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A Survey of Merger Remnants. II. The Emerging Kinematic and Photometric Correlations
This paper is the second in a series exploring the properties of 51optically selected, single-nuclei merger remnants. Spectroscopic datahave been obtained for a subsample of 38 mergers and combined withpreviously obtained infrared photometry to test whether mergers exhibitthe same correlations as elliptical galaxies among parameters such asstellar luminosity and distribution, central stellar velocity dispersion(σ0), and metallicity. Paramount to the study is totest whether mergers lie on the fundamental plane. Measurements ofσ0 have been made using the Ca triplet absorption lineat 8500 Å for all 38 mergers in the subsample. Additionalmeasurements of σ0 were made for two of the mergers inthe subsample using the CO absorption line at 2.29 μm. The resultsindicate that mergers show a strong correlation among the parameters ofthe fundamental plane but fail to show a strong correlation betweenσ0 and metallicity (Mg2). In contrast toearlier studies, the σ0 values of the mergers areconsistent with objects that lie somewhere between intermediate-mass andluminous giant elliptical galaxies. However, the discrepancies withearlier studies appear to correlate with whether the Ca triplet or COabsorption lines are used to derive σ0, with the latteralmost always producing smaller values. Finally, the photometric andkinematic data are used to demonstrate for the first time that thecentral phase-space densities of mergers are equivalent to those inelliptical galaxies. This resolves a long-standing criticism of themerger hypothesis.Some of the data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation.
| 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.
| The Classification of Galaxies: Early History and Ongoing Developments
"You ask what is the use of classification, arrangement,systematization. I answer you; order and simplification are the firststeps toward the mastery of a subject the actual enemy is the unknown."
| Molecular Disks in the Elliptical Galaxies NGC 83 and NGC 2320
The molecular gas in (some) early-type galaxies holds important clues tothe history and the future of these galaxies. In pursuit of these clues,we have used the BIMA millimeter array to map CO emission in the giantelliptical galaxies NGC 83 and NGC 2320 and to search for CO emissionfrom the S0 galaxy NGC 5838. We also present V and R images of NGC 83and NGC 2320 that trace their dust distributions and enable a search fordisky stellar structures. The molecular gas in NGC 83 is well relaxed,but both CO and dust in NGC 2320 show asymmetric structures that may belinked to a recent acquisition of the gas. However, the specific angularmomentum distribution of molecular gas in NGC 2320 is consistent withthat of the stars. Internal origin of the gas (stellar mass loss)cannot, therefore, be ruled out on angular momentum grounds alone. Wealso consider the evidence for star formation activity and disk growthin these two elliptical galaxies. Radio continuum and FIR fluxes of NGC83 suggest star formation activity. NGC 2320 has bright [O III]emission, but its large radio-FIR flux ratio and the mismatch betweenthe kinematics of CO and [O III] suggest that the ionized gas should notbe attributed to star formation. The origin and future of these twoCO-rich early-type galaxies are thus complex, multifaceted stories.
| The peculiar galaxy Mkn 298 revisited with integral field spectroscopy
Spectroscopic and imaging data of the peculiar galaxy Mkn 298 arepresented. Narrow-band Hα and broad-band R images are used tostudy the star formation rate in the galaxy and its morphology, which istypical of a merging system. Long-slit and integral field spectra areused to assess the kinematics of gas and stars, and the nature of theionizing source at different distances from the nucleus. In particular,the nucleus of Mkn 298 is characterized by peculiar line ratios: [NII]λ6583/Hα is typical of H II-like regions, while [OI]λ6300/Hα could indicate the presence of an activegalactic nucleus. We show that models where a shock component is addedto photoionization from a starburst allow us to reproduce the observedline ratios. Mkn 298 is thus most likely a star-forming galaxy, ratherthan a galaxy hosting an active nucleus.Based on data obtained at the 2.2m and NTT telescopes of ESO-la Silla(Chile), at the 2.2m telescope of DSAZ-Calar Alto (Spain), and at the 6mtelescope of SAO (Russia).
