The Formation of Galactic Bulges

We summarise some recent results about nearby galactic bulges that are relevant to their formation. We highlight a number of significant advances in our understanding of the surface brightness profiles, stellar populations, and especially the very centers of spiral galaxies. We also view our own Milky Way as if it were an external galaxy. Our main conclusions are that bulges of early-type spirals (S0 -- Sb) contain central nuclear components, just like late-type spirals and most other types of galaxies. The luminosities of these central components correlate best with total bulge luminosity, and not as well with morphological type. Bulges of early-type spiral galaxies follow the fundamental plane and the colour/line strength vs. luminosity relations of elliptical galaxies. Although we have a reasonable idea about bulges of early-type spirals we know much less about late-type bulges. However, the close resemblance of our Milky Way Bulge to bulges in external disk galaxies makes us suspect that bulges of late-type spirals might be very similar as well.Comment: 10 pages, invited review presented at 'Baryons in Dark Matter', Novigrad Oct 5-9, 2004; eds. R. Dettmar, U. Klein and P. Salucci. On-line publication at http://pos.sissa.i

Deficiency of `Thin' Stellar Bars in Seyfert Host Galaxies

Using all available major samples of Seyfert galaxies and their corresponding control samples of closely matched non-active galaxies, we find that the bar ellipticities (or axial ratios) in Seyfert galaxies are systematically different from those in non-active galaxies. Overall, there is a deficiency of bars with large ellipticities (i.e., `fat' or `weak' bars) in Seyferts, compared to non-active galaxies. Accompanied with a large dispersion due to small number statistics, this effect is strictly speaking at the `2sigma' level. To obtain this result, the active galaxy samples of near-infrared surface photometry were matched to those of normal galaxies in type, host galaxy ellipticity, absolute magnitude, and, to some extent, in redshift. We discuss possible theoretical explanations of this phenomenon within the framework of galactic evolution, and, in particular, of radial gas redistribution in barred galaxies. Our conclusions provide further evidence that Seyfert hosts differ systematically from their non-active counterparts on scales of a few kpc.Comment: Astrophysical Journal Letters, in press. Latex, 2 postscript figure

Velocity Fields of Spiral Galaxies in z~0.5 Clusters

Spiral galaxies can be affected by interactions in clusters, that also may distort the internal velocity field. If unrecognized from single-slit spectroscopy, this could lead to a wrong determination of the maximum rotation velocity as pointed out by Ziegler et al. (2003). This parameter directly enters into the Tully-Fisher relation, an important tool to investigate the evolution of spiral galaxies. To overcome this problem, we measure the 2D-velocity fields by observing three different slit positions per galaxy using FORS2 at the VLT providing us with full coverage of each galaxy and an adequate spatial resolution. The kinematic properties are compared to structural features determined on the HST/ACS images to assess possible interaction processes. As a next step, the whole analysis will be performed for three more clusters, so that we will be able to establish a high-accuracy TFR for spirals at z~0.5.Comment: 2 pages, 2 figures, going to be published in the proceedings of the IAU Symp. 241, "Stellar Populations as Building Blocks of Galaxies

Scale Length of Disk Galaxies

As a part of a Euro-VO research initiative, we have undertaken a programme aimed at studying the scale length of 54909 Sa-Sd spiral galaxies from the SDSS DR6 catalogue. We have retrieved u,g,r,i,z-band images for all galaxies in order to derive the light profiles. We also calculate asymmetry parameters to select non-disturbed disks for which we will derive exponential disk scale lengths. As images in different bands probe different optical depths and stellar populations, it is likely that a derived scale length value should depend on waveband, and our goal is to use the scale length variations with band pass, inclination, galaxy type, redshift, and surface brightness, in order to better understand the nature of spiral galaxies.Comment: Invited talk at the workshop "Multiwavelegth Astronomy and Virtual Observatory" at ESA/ESAC in december 200