SKY-MAP.ORG
 Home Getting Started To Survive in the Universe News@Sky Astro Photo The Collection Forum Blog New! FAQ Press Login

# NGC 7391

Contents

### Images

DSS Images   Other Images

### Related articles

 Peculiarities and populations in elliptical galaxies. I. An old question revisitedMorphological peculiarities, as defined from isophote asymmetries andnumber of detected shells, jets or similar features, have been estimatedin a sample of 117 E classified galaxies, and qualified by an ad hocΣ2 index. The overall frequency of peculiar'' objects(Pec subsample) is 32.5%. It decreases with the cosmic density of theenvironment, being minimal for the Virgo cluster, the densestenvironment in the sampled volume. This environmental effect is strongerfor galaxies with relatively large Σ2.The Pec subsample objects are compared with normal'' objects (Nopsubsample) as regards their basic properties. Firstly, theysystematically deviate from the Fundamental Plane and the Faber-Jacksonrelation derived for the Nop subsample, being too bright for their mass.Secondly, the dust content of galaxies, as estimated from IRAS fluxes,are similar in both subsamples. Third, the same is true of the frequencyof Kinematically Distinct cores (KDC), suggesting that KDC andmorphological peculiarities do not result from the same events in thehistory of E-galaxies.Using the Nop sample alone, we obtain very tight reference relationsbetween stellar population indicators (U-B, B-V, B-R, V-I,Mg2, Hβ, , Mgb) and the central velocitydispersion σ0. The discussion of the residuals of theserelations allows us to classify the Pec galaxies in two families i.e.the YP or NGC 2865 family, and the NP or NGC 3923 one. Galaxies in thefirst group show consistent evidence for a younger stellar populationmixed with the old one, in agreement with classical results (Schweizeret al. \cite{Schweizer1990}; Schweizer & Seitzer\cite{Schweizer1992}). The second group, however, has normal, orreddish, populations. It is remarkable that a fraction (circa 40%) ofmorphologically perturbed objects do not display any signature of ayoung population, either because the event responsible for thepecularity is too ancient, or because it did not produce significantstar formation (or eventually that the young sub-population has highmetallicity).A preliminary attempt is made to interpret the populations of Pecobjects by combining a young Single Stellar Population with a Nopgalaxy, with only limited success, perhaps largely due to uncertaintiesin the SSP indices used.Based in part on observations collected at the Observatoire deHaute-Provence.Figures \ref{fig1}-\ref{fig3} are only available in electronic form athttp://www.edpsciences.orgTable 10 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/423/833 Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic DataWe 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. Star Formation Histories of Early-Type Galaxies. I. Higher Order Balmer Lines as Age IndicatorsWe have obtained blue integrated spectra of 175 nearby early-typegalaxies, covering a wide range in galaxy velocity dispersion andemphasizing those with σ<100 km s-1. Galaxies havebeen observed both in the Virgo Cluster and in lower densityenvironments. The main goals are the evaluation of higher order Balmerlines as age indicators and differences in stellar populations as afunction of mass, environment, and morphology. In this first paper, ouremphasis is on presenting the methods used to characterize the behaviorof the Balmer lines through evolutionary population synthesis models.Lower σ galaxies exhibit a substantially greater intrinsicscatter, in a variety of line-strength indicators, than do higherσ galaxies, with the large intrinsic scatter setting in below aσ of 100 km s-1. Moreover, a greater contrast inscatter is present in the Balmer lines than in the lines of metalfeatures. Evolutionary synthesis modeling of the observed spectralindexes indicates that the strong Balmer lines found primarily among thelow-σ galaxies are caused by young age, rather than by lowmetallicity. Thus we find a trend between the population age and thecentral velocity dispersion, such that low-σ galaxies have youngerluminosity-weighted mean ages. We have repeated this analysis usingseveral different Balmer lines and find consistent results from onespectral indicator to another. A Test for Large-Scale Systematic Errors in Maps of Galactic ReddeningAccurate maps of Galactic reddening are important for a number ofapplications, such as mapping the peculiar velocity field in the nearbyuniverse. Of particular concern are systematic errors which vary slowlyas a function of position on the sky, as these would induce spuriousbulk flow. We have compared the reddenings of Burstein & Heiles (BH)and those of Schlegel, Finkbeiner, & Davis (SFD) to independentestimates of the reddening, for Galactic latitudes |b|>10^deg. Ourprimary source of Galactic reddening estimates comes from comparing thedifference between the observed B-V colors of early-type galaxies, andthe predicted B-V