41 research outputs found
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
Internal kinematics of modelled interacting disc galaxies
We present an investigation of galaxy-galaxy interactions and their effects
on the velocity fields of disc galaxies in combined N-body/hydrodynamic
simulations, which include cooling, star formation with feedback, and galactic
winds. Rotation curves (RCs) of the gas are extracted from these simulations in
a way that follows the procedure applied to observations of distant, small, and
faint galaxies as closely as possible. We show that galaxy-galaxy mergers and
fly-bys disturb the velocity fields significantly and hence the RCs of the
interacting galaxies, leading to asymmetries and distortions in the RCs.
Typical features of disturbed kinematics are significantly rising or falling
profiles in the direction of the companion galaxy and pronounced bumps in the
RCs. In addition, tidal tails can leave strong imprints on the rotation curve.
All these features are observable for intermediate redshift galaxies, on which
we focus our investigations. We use a quantitative measure for the asymmetry of
rotation curves to show that the appearance of these distortions strongly
depends on the viewing angle. We also find in this way that the velocity fields
settle back into relatively undisturbed equilibrium states after unequal mass
mergers and fly-bys. About 1 Gyr after the first encounter, the RCs show no
severe distortions anymore. These results are consistent with previous
theoretical and observational studies. As an illustration of our results, we
compare our simulated velocity fields and direct images with rotation curves
from VLT/FORS spectroscopy and ACS images of a cluster at z=0.53 and find
remarkable similarities.Comment: 13 pages, 14 figures, accepted for publication in A&A, some
improvements and changes, main conclusions are unaffecte
Internal kinematics of spiral galaxies in distant clusters III. Velocity fields from FORS2/MXU spectroscopy
(Abridged) We study the impact of cluster environment on the evolution of
spiral galaxies by examining their structure and kinematics. Rather than
two-dimensional rotation curves, we observe complete velocity fields by placing
three adjacent and parallel FORS2 MXU slits on each object, yielding several
emission and absorption lines. The gas velocity fields are reconstructed and
decomposed into circular rotation and irregular motions using kinemetry. To
quantify irregularities in the gas kinematics, we define three parameters:
sigma_{PA} (standard deviation of the kinematic position angle), Delta phi (the
average misalignment between kinematic and photometric position angles) and
k_{3,5} (squared sum of the higher order Fourier terms). Using local,
undistorted galaxies from SINGS, these can be used to establish the regularity
of the gas velocity fields. Here we present the analysis of 22 distant galaxies
in the MS0451.6-0305 field with 11 members at z=0.54. In this sample we find
both field (4 out of 8) and cluster (3 out of 4) galaxies with velocity fields
that are both irregular and asymmetric. We show that these fractions are
underestimates of the actual number of galaxies with irregular velocity fields.
The values of the (ir)regularity parameters for cluster galaxies are not very
different from those of the field galaxies, implying that there are isolated
field galaxies that are as distorted as the cluster members. None of the
deviations in our small sample correlate with photometric/structural properties
like luminosity or disk scale length in a significant way.
Our 3D-spectroscopic method successfully maps the velocity field of distant
galaxies, enabling the importance and efficiency of cluster specific
interactions to be assessed quantitatively.Comment: accepted for publication in A&A, high resolution version available at
http://www.astro.rug.nl/~kutdemir/papers
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