תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
Globular Cluster Systems in Brightest Cluster Galaxies: Bimodal Metallicity Distributions and the Nature of the High-Luminosity Clusters
We present new (B, I) photometry for the globular cluster systems ineight brightest cluster galaxies (BCGs), obtained with the ACS/WFCcamera on the Hubble Space Telescope. In the very rich cluster systemsthat reside within these giant galaxies, we find that all have stronglybimodal color distributions that are clearly resolved by themetallicity-sensitive (B-I) index. Furthermore, the mean colors andinternal color range of the blue subpopulation are remarkably similarfrom one galaxy to the next, to well within the +/-0.02-0.03 maguncertainties in the foreground reddenings and photometric zero points.By contrast, the mean color and internal color range for the redsubpopulation differ from one galaxy to the next by twice as much as theblue population. All the BCGs show population gradients, with muchhigher relative numbers of red clusters within 5 kpc of their centers,consistent with their having formed at later times than the blue,metal-poor population. A striking new feature of the color distributionsemerging from our data is that for the brightest clusters(MI<-10.5) the color distribution becomes broad and lessobviously bimodal. This effect was first noticed by Ostrov et al. andDirsch et al. for the Fornax giant NGC 1399; our data suggest that itmay be a characteristic of many BCGs and perhaps other large galaxies.Our data indicate that the blue (metal-poor) clusters brighter thanMI~=-10 become progressively redder with increasingluminosity, following a mass/metallicity scaling relationZ~M0.55. A basically similar relation has been found for M87by Strader et al. (2005). We argue that these GCS characteristics areconsistent with a hierarchical-merging galaxy formation picture in whichthe metal-poor clusters formed in protogalactic clouds or densestarburst complexes with gas masses in the range107-1010 Msolar, but where the moremassive clusters on average formed in bigger clouds with deeperpotential wells where more preenrichment could occur.
| Stellar populations in a complete sample of local radio galaxies
We investigate the nature of the continuum emission and stellarpopulations in the inner 1-3 kpc of a complete sample of 24 southernradio galaxies, and we compare the results with a control sample of 18non-active early-type galaxies. 12 of the radio galaxies are classifiedas Fanaroff-Riley type I (FR I), eight as FR II and four as intermediateor undefined type (FR x). Optical long-slit spectra are used to performspectral synthesis as a function of distance from the nucleus at anaverage sampling of 0.5-1.0 kpc and to quantify the relativecontributions of a blue featureless continuum and stellar populationcomponents of different ages. Our main finding is a systematicdifference between the stellar populations of the radio and controlsample galaxies: the former have a larger contribution from anintermediate-age (1 Gyr) component, suggesting a connection between thepresent radio activity and a starburst which occurred ~1 Gyr ago. Inaddition, we find a correlation between the contribution of the 1-Gyrcomponent and the radio power, suggesting that more massive starburstshave led to more powerful radio emission. A similar relation is foundbetween the radio power and the mean age of the stellar population, inthe sense that stronger nuclear activity is found in younger galaxies.We also find that the stellar populations of FR I galaxies are, onaverage, older and more homogeneous than those of FR IIs. Significantpopulation gradients were found in only four radio galaxies, which arealso those with more than 10 per cent of their total flux at 4020Åcontributed by age components younger than 100 Myr and/or afeatureless continuum (indistinguishable from a 3-Myr-old stellarpopulation).
