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We examine the prevalence of truncated star-forming disks in the Virgo cluster down to $M_* \simeq 10^7 ~\text{M}_{\odot}$. This work makes use of deep, high-resolution imaging in the H$\alpha$+[NII] narrow-band from the Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) and optical imaging from the Next Generation Virgo Survey (NGVS). To aid in understanding the effects of the cluster environment on star formation in Virgo galaxies, we take a physically-motivated approach to define the edge of the star-forming disk via a drop-off in the radial specific star formation rate profile. Comparing with the expected sizes of normal galactic disks provides a measure of how truncated star-forming disks are in the cluster. We find that truncated star-forming disks are nearly ubiquitous across all regions of the Virgo cluster, including beyond the virial radius (0.974 Mpc). The majority of truncated disks at large clustercentric radii are of galaxies likely on first infall. As the intra-cluster medium density is low in this region, it is difficult to explain this population with solely ram-pressure stripping. A plausible explanation is that these galaxies are undergoing starvation of their gas supply before ram-pressure stripping becomes the dominant quenching mechanism. A simple model of starvation shows that this mechanism can produce moderate disk truncations within 1-2 Gyr. This model is consistent with `slow-then-rapid' or `delayed-then-rapid' quenching, where the early starvation mode drives disk truncations without significant change to the integrated star formation rate, and the later ram-pressure stripping mode rapidly quenches the galaxy. The origin of starvation may be in the group structures that exist around the main Virgo cluster, which indicates the importance of understanding pre-processing of galaxies beyond the cluster virial radius., Comment: 22 pages, 12 figures, accepted in Astronomy&Astrophysics

We present the first results of a 21 cm HI line pilot observation carried out with MeerKAT in preparation for the ViCTORIA project, an untargeted survey of the Virgo galaxy cluster. The extraordinary quality of the data in terms of sensitivity and angular resolution (rms~0.65 mJy beam^-1 at ~27"x39" and 11 km/s resolution) allowed us to detect an extended (~10 kpc projected length) low column density (N(HI) < 2.5x10^20 cm^-2) HI gas tail associated with the dwarf irregular galaxy NGC4523 at the northern edge of the cluster. The morphology of the tail and of the stellar disc suggest that the galaxy is suffering a hydrodynamic interaction with the surrounding hot intracluster medium (ICM; ram pressure stripping). The orientation of the trailing tail, the gradient in the HI gas column density at the interface between the cold ISM and the hot ICM, the velocity of the galaxy with respect to that of the cluster, and its position indicate that NGC4523 is infalling for the first time into Virgo from the NNW background of the cluster. Using a grid of hydrodynamic simulations we derive the impact parameters with the surrounding ICM, and estimate that the galaxy will be at pericentre (D~500-600 kpc) in ~1 Gyr, where ram pressure stripping will be able to remove most, if not all, of its gas. The galaxy is located on the star formation main sequence when its star formation rate is derived using Halpha images obtained during the VESTIGE survey, suggesting that NGC4523 is only at the beginning of its interaction with the surrounding environment. A few HII regions are detected in the Halpha images within the HI gas tail outside the stellar disc. Their ages, derived by comparing their Halpha, FUV, NUV, and optical colours with the predictions of SED fitting models, are <30 Myr, and suggest that these HII regions have formed within the stripped gas., Comment: Accepted for publication in A&A

We use a complete set of deep narrow-band imaging data for 384 galaxies gathered during the VESTIGE survey to derive the first Halpha luminosity function (LF) of the Virgo cluster within R200. The data allow us to cover the whole dynamic range of the Halpha LF (10^3610^14 Mo. The comparison with the IllustrisTNG cosmological hydrodynamical simulations shows a more pronounced decrease at the faint end of the distribution. If Virgo is representative of typical nearby clusters of similar mass, this difference suggests that the stripping process in simulated galaxies in these environments is more efficient than observed., Comment: Accepted for publication on A&A

Using a compilation of Halpha fluxes for 384 star forming galaxies detected during the VESTIGE survey, we study several important scaling relations for a complete sample of galaxies in a rich environment. The extraordinary sensitivity of the data allows us to sample the whole dynamic range of the Halpha luminosity function, from massive (M*~10^11 Mo) to dwarf systems (M*~10^6 Mo). This extends previous works to a dynamic range in stellar mass and star formation rate (10^-4

Low-surface-brightness galaxies (LSBs) contribute to a significant fraction of all the galaxies in the Universe. Ultra-diffuse galaxies (UDGs) form a subclass of LSBs that has attracted a lot of attention in recent years (although its definition may vary between studies). Although UDGs are found in large numbers in galaxy clusters, groups, and in the field, their formation and evolution are still very much debated. Using a comprehensive set of multiwavelength data from the NGVS (optical), VESTIGE (H$\alpha$ narrowband), and GUViCS (UV) surveys, we studied a sample of 64 diffuse galaxies and UDGs in the Virgo cluster to investigate their formation history. We analyzed the photometric colors and surface-brightness profiles of these galaxies and then compared them to models of galaxy evolution, including ram-pressure stripping (RPS) events to infer any possible strong interactions with the hot cluster gas in the past. While our sample consists mainly of red LSBs, which is typical in cluster environments, we found evidence of a color variation with the cluster-centric distance. Blue, HI-bearing, star-forming diffuse galaxies are found at larger distances from the cluster center than the rest of the sample. The comparison of our models with multifrequency observations suggests that most of the galaxies of the sample might have undergone a strong RPS event in their lifetime, on average 1.6 Gyr ago (with a large dispersion, and RPS still ongoing for some of them). This process resulted in the transformation of initially gas-rich diffuse blue galaxies into gas-poor and red ones that form the dominant population now, the more extreme UDGs having undergone the process in a more distant past on average. The RPS in dense environments could be one of the major mechanisms for the formation of the large number of quiescent UDGs we observe in galaxy clusters., Comment: 57 pages, 14 Figures, accepted for publication in A&A

Using the VESTIGE survey, a deep narrow-band H$\alpha$ imaging survey of the Virgo cluster carried on at the CFHT with MegaCam, we discovered a long diffuse tail of ionised gas in the edge-on late-type galaxy NGC 4330. This peculiar feature witnesses an ongoing ram pressure stripping (RPS) event able to remove the gas in the outer disc region. Tuned hydrodynamic simulations suggest that the RPS event is occurring almost face-on, making NGC 4330 the ideal candidate to study the effects of the perturbation in the direction perpendicular to the disc plane. We present here two new independent sets of Fabry-Perot observations (R$\simeq$10000) in order to understand the effects of the RPS process on the ionised gas kinematics. Despite their limited sensitivity to the diffuse gas emission, the data allowed us to measure the velocity and the velocity dispersion fields over the galaxy disc and in several features at the edges or outside the stellar disc formed after the RPS event. We have constructed the position-velocity diagrams and the rotation curves of the galaxy using three different techniques. The data show, consistent with the hydrodynamic simulations, that the galaxy has an inner solid-body rotation up to $\sim$2.4 kpc, with non-circular streaming motions outwards the disc and in the several external features formed during the interaction of the galaxy with the surrounding intracluster medium. The data also indicate a decrease of the rotational velocity of the gas with increasing distance from the galaxy disc along the tails, suggesting a gradual but not linear loss of angular momentum in the stripped gas. Consistent with a RPS scenario, the $i$-band image shows a boxy shape at the southwest edge of the disc, where the stellar orbits might have been perturbed by the modification of the gravitational potential well of the galaxy due to the displacement of the gas in the $z$-direction., Comment: Accepted for publication on A&A

