Dumbbell Galaxies Research Articles

Multifrequency JVLA observations of the X-shaped radio galaxy in Abell 3670

Context.X-shaped radio galaxies (XRGs) exhibit a pair of bright primary lobes and a pair of weak secondary lobes (“wings”), which are oriented with an angle that gives the structure a cross-like shape. Though several theoretical models have been proposed to explain their origin, there is currently not a general consensus on a formation scenario.Aims.We analysed new multifrequencyKarl G. JanskyVery Large Array (JVLA) radio data at 1.5, 5.5, 6, and 9 GHz of the candidate XRG in Abell 3670 (A3670) in order to characterise and classify it for the first time and to investigate its origin.Methods.We produced flux, spectral index, and radiative age maps of A3670 by means of the new radio data. We investigated the connection between the radio galaxy and its host, a brightest cluster galaxy (BCG) with two optical nuclei classified as a dumbbell galaxy. Finally we discussed the literature models and compared them to the observed properties of A3670.Results.We classify A3670 as a Fanaroff–Riley I-type XRG and measured a 1.4 GHz radio power ofP1.4 = 1.7 × 1025W Hz−1. By estimating the radiative age of the various source components, we find that the wings are Δt ≃ 20 Myr older than the lobes. We verified that the lobes and wings are aligned with the major and minor axes of the optical galaxy, respectively, and we estimated a black hole mass ofMBH ∼ 109 M⊙, which is in agreement with the typical properties of the XRGs.Conclusions.Among the discussed scenarios, the jet-shell interaction model may best reproduce the observed properties of A3670. The gas of a stellar shell is responsible for the deflection of the jets, thus forming the wings. The presence of stellar shells in A3670 is plausible, but it needs further optical observations to be confirmed.

Intergalactic stellar populations in intermediate redshift clusters

A substantial fraction of the total stellar mass in rich clusters of galaxies resides in a diffuse intergalactic component usually referred to as the Intra-Cluster Light (ICL). Theoretical models indicate that these intergalactic stars originate mostly from the tidal interaction of the cluster galaxies during the assembly history of the cluster, and that a significant fraction of these stars could have formed in-situ from the late infall of cold metal-poor gas clouds onto the cluster. The models make predictions about the age distribution of the ICL stars, which may provide additional observational constraints. However, these models also over-predict the fraction of stellar mass in the ICL by a substantial margin. Here we present population synthesis models for the ICL of a dumb-bell dominated intermediate redshift (z=0.29) X-ray cluster for which we have deep MOS data obtained with the FORS2 instrument. In a previous paper we have proposed that the dumbell galaxy act as a grinding machine tearing to pieces the galaxies that pass nearby thus enriching the intergalactic medium. In this paper we analyze the spectra at different locations within the ICL and find that it is dominated by old metal rich stars, at odds with what has been found in nearby clusters where the stars that dominate the ICL are old and metal poor. While we see a weak evidence of a young, metal poor, component, if real, these young stars would amount to less than 1% of the total ICL mass, much less than the up to 30% predicted by the models. We propose that the very metal rich (i.e. 2.5 times solar) stars in the ICL of our cluster, which comprise approximately 40% of the total mass, originate mostly from the central dumb-bell galaxy, while the remaining solar and metal poor stars come from spiral, post-starburst (E+A), and metal poor dwarf galaxies. About 16% of the ICL stars are old and metal poor.

High relative velocity central dumbbells in poor clusters

AbstractWe propose that some high relative velocity dumbbell galaxies are the centers of poor clusters or groups that are coming into a merging process. The components of these galaxies closely follow the incoming velocity of the merging groups, as revealed by the bimodality of the velocity histograms. Only mergers in a direction with a small angle to the line of sight can show the large velocity difference of the components and the velocity separation of incoming subgroups in the histograms. In this case the simple interpretation would be that the dumbbells components are also in an early phase of their merger, as they still keep the information of the incoming orbits, but analysis of a numerous sample is needed to prove this suggestion (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Are Dumbbell Brightest Cluster Members Signposts to Galaxy Cluster Activity?

AbstractWe assemble a sample of galaxy clusters whose brightest members are dumbbell galaxies and compare them with a control sample in order to investigate if they are the result of recent mergers. We show that the dumbbell sample is no more likely than other clusters to exhibit subclustering. However, they are much more likely to have at least one dumbbell component possessing a significant peculiar velocity with respect to the parent cluster than a non-dumbbell brightest cluster member. We interpret this in the context of seeing the clusters at various stages of post-merger relaxation.

