector and simple model mixtures of young and oldpopulations, thus neither reddening nor the fraction of the youngpopulation can produce the observed separation between the plumes. Theimages and radial surface brightness and color plots indicate that theseparate plumes are caused by sharp declines in the surface densities ofthe old populations at radii corresponding to disk resonances. Themaximum surface brightness of the NUV light remains essentially constantwith radius, while the maximum I814 surface brightnessdeclines sharply with radius. A mid-ultraviolet (MUV) image of NGC 6782shows emission from the nuclear ring. The distribution of points in an(MUV-NUV)-(NUV-I814) pixel color-color diagram is broadlyconsistent with the simple mixture model but shows a residual trend thatthe bluest pixels in (MUV-NUV) are the reddest pixels in(NUV-I814). This may be due to a combination of red continuumfrom late-type supergiants and [S III] emission lines associated with HII regions in active star-forming regions. We have shown that pixelmapping is a powerful tool for studying the distribution and strength ofongoing star formation in galaxies. Deep, multicolor imaging can extendthis to studies of extinction and the ages and metallicities ofcomposite stellar populations in nearby galaxies.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Sciences Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| HYPERLEDA. II. The homogenized HI data
After a compilation of HI data from 611 references and new observationsmade in Nançay, we produce a catalog of homogenized HI data for16781 galaxies. The homogenization is made using the EPIDEMIC methodfrom which all data are progressively converted into the adoptedstandard. The result is a catalog giving: 1) the logarithm of twice themaximum rotation velocity, log 2V_Msin i, converted to thesystem of Mathewson et al. (\cite{Mathewson1996}). This quantity isgiven without correction for inclination; 2) the HI magnitude,m21, (area of the 21-cm line width expressed in magnitude)converted to the flux system of Theureau et al. (\cite{Theureau1998});3) the HI velocity, V_HI, expressed with the optical definition (i.e.,using wavelengths instead frequencies). The typical uncertainties are:0.04 for log 2V_Msin i, 0.25 mag for m21 and 9 kms-1 for V_HI.Full Tables \ref{epidemicw}, \ref{epidemicw2}, \ref{epidemicf},\ref{epidemicf2} and Fig. \ref{profiles} are available in electronicform at http://www.edpsciences.org. Full Tables \ref{references},\ref{cataf}, \ref{newdata} and \ref{notes} are available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/412/57
| 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
| Bar strengths in spiral galaxies estimated from 2MASS images
Non-axisymmetric forces are presented for a sample of 107 spiralgalaxies, of which 31 are barred (SB) and 53 show nuclear activity. As adata base we use JHK images from the 2 Micron All-sky Survey, and thenon-axisymmetries are characterized by the ratio of the tangential forceto the mean axisymmetric radial force field, following Buta & Block.Bar strengths have an important role in many extragalactic problems andtherefore it is important to verify that the different numerical methodsapplied for calculating the forces give mutually consistent results. Weapply both direct Cartesian integration and a polar grid integrationutilizing a limited number of azimuthal Fourier components of density.We find that the bar strength is independent of the method used toevaluate the gravitational potential. However, because of thedistance-dependent smoothing by Fourier decomposition, the polar methodis more suitable for weak and noisy images. The largest source ofuncertainty in the derived bar strength appears to be the uncertainty inthe vertical scaleheight, which is difficult to measure directly formost galaxies. On the other hand, the derived bar strength is ratherinsensitive to the possible gradient in the vertical scaleheight of thedisc or to the exact model of the vertical density distribution,provided that the same effective vertical dispersion is assumed in allmodels. In comparison with the pioneering study by Buta & Block, thebar strength estimate is improved here by taking into account thedependence of the vertical scaleheight on the Hubble type: we find thatfor thin discs bar strengths are stronger than for thick discs by anamount that may correspond to as much as one bar strength class. Weconfirm the previous result by Buta and co-workers showing that thedispersion in bar strength is large among all the de Vaucouleurs opticalbar classes. In the near-infrared 40 per cent of the galaxies in oursample have bars (showing constant phases in the m= 2 Fourier amplitudesin the bar region), while in the optical band one-third of these barsare obscured by dust. Significant non-axisymmetric forces can also beinduced by the spiral arms, generally in the outer parts of the galacticdiscs, which may have important implications on galaxy evolution.Possible biases of the selected sample are also studied: we find thatthe number of bars identified drops rapidly when the inclination of thegalactic disc is larger than 50°. A similar bias is found in theThird Reference Catalogue of Bright Galaxies, which might be of interestwhen comparing bar frequencies at high and low redshifts.