color determined from the B-V-Mg_2 relation. We havefitted a dipole to the residuals in order to look for large-scalesystematic deviations. There is marginal evidence for a dipolar residualin the comparison between the SFD maps and the observed early-typegalaxy reddenings. If this is due to an error in the SFD maps, then itcan be corrected with a small (13%) multiplicative dipole term. Weargue, however, that this difference is more likely to be due to a small(0.01 mag) systematic error in the measured B-V colors of the early-typegalaxies. This interpretation is supported by a smaller, independentdata set (globular cluster and RR Lyrae stars), which yields a resultinconsistent with the early-type galaxy residual dipole. BH reddeningsare found to have no significant systematic residuals, apart from theknown problem in the region 230^deg Stellar population of ellipticals in different environments: near-infrared spectroscopic observationsNear-infrared spectra of 50 elliptical galaxies in the Pisces, Abell2199 and 2634 clusters, and in the general field, have been obtained.The strength of the CO (2.3-mu m) absorption feature in these galaxiesis used to explore the presence of an intermediate-age population (e.g.asymptotic giant branch stars) in ellipticals in different environments.We find that the strongest evidence for such a population comes fromellipticals in groups of a few members, which we interpret as the resultof recent minor merging of these galaxies with later-type galaxies.Field galaxies from very isolated environments, on the other hand, showno evidence for young or intermediate-age stars as revealed by Hβand CO absorptions, and appear to form a very uniform, old populationwith very little scatter in metallicity and star formation history. Arcsecond Positions of UGC GalaxiesWe 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. A catalogue of Mg_2 indices of galaxies and globular clustersWe present a catalogue of published absorption-line Mg_2 indices ofgalaxies and globular clusters. The catalogue is maintained up-to-datein the HYPERCAT database. The measurements are listed together with thereferences to the articles where the data were published. A codeddescription of the observations is provided. The catalogue gathers 3541measurements for 1491 objects (galaxies or globular clusters) from 55datasets. Compiled raw data for 1060 galaxies are zero-point correctedand transformed to a homogeneous system. Tables 1, 3, and 4 areavailable in electronic form only at the CDS, Strasbourg, via anonymousftp 130.79.128.5. Table 2 is available both in text and electronic form. Kinematical data on early-type galaxies. IV.We present kinematical data for a sample of 25 galaxies. Rotation curvesand velocity-dispersion profiles are determined for 16 objects, whilethe central velocity dispersions are given for the whole sample. This isour fourth paper in a series devoted to the presentation of kinematicaldata on elliptical and S0 galaxies, derived from long-slit absorptionspectroscopy. Based on observations collected at the Observatoire deHaute-Provence. Total magnitude, radius, colour indices, colour gradients and photometric type of galaxiesWe 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. A catalogue of spatially resolved kinematics of galaxies: BibliographyWe present a catalogue of galaxies for which spatially resolved data ontheir internal kinematics have been published; there is no a priorirestriction regarding their morphological type. The catalogue lists thereferences to the articles where the data are published, as well as acoded description of these data: observed emission or absorption lines,velocity or velocity dispersion, radial profile or 2D field, positionangle. Tables 1, 2, and 3 are proposed in electronic form only, and areavailable from the CDS, via anonymous ftp to cdsarc.u-strasbg.fr (to130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html Galaxy clusters in the Perseus-Pisces region. I - Spectroscopic and photometric data for early-type galaxiesWe present new spectroscopic and photometric data for 137 early-typegalaxies in nine clusters and for a set of nearby standard galaxies. Ourspectroscopic data comprise radial velocities, central velocitydispersions, and magnesium line strength indices. We demonstrate thatour new velocity dispersion data can be brought into consistency withthe standard system, to an uncertainty of percent 0.01 dex. From R-bandCCD photometry, we derive the effective diameter, the mean surfacebrightness within the effective diameter, and an R-band diameterequivalent to the Dn parameter of Dressler et al. Internal comparisonsindicate an average error of 0.005 in each measurement of log Dn. Thephotometric data can be brought on to a system consistent with externaldata at the level of 0.5 per cent in distance. An image database. II. Catalogue between δ=-30deg and δ=70deg.A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect. The fundamental plane of early-type galaxies: stellar populations and mass-to-light ratio.We analyse the residuals to