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1.
We present V -band surface photometry and major-axis kinematics of stars and ionized gas of three early-type spiral galaxies, namely NGC 772, 3898 and 7782. For each galaxy we present a self-consistent Jeans model for the stellar kinematics, adopting the light distribution of bulge and disc derived by means of a two-dimensional parametric photometric decomposition. This allows us to investigate the presence of non-circular gas motions, and derive the mass distribution of luminous and dark matter in these objects.
NGC 772 and 7782 have apparently normal kinematics with the ionized gas tracing the gravitational equilibrium circular speed. This is not true in the innermost region (| r |≲8 arcsec) of NGC 3898, where the ionized gas is rotating more slowly than the circular velocity predicted by dynamical modelling. This phenomenon is common in the bulge-dominated galaxies for which dynamical modelling enables us to make the direct comparison between the gas velocity and the circular speed, and it poses questions about the reliability of galaxy mass distributions derived by the direct decomposition of the observed ionized-gas rotation curve into the contributions of luminous and dark matter.  相似文献   

2.
We present near-infrared adaptive optics, Very Large Array (VLA) radio and Hubble Space Telescope ( HST ) optical imaging of the nearby Seyfert galaxy NGC 2992. Spiral structure and an extension to the west are traced down to the core region at the limiting resolution of our near-infrared images. A faint, diffuse loop of near-infrared and radio emission is also observed to the north, embedded within the prominent 2-arcsec radio loop previously observed to the north-west. Near-infrared colour maps and CO narrow-band imaging are then used to identify which regions may not be purely reddened stellar populations. Our new data provide evidence that the VLA radio-loop morphology in the shape of a figure of 8 represents two components superimposed: (1) outflow bubbles out of the plane of the disc, coincident with the extended emission-line region (EELR); (2) star formation along the spiral arm within the galaxy disc and through the dust lane. The near-infrared continuum emission associated with the outflowing radio bubbles suggests that the radio loops are driven by the active nucleus.  相似文献   

3.
We present the results based on multiwavelength imaging observations of the prominent dust lane starburst galaxy NGC 1482 aimed to investigate the extinction properties of dust existing in the extreme environment. (B-V) colour-index map derived for the starburst galaxy NGC 1482 confirms two prominent dust lanes running along its optical major axis and are found to extend up to ∼11 kpc. In addition to the main lanes, several filamentary structures of dust originating from the central starburst are also evident. Though, the dust is surrounded by exotic environment, the average extinction curve derived for this target galaxy is compatible with the Galactic curve, with RV = 3.05, and imply that the dust grains responsible for the optical extinction in the target galaxy are not really different than the canonical grains in the Milky Way. Our estimate of total dust content of NGC 1482 assuming screening effect of dust is ∼2.7 × 105 M⊙, and provide lower limit due to the fact that our method is not sensitive to the intermix component of dust. Comparison of the observed dust in the galaxy with that supplied by the SNe to the ISM, imply that this supply is not sufficient to account for the observed dust and hence point towards the origin of dust in this galaxy through a merger like event.Our multiband imaging analysis reveals a qualitative physical correspondence between the morphologies of the dust and Hα emission lines as well as diffuse X-ray emission in this galaxy. Spatially resolved spectral analysis of the hot gas along outflows exhibit a gradient in the temperature. Similar gradient was also noticed in the measured values of metallicity, indicating that the gas in the halo is not yet enriched. High resolution, 2-8 keV Chandra image reveals a pair of point sources in the nuclear region with their luminosities equal to 2.27 × 1039 erg s−1 and 9.34 × 1039 erg s−1, and are in excess of the Eddington-limit of 1.5 M⊙ accreting source. Spectral analysis of these sources exhibit an absorbed-power law with the hydrogen column density higher than that derived from the optical measurements.  相似文献   

