Molecular and Atomic Gas in Star-forming Complexes: NGC 5194, NGC 5457, NGC 628, and NGC 6946

Astronomy Reports - We use observations of CO and HI emission in star-forming complexes (SFCs) in galaxies NGC 5457, NGC 5194, NGC 628, and NGC 6946 to search for possible correlations...     

Star-forming regions in the ring galaxies NGC 5585 and IC 1525

We use UBVRI CCD photometry to study star-forming regions (SFRs) in the galaxies NGC 5585 and IC 1525. The observations were acquired with the 1.5-m telescope of the Mt. Maidanak Observatory of the Astronomical Institute of the Uzbek Academy of Sciences (Uzbekistan), with seeing of 0.8″–1.8″. We identified 47 SFRs in NGC 5585 and 16 SFRs in IC 1525. We estimated the ages and internal extinctions of the SFRs using the PEGASE2 evolution models. The sizes of the SFRs were also determined. We discuss in detail the techniques applied to evaluate the SFR parameters from photometric analysis. The age range for the studied SFRs is (2–40) × 10⁶ yrs, and the internal extinctions are A(V ) ≤ 1.5m. The age distributions of the SFRs in both galaxies are typical of stellar systems with intense, extended star formation. The internal extinction in the SFRs decreases with distance from the galactic centers: A(V ) ∝ −r. For both galaxies, the scale length for the decrease of the dust surface density, estimated from the A(V )−r relation for SFRs, is close to the scale length for the disk brightness decrease in the V and R bands. Relatively larger and older SFRs are observed in the galaxies’ rings, while such SFRs are not found in the spiral arms. We detected different SFR parameters for different spiral arms of NGC 5585.     

Star formation and the kinematics of gas in the disk of NGC 628

The radial profile of the star-formation rate (SFR) in the galaxy NGC 628 is shown to be modulated by a spiral-density wave. The radial profile of the velocity of gas inflow into the spiral arm is similar to the radial distribution of the surface density of the SFR. The position of the corotation resonance is determined along with other parameters of the spiral-density wave via a Fourier analysis of the azimuthal distribution of the observed radial velocities in annular zones of the disk of NGC 628. The radial profile of the surface density of the SFR is determined using the empirical SFR—linear size relation for star-formation complexes (giant HII regions) and measurements of the coordinates, Hα fluxes, and the sizes of HII regions in NGC 628.     

Age and interstellar absorption in young star-formation regions in the galaxies NGC 1068, NGC 4449, NGC 4490, NGC 4631, and NGC 4656/57 derived from multicolor photometry

We have compared the results of multicolor U BV R and Hα photometry for 169 young star-formation complexes in five galaxies using a grid of evolutionary models for young star clusters. The ages and interstellar absorptions are estimated for 102 star-formation complexes with the standard uncertainties σ _t = 0.30 dex and $ \sigma _{A_V } = 0.45^m We have compared the results of multicolor U BV R and Hα photometry for 169 young star-formation complexes in five galaxies using a grid of evolutionary models for young star clusters. The ages and interstellar absorptions are estimated for 102 star-formation complexes with the standard uncertainties σ _t = 0.30 dex and . The accuracies of these parameters were verified using numerical simulations. Original Russian Text ? A.S. Gusev, V.I. Myakutin, A.E. Piskunov, F.K. Sakhibov, M.S. Khramtsova, 2008, published in Astronomicheskiĭ Zhurnal, 2008, Vol. 85, No. 9, pp. 794–809.     

Galaxies and Clusters of Galaxies in Observations and Numerical Models

Astronomy Reports - An analysis of the properties of 1157 galaxies, groups and clusters of galaxies confirms the dependence of the virial velocity on the halo mass $${{v}_{{{text{vir}}}}} =...     

Logarithmic density range and the percentage of stars in the cores of various subsystems of the globular clusters M56, M12, NGC 6535, NGC 6171, NGC 5466, and M92

Lower limits for the percentages of stars with various luminosities in the cores of six globular clusters are derived using stellar spatial density distributions f(r) to deep limiting B magnitudes obtained earlier. For NGC 6535 and NGC 5466, the logarithmic density range and Kholopov parameters D_f and D_r are also determined. These two parameters are correlated with the mean masses of stars of various subsystems and the total mass (number) of stars in the cluster.     

