Search

We present MeerKAT HI observations of six jellyfish candidate galaxies (JFCGs) in the galaxy cluster, A2626. Two of the six galaxies JW100 and JW103, that were identified as JFCGs from B-band images, are confirmed as jellyfish galaxies (JFGs). Both of the JFGs have low HI content, reside in the cluster core, and move at very high velocities ($\sim$ 3$\sigma_{cl}$). The other JFCGs, identified as non-jellyfish galaxies, are HI rich, with HI morphologies revealing warps, asymmetries, and possible tidal interactions. Both the A2626 JFGs and three other confirmed JFGs from the GASP sample show that these galaxies are HI stripped but not yet quenched. We detect HI, Halpha, and CO tails of similar extent ($\sim$ 50 kpc) in JW100. Comparing the multi-phase velocity channels, we do not detect any HI or CO emission in the northern section of the tail where Halpha emission is present, possibly due to prolonged interaction between the stripped gas and the ICM. We also observe an anti-correlation between HI and CO, which hints at an efficient conversion of HI to H2 in the southern part of the tail. We find that both RPS and HI-to-H2 conversion are significant depletion channels for atomic gas. HI-to-H2 conversion is more efficient in the disc than in the tail., Comment: 15 pages, 10 figures, accepted for publication in MNRAS

WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini' integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366$-$959\,nm at $R\sim5000$, or two shorter ranges at $R\sim20\,000$. After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy's origins by completing Gaia's phase-space information, providing metallicities to its limiting magnitude for $\sim$3 million stars and detailed abundances for $\sim1.5$ million brighter field and open-cluster stars; (ii) survey $\sim0.4$ million Galactic-plane OBA stars, young stellar objects and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey $\sim400$ neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionised gas in $z1$ million spectra of LOFAR-selected radio sources; (viii) trace structures using intergalactic/circumgalactic gas at $z>2$. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator., 41 pages, 27 figures, accepted for publication by MNRAS

In this paper, we present data from the Blind Ultra-Deep H i Environmental Survey (BUDHiES), which is a blind 21-cm H i spectral line imaging survey undertaken with the Westerbork Synthesis Radio Telescope. Two volumes were surveyed, each with a single pointing and covering a redshift range of 0.164 < z < 0.224. Within these two volumes, this survey targeted the clusters Abell 963 and Abell 2192, which are dynamically different and offer unique environments to study the process of galaxy evolution within clusters. With an integration time of 117 × 12 h on Abell 963 and 72 × 12 h on Abell 2192, a total of 166 galaxies were detected and imaged in H i. While the clusters themselves occupy only 4 per cent of the 73 400 Mpc3 surveyed by BUDHiES, most of the volume consists of large-scale structures in which the clusters are embedded, including foreground and background overdensities and voids. We present the data processing and source detection techniques and counterpart identification based on a wide-field optical imaging survey using the Isaac Newton Telescope and deep ultraviolet (UV) Galaxy Evolution Explorer (GALEX) imaging. Finally, we present H i and optical catalogues of the detected sources as well as atlases of their global H i properties, which include integrated column density maps, position–velocity diagrams, global H i profiles, and optical and UV images of the H i sources.

X-ray studies of jellyfish galaxies opened a window in the physics of the interplay between intracluster medium (ICM) and interstellar medium (ISM). In this paper, we present the study of an archival \textit{Chandra} observation of the GASP jellyfish galaxy JO194. We observe X-ray emission extending from the stellar disk to the unwinding spiral arms with an average temperature of $kT=0.79\pm0.03$ keV. To investigate the origin of the X-ray emission, we compare the observed X-ray luminosities with those expected from the star formation rates (SFR) obtained from H$\alpha$ emission. We estimate an X-ray luminosity excess of a factor $\sim2-4$ with respect to the SF, therefore we conclude that SF is not the main responsible for the extended X-ray emission of JO194. The metallicity in the spiral arms ($Z=0.24^{+0.19}_{-0.12} Z_{\odot}$) is consistent with that of the ICM around JO194 ($Z=0.35\pm0.07$), thus we suggest that the ICM radiative cooling dominates the X-ray emission of the arms. We speculate that the X-ray plasma results from the ISM-ICM interplay, although the nature of this interplay is still mostly unknown. Finally, we observe that the X-ray properties of JO194 are consistent with those of two other GASP galaxies with different stellar mass, phase-space conditions in their hosting clusters, and local ICM conditions. We suggest that the conditions required to induce extended X-ray emission in jellyfish galaxies are established at the beginning of the stripping, and they can persist on long time scales so that galaxies in different clusters and evolutionary stages can present similar extended X-ray emission., Comment: 16 pages, 6 figures, accepted for publication on ApJ, on date 1st August 2022