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| Supernovae in isolated galaxies, in pairs and in groups of galaxies
In order to investigate the influence of environment on supernova (SN)production, we have performed a statistical investigation of the SNediscovered in isolated galaxies, in pairs and in groups of galaxies. 22SNe in 18 isolated galaxies, 48 SNe in 40 galaxy members of 37 pairs and211 SNe in 170 galaxy members of 116 groups have been selected andstudied. We found that the radial distributions of core-collapse SNe ingalaxies located in different environments are similar, and consistentwith those reported by Bartunov, Makarova & Tsvetkov. SNe discoveredin pairs do not favour a particular direction with respect to thecompanion galaxy. Also, the azimuthal distributions inside the hostmembers of galaxy groups are consistent with being isotropics. The factthat SNe are more frequent in the brighter components of the pairs andgroups is expected from the dependence of the SN rates on the galaxyluminosity. There is an indication that the SN rate is higher in galaxypairs compared with that in groups. This can be related to the enhancedstar formation rate in strongly interacting systems. It is concludedthat, with the possible exception of strongly interacting systems, theparent galaxy environment has no direct influence on SN production.
| A catalogue and analysis of X-ray luminosities of early-type galaxies
We present a catalogue of X-ray luminosities for 401 early-typegalaxies, of which 136 are based on newly analysed ROSAT PSPC pointedobservations. The remaining luminosities are taken from the literatureand converted to a common energy band, spectral model and distancescale. Using this sample we fit the LX:LB relationfor early-type galaxies and find a best-fit slope for the catalogue of~2.2. We demonstrate the influence of group-dominant galaxies on the fitand present evidence that the relation is not well modelled by a singlepower-law fit. We also derive estimates of the contribution to galaxyX-ray luminosities from discrete-sources and conclude that they provideLdscr/LB~=29.5ergs-1LBsolar-1. Wecompare this result with luminosities from our catalogue. Lastly, weexamine the influence of environment on galaxy X-ray luminosity and onthe form of the LX:LB relation. We conclude thatalthough environment undoubtedly affects the X-ray properties ofindividual galaxies, particularly those in the centres of groups andclusters, it does not change the nature of whole populations.
| Nuclear spectra of polar-ring galaxies
We report the results of spectroscopic observations of eight southernpolar-ring galaxies (PRGs), in the wavelength range 5900-7300Å. Wefind that five out of eight galaxies contain LINERs or Sy nuclei. Takinginto consideration all PRGs with available spectral data, we estimatethat about half of all PRGs and PRG candidates have either LINER orSeyfert nuclei. The observed widths of the [Nii]λ6583 line in thenuclei of early-type PRGs follow the linewidth-absolute luminosityrelation for normal E/S0 galaxies. We found that one of the observedgalaxies - ESO 576-G69 - is a new kinematically-confirmed polar-ringgalaxy with a spiral host.
