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The evolution of galaxies is influenced by many physical processes which may vary depending on their environment. We combine Hubble Space Telescope (HST) and Multi-Unit Spectroscopic Explorer (MUSE) data of galaxies at 0.25, Comment: 32 pages, 29 figures, 5 tables, 7 appendices, language checked and appendix table updated (accepted for publication in A&A)

MUSE observations of the cluster of galaxies CGr32 ($M_{200}$ $\simeq$ 2 $\times$ 10$^{14}$ M$_{\odot}$) at $z$ = 0.73 reveal the presence of two massive star forming galaxies with extended tails of diffuse gas detected in the [OII]$\lambda\lambda$3727-3729 A emission-line doublet. The tails, which have a cometary shape with a typical surface brightness of a few 10$^{-18}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$, extend up to $\simeq$ 100 kpc (projected distance) from the galaxy discs and are not associated to any stellar component. All this observational evidence suggests that the gas has been removed during a ram-pressure stripping event. This observation is thus the first evidence that dynamical interactions with the intracluster medium were active when the Universe had only half of its present age. The density of the gas derived using the observed [OII]$\lambda$3729/[OII]$\lambda$3726 line ratio implies a very short recombination time, suggesting that a source of ionisation is necessary to keep the gas ionised within the tail., Comment: 10 pages, 6 figures, accepted in A&A

Several deep observations such as those carried out at the Canada-France-Hawaii Telescope (CFHT) have revealed prominent Low Surface Brightness (LSB) fine structures that change the apparent morphology of galaxies. Previous photometry surveys have developed observational techniques which exploit the diffuse light detected in the external regions of galaxies. In these studies the outer perturbations have been identified and classified like tidal tails, stellar streams, and shells. These structures are tracers of interacting and merging events and they keep a memory of the mass assembly of galaxies. Cosmological numerical simulations are needed to estimate their visibility time-scale (among other properties) in order to reconstruct the past merger history of galaxies. In the present work, we analyze a hydrodynamical cosmological simulation to build a comprehensive interpretation of the properties of fine structures. We make a census of several types of LSB fine structures by visual inspection of individual snapshots at various time. We reconstruct the evolution of the number of fine structures detected around an early-type galaxy and we compare with the merger history of the galaxy. We find that most of fine structures are associated with major and intermediate mass merger events. Their survival time scale ranges between 0.7 and 4 Gyr. Shells and streams remain visible for a longer time than tidal tails. These estimates of survival times provide clues to interpret the shape and frequency of fine structures observed in deep images in terms of mass assembly. We find that the detectability of stellar streams is the most sensitive to the surface brightness limit. We see 2-3 times more streams with a surface brightness cut of 33 mag arcsec$^{-2}$ than with 29 mag arcsec$^{-2}$. The detection of shells display a strong dependence on the projection angle., 16 pages, 14 figures, accepted in A&A (v2 after language editing)

The physical origin of the near-ultraviolet Mg II emission remains an underexplored domain, unlike more typical emission lines that are detected in the spectra of star-forming galaxies. We explore the nebular and physical properties of a sample of 381 galaxies between 0.70 < z < 2.34 drawn from the MUSE Hubble Ultra Deep Survey. The spectra of these galaxies show a wide variety of profiles of the Mg II λλ2796, 2803 resonant doublet, from absorption to emission. We present a study on the main drivers for the detection of Mg II emission in galaxy spectra. By exploiting photoionization models, we verified that the emission-line ratios observed in galaxies with Mg II in emission are consistent with nebular emission from HII regions. From a simultaneous analysis of MUSE spectra and ancillary Hubble Space Telescope information through spectral energy distribution fitting, we find that galaxies with Mg II in emission have lower stellar masses, smaller sizes, bluer spectral slopes, and lower optical depth than those with absorption. This leads us to suggest that Mg II emission is a potential tracer of physical conditions that are not merely related to those of the ionized gas. We show that these differences in Mg II emission and absorption can be explained in terms of a higher dust and neutral gas content in the interstellar medium (ISM) of galaxies showing Mg II in absorption, which confirms the extreme sensitivity of Mg II to the presence of the neutral ISM. We conclude with an analogy between the Mg II doublet and the Ly α line that lies in their resonant nature. Further investigations with current and future facilities, including the James Webb Space Telescope, are promising because the detection of Mg II emission and its potential connection with Lyα could provide new insights into the ISM content in the early Universe., Astronomy & Astrophysics, 617, ISSN:0004-6361, ISSN:1432-0746