As part of the VESTIGE survey, a blind narrow-band Ha+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the CFHT, we discovered 8 massive lenticular galaxies with prominent ionised gas emission features in their inner (few kpc) regions. These features are either ionised gas filaments similar to those observed in cooling flows (2 gal), or thin discs with sizes 0.7

The evolution of galaxies depends on their interaction with the surrounding environment. Ultra-diffuse galaxies (UDGs) have been found in large numbers in clusters. We detected a few star-forming blobs in the VESTIGE survey, located at $\sim$5 kpc from a UDG, namely NGVS 3543, in association with an HI gas cloud AGC 226178, suggesting a recent interaction between this low-surface-brightness system and the surrounding cluster environment. We use a complete set of multi-frequency data including deep optical, UV, and narrow-band H${\alpha}$ imaging and HI data to understand the formation process that gave birth to this peculiar system. For this purpose, we measured (i) the multi-wavelength radial surface brightness profiles of NGVS 3543 and compared them to the predictions of spectro-photometric models of galaxy evolution in rich clusters; and (ii) the aperture photometry of the blue regions in the vicinity of NGVS 3543 in order to determine their age and stellar mass. Comparisons of the observations with evolutionary models indicate that NGVS 3543 has undergone a ram-pressure stripping (RPS) that peaked $\sim$100 Myr ago, transforming a blue gas-rich UDG into a red gas-poor UDG. Star formation has taken place in the ram pressure stripped gas, the mass of which is $\sim$10$^8$ M$_{\odot}$, forming star complexes with a typical age of $\sim$20 Myr and a stellar mass of $\sim$10$^4$ M$_{\odot}$. These results suggest that we are observing for the first time the ongoing transformation of a gas-rich UDG into a red and quiescent UDG under the effect of a ram pressure stripping event. The same process could explain the lack of star-forming UDGs in rich environments observed in several nearby clusters., Comment: 20 pages, 11 Figures, accepted for publication in A&A

We study the IB(s)m galaxy IC 3476 observed in the context of VESTIGE, a blind narrow-band Halpha+[NII] imaging survey of the Virgo cluster. The deep narrow-band (NB) image reveals a very pertubed ionised gas distribution, characterised by a prominent banana-shaped structure in the front of the galaxy formed of giant HII regions crossing the stellar disc, with star forming structures at ~8 kpc from the edges of the stellar disc, detected also in a deep FUV ASTROSAT/UVIT image. This particular morphology indicates that the galaxy is undergoing an almost edge-on ram pressure stripping event. The NB image also shows that the star formation activity is totally quenched in the leading edge of the disc, where the gas has been removed during the interaction. The SED fitting analysis indicates that this quenching episode is very recent (~50 Myr), and roughly corresponds to an increase of the star formation activity in the inner regions with respect to what expected for secular evolution. The analysis of these data, whose angular resolution allows the study of the induced effects of the perturbation down to the scale of individual HII regions, also suggests that the increase of the star formation activity is due to the compression of the gas along the stellar disc of the galaxy, which is able to increase its mean electron density and boost the star formation process producing bright HII regions. The hydrodynamic interaction has deeply perturbed the velocity field of the ionised gas component while leaving unaffected that of the stellar disc. The comparison of the data with hydrodynamic simulations accounting for the different gas phases (atomic, molecular, ionised) consistently indicates that the perturbing event is very recent, once again confirming that ram pressure stripping is a violent phenomenon able to perturb on short timescales the evolution of galaxies in rich environments., Comment: Accepted for publication on Astronomy & Astrophysics

NGC 4330 is one of the Virgo galaxies whose UV distribution shows a tail structure. An associated tail structure is also observed in the HI and H$\alpha$ emission distributions. Previous dynamical modeling showed that the galaxy is approaching the cluster center and is therefore undergoing increasing ram pressure stripping. Recent stellar population fitting of deep optical spectra together with multiband photometry lead to the determination of the time when star formation was quenched in the galactic disk. We introduce a new version of the dynamical model that includes the diffuse ionized gas and aim to reproduce the HI, H$\alpha$, UV distributions together with the star formation histories of the outer gas-free parts of the galactic disk. The results of 50 simulations with five different Lorentzian temporal ram-pressure profiles and five different delays between the simulation onset and peak ram pressure are presented. The inclusion of diffuse gas stripping changes significantly the HI, UV, and H$\alpha$ emission distributions. The simulations with diffuse gas stripping naturally lead to vertical low surface density filaments in the downwind region of the galactic disk. These filaments occur less frequently in the simulations without diffuse gas stripping. The simulations with diffuse gas stripping lead to better joint fits to the SEDs and optical spectra. The HI, NUV, and H$\alpha$ morphologies of the model snapshots which best reproduce the SEDs and optical spectra are sufficiently different to permit a selection of best-fit models. We conclude that the inclusion of diffuse gas stripping significantly improves the resemblance between the model and observations. Our preferred model yields a time to peak ram pressure of 140 Myr in the future. The spatial coincidence of the radio continuum and diffuse H$\alpha$ tails suggests that both gas phases are stripped together., Comment: accepted for publication in A&A

The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band Halpha+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the Canada-French-Hawaii telescope (CFHT). We use a new set of data extracted from VESTIGE to study the impact of the hostile cluster environment on the star formation process down to the scale of HII regions (~ 50 pc). HII regions are identified and their parameters measured using the HIIphot code on a sample of 114 late-type galaxies spanning a wide range in morphological type (Sa-Sd, Im, BCD), stellar mass (10^6.5 <= M_star <= 10^11 Mo), and star formation activity (10^-3 <= SFR <= 10 Mo yr^-1). Owing to the exquisite average resolution of the VESTIGE data (0.65 arcsec), we detect 11302 HII regions with an Halpha luminosity L(Halpha) >= 10^37 erg s^-1. We show that the typical number of HII regions in gas-stripped objects is significantly lower than in healthy late-types of similar stellar mass. We also show that in these gas-stripped galaxies the number of HII regions significantly drops outside the effective radius, suggesting that the quenching process occurs outside-in, in agreement with other multifrequency observations. These new results consistently confirm that the main mechanism responsible for the decrease of the star formation activity observed in cluster galaxies is ram pressure, allowing us to discard other milder processes such as starvation or strangulation unable to reproduce the observed radially truncated profiles., Comment: Accepted for publication on A&A Letter

We have observed the giant elliptical galaxy M87 during the Virgo Environmental Survey Tracing Galaxy Evolution (VESTIGE), a blind narrow-band Halpha+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the Canada French Hawaii Telescope (CFHT). The deep narrow-band image confirmed the presence of a filament of ionised gas extending up to ~ 3 kpc in the north-western direction and ~ 8 kpc to the south-east, with a couple of plumes of ionised gas, the weakest of which, at ~ 18 kpc from the nucleus, was previously unknown. The analysis of deep optical images taken from the NGVS survey confirms that this gas filament is associated with dust seen in absorption which is now detected up to ~ 2.4 kpc from the nucleus. We have also analysed the physical and kinematical properties of the ionised gas filament using deep IFU MUSE data covering the central 4.8 x 4.8 kpc^2 of the galaxy. The spectroscopic data confirms a perturbed kinematics of the ionised gas, with differences in velocity of ~ 700-800 km s^-1 on scales of < 1 kpc. The analysis of 2D diagnostic diagrams and the observed relationship between the shock-sensitive [OI]/Halpha line ratio and the velocity dispersion of the gas suggest that the gas is shock-ionised., Comment: Accepted for publication to Astronomy & Astrophysics

