We present a catalog of true edge-on disk galaxies automatically selected from the Seventh Data Release (DR7) of the Sloan Digital Sky Survey. A visual inspection of the g, r and i images of about 15000 galaxies allowed us to split the initial sample of edge-on galaxy candidates into 4768 (31.8% of the initial sample) genuine edge-on galaxies, 8350 (55.7%) non-edge-ons, and 1865 (12.5%) edge-on galaxies not suitable for simple automatic analysis because these objects show signs of interaction, warps, or nearby bright stars project on it. We added more candidate galaxies from RFGC, EFIGI, RC3, and Galaxy Zoo catalogs found in the SDSS footprints. Our final sample consists of 5747 genuine edge-on galaxies. We estimate the structural parameters of the stellar disks (the stellar disk thickness, radial scale length, and central surface brightness) in the galaxies by analyzing photometric profiles in each of the g, r, and i images. We also perform simplified 3-D modeling of the light distribution in the stellar disks of edge-on galaxies from our sample. Our large sample is intended to be used for studying scaling relations in the stellar disks and bulges and for estimating parameters of the thick disks in different types of galaxies via the image stacking. In this paper we present the sample selection procedure and general description of the sample.

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We present a new method for constructing equilibrium phase models for stellar systems , which we call the iterative method. It relies on constrained, or guided evolution , so that the equilibrium solution has a number of desired parameters and/or constraints. This method is very powerful, to a large extent due to its simplicity. It can be used for mass distributions with an arbitrary geometry and a large variety of kinematical constraints. We present several examples illustrating it. Applications of this method include the creation of initial conditions for N-body simulations and the modelling of galaxies from their photometric and kinematic observations.

Recent observational studies of X-shaped structures revealed that values of their opening angles lie in a narrow range: from 20 • to 43 • with smaller X-shaped structures appearing to follow a characteristic opening angle ∼ 27 • -31 • . We use self-consistent numerical simulations to uncover what parameters of host galaxies govern the opening angle spread. We constructed a series of equilibrium models of galaxies with high spatial resolution, varying the dark halo and bulge contribution in the overall gravitational potential, the initial disc thickness of models and the Toomre parameter Q and followed their evolution for almost 8 Gyrs. Each model demonstrated the formation of clear X-structures with different flatness. We have obtained that opening angles lie in the range from 25 • to 42 • throughout the entire evolution. These values are roughly consistent with observational data. The greatest variation in the opening angles is obtained by varying the mass of the dark halo. The initial thickness of the disc and the Toomre parameter are responsible for smaller variations of the angle and shorter X-structures. An increase of both parameters changes the morphology of in-plane bars and X-structures. In some cases we observed even double X-structures. The main effect of the bulge is to prevent buckling at intermediate and late stages of the disc evolution. Comparison of models with different halo masses indicates that the smallest observable values of opening angles can be associated with the presence of a heavy dark halo (more than 3 masses of the disc within the optical radius).

We present a detailed photometric study of a sample of 22 edge-on galaxies with clearly visible X-shaped structures. We propose a novel method to derive geometrical parameters of these features, along with the parameters of their host galaxies based on the multi-component photometric decomposition of galactic images. To include the X-shaped structure into our photometric model, we use the IMFIT package, in which we implement a new component describing the X-shaped structure. This method is applied for a sample of galaxies with available SDSS and Spitzer IRAC 3.6 µm observations. In order to explain our results, we perform realistic N -body simulations of a Milky Way-type galaxy and compare the observed and the model X-shaped structures. Our main conclusions are as follows: (1) galaxies with strong Xshaped structures reside in approximately the same local environments as field galaxies; (2) the characteristic size of the X-shaped structures is about 2/3 of the bar size; (3) there is a correlation between the X-shaped structure size and its observed flatness: the larger structures are more flattened; (4) our N -body simulations qualitatively confirm the observational results and support the bar-driven scenario for the X-shaped structure formation.

