Contents
Images
Upload your image
DSS Images Other Images
Related articles
Spatial distribution of galaxies in the Puppis region
We determine the spatial distribution of the galaxies located behind thepart of the zone of avoidance of the Milky Way defined by 220°
| Line-of-Sight Reddening Predictions: Zero Points, Accuracies, the Interstellar Medium, and the Stellar Populations of Elliptical Galaxies
Revised (B-V)0-Mg2 data, which are used to testreddening predictions, are presented for 402 elliptical galaxies. Thesereddening predictions can tell us both what the intrinsic errors are inthis relationship among gE galaxy stellar populations as well as detailsof nearby structure in the interstellar medium (ISM) of our Galaxy, andof the intrinsic errors in reddening predictions. Using least-squaresfits, the explicit 1 σ errors in reddenings predicted by theBurstein-Heiles (BH) method and the Schlegel and coworkers (IR) methodare calculated, as well as the 1 σ observational error in the(B-V)0-Mg2 for gE galaxies. It is found that indirections with E(B-V)<0.100 mag (where most of these galaxies lie),1 σ errors in the IR reddening predictions are 0.006-0.009 mag inE(B-V), those for BH reddening predictions are 0.011 mag, and the 1σ agreement between the two reddening predictions is 0.007 mag.The IR predictions have an accuracy of 0.010-0.011 mag in directionswith E(B-V)>=0.100 mag, significantly better than those of the BHpredictions (0.024-0.025). Both methods yield good evidence thatgas-to-dust variations that vary by a factor of 3, both high and low,exist along many lines of sight in our Galaxy. Both methods also predictmany directions with E(B-V)<0.015 mag, despite the difference in zeropoint that each has assumed. The ~0.02 higher reddening zero point inE(B-V) previously determined by Schlegel and coworkers is confirmed,primarily at the Galactic poles. Independent evidence of reddening atthe north Galactic pole (NGP) is reviewed, with the conclusion thatdirections still exist at the NGP that have E(B-V)<<0.01. Twolines of evidence suggest that IR reddenings are overpredicted indirections with high gas-to-dust ratios. As high gas-to-dust directionsin the ISM also include the Galactic poles, this overprediction is thelikely cause of the E(B-V)~0.02 mag larger IR reddening zero pointrelative to that of BH.
| 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.
| On the calibration of the COBE/IRAS dust emission reddening maps
In this work we study the spectral properties (3600-6800 Å) of thenuclear region of early-type galaxies at low (|b|<25deg),intermediate (including surroundings of the Magellanic Clouds) and high(South Polar Cap) Galactic latitudes. We determine the E(B-V) reddeningvalues of the galaxies by matching their continuum distribution withrespect to those of reddening-free spectral galaxy templates withsimilar stellar populations. We also compare the spectroscopic reddeningvalue of each galaxy with that derived from 100 mu m dust emission(E(B-V)FIR) in its line of sight, and we find that there isagreement up to E(B-V)=0.25. Beyond this limit E(B-V)FIRvalues are higher. Taking into account the data up to E(B-V) ~ 0.7, wederive a calibration factor of 0.016 between the spectroscopic E(B-V)values and Schlegel et al.'s (\cite{Schlegel1998}) opacities. Bycombining this result with an AK extinction map built withinten degrees of the Galactic centre using Bulge giants as probes (Dutraet al. \cite{Dutra2003}), we extended the calibration of dust emissionreddening maps to low Galactic latitudes down to |b|=4deg andE(B-V)= 1.6 (AV ~ 5). According to this new calibration, amultiplicative factor of ~0.75 must be applied to the COBE/IRAS dustemission reddening maps.Based on observations made at Complejo Astronómico El Leoncito,which is operated under agreement between the Consejo Nacional deInvestigaciones Científicas y Técnicas de laRepública Argentina and the National Universities of La Pata,Córdoba and San Juan, Argentina.
| 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
| 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.
| The LX-σ Relation for Galaxies and Clusters of Galaxies
We demonstrate that individual elliptical galaxies and clusters ofgalaxies form a continuous X-ray luminosity-velocity dispersion(LX-σ) relation. Our samples of 280 clusters and 57galaxies have LX~σ4.4 andLX~σ10, respectively. This unifiedLX-σ relation spans 8 orders of magnitude inLX and is fully consistent with the observed and theoreticalluminosity-temperature scaling laws. Our results support the notion thatgalaxies and clusters of galaxies are the luminous tracers of similardark matter halos.
| 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.
| 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
| A Test for Large-Scale Systematic Errors in Maps of Galactic Reddening
Accurate 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
| 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.
