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

Warm ionized gas in the blue compact galaxy Haro 14 viewed by MUSE

We investigate the warm ionized gas in the blue compact galaxy (BCG) Haro 14 by means of integral field spectroscopic observations taken with the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope. The large field of view of MUSE and its unprecedented sensitivity enable observations of the galaxy nebular emission up to large galactocentric distances, even in the important but very faint [O i] λ6300 diagnostic line. This allowed us to trace the ionized gas morphology and ionization structure of Haro 14 up to kiloparsec scales and, for the first time, to accurately investigate the excitation mechanism operating in the outskirts of a typical BCG. The intensity and diagnostic maps reveal at least two highly distinct components of ionized gas: the bright central regions, mostly made of individual clumps, and a faint component which extends up to kiloparsec scales and consists of widespread diffuse emission, well-delineated filamentary structures, and faint knots. Noteworthy are the two curvilinear filaments extending up to 2 and 2.3 kpc southwest, which likely trace the edges of supergiant expanding bubbles driven by galactic outflows. We find that while the central clumps in Haro 14 are Hii-region complexes, the morphology and line ratios of the whole low-surface-brightness component are not compatible with star formation photoionization. In the spatially resolved emission-line-ratio diagnostic diagrams, spaxels above the maximum starburst line form the majority (∼75% and ∼50% in the diagnostic diagrams involving [O i] and [S ii] respectively). Moreover, our findings suggest that more than one alternative mechanism is ionizing the outer galaxy regions. The properties of the diffiuse component are consistent with ionization by diluted radiation and the large filaments and shells are most probably shocked areas at the edge of bubbles. The mechanism responsible for the ionization of the faint individual clumps observed in the galaxy periphery is more difficult to assess. These clumps could be the shocked debris of fragmented shells or regions where star formation is proceeding under extreme conditions

Optical emission lines in the most massive galaxies: morphology, kinematics, and ionisation properties

Galaxie

MUSE crowded field 3D spectroscopy in NGC 300: III. Characterizing extremely faint HII regions and diffuse ionized gas

Interstellar matter and star formatio

Spatial modulation of water ordering in lecithin bilayers. Evidence for a ripple-ripple phase transition

Intense motional averaging effects on the 2H nuclear magnetic resonance (NMR) spectrum of 2H2O that occur in aqueous dispersions of dimyristoyl-sn-glycero-3-phosphocholine (Myr2-PtdCho) are explained by a spatial modulation in the orientational order of the water induced by ripplelike structures. The ratio of the amplitude to the periodic length of the ripples, A/lambda, at a molar ratio of water/Myr2-PtdCho of 9.5:1, is measured by 2H NMR and found to be consistent with x-ray measurements of this ratio in the P beta phase of dipalmitoyl-sn-glycero-3-phosphocholine (Pam2-PtdCho) bilayers. The sensitivity of 2H NMR allows us to report the presence of two distinct ripple phases mediated with a discontinuous change in the value of A/lambda. This result suggests that the two ripple structures observed for several phospholipid systems in excess water by freeze-fracture electron microscopy may be associated with two different phases instead of the same phase as previously assumed

Tidal Dwarf Galaxies at Intermediate Redshifts

We present the first attempt at measuring the production rate of tidal dwarf galaxies (TDGs) and estimating their contribution to the overall dwarf population. Using HST/ACS deep imaging data from GOODS and GEMS surveys in conjunction with photometric redshifts from COMBO-17 survey, we performed a morphological analysis for a sample of merging/interacting galaxies in the Extended Chandra Deep Field South and identified tidal dwarf candidates in the rest-frame optical bands. We estimated a production rate about 1.4 {\times} 10^{-5} per Gyr per comoving volume for long-lived TDGs with stellar mass 3 {\times} 10^{8-9} solar mass at 0.5<z<1.1. Together with galaxy merger rates and TDG survival rate from the literature, our results suggest that only a marginal fraction (less than 10%) of dwarf galaxies in the local universe could be tidally-originated. TDGs in our sample are on average bluer than their host galaxies in the optical. Stellar population modelling of optical to near-infrared spectral energy distributions (SEDs) for two TDGs favors a burst component with age 400/200 Myr and stellar mass 40%/26% of the total, indicating that a young stellar population newly formed in TDGs. This is consistent with the episodic star formation histories found for nearby TDGs.Comment: 9 pages, 5 figures, Accepted for publication in Astrophysics & Space Scienc

A Stellar Census in NGC 6397 with MUSE

Galaxie

Galactic winds with MUSE: A direct detection of Fe II* emission from a z 1.29 galaxy

Interstellar matter and star formationGalaxie

Tides in colliding galaxies

Long tails and streams of stars are the most noticeable upshots of galaxy collisions. Their origin as gravitational, tidal, disturbances has however been recognized only less than fifty years ago and more than ten years after their first observations. This Review describes how the idea of galactic tides emerged, in particular thanks to the advances in numerical simulations, from the first ones that included tens of particles to the most sophisticated ones with tens of millions of them and state-of-the-art hydrodynamical prescriptions. Theoretical aspects pertaining to the formation of tidal tails are then presented. The third part of the review turns to observations and underlines the need for collecting deep multi-wavelength data to tackle the variety of physical processes exhibited by collisional debris. Tidal tails are not just stellar structures, but turn out to contain all the components usually found in galactic disks, in particular atomic / molecular gas and dust. They host star-forming complexes and are able to form star-clusters or even second-generation dwarf galaxies. The final part of the review discusses what tidal tails can tell us (or not) about the structure and content of present-day galaxies, including their dark components, and explains how tidal tails may be used to probe the past evolution of galaxies and their mass assembly history. On-going deep wide-field surveys disclose many new low-surface brightness structures in the nearby Universe, offering great opportunities for attempting galactic archeology with tidal tails.Comment: 46 pages, 13 figures, Review to be published in "Tidal effects in Astronomy and Astrophysics", Lecture Notes in Physics. Comments are most welcom