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| Abstracts |
Atomic Hydrogen Deficiency in Spiral Galaxies in Clusters: A New Metho
Shaldenkova E.S.
We applied a new method of estimation of atomic hydrogen deficiency in spiral galaxies, which is based on the relation between total HI mass and specific angular momentum of the disk for isolated galaxies. We estimated HI deficiency for Virgo and Coma cluster galaxies and for Local Volume galaxies, and compared this method with standard method of estimation of HI deficiency, which is based on dependence of HI mass on optical diameter and galaxy type. We found out that for these samples averaged HI deficiency values obtained with different methods are virtually the same. For galaxies in the Local Volume we obtained no appreciable HI deficiency as compared with isolated galaxies, though substantial part of these galaxies belongs to different groups. For Virgo and Coma cluster galaxies we confirmed the existence of relation between HI deficiency and distance from cluster center. In Virgo cluster we observed substantial HI deficiency up to nearly 2 Mpc from cluster center, in Coma – up to 3-4 Mpc from cluster center. In both cases the majority of galaxies have normal hydrogen content and are observed at all distances. Also we showed that in Virgo cluster on distances where galaxies with substantial HI deficiency are being observed the ram pressure is not sufficient for sweeping of considerable amount of gas. These galaxies either passed through the dense core of the cluster or HI deficiency is related with other reasons, for example with starvation effect or with galaxy interaction with gas, which is more cold than intergalaxy gas. HI deficiency can be partly caused by amplified star formation rate due to compression of interstellar gas by outer pressure.
| Bar driven dynamic structures in local velocity space.
Esko Gardner, Chris Flynn
The theoretical analysis of local velocity space has had a long history. Especially the Hercules stream has been analyzed ever since Dehnen (2000) and Fux (2001). We will present some additional theoretical-statistical work on the pattern speed, angle, and mass of the Galaxys bar(s), showing what impact it has on local dynamical structure. We have employed a backward integrating technique in a potential model of an axisymmetric system with triaxial bar(s) that aims to represent the Milky Way. We show that it is possible to create dynamical features by both resonances and direct interaction.
| Barred Galaxies: Secular Evolution and the Origin of their Double Exponential Light Profiles.
Patricia Sanchez-Blazquez
I present the analysis of a high-resolution, cosmological, hydrodynamical, disc galaxy simulation, in order to study the source of the double-exponential light profiles seen in many stellar discs, and the effects of stellar radial migration upon the spatio-temporal evolution of both the disc age and metallicity distribution functions. I also present observational data of barred galaxies extending to 2-3 disc scalelengths and discuss what can be learnt from their comparison with simulations.
| Distribution functions of infinitely thin gravitating discs
L. P. Ossipkov
The general theory of collisionles equilibrium for disc
galaxies was developed by S. Aoki, A. Kalnajs, L. Ossipkov
and others. Now we rediscuss the integral equation for
finding the even part of the distribution function. Some
new examples are considered. Also, the problem of finding
the odd part of the distribution function is discussed.
| Do low surface brightness galaxies have dense discs?
Saburova A.S.
Some investigations of low surface brightness (LSB) galaxies led to the conclusion that their disks may be significantly more massive than it is predicted by stellar population models (see for example Fuchs (2003)). In this case the commonly used point of view that LSB galaxies are systems of low surface density where a dark halo dominates at all radii, appears to be doubtful. To verify the possibility of high density of stellar disks of LSBs I considered four galaxies of this type for which radial distributions of velocity dispersion and rotation curves of stars and gas were obtained by Pizzella et al (2008). These data allowed me to obtain the independent estimation of masses of LSB disks using the criterion of gravitational stability. I came to the conclusion that either the surface densities of stellar discs of LSBs and their light-to-dark mass ratios are quite typical for normal spiral galaxies, or, unlike the discs of most of spiral galaxies, the LSB discs are dynamically overheated.
| Pattern Speed Estimates of Barred Galaxies from CINGS: A Connection Between Central Dark Halo Concentration and SMBH Mass?