We present a new approach to observationally constrain where the tails of Jellyfish (JF) galaxies in groups and clusters first appear and how long they remain visible with respect to the moment of their orbital pericenter. This is accomplished by measuring the distribution of their tail directions with respect to their host's center, and their distribution in a projected velocity-radius phase-diagram. We then model these observed distributions using a fast and flexible approach where JF tails are painted onto dark matter halos according to a simple parameterised prescription, and perform a Bayesian analysis to estimate the parameters. We demonstrate the effectiveness of our approach using observational mocks, and then apply it to a known observational sample of 106 JF galaxies with radio continuum tails located inside 68 hosts such as groups and clusters. We find that, typically, the radio continuum tails become visible on first infall when the galaxy reaches roughly three quarters of r$_{200}$, and the tails remain visible for a few hundred Myr after pericenter passage. Lower mass galaxies in more massive hosts tend to form visible tails further out and their tails disappear more quickly after pericenter. We argue that this indicates they are more sensitive to ram pressure stripping. With upcoming large area surveys of JF galaxies in progress, this is a promising new method to constrain the environmental conditions in which visible JF tails exist., Accepted to ApJ June 2022, 24 pages, 13 figures, 2 tables

We present the first study of the effect of ram-pressure "unwinding" the spiral arms of cluster galaxies. We study 11 ram-pressure stripped galaxies from GASP (GAs Stripping Phenomena in galaxies) in which, in addition to more commonly observed "jellyfish" features, dislodged material also appears to retain the original structure of the spiral arms. Gravitational influence from neighbours is ruled out and we compare the sample with a control group of undisturbed spiral galaxies and simulated stripped galaxies. We first confirm the unwinding nature, finding the spiral arm pitch angle increases radially in 10 stripped galaxies and also simulated face-on and edge-on stripped galaxies. We find only younger stars in the unwound component, while older stars in the disc remain undisturbed. We compare the morphology and kinematics with simulated ram-pressure stripping galaxies, taking into account the estimated inclination with respect to the intracluster medium and find that in edge-on stripping, unwinding can occur due to differential ram-pressure caused by the disc rotation, causing stripped material to slow and "pile-up". In face-on cases, gas removed from the outer edges falls to higher orbits, appearing to "unwind". The pattern is fairly short-lived (, Accepted for publication in MNRAS, 30 pages, 17 figures

We present JVLA-C observations of the HI gas in JO204, one of the most striking jellyfish galaxies from the GASP survey. JO204 is a massive galaxy in the low-mass cluster Abell 957 at z=0.04243. The HI map reveals an extended 90 kpc long ram-pressure stripped tail of neutral gas, stretching beyond the 30 kpc long ionized gas tail and pointing away from the cluster center. The HI mass seen in emission is (1.32 $ \pm 0.13) \times 10^{9} \rm M_{\odot}$, mostly located in the tail. The northern part of the galaxy disk has retained some HI gas, while the southern part has already been completely stripped and displaced into an extended unilateral tail. Comparing the distribution and kinematics of the neutral and ionized gas in the tail indicates a highly turbulent medium. Moreover, we observe associated HI absorption against the 11 mJy central radio continuum source with an estimated HI absorption column density of 3.2 $\times 10^{20}$ cm$^{-2}$. The absorption profile is significantly asymmetric with a wing towards higher velocities. We modelled the HI absorption by assuming that the HI and ionized gas disks have the same kinematics in front of the central continuum source, and deduced a wider absorption profile than observed. The observed asymmetric absorption profile can therefore be explained by a clumpy, rotating HI gas disk seen partially in front of the central continuum source, or by ram-pressure pushing the neutral gas towards the center of the continuum source, triggering the AGN activity., Comment: 16 pages, 10 figures, accepted for publication in MNRAS

Ram pressure stripping is a crucial evolutionary driver for cluster galaxies. It is thought to be able to accelerate the evolution of their star formation, trigger the activity of their central active galactic nucleus (AGN) and the interplay between the galactic and environmental gas, and eventually dissipate their gas reservoir. We explored the outcomes of ram pressure stripping by studying the non-thermal radio emission of the jellyfish galaxy JW100 in the cluster Abell 2626 ($z=0.055$) by combining LOFAR, MeerKAT, and VLA observations from 0.144 to 5.5 GHz. We studied the integrated spectra of the stellar disk, the stripped tail and the AGN, mapped the spectral index over the galaxy, and constrained the magnetic field intensity to be between 11 and 18 $��$G in the disk and $, 20 pages, 12 figures. Accepted for publication on ApJ on 24/10/2021