X‐Ray Constraints on Galaxy‐Gas‐Jet Interactions in the Dumbbell Galaxies NGC 4782 and NGC 4783 in the LGG 316 Galaxy Group

We present results from a 49.3 ks Chandra X-ray observation of the strongly interacting dumbbell galaxies NGC4782(3C278) and NGC4783 that constrain the kinematics of the interaction and models for bending the radio jets associated with NGC4782. The galaxies are embedded in an approximately spherical distribution of group gas, centered on NGC4782,that is nearly isothermal with mean kT ~ 1.4+/- 0.4 keV. The X-ray morphology suggests that NGC4783 is infalling into a single, massive galaxy group (LGG316) with NGC4782 nearly at rest at the center of the group potential.NGC4783 shows a sharp X-ray surface brightness edge (cold front) to the east and a ~15 kpc ram-pressure-stripped tail to the west. Analysis of this cold front indicates NGC4783 is moving east with a total velocity ~870+270-400 km/s (Mach ~1.4+0.5-0.7) at an inclination angle ~46 deg.(>33 deg.)towards us with respect to theplane of the sky. A ~45Myr old X-ray cavity, with enthalpy of 4.4 x 10^{57}ergs, coincides with the eastern radio lobe of 3C278. X-ray knots are found on both the radio jet and counter-jet, coincident with peaks in the radio emission. Assuming a light, mildly relativistic jet in 3C278, ram pressure velocities of 100-200 km/s impacting the eastern jet and ~170 km/s acting on the western radio lobe are sufficient to produce their observed bending. These velocities may be caused by bulk motions established in the IGM by the high velocity interaction between the galaxies, by the motion of NGC4782 relative to the IGM, or both.

Abell 3560, a galaxy cluster at the edge of a major merging event

In this paper we study A3560, a rich cluster at the southern periphery of the A3558 complex, a chain of interacting clusters in the central part of the Shapley Concentration supercluster. From a ROSAT-PSPC map we find that the X-ray surface brightness distribution of A3560 is well described by two components, an elliptical King law and a more peaked and fainter structure, which has been modeled with a Gaussian. The main component, corresponding to the cluster, is elongated with the major axis pointing toward the A3558 complex. The second component, centered on the Dumb-bell galaxy which dominates the cluster, appears significantly offset (by about 0.15 Mpc) from the cluster X-ray centroid. From a Beppo-SAX observation we derive the radial temperature profile, finding that the temperature is constant (at kT~3.7 keV) up to 8 arcmin, corresponding to 0.3 Mpc: for larger distances, the temperature significantly drops to kT~1.7 keV. We analyze also temperature maps, dividing the cluster in 4 sectors and deriving the temperature profiles in each sector: we find that the temperature drop is more sudden in the sectors which point towards the A3558 complex. From VLA radio data, at 20 and 6 cm, we find a peculiar bright extended radio source (J1332-3308), composed by a core (centered on the northern component of the Dumb-bell galaxy), two lobes, a "filament" and a diffuse component. The morphology of the source could be interpreted either with a strong interaction of the radio source with the intracluster medium or with the model of intermittency of the central engine.

Radio study of X-ray clusters of galaxies — I. A3528: a pre-merging cluster in the core of the Shapley Supercluster

As part of an extensive radio-IR-optical-X-ray study of ROSAT clusters of galaxies in the Hydra region we have observed the bimodal Abell cluster A3528, located in the core of the Shapley Supercluster (z ≃ 0.053), with the Molonglo Observatory Synthesis Telescope at 843 MHz and the Australia Telescope Compact Array at 1.4 and 2.4 GHz. This is part I in a series of papers which looks at the relationship between the radio and X-ray emission in samples of ROSAT selected clusters. The radio source characteristics — tailed morphologies and steep spectra — are consistent with the effects of a dense intracluster medium and the pre-merging environment of A3528. In particular, we present evidence that the minor member of the radio-loud dumbbell galaxy located at the centre of the northern component of A3528 is on a plunging orbit. We speculate that this orbit may have been induced by the tidal interactions between the merging components of A3528. In addition, the radio source associated with the dominant member of the dumbbell galaxy exhibits many of the characteristics of compact steep spectrum sources. We argue that the radio emission from this source was triggered ∼ 106 yr ago by tidal interactions between the two members of the dumbbell galaxy, strengthening the argument that compact steep spectrum (CSS) sources are young. Re-analysis of archive pointed Position Sensitive Proportional Counter (PSPC) data using multiresolution filtering suggests the presence of an AGN and/or a cooling flow in the southern component of A3528.