We trace the formation and advection of several elements within a cosmological adaptive mesh refinement simulation of an L� galaxy. We use nine realizations of the same initial conditions with different stellar initial mass functions (IMFs), mass limits for Type II and Type Ia supernovae (SNII, SNIa) and stellar lifetimes to constrain these subgrid phenomena. Our code includes self-gravity, hydrodynamics, star formation, radiative cooling and feedback from multiple sources within a cosmological framework. Under our assumptions of nucleosynthesis we find that SNII with progenitor masses of up to 100 M� are required to match low-metallicity gas oxygen abundances. Tardy SNIa are necessary to reproduce the classical chemical evolution ‘knee’ in [O/Fe]–[Fe/H]: more prompt SNIa delayed time distributions do not reproduce this feature. Within our framework of hydrodynamical mixing of metals and galaxy mergers we find that chemical evolution is sensitive to the shape of the IMF and that there exists a degeneracy with the mass range of SNII. We look at the abundance plane and present the properties of different regions of the plot, noting the distinct chemical properties of satellites and a series of nested discs that have greater velocity dispersions are more α-rich and metal poor with age.

We examine the chemical properties of 5 cosmological hydrodynamical simulations of an M33-like disc galaxy which have been shown to be consistent with the morphological characteristics and bulk scaling relations expected of late-type spirals. These simulations are part of the Making Galaxies In a Cosmological Context (MaGICC) Project, in which stellar feedback is tuned to match the stellar mass -- halo mass relationship. Each realisation employed identical initial conditions and assembly histories, but differed from one another in their underlying baryonic physics prescriptions, including (a) the efficiency with which each supernova energy couples to the ISM, (b) the impact of feedback associated with massive star radiation pressure, (c) the role of the minimum shut-off time for radiative cooling of Type II SNe remnants, (d) the treatment of metal diffusion, and (e) varying the IMF. Our analysis focusses on the resulting stellar metallicity distribution functions (MDFs) in each simulated (analogous) `solar neighbourhood' and central `bulge' region. We compare the simulated MDFs' skewness, kurtosis, and dispersion (inter-quartile, inter-decile, inter-centile, and inter-tenth-percentile regions) with that of the empirical solar neighbourhood MDF and Local Group dwarfs. We find that the MDFs of the simulated discs are more negatively skewed, with higher kurtosis, than those observed locally. We can trace this difference to the simulations' tight and correlated age-metallicity relations (compared with that of the Milky Way), suggesting that these relations within `dwarf' discs might be steeper than in L* discs and/or the degree of stellar orbital re-distribution and migration inferred locally has not been captured in their entirety, at the resolution of our simulations. The important role of metal diffusion in ameliorating the over-production of extremely metal-poor stars is highlighted.

We investigate the accuracy in the recovery of the stellar dynamics of barred galaxies when using axisymmetric dynamical models. We do this by trying to recover the mass-to-light ratio (M/L) and the anisotropy of realistic galaxy simulations using the Jeans Anisotropic Multi-Gaussian Expansion (JAM) method. However, given that the biases we find are mostly due to an application of an axisymmetric modeling algorithm to a non-axisymmetric system and in particular to inaccuracies in the de-projected mass model, our results are relevant for general axisymmetric modelling methods. We run N-body collisionless simulations to build a library with various luminosity distribution, constructed to mimic real individual galaxies, with realistic anisotropy. The final result of our evolved library of simulations contains both barred and unbarred galaxies. The JAM method assumes an axisymmetric mass distribution, and we adopt a spatially constant M/L and anisotropy beta_z=1-sigma_z^2/sigma_R^2 distributions. The models are fitted to two-dimensional maps of the second velocity moments V_rms=sqrt(V^2+sigma^2) of the simulations for various viewing angles (position angle of the bar and inclination of the galaxy). We find that the inclination is generally well recovered by the JAM models, for both barred and unbarred simulations. For unbarred simulations the M/L is also accurately recovered, with negligible median bias and with a maximum one of just Delta(M/L)

