Contents
Images
Upload your image
DSS Images Other Images
Related articles
The host galaxy/AGN connection in nearby early-type galaxies. A new view of the origin of the radio-quiet/radio-loud dichotomy?
This is the third in a series of three papers exploring the connectionbetween the multiwavelength properties of AGN in nearby early-typegalaxies and the characteristics of their hosts. Starting from aninitial sample of 332 galaxies, we selected 116 AGN candidates requiringthe detection of a radio source with a flux limit of ~1 mJy, as measuredfrom 5 GHz VLA observations. In Paper I we classified the objects withavailable archival HST images into "core" and "power-law" galaxies,discriminating on the basis of the nuclear slope of their brightnessprofiles. We used HST and Chandra data to isolate the nuclear emissionof these galaxies in the optical and X-ray bands, thus enabling us (oncecombined with the radio data) to study the multiwavelength behaviour oftheir nuclei. The properties of the nuclei hosted by the 29 coregalaxies were presented in Paper II Core galaxies invariably host aradio-loud nucleus, with a median radio-loudness of Log R = 3.6 and anX-ray based radio-loudness parameter of Log RX = -1.3. Herewe discuss the properties of the nuclei of the 22 "power-law" galaxies.They show a substantial excess of optical and X-ray emission withrespect to core galaxies at the same level of radio luminosity.Conversely, their radio-loudness parameters, Log R 1.6 and LogRX -3.3, are similar to those measured in Seyfertgalaxies. Thus the radio-loudness of AGN hosted by early-type galaxiesappears to be univocally related to the host's brightness profile:radio-loud AGN are only hosted by core galaxies, while radio-quiet AGNare found only in power-law galaxies. The brightness profile isdetermined by the galaxy's evolution, through its merger history; ourresults suggest that the same process sets the AGN flavour. In thisscenario, the black holes hosted by the merging galaxies rapidly sinktoward the centre of the newly formed object, setting its nuclearconfiguration, described by e.g. the total mass, spin, mass ratio, orseparation of the SMBHs. These parameters are most likely at the originof the different levels of the AGN radio-loudness. This connection mightopen a new path toward understanding the origin of theradio-loud/radio-quiet AGN dichotomy and provide us with a further toolfor exploring the co-evolution of galaxies and supermassive black holes.
| A wide-field HI study of the NGC 1566 group
We report on neutral hydrogen observations of a ~ 5.5 × 5.5deg2 field around the NGC 1566 galaxy group with themultibeam narrow-band system on the 64-m Parkes Telescope. We detected13 HI sources in the field, including two galaxies not previously knownto be members of the group, bringing the total number of confirmedgalaxies in this group to 26. Each of the HI galaxies can be associatedwith an optically catalogued galaxy. No `intergalactic HI clouds' werefound to an HI mass limit of ~3.5 ×108Msolar. We have estimated the expected HIcontent of the late-type galaxies in this group and find that the totaldetected HI is consistent with our expectations. However, while noglobal HI deficiency is inferred for this group, two galaxies exhibitindividual HI deficiencies. Further observations are needed to determinethe gas removal mechanisms in these galaxies.
| The host galaxy/AGN connection in nearby early-type galaxies. Sample selection and hosts brightness profiles
This is the first of a series of three papers exploring the connectionbetween the multiwavelength properties of AGNs in nearby early-typegalaxies and the characteristics of their hosts. We selected twosamples, both with high resolution 5 GHz VLA observations available andproviding measurements down to 1 mJy level, reaching radio-luminositiesas low as 1019 W Hz-1. We focus on the 116radio-detected galaxies as to boost the fraction of AGN with respect toa purely optically selected sample. Here we present the analysis of theoptical brightness profiles based on archival HST images, available for65 objects. We separate early-type galaxies on the basis of the slope oftheir nuclear brightness profiles, into core and power-law galaxiesfollowing the Nuker's scheme, rather than on the traditionalmorphological classification (i.e. into E and S0 galaxies). Our sampleof AGN candidates is indistinguishable, when their brightness profilesare concerned, from galaxies of similar optical luminosity but hostingweaker (or no) radio-sources. We confirm previous findings thatrelatively bright radio-sources (Lr > 1021.5 WHz-1) are uniquely associated to core galaxies. However,below this threshold in radio-luminosity core and power-law galaxiescoexist and they do not show any apparent difference in theirradio-properties. Not surprisingly, since our sample is deliberatelybiased to favour the inclusion of active galaxies, we found a higherfraction of optically nucleated galaxies. Addressing the multiwavelengthproperties of these nuclei will be the aim of the two forthcomingpapers.
