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

Kinematic and Structural Evolution of Field and Cluster Spiral Galaxies

To understand the processes that build up galaxies we investigate the stellar structure and gas kinematics of spiral and irregular galaxies out to redshift 1. We target 92 galaxies in four cluster (z = 0.3 & 0.5) fields to study the environmental influence. Their stellar masses derived from multiband VLT/FORS photometry are distributed around but mostly below the characteristic Schechter-fit mass. From HST/ACS images we determine morphologies and structural parameters like disk length, position angle and ellipticity. Combining the spectra of three slit positions per galaxy using the MXU mode of VLT/FORS2 we construct the two-dimensional velocity field from gas emission lines for 16 cluster members and 33 field galaxies. The kinematic position angle and flatness are derived by a Fourier expansion of elliptical velocity profiles. To trace possible interaction processes, we define three irregularity indicators based on an identical analysis of local galaxies from the SINGS project. Our distant sample displays a higher fraction of disturbed velocity fields with varying percentages (10%, 30% and 70%) because they trace different features. While we find far fewer candidates for major mergers than the SINS sample at z~2, our data are sensitive enough to trace less violent processes. Most irregular signatures are related to star formation events and less massive disks are affected more than Milky-Way type objects. We detect similarly high fractions of irregular objects both for the distant field and cluster galaxies with similar distributions. We conclude that we may witness the building-up of disk galaxies still at redshifts z~0.5 via minor mergers and gas accretion, while some cluster members may additionally experience stripping, evaporation or harassment interactions.Comment: 4 pages, 2 colour figures, to appear in the ASP Conference Series Proceedings of "Galaxies in Isolation: Exloring Nature vs. Nurture", Granada, 200

The evolution of spiral galaxies in clusters

Spiral galaxies are transformed into lenticular galaxies in denser regions of the universe. Therefore, galaxy clusters are very good laboratories for investigating galaxy evolution. In this thesis we look at distant clusters (z~0.4), where galaxies are still in the process of being transformed. We focus on gas in galaxies, as its distribution and motions are sensitive to external impacts. By studying the irregularities in the kinematics of the gas, we try to understand the nature of the interaction processes in galaxy clusters. We define the irregularities with respect to their thresholds based on local, undisturbed galaxies. We then use this information to investigate how cluster members and field galaxies in the distant universe compare with each other. We find remarkably similar irregularity distributions and fractions for them which most probably indicates that field galaxies at intermediate redshifts are still in the process of building their disks via accretion and mergers. We also make a comparison with $zsim2$ galaxies and find that galaxies at intermediate redshifts have more regular gas kinematics. In the last part of this thesis we study a different topic and introduce a new tool for studying stellar populations in early type galaxies. We find that the 3.6-4.5 micron color is a good metallicity indicator and together with the Mgb index, it provides a plane where age and metallicity can be obtained without degeneracy.

Velocity fields of distant galaxies with FORS2 and the VLT

We describe a method to efficiently obtain two-dimensional velocity fields of distant, faint and small, emission-line galaxies with FORS2 at the VLT