Stellar bars have been found to substantially influence the properties of stellar populations in galaxies, affecting their ability to form stars. While this can be easily seen when studying galaxies in relatively isolated environments, such type of analysis requires a higher degree of complexity when cluster galaxies are considered, due to the variety of interactions that can potentially occur in these denser environments. We use IFU MUSE data from the GASP survey to study the combined effect of the presence of a stellar bar and ram pressure, on spatially resolved properties of stellar populations. We have analyzed spatially resolved indicators of both recent star formation rates (SFRs) and average stellar population ages to check for signatures of anomalous central star formation activity, also taking into account the possible presence of nuclear activity. We found an increase in central SFR in ram-pressure-affected galaxies when compared with unperturbed ones. The most extreme cases of increased SFR and central rejuvenation occur in barred galaxies that are at advanced stages of ram pressure stripping. For low-mass barred galaxies affected by ram pressure, the combined effect is the systematic enhancement of the star formation activity as opposed to the case of high-mass galaxies, which present both enhancement and suppression. Barred galaxies that present suppression of their star formation activity also present signatures of nuclear activity. Our results indicate that the combined effect of the presence of a bar and strong perturbation by ram pressure is able to trigger the central star formation activity and probably ignite nuclear activity.

Determining which between projected local density and distance from the cluster center plays a major role in regulating morphological fractions in clusters is a longstanding debate. Reaching a definitive answer will shed light on the main physical mechanisms at play in the most extreme environments. Here we make use of the data from the OmegaWINGS survey, currently the largest survey of clusters in the local Universe extending beyond 2 virial radii from the cluster cores, to extend previous analysis outside the virial radius. Local density and clustercentric distance seems to play different roles for galaxies of different morphology: the fraction of elliptical galaxies mainly depends on local density, suggesting that their formation was linked to the primordial densities, which now correspond to the cluster cores. Only the fraction of low mass ellipticals shows an anticorrelation with clustercentric distance, suggesting a different origin for these objects. Excluding elliptical galaxies, the relative fraction of S0s and spirals instead depends on local density only far from the cluster cores, while within the virial radius their proportion is regulated by distance, suggesting that cluster specific processes halt the star formation and transform Sp galaxies into S0s. This interpretation is supported by literature results on the kinematical analysis of early and late type galaxies, according to which fast and slow rotators have distinct dependencies on halo mass and local density.

We present a multi-wavelength analysis of the galaxies in nine clusters selected from the WINGS dataset, examining how galaxy structure varies as a function of wavelength and environment using the state of the art software GALAPAGOS-2. We simultaneously fit single-Sérsic functions on three optical (u, B and V) and two near-infrared (J and K) bands thus creating a wavelength-dependent model of each galaxy. We measure the magnitudes, effective radius (Re), the Sérsic index (n), axis ratio, and position angle in each band. The sample contains 790 cluster members (located close to the cluster centre < 0.64 × R200) and 254 non-member galaxies that we further separate based on their morphology into ellipticals, lenticulars, and spirals. We find that the Sérsic index of all galaxies inside clusters remains nearly constant with wavelength while Re decreases as wavelength increases for all morphological types. We do not observe a significant variation on n and Re as a function of projected local density and distance from the clusters centre. Comparing the n and Re of bright cluster galaxies with a subsample of non-member galaxies we find that bright cluster galaxies are more concentrated (display high n values) and are more compact (low Re). Moreover, the light profile (𝒩) and size (ℛ) of bright cluster galaxies does not change as a function of wavelength in the same manner as non-member galaxies.

We examine a magnitude limited (M-B <= -18.7) sample of post-starburst (PSB) galaxies at 0.03 < z < 0.11 in the different environments from the spectroscopic data set of the Padova Millennium Galaxy Group Catalogue and compare their incidence and properties with those of passive (PAS) and emission line galaxies (EML). PSB galaxies have a quite precise lifetime (< 1-1.5 Gyr), and they hold important clues for understanding galaxy evolution. While the properties (stellar mass, absolute magnitude, colour) of PSBs do not depend on environment, their frequency increases going from single galaxies to binary systems to groups, both considering the incidence with respect to the global number of galaxies and to the number of currently+recently star-forming galaxies. Including in our analysis, the sample of cluster PSBs drawn from the WIde-field Nearby Galaxy-cluster Survey presented in Paccagnella et al., we extend the halo mass range covered and present a coherent picture of the effect of the environment on galaxy transformations. We find that the PSB/(PSB + EML) fraction steadily increases with halo mass going from 1 per cent in 10(11) M-circle dot haloes to similar to 15 per cent in the most massive haloes (10(15.5) M-circle dot). This provides evidence that processes specific to the densest environments, such as ram-pressure stripping, are responsible for a large fraction of PSB galaxies in dense environments. These processes act on a larger fraction of galaxies than alternative processes leading to PSB galaxies in the sparsest environments, such as galaxy interactions.

