To extend our recent study of structural parameters of Globular Clusters (GCs) in the giant elliptical NGC 5128 (Gómez et al. 2006), we have obtained new high resolution images with the Magellan 6.5m at Las Campanas Observatory and the IMACS camera. Our images cover an area of 1.2 × 1.2 sq. degrees and have a seeing between 0.4 and 0.7'', thus making it possible to resolve a significant fraction of the GC population, which is now virtually entirely observed given the large spatial and magnitude range.

Convolution techniques allow us to find and to study the cluster candidates using the stellar PSF and analytical profiles for their light distribution. We therefore are able to derive structural parameters like size (effective and core radii), ellipticity, position angle and concentration. This is combined with the extensive database in the Washington photometric system by Harris et al. (2004) to select clusters according to shape, extendedness and Washington magnitudes and colours, which has proven very useful in discriminating GCs from foreground stars and background galaxies and for deriving metallicities.

Our first results for the central field (15'×15’) indicate that the GCs populate a large range of (MV, rh) parameter space, with typical sizes of Galactic GCs as well as much larger. Combined with our previous data, we find a continuum of clusters in this diagram, with no clear distinction between a variety of different ‘types’ often referred to, such as UCDs, Faint Fuzzies, etc.

In addition, a large fraction of GCs show a significant ellipticity whereas a paucity of round clusters is observed. We also confirm with a large (~250) sample that metal-rich clusters are smaller than metal-poor ones, which is in keeping with the general trend found in other galaxies. (e.g. Jordán et al. 2005)

In this poster contribution, we present results from high spatial resolution integral-field spectroscopy of elliptical (E) and lenticular (S0) galaxies from the SAURON representative survey, obtained with the OASIS and GMOS spectrographs. These seeing-limited observations explore the central ∼10''10″ (typically one kiloparsec diameter) regions of these galaxies using a spatial sampling four times higher than SAURON (0″27 vs. 0″94 spatial elements), resulting in almost a factor of two improvement in the median PSF. These data allow accurate study of the central regions to complement the large-scale view provided by SAURON. We derive the stellar and gas kinematics, stellar absorption-line strengths and nebular emission-line strengths for our sample, and derive maps of the luminosity-weighted stellar age, metallicity and abundance ratio via stellar population models. From these data we find a wealth of structures either not seen or poorly resolved in the SAURON data, including a number of kinematically-decoupled cores (KDCs) in the centres of some galaxies. We compare the intrinsic size and luminosity-weighted stellar age of all the visible KDCs in the full SAURON sample, and find two types of components: kiloparsec-scale KDCs, which are older than 8 Gyr, and are found in galaxies with little net rotation; and compact KDCs, which have intrinsic diameters of less than a few hundred parsec, show a range of stellar ages from 0.5 - 15 Gyr (with 5/6 younger than 5 Gyr), are found exclusively in fast-rotating galaxies, and are close to counter-rotating around the same axis as their host. Of the 7 galaxies in the SAURON sample with integrated luminosity-weighted ages less than 5 Gyr, 5 show such compact KDCs, suggesting a link between counter-rotation and recent star-formation. We show that this may be partly due to a combination of small sample size at young ages, and an observational bias, since young KDCs are easier to detect than their older and/or co-rot ating counterparts.

We analyzed the 2MASS images of a sample of 148 bright, nearby and unbarred galaxies to derive the photometric parameters of their bulge and disk by applying an accurate 2D decomposition algorithm. As a model for the bulge we have considered a system where the surfaces of equal density of light are coaxial and concentric ellipsoids with independent values of the principal axes A > B > C. If the emitting surfaces are concentric, coaxial but non-homologous ellipsoids, their projection on the plane of the sky will be concentric, non-homologous and non-coaxial ellipses (Stark 1977). Therefore if we identify the projected ellipses with the isophotal contours of a bulge, the observed twist between the position angle of the bulge and disk components can be understood as a hint for triaxiality.

Following the procedure described by Simonneau et al. (1998), we are able to express the intrinsic semi-axis values (A, B, C) of the triaxial ellipsoid as a function of the semi-axis measured on to its projected ellipse (a, b), position angle of the ellipse (δ), and angles which define the line of sight with respect to the ellipsoid (θ, φ).

However, since the φ angle is observationally undetermined, the intrinsic shape of bulges is still an ambiguous problem. Thus, it is customary to resort to a statistical approach for deducing the probability distribution function (PDF) of the intrinsic axis ratio of bulges. Since we have already inverted the problem, putting the intrinsic variables as a function of the measured variables (E, δ) and the variables (θ, φ) which are defined in a probabilistic way, and we have assumed that they are independent, the PDF can be determined simply by the multiplication of the integrated single probabilities of these variables.

We have found that integrating the derived PDF over the different ellipsoid regions (prolate, triaxial and oblate), ~45% of bulges have a triaxial structure, about 26% are oblate ellipsoids, 23% are prolate ellipsoids and the remaining 5% are spherical.