| Tidally Triggered Star Formation in Close Pairs of Galaxies. II. Constraints on Burst Strengths and Ages
Galaxy-galaxy interactions rearrange the baryons in galaxies and triggersubstantial star formation; the aggregate effects of these interactionson the evolutionary histories of galaxies in the universe are poorlyunderstood. We combine B- and R-band photometry and optical spectroscopyto estimate the strengths and timescales of bursts of triggered starformation in the centers of 190 galaxies in pairs and compact groups.Based on an analysis of the measured colors and EW(Hα), wecharacterize the preexisting and triggered populations separately. Thebest-fitting burst scenarios assume stronger reddening corrections forline emission than for the continuum and continuous star formationlasting for >~100 Myr. The most realistic scenarios require aninitial mass function that is deficient in the highest mass stars. Thecolor of the preexisting stellar population is the most significantsource of uncertainty. Triggered star formation contributessubstantially (probably >~50%) to the R-band flux in the centralregions of several galaxies; tidal tails do not necessarily accompanythis star formation. Many of the galaxies in our sample have bluercenters than outskirts, suggesting that pre- or nonmerger interactionsmay lead to evolution along the Hubble sequence. These objects wouldappear blue and compact at higher redshifts; the older, redder outskirtsof the disks would be difficult to detect. Our data indicate thatgalaxies with larger separations on the sky contain weaker, and probablyolder, bursts of star formation on average. However, confirmation ofthese trends requires further constraints on the colors of the olderstellar populations and on the reddening for individual galaxies.
| 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
| Galaxy cores as relics of black hole mergers
We investigate the hypothesis that the cores of elliptical galaxies andbulges are created from the binding energy liberated by the coalescenceof supermassive binary black holes during galaxy mergers. Assuming thatthe central density profiles of galaxies were initially steep powerlaws, ρ ~r -2 , we define the `mass deficit' as the massin stars that had to be removed from the nucleus in order to produce theobserved core. We use non-parametric deprojection to compute the massdeficit in a sample of 35 early-type galaxies with high-resolutionimaging data. We find that the mass deficit correlates well with themass of the nuclear black hole, consistent with the predictions ofmerger models. We argue that cores in haloes of non-interacting darkmatter particles should be comparable in size to those observed in thestars.
| Nuclear Cusps and Cores in Early-Type Galaxies as Relics of Binary Black Hole Mergers
We present an analysis of the central cusp slopes and core parameters ofearly-type galaxies using a large database of surface brightnessprofiles obtained from Hubble Space Telescope observations. We examinethe relation between the central cusp slopes, core parameters, and blackhole masses in early-type galaxies, in light of two models that attemptto explain the formation of cores and density cusps via the dynamicalinfluence of black holes. Contrary to the expectations fromadiabatic-growth models, we find that the cusp slopes do not steepenwith increasing black hole mass fraction. Moreover, a comparison ofkinematic black hole mass measurements with the masses predicted by theadiabatic models shows that they overpredict the masses by a factor of~3. Simulations involving binary black hole mergers predict that boththe size of the core and the central mass deficit correlate with thefinal black hole mass. These relations are qualitatively supported bythe present data.
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| Relation between dust and radio luminosity in optically selected early type galaxies
We have surveyed an optical/IR selected sample of nearby E/S0 galaxieswith and without nuclear dust structures with the VLA at 3.6 cm to asensitivity of 100 mu Jy. We can construct a Radio Luminosity Function(RLF) of these galaxies to ~ 1019 W Hz-1 and findthat ~ 50% of these galaxies have AGNs at this level. The space densityof these AGNs equals that of starburst galaxies at this luminosity.Several dust-free galaxies have low luminosity radio cores, and theirRLF is not significantly less than that of the dusty galaxies.
| A targeted survey for H i clouds in galaxy groups
Five galaxy groups with properties similar to those of the Local Grouphave been surveyed for Hi clouds with the Arecibo Telescope. In total300 pointings have been observed on grids of approximately2.5×1.5Mpc2 centred on the groups. The 4.5σdetection limit on the minimal detectable Hi masses is approximately7×106Msolar(H0=65kms-1Mpc-1). All detections couldbe attributed to optical galaxies; no significant detections of Hiclouds have been made. This null result leads to the conclusion that thetotal Hi mass of intragroup clouds must be less than 10 per cent of thetotal Hi mass of galaxy groups and less than 0.05 per cent of thedynamical mass. The recent hypothesis that Galactic high-velocity cloudsare Local Group satellite galaxies is highly inconsistent with theseobservations.