We report evidence for star formation quenching in the central 8.6 kpc region of the jellyfish galaxy JO201 that hosts an active galactic nucleus (AGN), while undergoing strong ram pressure stripping. The ultraviolet imaging data of the galaxy disc reveal a region with reduced flux around the centre of the galaxy and a horse-shoe-shaped region with enhanced flux in the outer disc. The characterization of the ionization regions based on emission line diagnostic diagrams shows that the region of reduced flux seen in the ultraviolet is within the AGN-dominated area. The CO J(2-1) map of the galaxy disc reveals a cavity in the central region. The image of the galaxy disc at redder wavelengths (9050-9250 angstrom) reveals the presence of a stellar bar. The star formation rate map of the galaxy disc shows that the star formation suppression in the cavity occurred in the last few 10(8) yr. We present several lines of evidence supporting the scenario that suppression of star formation in the central region of the disc is most likely due to the feedback from the AGN, The observations reported here make JO201 a unique case of AGN-feedback and environmental effects suppressing star formation in a spiral. galaxy.

We present a study of the physical properties of JO201, a unique disc galaxy with extended tails undergoing extreme ram-pressure stripping (RPS) as it moves through the massive cluster Abell 85 at supersonic speeds mostly along the line of sight. JO201 was observed with multi-unit spectroscopic explorer as part of the GASP programme. In a previous paper (GASP II) we studied the stellar and gas kinematics. In this paper we present emission-line ratios, gas-phase metallicities, and ages of the stellar populations across the galaxy disc and tails. We find that while the emission at the core of the galaxy is dominated by an active galactic nucleus (AGN), the disc is composed of star-forming knots surrounded by excited diffuse gas. The collection of star-forming knots presents a metallicity gradient steadily decreasing from the centre of the galaxy outwards, and the ages of the stars across the galaxy show that the tails formed less than or similar to 10(9) yr ago. This result is consistent with an estimate of the stripping time-scale (similar to 1 Gyr), obtained from a toy orbital model. Overall, our results independently and consistently support a scenario in which a recent or ongoing event of intense RPS acting from the outer disc inwards, causes removal and compression of gas, thus altering the AGN and star formation activity within and around the galaxy.

ABSTRACT Exploiting the sample of 30 local star-forming, undisturbed late-type galaxies in different environments drawn from the GAs Stripping Phenomena in galaxies with MUSE (GASP), we investigate the spatially resolved star formation rate–mass ($\rm \Sigma _{SFR}$–$\rm \Sigma _\ast$) relation. Our analysis includes also the galaxy outskirts (up to >4 effective radii, re), a regime poorly explored by other Integral Field Spectrograph surveys. Our observational strategy allows us to detect H α out to more than 2.7re for 75 per cent of the sample. Considering all galaxies together, the correlation between the $\rm \Sigma _{SFR}$ and $\rm \Sigma _\ast$ is quite broad, with a scatter of 0.3 dex. It gets steeper and shifts to higher $\rm \Sigma _\ast$ values when external spaxels are excluded and moving from less to more massive galaxies. The broadness of the overall relation suggests galaxy-by-galaxy variations. Indeed, each object is characterized by a distinct $\rm \Sigma _{SFR}$ –$\rm \Sigma _\ast$ relation and in some cases the correlation is very loose. The scatter of the relation mainly arises from the existence of bright off-centre star-forming knots whose $\rm \Sigma _{SFR}$–$\rm \Sigma _\ast$ relation is systematically broader than that of the diffuse component. The $\rm \Sigma _{SFR}$–$\rm \Sigma _{tot \, gas}$ (total gas surface density) relation is as broad as the $\rm \Sigma _{SFR}$–$\rm \Sigma _\ast$ relation, indicating that the surface gas density is not a primary driver of the relation. Even though a large galaxy-by-galaxy variation exists, mean $\rm \Sigma _{SFR}$ and $\rm \Sigma _\ast$ values vary of at most 0.7 dex across galaxies. We investigate the relationship between the local and global SFR–M* relation, finding that the latter is driven by the existence of the size–mass relation.