The mass assembly of galaxies leaves imprints in their outskirts, such as shells and tidal tails. The frequency and properties of such fine structures depend on the main acting mechanisms - secular evolution, minor or major mergers - and on the age of the last substantial accretion event. We use this to constrain the mass assembly history of two apparently relaxed nearby Early-Type Galaxies (ETGs) selected from the Atlas-3D sample, NGC 680 and NGC 5557. Our ultra deep optical images obtained with MegaCam on the Canada-France-Hawaii Telescope reach 29 mag/arcsec^2 in the g-band. They reveal very low-surface brightness (LSB) filamentary structures around these ellipticals. Among them, a gigantic 160 kpc long tail East of NGC 5557 hosts gas-rich star-forming objects. NGC 680 exhibits two major diffuse plumes apparently connected to extended HI tails, as well as a series of arcs and shells. Comparing the outer stellar and gaseous morphology of the two ellipticals with that predicted from models of colliding galaxies, we argue that the LSB features are tidal debris, the star-forming objects near NGC 5557, long lived Tidal Dwarf Galaxies and that each of the two ETGs was assembled during a relatively recent, major wet merger, which likely occurred at a redshift below z = 0.5. The inner kinematics of NGC 680 is typical for fast rotators which make the bulk of nearby ETGs in the Atlas-3D sample. NGC 5557 belongs to the poorly populated class of massive, round, slow rotators that are predicted by semi-analytic models and cosmological simulations to be the end-product of a complex mass accretion history, involving ancient major mergers and more recent minor mergers. Our observations suggest that under specific circumstances a single binary merger may dominate the formation history of such objects and thus that at least some massive ETGs may form at relatively low redshift (abridged).

We investigate whether the formation mechanism of boxy and peanut-shaped (B/PS) bulges could depend on the gas content of the galaxy. We have performed N-body simulations with and without a gaseous component. In the second case star formation/feedback recipes have also been implemented to create new stellar populations. As in many previous studies, in our N-body collisionless simulation, the B/PS is due to the classical break in the z mirror symmetry lasting roughly 200 Myr. When a gaseous component and star formation recipes are added to the simulation, the bulge-growing mechanism is quite different. The young stellar population that is born in the thin gaseous disc rapidly populates vertical resonant orbits triggered by the combined effects of the linear horizontal and vertical ILRs. This leads to a B/PS bulge mainly made of stellar material younger than the surrounding population. The non-linear analysis of the orbital structure shows that the main orbit family responsible for the B/PS is not the same in the two cases. The 2:2:1 orbits prevail in the collisionless simulation whereas additional asymmetrical families contribute to the B/PS if a dissipative component is present and can form new stars. We found that 2:3:1 and 2:5:1 orbits trap a significant fraction of the mass. A flat ringed discy stellar component also appears simultaneously with the thickening of the young population. It is due to the star formation in a nuclear gaseous disc located in the central kpc, inside the ILR, and accumulated there by the torques exerted by the large-scale bar. Remarkably, it remains flat throughout the simulation although it develops a nuclear bar, leading to a double-barred galaxy. We predict that two populations of B/PS bulges could exist and even coexist in the same galaxy., 10 pages, 11 Postscript figures, published in A&A

Chemodynamical disc galaxy simulations coupled with stellar populations synthesis models allow to build multi-wavelength images from numerical simulations, and then to follow their morphological evolution in colour and not only on the mass distribution. Using such technique, we present the evolution of several photometric observables, of the Tully-Fisher relation, as well as the evolution of disc structural parameters.