Jellyfish galaxies, characterized by long filaments of stripped interstellar medium extending from their disks, are the prime laboratories to study the outcomes of ram pressure stripping. At radio wavelengths, they often show unilateral emission extending beyond the stellar disk, and an excess of radio luminosity with respect to that expected from their current star formation rate. We present new 144 MHz images provided by the LOFAR Two-metre Sky Survey for a sample of six galaxies from the GASP survey. These galaxies are characterized by a high global luminosity at 144 MHz ($6-27\times10^{22}$ W Hz$^{-1}$), in excess compared to their ongoing star formation rate. The comparison of radio and H$\alpha$ images smoothed with a Gaussian beam corresponding to $\sim$10 kpc reveals a sub-linear spatial correlation between the two emissions with an average slope $k=0.50$. In their stellar disk we measure $k=0.77$, which is close to the radio-to-star formation linear relation. We speculate that, as a consequence of the ram pressure, in these jellyfish galaxies the cosmic rays transport is more efficient than in normal galaxies. Radio tails typically have higher radio-to-H$\alpha$ ratios than the disks, thus we suggest that the radio emission is boosted by the electrons stripped from the disks. In all galaxies, the star formation rate has decreased by a factor $\leq10$ within the last $\sim10^8$ yr. The observed radio emission is consistent with the past star formation, so we propose that this recent decline may be the cause of their radio luminosity-to-star formation rate excess., Comment: 22 pages, 7 figures. Accepted for publication on ApJ on 24/08/2022

Ram pressure stripping is one of the most efficient mechanisms able to affect the gas reservoir in cluster galaxies and in the last decades many studies have characterized the properties of stripped galaxies. A definite census of the importance of this process in local clusters is though still missing. Here we characterize the fraction of galaxies showing signs of stripping at optical wavelengths, using the data of 66 clusters from the WINGS and OMEGAWINGS surveys. We focus on the infalling galaxy population and hence only consider blue, bright (B, ApJ in press (accepted on 2021/12/29). 18 pages, 9 figures

Hydrodynamical simulations show that the ram-pressure stripping in galaxy clusters fosters a strong interaction between stripped interstellar medium (ISM) and the surrounding medium, with the possibility of intracluster medium (ICM) cooling into cold gas clouds. Exploiting the MUSE observation of three jellyfish galaxies from the GAs Stripping Phenomena in galaxies with MUSE (GASP) survey, we explore the gas metallicity of star-forming clumps in their gas tails. We find that the oxygen abundance of the stripped gas decreases as a function of the distance from the parent galaxy disk; the observed metallicity profiles indicate that more than 40% of the most metal-poor stripped clouds are constituted by cooled ICM, in qualitative agreement with simulations that predict mixing between the metal-rich ISM and the metal-poor ICM., Accepted for pubblication in ApJL. 9 pages, 4 figures, and 1 table

Ram-pressure stripping by the intracluster medium (ICM) is one of the most advocated mechanisms that affect the properties of cluster galaxies. A recent study based on a small sample has found that many galaxies showing strong signatures of ram-pressure stripping also possess an active galactic nucleus (AGN), suggesting a possible correlation between the two phenomena. This result has not been confirmed by a subsequent study. Building upon previous findings, here we combine MUSE observations conducted within the GASP program and a general survey of the literature to robustly measure the AGN fraction in cluster's ram pressure stripped galaxies using BPT emission line diagrams. Considering a sample of 115 ram pressure stripped galaxies with stellar masses $\geq 10^9 \, M_{\odot}$, we find an AGN fraction of $\sim27\%$. This fraction strongly depends on stellar mass: it raises to 51% when only ram-pressure stripped galaxies of masses $M_* \geq 10^{10} \, M_{\odot}$ are considered. We then investigate whether the AGN incidence is in excess in ram pressure stripped galaxies compared to non-stripped galaxies, using as comparison a sample of non-cluster galaxies observed by the survey MaNGA. Considering mass-matched samples, we find that the incidence of AGN activity is significantly higher (at a confidence level $>99.95\%$) when ram-pressure stripping is on act, supporting the hypothesis of an AGN-ram pressure connection., 18 pages, 5 figures, table3 and table4 available in machine-readable format. Accepted for publication on ApJ on 03/11/2021

We present a study of barred galaxies in the cluster environment, exploiting a sample of galaxies drawn from the extended WIde-field Nearby Galaxy-cluster Survey (OmegaWINGS) that covers up to the outer regions of 32 local X-ray selected clusters. Barred galaxies are identified through a semi-automatic analysis of ellipticity and position angle profiles. We find, in agreement with previous studies, a strong co-dependence of the bar fraction with the galaxy stellar mass and morphological type, being maximum for massive late-type galaxies. The fraction of barred galaxies decreases with increasing cluster mass and with decreasing clustercentric distance, a dependence that vanishes once we control for morphological type, which indicates that the likelihood of a galaxy hosting a bar in the cluster environment is determined by its morphological transformation. At large clustercentric distances, we detect a dependence on the distance to the nearest neighbor galaxy, suggesting that tidal forces with close companions are able to suppress the formation of bars or even destroy them. Barred galaxies in our sample are either early-type, star forming galaxies located within the virial radii of the clusters or late-type quenched galaxies found beyond the virial radii of the clusters. We propose a scenario in which already quenched barred galaxies that fall into the clusters are centrally rejuvenated by the interplay of the perturbed gas by ram-pressure and the bar, in galaxies that are undergoing a morphological transformation., 17 pages,9 figures, 1 table, accepted in ApJ

