Photometry of the low-luminosity spiral galaxy NGC 4136

Multicolor BVRI surface photometry of the low-luminosity (M _V ≈?18^m) spiral galaxy NGC 4136 is presented. The photometric parameters of its components and the color distribution over the galactic disk are estimated. The color indices and the corresponding effective ages are determined for the brightest star-forming regions. The disk-to-dark halo mass ratio is derived from the measured rotation curve of the galaxy. The disk mass dominates within the optical boundaries of the galaxy, so its disk can be considered as a self-gravitating system.     

Observational study of the candidate polar-ring galaxies NGC 304 and NGC 7625

We present the results of our photometric (BV R) and spectroscopic CCD observations of NGC 304 and NGC 7625, candidate polar-ring galaxies, performed with the 6-m Special Astrophysical Observatory telescope. For NGC 304, such a study has been carried out for the first time. We have obtained basic integrated characteristics of the galaxies and determined their morphological types (S0 for NGC 304 and Sa for NGC 7625). The absolute magnitudes of the galaxies, M _B = ?20^m.81 for NGC 304 and M _B = ?19^m.34 for NGC7625, are indicative of their fairly high luminosities. The disk and bulge parameters have been determined forNGC 304 (µ₀ = 20^m.60, h = 3.86 kpc, µ _e = 21^m.59, r _e = 1.26 kpc in the B band); these correspond to the parameters of S0-type objects. The rotation velocity for NGC 304 (200 km s^?1) reaches its maximum at a galactocentric distance of 3.1 kpc, which yields a mass estimate for the galaxy of 2.8 × 10¹⁰ \(\mathcal{M}_ \odot \). The observed photometric features at the center of NGC 304 indicate that it may have an inner ring structure, although we have failed to confirm the existence of two kinematic systems based on our spectroscopic observations. In NGC 7625, the disk makes a dominant contribution to the total brightness. The derived integrated color indices (B-V = 0^m.81 and V-R = 0^m.61) agree with previous determinations of other authors. We have estimated the учештсешщт in the inner galactic regions. In the outer regions, we have detected structures with bluer colors (B-V = 0^m.60), which may be indicative of a polar ring with a minor stellar component.     

Stellar velocity dispersion and mass estimation for galactic disks

Available velocity dispersion estimates for the old stellar population of galactic disks at galactocentric distances r?2L (where L is the photometric radial scale length of the disk) are used to determine the threshold local surface density of disks that are stable against gravitational perturbations. The mass of the disk M_d calculated under the assumption of its marginal stability is compared with the total mass M_t and luminosity L _B of the galaxy within r=4L. We corroborate the conclusion that a substantial fraction of the mass in galaxies is probably located in their dark halos. The ratio of the radial velocity dispersion to the circular velocity increases along the sequence of galactic color indices and decreases from the early to late morphological types. For most of the galaxies with large color indices (B–V)₀>0.75, which mainly belong to the S0 type, the velocity dispersion exceeds significantly the threshold value required for the disk to be stable. The reverse situation is true for spiral galaxies: the ratios M_d/L_B for these agree well with those expected for evolving stellar systems with the observed color indices. This suggests that the disks of spiral galaxies underwent no significant dynamical heating after they reached a quasi-equilibrium stable state.     

Detailed surface photometry of the cD galaxies NGC 4839 and NGC 4874

We present a detailed photometric study of the cD galaxies NGC 4839 and NGC 4874 based on the technique of surface photometry by fitting ellipses to the isophotes of the galaxies in the u, g, r, i, and z bands using Data Release 7 (DR7) of the Sloan Digital Sky Survey (SDSS). The motivation of this paper is to study the properties (e.g. break radius and surface brightness, color gradient, etc.) of the extended envelope of the two cD galaxies. The surface brightness profile in each band is obtained and fitted to the de Vaucouleurs r ^1/4 model. A deviation of the observed profile brighter than the fitted r ^1/4 model is noticed especially in the outer part of each galaxy. The profiles of ellipticity, position angle, B4 and shifts with respect to the center of each isophote are also obtained. The color index profiles, u-g, g-r, r-i, and i-z are also obtained and no significant color gradients are noticed except in the outer parts of the two galaxies. The integrated magnitude in each band and color indices are obtained and found to be in good agreement with the published ones.     

Stellar content and distances to the isolated spiral galaxies NGC 6503 and NGC 6946

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.     

New active galactic nuclei among the INTEGRAL and SWIFT X-ray sources

We present the results of our optical identifications of a set of X-ray sources from the INTEGRAL and SWIFT all-sky surveys. The optical data have been obtained with the 1.5-m Russian-Turkish Telescope (RTT-150). Nine X-ray sources have been identified with active galactic nuclei (AGNs). Two of them are located in the nearby spiral galaxies MCG-01-05-047 and NGC 973 seen almost edge-on. One source, IGR J16562-3301, is probably a BL Lac object (blazar). The remaining AGNs are observed as the starlike nuclei of spiral galaxies whose spectra exhibit broad emission lines. The relation between the hard X-ray (17–60 keV) luminosity and the [O III] 5007 line luminosity, log L _x/L _{[O III]} ≈ 2.1, holds good for most of the AGNs detected in hard X rays. However, the luminosities of some AGNs deviate from this relation. The fraction of such objects can reach ～20%. In particular, the [O III] line flux is lower for two nearby edge-on spiral galaxies. This can be explained by the effect of absorption in the galactic disks.     