Do the galaxies NGC 936 and NGC 3198 possess massive spheroidal subsystems?

The condition for gravitational stability of the stellar disks of the galaxies NGC 936 and NGC 3198 makes maximum disk models unacceptable. We present mass estimates for these objects' spheroidal components. The mass of the dark halo of NGC 3198, within four disk radial scale lengths, exceeds its disk mass by a factor of 1.6 to 2. The masses of the disk and spheroidal subsystem (halo + bulge), within four radial scale lengths, are approximately the same for NGC 936.     

Galaxies in Observations and Numerical Models

Astronomy Reports - A comparison of the virial parameters of galaxies and galaxy clusters (radius, density, and entropy function) in a wide range of masses, $${{10}^{6}} \leqslant...     

A spectroscopic and photometric study of NGC 2685, the prototype polar-ring galaxy

We present and analyze spectroscopic and photometric observations for NGC 2685, the prototype polar-ring galaxy. The spectroscopic data were acquired using the 6 m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with the UAGS spectrograph and a scanning Fabry-Perot interferometer, while the photometric analysis was based on images from the Hubble Space Telescope archive. We demonstrate that the subsystem usually called the “inner polar ring” is a highly inhomogeneous gas and dust disk rotating approximately in the polar plane relative to the galaxy’s main body. When the self-absorption in the disk is taken into account, a comparison of its color indices with those from model computations of the color evolution of galaxies results in an age for the disk of about 1.4 × 10⁹ years, much lower than the previously accepted estimate.     

Dynamical Models and Anisotropy of the Velocity Dispersions in Elliptical Galaxies

Models for 12 elliptical galaxies are constructed based on the second-order tensor virial theorem. This method takes into account the spatial shape and structure of the internal density layers for each galaxy. New data for the surface brightness and isophote structure of the E galaxies derived from deep photometric observations are used. A system of equations is used to find the components of the gravitational-energy, rotational-energy, and velocity-dispersion tensors. This makes it possible to calculate the anisotropy index β of the velocity dispersion of each galaxy. The values for the entire sample lie in the range 0.012 ? β ? 0.246. It is shown that taking into account variations in the mass-to-light ratio M/L (for the stellar component) can reduce the value of β by roughly 20%. The results are compared with those from other studies. Our values of β for small E galaxies (rapid rotators) agree with those found in the ATLAS^3D project based on Jeans anisotropy models. However, our models for giant E galaxies (slow rotators) taking into account the triaxial shape and realistic structure of the density layers provide a much better agreement with observations than the simple axially symmetrical models from the SAURON project.

     

On the Formation of Spiral Arms in Dwarf Galaxies

Astronomy Reports - Spiral structure (both flocculent and Grand Design types) is very rarely observed in dwarf galaxies because the formation of spiral arms requires special conditions. In this...     

Multicolor CCD photometry of the dusty,giant, late-type spiral galaxy NGC 5351

The paper reports the results of BV RI surface photometry of the giant galaxy NGC 5351 based on CCD observations obtained on the 1-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. Analysis of the structure and radial brightness distribution in the galaxy shows that NGC 5351 has a complex and, in some places, asymmetric structure. The galaxy possesses a large quantity of dust. The average internal extinction due to dust is A_V=1.2^m±0.4^m. After correcting for the effect of this dust, the parameters of the galaxy are typical of late-type spirals. The compositions of the stellar population in various parts of the galaxy are estimated using two-color diagrams. Star-forming regions in NGC 5351 are identified and studied. Most of the star-forming regions are located in the ring of the galaxy. Evolutionary modeling is used to estimate the ages of regions of violent star formation. An elliptical companion galaxy to NGC 5351 was found. The rotation curve of the galaxy is modeled and its mass estimated. The disk of NGC 5351 is self-gravitating within its optical radius.     