Galaxies inhabit a wide range of environments and therefore are affected by different physical mechanisms. Spatially resolved maps combined with the knowledge of the hosting environment are very powerful to classify galaxies by physical process. In the context of the GAs Stripping Phenomena in galaxies (GASP), we present a study of 27 non-cluster galaxies: 24 of them were selected for showing asymmetries and disturbances in the optical morphology, suggestive of gas stripping, three of them are passive galaxies and were included to characterize the final stages of galaxy evolution. We therefore provide a panorama of the different processes taking place in low-density environments. The analysis of VLT/MUSE data allows us to separate galaxies into the following categories: Galaxy-galaxy interactions (2 galaxies), mergers (6), ram pressure stripping (4), cosmic web stripping (2), cosmic web enhancement (5), gas accretion (3), starvation (3). In one galaxy we identify the combination of merger and ram pressure stripping. Only 6/27 of these galaxies have just a tentative classification. We then investigate where these galaxies are located on scaling relations determined for a sample of undisturbed galaxies. Our analysis shows the successes and limitations of a visual optical selection in identifying the processes that deplete galaxies of their gas content and probes the power of IFU data in pinning down the acting mechanism., ApJ in press

International audience; We present an update on the overall integration progress of the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT), now scheduled for first light in early-2021, with almost all components now arrived at the observatory. We also present a summary of the current planning behind the 5-year initial phase of survey operations, and some detailed end-to-end science simulations that have been implemented to evaluate the final on-sky performance after data processing. WEAVE will provide optical ground-based follow up of ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multi-object (MOS) fibres, 20 mini integral field units, or a single large IFU for each observation. The fibres are fed to a single (dual-beam) spectrograph, with total of 16k spectral pixels, located within the WHT GHRIL enclosure on the telescope Nasmyth platform, supporting observations at R~5000 over the full 370-1000nm wavelength range in a single exposure, or a high resolution mode with limited coverage in each arm at R~20000.

Relatively few X-ray sources are known that have low-mass galaxies as hosts. This is an important restriction on studies of active galactic nuclei (AGNs), hence black holes, and of X-ray binaries (XRBs) in low-mass galaxies; addressing it requires very large samples of both galaxies and X-ray sources. Here, we have matched the X-ray point sources found in the XXL-N field of the XXL survey (with an X-ray flux limit of ∼6 × 10−15 erg s−1 cm−2 in the [0.5–2] keV band) to galaxies with redshifts from the Galaxy And Mass Assembly (GAMA) G02 survey field (down to a magnitude limit r = 19.8) in order to search for AGNs and XRBs in GAMA galaxies, particularly those of low optical luminosity or stellar mass (fainter than Mr = −19 or $M_* \lesssim 10^{9.5}\, \mathrm{M}_{\odot }$). Out of a total of 1200 low-mass galaxies in the overlap region, we find a total of 28 potential X-ray source hosts, though this includes possible background contaminants. From a combination of photometry (optical and infrared colours), positional information, and optical spectra, we deduce that most of the ≃20 X-ray sources genuinely in low-mass galaxies are high-mass X-ray binaries in star-forming galaxies. None of the matched sources in a low-mass galaxy has a BPT classification as an AGN, and even ignoring this requirement, none passes both criteria of close match between the X-ray source position and optical galaxy centre (separation ≤3 arcsec) and high [O iii] line luminosity (above 1040.3 erg s−1).

We measure the rate of environmentally-driven star formation quenching in galaxies at $z\sim 1$, using eleven massive ($M\approx 2\times10^{14}\,\mathrm{M}_\odot$) galaxy clusters spanning a redshift range $1.010.5$) we do not find any significant excess of transition galaxies in clusters, relative to a comparison field sample at the same redshift. It is likely that such galaxies were quenched prior to their accretion in the cluster, in group, filament or protocluster environments. For lower stellar mass galaxies ($9.5, Comment: Accepted for publication in MNRAS Sept 6, 2021

We present deep JVLA observations at 1.4 GHz and 2.7 GHz (full polarization), as well as optical OmegaWINGS/WINGS and X-ray observations of two extended radio galaxies in the IIZW108 galaxy cluster at z = 0.04889. They show a bent tail morphology in agreement with a radio lobed galaxy falling into the cluster potential. Both galaxies are found to possess properties comparable with {narrow-angle} tail galaxies in the literature even though they are part of a low mass cluster. We find a spectral index steepening and an increase in fractional polarization through the galaxy jets and an ordered magnetic field component mostly aligned with the jet direction. This is likely caused by either shear due to the velocity difference of the intracluster medium and the jet fluid and/or magnetic draping of the intracluster medium across the galaxy jets. We find clear evidence that one source is showing two active galactic nuclei (AGN) outbursts from which we expect the AGN has never turned off completely. We show that pure standard electron cooling cannot explain the jet length. We demonstrate therefore that these galaxies can be used as a laboratory to study gentle re-acceleration of relativistic electrons in galaxy jets via transition from laminar to turbulent motion., Comment: accepted for publication in MNRAS

