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

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

The relation between bar formation, galaxy luminosity, and environment

We derive the bar fraction in three different environments ranging from the field to Virgo and Coma clusters, covering an unprecedentedly large range of galaxy luminosities (or, equivalently, stellar masses). We confirm that the fraction of barred galaxies strongly depends on galaxy luminosity. We also show that the difference between the bar fraction distributions as a function of galaxy luminosity (and mass) in the field and Coma cluster are statistically significant, with Virgo being an intermediate case. We interpret this result as a variation of the effect of environment on bar formation depending on galaxy luminosity. We speculate that brighter disk galaxies are stable enough against interactions to keep their cold structure, thus, the interactions are able to trigger bar formation. For fainter galaxies the interactions become strong enough to heat up the disks inhibiting bar formation and even destroying the disks. Finally, we point out that the controversy regarding whether the bar fraction depends on environment could be resolved by taking into account the different luminosity ranges of the galaxy samples studied so far.Comment: 4 pages, 2 figures. To appear in the proceedings of EWASS 2012 Special Session 4, Structure of galaxy disks shaped by secular evolution and environmental processes, ed. P. Di Matteo and C. Jog, Memorie della Societ\`a Astronomica Italiana Supplement Serie

The Circumnuclear Ring of Ionized Gas in NGC3593

We present the results of narrow-band Halpha+NII imaging of the early-type spiral NGC3593 in combination with a study of the flux radial profiles of the NII (lambda: 654.80, 658.34 nm), Halpha, and SII (lambda: 671.65, 673.08 nm) emission lines along its major axis. The galaxy is known to contain two counterrotating stellar discs of different size and luminosity. We find that the Halpha emission mainly derives from a small central region of 57 arcsec x 25 arcsec. It consists of a filamentary pattern with a central ring. This has a diameter of about 17 arcsec (~ 0.6/h kpc) and it contributes about half of the total Halpha flux. The ring is interpreted as the result of the interaction between the acquired retrograde gas which later formed the smaller counterrotating stellar disc and the pre-existing prograde gas of the galaxy.Comment: Accepted for pubblication in Astronomy and Astrophysics; one latex file (corsini.tex), and 2 encapsulated postscript figures (corsini_fig1.ps,corsini_fig2.ps). To be compiled with aa.cls latex2e macro style (pslatex option): 6 pages after latex compilatio

The CLIC Multi-Drive Beam Scheme

The CLIC study of an e+ / e- linear collider in the TeV energy range is based on Two-Beam Acceleration (TBA) in which the RF power needed to accelerate the beam is extracted from high intensity relativistic electron beams, the so-called drive beams. The generation, acceleration and transport of the high-intensity drive beams in an efficient and reliable way constitute a challenging task. An overview of a potentially very effective scheme is presented. It is based on the generation of trains of short bunches, accelerated sequentially in low frequency superconducting cavities in a c.w. mode, stored in an isochronous ring and combined at high energy by funnelling before injection by sectors into the drive linac for RF power production. The various systems of the complex are discussed

The Bulge-Disk Orthogonal Decoupling in Galaxies: NGC 4698

The R-band isophotal map of the Sa galaxy NGC 4698 shows that the inner region of the bulge structure is elongated perpendicularly to the major axis of the disk, this is also true for the outer parts of the bulge if a parametric photometric decomposition is adopted. At the same time the stellar component is characterized by an inner velocity gradient and a central zero-velocity plateau along the minor and major axis of the disk respectively. This remarkable geometric and kinematic decoupling suggests that a second event occurred in the formation history of this galaxy.Comment: 12 pages, LaTex, with 4 PostScript figures. Accepted for publication in The Astrophysical Journal Letter

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