Distribution by Scientific Domains

Kinds of NGC

  • cluster ngc
  • galaxy ngc
  • spiral galaxy ngc
  • starburst galaxy ngc

  • Selected Abstracts

    Fas and Fas ligand expression on germinal center type-diffuse large B-cell lymphoma is associated with the clinical outcome

    Yasushi Kojima
    Abstract:, In recent years, diffuse large B-cell lymphoma (DLBCL) has been classified by DNA microarray analysis into the germinal center B-cell-like (GC) type, the activated B-cell-like (ABC) type and type 3. The latter two types can be collectively categorized as the non-GC (NGC) type. From the prognostic perspective, the GC type has a favorable clinical outcome when compared with the NGC type. The protein Fas induces apoptosis of lymphocytes by binding with the Fas ligand (FasL), and escape from such apoptosis is considered to lead to malignant transformation of the cells and unrestricted growth of lymphoma. We proposed a hypothesis that Fas/FasL expression could be possibly related with a better survival of GC type DLBCL and evaluated 69 DLBCL cases immunohistochemically with CD10, Bcl-6, MUM1, Fas and FasL. These lymphomas were classified as GC type (positive for CD10 or Bcl-6 and negative for MUM1) or NGC type. The GC type had a better overall survival rate than the NGC type (P = 0.0723). Among markers as given above, positive CD10 was the most significant prognostic factor for overall survival in total DLBCL (P < 0.05). In the GC type, Fas and FasL expressions were significantly associated with a favorable overall survival (Fas: P < 0.005; FasL: P < 0.05). Hence, Fas or FasL expression might contribute to a better prognosis of this type of DLBCL. [source]

    Expression and identification of a new splice variant of neuroglycan C, a transmembrane chondroitin sulfate proteoglycan, in the human brain

    Sachiko Aono
    Abstract Neuroglycan C (NGC) is a transmembrane chondroitin sulfate proteoglycan with an EGF module. We studied the expression of NGC in the human brain, mainly in the hippocampus, and confirmed some observations by conducting experiments using rat brain. In humans, NGC mRNA was expressed exclusively in the brain, especially in the immature brain. The telencephalon, including the hippocampus and neocortex, showed strong mRNA expression. NGC was immunolocalized to neuropils in the hippocampus and neocortex of the adult rat. RT-PCR experiments showed that four splice variants (NGC-I, -II, -III, and -IV) were expressed in the adult human hippocampus. By Western blotting, the expression as proteins of all splice variants except NGC-II was confirmed in the adult rat hippocampus. NGC-IV, which was first found in the present study, had the shortest cytoplasmic domain among the four variants. NGC-IV mRNA was expressed by neurons, but not by astrocytes, in culture prepared from the fetal rat hippocampus, suggesting that NGC-IV plays a role specific to neurons. In addition, the human NGC gene, which is registered as CSPG5, comprised six exons and was approximately 19 kb in size. In exon 2, a single nucleotide polymorphism resulting in Val188Gly in the NGC ectodomain was observed. © 2005 Wiley-Liss, Inc. [source]

    Implications of ,cyclical' population dynamics for the conservation of Irish hares (Lepus timidus hibernicus)

    JOURNAL OF ZOOLOGY, Issue 3 2006
    J. C. Reynolds
    Abstract The Irish hare Lepus timidus hibernicus is of priority conservation concern in Northern Ireland, based on a perceived decline in abundance during the 20th century and on two surveys in 1994,1996 and 2002 that suggested low densities. We reanalysed a 10-year time series [Northern Ireland Rabbit Survey (NIRS)] that has been key evidence of decline, to derive an annual index of abundance during 1986,1995. This showed a rise to a double peak followed by a trough. We compared these Northern Ireland data with two datasets for Lepus timidus scoticus. A 40-year annual index derived from hare bags on Scottish shooting estates [National Game-Bag Census (NGC)] showed strong fluctuations, each lasting several years. Autocorrelation analysis of the NGC data showed elements of cyclical behaviour, with distinct phases and a 16-year period. A previously published 30-year survey of introduced L. t. scoticus in northern England also showed large multi-year fluctuations and phasic behaviour, albeit on a shorter time scale. The NIRS index was strongly correlated with NGC data for the same years, suggesting that it too reflected part of a natural population dynamic. The Species Action Plan for L. t. hibernicus in Northern Ireland includes the aims of maintaining the existing range and demonstrating increase by 2005, and of doubling the population by 2010. We suggest that these aims and the supporting monitoring strategy are inappropriate for a species that shows multi-annual fluctuations in abundance throughout its geographical range. It is important to distinguish self-correcting population processes from trends requiring remedial conservation action. [source]

    Ionized gas in E/S0 galaxies with dust lanes

    Ido Finkelman
    ABSTRACT We report the results of multicolour observations of 30 E/S0 galaxies with dust lanes. For each galaxy we obtained broad-band images and narrow-band images using interference filters isolating the H,+[N ii] emission lines to derive the amount and morphology of dust and ionized gas. To improve the wavelength coverage we retrieved data from the Sloan Digital Sky Survey and Two Micron All Sky Survey and combined these with our data. Ionized gas is detected in 25 galaxies and shows in most cases a smooth morphology, although knots and filamentary structure are also observed in some objects. The extended gas distribution closely follows the dust structure, with a clear correlation between the mass of both components. An extinction law by the extragalactic dust in the dark lanes is derived and is used to estimate the dust content of the galaxies. The derived extinction law is used to correct the measured colours for intrinsic dust extinction and the data are fitted with a stellar population synthesis model. We find that the H, emission and colours of most objects are consistent with the presence of an ,old' stellar population (,10 Gyr) and a small fraction of a ,young' population (, 10,100 Myr). To check this we closely examine NGC 5363, for which archival Spitzer/Infrared Array Camera and Galaxy Evolution Explorer data are available, as a representative dust-lane E/S0 galaxy of the sample. [source]