| A Deep K-Band Photometric Survey of Merger Remnants
We present K-band photometry for 51 candidate merger remnants to assessthe viability of whether spiral-spiral mergers can produce bona fideelliptical galaxies. Using both the de Vaucouleurs r1/4 andSérsic r1/n fitting laws, it is found that the stellarcomponent in a majority of the galaxies in the sample has undergoneviolent relaxation. However, the sample shows evidence for incompletephase mixing. The analysis also indicates the presence of ``excesslight'' in the surface brightness profiles of nearly one-third of themerger remnants. Circumstantial evidence suggests that this is due tothe effects of a starburst induced by the dissipative collapse of thegas. The integrated light of the galaxies also shows that mergers canmake L* elliptical galaxies, in contrast to earlier infrared studies.The isophotal shapes and related structural parameters are alsodiscussed, including the fact that 70% of the sample show evidence fordisky isophotes. The data and results presented are part of a largerphotometric and spectroscopic campaign to thoroughly investigate a largesample of mergers in the local universe.
| First detection of cold dust in the northern shell of NGC 5128 (Centaurus A)
Deep far-infrared (FIR) imaging data obtained with ISOPHOT at 90 μm,150 μm, and 200 μm detected the thermal emission from cold dust inthe northern shell region of NGC 5128 (Centaurus A), where previouslyneutral hydrogen and molecular gas has been found. A somewhat extendedFIR emission region is present in both the 150 μm and 200 μm map,while only an upper flux limit could be derived from the 90 μm data.The FIR spectral energy distribution can be reconciled with a modifiedblackbody spectrum with very cold dust color temperatures and emissivityindices in the range 13 K < TDust < 15.5 K and 2 >β > 1, respectively, where the data favor the low temperatureend. A representative value for the associated dust mass isMDust ≈ 7×104 Mȯ, whichtogether with the HI gas mass gives a gas-to-dust ratio of ≈300,close the average values of normal inactive spiral galaxies. This value,in conjunction with the atomic to molecular gas mass ratio typical for aspiral galaxy, indicates that the interstellar medium (ISM) from theinner part of a captured disk galaxy is likely the origin of theoutlying gas and dust. These observations are in agreement with recenttheoretical considerations that in galaxy interactions leading tostellar shell structures the less dissipative clumpy component of theISM from the captured galaxy can lead to gaseous shells. Alternatively,the outlying gas and dust could be a rotating ring structure resultingfrom an interaction or even late infall of tidal material of a merger inthe distant past. With all three components (atomic gas, molecular gas,dust) of the ISM present in the northern shell region, local starformation may account for the chains of young blue stars surrounding theregion to the east and north. The dust cloud may also be involved in thedisruption of the large scale radio jet before entering the brighterregion of the northern radio lobe.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.
| Warm gas kinematics in shell galaxies
Shells are interpreted as debris from interaction/acquisition episodesthat occur in a galaxy. We present a study of the warm (T~104 K) gas component in a sample of five shell galaxiesbelonging to the Malin & Carter compilation. Hα observationshave been obtained at the ESO 3.6-m telescope equipped with a CIGALEscanning Fabry-Perot interferometer coupled with a new IPCS camera.Most of our sample galaxies show disturbed/irregular gaseous velocityfields. The gas distribution in NGC 7070A and 7135 shows elongated,asymmetric structure relative to the stellar body. The continuum andline maps for ESO 2400100 show a double nucleus. The nuclei are slightlyoff-centre with respect to the barycentre of the pair, a deformationthat cannot arise from projection effects and that suggests a strongon-going tidal interaction.Kinematics of the stellar and gas component derived for NGC 1553 aresimilar, although the gas component shows evidence for non-circularmotion. In most of our objects the gas and the stellar kinematics appeardecoupled, but no rings of gas nor diffuse gas shells are detected. Ifshell galaxies form through an acquisition/merging event, the generalhypothesis according to which the gas in Es is accreted from outside thegalaxy is further supported by these data. We speculate concerning shellgalaxy evolution using additional information coming from studies ofline-strength indices.
