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1.
Based on archival Hubble Space Telescope images, we have performed stellar photometry for eight edge-on spiral and irregular galaxies. We have identified stars of three ages in the derived Hertzsprung-Russell diagrams and constructed their number density distribution perpendicularly to the plane of the galactic disk. The sizes of the stellar subsystems of young (up to 100 Myr), middle (0.1–1.0 Gyr), and old (up to 12 Gyr) ages have been determined. A relationship between the age of a subsystem and its size has been found in all of the galaxies studied. Our results can be explained by the model of galactic thick-disk formation through thin-disk expansion. In this case, the middle-age stellar subsystem is a transitional stage from the thin disk to the thick one.  相似文献   

2.
Based on archival Hubble Space Telescope ACS/WFC images, we have performed stellar photometry for the young tidal dwarf galaxy Ho IX. We have determined that star formation in Ho IX began 110 Myr ago and ended 20 Myr ago. We have identified 20 young star clusters in the galaxy with ages from 25 to 100 Myr. For the main star-forming region of Ho IX along one direction, we have determined the change in the number density of stars with three ages: 30, 50, and 90 Myr. A relation has been found between the ages of stars and the spatial sizes of the subsystem formed by them. This relation can be explained by expansion of the stellar subsystems. Under this assumption, the expansion velocity is 9.8 km s?1 as the age changes from 50 to 90 Myr. Edge-on low-mass late-type galaxies have similar relations between the ages and sizes of their stellar subsystems.  相似文献   

3.
Stellar photometry for three fields in the Virgo cluster of galaxies has been performed on the basis of archival Hubble Space Telescope ACS/WFC images. The densely populated red giant branches belonging to cluster galaxies are seen on the constructed Hertzsprung–Russell diagrams. The distances to eight galaxies in the Virgo cluster have been determined by the TRGB method. The sizes of the stellar subsystems and the gradients in the number density of red giants along the galactic radius have been determined for the investigated galaxies. The stellar periphery of the galaxies has been found to extend to great distances and to cover the entire area of the images used. Therefore, the stars that have previously been thought to be intracluster stars actually belong to the periphery of neighboring galaxies.  相似文献   

4.
Based on archival Hubble Space Telescope images, we have performed stellar photometry of several fields in the isolated spiral galaxies NGC 6503 and NGC 6946 with high peculiar velocities. Based on the TRGB method, we have determined the distances to the galaxies: D = 6.30 ± 0.10 Mpc for NGC 6503 and D = 6.72 ± 0.15 Mpc for NGC 6946. The current stellar content of the galaxies does not differ from that of other similar galaxies. The metallicity for young stars in NGC 6503 is Z = 0.02 (corresponding to the solar metallicity), while the metallicity for stars in NGC 6946 reaches Z = 0.05. Very few old globular clusters have been found in NGC 6946, while they have not been found at all in NGC 6503. The number density distribution of stars with different ages in NGC 6503 does not differ from the analogous distributions in other galaxies. The large sizes of the thick disk in NGC 6503, which is clearly seen up to 6 kpc from the galactic disk plane and whose possible extension is noticeable up to 8.6 kpc from the plane, are a difference. The sizes of the region occupied by red giants of the disk in NGC 6503 are 51 × 17 kpc, which are not much larger than the sizes of this galaxy from H I radio observations.  相似文献   

5.
Based on archival Hubble Space Telescope ACS/WFC images, we have performed stellar photometry for eight dwarf galaxies of different types (Irr, S0, E) with a populated horizontal branch on their Hertzsprung-Russell diagrams. We have identified probable RR Lyr stars in these galaxies and constructed the distribution of their number density along the minor axes of the galaxies. For comparison, similar distributions have also been constructed for red giants in the same galaxies. In all cases, the size of the subsystem of RR Lyr stars exceeds that of the subsystem of, on average, younger stars, red giants. Our results are consistent with the hypothesis about expansion of the stellar subsystems in dwarf galaxies that we suggested previously.  相似文献   