| Evidence for Asphericity in a Subluminous Type Ia Supernova: Spectropolarimetry of SN 1999by
We present polarization spectra near maximum light for the stronglysubluminous Type Ia supernova SN 1999by that show that the supernova isintrinsically polarized. SN 1999by has an observed, overall level ofpolarization of ~0.3%-0.8%, a rise of the polarization P redward of 6500Å, and a change in polarization across the Si II λ6150feature of about 0.4%. The presentation of the polarization at differentwavelengths in the Q-U plane is shown to be a powerful tool to determinethe overall geometry and the interstellar component. The distribution ofpoints with wavelength using this empirical Q-U plane method revealsthat SN 1999by has a well-defined axis of symmetry and suggests aninterstellar polarization (ISP) vector with PISP=0.3% andposition angle Θ=150deg with an error circle in the Q-Uplane of radius about 0.1%. Synthetic non-LTE spectra for axisymmetricconfigurations based on delayed-detonation models have been computedassuming ellipsoidal geometry. The input ejecta structure andcomposition are based on a Chandrasekhar mass delayed-detonation model.The parameters of the explosion are chosen to reproduce the timeevolution of IR spectra of SN 1999by without further adjustments.Spherical models are then mapped onto ellipsoidal geometries and theaxis ratio, viewing angle, and ISP adjusted to provide the bestagreement with the polarization spectra. Both flux and polarizationspectra can be reasonably well reproduced by models with an asphericityof ~20% observed equator-on. The general properties of the polarizationcan be understood as a consequence of the structure of subluminousmodels. Best fits are obtained for the theoretical models withPISP=0.25% and Θ=140deg, consistent with theempirical method. We discuss our results for this subluminous Type Ia inthe context of ``normally bright'' Type Ia supernovae. For normallybright Type Ia, the photosphere is near the inner iron-rich layers atmaximum light and the ubiquitous iron lines give a rapid variation tothe model polarization spectra. In subluminous models, the photospherenear maximum is in the silicon layers with fewer lines and a smootheroverall polarization spectrum, as observed for SN 1999by. Though dataare sparse, the low upper limits for polarization determined for manynormal events in contrast to the high polarization in SN 1999by maysuggest a relation between the asymmetry we observed and the mechanismthat produces a subluminous Type Ia. Among various mechanisms, rapidrotation of the progenitor white dwarf and/or an explosion during abinary white dwarf merger process are likely candidates to explain theasphericity in SN 1999by.
| The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances
We report data for I-band surface brightness fluctuation (SBF)magnitudes, (V-I) colors, and distance moduli for 300 galaxies. Thesurvey contains E, S0, and early-type spiral galaxies in the proportionsof 49:42:9 and is essentially complete for E galaxies to Hubblevelocities of 2000 km s-1, with a substantial sampling of Egalaxies out to 4000 km s-1. The median error in distancemodulus is 0.22 mag. We also present two new results from the survey.(1) We compare the mean peculiar flow velocity (bulk flow) implied byour distances with predictions of typical cold dark matter transferfunctions as a function of scale, and we find very good agreement withcold, dark matter cosmologies if the transfer function scale parameterΓ and the power spectrum normalization σ8 arerelated by σ8Γ-0.5~2+/-0.5. Deriveddirectly from velocities, this result is independent of the distributionof galaxies or models for biasing. This modest bulk flow contradictsreports of large-scale, large-amplitude flows in the ~200 Mpc diametervolume surrounding our survey volume. (2) We present adistance-independent measure of absolute galaxy luminosity, N and showhow it correlates with galaxy properties such as color and velocitydispersion, demonstrating its utility for measuring galaxy distancesthrough large and unknown extinction. Observations in part from theMichigan-Dartmouth-MIT (MDM) Observatory.
| Multicolour broadband study of a lenticular galaxy : NGC 4753
Based on VBT observations, we report multicolour broadband study of alenticular galaxy, NGC 4753 with prominent dust lanes. The extinctioncurve derived for NGC 4753 is similar to the Galactic extinction curve.The dust mass estimated from optical extinction is 1.51 x 105 M? andfrom the far infrared fluxes observed with Infrared AstronomicalSatellite (IRAS) is 3.46 x 105 M?. The dust observed within NGC 4753 canbe argued to be internal in origin.
| 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.
