Contents
Images
Upload your image
DSS Images Other Images
Related articles
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.
| Inner-truncated Disks in Galaxies
We present an analysis of the disk brightness profiles of 218 spiral andlenticular galaxies. At least 28% of disk galaxies exhibit innertruncations in these profiles. There are no significant trends oftruncation incidence with Hubble type, but the incidence among barredsystems is 49%, more than 4 times that for nonbarred galaxies. However,not all barred systems have inner truncations, and not allinner-truncated systems are currently barred. Truncations represent areal dearth of disk stars in the inner regions and are not an artifactof our selection or fitting procedures nor the result of obscuration bydust. Disk surface brightness profiles in the outer regions are wellrepresented by simple exponentials for both truncated and nontruncateddisks. However, truncated and nontruncated systems have systematicallydifferent slopes and central surface brightness parameters for theirdisk brightness distributions. Truncation radii do not appear tocorrelate well with the sizes or brightnesses of the bulges. Thissuggests that the low angular momentum material apparently missing fromthe inner disk was not simply consumed in forming the bulge population.Disk parameters and the statistics of bar orientations in our sampleindicate that the missing stars of the inner disk have not simply beenredistributed azimuthally into bar structures. The sharpness of thebrightness truncations and their locations with respect to othergalactic structures suggest that resonances associated with diskkinematics, or tidal interactions with the mass of bulge stars, might beresponsible for this phenomenon.
| Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
We present central velocity dispersions and Mg2 line indicesfor an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984had no previous measures. This sample contains the largest set ofhomogeneous spectroscopic data for a uniform sample of ellipticalgalaxies in the nearby universe. These galaxies were observed as part ofthe ENEAR project, designed to study the peculiar motions and internalproperties of the local early-type galaxies. Using 523 repeatedobservations of 317 galaxies obtained during different runs, the dataare brought to a common zero point. These multiple observations, takenduring the many runs and different instrumental setups employed for thisproject, are used to derive statistical corrections to the data and arefound to be relatively small, typically <~5% of the velocitydispersion and 0.01 mag in the Mg2 line strength. Typicalerrors are about 8% in velocity dispersion and 0.01 mag inMg2, in good agreement with values published elsewhere.
| Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
| 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 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.
| 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.
| Bulge-Disk Decomposition of 659 Spiral and Lenticular Galaxy Brightness Profiles
We present one of the largest homogeneous sets of spiral and lenticulargalaxy brightness profile decompositions completed to date. The 659galaxies in our sample have been fitted with a de Vaucouleurs law forthe bulge component and an inner-truncated exponential for the diskcomponent. Of the 659 galaxies in the sample, 620 were successfullyfitted with the chosen fitting functions. The fits are generally welldefined, with more than 90% having rms deviations from the observedprofile of less than 0.35 mag. We find no correlations of fittingquality, as measured by these rms residuals, with either morphologicaltype or inclination. Similarly, the estimated errors of the fittedcoefficients show no significant trends with type or inclination. Thesedecompositions form a useful basis for the study of the lightdistributions of spiral and lenticular galaxies. The object base issufficiently large that well-defined samples of galaxies can be selectedfrom it.
| The Southern Sky Redshift Survey
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| The statistics analysis of recent supernovae.
Not Available
| Hydrogen in the Spectrum of SN 1990M: No More?
The detection of hydrogen in the spectra of Type Ia supernovae is matterof recurrent debates, in that it could provide an important constrainton the nature of the progenitors. Currently, the most "robust" evidencefor hydrogen in spectra of Type Ia supernovae is given by an H alphaabsorption line measured by Polcaro & Viotti in an early stagespectrum of SN 1990M. Through the analysis of an unpublished spectrum ofthis object, obtained with the 1.52 m ESO telescope one day after the SNdiscovery, we show that the claimed H alpha detection is originated byan observational bias. Once the subtraction of the parent galaxybackground is properly done, no evidence for an H alpha absorption isfound in the spectrum of SN 1990M. We set a rough upper limit of to thehydrogen abundance in the supernova atmosphere of H/Si <= 2 x 10-6.