6.
Stellar photometry of images from the ACS and WFPC2 cameras on the Hubble Space Telescope (HST) is used to study the star composition and spatial distribution of stars in three edge-on visible spiral galaxies: NGC 891, NGC 4144, and NGC 4244. Measurements of the surface number density of old stars revealed two stellar subsystems in these galaxies: a thick disk and a halo. The boundaries of these subsystems, which consist mainly of red giants, are determined from the change in the gradient of the number density of the stars. The halos are flattened at the poles of the galaxies and extend to distances of 8–25 kpc from the planes of the galaxies. The present results on the number density distribution of stars with different ages perpendicular to the planes of these galaxies make it possible to improve our model for the stellar structure of spiral galaxies. The distances to these galaxies are calculated using a determination of the tip of the red giant branches (the TRGB method): D = 9.82 Mpc (NGC 891), D = 7.24 Mpc (NGC 4144), and D = 4.29 Mpc (NGC 4244).__________Translated from Astrofizika, Vol. 48, No. 2, pp. 261–280 (May 2005).  相似文献   

7.
Based on archival Hubble Space Telescope ACS/WFC images, we have performed stellar photometry for an isolated pair of interacting galaxies, IC 1727 and NGC 672, and constructed their Hertzsprung-Russell diagrams. The galaxy IC 1727 exhibits a strong asymmetry in the apparent distribution of young stars. The distribution of old stars is smoother and less asymmetric. In the galaxy NGC672, there is no noticeable asymmetry in the distribution of stars of different ages. Based on the TRGB method, we have determined an accurate distance to each galaxy for the first time: D = 7.14 ± 0.10 Mpc for IC 1727 and D = 7.22 ± 0.10 Mpc for NGC 672, confirming that these galaxies are closely spaced. The luminosity functions of red supergiants and peripheral AGB stars in both galaxies have positionally coincident local maxima, suggesting the simultaneous enhancement of star formation in the two galaxies occurred in the intervals 20–30 and 450–700 Myr ago. The results obtained point to an enhancement of star formation processes in the interacting galaxies.  相似文献   

8.
Simple theoretical arguments indicate that cooled interstellar gas in bright elliptical galaxies forms into a young stellar population having a bottom-heavy but optically luminous initial mass function extending to approximately 2 M middle dot in circle. When the colors and spectral features of this young population are combined with those of the underlying old stellar population, the apparent ages are significantly reduced, similar to the relatively young apparent ages observed in many elliptical galaxies. Galactic mergers are not required to resupply young stars. The sensitivity of continuous star formation to LB and LX&solm0;LB is likely to account for the observed spread in apparent ages among elliptical galaxies. Local star formation is accompanied by enhanced stellar Hbeta equivalent widths, stronger optical emission lines, more thermal X-ray emission, and lower apparent temperatures in the hot gas. The young stars should cause M&solm0;L to vary with galactic radius, perturbing the fundamental plane of the old stars alone.  相似文献   

9.
G01 New evidence for a connection between massive black holes and ULX G02 Long‐Term Evolution of Massive Black Hole Binaries G03 NBODY Meets Stellar Population Synthesis G04 N‐body modelling of real globular star clusters G05 Fokker‐Planck rotating models of globular clusters with black hole G06 Observational Manifestation of chaos in spiral galaxies: quantitative analysis and qualitative explanation G07 GRAPE Clusters: Beyond the Million‐Body Problem G08 Orbital decay of star clusters and Massive Black Holes in cuspy galactic nuclei G09 An Edge‐on Disk Galaxy Catalog G10 Complexes of open clusters in the Solar neighborhood G11 Search for and investigation of new stellar clusters using the data from huge stellar catalogues G12 Computing 2D images of 3D galactic disk models G13 Outer Pseudoring in the Galaxy G14 Where are tidal‐dwarf galaxies? G15 Ultra compact dwarf galaxies in nearby clusters G16 Impact of an Accretion Disk on the Structure of a stellar cluster in active galactic nuclei G17 Order and Chaos in the edge‐on profiles of disk galaxies G18 On the stability of OB‐star configurations in the Orion Nebula cluster G19 Older stars captured in young star clusters by cloud collapse G20 General features of the population of open clusters within 1 kpc from the Sun G21 Unstable modes in thin stellar disks G22 From Newton to Einstein – Dynamics of N‐body systems G23 On the relation between the maximum stellar mass and the star cluster mass  相似文献   

