We study the density profiles of collapsed galaxy-size dark matter halos with masses 10 11 − 5 · 10 12 M ⊙ focusing mostly on the halo outer regions from the formal virial radius R vir up to 5-7R vir . We find that isolated halos in this mass range extend well beyond R vir exhibiting all properties of virialized objects up to 2-3R vir : relatively smooth density profiles and no systematic infall velocities. The dark matter halos in this mass range do not grow as one naively may expect through a steady accretion of satellites, i.e., on average there is no mass infall. This is strikingly different from more massive halos, which have large infall velocities outside of the virial radius. We provide accurate fit for the density profile of these galaxy-size halos. For a wide range (0.01 − 2)R vir of radii the halo density profiles are fit with the approximation ρ = ρ s exp −2n[x 1/n − 1] + ρ m , where x ≡ r/r s , ρ m is the mean matter density of the Universe, and the index n is in the range n = 6 − 7.5. These profiles do not show a sudden change of behavior beyond the virial radius. For larger radii we combine the statistics of the initial fluctuations with the spherical collapse model to obtain predictions for the mean and most probable density profiles for halos of several masses. The model give excellent results beyond 2-3 formal virial radii.

Context. A variety of formation scenarios have been proposed to explain the diversity of properties observed in bulges. Studying their intrinsic shape can help to constrain the dominant mechanisms at the epochs of their assembly. Aims. The structural parameters of a magnitude-limited sample of 148 unbarred S0-Sb galaxies were derived in order to study the correlations between bulges and disks, as well as the probability distribution function of the intrinsic equatorial ellipticity of bulges. Methods. We present a new fitting algorithm (GASP2D) to perform two-dimensional photometric decomposition of the galaxy surface-brightness distribution. This was assumed to be the sum of the contribution of a bulge and disk component characterized by elliptical and concentric isophotes with constant (but possibly different) ellipticity and position angles. Bulge and disk parameters of the sample galaxies were derived from the J-band images, which were available in the Two Micron All Sky Survey. The probability distribution function of the equatorial ellipticity of the bulges was derived from the distribution of the observed ellipticities of bulges and misalignments between bulges and disks. Results. Strong correlations between the bulge and disk parameters were found. About 80% of bulges in unbarred lenticular and earlyto-intermediate spiral galaxies are not oblate but triaxial ellipsoids. Their mean axial ratio in the equatorial plane is B/A = 0.85. Their probability distribution function is not significantly dependent on morphology, light concentration or luminosity. The possible presence of nuclear bars does not influence our results. Conclusions. The interplay between bulge and disk parameters favors scenarios in which bulges have assembled from mergers and/or have grown over long times through disk secular evolution. However, all these mechanisms have to be tested against the derived distribution of bulge intrinsic ellipticities.

If the dark matter (DM), which is considered to constitute most of the mass of galaxies, is made of supersymmetric particles, the central region of our Galaxy should emit gamma rays produced by their annihilation. We use detailed models of the Milky Way to make accurate estimates of continuum gamma-ray fluxes. We argue that the most important effect, which was previously neglected, is the compression of the dark matter due to the infall of baryons to the galactic center: it boosts the expected signal by a factor 1000. To illustrate this effect, we computed the expected gamma fluxes in the minimal supergravity scenario. Our models predict that the signal could be detected at high confidence levels by imaging atmospheric C erenkov telescopes assuming that neutralinos make up most of the DM in the Universe.

A method based on Lucy’s iterative algorithm is developed to invert the equation of stellar statistics for the Galactic bulge and is then applied to the K‐band star counts from the Two‐Micron Galactic Survey in a number of off‐plane regions (10°>|b|>2°, |l|<15°). The top end of the K‐band luminosity function is derived and the morphology of the stellar density function is fitted to triaxial ellipsoids, assuming a non‐variable luminosity function within the bulge. The results, which have already been outlined by López‐Corredoira et al., are shown in this paper with a full explanation of the steps of the inversion: the luminosity function shows a sharp decrease brighter than MK=−8.0  mag when compared with the disc population; the bulge fits triaxial ellipsoids with the major axis in the Galactic plane at an angle with the line of sight to the Galactic centre of 12° in the first quadrant; the axial ratios are 1:0.54:0.33, and the distance of the Sun from the centre of the triaxial ellipsoid is 7860 pc. The major–minor axial ratio of the ellipsoids is found not to be constant, the best fit to the gradient being Kz=(8.4±1.7)×exp(−t/(2000±920) pc), where t is the distance along the major axis of the ellipsoid in parsecs. However, the interpretation of this is controversial. An eccentricity of the true density‐ellipsoid gradient and a population gradient are two possible explanations. The best fit for the stellar density, for 1300 pc

Context. Knowledge of the intrinsic shapes of galaxy components provides crucial information when constraining phenomena driving their formation and evolution. Aims. We analize the structural parameters of a magnitude-limited sample of 148 unbarred S0-Sb galaxies to derive the intrinsic shape of their bulges. Methods. We developed a new method to derive the intrinsic shapes of bulges based on geometrical relationships between the apparent and intrinsic shapes of bulges and disks. Bulges were assumed to be triaxial ellipsoids sharing the same center and polar axis of their surrounding disks. Disks were assumed to be circular, infinitesimally thin, and to lie on the equatorial plane of bulges. The equatorial ellipticity and intrinsic flattening of bulges were obtained from the length of the apparent major and minor semi-axes of the bulge, the twist angle between the apparent major axis of the bulge and the galaxy line of nodes, and the galaxy inclination. Results. We find that the intrinsic shape is well constrained for a subsample of 115 bulges with favorable viewing angles. A large fraction of them are characterized by an elliptical section (B/A < 0.9). This fraction is 33%, 55%, and 43% if using their maximum, mean, or median equatorial ellipticity, respectively. Most are flattened along their polar axis (C < (A + B)/2). Only 18% of the observed bulges have a probability >50% and none has a probability >90% of being elongated along the polar axis. The distribution of triaxiality is strongly bimodal. This bimodality is driven by bulges with Sérsic index n > 2, or equivalently, by the bulges of galaxies with a bulge-to-total ratio B/T > 0.3. Bulges with n ≤ 2 and with B/T ≤ 0.3 follow a similar distribution, which differs from that of bulges with n > 2 and B/T > 0.3. In particular, bulges with n ≤ 2 and B/T ≤ 0.3 exhibit a larger fraction of oblate axisymmetric (or nearly axisymmetric) bulges, a smaller fraction of triaxial bulges, and fewer prolate axisymmetric (or nearly axisymmetric) bulges with respect to bulges with n > 2 and with B/T > 0.3, respectively. No correlation is found between the intrinsic shape and either the luminosity or velocity dispersion of bulges. Conclusions. According to predictions of the numerical simulations of bulge formation, bulges with n ≤ 2, which show a high fraction of oblate axisymmetric (or nearly axisymmetric) shapes and have B/T ≤ 0.3, may 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.