V. P. Reshetnikov

2MASS photometry of edge-on spiral galaxies – I. Sample and general results

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 Ks filters. The sources were selected according to their angular size mainly on the basis of the 2MASS-selected Flat Galaxy Catalog (2MFGC). The sample consists of 175 galaxies in the Ks 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 Sersic 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 Sersic index n≲ 2 have quite different distributions of their structural parameters than galaxies with n≳ 2 bulges. At a first approximation the Sersic 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 qb 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 re,b, the disc scalelength h and the disc scaleheight z0 are well correlated. However, there is a clear trend for the ratio re,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 z0 and re,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/z0 and the relative mass of a spherical component, including a dark halo, is confirmed not for bulgeless galaxies but for galaxies with massive bulges. Many of our results are in good agreement with the results of other authors, several ones are new. Thus, our sample is very useful for further detailed studying and modelling of the edge-on spiral galaxies.

THE CATALOG OF EDGE-ON DISK GALAXIES FROM SDSS. I. THE CATALOG AND THE STRUCTURAL PARAMETERS OF STELLAR DISKS

We present a catalog of true edge-on disk galaxies automatically selected from the Seventh Data Release of the Sloan Digital Sky Survey (SDSS). A visual inspection of the g, r, and i images of about 15,000 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-on galaxies, and 1865 (12.5%) edge-on galaxies not suitable for simple automatic analysis because these objects either show signs of interaction and 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 three-dimensional 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.

Spiral galaxies with large optical warps

As a result of our statistical study of 540 edge- on galaxies, we present here the images and preliminary statistical analysis of a sub-sample of 60 galaxies, that were selected to be S-type warped spirals. Computing the average volumic density of galaxies from available red- shift surveys, a rst analysis suggests that warped galaxies are found in denser environments. Only the clearest and strongest warps have been extracted here, and therefore this sample of 60 objects gather the best candidates for future HI or optical works on galaxy warps.

Pitch angle variations in spiral galaxies

We present a detailed photometric study and measurements of spiral arm pitch angles for a sample of 50 non-barred or weakly barred grand-design spiral galaxies selected from Sloan Digital Sky Survey. In order to find pitch angles, we used a new method based on the window Fourier analysis of their images. This method allows us not only to infer the average pitch angle, but to obtain its value as a function of galactocentric radius as well. Our main results are as follows: (1) Spiral arms of most galaxies cannot be described by a single value of the pitch angle. About 2/3 of galaxies demonstrate pitch angle variations exceeding 20%. In most galaxies in the sample their pitch angle decreases by increasing the distance from the centre. (2) Pitch angle variations correlate with the properties of galaxies - with the shape of the surface brightness distribution (envelope-type or truncated disc), and with the sign of stellar disc colour gradient. (3) More luminous and bright bulges produce more tightly wound spiral arms, that is in agreement with current models for spiral arms formation.

Nuclear spectra of polar-ring galaxies

We report the results of spectroscopic observations of 8 southern polar-ring galaxies (PRGs), in the wavelength range 5 900–7300 Å. We find that 5 out of 8 galaxies contain LINERs or Sy nuclei. Taking into consideration all PRGs with available spectral data, we estimate that about half of all PRGs and PRG candidates have either LINER or Seyfert nuclei. The observed widths of the [N ii]λ6583 line in the nuclei of early-type PRGs follow the linewidth–absolute luminosity relation for normal E/S0 galaxies. We found that one of the observed galaxies – ESO 576-G69 – is a new kinematically-confirmed polar-ring galaxy with a spiral host.