A typical bulge from our PDF, calculated as the mean value of the axis ratios of the ellipsoids weighted with the PDF, have axis ratios <P>=1.66 and <Q>=1.34. This means that the axis ratio in the equatorial plane of the galaxy is B/A=0.81, the ratio between the major and the polar axis is C/A=0.60 and the triaxiality parameter is T=0.55, which is in good agreement with the previous results by Bertola et al. (1991).

We also found a correlation between the Sérsic index and the intrinsic flattening of the bulges. We observed that bulges tend to be less flattened (C/A=0.64) in more-concentrated galaxies (n > 2) and more flattened (C/A=0.54) in less-concentrated galaxies.

For nearly a decade, N-body simulations have revealed a nearly universal dark matter density profile. This density profile appears to be robust to changes in the overall density of the universe and the underlying power spectrum. Despite its universality, however, the physical origin of this profile has not yet been well understood. Semi-analytic models have suggested that scale lengths in dark matter halos may be determined by the onset of the radial orbit instability. We have tested this theory using N-body simulations of collapsing dark matter halos. The resulting halo structures are prolate in shape, due to the mild aspect of the instability. We find that the radial orbit instability sets a scale length at which the velocity dispersion changes rapidly from isotropic to radially anisotropic. Preliminary analysis suggests that this scale length is proportional to the radius at which the density profile changes shape, as is the case in the semi-analytic models; however, the coefficient of proportionality is different by a factor of ~2. We conclude that the radial orbit instability may be a key physical mechanism responsible for the nearly universal profiles of simulated dark matter halos.

We review the results recently obtained by means of panoramic (3D) spectroscopy on the 6-m telescope BTA (SAO RAS). This research is devoted to observational evidences of gas inflow into the centers of galaxies, which must ensure the fueling of an active nucleus. 3D spectroscopy allows us to trace the behavior of gas and stars in the one-kiloparsec size vicinity of an AGN and also far from the center.

The Geneva-Copenhagen Survey (Nordström et al., 2004) gives ages, metallicities, velocities, and Galactic orbits for a complete, magnitude-limited sample of 14,000 F and G dwarfs. We have verified the calibrations used in the GCS, improved those of Teff, [Fe/H], distance, and age from uvby β, and checked the effect on the resulting Galactic relations by end- to-end numerical simulations. All the main results of the GCS remain unchanged.

We study subhalo populations surrounding massive dark matter haloes by using three AMIGA simulations each having different mass and spatial resolutions. Our analysis shows that the slope of the subhalo mass function has a value 0.9, which agrees with previous studies. The dependence of mass functions on redshift is the same for subhaloes and main haloes. In all simulations, combined subhalo masses are about 0.1-0.2 of main halo masses and this mass fraction increases slightly with redshift and the mass of the main halo. The distribution of mass fractions for subhaloes is close to Gaussian at z = 0 and differs slightly at earlier epochs. Spatial distribution of subhaloes as measured in units of virial radius Rvir of the main halo does not depend on redshift and follows r1/3 rule. Spatial distribution of all haloes surrounding main haloes continues up to 3 times Rvir with equal slope but lower amplitude. Beyond 16 times Rvir, the average distribution of haloes becomes uniform.

Assuming that most stars form in clusters (Lada & Lada 2003), one might initially expect to find most massive stars in stellar clusters and to detect most of the UV emission in young compact stellar clusters. However, Meurer et al. (1995) showed that in starburst galaxies only 20% of the UV emission at 2200Å is detected in clusters while 80% is diffuse emission from sources in the inter-cluster medium. This phenomenon is also observed for normal galaxies (Hoopes et al. 2001).

The results of a pilot study on the intrinsic 3D distribution of stars in edge-on disk galaxies are presented. The 3D disk structure of a sample of 12 edge-on galaxies has been reconstructed through a direct deprojection of the observed two-dimensional images. The deprojection method – which utilises the so called Fourier slice theorem and assumes axial symmetry – has been tested with a large set of artificial galaxy models seen under a variety of inclinations (i = 80–90°) and with different spatial dust and optical depths distributions.

By using bidimensional Fourier techniques, we have analyzed H (1.6μm) images of a sample of 48 spiral galaxies taken from the OSUBSGS. We found that two-armed spirals (m = 2) are the more important structures in the sample, but some galaxies present higher m = 1 (lopsided) or m = 3 (three armed spirals). A weak correlation between m = 2 pitch angles and Eskridge et al. (2002) classification is also evident, but there is no correlation at all between those angles and RC3 classification or Elmegreen arm class.

We present a new class of spherical galactic models with mild central cusps whose distribution function (DF) and intrinsic velocity dispersion (IV) can be represented analytically in a unified way in terms of hypergeometric functions for a large number of parameters. This allows an easy comparison of these quantities for models having varying degrees of central cuspiness or outer density falloff. In particular, we study the models for the innermost regions of galaxies harbouring mild cuspy centers with or without supermassive black holes (SBH). Important properties infered from the observed behaviour of the velocity dispersions can be reproduced.