A sample of edge-on spiral galaxies aimed at a thorough study of the main structural and photometric parameters of edge-on galaxies, both of early-and late-types, is presented. The data were taken from the Two Micron All Sky Survey (2MASS) in the J , H and K s filters. The sources were selected according to their angular size mainly on the basis of the 2MASSselected Flat Galaxy Catalog (2MFGC). The sample consists of 175 galaxies in the K s filter, 169 galaxies in the H filter and 165 galaxies in the J filter. We present bulge and disc decompositions of each galaxy image. All galaxies have been modelled with a Sérsic bulge and exponential disc with the BUDDA v2.1 package. Bulge and disc sizes, profile shapes, surface brightnesses are provided. Our sample is the biggest up-to-date sample of edge-on galaxies with derived structural parameters for discs and bulges. In this paper, we present the general results of the study of this sample. We determine several scaling relations for bulges and discs which indicate a tight link between their formation and evolution. We show that galaxies with bulges fitted by the Sérsic index n 2 have quite different distributions of their structural parameters than galaxies with n 2 bulges. At a first approximation the Sérsic index threshold n 2 can be used to identify pseudobulges and classical bulges. Thus, the difference in parameter distributions and scaling relations for these subsamples suggests that two or more processes are responsible for disc galaxy formation. The main conclusions of our general statistical analysis of the sample are as follows.(i) The distribution of the apparent bulge axis ratio q b for the subsample with n 2 can be attributed to triaxial, nearly prolate bulges that are seen from different projections, while n 2 bulges seem to be oblate spheroids with moderate flattening. Triaxiality of late-type bulges may be due to the presence of a bar that thickened in the vertical direction during its secular evolution.(ii) For the sample galaxies, the effective radius of the bulge r e,b , the disc scalelength h and the disc scaleheight z 0 are well correlated. However, there is a clear trend for the ratio r e,b /h to increase with n. As n is an indicator of the Hubble type, such a trend unambiguously rules out the widely discussed hypothesis of a scale-free Hubble sequence. The found correlation between z 0 and r e,b is new and was not described earlier.(iii) There is a hint that the fundamental planes of discs, which links only disc parameters and the maximum rotational velocity of gas, are different for galaxies with different bulges. This may indicate a real difference of discs in galaxies with low-and high-concentration bulges.(iv) The most surprising result arises from the investigation of the photometric plane of sample bulges. It turns that the plane is not flat and has a prominent curvature towards small values of n. For bulges, this fact was not noted earlier.(v) The clear relation between the flattening of stellar discs h/z 0 and the relative mass of a sphe...

We analyze the dependence of the stellar disc flatness on the galaxy morphological type using 2D decomposition of galaxies from the reliable subsample of the Edge-on Galaxies in SDSS (EGIS) catalogue. Combining these data with the retrieved models of the edge-on galaxies from the Two Micron All Sky Survey (2MASS) and the Spitzer Survey of Stellar Structure in Galaxies (S 4 G) catalogue, we make the following conclusions:(1) The disc relative thickness z 0 /h in the near-and mid-infrared passbands correlates weakly with morphological type and does not correlate with the bulge-to-total luminosity ratio B/T in all studied bands.(2) Applying an 1D photometric profile analysis overestimates the disc thickness in galaxies with large bulges making an illusion of the relationship between the disc flattening and the ratio B/T .(3) In our sample the early-type disc galaxies (S0/a) have both flat and "puffed" discs. The early spirals and intermediate-type galaxies have a large scatter of the disc flatness, which can be caused by the presence of a bar: barred galaxies have thicker stellar discs, on average. On the other hand, the late-type spirals are mostly thin galaxies, whereas irregular galaxies have puffed stellar discs.

NGC 7217 is an unbarred early-type spiral galaxy having a multisegment exponential light profile and a system of star-forming rings of the unknown origin; it also possesses a circumnuclear gaseous polar disc. We analysed new long-slit spectroscopic data for NGC 7217 and derived the radial distributions of its stellar population parameters, and stellar and gaseous kinematics up to the radius of r ≈ 100 arcsec (∼8 kpc). We performed the dynamical analysis of the galaxy by recovering its velocity ellipsoid at different radii and estimated the scaleheights of its two exponential discs. The inner exponential stellar disc of NGC 7217 appears to be thin and harbours intermediate-age stars (t SSP ≈ 5 Gyr). The outer stellar disc seen between the radii of 4 and 7 kpc is very thick (z 0 = 1, . . . , 3 kpc), metal-poor, [Fe/H] < −0.4 dex, and has predominantly young stars, t SSP = 2 Gyr. The remnants of minor mergers of gas-rich satellites with an early-type giant disc galaxy available in the GalMer data base well resemble different structural components of NGC 7217, suggesting two minor merger events in the past responsible for the formation of the inner polar gaseous disc and large outer star-forming ring. Another possibility to form the outer ring is the re-accretion of the tidal streams created by the first minor merger.