Photometric structure of polar-ring galaxies

The results of B, V, R surface photometry of three polar-ring galaxies (PRGs) - A 0017+2212, UGC 1198, UGC 4385 - are presented. The data were acquired at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. It was shown that all three galaxies are peculiar late-type spirals in the state of ongoing interac- tion or merging. We discuss available photometric properties of the PRGs with spiral hosts and consider the Tully-Fisher relation for different types of PRGs. In agreement with Iodice et al. (2003), we have shown that true PRGs demonstrate ∼1/3 larger maximum ro- tation velocities than spiral galaxies of the same luminosity. Peculiar objects with forming polar structures satisfy, on average, the Tully-Fisher relation for disk galaxies but with large scatter.The results of B, V, R surface photometry of three polar-ring galaxies (PRGs) -- A0017+2212, UGC1198, UGC4385 -- are presented. The data were acquired at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. It was shown that all three galaxies are peculiar late-type spirals in the state of ongoing interaction or merging. We discuss available photometric properties of the PRGs with spiral hosts and consider the Tully-Fisher relation for different types of PRGs. In agreement with Iodice et al. (2003), we have shown that true PRGs demonstrate ~1/3 larger maximum rotation velocities than spiral galaxies of the same luminosity. Peculiar objects with forming polar structures satisfy, on average, the Tully-Fisher relation for disk galaxies but with large scatter.

The Polar Stellar Ring and Dark Halo of NGC 5907

Numerical simulations of the disruption of a dwarf companion moving in the polar plane of a massive galaxy are presented. The constructed model is compared with observational data on the recently discovered low-surface-brightness stellar ring around the galaxy NGC 5907. Constraints on the ring lifetime (≤ 1.5 Gyr after the first approach of the galaxies), on the structure of the companion—the ring precursor, and on the mass of the dark halo of the main galaxy in whose gravitational field the companion moves are provided. The dark-halo mass within 50 kpc of the NGC 5907 center cannot exceed 3 or 4 “visible” masses.

Molecular content of polar-ring galaxies

We have searched for CO lines in a sample of 21 new morphologically determined polar-ring galaxies (of which nine are kinematically confirmed), obtained from a wide search in the Galaxy Zoo proj ect by Moiseev and collaborators. Polar-ring galaxies (PRGs) are a unique class of objects, tracing special episodes in the ga laxy mass assembly: they can be formed through galaxy interaction and merging, but also through accretion from cosmic filament s. Furthermore, they enable the study of dark matter haloes in three dimensions. The polar ring itself is a sub-system rich in gas, where molecular gas is expected, and new stars are formed. Among the sample of 21 PRGs, we have detected five CO-rich systems, that can now be followed up with higher spatial resolution. Their average molecular mass is 9.4 10 9 M⊙, and their average gas fraction is 27% of their baryonic mass, with a range from 15 to 43%, implying that they have just accreted a large amount of gas. The position of the detected objects in the velocity-magnitude diagram is offset from the Tully-Fisher relation of normal spirals, as was alr eady found for PRGs. This work is part of our multi-wavelength project to determine the detailed morphology and dynamics of polar-ring galaxies, test through numerical models their formation scenario, and deduce their dark matter content and 3D-shape.

Statistical study of M 51-type galaxies

We present a statistical analysis of a new sample of M 51-type galaxies. Using the MCG and VV catalogues, we selected 32 such binary systems. We found that a typical M 51-type pair consists of a bright L spiral galaxy and a satellite with blue luminosity 1/30{1/3 of the primary one. The main galaxies in such pairs are often barred and have two well-dened spiral arms. M 51-type systems show an enhanced star formation rate (from FIR luminosities). We found a weak dependence of the star formation rate of the system on relative luminosity of the companion. M 51-type galaxies are relatively frequent: about 1/12 of all pairs are of M 51-type.

Galaxies with conspicuous optical warps

In this paper, we present results of a photometric and kinematic study for a sample of 13 edge-on spiral galaxies with pronounced integral-shape warps of their stellar discs. The global structure of the galaxies is analyzed on the basis of the Sloan Digital Sky Survey (SDSS) imaging, in the g, r and i passbands. Spectroscopic observations are obtained with the 6-m Special Astrophysical Observatory telescope. In general, galaxies of the sample are typical bright spiral galaxies satisfying the Tully-Fisher relation. Most of the galaxies reside in dense spatial environments and, therefore, tidal encounters are the most probable mechanism for generating their stellar warps. We carried out a detailed analysis of the galaxies and their warps and obtained the following main results: (i) maximum angles of stellar warps in our sample are about 20°; (ii) warps start, on average, between 2 and 3 exponential scale lengths of a disc; (iii) stronger warps start closer to the center, weak warps start farther; (iv) warps are asymmetric, with the typical degree of asymmetry of about several degrees (warp angle); (v) massive dark halo is likely to preclude the formation of strong and asymmetric warps.