| CO (3-2) Observations of Early-Type Galaxies with the Heinrich Hertz Telescope
We present Heinrich Hertz Telescope CO (3-2) observations of a sample of10 early-type galaxies detected both in far-infrared (IRAS) and in CO(1-0). Six of the objects (i.e., 60% of the sample) were detected in theCO (3-2) transition. Comparison of the beam-matched CO (3-2)/CO (1-0)and CO (2-1)/CO (1-0) intensity ratios with simple large velocitygradient and photodissociation region models reveals that early-typeobjects can be broadly classified into two categories. The majority ofobjects have a molecular interstellar medium of moderate density(nH2<=1000 cm-3) and temperature(T<=30 K). Two objects, NGC 3593 and NGC 4691, show indications ofquite denser and warmer environments, as well as gradients in theirphysical properties, compatible with their classification as starbursts.The heating source of the molecular gas and dust in all the objects inour sample appears to be ongoing star formation.
| Dwarfs after mergers? The case of NGC 520, NGC 772, Arp 141, NGC 3226/7, NGC 3656 and Arp 299
We present results from a survey of dwarf galaxy candidates in thevicinity of strongly interacting galaxies. The goal of the survey was atest of the hypothesis that massive condensations of stars and HI intidal tails of large interacting galaxies may be a significant source ofindependent, self-gravitating dwarf galaxies. These so called tidaldwarf galaxies (TDG) can be expected to resemble the blue luminous knotsfound in tidal tails, but also might appear as redder, evolved systemsif formed much before they are being observed. For the present study, ahomogeneous subsample of 6 fields was selected from the catalog ofextended objects in fields around 15 strongly interacting galaxies byDeeg et al. (\cite{Deeg98}). Criteria for the subsample were: similarredshifts of the central interacting galaxies, and photometriccompleteness of the extended objects in V and R. The number density ofthese TDG candidates was compared with expected background galaxydensities. Within the statistical errors, background galaxies accountfor most, if not all of the extended objects. There is no evidence for asubstantial locally formed dwarf galaxy population. Thus, we concludethat field galaxy-galaxy interactions are likely to result in theformation of only a few long-lived TDG.
| Formation of gas discs in merging galaxies
Observations indicate that much of the interstellar gas in merginggalaxies may settle into extended gaseous discs. Here, I presentsimulations of disc formation in mergers of gas-rich galaxies. Up tohalf of the total gas settles into embedded discs; the most massiveinstances result from encounters in which both galaxies are inclined tothe orbital plane. These discs are often warped, many have rathercomplex kinematics, and roughly a quarter have counter-rotating orotherwise decoupled central components. Discs typically grow from theinside out; infall from tidal tails may continue disc formation overlong periods of time.
| A catalogue and analysis of local galaxy ages and metallicities
We have assembled a catalogue of relative ages, metallicities andabundance ratios for about 150 local galaxies in field, group andcluster environments. The galaxies span morphological types from cD andellipticals, to late-type spirals. Ages and metallicities were estimatedfrom high-quality published spectral line indices using Worthey &Ottaviani (1997) single stellar population evolutionary models. Theidentification of galaxy age as a fourth parameter in the fundamentalplane (Forbes, Ponman & Brown 1998) is confirmed by our largersample of ages. We investigate trends between age and metallicity, andwith other physical parameters of the galaxies, such as ellipticity,luminosity and kinematic anisotropy. We demonstrate the existence of agalaxy age-metallicity relation similar to that seen for local galacticdisc stars, whereby young galaxies have high metallicity, while oldgalaxies span a large range in metallicities. We also investigate theinfluence of environment and morphology on the galaxy age andmetallicity, especially the predictions made by semi-analytichierarchical clustering models (HCM). We confirm that non-clusterellipticals are indeed younger on average than cluster ellipticals aspredicted by the HCM models. However we also find a trend for the moreluminous galaxies to have a higher [Mg/Fe] ratio than the lowerluminosity galaxies, which is opposite to the expectation from HCMmodels.