| The Canaris Type IA Supernovae Archive (I)
This paper presents an atlas containing 59 low-resolution supernova
spectra which correspond to 27 type Ia supernovae. These 59spectra spectra which correspond to 27 type Ia supernovae. These 59spectra refer to different ages along the postmaximum type Ia evolution,covering from the photospheric to the old (~>300 days) nebularphases. These supernovae were observed as a part of the long-termobservational program Supernova Monitoring Project, carried out at theObservatorio del Roque de los Muchachos (La Palma, Spain) from 1990 Julyto 1994 July. Most of these observations were taken with the FaintObject Spectrograph (FOS) and a few spectra were obtained by means theISIS spectrograph. Three or more spectra were obtained for ten of thesesupernovae. Concerning the homogeneity among the type Ia supernovasubclass, our sample points to a "first-order" overall homogeneousspectroscopic behavior. However, a finer analysis - comparing spectra atsimilar evolutionary phase-allows differences to be found in relation tostrengths, wavelength positions, and evolution with time of the moresignificant spectral type Ia supernova features. Furthermore, someobjects that exhibit clear signs of spectroscopic peculiarities (SNe1991F, 1991bg, and 1991bj) are also included in our sample. The parentgalaxies of these supernovae present redshifts ranging from z = 0.003 toz = 0.07. Four of these (SNe 1991S, 1991ad, 1992R, and 1992ac) wereobserved in galaxies with z~>0.05. Only six events in our sample weredetected in an early-type (i.e., elliptical or lenticular) galaxy,whereas multiple supernova events were detected in five of the parentgalaxies in our supernova sample.
| A comparative study of morphological classifications of APM galaxies
We investigate the consistency of visual morphological classificationsof galaxies by comparing classifications for 831 galaxies from sixindependent observers. The galaxies were classified on laser print copyimages or on computer screen using scans made with the Automated PlateMeasuring (APM) machine. Classifications are compared using the RevisedHubble numerical type index T. We find that individual observers agreewith one another with rms combined dispersions of between 1.3 and 2.3type units, typically about 1.8 units. The dispersions tend to decreaseslightly with increasing angular diameter and, in some cases, withincreasing axial ratio (b/a). The agreement between independentobservers is reasonably good but the scatter is non-negligible. In spiteof the scatter, the Revised Hubble T system can be used to train anautomated galaxy classifier, e.g. an artificial neural network, tohandle the large number of galaxy images that are being compiled in theAPM and other surveys.
| Integrated photoelectric magnitudes and color indices of bright galaxies in the Johnson UBV system
The photoelectric total magnitudes and color indices published in theThird Reference Catalogue of Bright Galaxies (RC3) are based on ananalysis of approximately equals 26,000 B, 25,000 B-V, and 17,000 U-Bmultiaperture measurements available up to mid 1987 from nearly 350sources. This paper provides the full details of the analysis andestimates of internal and external errors in the parameters. Thederivation of the parameters is based on techniques described by theVaucouleurs & Corwin (1977) whereby photoelectric multiaperture dataare fitted by mean Hubble-type-dependent curves which describe theintegral of the B-band flux and the typical B-V and U-B integrated colorgradients. A sophisticated analysis of the residuals of thesemeasurements from the curves was made to allow for the random andsystematic errors that effect such data. The result is a homogeneous setof total magnitudes BTA total colors(B-V)T and (U-B)T, and effective colors(B-V)e and (U-B)e for more than 3000 brightgalaxies in RC3.
| Searching for supernovae--Visually and otherwise
The main features of visual searching for supernovae in other galaxiesby amateur astronomers are described, and an outline is given of theresults which have been achieved so far by this method. A shortcomparison is made between visual searching and photographic searching.A more extensive comparison is then made between visual searching forsupernovae in Australia, and the work of the Berkeley AutomaticSupernova Search at Leuschner Observatory, since 1986. Among theconclusions is the claim that a competent visual observer could producesimilar results to those produced by the Berkeley group if a telescopeof similar aperture was used for a similar amount of observing time, andfrom a good observing site. Indeed, visual searching might possiblyproduce more results, and such a search would only cost a small fractionof what was spent on this automatic search. It would be a worthwhileproject to conduct a visual search with a suitably desinged 76-cmtelescope, or a one metre telescope, over a period of a few years, tosee if this conclusion could be supported in practice.
| Do we really need an interactive binary system to build up asymmetric nebulae?
Not Available
| A catalog of recent supernovae
A listing is given of all supernovae discovered between 1 Jan 1989 and 1Apr 1993. The data show no evidence for a significant dependence of thediscovery probability of supernovae on parent galaxy inclination to theline of sight. If no inclination corrections need to be applied then thesupernova rates in spirals are only about half as large as previouslybelieved. The mean linear separation of supernovae of Type II (SNe II)from the center of their parent galaxy increases with increasingdistance (Shaw effect). The Shaw effect appears less evident, or absent,for (more luminous) supernovae of Type Ia. The data are consistent with,but do not prove, the hypothesis that (presumably reddended) SNe II aremore likely to be discovered in the red than in the blue. Due tointensive surveillance, most bright SNe Ia tend to be found beforemaximum, whereas the majority of faint SNe Ia are discovered aftermaximum light.