| Dusty Nuclear Disks and Filaments in Early-Type Galaxies
We examine the dust properties of a nearby distance-limited sample ofearly-type galaxies using WFPC2 of the Hubble Space Telescope. Dust isdetected in 29 out of 67 galaxies (43%), including 12 with small nucleardusty disks. In a separate sample of 40 galaxies biased for thedetection of dust by virtue of their detection in IRAS 100 μm band,dust is found in ~78% of the galaxies, 15 of which contain dusty disks.In those galaxies with detectable dust, the apparent mass of the dustcorrelates with radio and far-infrared luminosity, becoming moresignificant for systems with filamentary dust. A majority of IRAS andradio detections are also associated with dusty galaxies rather thandustless galaxies. This indicates that thermal emission from clumpy,filamentary dust is the main source of the far-IR radiation inearly-type galaxies. Dust in small disklike morphology tends to be wellaligned with the major axis of the host galaxies, while filamentary dustappears to be more randomly distributed with no preference for alignmentwith any major galactic structure. This suggests that, if the dustydisks and filaments have a common origin, the dust originates externallyand requires time to dynamically relax and settle in the galaxypotential in the form of compact disks. More galaxies with visible dustthan without dust display emission lines, indicative of ionized gas,although such nuclear activity does not show a preference for dusty diskover filamentary dust. There appears to be a weak relationship betweenthe mass of the dusty disks and central velocity dispersion of thegalaxy, suggesting a connection with a similar recently recognizedrelationship between the latter and the black hole mass. Based onobservations with the NASA/ESA Hubble Space Telescope, obtained at theSpace Telescope Science Institute, which is operated by the Associationof Universities for Research in Astronomy, Inc., under NASA contractNAS5-26555.
| WFPC2 Images of the Central Regions of Early-Type Galaxies. I. The Data
We present high-resolution R-band images of the central regions of 67early-type galaxies obtained with the Wide Field and Planetary Camera 2(WFPC2) aboard the Hubble Space Telescope (HST). This homogeneouslyselected sample roughly doubles the number of early-type galaxies thathave now been imaged at HST resolution and complements similar data onthe central regions of radio galaxies and the bulges of spiral galaxies.Our sample strikingly confirms the complex morphologies of the centralregions of early-type galaxies which have become apparent from previousstudies with HST. In particular, we detect dust, either in the form ofnuclear disks or with a filamentary distribution, in 43% of allgalaxies, in good agreement with previous estimates. In addition, wefind evidence for embedded stellar disks in a remarkably large fractionof 51%. In 14 of those galaxies the disklike structures are misalignedwith the main galaxy, suggesting that they correspond to stellar bars inS0 galaxies. We analyze the luminosity profiles of the galaxies in oursample and classify galaxies according to their central cusp slope. To alarge extent we confirm the results from previous HST surveys in thatearly-type galaxies reveal a clear dichotomy: the bright ellipticals(MB<~-20.5) are generally boxy and have luminosityprofiles that break from steep outer power laws to shallow inner cusps(referred to as ``core'' galaxies). The fainter ellipticals, on theother hand, typically have disky isophotes and luminosity profiles thatlack a clear break and have a steep central cusp (referred to as``power-law'' galaxies). The advantages and shortcomings ofclassification schemes utilizing the extrapolated central cusp slopeγ are discussed, and it is shown that γ might be aninadequate representation for galaxies whose luminosity profile slopechanges smoothly with radius rather than resembling a broken power law.Thus, we introduce a new, alternative parameter and show how thisaffects the classification. In fact, we find evidence for an``intermediate'' class of galaxies that cannot unambiguously beclassified as either core or power-law galaxies and that have centralcusp slopes and absolute magnitudes intermediate between those of coreand power-law galaxies. It is unclear at present, however, whether thesegalaxies make up a physically distinct class or whether distance and/orresolution effects cause them to lose their distinct core or power-lawcharacteristics.
| 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.