| Molecular Gas in Elliptical Galaxies: Distribution and Kinematics
I present interferometric images (~7" resolution) of CO emission in fiveelliptical galaxies and nondetections in two others. These data doublethe number of elliptical galaxies whose CO emission has been fullymapped. The sample galaxies have 108 to5×109 Msolar of molecular gas distributed inmostly symmetric rotating disks with diameters of 2-12 kpc. Four out ofthe five molecular disks show remarkable alignment with the opticalmajor axes of their host galaxies. The molecular masses are a fewpercent of the total dynamical masses that are implied if the gas is oncircular orbits. If the molecular gas forms stars, it will makerotationally supported stellar disks that will be very similar incharacter to the stellar disks now known to be present in manyellipticals. Comparison of stellar kinematics to gas kinematics in NGC4476 implies that the molecular gas did not come from internal stellarmass loss because the specific angular momentum of the gas is about 3times larger than that of the stars.
| Supernovae in isolated galaxies, in pairs and in groups of galaxies
In order to investigate the influence of environment on supernova (SN)production, we have performed a statistical investigation of the SNediscovered in isolated galaxies, in pairs and in groups of galaxies. 22SNe in 18 isolated galaxies, 48 SNe in 40 galaxy members of 37 pairs and211 SNe in 170 galaxy members of 116 groups have been selected andstudied. We found that the radial distributions of core-collapse SNe ingalaxies located in different environments are similar, and consistentwith those reported by Bartunov, Makarova & Tsvetkov. SNe discoveredin pairs do not favour a particular direction with respect to thecompanion galaxy. Also, the azimuthal distributions inside the hostmembers of galaxy groups are consistent with being isotropics. The factthat SNe are more frequent in the brighter components of the pairs andgroups is expected from the dependence of the SN rates on the galaxyluminosity. There is an indication that the SN rate is higher in galaxypairs compared with that in groups. This can be related to the enhancedstar formation rate in strongly interacting systems. It is concludedthat, with the possible exception of strongly interacting systems, theparent galaxy environment has no direct influence on SN production.
| 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.
| Empirical Diagnostics of the Starburst-AGN Connection
We examine a representative sample of 35 Seyfert 2 nuclei. Previous workhas shown that nearly half (15) of these nuclei show the direct (butdifficult to detect) spectroscopic signature at optical/near-UVwavelengths of the hot massive stars that power circumnuclearstarbursts. In the present paper we examine a variety of more easilymeasured quantities for this sample, such as the equivalent widths ofstrong absorption features, continuum colors, emission line equivalentwidths, emission line ratios and profiles, far-IR luminosities, andnear-UV surface brightness. We compare the composite starburst+Seyfert 2nuclei to ``pure'' Seyfert 2 nuclei, Starburst galaxies, and normalgalactic nuclei. Our goals are to verify whether the easily measuredproperties of the composite nuclei are consistent with the expectedimpact of a starburst and to investigate alternative less demandingmethods to infer the presence of starbursts in Seyfert 2 nuclei,applicable to larger or more distant samples. We show that starbursts doindeed leave clear and easily quantifiable imprints on the near-UV tooptical continuum and emission line properties of Seyfert 2's. Compositestarburst+Seyfert 2 systems can be recognized by: (1) a strong``featureless continuum'' (FC), which dilutes the Ca II K line from oldstars in the host's bulge to an equivalent width WK<10Å (2) emission lines whose equivalent widths are intermediatebetween starburst galaxies and ``pure'' Seyfert 2's (3) relatively lowexcitation line ratios, which indicate that part of the gas ionizationin these Seyfert 2's (typically ~50% of Hβ) is due tophotoionization by OB stars; (4) large far-IR luminosities(>~1010 Lsolar) (5) high near-UV surfacebrightness (~103 Lsolar pc-2). Thesecharacteristics are all consistent with the expected impact ofcircumnuclear starbursts on the observed properties of Seyfert 2's.Furthermore, they offer alternative empirical diagnostics of thepresence of circumnuclear starbursts from a few easily measuredquantities.
