共查询到20条相似文献，搜索用时 31 毫秒
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Arthur D. Chernin 《Monthly notices of the Royal Astronomical Society》1999,308(2):321-332
The phenomenon of 'rows', which are straight geometrical segments in the spiral arms of galaxies, is studied. The Whirlpool nebula, Messier 51 (NGC 5194) in Canes Venatici, is considered to be an example of a giant grand design galaxy. Optical photographs, H α , ultraviolet and far-ultraviolet images, CO, 21-cm and synchrotron emission maps, and a K s -band mosaic of M51 are studied. With this observational material, multiple rows can be recognized in the spiral arms of the galaxy. The rows comprise a major part of the arms. The lengths of the rows increase almost linearly with distance from the centre. They intersect one another at an (average) angle ≈2π/3. A possible physical explanation of the phenomenon of rows is discussed on the basis of the assumption that the formation of straight arm segments might be due to the gas-dynamical effect of stability of flat shock fronts, and the tendency of a slightly curved shock front to become flat. A quantitative flattening criterion enables an explanation of the geometrical properties of the arm patterns found in M51 and also in M101. A brief list of spirals with rows is given. 相似文献
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A. P. Huxor N. R. Tanvir M. J. Irwin R. Ibata J. L. Collett A. M. N. Ferguson T. Bridges G. F. Lewis 《Monthly notices of the Royal Astronomical Society》2005,360(3):1007-1012
We present three new clusters discovered in the halo of M31 which, although having globular-like colours and luminosities, have unusually large half-light radii, ∼30 pc. They lie at projected galactocentric distances of ≈15 to ≈35 kpc. These objects begin to fill the gap in parameter space between globular clusters and dwarf spheroidals, and are unlike any clusters found in the Milky Way, or elsewhere to date. Colour–magnitude diagrams, integrated photometric properties and derived King profile fit parameters are given, and we discuss possible origins of these clusters and their relationships to other populations. 相似文献
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C. Halliday D. Carter T. J. Bridges Z. C. Jackson M. I. Wilkinson D. P. Quinn N. W. Evans N. G. Douglas H. R. Merrett M. R. Merrifield A. J. Romanowsky K. Kuijken M. J. Irwin 《Monthly notices of the Royal Astronomical Society》2006,369(1):97-119
We present radial velocities for a sample of 723 planetary nebulae in the disc and bulge of M31, measured using the WYFFOS fibre spectrograph on the William Herschel Telescope. Velocities are determined using the [O iii ] λ5007 emission line. Rotation and velocity dispersion are measured to a radius of 50 arcmin (11.5 kpc), the first stellar rotation curve and velocity dispersion profile for M31 to such a radius. Our kinematics are consistent with rotational support at radii well beyond the bulge effective radius of 1.4 kpc, although our data beyond a radius of 5 kpc are limited. We present tentative evidence for kinematic substructure in the bulge of M31 to be studied fully in a later work. This paper is part of an ongoing project to constrain the total mass, mass distribution and velocity anisotropy of the disc, bulge and halo of M31. 相似文献
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Guillermo Bosch † Elena Terlevich ‡ Roberto Terlevich § 《Monthly notices of the Royal Astronomical Society》2002,329(3):481-496
We have obtained accurate CCD narrow-band Hβ and Hα photometry of giant H ii regions (GEHRs) in M33, NGC 6822 and M101. Comparison with previous determinations of emission-line fluxes shows large discrepancies; their probable origins are discussed. Combining our new photometric data with global velocity dispersion ( σ ) derived from emission linewidths, we review the relation. A re-analysis of the properties of the GEHRs included in our sample shows that age spread and the superposition of components in multiple regions introduce a considerable spread in the regression. Combining the information available in the literature regarding ages of the associated clusters, evolutionary footprints on the interstellar medium, and kinematical properties of the knots that build up the multiple GEHRs, we find that a subsample – which we refer to as young and single GEHRs – do follow a tight relation in the plane. 相似文献
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Benjamin F.Williams 《Monthly notices of the Royal Astronomical Society》2002,331(2):293-312
Over the past several years, the Hubble Space Telescope ( HST ) has acquired many broad-band images of various regions in the M31 disc. I have obtained 27 such fields from the HST data archive in order to produce colour–magnitude diagrams (CMDs) of the stellar populations contained within these areas of the disc. I have attempted to reproduce these CMDs using theoretical stellar evolution models in conjunction with statistical tools for determining the star formation history that best fits the observations. The wide range of extinction values within any given field makes the data difficult to reproduce accurately; nevertheless, I have managed to find star formation histories that roughly reproduce the data. These statistically determined star formation histories reveal that, like the disc of the Galaxy, the disc of M31 contains very few old metal-poor stars. The histories also suggest that the star formation rate of the disc as a whole has been low over the past ∼1 Gyr. 相似文献