A spatial, kinematical, and dynamical analysis of Abell 400

The paper presents a detailed spatial, kinematical, and dynamical analysis for the cluster A400, based on a nearly complete redshift survey of bright galaxies within 1 Mpc of the cluster center. A dispersed component with a high fraction of spiral galaxies at a velocity of 8200 km/s, and a background group with a mean velocity of 13,400 km/s are identified. It is proposed that the main body of A400 is composed of at least two individual subclusters. If subclustering is ignored, the derived dispersion of the 88 galaxies with measured velocities within 4000 km/s of the bright dumbbell galaxy near the cluster center is 702 km/s. When kinematic information is used to split A400 into likely subclusters, the velocity dispersions of the individual units which make up this cluster are on the order of 200-300 km/s. If A400 is considered a single entity, the inferred blue mass-to-light ratio is 1210 solar masses/solar luminosities. It is argued that A400 is an example of a presently occurring merger, and that the individual components of the dumbbell galaxy were once individual D galaxies within the premerger subclusters.

Very large array observations of radio-selected dumbbell galaxies

An unbiased sample of radio sources associated with optical dumbbell galaxies is presented. This sample has been assembled to study the relationship between the radio and optical properties of radio-loud dumbbell galaxies. The radio sources were selected from the Parkes, B2 and 3C catalogues. High-quality radio data already exist for a number of the sources in our sample, but those sources without good data have been observed with the very large array at 20 or 6 cm. These new observations are described here and radio images are presented. Analysis of both the radio structure of the sources and their radio luminosity has been carried out, and a comparison is made with the properties of a complete sample of radio sources associated with single galaxies

The NGC 4782/3 dumbbell massive group

The group of mostly faint galaxies surrounding the dumbbell galaxy NGC 4782/3 is examined. Assuming that the group mass is negligible compared to the dumbbell galaxy, an orbit-independent estimate for an upper limit of the mass of the galaxies is obtained using the virial theorem. Spectroscopic observations of 13 galaxies in the group suggest that the group has mass values in the range (1.8-6) X 10 to the 13th/h solar mass. If mass is distributed as luminosity, the dumbbell galaxy has a total mass in the range (0.8-3) X 10 to the 13th/h solar mass. 21 refs.

Dynamics of Groups around Interacting Double Ellipticals: Measuring Dark Matter Haloes

Binary galaxies, as binary stars, are important to measure masses, as suggested by Page (1952). Because three orbit parameters are measurable for galaxies at one instant of time, severe uncertainties remain in the orbit and mass determinations. These uncertainties can partly be overcome by statistical studies of selected samples and/or n-body simulations. Close double galaxies (and isolated galaxies) could also be useful to estimate dynamical masses if we can find test particles around them.Interacting elliptical pairs or dumb-bell galaxies are found with a large range, between 0-1200 km s-1, of relative radial velocities. Standard 2-body orbit calculations, highly uncertain due to projection factors, suggest for the largest velocity differences very large galaxy masses, if the systems are bound and stationary. However, recent n-body simulations model these binaries as galaxies captured from hyperbolic orbits, requiring masses of order a few times 1011M⊙) (Borne et al. 1988), but producing systems that are short lived.

Dumb-Bell Galaxies in Southern Clusters: Catalog and Preliminary Statistical Results

The dominant galaxy of a rich cluster is often an object whose formation and evolution is closely connected to the dynamics of the cluster itself. Hoessel (1980) and Schneider et al. (1983) estimate that 50 % of the dominant galaxies are either of the dumb-bell type or have companions at projected distances less than 20 kpc, which is far in excess of the number expected from chance projection (see also Rood and Leir 1979).Presently there is no complete sample of these objects, with the exception of the listing of dumb-bell galaxies in BM type I and I-II clusters in the Abell statistical sample of Rood and Leir (1979).