the fundamental plane (FP) of ellipticalgalaxies as a function of stellar-population indicators; these are basedon the line-strength parameter Mg_2_ and on UBVRI broad-band colors, andare partly derived from new observations. The effect of the stellarpopulations accounts for approximately half the observed variation ofthe mass-to-light ratio responsible for the FP tilt. The residual tiltcan be explained by the contribution of two additional effects: thedependence of the rotational support, and possibly that of the spatialstructure, on the luminosity. We conclude to a constancy of thedynamical-to-stellar mass ratio. This probably extends to globularclusters as well, but the dominant factor would be here the luminositydependence of the structure rather than that of the stellar population.This result also implies a constancy of the fraction of dark matter overall the scalelength covered by stellar systems. Our compilation ofinternal stellar kinematics of galaxies is appended. A Catalog of Stellar Velocity Dispersions. II. 1994 UpdateA catalog of central velocity dispersion measurements is presented,current through 1993 September. The catalog includes 2474 measurementsof 1563 galaxies. A standard set of 86 galaxies is defined, consistingof galaxies with at least three reliable, concordant measurements. It issuggested that future studies observe some of these standard galaxies sothat different studies can be normalized to a consistent system. Allmeasurements are reduced to a normalized system using these standards. Integrated photoelectric magnitudes and color indices of bright galaxies in the Johnson UBV systemThe 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. Equilibrium and rotational support of elliptical galaxiesIn order to study the contribution of the rotation to the total kineticenergy of elliptical galaxies, we have obtained new rotation curves andvelocity dispersion profiles for 34 galaxies selected for their largeresiduals with respect to the Fundamental Plane. For a sample of 113galaxies from our new observations and the available literature, we haveanalyzed these residuals as a function of the rotational support,quantified by the Vmax/sigma0 parameter. Thecontribution of the rotation to the global equilibrium status ofelliptical galaxies is detected and is found to be in agreement with asimple prediction based on the virial theorem for isotropic rotators.The addition of a rotation term to the Fundamental-Plane relationextends its validity to fast rotators, with even a marginal decrease inits apparent thickness. CCD multi-object spectroscopy of galaxies at the UKSTA CCD detector system has been built for use with the FLAIR multi-objectspectrograph at the UKST. It is shown that using FLAIR, velocities canbe obtained for 80 percent of galaxies sampled uniformly to 16.75 mag.The velocity accuracy for absorption-line redshifts is typically +/-150km/s. These results apply to observations made in the blue (4000-5000 A)spectral range; the proportion of galaxies for which absorption-lineredshifts can be obtained is significantly higher than in initial testswhen only long wavelength (greater than 5000 A) observations werepossible. Using this observational configuration, a survey of galaxiesin nine UKST fields has been completed. A search for features in early-type galaxiesUsing data from the CCD surface-photometry survey of Djorgovski (1985),images of 159 galaxies were examined for the presence of dust lanes,incipient stellar disks, bars, shells, and other features that signifydeviations from elliptical symmetry. The sample contained 116 ellipticalgalaxies, 33 SO galaxies and 10 intermediate galaxies. It was found thatforty-two of the ellipticals either definitely or very likely containdust, either in patches or in well-defined lanes or rings. Five of theE/SO galaxies also show possible or definite dust, as do 15 of the SOs.Three of the elliptical galaxies definitely contain stellar disks, withseveral more possible candidates. The presence of these features inalmost half of the elliptical galaxies studied demonstrates thatelliptical galaxies are not the featureless objects they were oncethought to be. Moreover, the finding of weak stellar disks in some ofthem further blurs the distinction between ellipticals and SOs. Spectroscopy and photometry of elliptical galaxies. III - UBV aperture photometry, CCD photometry, and magnitude-related parametersPhotoelectric aperture photometry of nearly 2000 individual observationsof 449 elliptical galaxies combined with published measurements usingthe self-consistent UVB color catalog developed by Burstein et al.