| Supernova Type Ia Luminosities, Their Dependence on Second Parameters, and the Value of H0
A sample of 35 Type Ia supernovae (SNe Ia) with good to excellentphotometry in B and V, minimum internal absorption, and1200
| A neutral hydrogen survey of polar ring galaxies. III. Nançay observations and comparison with published data
A total of 50 optically selected polar ring galaxies, polar ring galaxycandidates and related objects were observed in the 21-cm H i line withthe Nançay decimetric radio telescope and 31 were detected. Theobjects, selected by their optical morphology, are all north ofdeclination -39o, and generally relatively nearby (V< 8000km s-1) and/or bright (mB< 15.5). The H i linedata are presented for all 74 galaxies observed for the survey with theEffelsberg, Green Bank or Nanç radio telescopes, as well as allother published H i line parameters of these objects. Three objects wereobserved and detected by us at Parkes. A total of 59 objects weredetected. For each object a brief description is given based on aliterature search.
| Relaxation in stellar systems, and the shape and rotation of the inner dark halo
Why do galactic bars rotate with high pattern speeds, when dynamicalfriction should rapidly couple the bar to the massive, slowly rotatingdark halo? This long-standing paradox may be resolved by considering thedynamical interactions between the galactic disc and structures in thedark halo. Dynamical friction between small-scale halo structure and thedisc spins up and flattens the inner halo, thereby quenching thedynamical friction exerted by the halo on the bar; at the same time thehalo heats and thickens the inner disc, perhaps forming a rapidlyrotating bulge. Two possible candidates for the required halo structuresare massive black holes and tidal streamers from disrupted precursorhaloes. More generally, gravitational scattering from phase-wrappedinhomogeneities represents a novel relaxation process in stellarsystems, intermediate between violent relaxation and two-bodyrelaxation, which can isotropize the distribution function at radiiwhere two-body relaxation is not effective.
| 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.
| M84: A Warp Caused by Jet-induced Pressure Gradients?
In radio galaxies such as M84 dust features tend to be nearlyperpendicular to radio jets yet are not aligned with the galaxyisophotes. The timescale for precession in the galaxy is short (~10^7 yrat 100 pc), suggesting that an alternative mechanism causes the gas diskto be misaligned with the galaxy. In M84 we estimate the pressure on thedisk required to overcome the torque from the galaxy and find that it issmall compared with the thermal pressure in the hot ambient interstellarmedium estimated from the X-ray emission. We therefore propose thatpressure gradients in a jet-associated hot interstellar medium exert atorque on the gas disk in M84 causing it to be misaligned with thegalaxy isophotal major axis. We propose that active galacticnuclei-associated outflows or associated hot low-density media in nearbyradio galaxies could strongly affect the orientation of their gas diskson 100 pc scales. This mechanism could explain the connection betweengas disk angular momentum and jet axes in nearby radio galaxies. Byintegrating the light of the galaxy through a warped gas and dust diskwe find that the geometry of a gas disk in M84 is likely to differ fromthat predicted from a simple precession model. We find that themorphology of the gas disk in M84 is consistent with a warped geometrywhere precession is caused by a combination of a galactic torque and alarger torque due to pressure gradients in the ambient X-ray-emittinggas. Precession occurs at an axis between the jet and galaxy major axis,but nearer to the jet axis, implying that the pressure torque is 2-4times larger than the galactic torque. We estimate that precession hasoccurred about this particular axis for about 10^7 yr. A better modelfor the morphology of the disk is achieved when precession takes placeabout an elliptical rather than circular path. This suggests that theisobars in the hot medium are strongly dependent on the angle from thejet axis.