| Minor-axis velocity gradients in disk galaxies
We present the ionized-gas kinematics and photometry of a sample of 4spiral galaxies which are characterized by a zero-velocity plateau alongthe major axis and a velocity gradient along the minor axis,respectively. By combining these new kinematical data with thoseavailable in the literature for the ionized-gas component of the S0s andspirals listed in the Revised Shapley-Ames Catalog of Bright Galaxies werealized that about 50% of unbarred galaxies show a remarkable gasvelocity gradient along the optical minor axis. This fraction rises toabout 60% if we include unbarred galaxies with an irregular velocityprofile along the minor axis. This phenomenon is observed all along theHubble sequence of disk galaxies, and it is particularly frequent inearly-type spirals. Since minor-axis velocity gradients are unexpectedif the gas is moving onto circular orbits in a disk coplanar to thestellar one, we conclude that non-circular and off-plane gas motions arenot rare in the inner regions of disk galaxies.Based on observations carried out at the European Southern Observatoryin La Silla (Chile) (ESO 69.B-0706 and 70.B-0338), with the MultipleMirror Telescope which is a joint facility of the SmithsonianInstitution and the University of Arizona, and with the ItalianTelescopio Nazionale Galileo (AOT-5, 3-18) at the Observatorio del Roquede los Muchachos in La Palma (Spain).Table 1 is only available in electronic form athttp://www.edpsciences.org. Table 5 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/507
| Stellar population gradients in Seyfert 2 galaxies: northern sample
We use high signal-to-noise ratio long-slit spectra in theλλ3600-4700 range of the 20 brightest northern Seyfert 2galaxies to study the variation of the stellar population properties asa function of distance from the nucleus. In order to characterize thestellar population and other continuum sources (e.g. featurelesscontinuum, FC) we have measured the equivalent width, W, of sixabsorption features, four continuum colours and their radial variations,and performed spectral population synthesis as a function of distancefrom the nucleus. About half of the sample has CaIIK and G band W valuessmaller at the nucleus than at 1 kpc from it, owing to a youngerpopulation and/or FC. The stellar population synthesis shows that, whileat the nucleus, 75 per cent of the galaxies present contribution >20per cent of ages <=100 Myr and/or of an FC, this proportion decreasesto 45 per cent at 3 kpc. In particular, 55 per cent of the galaxies havea contribution >10 per cent of the 3-Myr/FC component (a degeneratecomponent in which one cannot separate what is caused by an FC or by a3-Myr stellar population) at the nucleus, but only 25 per cent of themhave this contribution at 3 kpc. As a reference, the stellar populationof 10 non-Seyfert galaxies, spanning the Hubble types of the Seyfert(from S0 to Sc) was also studied. A comparison between the stellarpopulation of the Seyferts and that of the non-Seyferts shows systematicdifferences: the contribution of ages younger than 1 Gyr is in mostcases larger in the Seyfert galaxies than in non-Seyferts, not only atthe nucleus but up to 1 kpc from it.
| Inner polar disks in early-type spiral galaxies
We measured a remarkable gas velocity gradient along the minor axis of anumber of early-type spiral galaxies. This phenomenon suggests thepresence of a kinematically-decoupled component in orthogonal rotationwith respect to the galaxy disk which we named inner polar disk. If thisis the case a second event has taken place in the history of the galaxy.Alternatively the gas velocity gradient is the result of non-circularmotions induced by the potential of a triaxial bulge.
| 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.
| Minor-axis velocity gradients in spirals and the case of inner polar disks
We measured the ionized-gas and stellar kinematics along the major andminor axis of a sample of 10 early-type spirals. Much to our surprise wefound a remarkable gas velocity gradient along the minor axis of 8 ofthem. According to the kinematic features observed in their ionized-gasvelocity fields, we divide our sample galaxies in three classes ofobjects. (i) NGC 4984, NGC 7213, and NGC 7377 show an overall velocitycurve along the minor axis without zero-velocity points, out to the lastmeasured radius, which is interpreted as due to the warped structure ofthe gaseous disk. (ii) NGC 3885, NGC 4224, and NGC 4586 arecharacterized by a velocity gradient along both major and minor axis,although non-zero velocities along the minor axis are confined to thecentral regions. Such gas kinematics have been explained as being due tonon-circular motions induced by a triaxial potential. (iii) NGC 2855 andNGC 7049 show a change of slope of the velocity gradient measured alongthe major axis (which is shallower in the center and steeper away fromthe nucleus), as well as non-zero gas velocities in the central regionsof the minor axis. This has been attributed to the presence of akinematically-decoupled gaseous component in orthogonal rotation withrespect to the galaxy disk, namely an inner polar disk. The case andorigin of inner polar disks are discussed and the list of their hostgalaxies is presented.Based on observations carried out at the European Southern Observatory(ESO 62.A-0463 and 63.N-0305).Tables 3 and 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/408/873
