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Stellar Populations in Nearby Lenticular Galaxies
We have obtained two-dimensional spectral data for a sample of 58 nearbyS0 galaxies with the Multi-Pupil Fiber/Field Spectrograph of the 6 mtelescope of the Special Astrophysical Observatory of the RussianAcademy of Sciences. The Lick indices Hβ, Mg b, and arecalculated separately for the nuclei and for the bulges taken as therings between R=4'' and 7", and the luminosity-weighted ages,metallicities, and Mg/Fe ratios of the stellar populations are estimatedby comparing the data to single stellar population (SSP) models. Fourtypes of galaxy environments are considered: clusters, centers ofgroups, other places in groups, and the field. The nuclei are found tobe on average slightly younger than the bulges in any type ofenvironment, and the bulges of S0 galaxies in sparse environments areyounger than those in dense environments. The effect can be partlyattributed to the well-known age correlation with the stellar velocitydispersion in early-type galaxies (in our sample the galaxies in sparseenvironments are on average less massive than those in denseenvironments), but for the most massive S0 galaxies, withσ*=170-220 km s-1, the age dependence on theenvironment is still significant at the confidence level of 1.5 σ.Based on observations collected with the 6 m telescope (BTA) at theSpecial Astrophysical Observatory (SAO) of the Russian Academy ofSciences (RAS).
| The X-ray emission properties and the dichotomy in the central stellar cusp shapes of early-type galaxies
The Hubble Space Telescope has revealed a dichotomy in the centralsurface brightness profiles of early-type galaxies, which havesubsequently been grouped into two families: core, boxy, anisotropicsystems; and cuspy (`power-law'), discy, rotating ones. Here weinvestigate whether a dichotomy is also present in the X-ray propertiesof the two families. We consider both their total soft emission(LSX,tot), which is a measure of the galactic hot gascontent, and their nuclear hard emission (LHX,nuc), mostlycoming from Chandra observations, which is a measure of the nuclearactivity. At any optical luminosity, the highest LSX,totvalues are reached by core galaxies; this is explained by their beingthe central dominant galaxies of groups, subclusters or clusters, inmany of the logLSX,tot (ergs-1) >~ 41.5 cases.The highest LHX,nuc values, similar to those of classicalactive galactic nuclei (AGNs), in this sample are hosted only by core orintermediate galaxies; at low luminosity AGN levels, LHX,nucis independent of the central stellar profile shape. The presence ofoptical nuclei (also found by HST) is unrelated to the level ofLHX,nuc, even though the highest LHX,nuc are allassociated with optical nuclei. The implications of these findings forgalaxy evolution and accretion modalities at the present epoch arediscussed.
| Tidal Disruption of a Star by a Black Hole: Observational Signature
We have modeled the time-variable profiles of the Hα emission linefrom the nonaxisymmetric disk and debris tail created in the tidaldisruption of a solar-type star by a 106 Msolarblack hole. Two tidal disruption events were simulated using athree-dimensional relativistic smoothed particle hydrodynamics code todescribe the early evolution of the debris during the first 50-90 days.We have calculated the physical conditions and radiative processes inthe debris using the photoionization code CLOUDY. We model theemission-line profiles in the period immediately after the accretionrate onto the black hole became significant. We find that the lineprofiles at these very early stages of the evolution of thepostdisruption debris do not resemble the double-peaked profilesexpected from a rotating disk, since the debris has not yet settled intosuch a stable structure. As a result of the uneven distribution of thedebris and the existence of a ``tidal tail'' (the stream of returningdebris), the line profiles depend sensitively on the orientation of thetail relative to the line of sight. Moreover, the predicted lineprofiles vary on fairly short timescales (of the order of hours todays). Given the accretion rate onto the black hole, we also model theHα light curve from the debris and the evolution of the Hαline profiles in time.
