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Neutral hydrogen in nearby elliptical and lenticular galaxies: the continuing formation of early-type galaxies
We present the results of deep Westerbork Synthesis Radio Telescopeobservations of neutral hydrogen in 12 nearby elliptical and lenticulargalaxies. The selected objects come from a representative sample ofnearby galaxies earlier studied at optical wavelengths with theintegral-field spectrograph SAURON (Spectrographic Areal Unit forResearch on Optical Nebulae). They are field galaxies, or (in two cases)located in poor group environments. We detect HI - both in regular discsas well as in clouds and tails offset from the host galaxy - in 70 percent of the galaxies. This detection rate is much higher than inprevious, shallower single-dish surveys, and is similar to that for theionized gas. The results suggest that at faint detection levels thepresence of HI is a relatively common characteristic of field early-typegalaxies, confirming what was suggested twenty years ago by Jura basedon IRAS observations. The observed total HI masses range between a fewtimes 106 to just over 109Msolar. Thepresence of regular disc-like structures is a situation as common as HIin offset clouds and tails around early-type galaxies. All galaxieswhere HI is detected also contain ionized gas, whereas no HI is foundaround galaxies without ionized gas. Galaxies with regular HI discs tendto have strong emission from ionized gas. In these cases, the similarkinematics of the neutral hydrogen and ionized gas suggest that theyform one structure. The kinematical axis of the stellar component isnearly always misaligned with respect to that of the gas. We do not finda clear trend between the presence of HI and the global age of thestellar population or the global dynamical characteristics of thegalaxies. More specifically, HI detections are uniformly spread throughthe (V/σ, ɛ) diagram. If fast and slow rotators - galaxieswith high and low specific angular momentum - represent the relics ofdifferent formation paths, this does not appear in the presence andcharacteristics of the HI. Our observations support the idea that gasaccretion is common and does not happen exclusively in peculiarearly-type galaxies. The links observed between the large-scale gas andthe characteristics on the nuclear scale (e.g. the presence ofkinematically decoupled cores, radio continuum emission etc.) suggestthat for the majority of the cases the gas is acquired through merging,but the lack of correlation with the stellar population age suggeststhat smooth, cold accretion could be an alternative scenario, at leastin some galaxies. In either case, the data suggest that early-typegalaxies continue to build their mass up to the present.
| Neutral hydrogen in radio galaxies: Results from nearby, importance for far away
The study of neutral hydrogen emission and absorption in radio galaxiesis giving new and important insights on a variety of phenomena observedin these objects. Such observations are helping to understand the originof the host galaxy, the effects of the interaction between the radio jetand the ISM, the presence of fast gaseous outflows as well asjet-induced star formation. Recent results obtained on these phenomenaare summarized in this review. Although the {H I observationsconcentrate on nearby radio galaxies, the results also have relevancefor the high-z objects as all these phenomena are important, and likelyeven more common, in high-redshift radio sources.
| IC 4200: a gas-rich early-type galaxy formed via a major merger
We present the result of radio and optical observations of the S0 galaxyIC 4200. We observed the galaxy at the 21 cm wavelength with theAustralian Telescope Compact Array, and we obtained optical spectroscopyand V- and R-band images with ESO/NTT/EMMI. Our aim is to determine thelink between H I and stellar content of IC 4200 and derive a coherentpicture of its formation. We find that the galaxy hosts 8.5 ×109 Mȯ of H I rotating on a ~90 deg warpeddisk extended out to 60 kpc from the centre of the galaxy. Opticalspectroscopy reveals a simple-stellar-population-equivalent age of 1.5Gyr in the centre of the galaxy and V- and R-band images show stellarshells. Ionised gas is observed within the stellar body and iskinematically decoupled from the stars and characterised by LINER-likeline ratios. We interpret these observational results as evidence for amajor merger origin of IC 4200, and date the merger back to 1-3 Gyr ago.
| 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.
| The extinction, flux distribution and luminosity of Seyfert 1 nuclei derived from UBV(RI)C aperture photometry
UBV(RI)C aperture photometry was carried out over a four-yrperiod for 92 broad-line Seyfert galaxies. Where possible, theobservations were repeated at different epochs in order to try to detectbrightness variations. Significant variations were found in the majorityof the objects observed at more than one epoch. Plots of the fluxmeasurements through different bands against each other closely resemblelinear relationships. Error contours of the data points in these plotsare shown to be covariant ellipses. A statistical method is developedthat enables one to obtain the best linear fit taking into account theerror geometry peculiar to these data. The nuclear colors are determinedfor 50 significantly variable objects by calculating the beststraight-line fits according to this statistical method. Chi-squaredtests are used to show that, contrary to claims made in some recentstudies, there is no significant deviation of the data from thestraight-line fit in the vast majority of cases. The relationshipbetween galaxy inclination and nuclear extinction is found to be verypoorly defined, showing that the extinction largely depends on theamount of dust in in the circumnuclear region rather than interstellardust in the galaxy itself.
| 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.
| The supergalactic plane redshift survey
Redshift measurements, about 1000 of which are new, are presented for1314 galaxies in a survey toward the apex of the large-scale streamingflow for ellipticals. The velocity histogram shows that the excess ingalaxy number counts in this area is due to a substantial concentrationof galaxies with discrete peaks at V about 3000 km/s and V about 4500km/s. After correction for the sampling function, the centroid of thedensity distribution is found to be near V about 4500 km/s.Normalization to the more extensive SSRS survey, which was selected bythe same criteria, shows that the region studied contains a considerableoverdensity of galaxies from 2000 to 6000 km/s. This result is in goodagreement with the 'great attractor' model suggested by Lynden-Bell etal. (1988) which attributes the peculiar motions of elliptical galaxiesover a large region of space to an extensive mass overdensity whichincludes the Hydra-Centaurus and Pavo-Indus superclusters. The centroidof the density enhancement is also consistent with new data by Dresslerand Faber (1990) of peculiar motions of elliptical and spiral galaxies,both of which show a zero crossing of the Hubble line at approximately4500-5000 km/s.
| The components of mid- and far-infrared emission from S0 and early-type shell galaxies
The IRAS database has been used to study detections of about 150early-type elliptical and S0 galaxies exhibiting a shell structure. Nostrong evidence for the expected enhancement of either star formationrates or heating of the interstellar medium is found. It is suggestedthat for some of the sample galaxies either a contribution from warmdust surrounding evolved stars or emission from an active nucleus may besignificant.
| Spectra of shell ellipticals - Redshifts, velocity dispersions and evidence for recent nuclear star formation
Nuclear spectra are presented for 100 of the galaxies in the Malin andCarter (1983) catalog. Redshifts and velocity dispersions are given forsome of the galaxies. It is found that about 10 percent of the samplegalaxies have colors, absolute magnitudes, and spectra characteristic ofthe poststarburst galaxies in high reshift clusters. It is suggestedthat the more distant poststarburst galaxies may have undergone mergeror accretion events.
| Southern Galaxy Catalogue.
Not Available
| A catalog of elliptical galaxies with shells
We present a catalog of 137 elliptical galaxies south of -17 deg declination which exhibit shell or ripple features at large distances from the galaxy or in the outer envelope. Some of these galaxies show similar features in the inner envelope when suitable high resolution plate material is examined. Very few of the galaxies are associated with radio sources. We discuss the environment of shell galaxies, and the proportion of ellipticals which have these features. It appears that about half of the galaxies with shells are isolated and most of the rest are members of small groups. We discuss several individual examples which appear to be typical of this class of galaxy, and others which probably illustrate an evolutionary sequence.
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