The diffuse ionized gas (DIG) is an important component of the interstellar medium and it can be affected by many physical processes in galaxies. Measuring its distribution and contribution in emission allows us to properly study both its ionization and star formation in galaxies. Here, we measure for the first time the DIG emission in 38 gas-stripped galaxies in local clusters drawn from the GAs Stripping Phenomena in galaxies with MUSE survey (GASP). These galaxies are at different stages of stripping. We also compare the DIG properties to those of 33 normal galaxies from the same survey. To estimate the DIG fraction (C$_{DIG}$) and derive its maps, we combine attenuation corrected H$\alpha$ surface brightness with $\rm [SII]/H\alpha$ line ratio. Our results indicate that we cannot use neither a single H$\alpha$ or $\rm [SII]/H\alpha$ value, nor a threshold in equivalent width of H$\alpha$ emission line to separate spaxels dominated by DIG and non-DIG emission. Assuming a constant surface brightness of the DIG across galaxies underestimates C$_{DIG}$. Contrasting stripped and non-stripped galaxies, we find no clear differences in C$_{DIG}$. The DIG emission contributes between 20\% and 90\% of the total integrated flux, and does not correlate with the galactic stellar mass and star-formation rate (SFR). The C$_{DIG}$ anti-correlates with the specific SFR, which may indicate an older ($>10^8$ yr) stellar population as ionizing source of the DIG. The DIG fraction shows anti-correlations with the SFR surface density, which could be used for a robust estimation of integrated C$_{DIG}$ in galaxies., Comment: This article is currently in press for the ApJ. 28 pages of which the main text is 21 pages, 17 figures of which 11 are in the main text, 2 tables, Appendix on the end (with 6 figures)

Ram pressure stripping has been proven to be effective in shaping galaxy properties in dense environments at low redshift. The availability of MUSE observations of a sample of distant (z$\sim 0.3-0.5$) clusters has allowed to search for galaxies subject to this phenomenon at significant lookback times. In this paper we describe how we discovered and characterized 13 ram-pressure stripped galaxies in the central regions of two intermediate redshift (z$\sim$0.3-0.4) clusters, A2744 and A370, using the MUSE spectrograph. Emission line properties as well as stellar features have been analyzed to infer the presence of this gas--only stripping mechanism, that produces spectacular ionized gas tails (H$_{\alpha}$ and even more astonishing [OII](3727,3729) departing from the main galaxy body. The inner regions of these two clusters reveal the predominance of such galaxies among blue star-forming cluster members, suggesting that ram-pressure stripping was even more effective at intermediate redshift than in today's Universe. Interestingly, the resolved [OII]/H$_{\alpha}$ line ratio in the stripped tails is exceptionally high compared to that in the disks of these galaxies, (which is comparable to that in normal low-z galaxies), suggesting lower gas densities and/or an interaction with the hot surrounding ICM., Comment: Accepted for publication on ApJ

Large samples of galaxy clusters provide knowledge of both astrophysics in the most massive virialised environments and the properties of the cosmological model that defines our Universe. However, an important issue that affects the interpretation of galaxy cluster samples is the role played by the selection waveband and the potential for this to introduce a bias in the physical properties of clusters thus selected. We aim to investigate waveband-dependent selection effects in the identification of galaxy clusters by comparing the X-ray Multi-Mirror (XMM) Ultimate Extra-galactic Survey (XXL) and Subaru Hyper Suprime-Cam (HSC) CAMIRA cluster samples identified from a common 22.6 deg2 sky area. We compare 150 XXL and 270 CAMIRA clusters in a common parameter space defined by X-ray aperture brightness and optical richness. We find that 71/150 XXL clusters are matched to the location of a CAMIRA cluster, the majority of which (67/71) display richness values N>15 that exceed the CAMIRA catalogue richness threshold. We find that 67/270 CAMIRA clusters are matched to the location of an XXL cluster (defined within XXL as an extended X-ray source). Of the unmatched CAMIRA clusters, the majority display low X-ray fluxes consistent with the lack of an XXL counterpart. However, a significant fraction (64/107) CAMIRA clusters that display high X-ray fluxes are not asociated with an extended source in the XXL catalogue. We demonstrate that this disparity arises from a variety of effects including the morphological criteria employed to identify X-ray clusters and the properties of the XMM PSF., 15 pages, 14 figures, MNRAS accepted