One of the most important results in the study of Globular Clusters (GC) has been the discovery of bimodality in the broad-band colors of many systems. Observations of the Milky Way, M31 and Centaurus A strongly suggest this is a bi-modality in metallicity. One method of constraining, and perhaps better understanding the observed bimodality of GCs is to use semi-analytic models (SAMs) to test both the galaxy and GC formation scenarios. We present the results of a study to test whether SAMs can accurately reproduce the physical characteristics of both the parent galaxy (including luminosity, mass and metallicity) and GC populations. The focus of the work is to test whether the SAMs are capable of reproducing the observed properties of spiral galaxies, in particular the Milky Way and M31, and what, if any, constraints this may place on the formation scenarios of GCs. Among the results are indications that bimodality may be directly connected with reionization at z ~ 7–8.

We use sticky-particle simulations to estimate the bar pattern speeds in disk galaxies over a wide range of Hubble types. For early types our results agree with the fast rotation found in previous kinematical measurements, while for later types significantly slower bars are found. Slow bars tend to be small, and favor less luminous galaxies, for a given bulge-to-total ratio.

The theory of the Fundamental Plane (FP) proposed by Secco (2005) is based on the existence of a maximum in the Clausius' Virial (CV) potential energy of a stellar component when it is completely embedded inside a dark matter (DM) halo. At the first order approximation the theory was developed by modeling the two-components with two power-law density profiles and it produces some expectations in fairly good agreement with the observations. We add other predictions of the theory at the same level of approximation about the Zone of Exclusion (ZOE) in k-space and its possible relationship with cosmological scenario. Some of the consequences of the thermodynamical properties of CV maximum are also taken into account.

A new mass model for M31 is presented. The best possible baryonic mass profile for M31 is derived from the 2MASS Ks-band image and M/L ratios from Bell et al. (2003). The best fitting rotation curve is then found within the context of ΛCDM disk galaxy formation. We find that M31 is well-described by a model that includes an adiabatically contracted halo, with an initial NFW concentration, c = 20. Models without adiabatic contraction fail to reproduce the observed rotation curve at r>15 kpc. The derived halo virial mass is Mvir = (9.4 ± 0.8) × 1011M⊙, consistent with masses derived from other observational methods.

We have studied the ionized gas and stellar kinematics in several galaxies with active nuclei and elongated radio structures using 3D spectroscopy. The observations were performed at the SAO RAS 6-m telescope with the integral-field spectrograph MPFS (Afanasiev et al. 2001) and with a scanning Fabry-Perot interferometer (FPI) in the multimode device SCORPIO (Afanasiev & Moiseev 2005). Based on these data the intensity maps and velocity fields in the different emission lines of the ionizing gas were constructed. Using the lines-ratio diagrams we tried to search a source of the gas ionization: an active nucleus, hot young stars or shock waves.

We report new constraints on the local escape speed of our Galaxy. Our analysis is based on a sample of high velocity stars from the RAVE survey and two previously published datasets (the Geneva-Copenhagen survey and the Beers et al. catalogue of metal-poor stars). We use cosmological simulations of disk galaxy formation to motivate our assumptions on the shape of the velocity distribution, allowing for a significantly more precise measurement of the escape velocity compared to previous studies. We find that the escape velocity lies within the range 492 km s−1 < vesc <594 kms (90% confidence), with a median likelihood of 536 kms. The fact that v2esc is significantly greater than 2v2circ implies that there must be a significant amount of mass exterior to the Solar circle, i.e. this convincingly demonstrates the presence of a dark halo in the Galaxy. For a simple isothermal halo, one can calculate that the minimum radial extent is ~54 kpc. We use our constraints on vesc to determine the mass of the Milky Way halo for three halo profiles. For example, an adiabatically contracted NFW halo model results in a virial mass of 1.31+0.97−0.49 × 1012M⊙ and virial radius of 297+60−44 kpc (90% confidence). For this model the circular velocity at the virial radius is 141+27−19kms. Although our halo masses are model dependent, we find that they are in good agreement with each other.

We propose [Sobouti, arXiv:astro-ph/0603302] an f(R) modification of GR, which admits of a modified Schwarzschild metric. In the weak field limit this amounts to adding a small logarithmic correction to the newtonian potential. A test star moving in such a spacetime acquires a constant speed at large distances. From observations of the velocity curves of spirals, this speed turns out to be proportional to the fourth root of the mass of the central body, in compliance with the Tully-Fisher relation. A variance of MOND emerges as a consequence of the formalism.

We revisit the bimodality of the galaxy population seen in the local universe. We address this issue in terms of physical properties of galaxies, such as mean stellar ages and stellar masses, derived from the application of a spectral synthesis method to galaxy spectra from the SDSS. We show that the mean light-weighted stellar age of galaxies presents the best description of the bimodality seen in the galaxy population. The stellar mass has an additional role since most of the star-forming galaxies present in the local universe are low-mass galaxies. Our results give support to the existence of a ‘downsizing’ in galaxy formation, where nowadays massive galaxies tend to have stellar populations older than those found in less massive objects.

We present a set of optical observations of excited gas emission in the central kiloparsecs of nearby Seyfert galaxies, as obtained with the integral-field (3D) spectrograph OASIS. We map the 2D emission distribution as well as the gas kinematics, derive the electron density and estimate the extinction due to dust.