| Near-infrared Imaging of Early-Type Galaxies. II. Global Photometric Parameters
An imaging survey of 341 nearby early-type galaxies in the near-infraredK-band atmospheric window (2.2 μm) is described. The galaxiesprimarily reside in 13 nearby rich clusters (85%), while some additionalgalaxies are drawn from loose groups (12%) and the general field (3%).Surface photometry was measured for the entire sample. Detailedcorrections were derived from an extensive grid of seeing-convolvedr^1/4 models and then applied to the isophotal surface brightness,aperture magnitude, and ellipticity profiles. Global photometricparameters were derived from this seeing-corrected photometry. More than25% of the sample has been observed at least twice, and these repeatmeasurements demonstrate the small internal uncertainties on the derivedglobal photometric parameters. Extensive comparisons with aperturephotometry from the literature demonstrate that the photometric systemis fully consistent with other photometric systems to <=0.01 mag andconfirm the estimates of internal random uncertainties. Additionalglobal parameters are drawn from the literature in a homogeneous mannerin order to construct a large catalog of galaxy properties: 95% of thegalaxies have a velocity dispersion, 69% have a Mg_2 index, 80% have anoptical r_eff and μ_eff, 82% have a D_n, and 81% have a derivedoptical-infrared color measurement. This large data set providesexcellent source material for investigations of the physical origins ofthe global scaling relations of early-type galaxies, velocity fields inthe local universe, and comparisons to higher redshift early-typegalaxies.
| A catalogue of Mg_2 indices of galaxies and globular clusters
We 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.
| 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.
| A catalogue of spatially resolved kinematics of galaxies: Bibliography
We 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
| Color distributions in E-S0 galaxies. I. Frequency and importance of dust patterns for various brands of E classified galaxies
>From the consideration of a sample of color distributions in 67 Eclassified objects of the Local Supercluster, it is found that localdust features are much more frequent and important in disky E's thanboxy E's. The subclass of undeterminate objects, those which cannot beassigned to the diE or boE groups, is intermediate. Subsets of objectsof common properties are considered from the point of view of local dustfeatures occurrence: giant boxy E's; minor boxy E's with rotationalsupport; compact dwarfs; SB0-like E's. It is noted that the detection ofdust features is more than twice less frequent in Virgo clusterellipticals than in the full sample, but the significance of this resultis not clear. Based on observations collected at theCanada-France-Hawaii Telescope and at the Observatoire du Pic du Midi
| 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 Update
A 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.
| 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.
| Interstellar matter in Shapley-Ames elliptical galaxies. IV. A diffusely distributed component of dust and its effect on colour gradients.
We have investigated IRAS far-infrared observations of a complete, bluemagnitude limited sample of 56 elliptical galaxies selected from theRevised Shapley-Ames Catalog. Data from a homogeneous optical CCDimaging survey as well as published X-ray data from the EINSTEINsatellite are used to constrain the infrared data. Dust masses asdetermined from the IRAS flux densities are found to be roughly an orderof magnitude higher than those determined from optical extinction valuesof dust lanes and patches, in strong contrast with the situation inspiral galaxies. This "mass discrepancy" is found to be independent ofthe (apparent) inclination of the dust lanes. To resolve this dilemma wepostulate that the majority of the dust in elliptical galaxies exists asa diffusely distributed component of dust which is undetectable atoptical wavelengths. Using observed radial optical surface brightnessprofiles, we have systematically investigated possible heatingmechanisms for the dust within elliptical galaxies. We find that heatingof the dust in elliptical galaxies by the interstellar radiation fieldis generally sufficient to account for the dust temperatures asindicated by the IRAS flux densities. Collisions of dust grains with hotelectrons in elliptical galaxies which are embedded in a hot,X-ray-emitting gas is found to be another effective heating mechanismfor the dust. Employing model calculations which involve the transfer ofstellar radiation in a spherical distribution of stars mixed with adiffuse distribution of dust, we show that the observed infraredluminosities imply total dust optical depths of the postulated diffuselydistributed dust component in the range 0.1<~τ_V_<~0.7 andradial colour gradients 0.03<~{DELTA}(B-I)/{DELTA}log r<~0.25. Theobserved IRAS flux densities can be reproduced within the 1σuncertainties in virtually all ellipticals in this sample by this newlypostulated dust component, diffusely distributed over the inner few kpcof the galaxies, and heated by optical photons and/or hot electrons. Theradial colour gradients implied by the diffuse dust component are foundto be smaller than or equal to the observed colour gradients. Thus, weargue that the effect of dust extinction should be taken seriously inthe interpretation of colour gradients in elliptical galaxies. We showthat the amount of dust observed in luminous elliptical galaxies isgenerally higher than that expected from production by mass loss ofstars within elliptical galaxies and destruction by sputtering in hotgas. This suggests that most of the dust in elliptical galaxiesgenerally has an external origin.