    Gas dynamics of the central few parsec region of NGC 1068 fuelled by the evolving nuclear star cluster

    M. Schartmann
    ABSTRACT Recently, high-resolution observations with the help of the near-infrared adaptive optics integral field spectrograph Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) at the Very Large Telescope proved the existence of massive and young nuclear star clusters in the centres of a sample of Seyfert galaxies. With the help of three-dimensional high-resolution hydrodynamical simulations with the Pluto code, we follow the evolution of such clusters, especially focusing on stellar mass loss feeding gas into the ambient interstellar medium and driving turbulence. This leads to a vertically wide distributed clumpy or filamentary inflow of gas on large scales (tens of parsec), whereas a turbulent and very dense disc builds up on the parsec scale. In order to capture the relevant physics in the inner region, we treat this disc separately by viscously evolving the radial surface density distribution. This enables us to link the tens of parsec-scale region (accessible via SINFONI observations) to the (sub-)parsec-scale region (observable with the mid-infrared interferometer instrument and via water maser emission). Thereby, this procedure provides us with an ideal testbed for data comparison. In this work, we concentrate on the effects of a parametrized turbulent viscosity to generate angular momentum and mass transfer in the disc and additionally take star formation into account. Most of the input parameters are constrained by available observations of the nearby Seyfert 2 galaxy NGC 1068, and we discuss parameter studies for the free parameters. At the current age of its nuclear starburst of 250 Myr, our simulations yield disc sizes of the order of 0.8,0.9 pc, gas masses of 106 M, and mass transfer rates of 0.025 M, yr,1 through the inner rim of the disc. This shows that our large-scale torus model is able to approximately account for the disc size as inferred from interferometric observations in the mid-infrared and compares well to the extent and mass of a rotating disc structure as inferred from water maser observations. Several other observational constraints are discussed as well. [source]

    The haloes of planetary nebulae in the mid-infrared: evidence for interaction with the interstellar medium

    G. Ramos-Larios
    ABSTRACT The motion of planetary nebulae through the interstellar medium (ISM) is thought to lead to a variety of observational consequences, including the formation of bright rims, deformation and fragmentation of the shells, and a shift of the central stars away from the geometric centres of the envelopes. These and other characteristics have been noted through imaging in the visual wavelength regime. We report further observations of such shells taken in the mid-infrared (MIR), acquired through programmes of Infrared Array Camera imaging undertaken using the SpitzerSpace Telescope. NGC 2440 and NGC 6629 are shown to possess likely interacting haloes, together with ram-pressure-stripped material to one side of their shells. Similarly, the outer haloes of NGC 3242 and NGC 6772 appear to have been fragmented through Rayleigh,Taylor (RT) instabilities, leading to a possible flow of ISM material towards the inner portions of their envelopes. If this interpretation is correct, then it would suggest that NGC 3242 is moving towards the NE, a suggestion which is also supported through the presence of a 60 ,m tail extending in the opposite direction, and curved bands of H, emission in the direction of motion , components which may arise through RT instabilities in the magnetized ISM. NGC 2438 possesses strong scalloping at the outer limits of its asymptotic giant branch (AGB) halo, probably reflecting RT instabilities at the nebular/ISM interface We also note that the interior structure of the source has been interpreted in terms of a recombining shell, a hypothesis which may not be consistent with the central star luminosities. Finally, we point out that two of the rims (and likely shock interfaces) appear to have a distinct signature in the MIR, whereby relative levels of 8.0 ,m emission are reduced. This may imply that the grain emission agents are depleted in the post-shock AGB regimes. [source]

    Formation and evolution of dwarf elliptical galaxies , II.

    Spatially resolved star formation histories
    ABSTRACT We present optical Very Large Telescope spectroscopy of 16 dwarf elliptical galaxies (dEs) comparable in mass to NGC 205, and belonging to the Fornax cluster and to nearby groups of galaxies. Using full-spectrum fitting, we derive radial profiles of the SSP-equivalent ages and metallicities. We make a detailed analysis with ulyss and steckmap of the star formation history in the core of the galaxies and in an aperture of one effective radius. We resolved the history into one to four epochs. The statistical significance of these reconstructions was carefully tested; the two programs give remarkably consistent results. The old stellar population of the dEs, which dominates their mass, is likely coeval with that of massive ellipticals or bulges, but the star formation efficiency is lower. Important intermediate age (1,5 Gyr) populations and frequently tails of star formation until recent times are detected. These histories are reminiscent of their lower mass dwarf spheroidal counterparts of the Local Group. Most galaxies (10/16) show significant metallicity gradients, with metallicity declining by 0.5 dex over one half-light radius on average. These gradients are already present in the old population. The flattened (or discy), rotating objects (6/16) have flat metallicity profiles. This may be consistent with a distinct origin for these galaxies or it may be due to their geometry. The central single stellar population equivalent age varies between 1 and 6 Gyr, with the age slowly increasing with radius in the vast majority of objects. The group and cluster galaxies have similar radial gradients and star formation histories. The strong and old metallicity gradients place important constraints on the possible formation scenarios of dEs. Numerical simulations of the formation of spherical low-mass galaxies reproduce these gradients, but they require a longer time for them to build up. A gentle depletion of the gas, by ram pressure stripping or starvation, could drive the gas-rich, star-forming progenitors to the present dEs. [source]