Relationship between the thickness of stellar disks and the relative mass of a dark galactic halo

We analyze the R-and K _s-band photometric profiles for two independent samples of edge-on galaxies. The thickness of old stellar disks is shown to be related to the relative masses of the spherical and disk components of galaxies. The radial-to-vertical scale length ratio for galactic disks increases (the disks become thinner) with increasing total mass-to-light ratio of the galaxies, which reflects the relative contribution of the dark halo to the total mass, and with decreasing central deprojected disk brightness (density). Our results are in good agreement with numerical models of collisionless disks that evolved to a marginally stable equilibrium state. This suggests that, in most galaxies, the vertical stellar-velocity dispersion, on which the equilibrium-disk thickness depends, is close to a minimum value that ensures disk stability. The thinnest edge-on disks appear to be low-brightness galaxies in which the dark-halo mass far exceeds the stellar-disk mass.     

Stars and clusters of the coma galaxies NGC 4921 and NGC 4923

Based on deep Hubble Space Telescope ACS/WFC images, we have performed stellar photometry for the spiral and lenticular galaxies NGC 4921 and NGC 4923 in the Coma cluster. The derived Hertzsprung-Russell diagrams show that, apart from the stellar population, NGC 4921 has several thousand globular clusters. The asymmetry of their apparent distribution proves that NGC 4921 is in close spatial proximity to NGC 4923. We have determined the positions of the peaks for the luminosity functions of globular clusters in the two galaxies, which has allowed us to measure the distance to this pair (D = 97±5 Mpc). In many cases, compact star-forming regions at the periphery of NGC 4921 are located at the ends of extended (up to 1.5 kpc) radial gas and dust filaments. The metallicity of young stars in these star-forming regions is close to that of the Sun (Z = 0.02).     

Determination of Distances to Galaxies of the NGC 1023 Group. The Hubble Constant

On the basis of photographs from the 6 m Large Azimuthal Telescope and the Hubble Space Telescope, VRI photometry of stars in 11 galaxies in the NGC 1023 group has been carried out. The distances to these galaxies were determined by the method of brightest stars. The distances to NGC 925 and NGC 1023 were determined from the position of the top of the red giant branch (the TRGB method). From the calculated average and root-mean-square distances to the NGC 1023 group (10.3 ± 2.2 Mpc and 9.7 ± 0.5 Mpc) the Hubble constant in this direction was determined: H _0R = 75 ± 8 km·sec^-1·Mpc^-1 and H _0M = 81 ± 5 km ·sec^-1·Mpc^-1.     

Model of outgrowths in the spiral galaxies NGC 4921 and NGC 7049 and the origin of spiral arms

NGC 4921 and 7049 are two spiral galaxies presenting narrow, distinct dust features. A detailed study of the morphology of those features has been carried out using Hubble Space Telescope archival images. NGC 4921 shows a few but well-defined dust arms midway to its centre while NGC 7049 displays many more dusty features, mainly collected within a ring-shaped formation. Numerous dark and filamentary structures, called outgrowths, are found to protrude from the dusty arms in both galaxies. The outgrowths point both outwards and inwards in the galaxies. Mostly they are found to be V-shaped or Y-shaped with the branches connected to dark arm filaments. Often the stem of the Y appears to consist of intertwined filaments. Remarkably, the outgrowths show considerable similarities to elephant trunks in H ii regions. A model of the outgrowths, based on magnetized filaments, is proposed. The model provides explanations of both the shapes and orientations of the outgrowths. Most important, it can also give an account for their intertwined structures. It is found that the longest outgrowths are confusingly similar to dusty spiral arms. This suggests that some of the outgrowths can develop into such arms. The time-scale of the development is estimated to be on the order of the rotation period of the arms or shorter. Similar processes may also take place in other spiral galaxies. If so, the model of the outgrowths can offer a new approach to the old winding problem of spiral arms.     

Study of the structure and kinematics of the NGC 7465/64/63 triplet galaxies

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.     

A search for variable stars in the open clusters NGC7209, NGC1582 and Dolidze 18

CCD time-series photometric observations are presented for the stars in the fields of the open clusters NGC7209, NGC1582 and Dolidze 18 in Johnson V, together with some photometric observations in R, and B. The results reveal 14 variable stars in the three clusters in total, among which 13 are newly-discovered variables. With color–magnitude diagrams and color–color diagram, memberships of the variable stars are estimated. With the derived light curves, scales of time and amplitude of variability of these variable stars are obtained. Together with the spectral types due to the estimation of color temperatures, possible types of the variable stars are preliminarily discussed.     

Stellar subsystems of the galaxy NGC 1313

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.     

