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

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

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&