共查询到20条相似文献,搜索用时 15 毫秒
1.
H.B. Ann 《Astrophysics and Space Science》2001,276(2-4):683-690
We have conducted UBVRI and Hα CCD photometry of five barred galaxies (NGC 2523, NGC 2950, NGC 3412, NGC 3945 and NGC 5383),along with SPH simulations,
in order to understand the origin of young stellar populations in the nuclei of barred galaxies. The Hα emission, which is thought to be emitted by young stellar populations, is either absent or strongly concentrated in the nuclei
of early-type galaxies (NGC 2950, NGC 3412 and NGC 3945),while they are observed in the nuclei and circumnuclear regions of
intermediate-type galaxies with strong bars (NGC 2523 and NGC 5383).SPH simulations of realistic mass models for these galaxies
show that some disc material can be driven into the nuclear region by a strong bar potential. This implies that the young
stellar populations in the circumnuclear regions of barred galaxies can be formed out of such gas. The existence of nuclear
dust lanes is an indication of an ongoing gas inflow and extremely young stellar populations in these galaxies, because nuclear
dust lanes such as those in NGC 5383 are not long-lasting features according to our simulations.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
D. Pérez-Ramírez J. H. Knapen † R. F. Peletier S. Laine R. Doyon † D. Nadeau † 《Monthly notices of the Royal Astronomical Society》2000,317(2):234-248
We present subarcsecond-resolution, ground-based, near-infrared images of the central regions of a sample of 12 barred galaxies with circumnuclear star formation activity, which is organized in ring-like regions typically 1 kpc in diameter. We also present Hubble Space Telescope near-infrared images of 10 of our sample galaxies, and compare them with our ground-based data. Although our sample galaxies were selected for the presence of circumnuclear star formation activity, our broad-band near-infrared images are heterogeneous, showing a substantial amount of small-scale structure in some galaxies, and practically none in others. We argue that, where it exists, this structure is caused by young stars, which also cause the characteristic bumps or changes in slope in the radial profiles of ellipticity, major axis position angle, surface brightness and colour at the radius of the circumnuclear ring in most of our sample galaxies. In seven out of 10 HST images, star formation in the nuclear ring is clearly visible as a large number of small emitting regions, organized into spiral arm fragments, which are accompanied by dust lanes. Near-infrared colour index maps show much more clearly the location of dust lanes and, in certain cases, regions of star formation than single broad-band images. Circumnuclear spiral structure thus outlined appears to be common in barred spiral galaxies with circumnuclear star formation. 相似文献
3.
Joris Gerssen Konrad Kuijken Michael R. Merrifield 《Monthly notices of the Royal Astronomical Society》2003,345(1):261-268
The pattern speed is one of the fundamental parameters that determines the structure of barred galaxies. This quantity is usually derived from indirect methods or by employing model assumptions. The number of bar pattern speeds derived using the model-independent Tremaine & Weinberg technique is still very limited. We present the results of model-independent measurements of the bar pattern speed in four galaxies ranging in Hubble type from SB0 to SBbc. Three of the four galaxies in our sample are consistent with bars being fast rotators. The lack of slow bars is consistent with previous observations and suggests that barred galaxies do not have centrally concentrated dark matter haloes. This contradicts simulations of cosmological structure formation and observations of the central mass concentration in nonbarred galaxies. 相似文献
4.
Cheng Li Dimitri A. Gadotti Shude Mao Guinevere Kauffmann 《Monthly notices of the Royal Astronomical Society》2009,397(2):726-732
We study the clustering properties of barred galaxies using data from the Sloan Digital Sky Survey. We compute projected redshift-space two-point cross-correlation functions w p ( r p ) for a sample of nearly 1000 galaxies for which we have performed detailed structural decompositions using the methods described in Gadotti. The sample includes 286 barred galaxies. The clustering of barred and unbarred galaxies of similar stellar mass is indistinguishable over all the scales probed (∼20 kpc–30 Mpc). This result also holds even if the sample is restricted to bars with bluer g − i colours (and hence younger ages). Our result also does not change if we split our sample of barred galaxies according to bar-to-total luminosity ratio, bar boxyness, effective surface brightness, length or the shape of the surface density profile within the bar. There is a hint that red, elliptical bars are more strongly clustered than red and less elliptical bars, on scales ≳1 Mpc , although the statistical significance is not high. We conclude that there is no significant evidence that bars are a product of mergers or interactions. We tentatively interpret the stronger clustering of the more elliptical bars as evidence that they are located in older galaxies, which reside in more massive haloes. 相似文献
5.