| H I in the Shell Elliptical Galaxy NGC 3656
Very Large Array7 neutral hydrogenobservations of the shell elliptical galaxy NGC 3656 reveal an edge-on,warped minor-axis gaseous disk (MHI~2×109Msolar) extending 7 kpc. H I is also found outside theoptical image, on two complexes to the northeast and northwest that seemto trace one or two tidal tails, or possibly an outer broken H I disk orring. These complexes link with the outer edges of the inner disk andappear displaced with respect to the two optical tails in the galaxy.The disk kinematics is strongly lopsided, suggesting recent or ongoingaccretion. Integral-field optical fiber spectroscopy at the region ofthe bright southern shell of NGC 3656 has provided a determination ofthe stellar velocities of the shell. The shell, at 9 kpc from thecenter, has traces of H I with velocities bracketing the stellarvelocities, providing evidence for a dynamical association of H I andstars at the shell. Within the errors the stars have systemic velocity,suggesting a possible phase-wrapping origin for the shell. We probed aregion of 40'×40' (480 kpc×480kpc)×1160 km s-1 down to an H I mass sensitivity (6σ) of 3×107 Msolar and detect fivedwarf galaxies with H I masses ranging from 2×108 to2×109 Msolar, all within 180 kpc of NGC 3656and all within the velocity range (450 km s-1) of the H I ofNGC 3656. The dwarfs had been previously cataloged, but none had a knownredshift. For the NGC 3656 group to be bound requires a total mass of(3-7.4)×1012 Msolar, yielding amass-to-light ratio from 125 to 300. The overall H I picture presentedby NGC 3656 supports the hypothesis of a disk-disk merger origin orpossibly an ongoing process of multiple mergers with nearby dwarfs.Based on observations made with the William Herschel Telescope operatedon the island of La Palma by the Isaac Newton Group of Telescopes in theSpanish Observatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias.
| Environment status of blue compact galaxies and trigger of star formation
The work studies of the environment of low-mass galaxies with activestar formation (SF) and a possible trigger of SF bursts due togravitational interaction. Following the study by Taylor et al. (1995),we extend the search for possible disturbing galaxies of various massesto a much larger sample of 86 BCGs from the sky region of the SecondByurakan survey (SBS). The BCG magnitudes and radial velocities arerevised and up-dated. The sample under study is separated by thecriteria: EW([O III]λ5007) > 45 Å andVh < 6,000 kms and should be representative of alllow-mass galaxies which experience SF bursts. We argue that the moderatetidal disturbers should be taken into account, and incorporate therespective range of distances in the search for disturbing neighbours.The majority of the neighbours in the vicinity of the studied BCGs arefound through the study of their environment among UZC (Falco et al.\cite{Falco99}) galaxies, and the follow-up careful search of thefainter galaxies in the NED database. For the remaining BCGs, theneighbouring galaxies are found based on the results of the SAO 6mtelescope spectroscopy. By studing the data on the radial velocities ofgalaxies in the vicinity of BCGs we found: 1) 33 of the studied BCGs(~38.5%) are associated with significantly brighter galaxies (Δ B>= 1.5m); 2) 23 BCGs (~26.5%) have neighbours either ofcomparable or significantly lower brightness; 3) 14 of the studied BCGs(16\%) with no evident associated galaxy are either certain, orprobable, mergers. Summarizing, we conclude that in ~80% (or more) BCGsfrom the studied sample, the SF bursts are triggered either by tidalaction of various strengths from other galaxies, or due to mergers oflow-mass galaxies. We briefly discuss the implications of our mainconclusion for evolutionary links of BCGs to other types of low-massgalaxies. Part of our sample falls into the volume belonging to theLocal Supercluster. Therefore we formulate the results separately on the``Local Supercluster volume'' and ``general field region''. The totalfractions of BCGs likely triggered by interaction with other galaxy arerespectively, ~84.5% and 80% for the nearby volume and for the generalfield. The fractions of BCGs with significantly brighter disturbers inthese two groups are seemingly different (~54±14% vs.~31.5±7%, respectively). Among the so called ``isolated'' BCGs(that is, without a bright neighbouring galaxy) in both the LocalSupercluster volume and in general field, ~43±10% are probablydisturbed by dwarf galaxies and ~26±8% have a merger morphology.In the Appendix we present the results of the spectroscopy with the SAO6m telescope of 27 galaxies in an attempt to find possible disturbinggalaxies in the vicinity of some of the sample BCGs. Tables 2, 3 and A.1with their notes and Figs. A.1-A.3 are only available in electronic format http://www.edpsciences.org
| Imaging of the shell galaxies NGC 474 and 7600, and implications for their formation
We present photometric observations of two shell galaxies, NGC 474 and7600. We examine the photometric colours and surface brightnesses of theshells and their host galaxies, and the isophotal parameters of eachgalaxy. In the case of NGC 474, we find that the shell formation isconsistent with a merger origin, although it is possible that the closecompanion NGC 470 is contributing to the shell system via mass transfer.NGC 7600 exhibits shell geometry and colours which also favour a mergerorigin.