10.
Based on archival Hubble Space Telescope ACS/WFC images, we have performed stellar photometry for more than 0.6 million stars in the interacting galaxies NGC 5194 and NGC 5195 of the M51 system. Stars of various ages have been identified on the constructed Hertzsprung-Russell diagram: blue and red supergiants, AGB stars, and red giants. The distance to M51 has been measured from the position of the tip of the red giant branch, D = 9.9 ± 0.7 Mpc. We have determined the change in the metallicity of red supergiants along the galactic radius in NGC 5194. Despite the gravitational interaction, the distribution of stars in NGC 5194 does not differ from that in isolated galaxies. The asymmetric stellar structures of NGC5195 (the so-called “feathers”) formed through the interaction of two galaxies have been found to consist mostly of AGB stars.  相似文献   

11.
Observations of the pair of galaxies VV 330 with the SCORPIO multimode instrument on the 6-m Special Astrophysical Observatory telescope are presented. Large-scale velocity fields of the ionized gas in Hα and brightness distributions in continuum and Hα have been constructed for both galaxies with the help of a scanning Fabry-Perot interferometer. Long-slit spectroscopy is used to study the stellar kinematics. Analysis of the data obtained has revealed a complex structure in each of the pair components. Three kinematic subsystems have been identified in UGC 5600: a stellar disk, an “inner gas ring” turned with respect to the disk through ～80°, and an outer gas disk. The stellar and outer gas disks are noncoplanar. Possible scenarios for the formation of the observed multicomponent kinematic galactic structure are considered, including the case where the large-scale velocity field of the gas is represented by the kinematic model of a disk with a warp. The velocity field in the second galaxy of the pair, UGC 5609, is more regular. A joint analysis of the data on the photometric structure and the velocity field has shown that this is probably a late-type spiral galaxy whose shape is distorted by the gravitational interaction, possibly, with UGC 5600.  相似文献   

12.
We consider disk and spherical subsystems of stars with nearly radial orbits under conditions when the well-known radial orbit instability is not possible. This requires that the precession of stellar orbits be retrograde, i.e., in the direction opposite to the orbital rotation of stars. We show that an instability that is an analogue of the loss-cone instability known in plasma physics can then develop in the presence of a “loss cone” in the angular momentum distribution of stars, which ensures a deficit or even absence of stars with low angular momenta. Examples of systems with a loss cone are the centers of galaxies or star clusters with massive black holes. The instability can produce a flux of stars onto the galactic center, i.e., it can serve as a mechanism of fueling the nuclear activity of galaxies. Mathematically, the problem is reduced to analyzing simple characteristic equations that describe small perturbations in a disk and a sphere of radially highly elongated stellar orbits. In turn, these characteristics equations are derived through a number of successive simplifications of the general linearized Vlasov equations (i.e., the system that includes the collisionless Boltzmann kinetic equation and the Poisson equation) in action—angle variables.  相似文献   

13.
Using the MegaCam imager on the Canada–France–Hawaii Telescope, we have resolved individual stars in the outskirts of the nearby large spiral galaxy M81 (NGC 3031) well below the tip of the red giant branch of metal-poor stellar populations over  ∼60 × 58 kpc2  . In this paper, we report the discovery of new young stellar systems in the outskirts of M81. The most prominent feature is a chain of clumps of young stars distributed along the extended southern H  i tidal arm connecting M 81 and NGC 3077. The colour–magnitude diagrams of these stellar systems show plumes of bright main sequence stars and red supergiant stars, indicating extended events of star formation. The main sequence turn-offs of the youngest stars in the systems are consistent with ages of ∼40 Myr. The newly reported stellar systems show strong similarities with other known young stellar systems in the debris field around M81, with their properties best explained by these systems being of tidal origin.  相似文献   

14.
Based on archival Hubble Space Telescope (HST) ACS/WFC images, we have performed stellar photometry for eight fields of the spiral galaxy NGC 1313 and its satellite, the low-mass Sph/Irr galaxy AM0319-662. Stars of various ages have been identified on the constructed Hertzsprung–Russell diagrams: young supergiants, middle-aged stars, and old stars (red giants); their apparent distributions over the body of the galaxy are presented. The red supergiants and giants have been divided into groups with larger and smaller color indices, corresponding to a difference in stellar metallicity. These groups of stars are shown to have different spatial distributions and to belong to two galaxies, NGC1313 itself and the disrupted satellite. We have determined the distance to NGC 1313, D = 3.88 ± 0.07 Mpc, by the TRGB method from six fields. Our photometry of 2014 HST images has revealed an emerged charge transfer inefficiency on the ACS/WFC CCDs, which manifests itself as a dependence of the photometry of stars on their coordinates on the CCD.  相似文献   