We present a method to constrain galaxy parameters directly from three-dimensional data cubes. The algorithm compares directly the data with a parametric model mapped in $x,y,\lambda$ coordinates. It uses the spectral lines-spread function (LSF) and the spatial point-spread function (PSF) to generate a three-dimensional kernel whose characteristics are instrument specific or user generated. The algorithm returns the intrinsic modeled properties along with both an `intrinsic' model data cube and the modeled galaxy convolved with the 3D-kernel. The algorithm uses a Markov Chain Monte Carlo (MCMC) approach with a nontraditional proposal distribution in order to efficiently probe the parameter space. We demonstrate the robustness of the algorithm using 1728 mock galaxies and galaxies generated from hydrodynamical simulations in various seeing conditions from 0.6" to 1.2". We find that the algorithm can recover the morphological parameters (inclination, position angle) to within 10% and the kinematic parameters (maximum rotation velocity) to within 20%, irrespectively of the PSF in seeing (up to 1.2") provided that the maximum signal-to-noise ratio (SNR) is greater than $\sim3$ pixel$^{-1}$ and that the ratio of the galaxy half-light radius to seeing radius is greater than about 1.5. One can use such an algorithm to constrain simultaneously the kinematics and morphological parameters of (nonmerging) galaxies observed in nonoptimal seeing conditions. The algorithm can also be used on adaptive-optics (AO) data or on high-quality, high-SNR data to look for nonaxisymmetric structures in the residuals., Comment: 16 pages, 10 figures, accepted to publication in AJ, revised version after proofs corrections. Algorithm available at http://galpak.irap.omp.eu

International audience; The relation between the stellar mass (M⋆) and the star formation rate (SFR) characterizes how the instantaneous star formation is determined by the galaxy past star formation history and by the growth of the dark matter structures. We deconstruct the M⋆-SFR plane by measuring the specific SFR functions in several stellar mass bins from z = 0.2 out to z = 1.4 (specific SFR = SFR/M⋆, noted sSFR). Our analysis is primary based on a 24 μm selected catalogue combining the COSMOS and GOODS surveys. We estimate the SFR by combining mid- and far-infrared data for 20500 galaxies. The sSFR functions are derived in four stellar mass bins within the range 9.5 < log (M⋆ /M⊙) < 11.5. First, we demonstrate the importance of taking into account selection effects when studying the M⋆-SFR relation. Secondly, we find a mass-dependent evolution of the median sSFR with redshift varying as sSFR ∝ (1 + z)b, with b increasing from b = 2.88±0.12 to b = 3.78± 0.60 between M⋆ = 109.75 M⊙ and M⋆ = 1011.1 M⊙, respectively. At low masses, this evolution is consistent with the cosmological accretion rate and predictions from semi-analytical models (SAM). This agreement breaks down for more massive galaxies showing the need for a more comprehensive description of the star formation history in massive galaxies. Third, we obtain that the shape of the sSFR function is invariant with time at z< 1.4 but depends on the mass. We observe a broadening of the sSFR function ranging from 0.28 dex at M⋆ = 109.75 M⊙ to 0.46 dex at M⋆ = 1011.1 M⊙. Such increase in the intrinsic scatter of the M⋆-SFR relation suggests an increasing diversity ofstar formation histories (SFHs) as the stellar mass increases. Finally, we find a gradual decline of the sSFR with stellar mass as log 10(sSFR) ∝ −0.17M⋆. We discuss the numerous physical processes, as gas exhaustion in hot gas halos or secular evolution, which can gradually reduce the sSFR and increase the SFH diversity.