We have observed the late-type peculiar galaxy NGC 4424 during VESTIGE, a blind narrow-band Halpha[NII] imaging survey of the Virgo cluster carried out with MegaCam at the CFHT. The presence of a 110 kpc long HI tail in the S direction indicates that this galaxy is undergoing a ram pressure stripping event. The deep narrow-band image revealed the presence of a low surface brightness ionised gas tail ~10 kpc long extending from the centre of the galaxy to the NW direction, in the direction opposite to the HI tail. Chandra and XMM X-rays data do not show any compact source in the nucleus nor the presence of an extended tail of hot gas, while MUSE spectroscopy indicates that the gas is photo-ionised in the inner regions and shock-ionised in the outer parts. IFU spectroscopy confirms that the ionised gas is kinematically decoupled from the stellar component and indicates the presence of two kinematically distinct structures in the stellar disc. The analysis of the SED of the galaxy indicates that the activity of star formation has been totally quenched in the outer disc ~ 250-280 Myr ago, while only reduced by ~80% in the central regions. All this observational evidence suggests that NGC 4424 is the remnant of an unequal-mass merger occurred <= 500 Myr ago, when the galaxy was already a member of the Virgo cluster, now undergoing a ram pressure stripping event which has removed the gas and quenched the activity of star formation in the outer disc. The tail of ionised gas probably results from the outflow produced by a central starburst fed by the collapse of gas induced by the merging episode. This outflow is sufficiently powerful to overcome the ram pressure induced by the intracluster medium on the disc of the galaxy crossing the cluster. This analysis thus suggests that feedback can participate in the quenching process of galaxies in high-density regions., Comment: Accepted for publication on Astronomy & Astrophysics

During pilot observations of the Virgo Environmental Survey Tracing Galaxy Evolution (VESTIGE), a blind narrow-band Halpha+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the CFHT, we have observed the spiral galaxy NGC 4254 (M99). Deep Halpha+[NII] narrow-band and GALEX UV images revealed the presence of 60 compact (70-500 pc radius) star forming regions up to ~ 20 kpc outside the optical disc of the galaxy. These regions are located along a tail of HI gas stripped from the disc of the galaxy after a rapid gravitational encounter with another Virgo cluster member that simulations indicate occurred 280-750 Myr ago. We have combined the VESTIGE data with multifrequency data from the UV to the far-infrared to characterise the stellar populations of these regions and study the star formation process in an extreme environment such as the tails of stripped gas embedded in the hot intracluster medium. The colour, spectral energy distribution (SED), and linear size consistently indicate that these regions are coeval and have been formed after a single burst of star formation that occurred ~< 100 Myr ago. These regions might become free floating objects within the cluster potential well, and be the local analogues of compact sources produced after the interaction of gas-rich systems that occurred during the early formation of clusters., Comment: Accepted for publication on Astronomy & Astrophysics

The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band Halpha+[NII] imaging survey carried out with MegaCam at the Canada-France-Hawaii Telescope. The survey covers the whole Virgo cluster region from its core to one virial radius (104 deg^2). The sensitivity of the survey is of f(Halpha) ~ 4 x 10^-17 erg sec-1 cm^-2 (5 sigma detection limit) for point sources and Sigma (Halpha) ~ 2 x 10^-18 erg sec^-1 cm^-2 arcsec^-2 (1 sigma detection limit at 3 arcsec resolution) for extended sources, making VESTIGE the deepest and largest blind narrow-band survey of a nearby cluster. This paper presents the survey in all its technical aspects, including the survey design, the observing strategy, the achieved sensitivity in both the narrow-band Halpha+[NII] and in the broad-band r filter used for the stellar continuum subtraction, the data reduction, calibration, and products, as well as its status after the first observing semester. We briefly describe the Halpha properties of galaxies located in a 4x1 deg^2 strip in the core of the cluster north of M87, where several extended tails of ionised gas are detected. This paper also lists the main scientific motivations of VESTIGE, which include the study of the effects of the environment on galaxy evolution, the fate of the stripped gas in cluster objects, the star formation process in nearby galaxies of different type and stellar mass, the determination of the Halpha luminosity function and of the Halpha scaling relations down to ~ 10^6 Mo stellar mass objects, and the reconstruction of the dynamical structure of the Virgo cluster. This unique set of data will also be used to study the HII luminosity function in hundreds of galaxies, the diffuse Halpha+[NII] emission of the Milky Way at high Galactic latitude, and the properties of emission line galaxies at high redshift., Comment: Accepted for publication on Astronomy & Astrophysics

The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band H$\alpha$+[NII] imaging survey carried out with MegaCam at the CFHT. During pilot observations we have observed NGC 4330, an intermediate mass, edge-on star forming spiral currently falling into the core of the Virgo cluster. New deep observations revealed a low surface brightness 10 kpc tail exhibiting a peculiar filamentary structure. The filaments are remarkably parallel one another and clearly indicate the direction of motion of the galaxy in the Virgo potential. Motivated by the detection of these features, indicating ongoing gas stripping, we collected literature photometry in 15 bands from the far-UV to the far-IR and deep optical long slit spectroscopy using the FORS2 instrument at the ESO Very Large Telescope. Using a newly developed Monte Carlo code that jointly fits spectroscopy and photometry, we reconstructed the star formation histories in apertures along the major axis of the galaxy. Our results have been validated against the output of CIGALE, a fitting code which has been previously used for similar studies. We found a clear outside-in gradient with radius of the time when the quenching event started: the outermost radii have been stripped 500 Myr ago, while the stripping has reached the inner 5 kpc from the center in the last 100 Myr. Regions at even smaller radii are currently still forming stars fueled by the presence of HI and H2 gas. When compared to statistical studies of the quenching timescales in the local Universe we find that ram pressure stripping of the cold gas is an effective mechanism to reduce the transformation times for galaxies falling into massive clusters. Future systematic studies of all the active galaxies observed by VESTIGE in the Virgo cluster will extend these results to a robust statistical framework., Comment: 17 pages, 10 figures, 2 tables, A&A in press

We determine abundance ratios of 37 dwarf ellipticals (dEs) in the nearby Virgo cluster. This sample is representative of the early-type population of galaxies in the absolute magnitude range -19.0 < Mr < -16.0. We analyze their absorption line-strength indices by means of index-index diagrams and scaling relations and use the stellar population models to interpret them. We present ages, metallicities and abundance ratios obtained from these dEs within an aperture size of Re/8. We calculate [Na/Fe] from NaD, [Ca/Fe] from Ca4227 and [Mg/Fe] from Mgb. We find that [Na/Fe] is under-abundant with respect to solar while [Mg/Fe] is around solar. This is exactly opposite to what is found for giant ellipticals, but follows the trend with metallicity found previously for the Fornax dwarf NGC 1396. We discuss possible formation scenarios that can result in such elemental abundance patterns and we speculate that dEs have disk-like SFH favouring them to originate from late-type dwarfs or small spirals. Na-yields appear to be very metal-dependent, in agreement with studies of giant ellipticals, probably due to the large dependence on the neutron-excess in stars. We conclude that dEs have undergone a considerable amount of chemical evolution, they are therefore not uniformly old, but have extended SFH, similar to many of the Local Group galaxies., Comment: 15 pages, 5 figures; accepted for publication in MNRAS