4.
We present kinematic observations of NGC 3923, one of the best-known examples of an elliptical galaxy with shells. Although NGC 3923 has no rotation on its major axis, it has minor axis rotation with an amplitude of some 20 km s−1 out to 25 arcsec radius. This is possibily the result of a kinematically decoupled core, but we present arguments against this hypothesis, and if the core were formed by a merger, this must have been a different merger from that which gave rise to the shells. The minor axis rotation suggests that NGC 3923 is prolate or triaxial, at least in the inner region. A prolate geometry for the whole galaxy would favour the merger model over the interaction model for the shell formation mechanism. There is other evidence, however, that the shape of the underlying galaxy changes with radius, in which case it is possible that the minor axis rotation could be confined to the galaxy core. The kinematics could reflect a triaxial mass distribution, in which the long and short axes are aligned with the photometric major and minor axes, and the axial ratios change such that the galaxy is near-prolate in the inner regions and near-oblate at larger radii. Measuring the rotation curve to about double this radius along the minor axis, as well as offset from the nucleus along the major axis at the radius of the innermost shells, would enable the true extent of the minor axis rotation to be determined.  相似文献   

5.
We present observations of the spiral galaxy NGC 7331 using the Submillimetre Common User Bolometer Array (SCUBA) on the James Clark Maxwell Telescope. We have detected a dust ring of 45 arcsec radius (3.3 kpc) at wavelengths of 450 and 850 μm. The dust ring is in good correspondence with other observations of the ring in the mid-infrared (MIR), CO and radio continuum, suggesting that the observed dust is associated with molecular gas and star formation. A B  −  K colour map shows an analogous ring structure with an asymmetry about the major axis, consistent with the extinction being produced by a dust ring. The derived temperature of the dust lies between 16 and 31 K and the gas-to-dust ratio lies between 150 and 570, depending on the assumed dust emission efficiency index (β = 1.5 or 2).  相似文献   

6.
Submillimetre maps of NGC 891 have been obtained with the Programme National d'Observations Submillimétriques (PRONAOS) balloon-borne telescope and with the Infrared Space Observatory Photopolarimeter (ISOPHOT) on board the ISO satellite. In this article, we also gather data from the Infrared Astronomical Satellite ( IRAS ) and the Submillimetre Common-User Bolometer Array (SCUBA) to present the complete submillimetre spectrum of this nearby edge-on spiral galaxy. We derive submillimetre emission profiles along the major axis. The modified blackbody fits, assuming a single dust component, lead to temperatures of 19–24 K towards the centre and 18–20 K towards the edges, with possible variations in the dust spectral index from 1.4 to 2. The two-component fits lead to a warm-component temperature of 29 K all along the galaxy, with a cold component at 16 K. The interstellar medium (ISM) masses derived by these two methods are quite different:  4.6×109 M⊙  in the case of the one-component model and  12 × 109 M⊙  in the case of the two-component one. This two-component fit indicates that the cold dust to warm dust ratio is between 20 and 40, the highest values being in the wings of this galaxy. Compared to dust mass estimates, both estimates of the ISM mass are consistent with a gas to dust mass ratio of 240, which is close to the Milky Way value. Our results illustrate the importance of accurate submillimetre spectra in deriving masses of the ISM in galaxies.  相似文献   

7.
This is the first paper of a series focused on investigating the star formation and evolutionary history of the two early-type galaxies NGC 1407 and NGC 1400. They are the two brightest galaxies of the NGC 1407 (or Eridanus-A) group, one of the 60 groups studied as part of the Group Evolution Multi-wavelength Study.
Here, we present new high signal-to-noise ratio long-slit spectroscopic data obtained at the ESO 3.6-m telescope and high-resolution multiband imaging data from the Hubble Space Telescope /Advanced Camera for Surveys and wide-field imaging from Subaru Suprime-Cam. We spatially resolved integrated spectra out to ∼0.6 (NGC 1407) and ∼1.3 (NGC 1400) effective radii. The radial profiles of the kinematic parameters v rot, σ, h 3 and h 4 are measured. The surface brightness profiles are fitted to different galaxy light models and the colour distributions analysed. The multiband images are modelled to derive isophotal shape parameters and residual galaxy images. The parameters from the surface brightness profile fitting are used to estimate the mass of the possible central supermassive black hole in NGC 1407. The galaxies are found to be rotationally supported and to have a flat core in the surface brightness profiles. Elliptical isophotes are observed at all radii and no fine structures are detected in the residual galaxy images. From our results, we can also discard a possible interaction between NGC 1400, NGC 1407 and the group intergalactic medium. We estimate a mass of  ∼1.03 × 109 M⊙  for the supermassive black hole in NGC 1407 galaxy.  相似文献   