| Galaxy interactions - poor starburst triggers. III. A study of a complete sample of interacting galaxies
We report on a study of tidally triggered star formation in galaxiesbased on spectroscopic/photometric observations in the optical/near-IRof a magnitude limited sample of 59 systems of interacting and merginggalaxies and a comparison sample of 38 normal isolated galaxies. From astatistical point of view the sample gives us a unique opportunity totrace the effects of tidally induced star formation. In contrast toresults from previous investigations, our global UBV colours do notsupport a significant enhancement of starforming activity in theinteracting/merging galaxies. We also show that, contrary to previousclaims, there is no significantly increased scatter in the colours ofArp galaxies as compared to normal galaxies. We do find support formoderate (a factor of ~ 2-3) increase in star formation in the verycentres of the interacting galaxies of our sample, contributingmarginally to the total luminosity. The interacting and in particularthe merging galaxies are characterized by increased far infrared(hereafter FIR) luminosities and temperatures that weakly correlate withthe central activity. The LFIR/LB ratio however,is remarkably similar in the two samples, indicating that truestarbursts normally are not hiding in the central regions of the FIRluminous cases. The gas mass-to-luminosity ratio in optical-IR ispractically independent of luminosity, lending further support to thepaucity of true massive starburst galaxies triggered byinteractions/mergers. We estimate the frequency of such cases to be ofthe order of ~ 0.1% of the galaxies in an apparent magnitude limitedsample. Our conclusion is that interacting and merging galaxies, fromthe global star formation aspect, generally do not differ dramaticallyfrom scaled up versions of normal, isolated galaxies. No drastic changewith redshift is expected. One consequence is that galaxy formationprobably continued over a long period of time and did not peak at aspecific redshift. The effects of massive starbursts, like blowoutscaused by superwinds and cosmic reionization caused by starburstpopulations would also be less important than what is normally assumed.Based on observations collected at the European Southern Observatory, LaSilla, Chile.
| 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
| Extended H I Disks in Dust Lane Elliptical Galaxies
We present the results of H I observations of five dust lane ellipticalgalaxies with the Australia Telescope Compact Array. Two galaxies (NGC3108 and NGC 1947) are detected, and sensitive upper limits are obtainedfor the other three. In the two detected galaxies, the H I isdistributed in a regular, extended, and warped disklike structure of lowsurface brightness. Adding data from the literature, we find thatseveral more dust lane elliptical galaxies have regular H I structures.This H I is likely to be a remnant of accretions and/or mergers thattook place a considerable time ago and in which a significant fractionof the gas survived to form a disk. The presence of regular H Istructures suggests that some mergers lead to galaxies with extended lowsurface brightness density gas disks. These gas disks will evolve veryslowly, and these elliptical galaxies will remain gas-rich for a longperiod of time. One of the galaxies we observed (NGC 3108) has a verylarge amount of neutral hydrogen(MHI=4.5×109 MsolarMHI/LB~0.09), which is very regularly distributedin an annulus extending to a radius of ~6 Reff. Thekinematics of the H I distribution suggest that the rotation curve ofNGC 3108 is flat out to at least the last observed point. We estimate amass-to-light ratio of M/LB~18Msolar/LB,solar at a radius of ~6Refffrom the center. Several of the galaxies we observed have an unusuallylow gas-to-dust ratio MHI/Mdust, suggesting thattheir cold interstellar medium, if present as expected from the presenceof dust, may be mainly in molecular rather than atomic form. Based onobservations with the Australia Telescope Compact Array (ATCA), which isfunded by the Commonwealth of Australia for operation as a NationalFacility managed by CSIRO.
| Line-strength indices and velocity dispersions for 148 early-type galaxies in different environments
We have derived high quality line-strength indices and velocitydispersions for a sample of 148 early-type galaxies in differentenvironments. The wavelength region covered by the observations (lambda=~ 4600 to 6600 Å) includes the Lick/IDS indices Hβ,Mg1, Mg2, Mgb, Fe5015, Fe5270, Fe5335, Fe5406,Fe5709, Fe5782, NaD, TiO1 and TiO2. The data areintended to address possible differences of the stellar populations ofearly-type galaxies in low- and high-density environments. This paperdescribes the sample properties, explains the data reduction andpresents the complete list of all the measurements. Most galaxies of thesample (85%) had no previous measurements of any Lick/IDS indices andfor 30% of the galaxies we present first-time determinations of theirvelocity dispersions. Special care is taken to identify galaxies withemission lines. We found that 62 per cent of the galaxies in the samplehave emission lines, as measured by the equivalent width of the [OIII]5007Å line, EW[OIII] > 0.3 Å. Tables 5 and 6 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/ A+A/395/431. They are also available via ftp atftp.mpe.mpg.de in the directory people/dthomas/Beuing02 or via WWW atftp://ftp.mpe.mpg.de/people/dthomas/Beuing02.