    The stellar population content of the thick disc and halo of the Milky Way analogue NGC 891

    M. Rejkuba
    ABSTRACT We present deep VI images obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope, covering three fields in the north-east side of the edge-on disc galaxy NGC 891. The observed fields span a wide range of galactocentric distances along the eastern minor axis, extending from the plane of the disc to 12 kpc, and out to ,25 kpc along the major axis. The photometry of individual stars reaches ,2.5 mag below the tip of the red giant branch. We use the astrophotometric catalogue to probe the stellar content and metallicity distribution across the thick disc and spheroid of NGC 891. The colour,magnitude diagrams of thick disc and spheroid population are dominated by old red giant branch stars with a wide range of metallicities, from the sparsely populated metal-poor tail at [Fe/H],,2.4 dex, up to about half-solar metallicity. The peak of the metallicity distribution function of the thick disc is at ,0.9 dex. The inner parts of the thick disc, within ,14 kpc along the major axis show no vertical colour/metallicity gradient. In the outer parts, a mild vertical gradient of ,(V,I)0/,|Z| = 0.1 ± 0.05 kpc,1 or less than 0.1 dex kpc,1 is detected, with bluer colours or more metal-poor stars at larger distances from the plane. This gradient is, however, accounted for by the mixing with the metal-poor halo stars. No metallicity gradient along the major axis is present for thick-disc stars, but strong variations of about 0.35 dex around the mean of [Fe/H]=,1.13 dex are found. The properties of the asymmetric metallicity distribution functions of the thick-disc stars show no significant changes in both the radial and the vertical directions. The stellar populations situated within the solar-cylinder-like distances show strikingly different properties from those of the Galaxy populating similar distances. This suggests that the accretion histories of both galaxies have been different. The spheroid population, composed of the inner spheroid and the halo, shows remarkably uniform stellar population properties. The median metallicity of the halo stellar population shows a shallow gradient from about ,1.15 dex in the inner parts to ,1.27 dex at 24 kpc distance from the centre, corresponding to ,13reff. Similar to the thick-disc stars, large variations around the mean relation are present. [source]

    The Monitor project: rotation periods of low-mass stars in M50

    Jonathan Irwin
    ABSTRACT We report on the results of a time-series photometric survey of M50 (NGC 2323), a ,130 Myr open cluster, carried out using the Cerro Tololo Inter-American Observatory (CTIO) 4-m Blanco telescope and Mosaic-II detector as part of the Monitor project. Rotation periods were derived for 812 candidate cluster members over the mass range 0.2 ,M/M,, 1.1. The rotation period distributions show a clear mass-dependent morphology, statistically indistinguishable from those in NGC 2516 and M35 taken from the literature. Due to the availability of data from three observing runs separated by ,10 and 1 month time-scales, we are able to demonstrate clear evidence for evolution of the photometric amplitudes, and hence spot patterns, over the 10 month gap. We are not able to constrain the time-scales for these effects in detail due to limitations imposed by the large gaps in our sampling, which also prevent the use of the phase information. [source]

    Shock heating in the group atmosphere of the radio galaxy B2 0838+32A

    Nazirah N. Jetha
    ABSTRACT We present Chandra and radio observations, and analysis of Sloan Digital Sky Survey data, of the radio galaxy B2 0838+32A (4C 32.26) and its environment. The radio galaxy is at the centre of a nearby group that has often been identified with the cluster Abell 695, but we argue that the original Abell cluster is likely to be an unrelated and considerably more distant system. The radio source is a restarting radio galaxy and, using our Chandra data, we argue that the currently active lobes are expanding supersonically, driving a shock with Mach number 2.4+1.0,0.5 into the interstellar medium. This would be only the third strong shock round a young radio source to be discovered, after Centaurus A and NGC 3801. However, in contrast to both these systems, the host galaxy of B2 0838+32A shows no evidence for a recent merger, while the active galactic nuclei (AGN) spectrum shows no evidence for the dusty torus that would imply a large reservoir of cold gas close to the central black hole. On the contrary, the AGN spectrum is of a type that has been associated with the presence of a radiatively inefficient accretion flow that could be controlled by an AGN heating and subsequent cooling of the hot, X-ray emitting gas. If correct, this means that B2 0838+32A is the first source in which we can directly see entropy-increasing processes (shocks) driven by accretion from the hot phase of the interstellar medium. [source]

    Matching the frequency spectrum of pre-main sequence stars by means of standard and rotating models