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S. Kendall R. C. Kennicutt C. Clarke M. D. Thornley 《Monthly notices of the Royal Astronomical Society》2008,387(3):1007-1020
We use Spitzer IRAC 3.6 and 4.5 μm near-infrared data from the Spitzer Infrared Nearby Galaxies Survey (SINGS), optical B, V and I and Two-Micron All-Sky Survey K s -band data to produce mass surface density maps of M81. The IRAC 3.6- and 4.5-μm data, whilst dominated by emission from old stellar populations, are corrected for small-scale contamination by young stars and polycyclic aromatic hydrocarbon emission. The I -band data are used to produce a mass surface density map by a B − V colour correction, following the method of Bell and de Jong. We fit a bulge and exponential disc to each mass map, and subtract these components to reveal the non-axisymmetric mass surface density. From the residual mass maps, we are able to extract the amplitude and phase of the density wave, using azimuthal profiles. The response of the gas is observed via dust emission in the 8-μm IRAC band, allowing a comparison between the phase of the stellar density wave and gas shock. The relationship between this angular offset and radius suggests that the spiral structure is reasonably long-lived and allows the position of corotation to be determined. 相似文献
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K. A. Wills M. Das A. Pedlar T. W. B. Muxlow T. G. Robinson 《Monthly notices of the Royal Astronomical Society》2000,316(1):33-48
We present VLA A-array 21-cm atomic hydrogen (H i ) absorption observed against the central region of the starburst galaxy M82 with an angular resolution of ∼1.3 arcsec (≃20 pc). These observations, together with MERLIN H i absorption measurements, are compared with the molecular (CO) and ionized ([Ne ii ]) gas distributions and are used to constrain the dynamics and structure of the ionized, neutral and molecular gas in this starburst.
A position–velocity diagram of the H i distribution reveals an unusual 'hole' feature which, when previously observed in CO, has been interpreted as an expanding superbubble contained within a ring of gas in solid body rotation. However, we interpret this feature as a signature of a nearly edge-on barred galaxy. In addition, we note that the CO, H i and [Ne ii ] position–velocity diagrams reveal two main velocity gradients, and we interpret these as gas moving on x1 - and x2 -orbits within a bar potential. We find the best fit to the data to be produced using a bar potential with a flat rotation curve velocity v b =140 km s−1 and a total length of 1 kpc, a non-axisymmetry parameter q =0.9, an angular velocity of the bar Ωb =217 km s−1 arcsec−1 , a core radius R c =25 pc, an inclination angle i =80° and a projected angle between the bar and the major axis of the galaxy φ '=4°. We also discuss the orientation of the disc and bar in M82. 相似文献
A position–velocity diagram of the H i distribution reveals an unusual 'hole' feature which, when previously observed in CO, has been interpreted as an expanding superbubble contained within a ring of gas in solid body rotation. However, we interpret this feature as a signature of a nearly edge-on barred galaxy. In addition, we note that the CO, H i and [Ne ii ] position–velocity diagrams reveal two main velocity gradients, and we interpret these as gas moving on x
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Alessandro Patruno Luca Zampieri 《Monthly notices of the Royal Astronomical Society》2008,386(1):543-552
We present evolutionary tracks of binary systems with high-mass companion stars and stellar-through-intermediate mass black holes (BHs). Using Eggleton's stellar evolution code, we compute the luminosity produced by accretion from the donor during its entire evolution. We compute also the evolution of the optical luminosity and colours of the binary system taking the disc contribution and irradiation effects into account. The calculations presented here can be used to constrain the properties of the donor stars in ultraluminous X-ray sources by comparing their position on the Hertzsprung–Russell or colour–magnitude diagrams with the evolutionary tracks of massive BH binaries. This approach may actually provide interesting clues also on the properties of the binary system itself, including the BH mass. We found that, on the basis of their position on the colour–magnitude diagram, some of the candidate counterparts considered can be ruled out and more stringent constraints can be applied to the donor masses. 相似文献
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1 INTRODUCTION Globular clusters are thought to be among the oldest radiant objects in the Universe. Thestudies of these systems have played a key role in the development of our understanding of theUniverse, including the fundamental question of the age of the Universe. The globular clustersof Milky Way can be used to probe the way in which our Galaxy formed. Studies of similarclusters in other galaxies can also provide us the properties of those galaxies in the early periodafter their … 相似文献