| A catalogue and analysis of X-ray luminosities of early-type galaxies
We present a catalogue of X-ray luminosities for 401 early-typegalaxies, of which 136 are based on newly analysed ROSAT PSPC pointedobservations. The remaining luminosities are taken from the literatureand converted to a common energy band, spectral model and distancescale. Using this sample we fit the LX:LB relationfor early-type galaxies and find a best-fit slope for the catalogue of~2.2. We demonstrate the influence of group-dominant galaxies on the fitand present evidence that the relation is not well modelled by a singlepower-law fit. We also derive estimates of the contribution to galaxyX-ray luminosities from discrete-sources and conclude that they provideLdscr/LB~=29.5ergs-1LBsolar-1. Wecompare this result with luminosities from our catalogue. Lastly, weexamine the influence of environment on galaxy X-ray luminosity and onthe form of the LX:LB relation. We conclude thatalthough environment undoubtedly affects the X-ray properties ofindividual galaxies, particularly those in the centres of groups andclusters, it does not change the nature of whole populations.
| A synthesis of data from fundamental plane and surface brightness fluctuation surveys
We perform a series of comparisons between distance-independentphotometric and spectroscopic properties used in the surface brightnessfluctuation (SBF) and fundamental plane (FP) methods of early-typegalaxy distance estimation. The data are taken from two recent surveys:the SBF Survey of Galaxy Distances and the Streaming Motions of AbellClusters (SMAC) FP survey. We derive a relation between(V-I)0 colour and Mg2 index using nearly 200galaxies and discuss implications for Galactic extinction estimates andearly-type galaxy stellar populations. We find that the reddenings fromSchlegel et al. for galaxies with E(B-V)>~0.2mag appear to beoverestimated by 5-10 per cent, but we do not find significant evidencefor large-scale dipole errors in the extinction map. In comparison withstellar population models having solar elemental abundance ratios, thegalaxies in our sample are generally too blue at a given Mg2;we ascribe this to the well-known enhancement of the α-elements inluminous early-type galaxies. We confirm a tight relation betweenstellar velocity dispersion σ and the SBF `fluctuation count'parameter N, which is a luminosity-weighted measure of the total numberof stars in a galaxy. The correlation between N and σ is eventighter than that between Mg2 and σ. Finally, we deriveFP photometric parameters for 280 galaxies from the SBF survey data set.Comparisons with external sources allow us to estimate the errors onthese parameters and derive the correction necessary to bring them on tothe SMAC system. The data are used in a forthcoming paper, whichcompares the distances derived from the FP and SBF methods.
| Stellar population gradients in normal and active galaxies
We use high signal-to-noise ratio long-slit spectra in theλλ3500-7000-Å range of three early-type (Hubble typeS0) normal, two low-ionization nuclear emission region (LINER) and threeSeyfert 2 galaxies to make a comparative study of the variation of thestellar population properties as a function of distance from thenucleus. In order to characterize the stellar population and othercontinuum sources (e.g. featureless continuum) we have measuredequivalent widths (Ws) of six absorption features, continuum colours andtheir radial variations, and performed spectral population synthesis asa function of distance from the nucleus. The Ws for the normal galaxiesare strongest at the nucleus and decrease outwards. The two LINERgalaxies show a similar behaviour, but with the nuclear Ws in the blue(λ<4500Å)~10-20 per cent smaller. Both normal galaxiesand LINERs present a redder nucleus than their surroundings. The threeSeyfert 2 galaxies present the opposite behaviour, with most Ws in theblue being smaller at the nucleus, which is also bluer than outside. Bycombining the results of the present work with those of a previousstudy, we conclude that, in a sample of 12 Seyfert 2s of Hubble type S0,10 (~80 per cent) present nuclear Ws smaller than those of normalgalaxies, while at ~1kpc from the nucleus this number decreases to 4(~30 per cent). Sampling regions of ~100-200pc, we conclude that thenormal galaxies have nuclear stellar populations dominated by thecomponents with an age of 10Gyr and metallicity solar or above. Thecontribution of this component decreases, while that of 1Gyr increases,with increasing distance from the nucleus. The LINERs present a similarbehaviour but have a ~10-20 per cent larger contribution of the 1-Gyrcomponent at the nucleus. For the Seyfert 2 galaxies, there areadditional components: in the three cases studied here, there is asignificant contribution from a 100-Myr-old population at the nucleusplus featureless continuum in two cases and also of a 3-Myr-oldcomponent in Mrk463E. Outside the nucleus, the stellar population issimilar to that of normal galaxies in ESO138-G1, but it has an excess ofold metal-poor components in NGC7743 and of young components in Mrk463E,when compared with normal galaxies. The reddening of the continuum islowest in the normal galaxy nuclei [E(B-V)i~0.00] and highestin the Seyfert [E(B-V)i~0.20] nuclei.
