Bar pattern speed evolution over the last 7 Gyr

The tumbling pattern of a bar is the main parameter characterising its dynamics. From numerical simulations, its evolution since bar formation is tightly linked to the dark halo in which the bar is formed through dynamical friction and angular momentum exchange. Observational measurements of the bar pattern speed with redshift can restrict models of galaxy formation and bar evolution. We aim to determine, for the first time, the bar pattern speed evolution with redshift based on morphological measurements. We have selected a sample of 44 low inclination ringed galaxies from the SDSS and COSMOS surveys covering the redshift range 0 <z< 0.8 to investigate the evolution of the bar pattern speed. We have derived morphological ratios between the deprojected outer ring radius (R_{ring}) and the bar size (R_{bar}). This quantity is related to the parameter {\cal R}=R_{CR}/R_{bar} used for classifiying bars in slow and fast rotators, and allow us to investigate possible differences with redshift. We obtain a similar distribution of $R$ at all redshifts. We do not find any systematic effect that could be forcing this result. The results obtained here are compatible with both, the bulk of the bar population (~70%) being fast-rotators and no evolution of the pattern speed with redshift. We argue that if bars are long-lasting structures, the results presented here imply that there has not been a substantial angular momentum exchange between the bar and halo, as predicted by numerical simulations. In consequence, this might imply that the discs of these high surface-brightness galaxies are maximal.Comment: Accepted for publication in A&

Properties of bars in the local universe

We studied the fraction and properties of bars in a sample of about 3000 galaxies extracted from SDSS-DR5. This represents a volume limited sample with galaxies located between redshift 0.01-20, and inclination i < 60. Interacting galaxies were excluded from the sample. The fraction of barred galaxies in our sample is 45%. We found that 32% of S0s, 55% of early-type spirals, and 52% of late-type spirals are barred galaxies. The bars in S0s galaxies are weaker than those in later-type galaxies. The bar length and galaxy size are correlated, being larger bars located in larger galaxies. Neither the bar strength nor bar length correlate with the local galaxy density. On the contrary, the bar properties correlate with the properties of their host galaxies. Galaxies with higher central light concentration host less and weaker bars.Comment: 2 pages, 1 figure to appear in the proceedings of "Formation and Evolution of Galaxy Disks", Rome, October 2007, Eds. J. Funes and E. M. Corsin

Deep spectroscopy in nearby galaxy clusters: III Orbital structure of galaxies in Abell 85

Galaxies in clusters are strongly affected by their environment. They evolve according to several physical mechanisms that are active in clusters. Their efficiency can strongly depend on the orbital configuration of the galaxies. Our aim is to analyse the orbits of the galaxies in the cluster Abell 85, based on the study of the galaxy velocity anisotropy parameter. We have solved the Jeans equation under the assumption that the galaxies in A85 are collisionless objects, within the spherically symmetric gravitational potential of the virialized cluster. The mass of the cluster was estimated with X-ray and caustic analyses. We find that the anisotropy profile of the full galaxy population in A85 is an increasing monotonic function of the distance from the cluster centre: on average, galaxies in the central region (r/r200 < 0.3) are on isotropic orbits, while galaxies in the outer regions are on radial orbits. We also find that the orbital properties of the galaxies strongly depend on their stellar colour. In particular, blue galaxies are on less radial orbits than red galaxies. The different families of cluster galaxies considered here have the pseudo phase-space density profiles Q(r) and Qr(r) consistent with the profiles expected in virialized dark matter halos in $N$-body simulations. This result suggests that the galaxies in A85 have reached dynamical equilibrium within the cluster potential. Our results indicate that the origin of the blue and red colour of the different galaxy populations is the different orbital shape rather than the accretion time.Comment: 15 pages, 15 figures. Accepted for publication at MNRA

Restrictions to the galaxy evolutionary models from the Hawaiian Deep Fields SSA13 and SSA22

Quantitative structural analysis of the galaxies present in the Hawaiian Deep Fields SSA13 and SSA22 is reported. The structural parameters of the galaxies have been obtained automatically by fitting a two-component model (Sérsic r1/n bulge and exponential disc) to the surface brightness of the galaxies. The galaxies were classified on the basis of the bulge-to-total luminosity ratio (B/T). The magnitude selection criteria and the reliability of our method have been checked by using Monte Carlo simulations. A complete sample of objects up to redshift 0.8 has been achieved. Spheroidal objects (E/S0) represent ≈33 per cent and spirals ≈41 per cent of the total number of galaxies, while mergers and unclassified objects represent ≈26 per cent. We have computed the comoving space density of the different kinds of object. In an Einstein-de Sitter universe, a decrease in the comoving density of E/S0 galaxies is observed as redshift increases (≈30 per cent less at z=0.8), while for spiral galaxies a relatively quiet evolution is reported. The framework of hierarchical clustering evolution models of galaxies seems to be the most appropriate to explain our result

The intrinsic three-dimensional shape of galactic bars

We present the first statistical study on the intrinsic three-dimensional (3D) shape of a sample of 83 galactic bars extracted from the CALIFA survey. We use the galaXYZ code to derive the bar intrinsic shape with a statistical approach. The method uses only the geometric information (ellipticities and position angles) of bars and discs obtained from a multi-component photometric decomposition of the galaxy surface-brightness distributions. We find that bars are predominantly prolate-triaxial ellipsoids (68%), with a small fraction of oblate-triaxial ellipsoids (32%). The typical flattening (intrinsic C/A semiaxis ratio) of the bars in our sample is 0.34, which matches well the typical intrinsic flattening of stellar discs at these galaxy masses. We demonstrate that, for prolate-triaxial bars, the intrinsic shape of bars depends on the galaxy Hubble type and stellar mass (bars in massive S0 galaxies are thicker and more circular than those in less massive spirals). The bar intrinsic shape correlates with bulge, disc, and bar parameters. In particular with the bulge-to-total (B/T) luminosity ratio, disc g-r color, and central surface brightness of the bar, confirming the tight link between bars and their host galaxies. Combining the probability distributions of the intrinsic shape of bulges and bars in our sample we show that 52% (16%) of bulges are thicker (flatter) than the surrounding bar at 1$\sigma$ level. We suggest that these percentages might be representative of the fraction of classical and disc-like bulges in our sample, respectively.Comment: 18 pages, 11 figures, accepted for publication in MNRA

Structural properties of disk galaxies I. The intrinsic ellipticity of bulges

(Abridged) A variety of formation scenarios was proposed to explain the diversity of properties observed in bulges. Studying their intrinsic shape can help in constraining the dominant mechanism at the epochs of their assembly. 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 (PDF) of the intrinsic equatorial ellipticity of bulges. It is presented a new fitting algorithm (GASP2D) to perform the two-dimensional photometric decomposition of 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 PDF of the equatorial ellipticity of the bulges was derived from the distribution of the observed ellipticities of bulges and misalignments between bulges and disks. Strong correlations between the bulge and disk parameters were found. About 80% of bulges in unbarred lenticular and early-to-intermediate spiral galaxies are not oblate but triaxial ellipsoids. Their mean axial ratio in the equatorial plane is = 0.85. There is not significant dependence of their PDF on morphology, light concentration, and luminosity. The interplay between bulge and disk parameters favors scenarios in which bulges assembled from mergers and/or grew over long times through disk secular evolution. But all these mechanisms have to be tested against the derived distribution of bulge intrinsic ellipticities.Comment: 24 pages, 13 figures, accepted for publication in A&A, corrected proof