We obtained using MegaCam at the CFHT a deep narrow band Halpha+[NII] wide field image of NGC 4569, the brightest late-type galaxy in the Virgo cluster. The image reveals the presence of long tails of diffuse ionised gas without any associated stellar component extending from the disc of the galaxy up to ~ 80 kpc (projected distance) with a typical surface brightness of a few 10^-18 erg s-1 cm-2 arcsec-2. These features provide direct evidence that NGC 4569 is undergoing a ram presure stripping event. The image also shows a prominent 8 kpc spur of ionised gas associated to the nucleus that spectroscopic data identify as an outflow. With some assumptions on the 3D distribution of the gas, we use the Halpha surface brightness of these extended low surface brightness features to derive the density and the mass of the gas stripped during the interaction of the galaxy with the ICM. The comparison with ad-hoc chemo-spectrophotometric models of galaxy evolution indicates that the mass of the Halpha emitting gas in the tail is comparable to that of the cold phase stripped from the disc, suggesting that the gas is ionised within the tail during the stripping process. The lack of star forming regions suggests that mechanisms other than photoionisation are responsible for the excitation of the gas (shocks, heat conduction, magneto hydrodynamic waves). This analysis indicates that ram pressure stripping is efficient in massive (M_star ~ 10^10.5 Mo) galaxies located in intermediate mass (~ 10^14 Mo) clusters under formation. It also shows that the mass of gas expelled by the nuclear outflow is ~ 1 % than that removed during the ram pressure stripping event. All together these results indicate that ram pressure stripping, rather than starvation through nuclear feedback, can be the dominant mechanism responsible for the quenching of the star formation activity of galaxies in high density environments., Comment: Accepted for publication on Astronomy & Astrophysics

Photoionization modelling allows to follow the transport, the emergence, and the absorption of photons taking into account all important processes in nebular plasmas. Such modelling needs the spatial distribution of density, chemical abundances and temperature, that can be provided by chemo-dynamical simulations (ChDS) of dwarf galaxies. We perform multicomponent photoionization modelling (MPhM) of the ionized gas using 2-D ChDSs of dwarf galaxies. We calculate emissivity maps for important nebular emission lines. Their intensities are used to derive the chemical abundance of oxygen by the so-called Te- and R23-methods. Some disagreements are found between oxygen abundances calculated with these methods and the ones coming from the ChDSs. We investigate the fraction of ionizing radiation emitted in the star-forming region which is able to leak out the galaxy. The time- and direction-averaged escape fraction in our simulation is 0.35-0.4. Finally, we have calculated the total Halpha lumi- nosity of our model galaxy using Kennicutt's calibration to derive the star-formation rate. This value has been compared to the 'true' rate in the ChDSs. The Halpha-based star-formation rate agrees with the true one only at the beginning of the simulation. Minor deviations arise later on and are due in part to the production of high-energy photons in the warm-hot gas, in part to the leakage of energetic photons out of the galaxy. The effect of artificially introduced thin dense shells (with thicknesses smaller than the ChDSs spatial resolution) is investigated, as well., Comment: 17 pages, 14 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society

We analyze the stellar kinematics of 39 dwarf early-type galaxies (dEs) in the Virgo cluster. Based on the specific stellar angular momentum lambda_e and the ellipticity, we find 11 slow rotators and 28 fast rotators. The fast rotators in the outer parts of the Virgo cluster rotate significantly faster than fast rotators in the inner parts of the cluster. Moreover, 10 out of the 11 slow rotators are located in the inner 3 degrees (D < 1 Mpc) of the cluster. The fast rotators contain subtle disky structures that are visible in high-pass filtered optical images, while the slow rotators do not exhibit these structures. In addition, two of the dEs have kinematically decoupled cores and four more have emission partially filling in the Balmer absorption lines. These properties suggest that Virgo cluster dEs may have originated from late-type star-forming galaxies that were transformed by the environment after their infall into the cluster. The correlation between lambda_e and the clustercentric distance can be explained by a scenario where low luminosity star-forming galaxies fall into the cluster, their gas is rapidly removed by ram pressure stripping, although some of it can be retained in their core, their star-formation is quenched but their stellar kinematics are preserved. After a long time in the cluster and several passes through its center, the galaxies are heated up and transformed into slow rotating dEs., Comment: Submitted to ApJ. Referee's comments included. 13 pages, 8 figures, 1 table

We present spatially resolved kinematics and global stellar populations and mass-to-light ratios for a sample of 39 dwarf early-type (dE) galaxies in the Virgo cluster studied as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey. This sample is representative of the early-type population in the absolute magnitude range -19.0 < M_r < -16.0. For each dE, we measure the rotation curve and velocity dispersion profile and fit an analytic function to the rotation curve. We study the significance of the departure of the rotation curve from the best fit analytic function (poorly fit) and of the difference between the approaching and receding sides of the rotation curve (asymmetry). We find that 62 +/- 8 % (23 out of the 39) of the dEs have a significant anomaly in their rotation curve. Analysis of the images reveals photometric anomalies for most galaxies. However, there is no clear correlation between the significance of the photometric and kinematic anomalies. We measure age-sensitive and metallicity-sensitive Lick spectral indices and find a wide range of ages and metallicities. We also find that 4 dEs have emission partially filling in the Balmer absorption lines. Finally, we estimate the total masses and dark matter fractions of the dEs. They have a median total mass and dark matter fraction within the Re of log Me = 9.1 +/- 0.2 and f_DM = 46 +/- 18 %. We plot several scaling relations and show that dEs seem to be the bridge between massive early-type and dwarf spheroidal galaxies., Comment: Accepted for publication in ApJS. 49 pages, 71 figures, 8 tables

We present evidence for kinematically decoupled cores (KDCs) in two dwarf early-type (dE) galaxies in the Virgo cluster, VCC 1183 and VCC 1453, studied as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey. These KDCs have radii of 1.8'' (0.14 kpc) and 4.2'' (0.33 kpc), respectively. Each of these KDCs is distinct from the main body of its host galaxy in two ways: (1) inverted sense of rotation; and (2) younger (and possibly more metal-rich) stellar population. The observed stellar population differences are probably associated with the KDC, although we cannot rule out the possibility of intrinsic radial gradients in the host galaxy. We describe a statistical analysis method to detect, quantify the significance of, and characterize KDCs in long-slit rotation curve data. We apply this method to the two dE galaxies presented in this paper and to five other dEs for which KDCs have been reported in the literature. Among these seven dEs, there are four significant KDC detections, two marginal KDC detections, and one dE with an unusual central kinematic anomaly that may be an asymmetric KDC.The frequency of occurence of KDCs and their properties provide important constraints on the formation history of their host galaxies. We discuss different formation scenarios for these KDCs in cluster environments and find that dwarf-dwarf wet mergers or gas accretion can explain the properties of these KDCs. Both of these mechanisms require that the progenitor had a close companion with a low relative velocity. This suggests that KDCs were formed in galaxy pairs residing in a poor group environment or in isolation whose subsequent infall into the cluster quenched star formation., Comment: 14 pages, accepted for publication in ApJ