| The size of the broad-line regions in dwarf active galaxies
Using the empirical relation between black hole mass and bulge velocitydispersion established for active and quiescent galaxies, we derive thesizes of the broad-line regions (BLRs) for 22 dwarf active galaxies.These sizes are compared with those of Seyfert 1 galaxies and quasars.We find that the size of the BLRs of Seyfert 1s and quasars is wellscaled with the luminosity of the Hα line with a slope of ~=0.5,and dwarf active galaxies show larger BLRs than the values predicted bythe BLR size-luminosity relation for Seyfert 1 galaxies andquasi-stellar objects (QSOs). The results suggest that the BLRs of dwarfactive galactic nuclei (AGN) have lower ionization or/and lower densitythan those of Seyfert 1 galaxies and QSOs. Photoionization calculationsshow that the large BLRs are consistent with observed emission linespectra.
| 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
| 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.
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| Balmer lines emission region in NGC 3516: Kinematical and physical properties
We have studied the Balmer line shapes of NGC 3516 in order to find thestructure of central Emission Line Region (ELR) and the physicalparameters of the emitting plasma. The shapes of these broad emissionlines show evidences of a multicomponent origin and also features whichcould be identified as the peaks of a rotating disc. We have proposed atwo component Broad Line Region (BLR) model consisting of an innerKeplerian relativistic disc and an outer structure surrounding the discwhich is composed by Broad Line and Narrow Line Regions (BLR and NLR).Adopting a mass of ~ 4 x 107 Msun for the centralobject we found that the emitting disc is located from 0.004 pc to 0.018pc. Using a well known method for laboratory plasma diagnostic, theBoltzmann plot, we estimated the electron temperature (~12 500 K) andelectron density ( ~ 1015 cm-3) of the disc andthe surrounding region (Te~ 20 000 K and Ne ~1015 cm-3).
| 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.
| Do LINER 2 galaxies harbour low-luminosity active galactic nuclei?
We use ROSAT HRI spatial data and ASCA spectral measurements for asample of seven nearby, early-type spiral galaxies, to address thequestion of whether a low-luminosity active galactic nucleus (LLAGN) ispresent in galaxies that have a LINER 2 classification. The brightestdiscrete X-ray source in the ROSAT HRI observations is invariably foundto be positionally coincident with the optical galactic nucleus, and inmost cases its flux dominates the X-ray emission from the central regionof the galaxy. All seven galaxies have X-ray spectra consistent with atwo-component, soft thermal plus hard power-law, spectral form. If weexclude the two galaxies with relatively hard X-ray spectra, NGC 3628and NGC 4594, for which there is supporting evidence for a LLAGN (oralternatively in the case of NGC 3628 a dominant ultraluminous X-raybinary), then the remaining galaxies show surprisingly similar X-rayspectral properties. Specifically the flux ratioFX(0.5-1)/FX(2-5), which measures the relativestrengths of the thermal and non-thermal emission components, showslittle scatter about a mean of 0.66, a value very similar to thatmeasured in the classic starburst galaxy NGC 253. As there is no obviousreason why the luminosity of the hard power-law continuum emanating froma putative LLAGN should be very closely correlated with the thermalemission of the surrounding region, this suggests that that thebroad-band (0.5-5keV) X-ray emission from these LINER 2 galaxies mayoriginate in a common set of processes probably associated with thestarburst phenomenon. Conversely, it appears that in many LINER 2galaxies and perhaps the majority, the nuclear X-ray luminosity does notderive directly from the presence of a LLAGN.