| The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances
We report data for I-band surface brightness fluctuation (SBF)magnitudes, (V-I) colors, and distance moduli for 300 galaxies. Thesurvey contains E, S0, and early-type spiral galaxies in the proportionsof 49:42:9 and is essentially complete for E galaxies to Hubblevelocities of 2000 km s-1, with a substantial sampling of Egalaxies out to 4000 km s-1. The median error in distancemodulus is 0.22 mag. We also present two new results from the survey.(1) We compare the mean peculiar flow velocity (bulk flow) implied byour distances with predictions of typical cold dark matter transferfunctions as a function of scale, and we find very good agreement withcold, dark matter cosmologies if the transfer function scale parameterΓ and the power spectrum normalization σ8 arerelated by σ8Γ-0.5~2+/-0.5. Deriveddirectly from velocities, this result is independent of the distributionof galaxies or models for biasing. This modest bulk flow contradictsreports of large-scale, large-amplitude flows in the ~200 Mpc diametervolume surrounding our survey volume. (2) We present adistance-independent measure of absolute galaxy luminosity, N and showhow it correlates with galaxy properties such as color and velocitydispersion, demonstrating its utility for measuring galaxy distancesthrough large and unknown extinction. Observations in part from theMichigan-Dartmouth-MIT (MDM) Observatory.
| 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.
| Line-of-sight velocity distributions of 53 early-type galaxies
55 long-slit spectra of 53 early-type galaxies were observed at LaSilla/ESO and reduced using standard methods. The line-of-sight velocitydistributions (LOSVDs) were measured using the fourier quotient methodand the fourier fitting method as described by van der Marel et al.(\cite{vdmarel93}). 32% of the examined galaxies contain kinematicallydecoupled stellar omponents, the size of these cores was 0.40 +/- 0.28kpc, in each case the core was smaller than 1 kpc. Analysis of thekinematics reveals in 49% of the sample galaxies the signature of astellar disk component, in 15% this is uncertain. There is evidence thatthe phenomenon of kinematically decoupled components is present in thewhole class of early-type galaxies. Several correlations betweenphotometric and kinematic parameters like the (v/sigma )* vs.epsilon diagram, the anisotropy - luminosity correlation or kappa -spacewere as well examined using measurement results for spectroscopic dataand photometric data out of literature. It is also shown that thosesample galaxies with kinematically decoupled components are more likelyto be found in groups of high density, strengthening the assumption thatsuch components are remnants of merging events. Full Fig. 6 is onlyavailable at http://www.edpsciences.org
| X-ray luminosities for a magnitude-limited sample of early-type galaxies from the ROSAT All-Sky Survey
For a magnitude-limited optical sample (B_T <= 13.5 mag) ofearly-type galaxies, we have derived X-ray luminosities from the ROSATAll-Sky Survey. The results are 101 detections and 192 useful upperlimits in the range from 10^36 to 10^44 erg s^-1. For most of thegalaxies no X-ray data have been available until now. On the basis ofthis sample with its full sky coverage, we find no galaxy with anunusually low flux from discrete emitters. Below log (L_B) ~ 9.2L_⊗ the X-ray emission is compatible with being entirely due todiscrete sources. Above log (L_B) ~ 11.2 L_osolar no galaxy with onlydiscrete emission is found. We further confirm earlier findings that L_xis strongly correlated with L_B. Over the entire data range the slope isfound to be 2.23 (+/- 0.12). We also find a luminosity dependence ofthis correlation. Below log L_x = 40.5 erg s^-1 it is consistent with aslope of 1, as expected from discrete emission. Above this value theslope is close to 2, as expected from gaseous emission. Comparing thedistribution of X-ray luminosities with the models of Ciotti et al.leads to the conclusion that the vast majority of early-type galaxiesare in the wind or outflow phase. Some of the galaxies may have alreadyexperienced the transition to the inflow phase. They show X-rayluminosities in excess of the value predicted by cooling flow modelswith the largest plausible standard supernova rates. A possibleexplanation for these super X-ray-luminous galaxies is suggested by thesmooth transition in the L_x--L_B plane from galaxies to clusters ofgalaxies. Gas connected to the group environment might cause the X-rayoverluminosity.