| The shell elliptical galaxy NGC 2865: evolutionary population synthesis of a kinematically distinct core
We report on the discovery of a rapidly corotating stellar and gascomponent in the nucleus of the shell elliptical NGC 2865. The stellarcomponent extends ~ 0.51 h_100^-1 kpc along the major axis, and showsdepressed velocity dispersion and absorption-line profiles skewed in theopposite sense to the mean velocity. Associated with it is a youngstellar population with enhanced Hβ, lowered Mg, and the same Feindices relative to the underlying elliptical. Its recent star formationhistory is constrained by considering `bulge+burst' models under fourphysically motivated scenarios, using evolutionary population synthesis.Scenarios in which the nuclear component is formed over a Hubble time orrecently from continuous gas inflow are ruled out. A recent starburstcan satisfy observational constraints only if its population hasmetallicity 2.5-6.3 times that of the bulge. The nucleariron-to-magnesium index ratio can be explained by a temperature effectin the atmospheres of stars at main-sequence turn-offs between A3 andF4, during which the Fe indices of the burst population are high enoughto compensate for dilution effects. It is therefore possible to modifyline-index ratios (and hence the inferred abundance ratio) simply by thepresence of a young population with the same abundance. The highmetallicity requirement suggests self-enrichment, and a burst durationlonger than the SN II feedback time-scale. No solution exists for burstslonger than 0.4 Gyr. Burst age estimates of 0.4-1.7 Gyr are larger thanthat for the shells (0.24 Gyr), assuming phase-wrapping. No starburst isrequired if the nuclear component is composed of stars with Fe abundanceenhanced by ~0.08 dex relative to the underlying elliptical, which areaccreted by an event which truncated the star formation. This relies onthe abundance differences between giant ellipticals and spirals. The ageestimates of 0.1-0.4 Gyr in this scenario are in closer agreement withthose for phase-wrapped shells. Our results argue for a gas-richaccretion or merger origin for the shells and kinematic subcomponent inNGC 2865. Arguments based on stellar populations and gas dynamicssuggest that one of the progenitors is probably an Sb or Sc spiral. Wedemonstrate that despite the age and metallicity degeneracy of theunderlying elliptical, the age and metallicity of the kinematicsubcomponent can be constrained. This work strengthens the link betweenkinematically distinct cores (KDCs) and shells, and demonstrates that aKDC can be formed from a late merger.
| 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.
| Galaxy Interactions: The HI Signature
Invited review in Session 3: Tidal Interactions.
| 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.
| Neutral Hydrogen and Dark Matter in Spiral Galaxies
The first part presents a brief review of the main HI properties ofisolated, normal spiral galaxies and of the phenomena which seem tocharacterize and dominate their internal metabolism. In the second partattention is drawn to all those processes, such as tidal interactions,accretion and mergers, that depend on the galaxy environment and mayplay a significant role in galaxy formation and evolution. In the thirdpart the observational evidence for the dark matter component of spiralgalaxies is discussed.