15.
旋涡星系的颜色梯度反映了其星族构成沿径向的分布,包含了星系恒星形成历史的信息.因此,对旋涡星系颜色梯度的研究有助于理解星系的形成和演化过程.大部分旋涡星系存在负的颜色梯度,其主要原因是旋涡星系存在星族梯度.颜色梯度与星系的面亮度之间存在内禀的相关,表明质量面密度在星系的形成和演化过程中具有重要作用.  相似文献   

16.
We investigate the dynamical effects of a molecular cloud complex with a mass ∼ 107 M⊙ and a size ∼ a few 100 pc on the vertical distribution of stars and atomic hydrogen gas in a spiral galactic disc. Such massive complexes have now been observed in a number of spiral galaxies. The extended mass distribution in a complex, with an average mass density 6 times higher than the Oort limit, is shown to dominate the local gravitational field. This results in a significant redistribution or clustering of the surrounding disc components towards the mid-plane, with a resulting decrease in their vertical scaleheights.
The modified, self-consistent stellar density distribution is obtained by solving the combined Poisson equation and the force equation along the z -direction for an isothermal stellar disc on which the complex is imposed. The effect of the complex is strongest at its centre, where the stellar mid-plane density increases by a factor of 2.6 and the vertical scaleheight decreases by a factor of 3.4 compared with the undisturbed stellar disc. A surprising result is the large radial distance of ∼ 500 pc from the complex centre over which the complex influences the disc; this is due to the extended mass distribution in a complex. The complex has a comparable effect on the vertical distribution of the atomic hydrogen gas in the galactic disc. This 'pinching' or constraining effect should be detectable in the nearby spiral galaxies, as for example has been done for NGC 2403 by Sicking. Thus the gravitational field of a complex results in local corrugations of the stellar and H  i vertical scaleheights, and the galactic disc potential is highly non-uniform on scales of the intercomplex separation of ∼ 1 kpc.  相似文献   

17.
Members of the Galaxy components are identified according to stellar ages, metallicities and galactic orbits. The local thin disk is found to have a maximum age of 11 billion years and a small abundance scatter partially controlled by the radial gradient of abundances. Metal-rich and old metal-poor stars belong to inner galactic populations and SMRs represent the ultimate star generation in the bulge. The thick disk forms a smooth transition between the halo and thin disk.  相似文献   

18.
We present the first results of a new technique to detect, locate, and characterize young dissolving star clusters. Using Hubble Space Telescope/Advanced Camera for Surveys archival images of the nearby galaxy IC2574, we performed stellar PSF photometry and selected the most massive stars as our first test sample. We used a group-finding algorithm on the selected massive stars to find cluster candidates. We then plot the color-magnitude diagrams for each group, and use stellar evolutionary models to estimate their age. So far, we found 79 groups with ages of up to about 100 Myr, displaying various sizes and densities.  相似文献   

19.
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   

20.
We present the results of our stellar photometry and spectroscopy for the new Local Group galaxy VV124 (UGC4879) obtainedwith the 6-m BTAtelescope. The presence of a fewbright supergiants in the galaxy indicates that the current star formation process is weak. The apparent distribution of stars with different ages in VV 124 does not differ from the analogous distributions of stars in irregular galaxies, but the ratio of the numbers of young and old stars indicates that VV 124 belongs to the rare Irr/Sph type of galaxies. The old stars (red giants) form the most extended structure, a thick disk with an exponential decrease in the star number density to the edge. Definitely, the young population unresolvable in images makes a great contribution to the background emission from the central galactic regions. The presence of young stars is also confirmed by the [OIII] emission line visible in the spectra that belongs to extensive diffuse galactic regions. The mean radial velocity of several components (two bright supergiants, the unresolvable stellar population, and the diffuse gas) is υ h = −70 ± 15 km s−1 and the velocity with which VV 124 falls into the Local Group is υ LG = −12 ± 15 km s−1. We confirm the distance to the galaxy (D = 1.1 ± 0.1 Mpc) and the metallicity of red giants ([Fe/H] = −1.37) found by Kopylov et al. (2008). VV 124 is located on the periphery of the Local Group approximately at the same distance from M31 and our Galaxy and is isolated from other galaxies. The galaxy LeoA nearest to it is 0.5 Mpc away.  相似文献   

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