Making use of both MUSE observations of 85 galaxies from the survey GASP (GAs Stripping Phenomena in galaxies with MUSE) and a large sample from MaNGA (Mapping Nearby Galaxies at Apache Point Observatory survey) we investigate the distribution of gas metallicity gradients as a function of stellar mass, for local cluster and field galaxies. Overall, metallicity profiles steepen with increasing stellar mass up to $10^{10.3}\,{\rm M_\odot}$ and flatten out at higher masses. Combining the results from the metallicity profiles and the stellar mass surface density gradients, we propose that the observed steepening is a consequence of local metal enrichment due to in-situ star formation during the inside-out formation of disk galaxies. The metallicity gradient-stellar mass relation is characterized by a rather large scatter, especially for $10^{9.8}, Comment: Accepted for pubblication in ApJ. 25 pages, 11 figures, and 2 tables

We study the star formation histories (SFHs) and mass-weighted ages of 331 UVJ-selected quiescent galaxies in 11 galaxy clusters and in the field at 11 has been driven by different physical processes than those at play at z=0., Comment: accepted Sept 7 2020, MNRAS

We present HI observations of the jellyfish galaxy, JO201. This massive galaxy (M$_{\ast} = 3.5 \times 10^{10}$ M$_\odot$) is falling along the line-of-sight towards the centre of a rich cluster (M$_{200} \sim 1.6 \times 10^{15}$ M$_\odot$, $\sigma_{cl} \sim 982$ km/s) at a high velocity $\geq$3363 km/s. Its H$\alpha$ emission shows a $\sim$40 kpc tail confined closely to its stellar disc and a $\sim$100 kpc tail extending further out. We find HI emission coinciding only with the shorter clumpy H$\alpha$ tail. In total, we measure an HI mass of M$_{\rm HI} = 1.65 \times 10^{9}$ M$_\odot$, which is about 60% lower than expected based on its stellar mass and stellar surface density. We compared JO201 to another jellyfish in the GASP sample, JO206 (of similar mass but residing in a 10$\times$ less massive cluster), and find that they are similarly HI-deficient. Of the total HI mass in JO201, about 30% lies outside the galaxy disc in projection. This HI fraction is probably a lower limit since most of the HI is redshifted relative to the stellar disc and could be outside the disc. The global star formation rate (SFR) analysis of JO201 suggests that its observed SFR would be expected if it had 10$\times$ its current HI mass. The disc is the main contributor of the high star formation efficiency at a given HI gas density for both galaxies, but their tails also show higher star formation efficiencies compared to the outer regions of field galaxies. Generally, we find that JO201 and JO206 are similar based on their HI content, stellar mass and star formation rate. This finding is unexpected considering their different environments. A toy model comparing the ram pressure of the ICM versus the restoring forces of these galaxies suggests that the ram pressure strength exerted on them could be comparable if we consider their 3D orbital velocities and radial distances relative to the clusters., Comment: 9 pages, 8 figures, Accepted for publication in A&A

In the disks of four jellyfish galaxies from the GASP sample at redshift $\sim 0.05$ we detect molecular gas masses systematically higher than in field galaxies. These galaxies are being stripped of their gas by ram pressure from the intra cluster medium and are, in general, forming stars at high rate with respect to non-stripped galaxies of similar stellar masses. We find that, unless giant molecular clouds in the disk are unbound by ram pressure leading to exceptionally high CO--to--$\rm H_2$ conversion factors, these galaxies have a molecular gas content 4-5 times higher than normal galaxies of similar masses, and molecular gas depletion times ranging from $\sim$1 to 9 Gyr, corresponding to generally very low star formation efficiencies. The molecular gas mass within the disk is a factor between 4 and $\sim$100 times higher than the neutral gas mass, as opposed to the disks of normal spirals that contain similar amounts of molecular and neutral gas. Intriguingly, the molecular plus neutral total amount of gas is similar to that in normal spiral galaxies of similar stellar mass. These results strongly suggest that ram pressure in disks of galaxies during the jellyfish phase leads to a very efficient conversion of HI into $\rm H_2$., Accepted for publication on ApJL

The study of cluster post starburst galaxies gives useful insights on the physical processes quenching the star formation in the most massive environments. Exploiting the MUSE data of the GAs Stripping Phenomena in galaxies (GASP) project, we characterise the quenching history of 8 local cluster galaxies that were selected for not showing emission lines in their fiber spectra. We inspect the integrated colors, the Hb rest frame equivalent widths (EW), star formation histories (SFHs) and luminosity-weighted age (LWA) maps finding no signs of current star formation throughout the disks of these early-spiral/S0 galaxies. All of them have been passive for at least 20 Myr, but their SF declined on different timescales. In most of them the outskirts reached undetectable SFRs before the inner regions (outside-in quenching). Our sample includes three post-starforming galaxies, two passive galaxies and three galaxies with intermediate properties. The first population shows blue colors, deep Hb in absorption (EW>>2.8A), young ages (8.8, Comment: 24 pages, 10 figures accepted for publication in ApJ