| NGC 3065: A Certified LINER with Broad, Variable Balmer Lines
Motivated by the X-ray properties of the galaxy NGC 3065, we haveobtained new optical spectra that reveal that it has a low-ionizationnuclear emission-line region (LINER) as well as broad Balmer emissionlines, establishing it as an active galactic nucleus. We also examinedan older spectrum from the CfA Redshift Survey that lacks broad Balmerlines, indicating that these lines appeared sometime after 1980. ThusNGC 3065 joins the set of LINERs with broad, variable Balmer lines,which includes such well-known galaxies as NGC 1097 and M81. Inspired bythe sometimes double-peaked profiles of the variable Balmer lines inother LINERs, we speculate that the broad Balmer lines of NGC 3065 alsocome from an accretion disk. We illustrate the plausibility of thishypothesis by fitting a disk model to the observed Hα profile. Wealso estimate the mass of the central black hole to be(9+/-4)×107 Msolar from the properties ofthe host galaxy, which leads to the conclusion that the accretion rateis only ~2×10-4 times the Eddington value, a propertythat appears to be common among LINERs. At such a low relative accretionrate, the inner accretion disk can turn into a vertically extended iontorus, which can illuminate the outer thin disk and power the broad-lineemission. The reason for the sudden appearance of broad Balmer lines isan open question, although we suggest two possible explanations: (1)tidal disruption of a star or (2) a sudden transition in the structureof the accretion disk.
| 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.
| The Cold and Hot Gas Content of Fine-Structure E and S0 Galaxies
We investigate trends of the cold and hot gas content of early-typegalaxies with the presence of optical morphological peculiarities, asmeasured by the fine-structure index Σ. H I mapping observationsfrom the literature are used to track the cold gas content, and archivalROSAT Position Sensitive Proportional Counter data are used to quantifythe hot gas content. We find that E and S0 galaxies with a highincidence of optical peculiarities are exclusively X-ray underluminousand, therefore, deficient in hot gas. In contrast, more relaxed galaxieswith little or no signs of optical peculiarities span a wide range ofX-ray luminosities. That is, the X-ray excess anticorrelates withΣ. There appears to be no similar trend of cold gas content witheither fine-structure index or X-ray content. The fact that onlyapparently relaxed E and S0 galaxies are strong X-ray emitters isconsistent with the hypothesis that after strong disturbances, such as amerger, hot gas halos build up over a timescale of several gigayears.This is consistent with the expected mass loss from stars.
| ASCA Observation of the Low-Luminosity Seyfert 1.5 Galaxy NGC 5033
We present the results of an ASCA observation of the low-luminositySeyfert 1.5 galaxy NGC 5033. A point-like X-ray source with a luminosityof 2.3*E41 erg s-1 in the 2-10 keV band (at 18.7Mpc; Tully 1988, AAA 045.002.054) was detected at the nucleus. The X-raylight curve shows variability on a timescale of ~ 104 s withan amplitude of ~ 20%. The X-ray continuum is represented by a weaklyabsorbed (N_H ~9*E20 {cm-2}) power-law with aphoton index of 1.72+/-0.04, which is quite similar to Seyfert 1galaxies with higher luminosities. An Fe Kalpha emission line isdetected at 6.40+0.08-0.06 keV (redshiftcorrected) and the equivalent width is 290+/-100 eV. The line width isunresolved. The narrower line width and larger equivalent width comparedto Seyfert 1s imply that fluorescent Fe Kalpha emission from matterfurther out from the center than the accretion disk significantlycontributes to the observed Fe Kalpha line. We suggest that fluorescentFe Kalpha emission from the putative torus contributes to the observedFe Kalpha line.
| 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.
| Low-Luminosity X-Ray Active Galactic Nuclei in S0 Galaxies NGC 3065 and NGC 4203
We present ASCA X-ray results on two S0 galaxies, NGC 3065 and NGC 4203.In both galaxies, we detected hard X-ray emission from a pointlikesource at the nucleus. A single power-law model having a photon index of~1.8 well described the spectra of these sources, while thin thermalemission, which is common in S0 galaxies, was not detected. The 2-10 keVluminosities of these nuclear sources (2.2 x 1041 and 1.5 x 1040 ergss-1) are 1-2 orders of magnitude higher than those expected as anassembly of low-mass X-ray binaries in these galaxies. Our resultsstrongly suggest that NGC 3065 and NGC 4203 host low-luminosity activegalactic nuclei.