| Near-Infrared Spectroscopy of ARP Interacting Galaxies
We discuss near-infrared spectra of 20 interacting galaxies from the ArpCatalog and analyze the properties of similar galaxies for which onlyoptical spectra are available. We find excellent agreement between thetypes of activity determined from the infrared and optical,demonstrating that obscuration does not seriously bias the opticalresults. None of the 20 galaxies show infrared spectral characteristicsthat differ from expectations for isolated galaxies; the very strongshock-excited lines seen in a few interacting systems must be uncommon.Most of the galaxies in our infrared sample are the sites of starburststhat appear to have had durations of 1 to 5 Myr and to be observed 3 to10 Myr after the peak star-forming episode. Four of the 20 galaxies haveLINER or composite starburst/LINER spectra that are likely to arise fromshocks due to supernovae in late phase starbursts. In the fullinteracting galaxy sample, there is a substantial excess of Seyfert 2nuclei, supporting previous indications that this type of activity tendsto occur in interacting host galaxies.
| A catalogue of dwarf galaxy candidates around interacting galaxies
We present results from the imaging of a sample of 12 interactinggalaxies for which we have cataloged all potential dwarf systems in thevicinity of these strongly interacting galaxies. After careful cleaningof the images and applying a restrictive S/N criterion we haveidentified, measured and cataloged all possible extended objects in eachfield. On the frames, covering 11.4 x 10.5 arcmins, typically 100-200non-stellar faint, extended objects were found. The vast majority(>98%) of these objects had not been previously identified. Thenumber of expected objects in the magnitude range R= 18 - 19.5 exceedsthe expected count of background galaxies. This supports the possibilitythat a density enhancement of extended objects around some interactinggalaxies results from the addition of a locally formed dwarf galaxypopulation. Tables 4 to 15 only available in electronic form at CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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
| Cool dense gas in early-type galaxies
CO observations have shown that many lenticular and elliptical galaxiescontain significant amounts of cool dense gas. This review summarizesthe observational results related to the neutral gas phase and presentsa systematic comparison with other interstellar and stellar data. Thediscovery of very dense molecular gas in the nuclear regions ofearly-type galaxies, the possible existence of a dust component neitherseen optically nor in CO, internal inconsistencies of cooling flowscenarios, the origin of the cool gas, the presence of massive stars,aspects of galaxy evolution, and possibilities for future research arediscussed in the light of the new data.
| Two Tails in NGC 3656 and the Major Merger Origin of Shell and Minor-Axis Dust Lane Elliptical Galaxies
I report on the discovery of two faint (~26.8 R mag arcsec-2) tidaltails around the shell elliptical galaxy NGC 3656 (Arp 155). This galaxyhad previously been interpreted as a case of accretion, or minor merger.The two tidal tails are inconsistent with a minor merger and pointinstead to a disk-disk major merger origin. NGC 3656 extends Toomre'smerger sequence toward normal elliptical galaxies and hints at a majormerger origin for shells and minor-axis dust lanes. A dwarf galaxy liesat the tip of one of the tidal tails. A prominent shell, which showssharp azimuthal color discontinuities, belongs to a rotating dynamicalcomponent with young stars that includes the inner dust lane.
| A Dynamical Model for the Twisted Gas Disk in Centaurus A
The prominent minor-axis dust lane across the radio galaxy Cen A hasbeen extensively mapped in the emission lines of Hα, H I, and CO,revealing an ordered velocity field which has been interpreted as thatof a warped and twisted disk of gas seen nearly hedge-on. Here it isshown that the geometry of this disk can be explained as that of anear-polar structure precessing about the symmetry axis of anapproximately oblate galaxy potential which, like the stellar body, isnearly round at the center, becoming flattened farther out. Both freelyprecessing models and those taking account of the self-gravity of thegas are presented. The broken elliptical ring of H I gas recently foundto be associated with the faint outer shells of Cen A can be explainednaturally as a continuation of the same precessing disk. This precessingmodel for the gas disk assumes that the gravitational potential of Cen Ais close to axisymmetric; precession should be qualitatively similar ifthe figure is triaxial and tumbling about its short axis in the samesense as the rotation of the stars.
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