Based on MUSE data from the GASP survey, we study the H alpha-emitting extraplanar tails of 16 cluster galaxies at z similar to 0.05 undergoing ram pressure stripping. We demonstrate that the dominating ionization mechanism of this gas (between 64 per cent and 94 per cent of the H alpha emission in the tails depending on the diagnostic diagram used) is photoionization by young massive stars due to ongoing star formation (SF) taking place in the stripped tails. This SF occurs in dynamically quite cold H II clumps with a median H alpha velocity dispersion sigma = 27 km s(-1). We study the characteristics of over 500 star-forming clumps in the tails and find median values of H alpha luminosity L-H alpha = 4 x 10(38) erg s(-1), dust extinction A(V) = 0.5 mag, star formation rate SFR = 0.003 M-circle dot yr(-1), ionized gas density n(e) = 52 cm(-3), ionized gas mass M-gas = 4 x 10(4) M-circle dot, and stellar mass M-* = 3 x 10(6) M-circle dot. The tail clumps follow scaling relations (M-gas - M-*, L-H alpha - sigma, SFR-M-gas) similar to disc clumps, and their stellar masses are comparable to Ultra Compact Dwarfs and Globular Clusters. The diffuse gas component in the tails is ionized by a combination of SF and composite/LINER-like emission likely due to thermal conduction or turbulence. The stellar photoionization component of the diffuse gas can be due either to leakage of ionizing photons from the H II clumps with an average escape fraction of 18 per cent, or lower luminosity H II regions that we cannot individually identify.

Galaxy filaments are a peculiar environment, and their impact on the galaxy properties is still controversial. Exploiting the data from the GAs Stripping Phenomena in galaxies with MUSE, we provide the first characterization of the spatially resolved properties of galaxies embedded in filaments in the local Universe. The four galaxies we focus on show peculiar ionized gas distributions: Ha clouds have been observed beyond four times the effective radius. The gas kinematics, metallicity map, and the ratios of emission-line fluxes confirm that they do belong to the galaxy gas disc; the analysis of their spectra shows that very weak stellar continuum is associated with them. Similarly, the star formation history and luminosity weighted age maps point to a recent formation of such clouds. The clouds are powered by star formation, and are characterized by intermediate values of dust absorption. We hypothesize a scenario in which the observed features are due to 'Cosmic Web Enhancement': we are most likely witnessing galaxies passing through or flowing within filaments that assist the gas cooling and increase the extent of the star formation in the densest regions in the circumgalactic gas. Targeted simulations are mandatory to better understand this phenomenon.

It is well known that galaxies falling into clusters can experience gas stripping due to ram-pressure by the intra-cluster medium (ICM). The most spectacular examples are galaxies with extended tails of optically-bright stripped material known as "jellyfish". We use the first large homogeneous compilation of jellyfish galaxies in clusters from the WINGS and OmegaWINGS surveys, and follow-up MUSE observations from the GASP MUSE programme to investigate the orbital histories of jellyfish galaxies in clusters and reconstruct their stripping history through position vs. velocity phase- space diagrams. We construct analytic models to define the regions in phase-space where ram-pressure stripping is at play. We then study the distribution of cluster galaxies in phase-space and find that jellyfish galaxies have on average higher peculiar velocities (and higher cluster velocity dispersion) than the overall population of cluster galaxies at all clustercentric radii, which is indicative of recent infall into the cluster and radial orbits. In particular, the jellyfish galaxies with the longest gas tails reside very near the cluster cores (in projection) and are moving at very high speeds, which coincides with the conditions of the most intense ram-pressure. We conclude that many of the jellyfish galaxies seen in clusters likely formed via fast ( 1- 2 Gyr), incremental, outside-in ram-pressure stripping during first infall into the cluster in highly radial orbits.

Exploiting the data from the GAs Stripping Phenomena in galaxies with MUSE (GASP) program, we compare the integrated star formation rate–mass relation (SFR– M * ) relation of 42 cluster galaxies undergoing ram-pressure stripping (RPS; “stripping galaxies”) to that of 32 field and cluster undisturbed galaxies. Theoretical predictions have so far led to contradictory conclusions about whether or not ram pressure can enhance the star formation (SF) in the gas disks and tails, and until now a statistically significant observed sample of stripping galaxies was lacking. We find that stripping galaxies occupy the upper envelope of the control sample SFR– M * relation, showing a systematic enhancement of the SFR at any given mass. The star formation enhancement occurs in the disk (0.2 dex), and additional SF takes place in the tails. Our results suggest that strong RPS events can moderately enhance the SF also in the disk prior to gas removal.