| Quantitative morphology of E-S0 galaxies. III. Coded and parametric description of 108 galaxies in a complete sample
A survey has been performed of the morphological and photometricproperties of 108 E-S0 galaxies out of a complete sample of 112: thissample is built from the Revised Shapley-Ames Catalogue (RSA, Sandage& Tammann, 1981) keeping objects with δ>-10deg andV_0_<3000km/s, rejecting SB0's and Local Group dwarfs. The data weremainly derived from our CCD observations at Observatoire deHaute-Provence: the camera allowed fields of 4x7 arcmin (or 7x7 for thelast run), the seeing being generally in the 2-3 arcsec FWHM range. Themeasurements include the isophotal analysis according to Carter's(1978), principles,and the photometric profiles along the two main axis.Opposite semi-axis are measured separately to detect asymmetries.Partial results about strongly flattened galaxies were given anddiscussed in Paper I and II of this series (Michard & Marchal, 1993and 1994). The present paper gives in tabular form: - in Table 2a, 2bthe most useful morphological parameters and a coded description of the108 studied objects. This table includes a revised classificationaccording to Hubble types, this being completed by the subclassificationof ellipticals into "boxy", "disky" and "undeterminate". It alsoincludes the classifications of envelope geometry and disk extent, asintroduced in Paper I. - in Table 3a, b the usual photometric globalparameters, also converted to absolute units for future reference. Thetabular data is completed by individual notes for each galaxy, collectedin an Appendix. A discussion of the present data will be presented in aforthcoming Paper IV : it aims at checking the working hypothesis thatgalaxies of both E and S0 Hubble types belong, but for a small minority,to a common population of objects with similar structures.
| UBVRI photoelectric photometry of bright southern early-type galaxies
UBVRI multi-aperture photometry of 207 bright southern galaxies and of72 objects of an additional list is presented. These observations weremade for obtaining the magnitude scale zero-point as an accuratedetermination of the sky background for a two-dimensional photometryprogram concerning these galaxies. We have also inferred the asymptoticmagnitudes, color indices and effective apertures of these objects. Ourresults are in good agreement with those of others authors.
| Quantitative morphology of E-S0 galaxies IV. Ellipticals and lenticulars as a single population
The geometrical properties of E and S0 galaxies have been intercomparedusing the data collected in Paper III (Michard & Marchal 1994) for108 RSA objects in a complete, luminosity and distance limited, sample.As the apparent flattening (largely an effect of projection along theline of sight), is a determining factor in the segregation between E andS0 objects, the working hypothesis has been made that an important biasis introduced in the recognition of the two classes. It is perhaps aswell to assume that galaxies of both Hubble types belong, but for asmall(?) minority, to a common population of objects with similarstructures. This hypothesis receives strong support from thefrequency-diagrams of the ellipticity ɛ_max_, measured near itsmaximum or at the isophote of surface brightness V=21.5. The diagram forS0's alone cannot be generated by the random projection of any objects:it is clearly biased by the shift to the E type of many S0's of moderateinclination and relatively modest disk. This limits the significance ofthe same diagrams for E galaxies. The noted bias is much reduced if S0'sand disky E's are considered together. Because of the strong outwardsdecrease of the ellipticities in disky E's and in the S0's with non-thinenvelopes (thick disks and spheroidal haloes), the frequency diagrams ofthe ellipticities measured at the classical B=25, or at V=25, do notshow the bias noted above for S0's. The lack of round E's requires thespheroidal components to be faintly triaxial, as recently emphasized byother authors. Our hypothesis is also supported by the overlap of E andS0 galaxies in ad hoc classification schemes of ellipticity profiles andenvelope geometry, and in such correlation diagrams as: - theellipticity in the envelope, i.e. near μ(V)= 25, against theintermediate maximum ellipticity - the extremum of the Carter'scoefficient e_4_ (or a_4_ or c_4_ in other similar works) against themaximum ellipticity - the disk extent, as far as it can be estimatedwithout detailed modeling, against the maximum ellipticity. The"standard" structure of E-S0 objects includes a spheroidal, nearlyoblate component, that cannot be of constant ellipticity: this parameteroften increases outwards from its bulge value, then decreases again inthe envelope. Disks of various brightness and extent, between dominatingand vanishing, are the second essential component. Obviously, theirrelative importance is, together with the dust content, a physicalcriterion involved in the morphological separation between E and S0objects, besides the inclination effect. In the present sample, the diskcannot be detected in nearly half of E classified objects, and isprobably vanishing in about 40% of this class, or circa 17% of the totalof studied early-type objects. This minority contains mostly boxy E'swith non-standard ellipticity profiles, and, as is well known, nosignificant rotational support. From the convergent results ofquantitative morphology and kinematics, the early-type galaxies shouldbe segregated into the majority class of disky fast oblate rotators anda minority class of non-rotating ellipsoids.