8.
We present deep wide-field (16.4×16.4 arcmin2) Washington CT 1 CCD surface photometry of the giant elliptical galaxy NGC 4472, the brightest member of the Virgo cluster. Our data cover a wider and deeper field than any previous CCD photometry. A single King model does not give a good fit to the surface brightness profiles of NGC 4472, but they can be fitted approximately using two King models: with the separate models representing the inner and outer regions . Surface brightness profiles for the outer region can also be fitted approximately by a de Vaucouleurs law. There is clearly a negative colour gradient within 3 arcmin of NGC 4472, in the sense that the colour gets bluer with increasing radius. The slope of the colour gradient for this region is derived to be Δ μ ( C − T 1)=−0.08 mag arcsec−2 for Δ log  r =1, which corresponds to a metallicity gradient of Δ[Fe/H]=−0.2 dex. However, the surface colour becomes gradually redder with increasing radius beyond 3 arcmin. A comparison of the structural parameters of NGC 4472 in C and T 1 images has shown that there is little difference in the shapes of ellipses observed using isochromes or isophotes. In addition, photometric and structural parameters of NGC 4472 have been determined.  相似文献   

9.
An excellent candidate for a young elliptical, or 'protoelliptical' galaxy is NGC 1700. Here we present new B -, V - and I -band imaging using the Keck telescope, and reanalyse existing V - and I -band images from the Hubble Space Telescope . After subtracting a model of the galaxy from the Keck images, NGC 1700 reveals two symmetric tidal tail-like structures. If this interpretation is correct, it suggests a past merger event involving two spiral galaxies. These tails are largely responsible for the 'boxiness' of the galaxy isophotes observed at a radius of ∼13 kpc.
We also show that the B − I colour distribution of the globular cluster system is bimodal. The mean colour of the blue population is consistent with that of old Galactic globular clusters. Relative to this old, metal-poor population, we find that the red population is younger and more metal-rich. This young population has an age and metallicity similar to that inferred for the central stars, suggesting that both populations are associated with an episode of star formation triggered by the merger that may have formed the galaxy. We find that, although they have large errors, the majority of the age estimates of NGC 1700 are reasonably consistent and we adopt a 'best estimate' for the age of 3.0±1.0 Gyr. This relatively low age places NGC 1700 within the age range where there is a notable lack of obvious candidates for protoellipticals. The total globular cluster specific frequency is rather low for a typical elliptical, even after taking into account the fading of the galaxy over the next 10 Gyr. We speculate that NGC 1700 will eventually form a relatively 'globular cluster poor' elliptical galaxy.  相似文献   

10.
The pattern speed is a defining parameter of any barred galaxy. A large number of model-dependent techniques have therefore been developed to derive the pattern speed. However, the only model-independent technique for measuring this quantity – the Tremaine–Weinberg method – has hitherto been applied to just one case, the SB0 galaxy NGC 936. In this paper, we apply the technique to a second system, the SBa galaxy NGC 4596. The resulting estimate for the pattern speed is Ωp=52±13 km s−1 kpc−1. This result is corroborated by a spectrum obtained along the major axis of the bar in this system. The corotation radius associated with this pattern speed lies just beyond the end of the bar indicating a fast bar. Combining the bar major-axis spectra with data obtained from a Hubble Space Telescope WFPC2 image, we also find strong evidence for a nuclear disc.  相似文献   

11.
We present Gemini Multi-Object Spectrograph longslit spectroscopy of the isolated S0 galaxy NGC 3115. We have determined kinematical data and Lick/IDS absorption line-strength indices for the major axis out to around 9 kpc and for the minor axis out to around 5 kpc (around 2R e ). Using stellar population models which include the effects of variable [α/Fe] ratios, we derive metallicities, abundance ratios and ages for the stellar population of NGC 3115. We find that [α/Fe] remains fairly constant with increasing radius at around  [α/Fe]= 0.17  for the major axis but increases rapidly for the minor axis to around  [α/Fe]= 0.3  . We also find that to first order, this behaviour can be explained by a simple spheroid + disc model, where the spheroid has  [α/Fe]= 0.3  and the disc shows close to solar abundance ratios. The disc also appears considerably younger than the spheroid, having an age of around 6 Gyr compared to 12 Gyr for the spheroid. We compare these results to those previously presented for the globular cluster system of NGC 3115.  相似文献   