Ian R. Stevens & David K. Strickland 《Monthly notices of the Royal Astronomical Society》1998,301(1):215-230
We present results from an ongoing X-ray survey of Wolf–Rayet (WR) galaxies, a class of objects believed to be very young starbursts. This paper extends the first X-ray survey of WR galaxies by Stevens &38; Strickland by studying WR galaxies identified subsequent to the original WR galaxy catalogue of Conti. Out of a sample of 40 new WR galaxies a total of 10 have been observed with the ROSAT PSPC, and of these seven have been detected (NGC 1365, NGC 1569, I Zw 18, NGC 3353, NGC 4449, NGC 5408 and a marginal detection of NGC 2366). Of these, all are dwarf starbursts except for NGC 1365, which is a barred spiral galaxy possibly with an active nucleus. We also report on observations of the related emission-line galaxy IRAS 0833+6517. The X-ray properties of these galaxies are broadly in line with those found for the original sample; they are X-ray overluminous compared with their blue luminosity and have thermal spectra with typically kT ∼ 0.4 − 1.0 keV. There are some oddities: NGC 5408 is very overluminous in X-rays, even compared with other WR galaxies; I Zw 18 has a harder X-ray spectrum; NGC 1365, although thought to contain an active nucleus, has X-ray properties that are broadly similar to other WR galaxies, and we suggest that the X-ray emission from NGC 1365 is due to starburst activity. A good correlation between X-ray and blue luminosity is found for the WR galaxy sample as a whole. However, when just dwarf galaxies are considered there is little evidence of correlation. We discuss the implications of these results on our understanding of the X-ray emission from WR galaxies and suggest that the best explanation for the X-ray activity is starburst activity from a young starburst region. 相似文献
6.
O. A. Merkulova G. M. Karataeva V. A. Yakovleva A. N. Burenkov 《Astronomy Letters》2012,38(5):290-304
We analyze new observational data obtained at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with the multimode SCORPIO instrument and the Multi-Pupil Fiber Spectrograph for the group of galaxies NGC 7465/64/63. For one of the group members (NGC 7465), the presence of a polar ring has been suspected. We have constructed the large-scale brightness distributions, the ionized-gas velocity and velocity dispersion fields for all three galaxies as well as the line-of-sight velocity curves based on emission and absorption lines and the stellar velocity field in the central region for NGC 7465. As a result of our analysis of the data obtained, we have discovered an inner stellar disk (r ?? 0.5 kpc) and a warped gaseous disk in NGC 7465, in addition to the main stellar disk. Based on a joint study of our photometric and spectroscopic data, we have established that NGC 7464 is an irregular IrrI-type galaxy whose structural and kinematic peculiarities most likely resulted from its gravitational interaction with NGC 7465. The velocity field of the ionized gas in NGC 7463 turns out to be typical of barred spiral galaxies, and the warp of the outer parts of its disk could arise from a close encounter with one of the galaxies of the environment. 相似文献
7.
We summarize here some ongoing work by our group on the formation and evolution of barred galaxies. We first discuss the evolution
of bars in isolated disc galaxies. Then we address the problem of bar destruction during interactions and mergers. Finally
we describe work on generation and regeneration of bars in interactions.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
A. V. Moiseev 《Astronomy Letters》2002,28(11):755-768
We describe the results of our spectroscopy for a sample of barred galaxies whose inner regions exhibit an isophotal twist commonly interpreted as a secondary bar. The line-of-sight velocity fields of the ionized gas and stars and the light-of-sight velocity dispersion fields of the stars were constructed from two-dimensional spectroscopy with the 6-m Special Astrophysical Observatory telescope. We detected various types of noncircular motions of ionized gas: radial flows within large-scale bars, counterrotation of the gas and stars at the center of NGC 3945, a polar gaseous disk in NGC 5850, etc. Our analysis of the optical and near-infrared galaxy images (both ground-based and those from the Hubble Space Telescope) revealed circumnuclear minispirals in five objects. The presence of an inner (secondary) bar in the galaxy images is shown to have no effect on the circumnuclear kinematics of the gas and stars. Thus, contrary to popular belief, the secondary bar is not a dynamically decoupled galactic structure. We conclude that the so-called double-barred galaxies are not a separate type of galaxy but are a combination of objects with distinctly different morphologies of their circumnuclear regions. 相似文献
9.
J. Falcn‐Barroso R. Bacon M. Bureau M. Cappellari R. L. Davies E. Emsellem D. Krajnovi H. Kuntschner R. McDermid R. F. Peletier P. T. de Zeeuw 《Astronomische Nachrichten》2004,325(2):92-95
Kinematic and population studies show that bulges are generally rotationally flattened systems similar to lowluminosity ellipticals. However, observations with state‐of‐the‐art integral field spectrographs, such as SAURON, indicate that the situation is much more complex, and allow us to investigate phenomena such as triaxiality, kinematic decoupling and population substructure, and to study their connection to current formation and evolution scenarios for bulges of early‐type galaxies. We present the examples of two S0 bulges from galaxies in our sample of nearby galaxies: one that shows all the properties expected from classical bulges (NGC5866), and another case that presents kinematic features appropriate for barred disk galaxies (NGC7332). (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
10.