We present high-resolution simulations of tidal dwarf galaxies (TDG) to investigate their early chemo-dynamical evolution and test their survivability. In this work the simulation setup is introduced and the response of TDGs to self-consistent star formation (SF) and an external tidal field is examined. Throughout the simulation star cluster particles with variable masses down to $5\,M_{\odot}$ form, depending on the local gas reservoir. For low cluster masses $M_{\mathrm{cl}}$, the stellar initial mass function (IMF) is considered to be either filled or truncated at a maximal star mass $m_\mathrm{max}$ to represent the observed $m_{\mathrm{max}} - M_{\mathrm{cl}}$ relation (IGIMF theory). The evolution of TDGs with fully-populated and truncated IMFs are compared to study the impact of stellar energy feedback on their survivability. Both TDGs experience an initial starburst but after a dynamical time they evolve into dwarf galaxies with self-regulated and continuous SF. At this stage the truncated-IMF model contains about 6 times more stellar mass than the invariant IMF models, but the final bound gas mass is comparable in both models. In spite of their significantly different SF histories, both TDG models are not disrupted within the first 500 Myr. We conclude that TDGs can survive an early starburst, independent of the underlying IMF description, even though they do not harbor a stabilizing dark matter halo., Comment: 16 pages, 12 figures, accepted for publication in MNRAS

The fraction of star-forming to quiescent dwarf galaxies varies from almost infinity in the field to zero in the centers of rich galaxy clusters. What is causing this pronounced morphology-density relation? What do quiescent dwarf galaxies look like when studied in detail, and what conclusions can be drawn about their formation mechanism? Here we study a nearly magnitude-complete sample (-19 < M_r < -16 mag) of 121 Virgo cluster early types with deep near-infrared images from the SMAKCED project. We fit two-dimensional models with optional inner and outer components, as well as bar and lens components (in ~15% of the galaxies), to the galaxy images. While a single S\'ersic function may approximate the overall galaxy structure, it does not entirely capture the light distribution of two-thirds of our galaxies, for which multi-component models provide a better fit. This fraction of complex galaxies shows a strong dependence on luminosity, being larger for brighter objects. We analyze the global and component-specific photometric scaling relations of early-type dwarf galaxies and discuss similarities with bright early and late types. The dwarfs' global galaxy parameters show scaling relations that are similar to those of bright disk galaxies. The inner components are mostly fitted with S\'ersic n values close to 1. At a given magnitude they are systematically larger than the bulges of spirals, suggesting that they are not ordinary bulges. We argue that the multi-component structures in early-type dwarfs are mostly a phenomenon inherent to the disks, and may indeed stem from environmental processing., Comment: Accepted for publication in ApJS, 34 pages, 30 figures. Online figures: http://www.smakced.net/data.html

Energetic feedback from Supernovae and stellar winds can drive galactic winds. Dwarf galaxies, due to their shallower potential wells, are assumed to be more vulnerable to this phenomenon. Metal loss through galactic winds is also commonly invoked to explain the low metal content of dwarf galaxies. Our main aim in this paper is to show that galactic mass cannot be the only parameter determining the fraction of metals lost by a galaxy. In particular, the distribution of gas must play an equally important role. We perform 2-D chemo-dynamical simulations of galaxies characterized by different gas distributions, masses and gas fractions. The gas distribution can change the fraction of lost metals through galactic winds by up to one order of magnitude. In particular, disk-like galaxies tend to loose metals more easily than roundish ones. Consequently, also the final metallicities attained by models with the same mass but with different gas distributions can vary by up to one dex. Confirming previous studies, we also show that the fate of gas and freshly produced metals strongly depends on the mass of the galaxy. Smaller galaxies (with shallower potential wells) more easily develop large-scale outflows, therefore the fraction of lost metals tends to be higher., Comment: 13 pages, 11 figures, accepted for publication on Astronomy and Astrophysics

Several scenarios have been suggested to explain the phase-space distribution of the Milky Way (MW) satellite galaxies in a disc of satellites (DoS). To quantitatively compare these different possibilities, a new method analysing angular momentum directions in modelled data is presented. It determines how likely it is to find sets of angular momenta as concentrated and as close to a polar orientation as is observed for the MW satellite orbital poles. The method can be easily applied to orbital pole data from different models. The observed distribution of satellite orbital poles is compared to published angular momentum directions of subhalos derived from six cosmological state-of-the-art simulations in the Aquarius project. This tests the possibility that filamentary accretion might be able to naturally explain the satellite orbits within the DoS. For the most likely alignment of main halo and MW disc spin, the probability to reproduce the MW satellite orbital pole properties turns out to be less than 0.5 per cent in Aquarius models. Even an isotropic distribution of angular momenta has a higher likelihood to produce the observed distribution. The two Via Lactea cosmological simulations give results similar to the Aquarius simulations. Comparing instead with numerical models of galaxy-interactions gives a probability of up to 90 per cent for some models to draw the observed distribution of orbital poles from the angular momenta of tidal debris. This indicates that the formation as tidal dwarf galaxies in a single encounter is a viable, if not the only, process to explain the phase-space distribution of the MW satellite galaxies., Comment: 14 pages, 4 figures, 3 tables. Accepted for publication in MNRAS

Early-type dwarf galaxies, once believed to be simple systems, have recently been shown to exhibit an intriguing diversity in structure and stellar content. To analyze this further, we started the SMAKCED project, and obtained deep H-band images for 101 early-type dwarf galaxies in the Virgo cluster in a brightness range of -19 \leq M_r \leq -16 mag, typically reaching a signal-to-noise of 1 per pixel of \sim0.25" at surface brightnesses \sim22.5 mag/arcsec^2 in the H-band. Here we present the first results of decomposing their two-dimensional light distributions. This is the first study dedicated to early-type dwarf galaxies using the two-dimensional multi-component decomposition approach, which has been proven to be important for giant galaxies. Armed with this new technique, we find more structural components than previous studies: only a quarter of the galaxies fall into the simplest group, namely those represented by a single S\'ersic function, optionally with a nucleus. Furthermore, we find a bar fraction of 18%. We detect also a similar fraction of lenses which appear as shallow structures with sharp outer edges. Galaxies with bars and lenses are found to be more concentrated towards the Virgo galaxy center than the other sample galaxies., Comment: Accepted by ApJL, 6 pages, 4 figures, 1 table

(abridged) Predictions of the Concordance Cosmological Model (CCM) of the structures in the environment of large spiral galaxies are compared with observed properties of Local Group galaxies. Five new most probably irreconcilable problems are uncovered. However, the Local Group properties provide hints that may lead to a solution of the above problems The DoS and bulge--satellite correlation suggest that dissipational events forming bulges are related to the processes forming phase-space correlated satellite populations. Such events are well known to occur since in galaxy encounters energy and angular momentum are expelled in the form of tidal tails, which can fragment to form populations of tidal-dwarf galaxies (TDGs) and associated star clusters. If Local Group satellite galaxies are to be interpreted as TDGs then the sub-structure predictions of CCM are internally in conflict. All findings thus suggest that the CCM does not account for the Local Group observations and that therefore existing as well as new viable alternatives have to be further explored. These are discussed and natural solutions for the above problems emerge., Comment: A and A, in press, 25 pages, 9 figures; new version contains minor text adjustments for conformity with the published version and additional minor changes resulting from reader's feedback. The speculation on a dark force has been added. Also, the Fritz Zwicky Paradox is now included to agree with the published version

