202 research outputs found
News from the "Dentist's Chair": Observations of AM 1353-272 with the VIMOS IFU
The galaxy pair AM 1353-272 nicknamed "The Dentist's Chair" shows two ~30 kpc
long tidal tails. Previous observations using multi-slit masks showed that they
host up to seven tidal dwarf galaxies. The kinematics of these tidal dwarfs
appeared to be decoupled from the surrounding tidal material. New observations
of the tip of the southern tidal tail with the VIMOS integral field unit
confirm the results for two of these genuine tidal dwarfs but raise doubts
whether the velocity gradient attributed to the outermost tidal dwarf candidate
is real. We also discuss possible effects to explain the observational
difference of the strongest velocity gradient seen in the slit data which is
undetected in the new integral field data, but arrive at no firm conclusion.
Additionally, low-resolution data covering most of the two interacting partners
show that the strongest line emitting regions of this system are the central
parts.Comment: Comments welcome, especially ideas to explain the difference between
the two datasets. 5 pages, 3 figures, to appear in "Science Perspectives for
3D Spectroscopy", eds. M. Kissler-Patig, M. M. Roth and J. R. Walsh, ESO
Astrophysics Symposi
Tidal dwarf candidates in a sample of interacting galaxies: II. Properties and kinematics of the ionized gas
Peer reviewe
Ionization processes in a local analogue of distant clumpy galaxies: VLT MUSE IFU spectroscopy and FORS deep images of the TDG NGC 5291N
We present IFU observations with MUSE@VLT and deep imaging with FORS@VLT of a
dwarf galaxy recently formed within the giant collisional HI ring surrounding
NGC 5291. This TDG-like object has the characteristics of typical z=1-2
gas-rich spiral galaxies: a high gas fraction, a rather turbulent clumpy ISM,
the absence of an old stellar population, a moderate metallicity and star
formation efficiency. The MUSE spectra allow us to determine the physical
conditions within the various complex substructures revealed by the deep
optical images, and to scrutinize at unprecedented spatial resolution the
ionization processes at play in this specific medium. Starburst age, extinction
and metallicity maps of the TDG and surrounding regions were determined using
the strong emission lines Hbeta, [OIII], [OI], [NII], Halpha and [SII] combined
with empirical diagnostics. Discrimination between different ionization
mechanisms was made using BPT--like diagrams and shock plus photoionization
models. Globally, the physical conditions within the star--forming regions are
homogeneous, with in particular an uniform half-solar oxygen abundance. At
small scales, the derived extinction map shows narrow dust lanes. Regions with
atypically strong [OI] emission line immediately surround the TDG. The [OI] /
Halpha ratio cannot be easily accounted for by photoionization by young stars
or shock models. At larger distances from the main star--forming clumps, a
faint diffuse blue continuum emission is observed, both with the deep FORS
images and MUSE data. It does not have a clear counterpart in the UV regime
probed by GALEX. A stacked spectrum towards this region does not exhibit any
emission line, excluding faint levels of star formation, nor stellar absorption
lines that might have revealed the presence of old stars. Several hypotheses
are discussed for the origin of these intriguing features.Comment: 13 pages, 15 figures, accepted for publication in A&
p3d: a general data-reduction tool for fiber-fed integral-field spectrographs
The reduction of integral-field spectrograph (IFS) data is demanding work.
Many repetitive operations are required in order to convert raw data into,
typically a large number of, spectra. This effort can be markedly simplified
through the use of a tool or pipeline, which is designed to complete many of
the repetitive operations without human interaction. Here we present our
semi-automatic data-reduction tool p3d that is designed to be used with
fiber-fed IFSs. Important components of p3d include a novel algorithm for
automatic finding and tracing of spectra on the detector, and two methods of
optimal spectrum extraction in addition to standard aperture extraction. p3d
also provides tools to combine several images, perform wavelength calibration
and flat field data. p3d is at the moment configured for four IFSs. In order to
evaluate its performance we have tested the different components of the tool.