Through an ongoing MUSE program dedicated to study gas removal processes in galaxies (GAs Stripping Phenomena in galaxies with MUSE, GASP), we have obtained deep and wide integral field spectroscopy of the galaxy JO171. This galaxy resembles the Hoag's galaxy, one of the most spectacular examples of ring galaxies, characterized by a completely detached ring of young stars surrounding a central old spheroid. At odds with the isolated Hoag's galaxy, JO171 is part of a dense environment, the cluster Abell 3667, which is causing gas stripping along tentacles. Moreover, its ring counter-rotates with respect to the central spheroid. The joint analysis of the stellar populations and the gas/stellar kinematics shows that the origin of the ring was not due to an internal mechanism, but was related to a gas accretion event that happened in the distant past, prior to accretion onto Abell 3667, most probably within a filament. More recently, since infall in the cluster, the gas in the ring has been stripped by ram- pressure, causing the quenching of star formation in the stripped half of the ring. This is the first observed case of ram pressure stripping in action in a ring galaxy, and MUSE observations are able to reveal both of the events (accretion and stripping) that caused dramatic transformations in this galaxy.

Exploiting a sample of 680 star-forming galaxies from the Padova Millennium Galaxy Group Catalog (PM2GC; Calvi, Poggianti & Vulcani 2011) in the range 0.038 <= z <= 0.104, we present a detailed analysis of the star formation rate (SFR)-stellar mass (M-*) and specific SFR (SSFR)-M-* relations as a function of environment. We adopt three different parametrizations of environment to probe different scales. We consider separately (1) galaxies in groups, binary and single systems, defined in terms of a friends-of-friends algorithm, (2) galaxies located at different projected local densities, and (3) galaxies in haloes of different mass. Overall, above logM(*)/M > 10.25 and SSFR > 10(-12) yr(-1), the SFR-M-*, and SSFR-M-* relations do not depend on environment, when the global environment is used, while when the halo mass is considered, high-mass haloes might have a systematically lower (S) SFR-M-star relation. Finally, when local densities are exploited, at any given mass galaxies in less dense environments have systematically higher values of SFR. All the relations are characterized by a large scatter (sigma similar to 0.6), which is due to the coexistence of galaxies of different morphological types. Indeed, at any given mass, late types are characterized by systematically higher values of SFR and SSFR than S0s and ellipticals. Galaxies of the same morphology show similar trends in all the environments, but their incidence strongly depends on environment and on the environmental parametrization adopted, with late types generally becoming less common in denser environments, contrasted by the increase of ellipticals and/or S0s. Our results suggest that in the local Universe morphology and local interactions, probed by the local density parametrization, have dominant roles in driving the characteristics of the SFR-M-* relation.

Theoretically, inflowing filaments of gas are one of the main causes of growth for a galaxy. Nonetheless, observationally, probing ongoing gas accretion is challenging. As part of the Gas Stripping Phenomena in galaxies with MUSE (GASP) program, we present the analysis of a spiral galaxy at z=0.04648 whose characteristics indeed are consistent with a scenario in which gas accretion plays a major role. The most salient indirect parts of evidence that support this picture are: 1) The galaxy is isolated, its position rules out the mechanisms expected in dense environments. 2) It shows a pronounced lopsidedness extending toward West. According to the spatially resolved star formation history, this component was formed <6x10^8 yr ago. 3) It has many large and elongated HII regions that are indication of a fragmentation due to disk instability. 4) The stellar and gas kinematics are quite symmetric around the same axis, but in the gas the locus of negative velocities shows a convexity toward East, as if new gas has been infalling with different orientation and velocity. 5) The metallicity distribution is inhomogeneous and shows exceptionally steep gradients from the center toward the outskirts, especially in the South-West side. 6) The luminosity weighted age is generally low ( 8 Gyr) and particularly low (<7 Gyr) along a trail crossing the galaxy from South-West toward North. It might trace the path of the accreted gas. These findings point to an inflow of gas probably proceeding from the South-West side of the galaxy.