In the light of the question whether most early-type dwarf (dE) galaxies in clusters formed through infall and transformation of late-type progenitors, we search for an imprint of such an infall history in the oldest, most centrally concentrated dE subclass of the Virgo cluster: the nucleated dEs that show no signatures of disks or central residual star formation. We select dEs in a (projected) region around the central elliptical galaxies, and subdivide them by their line-of-sight velocity into fast-moving and slow-moving ones. These subsamples turn out to have significantly different shapes: while the fast dEs are relatively flat objects, the slow dEs are nearly round. Likewise, when subdividing the central dEs by their projected axial ratio into flat and round ones, their distributions of line-of-sight velocities differ significantly: the flat dEs have a broad, possibly two-peaked distribution, whereas the round dEs show a narrow single peak. We conclude that the round dEs probably are on circularized orbits, while the flat dEs are still on more eccentric or radial orbits typical for an infalling population. In this picture, the round dEs would have resided in the cluster already for a long time, or would even be a cluster-born species, explaining their nearly circular orbits. They would thus be the first generation of Virgo cluster dEs. Their shape could be caused by dynamical heating through repeated tidal interactions. Further investigations through stellar population measurements and studies of simulated galaxy clusters would be desirable to obtain definite conclusions on their origin., Comment: Accepted by ApJL, 6 pages, 4 figures. The astro-ph version includes the galaxy images as Fig. A1 for illustration purposes

We study the effects of clouds on the dynamical and chemical evolution of gas-rich dwarf galaxies, in particular focusing on two model galaxies similar to IZw18 and NGC1569. We consider both scenarios, clouds put at the beginning of the simulation and continuously created infalling ones. Due to dynamical processes and thermal evaporation, the clouds survive only a few tens of Myr, but during this time they act as an additional cooling agent and the internal energy of cloudy models is typically reduced by 20 - 40% in comparison with models without clouds. The clouds delay the development of large-scale outflows, therefore helping to retain a larger amount of gas inside the galaxy. However, especially in models with continuous creation of infalling clouds, their bullet effect can pierce the expanding supershell and create holes through which the superbubble can vent freshly produced metals. Moreover, assuming a pristine chemical composition for the clouds, their interaction with the superbubble dilutes the gas, reducing the metallicity (by up to ~ 0.4 dex) with respect to the one attained by diffuse models., Comment: 3 pages, 3 figures, to be published in Astronomische Nachrichten (proceedings of Symposium 6 of the JENAM 2008, Vienna)

Ram pressure stripping, i.e. the removal of a galaxy's gas disk due to its motion through the intracluster medium of a galaxy cluster, appears to be a common phenomenon. Not every galaxy, however, is completely stripped of its gas disk. If the ram pressure is insufficiently strong, only the outer parts of the gas disk are removed, and the inner gas disk is retained by the galaxy. One example of such a case is the Virgo spiral NGC 4402. Observations of NGC 4402 (Crowl et al. 2005) reveal structures at the leading edge of the gas disk, which resemble the characteristic finger-like structures produced by the Rayleigh-Taylor (RT) instability. We argue, however, that the RT instability is unlikely to be responsible for these structures. We demonstrate that the conditions under which a galaxy's disk gas experiences ram pressure stripping are identical to those that lead to RT instability. If the galaxy's gravity prevents ram pressure stripping of the inner disk, it also prevents the RT instability. In contrast, the stripped gas could still be subject to RT instability, and we discuss consequences for the stripped gas., Comment: accepted by A&A

(Abridged) We study the effects of interstellar clouds on the dynamical and chemical evolution of gas-rich dwarf galaxies. In particular, we focus on two model galaxies similar to IZw18 and NGC1569 in comparison to models in which a smooth initial distribution of gas is assumed. We use a 2-D hydrodynamical code coupled with a series of routines able to trace the chemical products of SNeII, SNeIa and intermediate-mass stars. Clouds are simulated by adding overdense regions in the computational grid, whose locations are chosen randomly and whose density profiles match observed ones. The clouds are inherently dynamically coupled to the diffuse gas, and they experience heat conduction from a hot surrounding gas. Due to dynamical processes and thermal evaporation, the clouds survive only a few tens of Myr. Due to the additional cooling agent, the internal energy of cloudy models is typically reduced by 20 - 40% compared with models of diffuse gas alone. The clouds delay the development of large-scale outflows by mass loading, therefore helping to retain a larger amount of gas inside the galaxy. However, their bullet effect can pierce the expanding supershell and create holes through which the superbubble can vent freshly produced metals. Moreover, assuming a pristine chemical composition for the clouds, their interaction with the superbubble dilutes the gas, reducing the metallicity. The resulting final metallicity is therefore generally lower (by ~ 0.2 - 0.4 dex) than the one attained by diffuse models., Comment: 13 pages, 11 figures, A&A accepted

Shortened version: The fate of IS clouds embedded in a hot tenuous medium depends on whether the clouds suffer from evaporation or whether material condensates onto them. Analytical solutions for the rate of evaporative mass loss from an isolated spherical cloud embedded in a hot tenuous gas are deduced by Cowie & McKee (1977). In order to test the validity of the analytical results for more realistic IS conditions the full hydrodynamical equations must be treated. Therefore, 2D numerical simulations of the evolution of IS clouds %are performed with different internal density structures and surrounded by a hot plasma reservoir. Self-gravity, interstellar heating and cooling effects and heat conduction by electrons are added. Classical thermal conductivity of a fully ionized hydrogen plasma and saturated heat flux are considered. Using pure hydrodynamics and classical heat flux we can reproduce the analytical results. Heat flux saturation reduces the evaporation rate by one order of magnitude below the analytical value. The evolution changes totally for more realistic conditions when interstellar heating and cooling effects stabilize the self-gravity. Evaporation then turns into condensation, because the additional energy by heat conduction can be transported away from the interface and radiated off efficiently from the cloud's inner parts. I.e. that the saturated heat flux consideration is inevitable for IS clouds embedded in hot tenuous gas. Various consequences are discussed in the paper., Comment: 16 pages, 24 figures, accepted in Astronomy and Astrophysics

Context: Dwarf galaxies can arise from self-gravitating structures emerging from tidal tails. What fraction of the known dwarf galaxies in the Local Universe can have this origin is still a matter of debate. Aims: In our effort to understand the origin and evolution of tidal dwarf galaxies and their correspondence with local objects, the first step is to understand how these galaxies (which are supposed to have a limited amount of dark matter) react to the feedback of the ongoing star formation. Methods: We make use of 2-D chemodynamical calculations in order to study the early evolution of isolated, dark matter-free dwarf galaxies. We present models in which feedback parameters are varied. We also compare the results with dark matter-dominated dwarf galaxy models. Results: All the considered models show that the star formation proceeds for more than 300 Myr, therefore dwarf galaxies without large dark matter halos are not necessarily quickly destroyed. The chemical evolution of these objects is consistent with the main chemical properties of the dSphs of the Local Group. Models with large dark matter halos show results consistent with models free of dark matter, indicating that the distribution of gas is more important than the depth of the potential well in determining the global behaviour of dSph-sized dwarf galaxies., Comment: 4 pages, 4 figures, accepted for publication in A&A Letters

To examine the evolution of giant molecular clouds in the stream of a hot plasma we performed two-dimensional hydrodynamical simulations that take full account of self-gravity, heating and cooling effects and heat conduction by electrons. We use the thermal conductivity of a fully ionized hydrogen plasma proposed by Spitzer and a saturated heat flux according to Cowie & McKee in regions where the mean free path of the electrons is large compared to the temperature scaleheight. Significant structural and evolutionary differences occur between simulations with and without heat conduction. Dense clouds in pure dynamical models experience dynamical destruction by Kelvin-Helmholtz (KH) instability. In static models heat conduction leads to evaporation of such clouds. Heat conduction acting on clouds in a gas stream smooths out steep temperature and density gradients at the edge of the cloud because the conduction timescale is shorter than the cooling timescale. This diminishes the velocity gradient between the streaming plasma and the cloud, so that the timescale for the onset of KH instabilities increases, and the surface of the cloud becomes less susceptible to KH instabilities. The stabilisation effect of heat conduction against KH instability is more pronounced for smaller and less massive clouds. As in the static case more realistic cloud conditions allow heat conduction to transfer hot material onto the cloud's surface and to mix the accreted gas deeper into the cloud., Comment: 19 pages, 12 figures, accepted in Astronomy and Astrophysics

