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We present the first results of a 21 cm H?I line pilot observation carried out with the MeerKAT radio telescope in preparation for the ViCTORIA (Virgo Cluster multi Telescope Observations in Radio of Interacting galaxies and AGN) 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? 39? and 11 km s-1 resolution) allowed us to detect an extended (~10 kpc projected length) low column density (N(HI)?2.5 1020 cm-2) H?I gas tail associated with the dwarf (Mstar = 1.6 109 M?) irregular galaxy NGC 4523 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 H?I gas column density at the interface between the cold interstellar medium (ISM) and the hot ICM, the velocity of the galaxy with respect to that of the cluster, and its position indicate that NGC 4523 is infalling for the first time into Virgo from the north-north-west 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 Hanarrow-band images obtained during the VESTIGE survey, suggesting that NGC 4523 is only at the beginning of its interaction with the surrounding environment. A few H?II regions are detected in the deep Hanarrow-band images within the H?I gas tail outside the stellar disc. Their ages, derived by comparing their Ha, far-ultraviolet (ASTROSAT/UVIT), near-ultraviolet (GALEX/GUViCS), and optical (NGVS) colours with the predict

As part of the Virgo Cluster Survey Tracing Ionised Gas Emission, a blind narrow-band H+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the CFHT, we discovered eight massive (1010 . Mstar . 1011 M) lenticular galaxies with prominent ionised gas emission features in their inner (a few kiloparsec) regions. These features are either ionised gas filaments similar to those observed in cooling flows (two galaxies), or they are thin discs with sizes 0:7 . R(H) . 2:0 kpc (six galaxies), thus significantly smaller than those of the stellar disc (R(H) ' 7 22%Riso(r)). The morphological properties of these discs are similar to those of the dust seen in absorption in high-resolution HST images. Using a unique set of multifrequency data, including new or archival ASTROSAT/UVIT, GALEX, HST, CFHT, Spitzer, and Herschel imaging data, combined with IFU (MUSE, ALMA) and long-slit (SOAR) spectroscopy, we show that while the gas that is located within these inner discs is photoionised by young stars, which signals ongoing star formation, the gas in the filamentary structures is shock ionised. The star formation surface brightness of these discs is similar to that observed in late-type galaxies. Because of their reduced size, however, these lenticular galaxies are located below the main sequence of unperturbed or cluster star-forming systems. By comparing the dust masses measured from absorption maps in optical images, from the Balmer decrement, or estimated by fitting the UV-to-far-IR spectral energy distribution of the target galaxies, we confirm that the dust masses derived from optical attenuation maps are heavily underestimated because of geometrical eects due to the relative distribution of the absorbing dust and the emitting stars. We also show that these galaxies have gas-to-dust ratios of G=D ' 80320 30 , and that the star formation within these discs follows the Schmidt relation, but with an eciency that is reduced by a factor of 2.5. Using our unique set

The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band H + [NII] imaging survey of the Virgo cluster carried out with MegaCam at the Canada-French-Hawaii telescope. 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). Here, 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 (106:5 - Mstar - 1011 M), and star formation activity (10-3 - SFR - 10 M yr-1). Owing to the exquisite average resolution of the VESTIGE data (0.65 arcsec), we detect 11302 HII regions with an H luminosity L(H) 1037 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 eective 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, which are unable to reproduce the observed radially truncated profiles.