Patrick Treuthardt, Marc Seigar, Heikki Salo
We present preliminary results of an investigation into the potential relationship between central dark halo concentration and supermassive black hole (SMBH) mass in the nuclei of disk galaxies. Barred disk galaxies with bar pattern speeds deemed ast exist in halos with a low central concentration, since the bar rotation rate would rapidly decrease due to dynamical friction with the halo. We estimated the pattern speeds of a sample of barred spiral galaxies from The Carnegie-Irvine Nearby Galaxy Survey (CINGS) by matching inelastically colliding gas particle simulations to B-band morphologies using near-infrared Ks-band images to define the gravitational potentials. The results from these models are compared to the SMBH mass of the same galaxies.
| Polygonal arms in grand-design spirals
Chernin A., Zasov A., Arkhipova V., Kravtsova A.
The phenomenon of regular polygonal spiral arms with straight geometrical segments is found in grand-design galaxies. The Whirlpool Nebula M 51 is the best studied example of the structure. Optical photographs, Hα, UV and far-UV images, CO, 21 cm, synchrotron emission maps, Ks-band mosaic of M 51 are used to recognize that the lengths of the segments increase with the distance from the galaxy center almost lineally and the segments intersect one another at an (average) angle ~ 2π/3. A possible physical nature of the phenomenon is discussed. It is suggested that the formation of straight segments might be due to the gas dynamics effect of stability of flat shock fronts and the tendency of a slightly curved front to get flat. A list of spirals with polygonal arms is compiled.
| Rotation curve of the Galaxy from the radial velocities and proper motions of open star clusters
A. Loktin, M. Popova
We check the possibility of explanation of well known feature of outer part of rotation curve of the Galaxy – the depression and then steep rise – by the influence of random errors in distance estimations. Series of numerical statistical experiments show that this possibility is very probable explanation for optical data. For new estimation of rotation curve of the Galaxy from the motions of the open clusters 434 cluster radial velocities and 415 proper motions are used. It is shown that modern proper motions of the open clusters contain enough information on the rotation of the Galaxy. The rotation curve for the interval of distances R = 3 - 15 kpc is constructed on the base of radial velocity and proper motion data of the open clusters jointly with the modern observational data of neutral hydrogen for the inner part of the Galaxy. It is approximated by the polynomial $\omega=30.2/R+2632.4/R^2-11556.4/R^3+15887.0/R^4$ with the use of progressive rejection of most deviations points from the sample. This rotation curve is not increase for large distances.
The work is supported by the Federal Educational Agency state contract P540 (05.08.2009) as a part of «Scientific and Scientific-pedagogical manpower of innovative Russia».
| Spiral density wave parameters on young open star clusters
Anisa Bajkova, Vadim Bobylev
Based on Bottlinger’s equations and currently available data on the three-dimensional field of space velocities of young (≤50 Myr) open star clusters we have found the Galactic spiral density wave parameters simultaneously with other kinematic parameters.
| Stellar subsystems of edge-on disk galaxies.
Galazutdinova O., Tikhonov N., Drozdovsky I.
The stellar populations of highly-inclined disk galaxies IC 1959, IC 2233, IC 5052, NGC 4631, NGC 5023 and ESO115-G121 are analyzed with the goal to quantify their vertical extent and structure. Based on the stellar photometry of the Hubble Space Telescope images, we separate various stellar populations of the galaxies and analyze their spatial distribution. We find that there is a profound change in slope of the number density profiles of the evolved RGB stars at extraplanar height of 4-8 kpc, that possibly reflects a truncation of the thick disk and reaching the 2-3 times more extended oblate stellar halo.
| The features of gas component in spiral galaxies of the Virgo cluster
Kasparova A.V.
Since the star formation in galaxies is determined by the amount of molecular hydrogen, and the formation of molecules is associated with gas pressure, it is important to analyse the radial dependence of the molecular gas density, as well as to investigate the fraction of molecular gas eta = SigmaH2/SigmaHI depending on the
the gas pressure Pgas for galaxies within the clusters and outside clusters in order to study the influence of the environment of galaxies on star formation. The calculation method consists of constructing a self-consistent model of an axisymmetric disk with finite thickness in a gravitational field of dark halo including the self-gravitation of gas and stars. Calculations for 12 isolated galaxies and 19 cluster galaxies have demonstrated that the galaxies can be roughly divided into several groups, which are characterized by different dependencies
of the fraction of molecular gas on pressure.
