4,216 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
Stability of plane Poiseuille-Couette flows of a piezo-viscous fluid
We examine stability of fully developed isothermal unidirectional plane Poiseuille--Couette flows of an incompressible fluid whose viscosity depends linearly on the pressure as previously considered in Hron01 and Suslov08. Stability results for a piezo-viscous fluid are compared with those for a Newtonian fluid with constant viscosity. We show that piezo-viscous effects generally lead to stabilisation of a primary flow when the applied pressure gradient is increased. We also show that the flow becomes less stable as the pressure and therefore the fluid viscosity decrease downstream. These features drastically distinguish flows of a piezo-viscous fluid from those of its constant-viscosity counterpart. At the same time the increase in the boundary velocity results in a flow stabilisation which is similar to that observed in Newtonian fluids with constant viscosity
Stability of plane Poiseuille flow of a fluid with pressure-dependent viscosity
We study the linear stability of a plane Poiseuille flow of an incompressible fluid whose viscosity depends linearly on the pressure. It is shown that the local critical Reynolds number is a sensitive function of the applied pressure gradient and that it decreases along the channel. While in the limit of small pressure gradients conventional results for a pressure-independent Newtonian fluid are recovered, a significant stabilisation of the flow and an elongation of the critical disturbance wavelength are observed when
the longitudinal pressure gradient is increased. These features drastically distinguish the stability characteristics of a piezo-viscous flow from its pressure-independent Newtonian counterpart
Revisiting plane Couette-Poiseuille flows of a piezo-viscous fluid
We re-examine fully developed isothermal unidirectional plane Couette-Poiseuille flows of an incompressible fluid whose viscosity depends linearly on the pressure as previously considered in Hron et al 2001. We show that the conclusion made there that, in contrast to Newtonian and power-law fluids, piezo-viscous fluids allow multiple solutions is not justified, and that the inflection velocity profiles reported in Hron et al 2001 cannot exist. Subsequently, we undertake a systematic parametric study of these flows and identify three distinct families of solutions which can exist in the considered geometry. One of these families has no similar counterpart for fluids with pressure-independent viscosity. We also show that the critical wall speed exists beyond which Poiseuille-type flows are impossible regardless of the magnitude of the applied pressure gradient. For smaller wall speeds channel choking occurs for Poiseuille-type flows at large pressure gradients. These features distinguish drastically piezo-viscous fluids from their Newtonian and power-law counterparts
Detection and Mapping of Decoupled Stellar and Ionized Gas Structures in the Ultraluminous Infrared Galaxy IRAS 12112+0305
Integral field optical spectroscopy with the INTEGRAL fiber-fed system and
HST optical imaging are used to map the complex stellar and warm ionized gas
structure in the ultraluminous infrared galaxy IRAS 12112+0305. Images
reconstructed from wavelength-delimited extractions of the integral field
spectra reveal that the observed ionized gas distribution is decoupled from the
stellar main body of the galaxy, with the dominant continuum and emission-line
regions separated by projected distances of up to 7.5 kpc. The two optical
nuclei are detected as apparently faint emission-line regions, and their
optical properties are consistent with being dust-enshrouded weak-[OI] LINERs.
The brightest emission-line region is associated with a faint (m_{I}= 20.4),
giant HII region of 600 pc diameter, where a young (about 5 Myr) massive
cluster of about 2 10 dominates the ionization.
Internal reddening towards the line-emitting regions and the optical nuclei
ranges from 1 to 8 magnitudes, in the visual. Taken the reddening into aacount,
the overall star formation in IRAS 12112+0305 is dominated by starbursts
associated with the two nuclei and corresponding to a star formation rate of 80
yr.Comment: 2 figures, accepted to Ap.J. Letter
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