The Role of Gravitational Radiation in the Evolution of Stars and Galaxies

The conditions for the formation of close binaries containing main-sequence stars, degenerate dwarfs of various types, neutron stars, and black holes of various masses are considered. The paper investigates the evolution of the closest binary systems under the influence of their gravitational-wave radiation. The conditions under which the binary components can merge on a time scale shorter than the Hubble time as a result of their emission of gravitational waves are estimated. A self-consistent scenario model is used to estimate the frequency of such events in the Galaxy, their observable manifestations, the nature of the merger products, and the role of these events in the evolution of stars and galaxies. The conditions for the formation and evolution of supermassive binary black holes during collisions andmergers of galaxies in their dense clusters are studied.

     

Galaxies with Abnormally High Gas Content in the Disk

Astronomy Reports - The content of gas in galaxies with an anomalously high relative mass of hydrogen $${{M}_{{{\text{HI}}}}}{\text{/}}{{M}_{*}}$$ for a given mass of the stellar population...     

Modeling the generation of the magnetic field in NGC 5775

A model for the generation of large-scale magnetic fields is constructed for the galaxy NGC 5775, in which the magnetic field has the form of a dipolar dynamo wave propagating along the galactic disk. The excitation of such a mode, which is unusual for galactic dynamos, can be explained by the strong variation of the galactic rotation with height above the plane of symmetry of the galactic disk.     

Stellar subsystems of the galaxy NGC 2366

Hubble Space Telescope archive data are used to perform photometry of stars in seven fields at the center and periphery of the galaxy NGC 2366. The variation of the number density of stars of various ages with galactocentric radius and along the minor axis of the galaxy are determined. The boundaries of the thin and thick disks of the galaxy are found. The inferred sizes of the subsystems of NGC 2366 (Z _thin = 4 kpc and Z _thick = 8 kpc for the thin and thick disks, respectively) are more typical for spiral galaxies. Evidence for a stellar halo is found at the periphery of NGC 2366 beyond the thick disk of the galaxy.     

Motion of Stars in Layered Inhomogeneous Elliptical Galaxies

Astronomy Reports - The problem of the spatial motion of a passively gravitating body (PGB) in the gravitational field of a layered inhomogeneous elliptical galaxy (LIEG) is considered on the basis...     

Angular Momentum Distribution in Galaxies and Inner Haloes Profile

We study the problem of the determination of a high precision cosmological mass function, which is of fundamental importance in several problems of astrophysics, like the building up of an halo model. The determination of a mass function through numerical simulation is time demanding, and restrict to particular cosmological parameters. Analytical methods, allow to determine high precision mass functions, without the limitations of the simulations. We improve on previous analytical models, reaching high level of precision. In particular, we improve the scheme of Del Popolo presented in older and more recent papers, based on the excursion set approach. We further improve the mass function with respect to the quoted papers, using an higher order first crossing distribution, and an improved barrier with respect previous papers. As a result, we can obtain a mass function with a precision of 1%, in the mass range ≃ (10⁹−10¹⁵) h⁻¹M☉, and in the redshift range 0 < z s< 10. The paper also shows how the use of the quoted improved first-crossing distribution, improves the agreement between the conditional mass function, and simulations.

     

BVRI surface photometry of the galaxy NGC 3726

We present BVRI surface photometry of the late-type spiral galaxy NGC 3627. The distributions of the color indices and extinction-independent Q indices show that the observed photometric asymmetry in the inner part of the galaxy, including the bar, is due to an asymmetric distribution of absorbing material. The bluest regions of star formation are located in a ring surrounding the bar. The background-subtracted color indices of individual blue knots are used to estimate the ages of young stellar aggregates. In combination with previously published photometric data, our measurements indicate that the R-band profile of the disk is rather flat in its inner part (r<50″) and becomes steeper further from its center. We estimate the mass of the disk and dark halo by decomposing the rotation curve. The mass-to-light ratio M/L _B for the stellar disk is ≈1.4. The galaxy possesses a massive dark halo; however, the mass of the disk exceeds that of the halo in the inner part of the galaxy, which displays a regular spiral structure.