    M. Di Criscienzo
    ABSTRACT We applied the aton evolutionary code to the computation of detailed grids of standard (non-rotating) and rotating pre-main sequence (PMS) models and computed their adiabatic oscillation spectra, with the aim of exploring the seismic properties of young stars. As, until now, only a few frequencies have been determined for ,40 PMS stars, the way of approaching the interpretation of the oscillations is not unique. We adopt a method similar to the matching mode method by Guenther and Brown making use, when necessary, also of our rotating evolutionary code to compute the models for PMS stars. The method is described by a preliminary application to the frequency spectrum of two PMS stars (85 and 278) in the young open cluster NGC 6530. For the Star 85, we confirm with self-consistent rotating models, previous interpretation of the data, attributing three close frequencies to the mode n= 4, l= 1 and m= 0, +1 and ,1. For the Star 278, we find a different fit for the frequencies, corresponding to a model within the original error box of the star, and dispute the possibility that this star has a Teff much cooler that the red boundary of the radial instability strip. [source]

    A shallow though extensive H2 2.122-,m imaging survey of Taurus,Auriga,Perseus , I. NGC 1333, L1455, L1448 and B1

    C. J. Davis
    ABSTRACT We discuss wide-field near-infrared (near-IR) imaging of the NGC 1333, L1448, L1455 and B1 star-forming regions in Perseus. The observations have been extracted from a much larger narrow-band imaging survey of the Taurus,Auriga,Perseus complex. These H2 2.122-,m observations are complemented by broad-band K imaging, mid-IR imaging and photometry from the Spitzer Space Telescope, and published submillimetre CO J= 3,2 maps of high-velocity molecular outflows. We detect and label 85 H2 features and associate these with 26 molecular outflows. Three are parsec-scale flows, with a mean flow lobe length exceeding 11.5 arcmin. 37 (44 per cent) of the detected H2 features are associated with a known Herbig,Haro object, while 72 (46 per cent) of catalogued HH objects are detected in H2 emission. Embedded Spitzer sources are identified for all but two of the 26 molecular outflows. These candidate outflow sources all have high near-to-mid-IR spectral indices (mean value of ,, 1.4) as well as red IRAC 3.6,4.5 ,m and IRAC/MIPS 4.5,24.0 ,m colours: 80 per cent have [3.6],[4.5] > 1.0 and [4.5],[24] > 1.5. These criteria , high , and red [4.5],[24] and [3.6],[4.5] colours , are powerful discriminants when searching for molecular outflow sources. However, we find no correlation between , and flow length or opening angle, and the outflows appear randomly orientated in each region. The more massive clouds are associated with a greater number of outflows, which suggests that the star formation efficiency is roughly the same in each region. [source]

    The Monitor project: the search for transits in the open cluster NGC 2362

    Adam A. Miller
    ABSTRACT We present the results of a systematic search for transiting planets in a ,5 Myr open cluster, NGC 2362. We observed ,1200 candidate cluster members, of which ,475 are believed to be genuine cluster members, for a total of ,100 h. We identify 15 light curves with reductions in flux that pass all our detection criteria, and six of the candidates have occultation depths compatible with a planetary companion. The variability in these six light curves would require very large planets to reproduce the observed transit depth. If we assume that none of our candidates are, in fact, planets then we can place upper limits on the fraction of stars with hot Jupiters (HJs) in NGC 2362. We obtain 99 per cent confidence upper limits of 0.22 and 0.70 on the fraction of stars with HJs (fp) for 1,3 and 3,10 d orbits, respectively, assuming all HJs have a planetary radius of 1.5RJup. These upper limits represent observational constraints on the number of stars with HJs at an age ,10 Myr, when the vast majority of stars are thought to have lost their protoplanetary discs. Finally, we extend our results to the entire Monitor project, a survey searching young, open clusters for planetary transits, and find that the survey as currently designed should be capable of placing upper limits on fp near the observed values of fp in the solar neighbourhood. [source]

    Erratum: Kinematics of gas and stars in the circumnuclear star-forming ring of NGC 3351

    Guillermo F. Hägele
    No abstract is available for this article. [source]

    Life in the last lane: star formation and chemical evolution in an extremely gas rich dwarf

    Ayesha Begum
    ABSTRACT We present an analysis of H i, H, and oxygen abundance data for NGC 3741. This galaxy has a very extended gas disc (,8.8 times the Holmberg radius), and a dark-to-luminous (i.e. stellar) mass ratio of ,149, which makes it one of the ,darkest' dwarf irregular galaxies known. However, its ratio of baryon (i.e. gas + stellar) mass to dark mass is typical of that in galaxies. Our new high-resolution H i images of the galaxy show evidence for a large-scale (purely gaseous) spiral arm and central bar. From our H i data, a rotation curve can be derived out to ,37,44 disc scalelengths in the J and B bands, respectively. This is just slightly short of the radius at which one would expect a Navarro,Frenk,White type rotation curve to start falling. The galaxy has an integrated star formation rate (SFR) of ,0.0034 M, yr,1, while the average SFR within the optical disc is ,0.0049 M, yr,1 kpc,2. Despite the gaseous spiral feature and the ongoing star formation, we find that the global gas density in NGC 3741 is significantly lower than the Toomre instability criterion. This is consistent with the behaviour seen in other dwarf galaxies. We also find that the SFR is consistent with that expected from the observed correlations between H i mass and SFR and the global Kennicutt,Schmidt law, respectively. We measure the oxygen abundance to be 12 + log(O/H) = 7.66 ± 0.10, which is consistent with that expected from the metallicity,luminosity relation, despite its extreme gas mass ratio. We also examine the issue of chemical evolution of NGC 3741 in the context of the closed-box model of chemical evolution. The effective oxygen yield of NGC 3741 is consistent with recent model estimates of closed-box yields, provided one assumes that the gas has been efficiently mixed all the way to the edge of the H i disc (i.e. greater than eight times the optical radius). This seems a priori unlikely. On the other hand, using a sample of galaxies with both interferometric H i maps and chemical abundance measurements, we find that the effective yield is anticorrelated with the total dynamical mass, as expected in leaky box models. [source]