Due to their low gravitational energies, dwarf galaxies are greatly exposed to energetical influences from internal and external sources. By means of chemodynamical models we show that their star formation is inherently self-regulated, that peculiar abundance ratios can only be achieved assuming different star-formation episodes and that evaporation of interstellar clouds embedded in a hot phase can lead to a fast mixing of the interstellar gas. Metal-enriched hot outflows can accrete onto infalling clouds by means of condensation leading to a large range of timescales for the self-enrichment of the ISM from local scales within a few tens of Myr up to a few Gyr for the large-range circulation. Infall of clouds is also required to explain abundance ratios of metal-poor galaxies at evolved stages because it reduces the metallicity altering only marginally the abundance ratios., Comment: 6 pages, 2 figures, to appear in the Proceedings of the CRAL conference "Chemodynamics: from first stars to local galaxies", Lyon, France, 10-14 July 2006

Our aim is to study the evolution of tidal dwarf galaxies. The first step is to understand whether a model galaxy without Dark Matter can sustain the feedback of the ongoing star formation. We present tests of the evolution of models in which star formation efficiency, temperature threshold, initial distribution of gas and infall are varied. We conclude that it is feasible to keep a fraction of gas bound for several hundreds of Myr and that the development of galactic winds does not necessarily stop continuous star formation., Comment: 2 pages, 1 figure, to appear in the Proceedings of the CRAL conference "Chemodynamics: from first stars to local galaxies", Lyon, France, 10-14 July 2006

Blue Compact Dwarf and Dwarf Irregular galaxies are generally believed to be unevolved objects, due to their blue colors, compact appearance and large gas fractions. Many of these objects show an ongoing intense burst of star formation or have experienced it in the recent past. By means of 2-D hydrodynamical simulations, coupled with detailed chemical yields originating from SNeII, SNeIa, and intermediate-mass stars, we study the dynamical and chemical evolution of model galaxies with structural parameters similar to NGC1569, a prototypical starburst galaxy. A burst of star formation with short duration is not able to account for the chemical and morphological properties of this galaxy. The best way to reproduce the chemical composition of this object is by assuming long-lasting episodes of star formation and a more recent burst, separated from the previous episodes by a short quiescent period. The last burst of star formation, in most of the explored cases, does not affect the chemical composition of the galaxy, since the enriched gas produced by young stars is in a too hot phase to be detectable with the optical spectroscopy. Models assuming the infall of a big cloud towards the center of the galaxy reproduce the chemical composition of the NGC1569, but the pressure exercised by the cloud hampers the expansion of the galactic wind, at variance with what observed in NGC1569., Comment: 16 pages, 10 figures, A&A accepted

The chemical evolution of galaxies that undergo an episode of massive and rapid accretion of metal-poor gas is investigated with models using both simplified and detailed nucleosynthesis recipes. The rapid decrease of the oxygen abundance during infall is followed by a slower evolution which leads back to the closed-box relation, thus forming a loop in the N/O-O/H diagram. For large excursions from the closed-box relation, the mass of the infalling material needs to be substantially larger than the gas remaining in the galaxy, and the accretion rate should be larger than the star formation rate. We apply this concept to the encounter of high velocity clouds with galaxies of various masses, finding that the observed properties of these clouds are indeed able to cause substantial effects not only in low mass galaxies, but also in the partial volumes in large massive galaxies that would be affected by the collision. Numerical models with detailed nucleosynthesis prescriptions are constructed. We assume star formation timescales and scaled yields that depend on the galactic mass, and which are adjusted to reproduce the average relations of gas fraction, oxygen abundance, and effective oxygen yield observed in irregular and spiral galaxies. The resulting excursions in the N/O-O/H diagram due to a single accretion event involving a high velocity cloud are found to be appreciable, which could thus provide a contribution to the large scatter in the N/O ratio found among irregular galaxies. Nonetheless, the N/O-O/H diagram remains an important indicator for stellar nucleosynthesis., Comment: 13 pages, 23 postscript figures, Latex, to appear in Astronomy & Astrophysics

(Abridged) We perform high resolution 2D hydrodynamical simulations of face-on ram pressure stripping (RPS) of disk galaxies to compile a comprehensive parameter study varying galaxy properties (mass, vertical structure of the gas disk) and covering a large range of ICM conditions, reaching from high density environments like in cluster centres to low density environments typical for cluster outskirts or groups. We find that the ICM-ISM interaction proceeds in three phases: firstly the instantaneous stripping phase, secondly the dynamic intermediate phase, thirdly the quasi-stable continuous viscous stripping phase. The stripping efficiency depends slightly on the Mach number of the flow, however, the main parameter is the ram pressure. The stripping efficiency does not depend on the vertical structure and thickness of the gas disk. We discuss uncertainties in the classic estimate of the stripping radius of \citet{gunn72}, and adapt the estimate used by \cite{mori00} for spherical galaxies, (comparison of central pressure with ram pressure). We find that the latter estimate predicts the radius and mass of the gas disk remaining at the end of the second phase very well, and better than the \citet{gunn72} criterion. From our simulations we conclude that gas disks of galaxies in high density environments are heavily truncated or even completely stripped, but also the gas disks of galaxies in low density environments are disturbed by the flow and back-falling material, so that they should also be pre-processed., Comment: 25 pages, 32 figures, accepted for publication in A&A, high resolution version at http://www.astrophysik.uni-kiel.de/~eroediger/publications.html

Blue Compact Dwarf and Dwarf Irregular galaxies are generally believed to be unevolved objects, due to their blue colors, compact appearance and large gas fractions. Many of these objects show an ongoing intense burst of star formation or have experienced it in the recent past. By means of 2-D hydrodynamical simulations, coupled with detailed chemical yields originating from SNeII, SNeIa and intermediate-mass stars, we study the dynamical and chemical evolution of model galaxies with structural parameters similar to IZw18 and NGC1569. Bursts of star formation with short duration are not able to account for the chemical and morphological properties of these galaxies. The best way to reproduce the chemical composition of these objects is by assuming long-lasting episodes of star formation and a more recent burst, separated from the previous episodes by a short quiescent period. The last burst of star formation, in most of the explored cases, does not affect the chemical composition of the galaxy observable in HII regions, since the enriched gas produced by young stars is in a too hot phase to be detectable with the optical spectroscopy., Comment: 16 pages, 6 figures, to be published in "Reviews in Modern Astronomy" of the Astronomische Gesellschaft, Vol. 18