Dimitri Alexei Gadotti Ronaldo Eustáquio de Souza 《Astrophysics and Space Science》2003,284(2):527-530
To further enhance our understanding on the formation and evolution of bars in lenticular (S0) galaxies, we are undertaking
a detailed photometric and spectroscopic study on a sample of 22 objects. Here we report the results of a 2D structural analysis
on two barred face-on S0's, which indicate that presently these galaxies do not possess disks. We discuss two possibilities
to explain these surprising results, namely strong secular evolution and bar formation without disks.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
Matt J. Jarvis Ross J. McLure 《Monthly notices of the Royal Astronomical Society》2006,369(1):182-188
We have identified two new galaxies with gas counter-rotation (NGC 1596 and 3203) and have confirmed similar behaviour in another one (NGC 128), this using results from separate studies of the ionized-gas and stellar kinematics of a well-defined sample of 30 edge-on disc galaxies. Gas counter-rotators thus represent 10 ± 5 per cent of our sample, but the fraction climbs to 21 ± 11 per cent when only lenticular (S0) galaxies are considered and to 27 ± 13 per cent for S0 galaxies with detected ionized gas only. Those fractions are consistent with but slightly higher than previous studies. A compilation from well-defined studies of S0 galaxies in the literature yields fractions of 15 ± 4 and 23 ± 5 per cent, respectively. Although mainly based on circumstantial evidence, we argue that the counter-rotating gas originates primarily from minor mergers and tidally induced transfer of material from nearby objects. Assuming isotropic accretion, twice those fractions of objects must have undergone similar processes, underlining the importance of (minor) accretion for galaxy evolution. Applications of gas counter-rotators to barred galaxy dynamics are also discussed. 相似文献
12.
Witold Maciejewski Linda S. Sparke 《Monthly notices of the Royal Astronomical Society》2000,313(4):745-760
High-resolution observations of the inner regions of barred disc galaxies have revealed many asymmetrical, small-scale central features, some of which are best described as secondary bars. Because orbital time-scales in the galaxy centre are short, secondary bars are likely to be dynamically decoupled from the main kiloparsec-scale bars. Here we show that regular orbits exist in such doubly barred potentials, and that they can support the bars in their motion. We find orbits in which particles remain on loops : closed curves which return to their original positions after two bars have come back to the same relative orientation. Stars trapped around stable loops could form the building blocks for a long-lived, doubly barred galaxy. Using the loop representation, we can find which orbits support the bars in their motion, and the constraints on the sizes and shapes of self-consistent double bars. In particular, it appears that a long-lived secondary bar may exist only when an inner Lindblad resonance is present in the primary bar, and that it would not extend beyond this resonance. 相似文献
13.
Joris Gerssen Victor P. Debattista 《Monthly notices of the Royal Astronomical Society》2007,378(1):189-197
We investigate the effect of dust on the observed rotation rate of a stellar bar. The only direct way to measure this quantity relies on the Tremaine & Weinberg (TW) method which requires that the tracer satisfies the continuity equation. Thus, it has been applied largely to early-type barred galaxies. We show using numerical simulations of barred galaxies that dust attenuation factors typically found in these systems change the observed bar pattern speed by 20–40 per cent. We also address the effect of star formation on the TW method and find that it does not change the results significantly. The results presented here suggest that applications of the TW method can be extended to include barred galaxies covering the full range of Hubble type. 相似文献
14.
H. C.Thomas L.Dunne M. S.Clemens P.Alexander S.Eales D. A.Green A.James 《Monthly notices of the Royal Astronomical Society》2002,331(4):853-864
We present SCUBA 850-μm, JCMT CO( J =2→1) , B -band imaging and VLA H i observations of the NGC 7465/4/3 group of galaxies. The 850-μm emission associated with NGC 7465 extends to at least ∼2 R 25 and is well correlated with the H i . We investigate a range of possible mechanisms by which dust beyond R 25 may be heated to give the observed extended submillimetre emission. By modelling the dust heating by stars in two extreme geometries, we fail to find any reasonable star formation scenario that is consistent with both the 850-μm and optical data. Furthermore, we do not detect any CO( J =2→1) emission coincident with the extended dust and atomic gas as would be expected if significant star formation were occurring. We show that shock-heating of dust via cloud–cloud collisions in the stripped interstellar medium of NGC 7465 could be sufficient to explain the extended 850-μm emission and lack of optical emission in the stripped gas, and suggest that cloud–cloud collisions may be an important dust heating mechanism in gas-rich systems. 相似文献
15.