We observed the Hubble Deep Field South with the new panoramic integral field spectrograph MUSE that we built and just commissioned at the VLT. The data cube resulting from 27 hours of integration covers one arcmin^2 field of view at an unprecedented depth with a 1 sigma emission line surface brightness limit of 1x$10^{-19}$ erg/s/cm$^2$/arcsec$^2$ and contains ~90,000 spectra. We present the combined and calibrated data cube, and we perform a first-pass analysis of the sources detected in the HDF-S imaging. We measured the redshifts of 189 sources up to a magnitude F814W = 29.5, increasing by more than an order of magnitude the number of known spectroscopic redshifts in this field. We also discovered 26 Lya emitting galaxies which are not detected in the HST WFPC2 deep broad band images. The intermediate spectral resolution of 2.3{\AA} allows us to separate resolved asymmetric Lya emitters, [O II] emitters, and C III] emitters and the large instantaneous wavelength range of 4500{\AA} helps to identify single emission lines. We also show how the three dimensional information of MUSE helps to resolve sources which are confused at ground-based image quality. Overall, secure identifications are provided for 83% of the 227 emission line sources detected in the MUSE data cube and for 32% of the 586 sources identified in the HST catalog of Casertano et al 2000. The overall redshift distribution is fairly flat to z=6.3, with a reduction between z=1.5 to 2.9, in the well-known redshift desert. The field of view of MUSE also allowed us to detect 17 groups within the field. We checked that the number counts of [O II] and Ly-a emitters are roughly consistent with predictions from the literature. Using two examples we demonstrate that MUSE is able to provide exquisite spatially resolved spectroscopic information on intermediate redshift galaxies present in the field., Comment: 21 pages, 20 figures. Note that the catalogues, data cube and associated spectra will be released upon acceptance of the paper

Aims: We examine radial and vertical metallicity gradients using a suite of disk galaxy hydrodynamical simulations, supplemented with two classic chemical evolution approaches. We determine the rate of change of gradient slope and reconcile the differences existing between extant models and observations within the canonical "inside-out" disk growth paradigm. Methods: A suite of 25 cosmological disks is used to examine the evolution of metallicity gradients; this consists of 19 galaxies selected from the RaDES (Ramses Disk Environment Study) sample, realised with the adaptive mesh refinement code ramses, including eight drawn from the "field" and six from "loose group" environments. Four disks are selected from the MUGS (McMaster Unbiased Galaxy Simulations) sample, generated with the smoothed particle hydrodynamics (SPH) code gasoline. Two chemical evolution models of inside-out disk growth were employed to contrast the temporal evolution of their radial gradients with those of the simulations. Results: We first show that generically flatter gradients are observed at redshift zero when comparing older stars with those forming today, consistent with expectations of kinematically hot simulations, but counter to that observed in the Milky Way. The vertical abundance gradients at ~1-3 disk scalelengths are comparable to those observed in the thick disk of the Milky Way, but significantly shallower than those seen in the thin disk. Most importantly, we find that systematic differences exist between the predicted evolution of radial abundance gradients in the RaDES and chemical evolution models, compared with the MUGS sample; specifically, the MUGS simulations are systematically steeper at high-redshift, and present much more rapid evolution in their gradients. Conclusions: We find that the majority of the models predict radial gradients today which are consistent with those observed in late-type disks, but they evolve to this self-similarity in different fashions, despite each adhering to classical "inside-out" growth. We find that radial dependence of the efficiency with which stars form as a function of time drives the differences seen in the gradients; systematic differences in the sub-grid physics between the various codes are responsible for setting these gradients. Recent, albeit limited, data at redshift z ~ 1.5 are consistent with the steeper gradients seen in our SPH sample, suggesting a modest revision of the classical chemical evolution models may be required.