Stellar Disks and Halos of Edge-on Spiral Galaxies: NGC 891, NGC 4144, and NGC 4244

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).     

Optical and X-ray variability of Seyfert galaxies NGC 5548, NGC 7469, NGC 3227, NGC 4051, NGC 4151, Mrk 509, Mrk 79, and Akn 564 and quasar 1E 0754

The results of a cross-correlation analysis of the optical and X-ray light curves for eight Seyfert galaxies, NGC 5548, NGC 7469, NGC 3227, NGC 4051, NGC 4151, Mrk 509, Mrk 79, and Akn 564 and for the optical spectra of the quasar 1E 0754 are presented. In the case of the galaxies NGC 5548 and NGC 7469, the maximum values of cross-correlation coefficients for optical and X-ray variations proved to be high (0.73 and 0.79, respectively). The lag time, determined from the maximum of cross-correlation function, is 2.800 _?1.58 ^+3.12 days for NGC 5548 and 0.6 _?4.3 ^+0.9 days for NGC 7469. This result favors downscattering of the X-ray emission into the optical range (direct Compton effect) for NGC 5548 and NGC 7469. In addition to the main maximum, which corresponds to the lag of the optical flux variations behind the X-ray flux, six objects (excluding Akn 564 and NGC 4151) show the wings in the intervals of cross-correlation functions that correspond to the time lags of X-ray emission behind the optical emission of approximately 10 days. A method of determining the masses of central black holes in AGNs through spectral line widths is presented; with this method the mass of the central black hole in the quasar 1E 0754 was found (M _BH = 1.01 × 10⁸ M _sun). The position of the quasar 1E 0754 in the mass-luminosity diagram meets the position of other NLS 1 galaxies.     

Stellar population and evolution of galaxies in groups: the NGC2300 group

Using panoramic and long-slit spectroscopy at the 6-m telescope of SAO RAS, we studied the stellar population and kinematics of five early-type disc galaxies—members of the NGC2300 group. The evolution of galaxies appears to be absolutely out of synch: while the average age of the stars in the central regions of the galaxies located close to the center of the group ranges from 2 to 7 Gyr, the peripheral spiral galaxies have old nuclei and bulges, with the ages of 10–15 Gyr. The brightest galaxy of the NGC2300 group, which up to now has been considered to be lenticular, of the SA0 type, turned out to be extremely hot dynamically: its bulge rotates slowly, v/σ = 0.06, and the outer parts do not rotate at all.We conclude that the kinematics of the stellar component of NGC2300 indicates that it is not a disc galaxy, but a triaxial spheroid.     

NGC 3310 and its tidal debris: remnants of galaxy evolution

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.     

Quasars Associated with NGC 613, NGC 936 and NGC 941

The association of low redshift, active galaxies with high redshift quasars is here tested in two regions uniformly surveyed for quasars to faint limits. Three active galaxies in these regions all show significant association with nearby quasars. Radio, optical and X-ray data available for these galaxies give new information on the processes which accompany the proposed ejection of the quasars. It is concluded that the quasars are originally relatively compact compared to the galactic medium through which they exit but can be slowed. It is argued that effects of ejection can be seen on the galaxies and may be connected with spiral structure. Evidence for periodicity of the redshifts is discussed.     

The phenomenon of the galaxy NGC 6286: A forming polar ring or a superwind?

We present our observations of the pair of interacting galaxies NGC 6285/86 carried out with the 6-m Special Astrophysical Observatory (SAO) telescope using 1D and 2D spectroscopy. The observations of NGC 6286 with a long-slit spectrograph (UAGS) near the Hα line revealed the rotation of the gaseous disk around an axis offset by 5″–7″ from the photometric center and a luminous gas at a distance up to 9 kpc in a direction perpendicular to the galactic plane. Using a multipupil fiber spectrograph (MPFS), we constructed the velocity fields of the stellar and gaseous components in the central region of this galaxy, which proved to be similar. The close radial velocities of the pair and the wide (5′×5′) field of view of the scanning Fabry-Perot interferometer (IFP) allowed us to simultaneously obtain images in the Hα and [N II]λ6583 lines and in the continuum, as well as to construct the radial velocity fields and to map the distribution of the [N II]λ6583/Hα ratio for both galaxies. Based on all these data, we studied the gas kinematics in the galaxies, constructed their rotation curves, and estimated their masses (2 × 10¹¹M_⊙ for NGC 6286 and 1.2 × 10¹⁰M_⊙ for NGC 6285). We found no evidence of gas rotation around the major axis of NGC 6286, which argues against the assumption that this galaxy has a forming polar ring. The IFP observations revealed an emission nebula around this galaxy with a structure characteristic of superwind galaxies. The large [N II]λ6583/Hα ratio, which suggests the collisional excitation of its emission, and the high infrared luminosity are additional arguments for the hypothesis of a superwind in the galaxy NGC 6286. A close encounter between the two galaxies was probably responsible for the starburst and the bipolar outflow of hot gas from the central region of the disk.     

Imaging of the shell galaxies NGC 474 and 7600, and implications for their formation

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.