    X-ray active galactic nuclei in the core of the Perseus cluster

    S. Santra
    ABSTRACT We present a study of the X-ray emission from the nuclei of galaxies observed in the core of the Perseus cluster in a deep exposure with Chandra. Point sources are found coincident with the nuclei of 13 early-type galaxies, as well as the central galaxy NGC 1275. This corresponds to all galaxies brighter than MB > ,18 in the Chandra field. All of these sources have a steep power-law spectral component and four have an additional thermal component. The unabsorbed power-law luminosities in the 0.5,7.0 keV band range from 8 × 1038 to 5 × 1040 erg s,1. We find no simple correlations between the K -band luminosity, or the FUV and NUV AB magnitudes of these galaxies and their X-ray properties. We have estimated the black hole masses of the nuclei using the K -band MBH,LKbol relation and again find no correlation between black hole mass and the X-ray luminosity. Bondi accretion on to the black holes in the galaxies with minihaloes should make them much more luminous than observed. [source]

    Intracluster light and the extended stellar envelopes of cD galaxies: an analytical description

    Marc S. Seigar
    ABSTRACT We have analysed deep R -band images, down to a limiting surface brightness of 26.5 R-mag arcsec,2 (equivalent to ,28 B-mag arcsec,2), of five cD galaxies to determine the shape of the surface brightness profiles of their extended stellar envelopes. Both de Vaucouleurs R1/4 and Sérsic R1/n models, on their own, provide a poor description of the surface brightness profiles of cD galaxies. This is due to the presence of outer stellar envelopes, thought to have accumulated over the merger history of the central cluster galaxy and also from the tidal stripping of galaxies at larger cluster radii. We therefore simultaneously fit two Sérsic functions to measure the shape of the inner and outer components of the cD galaxies. We show that, for three out of our five galaxies, the surface brightness profiles are best fitted by an inner Sérsic model, with indices n, 1 ,6, and an outer exponential component. For these systems, the galaxy-to-envelope size ratio is 0.1,0.4 and the contribution of the stellar envelope to the total R -band light (i.e. galaxy + envelope) is around 60,80 per cent (based on extrapolation to a 300 kpc radius). The exceptions are NGC 6173, for which our surface brightness profile modelling is consistent with just a single component (i.e. no envelope) and NGC 4874 which appears to have an envelope with a de Vaucouleurs, rather than exponential, profile. [source]

    Searches for ultracompact dwarf galaxies in galaxy groups

    E. A. Evstigneeva
    ABSTRACT We present the results of a search for ultracompact dwarf galaxies (UCDs) in six different galaxy groups: Dorado, NGC 1400, 0681, 4038, 4697 and 5084. We searched in the apparent magnitude range 17.5 ,bJ, 20.5 (except NGC 5084: 19.2 ,bJ, 21.0). We found one definite plus two possible UCD candidates in the Dorado group and two possible UCD candidates in the NGC 1400 group. No UCDs were found in the other groups. We compared these results with predicted luminosities of UCDs in the groups according to the hypothesis that UCDs are globular clusters formed in galaxies. The theoretical predictions broadly agree with the observational results, but deeper surveys are needed to fully test the predictions. [source]

    H i imaging of galaxies in X-ray bright groups

    Chandreyee Sengupta
    ABSTRACT Environment plays an important role in the evolution of the gas contents of galaxies. Gas deficiency of cluster spirals and the role of the hot intracluster medium in stripping gas from these galaxies is a well-studied subject. Loose groups with diffuse X-ray emission from the intragroup medium (IGM) offer an intermediate environment between clusters and groups without a hot IGM. These X-ray bright groups have smaller velocity dispersion and lower temperature than clusters, but higher IGM density than loose groups without diffuse X-ray emission. A single-dish comparative study of loose groups with and without diffuse X-ray emission from the IGM, showed that the galaxies in X-ray bright groups have lost more gas on average than the galaxies in non X-ray bright groups. In this paper we present GMRT H i observations of 13 galaxies from four X-ray bright groups: NGC 5044, 720, 1550 and IC1459. The aim of this work is to study the morphology of H i in these galaxies and to see if the hot IGM has in any way affected their H i content or distribution. In addition to disturbed H i morphology, we find that most galaxies have shrunken H i discs compared to the field spirals. This indicates that IGM-assisted stripping processes like ram pressure may have stripped gas from the outer edges of the galaxies. [source]