We have carried out 1mm/3mm continuum and 12CO(2−1) line high resolution observations to identify the footprints of AGN feedback on 3C 236. The CO emission comes from a spatially resolved disk characterized by a regular rotating pattern. Within the limits imposed by the sensitivity and velocity coverage of our data, we do not detect any outflow signatures in the cold molecular gas. Re-inspection of optical and IR spectra, shows the presence of a previously unknown ionized gas outflow. The star-formation efficiency in 3C 236, is consistent with the value measured in normal galaxies, which follow the canonical Kennicutt-Schmidt law. This result, confirmed to hold in other young radio sources examined in this work, is in stark contrast with the factor of 10–50 lower SFE that has been claimed to characterize evolved powerful radio galaxies. The recent reactivation of the AGN in 3C 236 is a likely explanation for the early evolutionary status of its molecular disk.

We present an investigation into the origins of a series of interlaced narrow filamentary stellar structures, loops and plumes in the vicinity of the Virgo Cluster, edge-on spiral galaxy, NGC 4216 that were previously identified by the Blackbird Telescope. Using the deeper, higher-resolution and precisely calibrated optical CFHT/MegaCam images obtained as part of the Next Generation Virgo Cluster Survey (NGVS), we confirm the previously identified features and identify a few additional structures. The NGVS data allowed us to make a physical study of these low-surface brightness features and investigate their origin. The likely progenitors of the structures were identified as either already catalogued VCC dwarfs or newly discovered satellites caught in the act of being destroyed. They have the same g-i color index and likely contain similar stellar populations. The alignment of three dwarfs along an apparently single stream is intriguing, and we cannot totally exclude that these are second-generation dwarf galaxies being born inside the filament from the debris of an original dwarf. The observed complex structures, including in particular a stream apparently emanating from a satellite of a satellite, point to a high rate of ongoing dwarf destruction/accretion in the region of the Virgo Cluster where NGC 4216 is located. We discuss the age of the interactions and whether they occurred in a group that is just falling into the cluster and shows signs of so-called "pre-processing" before it gets affected by the cluster environment, or in a group which already ventured towards the central regions of Virgo Cluster., 11 Pages, 7 Figures, 3 Tables, Accepted for publication in ApJ

We report the discovery of a giant HI tail in the intra-group medium of HCG 44 as part of the Atlas3D survey. The tail is ~300 kpc long in projection and contains ~5x10^8 M_sun of HI. We detect no diffuse stellar light at the location of the tail down to ~28.5 mag/arcsec^2 in g band. We speculate that the tail might have formed as gas was stripped from the outer regions of NGC 3187 (a member of HCG 44) by the group tidal field. In this case, a simple model indicates that about 1/3 of the galaxy's HI was stripped during a time interval of, MNRAS, accepted

The mass assembly of galaxies leaves various imprints on their surroundings, such as shells, streams and tidal tails. The frequency and properties of these fine structures depend on the mechanism driving the mass assembly: e.g. a monolithic collapse, rapid cold-gas accretion followed by violent disk instabilities, minor mergers or major dry/wet mergers. Therefore, by studying the outskirts of galaxies, one can learn about their main formation mechanism. I present here our on-going work to characterize the outskirts of Early-Type Galaxies (ETGs), which are powerful probes at low redshift of the hierarchical mass assembly of galaxies. This work relies on ultra–deep optical images obtained at CFHT with the wide-field of view MegaCam camera of field and cluster ETGs obtained as part of the ATLAS3D and NGVS projects. State of the art numerical simulations are used to interpret the data. The images reveal a wealth of unknown faint structures at levels as faint as 29 mag arcsec−2 in the g-band. Initial results for two galaxies are presented here., IAUS 277: Tracing the ancestry of galaxies (on the land of our ancestors), December 13-17, 2010, Ouagadougou, Burkina Faso, Series: Proceedings of the International Astronomical Union