A probable reason for these differencies is a remove of atomic gas from the periphery of galaxies during its passage through the cluster centre remaining the molecular gas, although this discrepancy cannot be explained completely in the way indicated above.
| The intrinsic shape of bulges
J. Mendez-Abreu, E. Simonneau, J. A. L. Aguerri, E. M. Corsini
In this talk I will describe a new method to derive the intrinsic three-dimensional shape of bulges based on the geometrical relationships between the apparent and intrinsic shapes of bulges and disks. We assumed that bulges are triaxial ellipsoids. The intrinsic shape of the bulge is recovered from photometric data only. The method is conceived as completely independent of the studied class of objects, and it can be applied whenever a triaxial ellipsoid embedded in (or embedding) an axisymmetric component is considered. Analyzing a magnitude limited sample of 148 unbarred S0-Sb galaxies, for which we derived the structural parameters of bulges and disks by a detailed photometric decomposition of their near-infrared surface-brightness distribution. We found that the intrinsic shape is well constrained for a subsample of 115 bulges due to their viewing angles. A large fraction (55%) of them is characterized by an elliptical section (B/A<0.9), and most are flattened along their polar axis (C<(A+B)/2). The distribution of triaxiality is strongly bimodal. This bimodality is driven by bulges with Sersic index n > 2 or equivalently by the bulges of galaxies with a bulge-to-disk ratio B/T > 0.3. In particular, bulges with n<2 and with B/T<0.3 show a larger fraction of oblate axisymmetric bulges, a smaller fraction of triaxial bulges, and fewer prolate axisymmetric bulges with respect to bulges with n > 2 and with B/T > 0.3, respectively. According to predictions of the numerical simulations of bulge formation, bulges with n < 2, which show a high fraction of oblate axisymmetric shapes and have B/T < 0.3, could be the result of dissipational minor mergers. Both major dissipational and dissipationless mergers seem to be required to explain the variety of shapes found for bulges with n > 2 and B/T > 0.3.
| The minimum mass of (thin) disc galaxies
R. Sánchez-Janssen, J. Méndez-Abreu, J.A.L. Aguerri
We investigate the role of stellar mass in shaping the intrinsic thickness of galaxy discs by determining the probability distribution of apparent axis ratios for two different samples that probe the faint end of the galaxy luminosity function (M_B < -8). We find that the (b/a) distribution has a characteristic U-shape and identify a limiting mass M ~ 2x10^9 Msun below which low-mass galaxies start to be systematically thicker. We argue that this is the result of the complex interplay between galaxy mass, specific angular momentum and stellar feedback effects: the increasing importance of turbulent motions in lower mass galaxies leads to the formation of thicker systems. We find a good agreement between our results and the latest numerical simulations of disc formation, and discuss several further implications of this finding.
| The nuclei and structure of pure disk galaxies
Walcher, C.J., Boeker, T., Meidt, S.
There is a special class of ideal disk galaxies that do not show obvious trace of having a bulge, therefore also called ulgeless galaxies. I will present the results of two new projects, aimed at gaining a better understanding of the structure of these galaxies. 1) Relations between galaxy spheroids and their nuclei are well-studied. I will address the question whether bulgeless disks also relate to their nuclei - so-called nuclear clusters. In particular I will present new integral-field velocity fields for a sample of 20 bulgeless disk galaxies and compare the relative locations of galaxy nucleus and kinematic center. 2) I will show the results of 2-D surface brightness fitting of a sample of 11 pure disk galaxies drawn from the S4G survey (Spitzer 3.6 micron imaging). We aim to understand how many structural components they contain (in particular whether no bulge) and thus to ascertain whether their life was truly as uneventful as the pure disk concept would suggest.
| What the shape of end-products does the radial-orbit instability lead
Natalia Sotnikova, Tilmann Piffl
We will discuss the structure and kinematics of final models formed due to the radial-orbit instability (ROI) from a set of equilibrium anisotropic spherical systems of the Osipkov-Merritt type.
We found that the shape of the density profiles for various initial spherical models from a family of gamma-models didn’t change despite of the systems were drastically rearranged into triaxial configurations (in general). The cusp was found to be an invariant feature of such rearranging. Starting from a certain unstable spherical
model we obtain a triaxial system with the same cusp.
We also found that extremly prolate systems formed due to the ROI experience an instability that is additional to the ROI and eventually transforms prolate models into oblate configurations. We discuss the implications of our results for the shapes of bulges, elliptical galaxies and dark-matter halos.
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