| The RSA survey of dwarf galaxies, 1: Optical photometry
We present detailed surface photometry, based on broad B-band chargecoupled device (CCD) images, of about 80 dwarf galaxies. Our samplerepresents approximately 10% of all dwarf galaxies identified in thevicinity of Revised Shapley-Ames (RSA) galaxies on high resolution bluephotographic plates, referred to as the RSA survey of dwarf galaxies. Wederive global properties and radial surface brightness profiles, andexamine the morphologies. The radial surface brightness profiles ofdwarf galaxies, whether early or late type, display the same varietiesin shape and complexity as those of classical giant galaxies. Only a feware well described by a pure r1/4 law. Exponential profilesprevail. Features typical of giant disk galaxies, such as exponentialprofiles with a central depression, lenses, and even, in one case (IC2041), a relatively prominent bulge are also found in dwarf galaxies.Our data suggest that the central region evolves from being bulge-like,with an r1/4 law profile, in bright galaxies to a lens-likestructure in dwarf galaxies. We prove detailed surface photometry to bea helpful if not always sufficient tool in investigating the structureof dwarf galaxies. In many cases kinematic information is needed tocomplete the picture. We find the shapes of the surface brightnessprofiles to be loosely associated with morphological type. Our samplecontains several new galaxies with properties intermediate between thoseof giant and dwarf ellipticals (but no M32-like objects). This showsthat such intermediate galaxies exist so that at least a fraction ofearly-type dwarf ellipticals is structurally related to early-typegiants instead of belonging to a totally unrelated, disjunct family.This supports an origin of early-type dwarf galaxies as originally moremassive systems that acquired their current morphology as a result ofsubstantial, presumable supernova-driven, mass loss. On the other hand,several early-type dwarfs in our sample are merger candidates. Mergerevents may lead to anisotropic velocity distributions in systems of anyluminosity, including dwarfs. The RSA sample of dwarf galaxies is morelikely to contain mergers because, in contrast to earlier dwarf galaxysurveys that have focused on clusters and rich groups of galaxies, theRSA dwarfs are typically located in low density environments. Theoccurrence of mergers among dwarf galaxies is of interest in connectionwith the rapid evolution of faint blue galaxy counts at redshift z lessthan 1 which suggests that dwarf galaxies were about five times morenumerous in the recent past.
| Multicolor surface photometry of early-type galaxies. I.
We have obtained v,g,r and i CCD surface photometry for a sample of 109early-type galaxies. Many of the galaxies covered have no previouslypublished CCD or aperture photometry. Our surface brightness profilestypically extend down to a surface brightness ofμ_r_~24mag/arcsec^2^. Detailed comparisons with previously publishedwork, and internal and external error estimates for all quantities areprovided. The complete surface photometry data set is made available ina computer-readable form.
| Kinematics of 14 early-type galaxies
We present rotation curves and velocity dispersion profiles at severalposition angles for 9 ellipticals and 5 early type disk systems. Akinematically decoupled inner component is detected in NGC 1374. Centralvelocity dispersions are provided for other 3 early-type galaxies.
| Interstellar matter in Shapley-Ames elliptical galaxies. II. The distribution of dust and ionized gas
We present results of deep optical CCD imaging for a complete, opticalmagnitude-limited sample of 56 elliptical galaxies from the RSA catalog.For each galaxy we have obtained broad-band images (in B, V, and I) andnarrow-band images using interference filters isolating theHα+[NII] emission lines to derive the amount and morphology ofdust and ionized gas. Detailed consideration of systematic errors due toeffects of sky background subtraction and removal of stellar continuumlight from the narrow-band images is described. The flux calibration ofthe narrow-band images is performed by deconvolving actually measuredspectral energy distributions with the filter transmission curves. Wealso present optical long-slit spectroscopy to determine the[NII]/Hα intensity ratio of the ionized gas. Dust lanes and/orpatches have been detected in 23 galaxies (41%) from this sample usingboth colour-index images and division by purely elliptical model images.We achieved a detection limit for dust absorption of A_B_~0.02.Accounting for selection effects, the true fraction of ellipticalgalaxies containing dust is estimated to be of order 80%. This detectionrate is comparable to that of the IRAS satellite, and significantlylarger than results of previous optical studies. Ionized gas has beendetected in 32 galaxies (57%). The spectroscopic data confirm thepresence and distribution of ionized gas as seen in the direct imaging.All elliptical galaxies in our sample in which a number of emissionlines is detected show very similar emission-line intensity ratios,which are typical of LINER nuclei. The amounts of detectable dust andionized gas are generally small--of order 10^4^-10^5^Msun_ ofdust and 10^3^-10^4^Msun_ of ionized gas. The dust andionized gas show a wide variety of distributions-extended along eitherthe apparent major axis, or the minor axis, or a skewed axis, indicatingthat triaxiality is in general required as a galaxy figure. In somecases (NGC 1275, NGC 2325, NGC 3136, NGC 3962, NGC 4696, NGC 5018, NGC5044, NGC 5813, IC 1459) the interstellar matter has a patchy orfilamentary distribution, suggestive of a recent interaction event. Thedistributions of dust and ionized gas are consistent with beingphysically associated with each other.