| ROSAT All-Sky Survey observations of IRAS galaxies. I. Soft X-ray and far-infrared properties
The 120 000 X-ray sources detected in the RASS II processing of theROSAT All-Sky Survey are correlated with the 14 315 IRAS galaxiesselected from the IRAS Point Source Catalogue: 372 IRAS galaxies showX-ray emission within a distance of 100 arcsec from the infraredposition. By inspecting the structure of the X-ray emission in overlayson optical images we quantify the likelihood that the X-rays originatefrom the IRAS galaxy. For 197 objects the soft X-ray emission is verylikely associated with the IRAS galaxy. Their soft X-ray properties aredetermined and compared with their far-infrared emission. X-ray contourplots overlaid on Palomar Digitized Sky Survey images are given for eachof the 372 potential identifications. All images and tables displayedhere are also available in electronic form.
| 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 APM Bright Galaxy Catalogue
The APM Bright Galaxy Catalogue lists positions, magnitudes, shapes andmorphological types for 14681 galaxies brighter than b_J magnitude16.44, over a 4180 deg^2 area of the southern sky. Galaxy and stellarimages have been located from glass copy plates of the United KingdomSchmidt Telescope (UKST) IIIaJ sky survey using the automatedphotographic measuring (APM) facility in Cambridge, England. Themajority of stellar images are rejected by the regularity of their imagesurface brightness profiles. Remaining images are inspected by eye onfilm copies of the survey material and classed as stellar, multiplestellar, galaxy, merger or noise. Galaxies are further classified aselliptical, lenticular, spiral, irregular or uncertain. The 180 surveyfields are put on to a uniform photometric system by comparing themagnitudes of galaxies in the overlap regions between neighbouringplates. The magnitude zero-point, photometric uniformity andphotographic saturation are checked with CCD photometry. Finally, thecompleteness and reliability of the catalogue are assessed by usingvarious internal tests and by comparison with several independentlyconstructed galaxy catalogues.
| A survey of the ISM in early-type galaxies. I. The ionized gas.
We present results of a CCD optical imaging survey of the ionized gas in73 luminous elliptical and lenticular galaxies, selected from the RC3catalog to represent a broad variety of X-ray, radio, infrared andkinematical properties. For each galaxy we have used broad-band R imagesand narrow-band images centered at the Hα and [NII] emission linesto derive the luminosity and distribution of the ionized gas. We foundthat a large fraction of E (72%) and S0 (85%) galaxies in our samplecontain ionized gas. The gas morphology appears to be rather smooth formost galaxies; however ~12% of the sample galaxies show a very extendedfilamentary structure. According to the morphology and size of the gasdistribution, the galaxies have been classified into three broad groups,named small disk (SD), regular extended (RE) and filamentary structure(F). The mean diameter of the emitting region ranges between 1 and10kpc; the derived mass of the ionized gas ranges between 10^3^ and10^5^ solar masses. A significant correlation between Hα+[NII] andX-ray luminosities is found for those galaxies (27% of the sample) forwhich we have detected ionized gas and are also listed as X-ray sources.However, there are relatively strong X-ray emitting galaxies for whichwe have not detected Hα+[NII] emission and objects which showemission-lines but are not listed either in the EINSTEIN or in the ROSATdatabases. The distribution of datapoint and upper limits in thisdiagram suggests that galaxies with warm gas are also X-ray emitters,while there are X-ray emitters without measurable Hα+[NII]emission. Similar characteristics are present in the correlation betweenthe infrared luminosity in the 12 μm band and L_Hα+[NII]_;correlations with other infrared wavelengths are weaker. A strongcorrelation was also found between the Hα+[NII] luminosity and theluminosity in the B band inside the region occupied by the line-emittinggas. We use these correlations to discuss the possible mechanismsresponsible for the gas ionization and excitation, analyzing inparticular the role of the post-AGB stars and the thermal conductionfrom the X-ray halo in providing the necessary source of ionization.