12.
Measuring the integrated stellar halo light around galaxies is very challenging. The surface brightness of these haloes is expected to be many magnitudes below dark sky and the central brightness of the galaxy. Here, I show that in some of the recent literature the effect of very extended Point Spread Function (PSF) tails on the measurements of halo light has been underestimated; especially in the case of edge-on disc galaxies. The detection of a halo along the minor axis of an edge-on galaxy in the Hubble Ultra Deep Field can largely be explained by scattered galaxy light. Similarly, depending on filter and the shape one assumes for the uncertain extended PSF, 20–80 per cent of the halo light found along the minor axis of scaled and stacked Sloan Digital Sky Survey (SDSS) edge-on galaxy images can be explained by scattered galaxy light. Scattered light also significantly contributes to the anomalous halo colours of stacked SDSS images. The scattered light fraction decreases when looking in the quadrants away from the minor axis. The remaining excess light is well modelled with a Sérsic profile halo with shape parameters based on star count halo detections of nearby galaxies. Even though, the contribution from PSF scattered light does not fully remove the need for extended components around these edge-on galaxies, it will be very challenging to make accurate halo light shape and colour measurements from integrated light without very careful PSF measurements and scattered light modelling.  相似文献   

13.
We present photometric observations of two shell galaxies, NGC 474 and 7600. We examine the photometric colours and surface brightnesses of the shells and their host galaxies, and the isophotal parameters of each galaxy. In the case of NGC 474, we find that the shell formation is consistent with a merger origin, although it is possible that the close companion NGC 470 is contributing to the shell system via mass transfer. NGC 7600 exhibits shell geometry and colours which also favour a merger origin.  相似文献   

14.
We present new observations at three frequencies (326, 615 and 1281 MHz) of the radio lobe spiral galaxy, NGC 3079, using the Giant Metrewave Radio Telescope. These observations are consistent with previous data obtained at other telescopes and reveal the structure of the nuclear radio lobes in exquisite detail. In addition, new features are observed, some with H  i counterparts, showing broad-scale radio continuum emission and extensions. The galaxy is surrounded by a radio halo that is at least 4.8 kpc in height. Two giant radio extensions/loops are seen on either side of the galaxy out to ∼11 kpc from the major axis, only slightly offset from the direction of the smaller nuclear radio lobes. If these are associated with the nuclear outflow, then the galaxy has experienced episodic nuclear activity. Emission along the southern major axis suggests motion through a local intergalactic medium (not yet detected), and it may be that NGC 3079 is itself creating this local intergalactic gas via outflows. We also present maps of the minimum energy parameters for this galaxy, including cosmic ray energy density, electron diffusion length, magnetic field strength, particle lifetime and power.  相似文献   

15.
We present an investigation of the relationships between the radio properties of a giant radio galaxy MRC B0319−454 and the surrounding galaxy distribution with the aim of examining the influence of intergalactic gas and gravity associated with the large-scale structure on the evolution in the radio morphology. Our new radio continuum observations of the radio source, with high surface brightness sensitivity, images the asymmetries in the megaparsec-scale radio structure in total intensity and polarization. We compare these with the three-dimensional galaxy distribution derived from galaxy redshift surveys. Galaxy density gradients are observed along and perpendicular to the radio axis: the large-scale structure is consistent with a model wherein the galaxies trace the ambient intergalactic gas and the evolution of the radio structures are ram-pressure limited by this associated gas. Additionally, we have modelled the off-axis evolution of the south-west radio lobe as deflection of a buoyant jet backflow by a transverse gravitational field: the model is plausible if entrainment is small. The case study presented here is a demonstration that giant radio galaxies may be useful probes of the warm-hot intergalactic medium believed to be associated with moderately over dense galaxy distributions.  相似文献   