| Interstellar matter in Shapley-Ames elliptical galaxies. I. Multicolour CCD surface photometry
We present accurate CCD surface photometry in Johnson B and V andCousins I for a complete, magnitude-limited sample of 56 ellipticalgalaxies from the RSA catalog. For each galaxy we have determined radialprofiles of surface brightness, B-V and/or B-I colour index,ellipticity, position angle, and the third- and fourth order Fouriercoefficients that describe the deviations of the B, V, and I isophotesfrom perfect ellipses, using a full two-dimensional fitting technique.The present sample contains 13 galaxies for which no previous isophoteanalysis has been published, and 26 without published colour gradients.The radial profiles of the ellipticity, position angle, and the third-and fourth-order Fourier coefficients are found to show considerabledetail. The profiles are mostly similar in all passbands, except incases where dust lanes or patches are present. In this respect, thehigher-order Fourier coefficients turn out to be sensitive diagnostictools for the presence of dust in elliptical galaxies. Isophotaldeviations from ellipses on the level of 0.5-1% are found to be commonin elliptical galaxies. As noted before by others, these deviations aredue to structures that do not necessarily align with the apparent majoror minor axes of the galaxies, advocating the use of both the cosine andsine higher-order terms in correlation studies. We show that fittingouter radial intensity profiles of elliptical galaxies is an excellenttool for determining the sky background for the surface photometry. Thesky values determined from a power-law fit to the outer intensityprofiles are found to be within 0.1% of the sky values at the corners ofpresent-day large CCDs where the contribution of galaxy light isnegligible. The average colour gradients for the sample galaxies in B-Vand B-I are 0.06 and 0.14 mag arcsec^-2^ per decade in radius,respectively. This compares well with colour gradients in ellipticalgalaxies found by others. The small uncertainty introduced by the skybackground determination method applied here results in an averageinternal uncertainty of only ~ 0.01 mag for our colour gradients, whichis significantly better than the results of previous studies. Theprofiles are compared extensively with results from other authors whenavailable. The result is encouraging, especially for the ellipticity andposition angle where we find mean RMS differences of 0.01 and 1.8deg ,respectively. The surface brightness profiles generally agree to within+/- 0.0.5mag.
| UBVRI photoelectric photometry of bright southern early-type galaxies
UBVRI multi-aperture photometry of 207 bright southern galaxies and of72 objects of an additional list is presented. These observations weremade for obtaining the magnitude scale zero-point as an accuratedetermination of the sky background for a two-dimensional photometryprogram concerning these galaxies. We have also inferred the asymptoticmagnitudes, color indices and effective apertures of these objects. Ourresults are in good agreement with those of others authors.
| Neutral hydrogen observations of elliptical galaxies
Detection of HI emission from a number of E galaxies is reported. 33galaxies were searched for HI the first time. Seven of the detected Egalaxies are isolated, 9 have nearby companions, and 11 are in compactgroups and/or strongly interacting systems. Nearby confusing sources maybe responsible for some of the detections. The large number ofelliptical galaxies in groups (in this sample) suggests thatgravitational interaction and mergers might be an important source ofsupply of interstellar matter for elliptical galaxies.
| Low-luminosity companions of early-type galaxies
Optical redshifts of nine low-luminosity companions of early-type giantgalaxies are obtained as part of a study of the small-scale clusteringproperties of dwarf galaxies. The velocity differences between thelow-luminosity companions and the nearest giant are typically less than300 km/s in the case of 'field' giants and larger for members of groupsof galaxies. Early-type companions of isolated giant galaxies may begravitationally bound satellites which can be used as dynamical probesof dark halos, while in groups of galaxies they are free-floating in thegeneral potential well of the group. The spectra of one nucleated dwarfelliptical and two dwarfs of composite dE and BCD morphology showevidence of recent star formation.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