We present a detailed analysis of star formation properties of galaxies in a nearby ($z\sim0.046$) young ($\sim$0.6 Gyr) post-merger cluster system A3376, with a moderate shock front ( $v_{s}\sim$1630 km/s) observed as symmetric radio relics. Exploiting the spectroscopic data from the wide-field OmegaWINGS survey and the associated photometric information, our investigations reveal the plausible effects of the dynamic post-merger environment differing from the putative pre-merger cluster environment. The remnants of the pre-merger relaxed cluster environment are realised through the existence of passive spiral galaxies located in the central regions of the cluster between the two BCGs. We discover A3376 to contain a population of massive $(M_{*}/M_{\odot})>10$) blue regular star-forming spirals in regions of maximum merger shock influence but exhibiting star formation rates similar to those in relaxed clusters at similar epoch. We further discover low-mass (Log $(M_{*}/M_{\odot})\leq 10$) late-type blue PSBs which could either be formed as a result of rapid quenching of low-mass spirals following the shock-induced star formation or due to the intense surge in the ICM pressures at the beginning of the merger. With the possibility of the merger shock affecting high- and low-mass spirals differently, our results bridge the seemingly contradictory results observed in known merging cluster systems so far and establish that different environmental effects are at play right from pre- to post-merger stage., 15 pages, 12 figures, submitted to Monthly Notices of Royal Astronomy Society (MNRAS)

Exploiting the data from the GAs Stripping Phenomena in galaxies with MUSE (GASP) survey, we study the gas-phase metallicity scaling relations of a sample of 29 cluster galaxies undergoing ram-pressure stripping and of a reference sample of (16 cluster and 16 field) galaxies with no significant signs of gas disturbance. We adopt the PYQZ code to infer the mean gas metallicity at the effective radius and achieve a well-defined mass-metallicity relation (MZR) in the stellar mass range $10^{9.25}\le M_\star \le 10^{11.5}\,{\rm M_\odot}$ with a scatter of 0.12 dex. At any given mass, reference cluster and stripping galaxies have similar metallicities, while the field galaxies with $M_\star < 10^{10.25}\,{\rm M_\odot}$ show on average lower gas metallicity than galaxies in clusters. Our results indicate that at the effective radius the chemical properties of the stripping galaxies are independent of the ram-pressure stripping mechanism. Nonetheless, at the lowest masses we detect 4 stripping galaxies well above the common MZR that suggest a more complex scenario. Overall, we find signs of an anti-correlation between the metallicity and both the star formation rate and the galaxy size, in agreement with previous studies. No significant trends are instead found with the halo mass, clustercentric distance and local galaxy density in clusters. In conclusion, we advise a more detailed analysis of the spatially resolved gas metallicity maps of the galaxies, able to highlight effects of gas redistribution inside the disk due to the ram-pressure stripping., accepted for publication in ApJ, 24 pages, 21 figures, 2 tables

The study of the spatially resolved Star Formation Rate-Mass (Sigma_SFR-Sigma_M) relation gives important insights on how galaxies assemble at different spatial scales. Here we present the analysis of the Sigma_SFR-Sigma_M of 40 local cluster galaxies undergoing ram pressure stripping drawn from the GAs Stripping Phenomena in galaxies (GASP) sample. Considering their integrated properties, these galaxies show a SFR enhancement with respect to undisturbed galaxies of similar stellar mass; we now exploit spatially resolved data to investigate the origin and location of the excess. Even on ~1kpc scales, stripping galaxies present a systematic enhancement of Sigma_SFR (~0.35 dex at Sigma_M =108^M_sun/kpc^2) at any given Sigma_M compared to their undisturbed counterparts. The excess is independent on the degree of stripping and of the amount of star formation in the tails and it is visible at all galactocentric distances within the disks, suggesting that the star formation is most likely induced by compression waves from ram pressure. Such excess is larger for less massive galaxies and decreases with increasing mass. As stripping galaxies are characterised by ionised gas beyond the stellar disk, we also investigate the properties of 411 star forming clumps found in the galaxy tails. At any given stellar mass density, these clumps are systematically forming stars at a higher rate than in the disk, but differences are reconciled when we just consider the mass formed in the last few 10^8yr ago, suggesting that on these timescales the local mode of star formation is similar in the tails and in the disks., 20 pages, 13 figures, accepted for publication in ApJ