    Structural parameters of Mayall II = G1 in M31

    J. Ma
    ABSTRACT Mayall II = G1 is one of the most luminous globular clusters (GCs) known in M31. New deep, high-resolution observations with the Advanced Camera for Surveys on the Hubble Space Telescope are used to provide accurate photometric data to the smallest radii yet. In particular, we present the precise variation of ellipticity and position angle, and of surface brightness for the core of the object. Based on these accurate photometric data, we redetermine the structural parameters of G1 by fitting a single-mass isotropic King model. We derive a core radius, rc= 0.21 ± 0.01 arcsec (= 0.78 ± 0.04 pc), a tidal radius, rt= 21.8 ± 1.1 arcsec (= 80.7 ± 3.9 pc), and a concentration index c= log (rt/rc) = 2.01 ± 0.02. The central surface brightness is 13.510 mag arcsec,2. We also calculate the half-light radius, at rh= 1.73 ± 0.07 arcsec (= 6.5 ± 0.3 pc). The results show that, within 10 core radii, a King model fits the surface brightness distribution well. We find that this object falls in the same region of the MV versus log Rh diagram as , Centauri, M54 and NGC 2419 in the Milky Way. All three of these objects have been claimed to be the stripped cores of now defunct dwarf galaxies. We discuss in detail whether GCs, stripped cores of dwarf spheroidals and normal dwarf galaxies form a continuous distribution in the MV versus log Rh plane, or if GCs and dwarf spheroidals constitute distinct classes of objects; we present arguments in favour of this latter view. [source]

    The evolution of binary star clusters and the nature of NGC 2136/NGC 2137

    S. F. Portegies Zwart
    ABSTRACT We study the evolution of bound pairs of star clusters by means of direct N -body simulations. Our simulations include mass loss by stellar evolution. The initial conditions are selected to mimic the observed binary star clusters, NGC 2136 and 2137, in the Large Magellanic Cloud. Based on their rather old ages (,100 Myr), masses, sizes and projected separation, we conclude that the cluster pair must have been born with an initial separation of 15,20 pc. Clusters with a smaller initial separation tend to merge in ,60 Myr due to loss of angular momentum from escaping stars. Clusters with a larger initial separation tend to become even more widely separated due to mass loss from the evolving stellar populations. The early orbital evolution of a binary cluster is governed by mass loss from the evolving stellar population and by loss of angular momentum from escaping stars. Mass loss by stellar winds and supernovae explosions in the first ,30 Myr causes the binary to expand and the orbit to become eccentric. The initially less massive cluster expands more quickly than the binary separation increases, and is therefore bound to initiate mass transfer to the more massive cluster. This process is quite contrary to stellar binaries in which the more massive star tends to initiate mass transfer. Since mass transfer proceeds on a thermal time-scale from the less massive to the more massive cluster, this semidetached phase is quite stable, even in an eccentric orbit until the orbital separation reaches the gyration radius of the two clusters, at which point both clusters merge to one. [source]

    The SAURON project , VIII.

    OASIS/CFHT integral-field spectroscopy of elliptical, lenticular galaxy centres
    ABSTRACT We present high spatial resolution integral-field spectroscopy of 28 elliptical (E) and lenticular (S0) galaxies from the SAURON representative survey obtained with the OASIS spectrograph during its operation at the Canada,France,Hawaii Telescope. These seeing-limited observations explore the central 8 × 10 arcsec2 (typically 1 kpc diameter) regions of these galaxies using a spatial sampling four times higher than SAURON (0.27-arcsec versus 0.94-arcsec spatial elements), resulting in almost a factor of 2 improvement in the median point spread function. These data allow accurate study of the central regions to complement the large-scale view provided by SAURON. Here we present the stellar and gas kinematics, stellar absorption-line strengths and nebular emission-line strengths for this sample. We also characterize the stellar velocity maps using the ,kinemetry' technique, and derive maps of the luminosity-weighted stellar age, metallicity and abundance ratio via stellar population models. We give a brief review of the structures found in our maps, linking also to larger-scale structures measured with SAURON. We present two previously unreported kinematically decoupled components (KDCs) in the centres of NGC 3032 and NGC 4382. We compare the intrinsic size and luminosity-weighted stellar age of all the visible KDCs in the full SAURON sample, and find two types of components: kiloparsec-scale KDCs, which are older than 8 Gyr, and are found in galaxies with little net rotation; and compact KDCs, which have intrinsic diameters of less than a few hundred parsec, show a range of stellar ages from 0.5 to 15 Gyr (with 5/6 younger than 5 Gyr), are found exclusively in fast-rotating galaxies, and are close to counter-rotating around the same axis as their host. Of the seven galaxies in the SAURON sample with integrated luminosity-weighted ages less than 5 Gyr, five show such compact KDCs, suggesting a link between counter-rotation and recent star formation. We show that this may be due to a combination of small sample size at young ages, and an observational bias, since young KDCs are easier to detect than their older and/or corotating counterparts. [source]

    A Subaru/Suprime-Cam wide-field survey of globular cluster populations around M87 , I. Observation, data analysis and luminosity function