In this paper, we investigate some chemokinematical properties of the Milky Way disk, by using a sample composed by 424 late-type dwarfs. We show that the velocity dispersion of a stellar group correlates with the age of this group, according to a law proportional to t^0.26, where t is the age of the stellar group. The temporal evolution of the vertex deviation is considered in detail. It is shown that the vertex deviation does not seem to depend strongly on the age of the stellar group. Previous studies in the literature seem to not have found it due to the use of statistical ages for stellar groups, rather than individual ages. The possibility to use the orbital parameters of a star to derive information about its birthplace is investigated, and we show that the mean galactocentric radius is likely to be the most reliable stellar birthplace indicator. However, this information cannot be presently used to derive radial evolutionary constraints, due to an intrinsic bias present in all samples constructed from nearby stars. An extensive discussion of the secular and stochastic heating mechanisms commonly invoked to explain the age-velocity dispersion relation is presented. We suggest that the age-velocity dispersion relation could reflect the gradual decrease in the turbulent velocity dispersion from which disk stars form, a suggestion originally made by Tinsley and Larson (1978) and supported by several more recent disk evolution calculations. A test to distinguish between the two types of models using high-redshift galaxies is proposed., Comment: 20 pages, 10 encapsulated postscript figures, LaTeX, uses Astronomy and Astrophysics macro aa.cls, graphicx package, to be published in Astronomy and Astrophysics (2004), Also available at: http://www.astro.iag.usp.br/~maciel

We present a modified TREESPH code to model galaxies in 3d. The model includes a multi-phase description of the interstellar medium which combines two numerical techniques. A diffuse warm/hot gas phase is modelled by SPH while a sticky particle scheme is used to represent a cloudy medium. Interaction processes, such as star formation and feedback, cooling and mixing by condensation and evaporation, are taken into account. Here we apply our model to the evolution of a Milky Way type galaxy. After an initial stage, a quasi-equilibrium state is reached. It is characterised by a star formation rate of ~1 M_sun/year. Condensation and evaporation rates are in balance at 0.1-1 M_sun/year., Comment: 6 pages, 7 figures, Refereed contribution to the 5th Galactic Chemodynamics conference held in Swinburne, July 2003. Accepted for publication in PASA

First we present a recently developed 3D chemodynamical code for galaxy evolution from the K**2 collaboration. It follows the evolution of all components of a galaxy such as dark matter, stars, molecular clouds and diffuse interstellar matter (ISM). Dark matter and stars are treated as collisionless N-body systems. The ISM is numerically described by a smoothed particle hydrodynamics (SPH) approach for the diffuse (hot) gas and a sticky particle scheme for the (cool) molecular clouds. Physical processs such as star formation, stellar death or condensation and evaporation processes of clouds interacting with the ISM are described locally. An example application of the model to a star forming dwarf galaxy will be shown for comparison with other codes. Secondly we will discuss new kinds of exotic chemodynamical processes, as they occur in dense gas-star systems in galactic nuclei, such as non-standard ``drag''-force interactions, destructive and gas producing stellar collisions. Their implementation in 1D dynamical models of galactic nuclei is presented. Future prospects to generalize these to 3D are work in progress and will be discussed., Comment: 4 pages, 4 figures, "The 5th Workshop on Galactic Chemodynamics" - Swinburne University (9-11 July 2003). To be published in the Publications of the Astronomical Society of Australia in 2004 (B.K. Gibson and D. Kawata, eds.). Accepted version, minor changes relative to original

Chemo-dynamical models have been introduced in the late eighties and are a generally accepted tool for understanding galaxy evolution. They have been successfully applied to one-dimensional problems, e.g. the evolution of non-rotating galaxies, and two-dimensional problems, e.g. the evolution of disk galaxies. Recently, also three-dimensional chemo-dynamical models have become available. In these models the dynamics of different components, i.e. dark matter, stars and a multi-phase interstellar medium, are treated in a self-consistent way and several processes allow for an exchange of matter, energy and momentum between the components or different gas phases. Some results of chemo-dynamical models and their comparison with observations of chemical abundances or star formation histories will be reviewed., Comment: 10 Pages, 5 Figures, to appear in "From Observations to Self-Consistent Modelling of the ISM in Galaxies", 2003, eds M. Avillez et al

We present a 3d code for the dynamical evolution of a multi-phase interstellar medium (ISM) coupled to stars via star formation (SF) and feedback processes. The multi-phase ISM consists of clouds (sticky particles) and diffuse gas (SPH): exchange of matter, energy and momentum is achieved by drag (due to ram pressure) and condensation or evaporation processes. The cycle of matter is completed by SF and feedback by SNe and PNe. A SF scheme based on a variable SF efficiency as proposed by Elmegreen & Efremov (1997) is presented. For a Milky Way type galaxy we get a SF rate of ~1 M_sun/yr with an average SF efficiency of ~5%., Comment: 4 Pages, 5 Figures, to appear in "The Evolution of Galaxies: III. From Simple Approaches to Self-Consistent Modelling", 2003, eds. Hensler et al

In this paper we present some test results of our newly developed Multi-Phase Chemo-Dynamical Smoothed Particle Hydrodynamics (MP- CD-SPH) code for galaxy evolution. At first, we present a test of the ``pure'' hydro SPH part of the code. Then we describe and test the multi-phase description of the gaseous components of the interstellar matter. In this second part we also compare our condensation and evaporation description with the results of a previous 2d multi-phase hydrodynamic mesh code., Comment: 4 pages, LaTeX2e, 4 ps figures, using the kluwer.cls and graphicx.sty. "The Evolution of Galaxies III. From Simple Approaches to Self-Consistent Models", eds: G.Hensler, G.Stasinska, S.Harfst, P.Kroupa, Ch.Theis, Kluwer Academic Publ., Dordrecht

We present our recently developed 3-dimensional chemodynamical code for galaxy evolution. It follows the evolution of all components of a galaxy such as dark matter, stars, molecular clouds and diffuse interstellar matter (ISM). Dark matter and stars are treated as collisionless $N$-body systems. The ISM is numerically described by a smoothed particle hydrodynamics (SPH) approach for the diffuse (hot) gas and a sticky particle scheme for the (cool) molecular clouds. Additionally, the galactic components are coupled by several phase transitions like star formation, stellar death or condensation and evaporation processes within the ISM. As an example here we present the dynamical, chemical and photometric evolution of a star forming dwarf galaxy with a total baryonic mass of $2 \times 10^9 {\rm M}_\odot$., Comment: 9 pages, LaTeX2e, 8 ps figures, using the ise2.cls, natbib.sty and graphicx.sty. Presented as oral contribution at the "Interaction of Stars with their Environment II". 15-19 May, 2002, Budapest, Hungary

We present our recently developed 3-dimensional chemodynamical code for galaxy evolution. This code follows the evolution of different galactic components like stars, dark matter and different components of the interstellar medium (ISM), i.e. a diffuse gaseous phase and the molecular clouds. Stars and dark matter are treated as collisionless N-body systems. The ISM is numerically described by a smoothed particle hydrodynamics (SPH) approach for the diffuse gas and a sticky particle scheme for the molecular clouds. Additionally, the galactic components are coupled by several phase transitions like star formation, stellar death or condensation and evaporation processes within the ISM. As an example we show the dynamical and chemical evolution of a star forming dwarf galaxy with a total baryonic mass of $2 \cdot 10^9 M_\odot$. After a moderate collapse phase the stars and the molecular clouds follow an exponential radial distribution, whereas the diffuse gas shows a central depression as a result of stellar feedback. The metallicities of the galactic components behave quite differently with respect to their temporal evolution as well as their radial distribution. Especially, the ISM is at no stage well mixed., Comment: 4 pages, LaTeX, 6 color eps figures, using the kluwer.cls and graphicx.sty, presented as oral contribution at the "Euroconference, The Evolution of Galaxies. II - Basic Building Blocks". 16 - 21 October, 2001, Island of La Reunion (France)