Jellyfish galaxies in clusters are key tools to understand environmental processes at work in dense environments. The advent of Integral Field Spectroscopy has recently allowed to study a significant sample of stripped galaxies in the cluster environment at z$\sim 0.05$, through the GAs Stripping Phenomena in galaxies with MUSE (GASP) survey. However, optical spectroscopy can only trace the ionized gas component through the H$_{\alpha}$ emission that can be spatially resolved on kpc scale at this redshift. The complex interplay between the various gas phases (ionized, neutral, molecular) is however yet to be understood. We report here the detection of large amounts of molecular gas both in the tails and in the disks of 4 jellyfish galaxies from the GASP sample with stellar masses $\sim 3.5\times 10^{10}-3\times 10^{11} M_{\odot}$, showing strong stripping. The mass of molecular gas that we measure in the tails amounts to several $10^9 M_{\odot}$ and the total mass of molecular gas ranges between 15 and 100 \% of the galaxy stellar mass. The molecular gas content within the galaxies is compatible with the one of normal spiral galaxies, suggesting that the molecular gas in the tails has been formed in-situ. We find a clear correlation between the ionized gas emission $\rm H\alpha$ and the amount of molecular gas. The CO velocities measured from APEX data are not always coincident with the underlying $\rm H\alpha$ emitting knots, and the derived Star Formation Efficiencies appear to be very low.

Context. Galaxy clusters are the largest virialized structures in the observable Universe. Knowledge of their properties provides many useful astrophysical and cosmological information. Aims. Our aim is to derive the luminosity and stellar mass profiles of the nearby galaxy clusters of the Omega-WINGS survey and to study the main scaling relations valid for such systems. Methods. We merged data from the WINGS and Omega-WINGS databases, sorted the sources according to the distance from the brightest cluster galaxy (BCG), and calculated the integrated luminosity profiles in the B and V bands, taking into account extinction, photometric and spatial completeness, K correction, and background contribution. Then, by exploiting the spectroscopic sample we derived the stellar mass profiles of the clusters. Results. We obtained the luminosity profiles of 46 galaxy clusters, reaching r200 in 30 cases, and the stellar mass profiles of 42 of our objects. We successfully fitted all the integrated luminosity growth profiles with one or two embedded Sérsic components, deriving the main clusters parameters. Finally, we checked the main scaling relation among the clusters parameters in comparison with those obtained for a selected sample of early-type galaxies (ETGs) of the same clusters. Conclusions. We found that the nearby galaxy clusters are non-homologous structures such as ETGs and exhibit a color–magnitude (CM) red-sequence relation very similar to that observed for galaxies in clusters. These properties are not expected in the current cluster formation scenarios. In particular the existence of a CM relation for clusters, shown here for the first time, suggests that the baryonic structures grow and evolve in a similar way at all scales.

Jellyfish are cluster galaxies that experience strong ram-pressure effects that strip their gas. Their Ha images reveal ionized gas tails up to 100 kpc, which could be hosting ongoing star formation. Here, we report the ultraviolet (UV) imaging observation of the jellyfish galaxy JO201 obtained at a spatial resolution similar to 1.3 kpc. The intense burst of star formation happening in the tentacles is the focus of this study. JO201 is the 'UV-brightest cluster galaxy' in Abell 85 (z similar to 0.056) with knots and streams of star formation in the UV. We identify star-forming knots both in the stripped gas and in the galaxy disc and compare the UV features with the ones traced by Ha emission. Overall, the two emissions remarkably correlate, both in the main body and along the tentacles. Similarly, also the star formation rates of individual knots derived from the extinction-corrected far-ultraviolet (FUV) emission agree with those derived from the Ha emission and range from similar to 0.01 to 2.07 M-circle dot yr(-1). The integrated star formation rate from FUV flux is similar to 15 M-circle dot yr(-1). The unprecedented deep UV imaging study of the jellyfish galaxy JO201 shows clear signs of extraplanar star formation activity due to a recent/ongoing gas stripping event.

GAs Stripping Phenomena in galaxies with MUSE (GASP) is a program aimed at studying gas removal processes in nearby galaxies in different environments. We present the study of four galaxies that are part of the same group (z= 0.06359) and highlight the multitude of mechanisms affecting the spatially resolved properties of the group members. One galaxy is passive and shows a regular stellar kinematics. The analysis of its star formation history indicates that the quenching process lasted for a few Gyr and that the star formation declined throughout the disk in a similar way, consistent with strangulation. Another galaxy is characterised by a two-component stellar disk with an extended gas disk that formed a few 10^8 yr ago, most likely as a consequence of gas accretion. The third member is a spiral galaxy at the edges of the group, but embedded in a filament. We hypothesise that the compression exerted by the sparse intergalactic medium on the dense circumgalactic gas switches on star formation in a number of clouds surrounding the galaxy ("cosmic web enhancement"). Alternatively, also ram pressure stripping might be effective. Finally, the fourth galaxy is a spiral with a truncated ionised gas disk and an undisturbed stellar kinematics. An analytical model of the galaxy's restoring pressure, and its location and velocity within the cluster, suggest ram pressure is the most likely physical mechanism in action. This is the first optical evidence for stripping in groups.