The intrinsic three-dimensional shape of galactic bars

Abstract

We present the first statistical study on the intrinsic three-dimensional\n(3D) shape of a sample of 83 galactic bars extracted from the CALIFA survey. We\nuse the galaXYZ code to derive the bar intrinsic shape with a statistical\napproach. The method uses only the geometric information (ellipticities and\nposition angles) of bars and discs obtained from a multi-component photometric\ndecomposition of the galaxy surface-brightness distributions. We find that bars\nare predominantly prolate-triaxial ellipsoids (68%), with a small fraction of\noblate-triaxial ellipsoids (32%). The typical flattening (intrinsic C/A\nsemiaxis ratio) of the bars in our sample is 0.34, which matches well the\ntypical intrinsic flattening of stellar discs at these galaxy masses. We\ndemonstrate that, for prolate-triaxial bars, the intrinsic shape of bars\ndepends on the galaxy Hubble type and stellar mass (bars in massive S0 galaxies\nare thicker and more circular than those in less massive spirals). The bar\nintrinsic shape correlates with bulge, disc, and bar parameters. In particular\nwith the bulge-to-total (B/T) luminosity ratio, disc g-r color, and central\nsurface brightness of the bar, confirming the tight link between bars and their\nhost galaxies. Combining the probability distributions of the intrinsic shape\nof bulges and bars in our sample we show that 52% (16%) of bulges are thicker\n(flatter) than the surrounding bar at 1$\\sigma$ level. We suggest that these\npercentages might be representative of the fraction of classical and disc-like\nbulges in our sample, respectively.\n