    Naoyuki Tamura
    ABSTRACT In this paper and a companion paper, we report on a wide-field imaging survey of the globular cluster (GC) populations around M87 carried out with Suprime-Cam on the 8.2-m Subaru telescope. Here, we describe the observations, data reduction and data analysis, and present luminosity functions of GC populations around M87 and NGC 4552, another luminous Virgo elliptical in our survey field. The imaging data were taken in the B, V and I bands with a sky coverage of extending from the M87 centre out to ,0.5 Mpc. GC candidates were selected by applying a colour criterion on the B,V and V,I diagram to unresolved objects, which greatly reduces contamination. The data from control fields taken with Subaru/Suprime-Cam were also analysed for subtraction of contamination in the GC sample. These control field data are compatible with those in the M87 field in terms of the filter set (BVI), limiting magnitudes and image quality, which minimize the possibility of introducing any systematic errors into the subtractive correction. We investigate GC luminosity functions (GCLFs) at distances , 10 arcmin (,45 kpc) from the host galaxy centre in detail. By fitting Gaussians to the GCLFs, the V -band turnover magnitude (VTO) is estimated to be 23.62 ± 0.06 and 23.56 ± 0.20 mag for the GC population in M87 and NGC 4552, respectively. The GCLF is found to be a function of GC colour; VTO of the red GC subpopulation (V,I > 1.1) is fainter than that of the blue GC subpopulation (V,I, 1.1) in both M87 and NGC 4552, as expected if the colour differences are primarily due to a metallicity effect, and the mass functions of the two subpopulations are similar. The radial dependence of the GCLF is also investigated for the GC population in M87. The GCLF of each subpopulation at 1 ,R, 5 arcmin is compared to that at 5 ,R, 10 arcmin, but no significant trend with distance is found in the shape of the GCLF. We also estimate GC-specific frequencies (SN) for M87 and NGC 4552. The SN of the M87 GC population is estimated to be 12.5 ± 0.8 within 25 arcmin. The SN value of the NGC 4552 GC population is estimated to be 5.0 ± 0.6 within 10 arcmin. [source]

    A Subaru/Suprime-Cam wide-field survey of globular cluster populations around M87 , II.

    Colour, spatial distribution
    ABSTRACT We have performed a wide-field imaging survey of the globular cluster (GC) populations around M87 with Suprime-Cam on the 8.2-m Subaru Telescope. A field extending from the centre of M87 out to a radius of ,0.5 Mpc was observed through the BVI filters. By investigating the GC colour distribution as a function of distance from M87 and NGC 4552, another luminous Virgo elliptical in our survey field, it is found that clear bimodality [(V,I)peak, 1.0 and 1.2] is seen only in the inner regions (,10 kpc) of the host galaxies and that it becomes weaker with radius due to the decreasing contribution of the red GC (V,I > 1.1) subpopulation. It is also found (both around M87 and around NGC 4552) that while the spatial distribution of the red GCs is as centrally concentrated as the host galaxy halo light distribution, the distribution of the blue GCs (V,I, 1.1) tends to be more extended. However, the blue GC distribution around M87 is not as extended as the Virgo cluster mass density profile. Based on these facts, we argue that the contribution of GCs associated with the Virgo cluster [e.g. intergalactic GCs (i-GCs)] is not significant around M87 and is not the primary reason for the high SN value of M87. Instead, most of the blue GCs around luminous ellipticals, as well as the red GCs, are presumed to be associated with the host galaxy. We model the radial profile of GC surface densities out to ,0.5 Mpc from M87 by a superposition of the GC populations associated with M87 and with NGC 4552. It is found that there are some regions where the GC surface densities are larger than that which is expected from this model, suggesting the existence of an additional i-GC population independent of the luminous ellipticals. By comparing the estimated i-GC surface density with the luminosity density of the intracluster stellar population inferred from the intergalactic planetary nebulae in the Virgo cluster, we obtain a crude estimate of i-GC specific frequency SN= 2.9+4.2,1.5. If this SN value represents the stellar population tidally stripped by a massive central galaxy from other (less-luminous) galaxies, the contribution of tidally captured GCs in the GC population of M87 would need to be low to be consistent with the high SN value of M87. [source]

    Discovery of large-scale methanol and hydroxyl maser filaments in W3(OH)

    L. Harvey-Smith
    ABSTRACT Images of the 6.7-GHz methanol maser emission from W3(OH) made at 50- and 100-mas angular resolution with the Multi-Element Radio-Linked Interferometer Network (MERLIN) are presented. The masers lie across the western face of the ultracompact H ii region in extended filaments which may trace large-scale shocks. There is a complex interrelation between the 6.7-GHz methanol masers and hydroxyl (OH) masers at 1.7 and 4.7 GHz. Together the two species trace an extended filamentary structure that stretches at least 3100 au across the face of the ultracompact H ii region. The dominant 6.7-GHz methanol emission coincides with the radio continuum peak and is populated by masers with broad spectral lines. The 6.7-GHz methanol emission is elongated at position angle 50° with a strong velocity gradient, and bears many similarities to the methanol maser disc structure reported in NGC 7538. It is surrounded by arcs of ground state OH masers at 1.7 GHz and highly excited OH masers at 13.44 GHz, some of which have the brightest methanol masers at their focus. We suggest that this region hosts the excitation centre for the ultracompact H ii region. [source]

    Chandra monitoring observations of the ultraluminous X-ray source NGC 5204 X-1

    T. P. Roberts
    ABSTRACT We report the results of a two-month campaign conducted with the Chandra X-ray observatory to monitor the ultraluminous X-ray source (ULX) NGC 5204 X-1. This was composed of a 50-ks observation, followed by ten 5-ks follow-ups spaced initially at ,3, then at ,10-d intervals. The ULX flux is seen to vary by factors ,5 on time-scales of a few days, but no strong variability is seen on time-scales shorter than an hour. There is no evidence for a periodic signal in the X-ray data. An examination of the X-ray colour variations over the period of the campaign shows the ULX emission consistently becomes spectrally harder as its flux increases. The X-ray spectrum from the 50-ks observation can be fitted by a number of disparate spectral models, all of which describe a smooth continuum with, unusually for a ULX, a broad emission feature evident at 0.96 keV. The spectral variations, both within the 50-ks observation and over the course of the whole campaign, can then be explained solely by variations in the continuum component. In the context of an optically thick corona model (as found in other recent results for ULXs) the spectral variations can be explained by the heating of the corona as the luminosity of the ULX increases, consistent with the behaviour of at least one Galactic black hole system in the strongly Comptonized very high state. We find no new evidence supporting the presence of an intermediate-mass black hole in this ULX. [source]