| Bulge-Disk Decomposition of 659 Spiral and Lenticular Galaxy Brightness Profiles
We present one of the largest homogeneous sets of spiral and lenticulargalaxy brightness profile decompositions completed to date. The 659galaxies in our sample have been fitted with a de Vaucouleurs law forthe bulge component and an inner-truncated exponential for the diskcomponent. Of the 659 galaxies in the sample, 620 were successfullyfitted with the chosen fitting functions. The fits are generally welldefined, with more than 90% having rms deviations from the observedprofile of less than 0.35 mag. We find no correlations of fittingquality, as measured by these rms residuals, with either morphologicaltype or inclination. Similarly, the estimated errors of the fittedcoefficients show no significant trends with type or inclination. Thesedecompositions form a useful basis for the study of the lightdistributions of spiral and lenticular galaxies. The object base issufficiently large that well-defined samples of galaxies can be selectedfrom it.
| 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.
| An Einstein X-Ray Survey of Optically Selected Galaxies. I. Data
We present the results of a complete Einstein imaging proportionalcounter X-ray survey of optically selected galaxies from theShapley-Ames Catalog, the Uppsala General Catalogue, and the EuropeanSouthern Observatory Catalog. Well-defined optical criteria are used toselect the galaxies, and X-ray fluxes are measured at the opticallydefined positions. The result is a comprehensive list of X-ray detectionand upper limit measurements for 1018 galaxies. Of these, 827 haveeither independent distance estimates or radial velocities. Associatedoptical, redshift, and distance data have been assembled for thesegalaxies, and their distances come from a combination of directlypredicted distances and those predicted from the Faber-Burstein GreatAttractor/Virgocentric infall model. The accuracy of the X-ray fluxeshas been checked in three different ways; all are consistent with thederived X-ray fluxes being of <=0.1 dex accuracy. In particular,there is agreement with previously published X-ray fluxes for galaxiesin common with a 1991 study by Roberts et al. and a 1992 study byFabbiano et al. The data presented here will be used in further studiesto characterize the X-ray output of galaxies of various morphologicaltypes and thus to enable the determination of the major sourcescontributing to the X-ray emission from galaxies.
| 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.
| A multiparametric analysis of the Einstein sample of early-type galaxies. 1: Luminosity and ISM parameters
We have conducted bivariate and multivariate statistical analysis ofdata measuring the luminosity and interstellar medium of the Einsteinsample of early-type galaxies (presented by Fabbiano, Kim, &Trinchieri 1992). We find a strong nonlinear correlation betweenLB and LX, with a power-law slope of 1.8 +/- 0.1,steepening to 2.0 +/- if we do not consider the Local Group dwarfgalaxies M32 and NGC 205. Considering only galaxies with logLX less than or equal to 40.5, we instead find a slope of 1.0+/- 0.2 (with or without the Local Group dwarfs). Although E and S0galaxies have consistent slopes for their LB-LXrelationships, the mean values of the distribution functions of bothLX and LX/LB for the S0 galaxies arelower than those for the E galaxies at the 2.8 sigma and 3.5 sigmalevels, respectively. We find clear evidence for a correlation betweenLX and the X-ray color C21, defined by Kim,Fabbiano, & Trinchieri (1992b), which indicates that X-rayluminosity is correlated with the spectral shape below 1 keV in thesense that low-LX systems have relatively large contributionsfrom a soft component compared with high-LX systems. We findevidence from our analysis of the 12 micron IRAS data for our samplethat our S0 sample has excess 12 micron emission compared with the Esample, scaled by their optical luminosities. This may be due toemission from dust heated in star-forming regions in S0 disks. Thisinterpretation is reinforced by the existence of a strongL12-L100 correlation for our S0 sample that is notfound for the E galaxies, and by an analysis of optical-IR colors. Wefind steep slopes for power-law relationships between radio luminosityand optical, X-ray, and far-IR (FIR) properties. This last point arguesthat the presence of an FIR-emitting interstellar medium (ISM) inearly-type galaxies is coupled to their ability to generate nonthermalradio continuum, as previously argued by, e.g., Walsh et al. (1989). Wealso find that, for a given L100, galaxies with largerLX/LB tend to be stronger nonthermal radiosources, as originally suggested by Kim & Fabbiano (1990). We notethat, while LB is most strongly correlated withL6, the total radio luminosity, both LX andLX/LB are more strongly correlated with L6CO, the core radio luminosity. These points support the argument(proposed by Fabbiano, Gioia, & Trinchieri 1989) that radio cores inearly-type galaxies are fueled by the hot ISM.