(1987) are presented. The data are placed on a standard magnitude andcolor system, and 'total' magnitudes and effective diameters are derivedby comparison with the standard elliptical magnitude growth curve. Agraphical representation of the standard growth curve and the residualsfrom it for each galaxy are given, and a new diameter measurement Dn ispresented which can be measured reliably for elliptical galaxies andserves as an accurate distance indicator when combined with centralvelocity dispersion. Individual magnitudes, surface brightnesses,effective diameters, and values of Dn are summarized for each galaxy incatalog form. Spectroscopy and photometry of elliptical galaxies. II - The spectroscopic parametersRadial velocities, velocity dispersions, and Mg line-strength indicesare measured for 469 elliptical galaxies using four telescope/detectorconfigurations. The data have been put on a common scale; the scatter ofrepeat measurements indicates an uncertainty of + or - 10 percent and +or - 0.01 mag for single determinations of sigma and Mg2, respectively.A correction for the change in linear aperture size as a function ofdistance has been derived, and mean corrected values of sigma and Mg2are adopted. The galaxies have been assigned to groups by combining thepresent velocities with those in the redshift catalog of Huchra et al.(1983) and using the algorithm of Huchra and Geller (1982). Fundamental properties of elliptical galaxiesThe global properties of elliptical galaxies, such as luminosity,radius, projected velocity dispersion, projected luminosity, etc., forma two-dimensional family. This 'fundamental plane' of ellipticalgalaxies can be defined in observable terms by the velocity dispersionand mean surface brightness. Its thickness is given by the presentmeasurement error bars, and there are no significant indications ofnonlinearity or higher dimensionality. This is indicative of a strongregularity in the process of galaxy formation. The equations of theplane can be used as new, substantially improved distance indicators forelliptical galaxies. However, all morphological parameters whichdescribe the shape of the light distribution (ellipticity, elippticitygradient, isophotal twist rate, slope of the surface brightness profile)and reflect dynamical anisotropies of stars are completely independentof this fundamental plane. Thus, the elliptical galaxies are actually a'2 + N' parameter family. The M/L ratios correlate only with thevelocity dispersions and show a small intrinsic scatter, perhaps onlyabout 30 percent, in a luminosity range spanning some four orders ofmagnitude; this suggests a constant fraction of the dark mattercontribution in elliptical galaxies. A catalog of stellar velocity dispersions. I - Compilation and standard galaxiesA catalog of central stellar velocity dispersion measurements ispresented, current through June 1984. The catalog includes 1096measurements of 725 galaxies. A set of 51 standard galaxies is definedwhich consists of galaxies with at least three reliable, concordantmeasurements. It is suggested that future studies observed some of thesestandard galaxies in the course of their observations so that differentstudies can be normalized to the same system. Previous studies arecompared with the derived standards to determine relative accuracies andto compute scale factors where necessary. Catalogue of central velocity dispersions of galaxiesA total of 880 measurements of velocity dispersions for 546 galaxieshave been compiled. These data have been used to look for biasesintroduced by the observational techniques and reduction procedures. Twomain effects have been corrected for, due to the reference and the slitwidth. A catalog of homogeneous data has been compiled, where the rawdata are corrected for these effects. Mass-to-light ratio of elliptical galaxiesTwo virial formulas, which take into account the observed flattening,are established for oblate ellipticals obeying the r to the 1/4th powerlaw and used to derive the mean mass to light ratios in their centralpart. One of them, which requires the knowledge of only one kinematicalparameter, the central (stellar) velocity dispersion, is applied to 197ellipticals. The other one, which uses in addition the maximum stellarrotation velocity, is shown to be less sensitive to the unknown trueflattenings and to possible velocity anisotropies. It is applied to 30ellipticals. Both methods give a mean blue mass to luminosity ratio ofabout 13, without any clear correlation with the absolute luminosity ofthe galaxy. A survey of galaxy redshifts. IV - The dataThe complete list of the best available radial velocities for the 2401galaxies in the merged Zwicky-Nilson catalog brighter than 14.5mz and with b (II) above +40 deg or below -30 deg ispresented. Almost 60 percent of the redshifts are from the CfA surveyand are accurate to typically 35 km/s. Redshifts for 115 galaxies near the equatorNew redshifts for 115 bright galaxies located near the celestial equatorare reported. The spectra were observed with a blue-sensitivephoton-counting Reticon on the 100-in. DuPont telescope, and theredshifts were derived using the data-analysis system developed for theCfA Redshift Survey. Comparisons with other measured redshifts suggestthat these data are similar in quality to the redshifts measured at Mt.Hopkins for the CfA Redshift Survey; the velocity zero point is good to10 or 15 km/s, with a typical error of 35 km/s for the individualmeasurements.
Submit a new article