The dynamics of dumb-bell galaxies

Des modeles theoriques sont presentes pour une classe particuliere de galaxies binaires (galaxies halteres) dans lesquels les 2 composantes de meme dimension sont en revolution sur des orbites circulaires a l'interieur d'une enveloppe commune d'etendue ajustable. Une serie d'equilibres sont construits pour ces sytemes, ces equilibres sont bases sur des fonctions de distribution qui ne dependent que du Jacobien de l'energie. La stabilite dynamique de ces modeles est ensuite exploree au moyen de simulations n corps

Two high-velocity encounters of elliptical galaxies

We present the results of our study of two collisions of binary elliptical galaxies, NGC 4782/4783 and NGC 2672/2673. Each pair has a high relative velocity (>500 km s−1 along the line-of-sight) but the two pairs differ in mass ratio (≈1 for the first pair, and ≈10 for the second). CCD images and velocities obtained from digital spectra are used to constrain simulations of the galaxy collisions. Once a solution has been found and its uniqueness verified, we derive the binary orbital elements, the orientation of the orbit in the sky, the time since pericenter, and the dynamical mass of the pair. This method provides a quantitative determination of galaxy masses on the scale of the binary separations free from uncertainties due to projection effects. We also derive accurate timing of the collision and information about the fate of the pairs (merger/escape). Among our conclusions, we find that the dumb-bell galaxy NGC 4782/4783 isnot a supermassive galaxy as claimed from the high relative velocity and the high central dispersions, but has a moderateM/LB≈10. Its trajectory has been changed from hyperbolic to elliptical as a result of energy lost during the collision. NGC 2672/2673 provides an interesting example of how the collision probes the internal structure and dynamics of a galaxy. It also has a moderateM/LB≈7.

Dumbbell galaxies and precessing radio jets

view Abstract Citations (79) References (72) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dumbbell galaxies and precessing radio jets. Wirth, A. ; Smarr, L. ; Gallagher, J. S. Abstract It is suggested that a subclass of inversion-symmetric distorted extended radio sources (Z-shapes) have shapes produced by effects on large scales compared with the central engine. The subclass is defined by those sources whose underlying galaxies have a dumbbell or multiple nuclei optical morphology. New optical observations are presented which indicate that in one well-studied Z-shape source, NGC 326, there are two galaxies passing at a projected distance of about 10 kpc and that the gravitational coupling of the nonradio galaxy on the radio galaxy's atmosphere may be the mechanism which has realigned the jet direction. If the proposed interpretation is correct, some large-scale jet properties of double radio sources reveal more about properties of the gas distribution in galaxies and less about the central engine than heretofore supposed. Publication: The Astronomical Journal Pub Date: April 1982 DOI: 10.1086/113135 Bibcode: 1982AJ.....87..602W Keywords: Astronomical Catalogs; Elliptical Galaxies; Radio Galaxies; Radio Jets (Astronomy); Circular Orbits; Eccentric Orbits; Galactic Clusters; Galactic Structure; Gravitational Effects; Interstellar Magnetic Fields; Red Shift; Tides; Astronomy full text sources ADS | data products SIMBAD (71) NED (1)

On the Determination of Velocity Dispersions for CD Clusters of Galaxies

view Abstract Citations (111) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the determination of velocity dispersions for cD clusters of galaxies. Quintana, H. ; Lawrie, D. G. Abstract The widely held belief that cD galaxies lie at the kinematical centers of their parent clusters is examined in detail. We find this assumption to be supported by a statistical analysis of all available velocity data. Such an assumption enables us to obtain a direct measure of the true mean velocity of the cluster. The difference between the cD velocity and the mean velocity of the galaxy sample provides a good statistical indication of how well a particular sample represents its parent cluster. For small galaxy samples which poorly represent their parent clusters, we show that the uncertainties in the velocity dispersion have been previously underestimated. A new estimate of the velocity dispersion can be made using the available galaxy sample, but with the cD velocity taken to be the true cluster mean. However, for those clusters with highly unrepresentative samples, this procedure is unlikely to result in an improved estimate of the velocity dispersion. We discuss some individual clusters and consider the extension of the above hypothesis to clusters which contain dumbbell galaxies, D galaxies, or dominant binary galaxies. We show that dumbbell clusters are also dynamically dominated by the corresponding central galaxies. However, for D or binary clusters the evidence is less conclusive. Publication: The Astronomical Journal Pub Date: January 1982 DOI: 10.1086/113080 Bibcode: 1982AJ.....87....1Q full text sources ADS | data products SIMBAD (28)