| Quantitative morphology of E-S0 galaxies. III. Coded and parametric description of 108 galaxies in a complete sample
A survey has been performed of the morphological and photometricproperties of 108 E-S0 galaxies out of a complete sample of 112: thissample is built from the Revised Shapley-Ames Catalogue (RSA, Sandage& Tammann, 1981) keeping objects with δ>-10deg andV_0_<3000km/s, rejecting SB0's and Local Group dwarfs. The data weremainly derived from our CCD observations at Observatoire deHaute-Provence: the camera allowed fields of 4x7 arcmin (or 7x7 for thelast run), the seeing being generally in the 2-3 arcsec FWHM range. Themeasurements include the isophotal analysis according to Carter's(1978), principles,and the photometric profiles along the two main axis.Opposite semi-axis are measured separately to detect asymmetries.Partial results about strongly flattened galaxies were given anddiscussed in Paper I and II of this series (Michard & Marchal, 1993and 1994). The present paper gives in tabular form: - in Table 2a, 2bthe most useful morphological parameters and a coded description of the108 studied objects. This table includes a revised classificationaccording to Hubble types, this being completed by the subclassificationof ellipticals into "boxy", "disky" and "undeterminate". It alsoincludes the classifications of envelope geometry and disk extent, asintroduced in Paper I. - in Table 3a, b the usual photometric globalparameters, also converted to absolute units for future reference. Thetabular data is completed by individual notes for each galaxy, collectedin an Appendix. A discussion of the present data will be presented in aforthcoming Paper IV : it aims at checking the working hypothesis thatgalaxies of both E and S0 Hubble types belong, but for a small minority,to a common population of objects with similar structures.
| Quantitative morphology of E-S0 galaxies IV. Ellipticals and lenticulars as a single population
The geometrical properties of E and S0 galaxies have been intercomparedusing the data collected in Paper III (Michard & Marchal 1994) for108 RSA objects in a complete, luminosity and distance limited, sample.As the apparent flattening (largely an effect of projection along theline of sight), is a determining factor in the segregation between E andS0 objects, the working hypothesis has been made that an important biasis introduced in the recognition of the two classes. It is perhaps aswell to assume that galaxies of both Hubble types belong, but for asmall(?) minority, to a common population of objects with similarstructures. This hypothesis receives strong support from thefrequency-diagrams of the ellipticity ɛ_max_, measured near itsmaximum or at the isophote of surface brightness V=21.5. The diagram forS0's alone cannot be generated by the random projection of any objects:it is clearly biased by the shift to the E type of many S0's of moderateinclination and relatively modest disk. This limits the significance ofthe same diagrams for E galaxies. The noted bias is much reduced if S0'sand disky E's are considered together. Because of the strong outwardsdecrease of the ellipticities in disky E's and in the S0's with non-thinenvelopes (thick disks and spheroidal haloes), the frequency diagrams ofthe ellipticities measured at the classical B=25, or at V=25, do notshow the bias noted above for S0's. The lack of round E's requires thespheroidal components to be faintly triaxial, as recently emphasized byother authors. Our hypothesis is also supported by the overlap of E andS0 galaxies in ad hoc classification schemes of ellipticity profiles andenvelope geometry, and in such correlation diagrams as: - theellipticity in the envelope, i.e. near μ(V)= 25, against theintermediate maximum ellipticity - the extremum of the Carter'scoefficient e_4_ (or a_4_ or c_4_ in other similar works) against themaximum ellipticity - the disk extent, as far as it can be estimatedwithout detailed modeling, against the maximum ellipticity. The"standard" structure of E-S0 objects includes a spheroidal, nearlyoblate component, that cannot be of constant ellipticity: this parameteroften increases outwards from its bulge value, then decreases again inthe envelope. Disks of various brightness and extent, between dominatingand vanishing, are the second essential component. Obviously, theirrelative importance is, together with the dust content, a physicalcriterion involved in the morphological separation between E and S0objects, besides the inclination effect. In the present sample, the diskcannot be detected in nearly half of E classified objects, and isprobably vanishing in about 40% of this class, or circa 17% of the totalof studied early-type objects. This minority contains mostly boxy E'swith non-standard ellipticity profiles, and, as is well known, nosignificant rotational support. From the convergent results ofquantitative morphology and kinematics, the early-type galaxies shouldbe segregated into the majority class of disky fast oblate rotators anda minority class of non-rotating ellipsoids.