We have investigated the effects of a bar and an asymmetric spiral structure on the neutral hydrogen distribution and kinematics in the strongly barred spiral galaxy NGC 7479. The strongest 21-cm line emission at 1-kpc resolution comes from the western spiral arm which appears to be slightly inclined to the plane of the main disc. In contrast, the area within the radius of the bar is devoid of 21-cm line emission. The radio continuum emission at 21 cm follows the bar dust lanes, but beyond 3 kpc from the nucleus the radio continuum emission has a peculiar morphology, unlike that of optical and near-infrared images. We did not detect any low surface brightness gas-rich companions in the near neighbourhood of NGC 7479. This leads us to propose that the strong western spiral arm was created in a recent minor merger. 相似文献
16.
Abdel-Fattah Attia H. A. Ismail I. M. Selim A. M. Osman I. A. Isaa M. A. Marie A. A. Shaker 《中国天文和天体物理学报》2005,5(4):347-355
We present a new method for determining the age and relative contribution of different stellar populations in galaxies based on the genetic algorithm. We apply this method to the barred spiral galaxy NGC 3384, using CCD images in U, B, V, R and I bands. This analysis indicates that the galaxy NGC 3384 is mainly inhabited by old stellar population (age >109yr). Some problems were encountered when numerical simulations are used for determining the contribution of different stellar populations in the integrated color of a galaxy. The results show that the proposed genetic algorithm can search efficiently through the very large space of the possible ages. 相似文献
17.
S. Laine 《Astrophysics and Space Science》2001,276(2-4):667-674
The most salient features of the barred spiral galaxy NGC 7479 include the unusually strong and long bar, asymmetric spiral
structure and peculiar dust lanes. The central, bar-dominated region has been robbed of neutral atomic gas. The neutral hydrogen
kinematics of the strong western spiral arm are consistent with substantial non-circular motions. In contrast, the molecular
gas is strongly concentrated in the nucleus and along the bar dust lanes. A molecular disc with near-circular motion is found
in the nuclear area. Outside this component, the molecular gas has a strong radial velocity component consistent with inflow.
The velocity gradients across the bar dust lanes show jumps of a few hundred km s-1. A comparison of the dust/gas lane morphology between the observations and numerical simulations suggests that the corotation
radius is at 1.1 times the bar length. I have modelled many of the peculiar morphological and kinematic features in numerical
simulations of a minor merger. The predicted position of the merging companion matches the position of a bright clump in the
bar with perturbed kinematics.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
J.A.L. Aguerri M. Prieto A.M. Varela C. Muñoz-Tuñón 《Astrophysics and Space Science》2001,276(2-4):611-618
The isophotal profiles and colour maps of a sample of 12 spiral galaxies allowed us to analyse the different structural components
that compose them. These components were parameterized by performing a decomposition of the galaxy brightness profiles. Inferring
the geometry for each component, we have obtained the spatial mass distribution and the gravitational potential for each object.
Here we present the detailed analysis for one of the galaxies in the sample, the barred galaxy NGC 1300.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
M. Imanishi 《Monthly notices of the Royal Astronomical Society》2000,319(1):331-336
The results of 3–4-μm spectroscopy towards the nuclei of NGC 3094, 7172, and 7479 are reported. In ground-based 8–13-μm spectra, all the sources have strong absorption-like features at ∼10 μm, but they do not have detectable polycyclic aromatic hydrocarbon (PAH) emission features. The 3.4-μm carbonaceous dust absorption features are detected towards all nuclei. NGC 3094 shows a detectable 3.3-μm PAH emission feature, while NGC 7172 and 7479 do not. Nuclear emission whose spectrum shows dust absorption features but no PAH emission features, is thought to be dominated by highly obscured active galactic nuclei (AGNs) activity. For NGC 7172, 7479, and three other such nuclei in the literature, we investigate the optical depth ratios between the 3.4-μm carbonaceous dust and 9.7-μm silicate dust absorption The ratios towards three highly obscured AGNs with face-on host galaxies are systematically larger than the ratios in the Galactic diffuse interstellar medium or the ratios for two highly obscured AGNs with edge-on host galaxies. We suggest that the larger ratios can be explained if the obscuring dust is so close to the central AGNs that a temperature gradient occurs in it. If this idea is correct, our results may provide spectroscopic evidence for the presence of the putative 'dusty tori' in the close vicinity of AGNs. 相似文献
20.
H.-E. Frhlich 《Astronomische Nachrichten》1982,303(2):97-103
In order to determine the quantitative influence of small amounts of dust on the luminosity profile of spherical galaxies, we represent an elliptical galaxy by a KING sphere filled with dust. The density of dust particles is assumed to be related to the density of stars according to a simple power law. Assuming that the observed central reddenings in NGC 4874 and NGC 4889 are really caused by dust, we estimate the optical depths in the centres of both galaxies to be about 0.75. 相似文献