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 GALAPAGOSII. We simultaneously fit single S��rsic 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 ($R_{e}$) the S��rsic index ($n$), axis ratio and position angle in each band. The sample contains 790 cluster members (located close to the cluster center < 0.64 R$_{200}$ and 254 non-member galaxies that we further separate based on their morphology into ellipticals, lenticulars and spirals. We find that the S��rsic index of all galaxies inside clusters remains nearly constant with wavelength while $R_{e}$ decreases as wavelength increases for all morphological types. We do not observe a significant variation on n and $R_{e}$ as a function of projected local density and distance from the clusters center. Comparing the n and $R_{e}$ 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 $R_{e}$). Moreover, the light profile ($\mathcal{N}$) and size ($\mathcal{R}$) of bright cluster galaxies does not change as a function of wavelength in the same manner as non-member galaxies., 16 pages, 17 figures and 5 tables

Using MUSE observations from the GASP survey, we study 54 galaxies undergoing ram-pressure stripping (RPS) spanning a wide range in galaxy mass and host cluster mass. We use this rich sample to study how the star formation rate (SFR) in the tails of stripped gas depends on the properties of the galaxy and its host cluster. We show that the interplay between all the parameters involved is complex and that there is not a single, dominant one in shaping the observed amount of SFR. Hence, we develop a simple analytical approach to describe the mass fraction of stripped gas and the SFR in the tail, as a function of the cluster velocity dispersion, galaxy stellar mass, clustercentric distance and speed in the intracluster medium. Our model provides a good description of the observed gas truncation radius and of the fraction of star-formation rate (SFR) observed in the stripped tails, once we take into account the fact that the star formation efficiency in the tails is a factor $\sim 5$ lower than in the galaxy disc, in agreement with GASP ongoing HI and CO observations. We finally estimate the contribution of RPS to the intracluster light (ICL) and find that the average SFR in the tails of ram-pressure stripped gas is $\sim 0.22 M_{\odot}\,\mathrm{yr}^{-1} $ per cluster. By extrapolating this result to evaluate the contribution to the ICL at different epochs, we compute an integrated average value per cluster of $\sim 4 \times 10^9 M_\odot$ of stars formed in the tails of RPS galaxies since $z\sim 1$., Comment: Accepted for publication in ApJ

Context. This is the second u-band extension of the WIde-field Nearby Galaxy-cluster Survey (WINGS) whereby 39 clusters were imaged with the ESO-VLT survey telescope. This follows the first part of the survey which was performed with several telescopes of the northern hemisphere in the U Cousin–Bessel filter band covering 17 clusters. Aims. The u-band data, in combination with those already collected by the WINGS survey, permit a detailed multi-wavelength investigation of the properties of the member galaxies from the cluster center out to the periphery. Methods. We used SExtractor to derive the main properties of the galaxies in the observed fields and measure the u − V colors on circular apertures of increasing radius. The photometric accuracy of the magnitudes was calibrated with the standard stars and was tested by means of comparisons with the u-band data of the Sloan Digital Sky Survey (SDSS). Results. We present the catalogs of the photometric analysis performed by SExtractor. We also provide a brief analysis of the u − V versus V color–magnitude diagram of our clusters, the plots of the color as a function of the cluster-centric distance (for cluster members only), the mass–color relation and the correlation of the current star formation rate (SFR) with the absolute V and u magnitudes for the galaxies in the observed fields.

We study the stellar mass functions (SMFs) of star-forming and quiescent galaxies in 11 galaxy clusters at 1.0, Comment: 19 pages, 9 figures (excluding appendices). Accepted for publication in A&A

Based on MUSE data from the GASP survey, we study the Halpha-emitting extraplanar tails of 16 cluster galaxies at z~0.05 undergoing ram pressure stripping. We demonstrate that the dominating ionization mechanism of this gas (between 64% and 94% of the Halpha 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 HII clumps with a median Halpha 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 Halpha luminosity L_{Halpha} = 4 X 10^38 erg s^-1, dust extinction A_V=0.5 mag, star formation rate SFR=0.003 M_sun yr^-1, ionized gas density n_e =52 cm^-3, ionized gas mass M_gas = 4 X 10^4 Msun, and stellar mass M_{*} = 3 X 10^6 Msun. The tail clumps follow scaling relations (M_gas-M_{*}, L_{Halpha} -sigma, SFR-M_gas) similar to disk 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 HII clumps with an average escape fraction of 18%, or lower luminosity HII regions that we cannot individually identify., Comment: accepted for publication in MNRAS

Jellyfish are cluster galaxies that experience strong ram-pressure effects that strip their gas. Their H$\alpha$ 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 $\sim$ 1.3 kpc. The intense burst of star formation happening in the tentacles is the focus of the present study. JO201 is the "UV-brightest cluster galaxy" in Abell 85 ($z \sim$ 0.056) with knots and streams of star formation in the ultraviolet. We identify star forming knots both in the stripped gas and in the galaxy disk and compare the UV features with the ones traced by H$\alpha$ 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 FUV emission agree with those derived from the H$\alpha$ emission and range from $\sim$ 0.01 -to- 2.07 $M_{\odot} \, yr^{-1}$. The integrated star formation rate from FUV flux is $\sim$ 15 $M_{\odot} \, yr^{-1}$. 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.