| The extent of CO in the early-type galaxy NGC 4472
NGC 4472, and E/SO system, is the earliest type normal galaxy withdetected CO emission, and here we present additional radio observationsin the lines of CO(1-0) and CO(2-1) to determine the distribution andinternal properties of this gas. The original detection is reconfirmed,but observations at five surrounding locations and at two otherlocations in the galaxy do not show the gas to be extended; the total H2gas mass is estimated to be 4 x 107 solar mass. A highCO(1-0)/CO(2-1) brightness temperature ratio is found (greater than 3),which is indicative of subthermal excitation of the CO(2-1) line thatcan occur at low gas temperatures and low gas densities. Also, upperlimits are given for the CO(2-1) fluxes in four other early-typegalaxies.
| A morphological filter for removing 'Cirrus-like' emission from far-infrared extragalactic IRAS fields
The presence of diffuse extended IR emission from the Galaxy in the formof the so called 'Galactic Cirrus' emission has hampered the explorationof the extragalactic sky at long IR wavelengths. We describe thedevelopment of a filter based on mathematical morphology which appearsto be a promising approach to the problem of cirrus removal. The methodof Greyscale Morphology was applied to a 100 micron IRAS image of theM81 group of galaxies. This is an extragalactic field which suffers fromserious contamination from foreground Galactic 'cirrus'. Using atechnique called 'sieving', it was found that the cirrus emission has acharacteristic behavior which can be quantified in terms of an averagespatial structure spectrum or growth function. This function was thenused to attempt to remove 'cirrus' from the entire image. The result wasa significant reduction of cirrus emission by an intensity factor of 15compared with the original input image. The method appears to preserveextended emission in the spatially extended IR disks of M81 and M82 aswell as distinguishing fainter galaxies within bright regions ofgalactic cirrus. The techniques may also be applicable to IR databasesobtained with the Cosmic Background Explorer.
| 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.
| Face-on disc galaxies
The paper presents bidimensional photometry for 40 bright S0 galaxieswith apparent flattening of not less than 0.9 at the 25-mag/sq arcseclevel. They represent all of the bright S0s in the RC2 catalog which areseen almost face-on. Ellipticity and PA profiles of each system wereanalyzed in order to test for the presence of triaxiality in theirbulges and in their disks. Many of these systems are found to be quitefar from face-on orientation, at inclination not less than 20 deg. About45 percent are barred; 67 percent of the bulges of the unbarred S0sconsidered show twisting of the isophotes and appear to be triaxial, ordominated by a triaxial component following the r exp 1/4 law. Abouthalf of the disks exhibit the same behavior, suggesting a slighttriaxiality. Some oblate disks are found. Disks of barred and unbarredsystems do not appear to differ much. Two galaxies of the presentsample, and possibly two more from the literature, show no indicationsof stellar streaming which is not coplanar with the galaxy plane.
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