| A Subarcsecond Resolution Near-Infrared Study of Seyfert and ``Normal'' Galaxies. II. Morphology
We present a detailed study of the bar fraction in the CfA sample ofSeyfert galaxies and in a carefully selected control sample of nonactivegalaxies to investigate the relation between the presence of bars and ofnuclear activity. To avoid the problems related to bar classification inthe Third Reference Catalogue (RC3), e.g., subjectivity, low resolution,and contamination by dust, we have developed an objective barclassification method, which we conservatively apply to our newsubarcsecond resolution near-infrared (NIR) imaging data set discussedin the first paper in this series. We are able to use stringent criteriabased on radial profiles of ellipticity and major axis position angle todetermine the presence of a bar and its axial ratio. Concentrating onnoninteracting galaxies in our sample for which morphologicalinformation can be obtained, we find that Seyfert hosts are barred moreoften (79%+/-7.5%) than the nonactive galaxies in our control sample(59%+/-9%), a result which is at the ~2.5 σ significance level.The fraction of nonaxisymmetric hosts becomes even larger wheninteracting galaxies are taken into account. We discuss the implicationsof this result for the fueling of central activity by large-scale bars.This paper improves on previous work by means of imaging at higherspatial resolution and by the use of a set of stringent criteria for barpresence and confirms that the use of NIR is superior to optical imagingfor detection of bars in disk galaxies.
| 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.
| A Subarcsecond-Resolution Near-Infrared Study of Seyfert and ``Normal'' Galaxies. I. Imaging Data
We present new high-resolution near-infrared observations in the J, H,and K bands, obtained to study the properties of Seyfert host galaxies.The data set consists of images in the three bands of practically theentire CfA sample of Seyfert galaxies, and K-band images of a controlsample of nonactive, ``normal,'' galaxies, matched to the Seyfert samplein the distribution of type and inclination. The spatial resolution andsampling of the new images is a factor of 2 better than previouslypublished K-band data. In this paper, we present the data in the form ofprofiles of surface brightness and color, ellipticity and major axisposition angle, as well as gray-scale maps of surface brightness in H orK and both J-H and H-K colors. We compare our surface brightness andcolor profiles with the literature and find good agreement. Our data arediscussed in detail in three subsequent publications, where we analyzethe morphologies of Seyfert and normal hosts, quantify the strength ofnonaxisymmetric features in disks and their relationship to nuclearactivity, address the question of bar fraction in Seyferts and normalgalaxies, and analyze the color information in the framework of emissionmechanisms in Seyfert 1's and 2's and in nonactive galaxies.
| 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.
| Molecular Gas in Elliptical Galaxies: CO Observations of an IRAS Flux-limited Sample
A search for CO(2-1) emission from 42 early-type galaxies with 100micron flux densities greater than 1 Jy detected (tentatively in somecases) 11 galaxies and tentatively found absorption against the activenucleus in two. Data from this survey and from the literature show thatthe overall detection rate of CO emission or absorption in ellipticalgalaxies is 45% and that the detection rate increases with increasing100 micron flux density. The data suggest that all elliptical galaxiescontain a small amount of cold interstellar matter. The CO andfar-infrared fluxes are well correlated, though the relationship shows alot of scatter, which does not appear to be caused by variations in thetemperature of the interstellar dust and probably indicates differencesin the physical state of the interstellar medium from galaxy to galaxy.The CO flux densities are completely uncorrelated with the galacticstarlight. The detection of CO emission shows that many ellipticalgalaxies have dense cold gas in their inner regions. The four galaxieswhich are known to have CO absorption, including the two from thepresent paper, have relatively narrow absorption components which are atthe galaxy's systemic velocity and/or redshifted with respect to thisvelocity, consistent with infall to the center of the galaxy.
| 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.
| Core properties of elliptical galaxies - I. A northern hemisphere sample at high resolution
We introduce an ongoing survey of core properties of elliptical galaxiesand present the first results from high-resolution direct imaging of asubsample. The data were obtained in the V, R and I bands at the NOTtelescope, with median seeings of 0.69, 0.65 and 0.62 arcsec FWHM,respectively. We determine the `classical' core parameters, and weintroduce a new parameter, pi_c, which is a measure of the deviation ofthe observed brightness profile from an isothermal profile, pi_cmeasures the intensity of a central brightness concentration in excessof an isothermal model, relative to the intensity of the core. Measuringpi_c for the objects presented here, we find that only five of 22objects are consistent with pi_c=0 at the 1sigma level, and that 14 of22 are inconsistent with pi_c at the 3sigma level. We see no evidencefor significant colour difference (in V, R and I) between the centralspike and the rest of the core, except for M87 and NGC 4278. For theremaining galaxies we find that the colours of the spike must matchthose of the core to within 0.4 mag. We conclude that the majority ofall ellipticals seem to have central intensity concentrations in therange 1-10 per cent of the core flux.
| Velocity dispersions for elliptical galaxies. I. First set of measurements.