    Stellar haloes and elliptical galaxy formation: origin of dynamical properties of the planetary nebula systems

    Kenji Bekki
    ABSTRACT Recent spectroscopic observations of planetary nebulae (PNe) in several elliptical galaxies have revealed structural and kinematical properties of the outer stellar halo regions. In order to elucidate the origin of the properties of these planetary nebula systems (PNSs), we consider the merger scenario in which an elliptical galaxy is formed by merging of spiral galaxies. Using numerical simulations, we particularly investigate radial profiles of projected PN number densities, rotational velocities and velocity dispersions of PNSs extending to the outer halo regions of elliptical galaxies formed from major and unequal-mass merging. We find that the radial profiles of the project number densities can be fitted to the power law and the mean number density in the outer haloes of the ellipticals can be more than an order of magnitude higher than that of the original spiral's halo. The PNSs are found to show a significant amount of rotation (V/, > 0.5) in the outer halo regions (R > 5Re) of the ellipticals. Two-dimensional velocity fields of PNSs are derived from the simulations and their dependences on model parameters of galaxy merging are discussed in detail. We compare the simulated kinematics of PNSs with that of the PNS observed in NGC 5128 and thereby discuss advantages and disadvantages of the merger model in explaining the observed kinematics of the PNS. We also find that the kinematics of PNSs in elliptical galaxies are quite diverse depending on the orbital configurations of galaxy merging, the mass ratio of merger progenitor spirals and the viewing angle of the galaxies. This variation translates directly into possible biases by a factor of 2 in observational mass estimation. However, the biases in the total mass estimates can be even larger. The best case systems viewed edge-on can appear to have masses lower than their true mass by a factor of 5, which suggests that current observational studies on PN kinematics of elliptical galaxies can significantly underestimate their real masses. [source]

    Anomalous extinction behaviour towards the Type Ia SN 2003cg

    N. Elias-Rosa
    ABSTRACT We present optical and near-infrared photometry and spectroscopy of the Type Ia SN 2003cg, which exploded in the nearby galaxy NGC 3169. The observations cover a period between ,8.5 and +414 d post-maximum. SN 2003cg is a normal but highly reddened Type Ia event. Its B magnitude at maximum Bmax= 15.94 ± 0.04 and ,m15(B)obs= 1.12 ± 0.04 [,m15(B)intrinsic= 1.25 ± 0.05]. Allowing RV to become a free parameter within the Cardelli et al. extinction law, simultaneous matches to a range of colour curves of normal SNe Ia yielded E(B,V) = 1.33 ± 0.11, and RV= 1.80 ± 0.19. While the value obtained for RV is small, such values have been invoked in the past, and may imply a grain size which is small compared with the average value for the local interstellar medium. [source]

    The SAURON project , VII.

    Integral-field absorption, emission-line kinematics of 24 spiral galaxy bulges
    ABSTRACT We present observations of the stellar and gas kinematics for a representative sample of 24 Sa galaxies obtained with our custom-built integral-field spectrograph SAURON operating on the William Herschel Telescope. The data have been homogeneously reduced and analysed by means of a dedicated pipeline. All resulting data cubes were spatially binned to a minimum mean signal-to-noise ratio of 60 per spatial and spectral resolution element. Our maps typically cover the bulge-dominated region. We find a significant fraction of kinematically decoupled components (12/24), many of them displaying central velocity dispersion minima. They are mostly aligned and co-rotating with the main body of the galaxies, and are usually associated with dust discs and rings detected in unsharp-masked images. Almost all the galaxies in the sample (22/24) contain significant amounts of ionized gas which, in general, is accompanied by the presence of dust. The kinematics of the ionized gas are consistent with circular rotation in a disc co-rotating with respect to the stars. The distribution of mean misalignments between the stellar and gaseous angular momenta in the sample suggests that the gas has an internal origin. The [O iii]/H, ratio is usually very low, indicative of current star formation, and shows various morphologies (ring-like structures, alignments with dust lanes or amorphous shapes). The star formation rates (SFRs) in the sample are comparable with that of normal disc galaxies. Low gas velocity dispersion values appear to be linked to regions of intense star formation activity. We interpret this result as stars being formed from dynamically cold gas in those regions. In the case of NGC 5953, the data suggest that we are witnessing the formation of a kinematically decoupled component from cold gas being acquired during the ongoing interaction with NGC 5954. [source]

    Magnetic fields in the centre of the Perseus cluster

    G. B. Taylor
    ABSTRACT We present Very Long Baseline Array (VLBA) observations of the nucleus of NGC 1275, the central, dominant galaxy in the Perseus cluster of galaxies. These are the first observations to resolve the linearly polarized emission from 3C 84, and from them we determine a Faraday rotation measure (RM) ranging from 6500 to 7500 rad m,2 across the tip of the bright southern jet component. At 22 GHz some polarization is also detected from the central pc of 3C 84, indicating the presence of even more extreme RMs that depolarize the core at lower frequencies. The nature of the Faraday screen is most consistent with being produced by magnetic fields associated with the optical filaments of ionized gas in the Perseus cluster. [source]