| Dust Properties of NGC 4753
We report on BVR surface photometry of a lenticular galaxy, NGC 4753,with prominent dust lanes. We have used the multicolor broadbandphotometry to study dust extinction as a function of wavelength andderived the extinction curve. We find the extinction curve of NGC 4753to be similar to the Galactic extinction curve in the visible region,which implies that the sizes of dust grains responsible for opticalextinction are similar to those in our Galaxy. We derive the dust massfrom optical extinction as well as from the far-infrared fluxes observedwith IRAS. The ratio of the two dust masses, M_d,IRAS/M_d,optical, is2.28 for NGC 4753, which is significantly lower than the value of8.4+/-1.3 found previously for a large sample of elliptical galaxies.The total mass of the observed dust within NGC 4753 is about a factor of10 higher than the mass of dust expected from loss of mass from redgiant stars and destruction by sputtering and grain-grain collisions inlow-velocity shocks and sputtering in supernova-driven blast waves. Wefind evidence for the coexistence of dust and Hα-emitting gaswithin NGC 4753. The current star formation rate of NGC 4753, averagedover the past 2x10^6 yr, is estimated to be less than 0.21 M_solaryr^-1. A substantial amount of dust within NGC 4753 exists in the formof cirrus.
| A Tully-Fisher Relation for S0 Galaxies
We present an I-band Tully-Fisher relation (TFR) for 18 nearby S0galaxies using kinematics derived from long-slit spectroscopy of stellarabsorption lines. Our estimates of the circular velocity, V_c, at 2-3exponential disk scale lengths account for line-of-sight projection andfor the stellar random motions through an asymmetric drift correction.Uniform and accurate distance calibration is available from recentsurface brightness fluctuation measurements. Despite the care taken inestimating both V_c and M_I, the TFR shows an intrinsic scatter of about0.7 mag in M_I or 0.15 in logV_c. This result is surprising, because S0galaxies appear to have both the simple kinematics of disk galaxies andthe simple stellar populations of early-type galaxies. Remarkably, inthis sample of overall rotation-dominated galaxies, the central stellarvelocity dispersion is a better predictor of the total I-band luminosity(through the fundamental plane relations) than the circular speed atseveral exponential scale lengths. Furthermore, the TFR zero point, orthe mean stellar I-band luminosity at a given V_c, differs by only about0.5 mag between our sample of S0s and a comparison sample of late-typespirals, once both data sets are brought onto a consistent distancescale. This offset is less than expected if S0s are former spiralgalaxies with prematurely truncated star formation (>~4 Gyrs ago).
| A search for candidate light echoes: Photometry of supernova environments
Supernova (SN) light echoes could be a powerful tool for determiningdistances to galaxies geometrically, \cite[Sparks (1994)]{S94}. In thispaper we present CCD photometry of the environments of 64 historicalsupernovae, the first results of a program designed to search for lightechoes from these SNe. We commonly find patches of optical emission at,or close to, the sites of the supernovae. The color distribution ofthese patches is broad, and generally consistent with stellar populationcolors, possibly with some reddening. However there are in additionpatches with both unusually red and unusually blue colors. We expectlight echoes to be blue, and while none of the objects are quite as bluein V-R as the known light echo of SN 1991T, there are features that areunusually blue and we identify these as candidate light echoes forfollow-on observations. Tables 2a and 2b are also available at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html and Figs. 1 through 36 are onlyavailable in the online version of the journal athttp://www.edpsciences.com
| Surface VRI photometry and the structure of the dusty galaxy NGC 972.
Not Available
| A Complete Redshift Survey to the Zwicky Catalog Limit in a 2^h X 15 deg Region around 3C 273
We compile 1113 redshifts (648 new measurements, 465 from theliterature) for Zwicky catalog galaxies in the region (-3.5d <= delta<= 8.5d, 11h5 <= alpha <= 13h5). We include redshifts for 114component objects in 78 Zwicky catalog multiplets. The redshift surveyin this region is 99.5% complete to the Zwicky catalog limit, m_Zw =15.7. It is 99.9% complete to m_Zw = 15.5, the CfA Redshift Survey(CfA2) magnitude limit. The survey region is adjacent to the northernportion of CfA2, overlaps the northernmost slice of the Las CampanasRedshift Survey, includes the southern extent of the Virgo Cluster, andis roughly centered on the QSO 3C 273. As in other portions of theZwicky catalog, bright and faint galaxies trace the same large-scalestructure.
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