We focus on an analysis of galaxies of high stellar mass and low metallicity. We cross-correlated the Millenium Galaxy Catalogue (MGC) and the Sloan Digital Sky Survey (SDSS) galaxy catalogue to provide a sample of MGC objects with high resolution imaging and both spectroscopic and photometric information available in the SDSS database. For each galaxy in our sample, we conducted a systematic morphological analysis by visual inspection of MGC images using their luminosity contours. The galaxies are classified as either disturbed or undisturbed objects. We divide the sample into three metallicity regions, within wich we compare the properties of disturbed and undisturbed objects. We find that the fraction of galaxies that are strongly disturbed, indicative of being merger remnants, is higher when lower metallicity objects are considered. The three bins analysed consist of approximatively 15%, 20%, and 50% disturbed galaxies (for high, medium, and low metallicity, respectively). Moreover, the ratio of the disturbed to undisturbed relative distributions of the population age indicator, Dn(4000), in the low metallicity bin, indicates that the disturbed objects have substantially younger stellar populations than their undisturbed counterparts. In addition, we find that an analysis of colour distributions provides similar results, showing that low metallicity galaxies with a disturbed morphology are bluer than those that are undisturbed. The bluer colours and younger populations of the low metallicity, morphologically disturbed objects suggest that they have experienced a recent merger with an associated enhanced star formation rate. [abridged], Comment: Astronomy & Astrophysics, in press

Major and minor galaxy mergers form a large number of stellar substructures, ranging from kinematically decoupled cores in the central kpc to faint streams, shells, tails and rings in the far outer regions, as well as massive star clusters. We study the formation of these substructures using cosmological simulations with an efficient zoom‐in technique. We analyze in particular the evolution of substructures, their transient or long‐lived nature, and their survival to subsequent mergers. We also discuss which features can unambiguously probe past mergers, and which ones could have been produced by different evolutionary processes at high redshift. Faint stellar streams are found to be one of the most robust probes of past major and minor mergers. They can survive subsequent mergers, without having their morphological and photometrical properties dramatically modified. The numerous streams surrounding modern early‐type galaxies hence likely trace merger events, and constrain the past occurrence of major and minor mergers, including their age and orbit.

We study the mass-metallicity relation of galaxies in pairs and in isolation taken from the SDSS-DR4 using the stellar masses and oxygen abundances derived by Tremonti et al. (2004). Close galaxy pairs, defined by projected separation r_p < 25kpc/h and radial velocity Delta_V < 350 km/s, are morphologically classified according to the strength of the interaction signs. We find that only for pairs showing signs of strong interactions, the mass-metallicity relation differs significantly from that of galaxies in isolation. In such pairs, the mean gas-phase oxygen abundances of galaxies with low stellar masses (Mstar ~< 10^9 Msun/h) exhibit an excess of 0.2 dex. Conversely, at larger masses (Mstar >~ 10^10 Msun/h) galaxies have a systematically lower metallicity, although with a smaller difference (-0.05 dex). Similar trends are obtained if g-band magnitudes are used instead of stellar masses. In minor interactions, we find that the less massive member is systematically enriched, while a galaxy in interaction with a comparable stellar mass companion shows a metallicity decrement with respect to galaxies in isolation. We argue that metal-rich starbursts triggered by a more massive component, and inflows of low metallicity gas induced by comparable or less massive companion galaxies, provide a natural scenario to explain our findings., Accepted for publication in MNRAS Letters

We report about the fact that the stellar population that is born in the gas inflowing towards the central regions can be vertically unstable leading to a B/PS feature remarkably bluer that the surrounding bulge. Using new chemodynamical simulations we show that this young population does not remain as flat as the gaseous nuclear disc and buckles out of the plane to form a new boxy bulge. We show that such a young B/PS bulge can be detected in colour maps., 2 pages, 5 figures, to appear in IAU Symposium 245, Formation and Evolution of Galaxy Bulges, M. Bureau, E. Athanassoula, and B. Barbuy (eds.), Oxford, 16-20 July 2007

The survey GHASP (Gassendi HAlpha survey of SPirals) will provide a 3-D sample of about 200 nearby spiral galaxies in the Hα line, using a Fabry-Perot system. The data cubes obtained for each galaxy allow to derive line maps, velocity fields and other moment analysis. This data base will allow the following four key ponts.