Measurements of central velocity dispersions and heliocentric radialvelocities are presented for 94 field galaxies. Among these, 5 newradial velocities and 80 new central velocity dispersions are obtained.Reduction was performed independently by cross-correlation,Fourier-quotient and Fourier-correlation-quotient methods.
| Metallicity gradients in early-type galaxies
A study of medium-to-bright early-type galaxies in six bandpasses from3500 A to 2.2 microns is presented in order to quantify their colors andcolor gradients and relate these to metallicity and properties of theunderlying stellar population. The Stromgren filter system chosen makesit possible to introduce a new calibration to the Mg(2) system from thepresent narrow-band v - y indices. A comparison is presented ofnarrow-band colors centered on particular spectral features vs a colordominated by the mean temperature of the giant branch (i.e., J - K) totest the effects of light vs heavy element abundances on knowledge ofthe total system metallicity, Z, and the effects of reddening. A goodcorrelation is found between v - y and Mg(2); it provides a connectionbetween one light element metallicity indicator (v - y centers on the CNblend) and another, Mg. The color-magnitude relations for all fiveoptical and near-IR colors are shown. The strongest correlation existsfor the metallicity colors, v - y and J - K.
| 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.
| Velocity differences in binary galaxies. I - Suggestions for a nonmonotonic, two-component distribution
A compilation of published high-precision velocities for 107 isolatedgalaxies is presented and used to obtain the distribution function oftheir velocity differences. The distribution shows a peak at the zerodifference as expected, but it also exhibits a preference for valuesnear 72 km/2. The distribution function declines smoothly beyond about72 km/s, with no significant peaks at multiples of 72 km/s, as claimedby Tifft (1977, 1980, 1982). It is argued that criteria for selectionprocedures on binary galaxy samples which are defined on the basis oftoo narrow a projected separation in the sky can produce a nonmonotonicdistribution if the orbits are eccentric. Such orbits can produce astrong secondary peak only if the level of incompleteness inbinary-galaxy samples is quite high, suggesting that the presentstatistical estimates of the masses of binary galaxies should bereevaluated.
| H I content and FIR emission of S0 galaxies
A sample of 252 S0 galaxies is used to study the relationship between HI content and far-IR emission. Logarithms of the H I content versus thefar-IR emission are employed statistically to develop a best-fit linearregression line which is compared to a slope of approximately unity. Theslopes are different for S0 and SB0 galaxies versus S0/a and SB0/agalaxies. The distribution of the 60-100 micron flux ratio is notsignificantly affected by the presence or absence of bars nor by thedifferences between the S0 and S0/a systems. The flux ratio is higherthan the critical value of Helou in 34 percent of the cases, and thevalue holds when nuclear emission is taken into account. In cases wherethe critical value is exceeded, most far-IR emissions are expected to bedue to star formation. S0 galaxies are generally found to have a normalISM, except where the systems have accreted their H I gas. Systems withdisproportionate FIR emission can be considered galaxies that areexperiencing enhanced star formation or that have had their H I gasswept away.
| Radio-continuum sources in nearby and bright E/S0 galaxies - Active nuclei versus star formation
Results of a sensitive VLA survey of nearby E/S0 galaxies are presented.The 204 galaxies surveyed, plus 12 additional galaxies with existing VLAimages, comprise a volume- and optical magnitude-limited sample. Thediscussion focuses on the relation between radio powers and opticalluminosities, whether the radio emission is driven by an active nucleusor by recent star formation, and what galaxian properties might enhancenuclear activity in an elliptical galaxy. It is suggested that the 67ellipticals in the sample should be targets of sensitive searches forHI, optical emission-line gas, and X-ray emitting gas.
| Radio-continuum sources in nearby and bright E/S0 galaxies - Sample selection and well-studied cases
A volume-limited sample of 216 nearby and optically bright E/S0 galaxieshas been compiled. Twelve of the galaxies are confirmed radio sourcesfor which VLA images are available. Most of the remaining galaxies havepowers less than or of the order of 10 to the 21st-22nd W/Hz, and thisinformation is used to establish the parameters of a new VLA survey ofthese galaxies. The basic optical properties of the galaxies in thesample are tabulated.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