| The dependence of the cool matter content on galaxy morphology in galaxies of types E/S0, S0, and SA
Using the material assembled in earlier papers, we examine the manner inwhich the interstellar matter content varies along the Hubble sequencefrom S0 galaxies to Sa galaxies selected from the RSA2 compilation. Forthis we make use of a new and more detailed classification which isdescribed here as applied to these early disk/spiral galaxies. Theprominence of the disk in S0's and the visibility of features (H IIregions) in the Sa's serve as the basis for the subtypes. Three S0categories: subtle, intermediate, and pronounced, and four Sadescriptors: very early, early, intermediate, and late are assigned tothe galaxies. It is found that the total amount of hydrogen (H I + H2)is a function of subtype, being low in the S0's and rising smoothly fromthe early Sa's to the later Sa's. The average surface density ofhydrogen exceeds 3 solar masses/pc-squared only in the latest subtypesof the Sa's. We conclude that the prominence of the disk of a galaxyclosely follows the amount of cool gas which the disk contains.
| Spectroscopic differences between supernovae of type IA in early-type and in late-type galaxies
Published data are used to derive a uniform set of blueshifts in thelambda 6355 feature of Si II for 33 SNe Ia. All seven SNe Ia withblueshifts at 10 days past maximum of 9500 km/s occurred in early-typegalaxies. The observed dependence of Si II blueshift on parent-galaxytype indicates that differing SNe Ia blueshifts are due to globalphysical differences, rather than to asymmetries in their expansion thatare viewed from different directions. It is speculated that SNe Ia withlow expansion velocities might, in the mean, have older progenitors thanthose with high expansion velocities.
| General study of group membership. II - Determination of nearby groups
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
| Interstellar matter in early-type galaxies. II - The relationship between gaseous components and galaxy types
Interstellar components of early-type galaxies are established bygalactic type and luminosity in order to search for relationshipsbetween the different interstellar components and to test thepredictions of theoretical models. Some of the data include observationsof neutral hydrogen, carbon monoxide, and radio continuum emission. Analternative distance model which yields LX varies as LB2.45,a relation which is in conflict with simple cooling flow models, isdiscussed. The dispersion of the X-ray luminosity about this regressionline is unlikely to result from stripping. The striking lack of clearcorrelations between hot and cold interstellar components, takentogether with their morphologies, suggests that the cold gas is a diskphenomenon while the hot gas is a bulge phenomenon, with littleinteraction between the two. The progression of galaxy type from E to Sais not only a sequence of decreasing stellar bulge-to-disk ratio, butalso of hot-to-cold-gas ratio.
| 0.9-1.35-micron spectra of five type IA supernovae near maximum light
Near-infrared (0.9-1.35-micron) spectra of type Ia supernovae 1989B,1989M, 1990M, 1990N, and 1991T obtained 22, 12, 15, -5, and 0 ds,respectively, after maximum B brightness are reported. Two spectra takenafter B maximum (1989B and 1989M) showed the unidentified J-bandabsorption, though with varying shapes and depths. Two spectra taken at,and before MAXIMA do not show the absorption. The dereddened slopes ofthe continua between 0.9 and 1.35 micron exceed that of a Rayleigh-Jeanscontinuum for all but one SN. From the present data and from opticalobservations, it appears that the Ca II IR absorption lines first appearat about the time of B maximum. This suggests that the physicalconditions necessary for their formation may also be connected with theformation of the J-band absorption. Although there are somesimilarities, the near-IR spectra of type Ia supernovae are nothomogeneous.
| Near Infrared Spectral Synthesis in Giant Early Type Galaxies
Not Available
| Groups of galaxies within 80 Mpc. II - The catalogue of groups and group members
This paper gives a catalog of the groups and associations obtained bymeans of a revised hierarchical algorithm applied to a sample of 4143galaxies with diameters larger than 100 arcsec and redshifts smallerthan 6000 km/s. The 264 groups of galaxies obtained in this way (andwhich contain at least three sample galaxies) are listed, with the looseassociations surrounding them and the individual members of eachaggregate as well; moreover, the location of every entity among 13regions corresponding roughly to superclusters is specified. Finally,1729 galaxies belong to the groups, and 466 to the associations, i.e.,the total fraction of galaxies within the various aggregates amounts to53 percent.
| On the external origin for dust in elliptical galaxies
Large samples of elliptical galaxies, observed at high signal-to-noiseratio with CCDs, are used with ADDSCAN 100 micron fluxes from IRAS toexamine evidence for the external origin of dust in these galaxies. Foursmall sets of galaxies are picked which show features stronglyindicative of a merger, that is, infalling H I gas, extensive dustlanes, and kinematically peculiar cores and shells. Though somecounterexamples exist, it is shown that the dust and isophotalproperties are consistent with the current merger model for thesegalaxies.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