16.
NGC 3310 is a local galaxy with an intense, ongoing starburst thought to result from a merger with a companion galaxy. It has several known tidal features in the northwest and southern regions around the main galactic disc, as well as a closed, tidal loop emerging from the eastern side of the disc and rejoining in the north. This loop appears to be distinct from the rest of the shells surrounding NGC 3310 and is the first of its kind to be detected in a starburst galaxy. In this work, we present U BV R photometry to faint surface brightness levels of this debris network, and we explore various strategies for modelling NGC 3310's disc and subtracting its contribution from each region of debris. We then compare these photometric results with the GALaxy EVolution (GALEV) spectral synthesis models, and find possible material from the intruder galaxy, suggesting that the recent accretion of several small galaxies is driving the evolution of NGC 3310.  相似文献   

17.
The overall morphology of the barred spiral galaxy NGC 7479 is modelled in numerical simulations of a minor merger. Special attention is paid to the morphology and velocity field of the asymmetric spiral structure and the strong stellar bar. The mass of the satellite galaxy is 1/10 of the mass of the primary disc, or 1/30 of the total mass of the primary. The satellite is placed initially in a circular prograde orbit at six disc scalelengths from the centre of the primary. We follow the evolution of the merger until the secondary galaxy reaches the nuclear region of the primary. A comparison between the modelled and observed morphologies of the stellar and the ionized and neutral gas distributions and velocity fields supports the hypothesis that the transient look of NGC 7479 is a result of a minor merger. We vary several of the initial parameters of the merger and discuss their effects on the resulting morphology. The merging satellite galaxy is likely to lie within the bar of NGC 7479. We identify a possible candidate in the observational data. We discuss briefly the most probable future evolution of NGC 7479 in the light of our minor-merger simulations, and conclude that NGC 7479 is likely to evolve toward an earlier Hubble type.  相似文献   

18.
We present new important results about the intermediate-type Seyfert galaxy Mrk 315, recently observed through optical imaging and integral-field spectroscopy. Broad-band images were used to study the morphology of the host galaxy, narrow-band Hα images to trace the star-forming regions, and middle-band [O  iii ] images to evidence the distribution of the highly ionized gas. Some extended emission regions were isolated and their physical properties studied by means of flux-calibrated spectra. High-resolution spectroscopy was used to separate different kinematic components in the velocity fields of gas and stars. Some peculiar features characterize this apparently undisturbed and moderately isolated active galaxy. Such features, already investigated by other authors, are re-analysed and discussed in the light of these new observations. The most relevant results we obtained are: the multitiers structure of the disc; the presence of a quasi-ring of regions with star formation much higher than previous claims; a secondary nucleus confirmed by a stellar component kinematically decoupled by the main galaxy; a new hypothesis about the controversial nature of the long filament, initially described as hook shaped, and more likely made of two independent filaments caused by interaction events between the main galaxy and two dwarf companions.  相似文献   

19.
The presence of two globular cluster subpopulations in early-type galaxies is now the norm rather than the exception. Here we present two more examples for which the host galaxy appears to have undergone a recent merger. Using multi-colour Keck imaging of NGC 1052 and 7332 we find evidence for a bimodal globular cluster colour distribution in both galaxies, with roughly equal numbers of blue and red globular clusters. The blue ones have similar colours to those in the Milky Way halo and are thus probably very old and metal-poor. If the red globular cluster subpopulations are at least of solar metallicity, then stellar population models indicate young ages. We discuss the origin of globular clusters within the framework of formation models. We conclude that recent merger events in these two galaxies have had little effect on their overall globular cluster systems. We also derive globular cluster density profiles, global specific frequencies and, in the case of NGC 1052, radial colour gradients and azimuthal distribution. In general these globular cluster properties are normal for early-type galaxies.  相似文献   

20.
We present a study of the origin of infrared (IR) emission in the optically normal, infrared luminous galaxy NGC 4418. By decomposing the stellar absorption features and continua in the range of 3600-8000 A from the Sloan Digital Sky Survey into a set of simple stellar populations, we derive the stellar properties for the nuclear region of NGC 4418. We compare the observed infrared luminosity with the one derived from the starburst model, and find that star-forming activity contributes only 7% to the total IR emission, that as the IR emission region is spatially very compact, the most possible source for the greater part of the IR emission is a deeply embedded AGN, though an AGN component is found to be unnecessary for fitting the optical spectrum.  相似文献   

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