| Total and effective colors of 501 galaxies in the Cousins VRI photometric system
Total color indices (V-R)T, (V-I)T and effectivecolor indices (V-R)e, (V-I)e in the Cousins VRIphotometric system are presented for 501 mostly normal galaxies. Thecolors are computed using a procedure outlined in the Third ReferenceCatalogue of Bright Galaxies (RC3) whereby standard color curvesapproximated by Laplace-Gauss integrals are fitted to observedphotoelectric multiaperture photometry. 11 sources of such photometrywere used for our analysis, each source being assigned an appropriateweight according to a rigorous analysis of residuals of the data fromthe best-fitting standard color curves. Together with the integrated B-Vand U-B colors provided in RC3, our analysis widens the range ofwavelength of homogeneously defined colors of normal galaxies of allHubble types. We present color-color and color-type relations that canbe modeled to understand the star formation history of galaxies.
| 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.
| Parsecscale Radio Cores in Early Type Galaxies
We find compact (<0.03 arcsec) radio-continuum cores in about 70 percent of radio-emitting elliptical and S0 galaxies over a wide range intotal radio power (10^21^-,10^26^ W Hz^-1^ at 5 GHz). The cores usuallyhave a flat or rising spectrum between 2.3 and 8.4 GHz, with a medianspectral index of + 0.3. Even at low luminosities, the radio emissionfrom most elliptical galaxies appears to be powered by a parsec-scale`engine' like those in classical radio galaxies and quasars. The coreand total radio power are related (P_core_ is proportional toP_total_^0.7^ on average), and the parsec-scale cores of radio galaxiesare typically one hundred times more powerful than those in `normal'giant elliptical galaxies.
| Photometrically distinct nuclei in elliptical and early-type disks galaxies.
Not Available
| Mean morphological types of bright galaxies
The revised Hubble classifications provided in the Third ReferenceCatalogue of Bright Galaxies (RC3) are based on nine lists andcatalogues, both published and unpublished, from five observers. Thispaper describes the procedures that were used to combine theseclassifications into mean classifications including the family, variety,and stage. The best classifications in RC3 are based on large-scalephotographic images taken with 1.5-5 m class reflectors. However, mostof the types in RC3 are based on the small-scale prints, plates, andfilms of the first Palomar Sky Survey and the UK Schmidt IIIa-J SouthernSky Survey. The overlap between the different observers, samples alloweddetermination of the reliability of sky survey types and the effects ofdiameter and inclination on the accuracy of these types. We find thatfor a typical galaxy having isophotal diameter D25approximately = 2 min and inclined by approximately 50 degs, types Tfrom the sky surveys have a mean error (averaged over all of theobservers) of sigma(T) = 0.7 step on the numerical scale of the revisedHubble system. With the new database of classifications, we rederive theclassical relations between Hubble type and integrated colors, surfacebrightnesses, and hydrogen index (hydrogen flux to blue light ratio) fora large sample of galaxies. We also present a table of galaxies which weconsider to be representative examples of each type.
| 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.
| Dynamics of the Pavo-Indus and Grus clouds of galaxies
A study of groups of galaxies in the above regions was carried out byselecting a sample extending one magnitude deeper than previous work inthe area, complete down to 15 mag. We report new redshift determinationsfor 58 galaxies in the region and 13 other miscellaneous galaxies, basedon La Silla observations. Using a total of 266 galaxies with measuredredshifts in the Pavo-Indus and Grus clouds, we perform a new analysisof groupings following a well-tested algorithm. A total of 18 groups issingled out, most of them known from previous work, even though a fewadditional members are added. For all the groups, we have calculateddynamical parameters and M/L ratios. All groups are found to be boundaggregates, but only one group can be virialized. For the six mostpopulated examples, having at least five members, we also calculateseveral mass estimators and discuss the wide range of observed M/Lratios, which extends from nine to nearly 500 M(solar)/L(solar). Weintroduce two parameters to measure the presence of either a dominantgalaxy or internal subcondensations, respectively, and test whether anycorrelation with the M/L ratios can be detected. No clear correlationsare found.
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
קטלוגים וכינוים:
|