For these tests we used both simulated and observational data. We demonstrate
that for three of the IFSs a correction for so-called cross-talk due to
overlapping spectra on the detector is required. Without such a correction
spectra will be inaccurate, in particular if there is a significant intensity
gradient across the object. Our tests showed that p3d is able to produce
accurate results. p3d is a highly general and freely available tool. It is
easily extended to include improved algorithms, new visualization tools and
support for additional instruments. The program code can be downloaded from the
p3d-project web site http://p3d.sourceforge.netComment: 18 pages, 15 figures, 3 tables, accepted for publication in A&
Large Velocity Gradients in the Tidal Tails of the Interacting Galaxy AM 1353-272 ("The Dentist's Chair")
We present VLT observations of the interacting system AM 1353-272. Using the
FORS2 instrument, we studied the kinematics of the ionized gas along its
prominent tidal tails and discovered strikingly large velocity gradients
associated with seven luminous tidal knots. These kinematical structures cannot
be caused by streaming motion and most likely do not result from projection
effects. More probably, instabilities in the tidal tails have lead to the
formation of kinematically decoupled objects which could be the progenitors of
self-gravitating Tidal Dwarf Galaxies.Comment: 3 color figures, to appear 10. Nov. 2002 in ApJ
Mapping the inner regions of the polar disk galaxy NGC4650A with MUSE
[abridged] The polar disk galaxy NGC4650A was observed during the
commissioning of the MUSE at the ESO VLT to obtain the first 2D map of the
velocity and velocity dispersion for both stars and gas. The new MUSE data
allow the analysis of the structure and kinematics towards the central regions
of NGC4650A, where the two components co-exist. These regions were unexplored
by the previous long-slit literature data available for this galaxy. The
extended view of NGC~4650A given by the MUSE data is a galaxy made of two
perpendicular disks that remain distinct and drive the kinematics right into
the very centre of this object. In order to match this observed structure for
NGC4650A, we constructed a multicomponent mass model made by the combined
projection of two disks. By comparing the observations with the 2D kinematics
derived from the model, we found that the modelled mass distribution in these
two disks can, on average, account for the complex kinematics revealed by the
MUSE data, also in the central regions of the galaxy where the two components
coexist. This result is a strong constraint on the dynamics and formation
history of this galaxy; it further supports the idea that polar disk galaxies
like NGC~4650A were formed through the accretion of material that has different
angular momentum.Comment: 14 pages, 10 figures; accepted for publication in Astronomy &
Astrophysic
Three-component modelling of O-rich AGB star winds I. Effects of drift using forsterite
Stellar winds of cool and pulsating asymptotic giant branch (AGB) stars
enrich the interstellar medium with large amounts of processed elements and
various types of dust. We present the first study on the influence of
gas-to-dust drift on ab initio simulations of stellar winds of M-type stars
driven by radiation pressure on forsterite particles. Our study is based on our
radiation hydrodynamic model code T-800 that includes frequency-dependent
radiative transfer, dust extinction based on Mie scattering, grain growth and
ablation, gas-to-dust drift using one mean grain size, a piston that simulates
stellar pulsations, and an accurate high spatial resolution numerical scheme.
To enable this study, we calculated new gas opacities based on the ExoMol
database, and we extended the model code to handle the formation of minerals
that may form in M-type stars. We determine the effects of drift by comparing
drift models to our new and extant non-drift models. Three out of four new
drift models show high drift velocities, 87-310 km/s. Our new drift model
mass-loss rates are 1.7-13 per cent of the corresponding values of our
non-drift models, but compared to the results of two extant non-drift models
that use the same stellar parameters, these same values are 0.33-1.5 per cent.
Meanwhile, a comparison of other properties such as the expansion velocity and
grain size show similar values. Our results, which are based on
single-component forsterite particles, show that the inclusion of gas-to-drift
is of fundamental importance in stellar wind models driven by such transparent
grains. Assuming that the drift velocity is insignificant, properties such as
the mass-loss rate may be off from more realistic values by a factor of 50 or
more.Comment: 15 pages, 6 figures, accepted and in pres
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