As part of the Virgo Cluster Survey Tracing Ionised Gas Emission, a blind narrow-band H+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the CFHT, we discovered eight massive (1010 . Mstar . 1011 M) lenticular galaxies with prominent ionised gas emission features in their inner (a few kiloparsec) regions. These features are either ionised gas filaments similar to those observed in cooling flows (two galaxies), or they are thin discs with sizes 0:7 . R(H) . 2:0 kpc (six galaxies), thus significantly smaller than those of the stellar disc (R(H) ' 7 22%Riso(r)). The morphological properties of these discs are similar to those of the dust seen in absorption in high-resolution HST images. Using a unique set of multifrequency data, including new or archival ASTROSAT/UVIT, GALEX, HST, CFHT, Spitzer, and Herschel imaging data, combined with IFU (MUSE, ALMA) and long-slit (SOAR) spectroscopy, we show that while the gas that is located within these inner discs is photoionised by young stars, which signals ongoing star formation, the gas in the filamentary structures is shock ionised. The star formation surface brightness of these discs is similar to that observed in late-type galaxies. Because of their reduced size, however, these lenticular galaxies are located below the main sequence of unperturbed or cluster star-forming systems. By comparing the dust masses measured from absorption maps in optical images, from the Balmer decrement, or estimated by fitting the UV-to-far-IR spectral energy distribution of the target galaxies, we confirm that the dust masses derived from optical attenuation maps are heavily underestimated because of geometrical eects due to the relative distribution of the absorbing dust and the emitting stars. We also show that these galaxies have gas-to-dust ratios of G=D ' 80320 30 , and that the star formation within these discs follows the Schmidt relation, but with an eciency that is reduced by a factor of 2.5. Using our unique set

We present an automatic procedure to perform reliable photometry of galaxies on SDSS images.We selected a sample of 5853 galaxies in the Coma and Virgo superclusters. For each galaxy, we derive Petrosian g and i magnitudes, surface brightness and color profiles. Unlike the SDSS pipeline, our procedure is not affected by the well known shredding problem and eficiently extracts Petrosian magnitudes for all galaxies. Hence we derived magnitudes even from the population of galaxies missed by the SDSS which represents ~25% of all local supercluster galaxies and ~95% of galaxies with g 11 mag. After correcting the g and i magnitudes for Galactic and internal extinction, the blue and red sequences in the color magnitude diagram are well separated, with similar slopes. In addition, we study (i) the color-magnitude diagrams in different galaxy regions, the inner (r ≥ 1 kpc), intermediate (0:2RPet ≥ r ≥ 0:3RPet) and outer, disk-dominated (r 0:35RPet)) zone; and (ii), we compute template color profiles, discussing the dependences of the templates on the galaxy masses and on their morphological type. The two analyses consistently lead to a picture where elliptical galaxies show no color gradients, irrespective of their masses. Spirals, instead, display a steeper gradient in their color profiles with increasing mass, which is consistent with the growing relevance of a bulge and/or a bar component above 1010.

We present Halpha line imaging observations of 122 galaxies obtained with the 1.20 m telescopes of the Observatoire de Haute Provence (OHP) and of Calar Alto. The observed galaxies are mostly Virgo cluster members (95), along with 10 objects in the Coma/A1367 supercluster, 6 in the clusters A2197 and A2199, and 11 nearby galaxies taken as fillers. Halpha+[NII] fluxes and equivalent widths, as well as images of all the detected targets, are presented

We study the role of the environment on galaxy evolution using a sample of 868 galaxies in the Virgo cluster and in its surrounding regions that are selected from the GALEX Ultraviolet Virgo Cluster Survey (GUViCS) with the purpose of understanding the origin of the red sequence in dense environments. The sample spans a wide range in morphological types (from dwarf ellipticals to Im and BCD) and stellar masses (107 Mstar 1011.5MâŠTM). We collected multifrequency data covering the whole electromagnetic spectrum for most of the galaxies, including UV, optical, mid-and far-infrared imaging data, as well as optical and HI spectroscopic data. We first identify the different dynamical substructures that compose the Virgo cluster, and we calculate the local density of galaxies using different methods. We then study the distribution of galaxies belonging to the red sequence, the green valley, and the blue cloud within the different cluster substructures or as a function of galaxy density. Our analysis indicates that all the most massive galaxies (Mstar 1011MâŠTM) are slow rotators and are the dominant galaxies of the different cluster substructures, which are generally associated with a diffuse X-ray emission. They are probably the result of major merging events that occurred at early epochs, as also indicated by their very old stellar populations. Slow rotators of lower stellar mass (108.5 Mstar 1011MâŠTM) are also preferentially located within the different high-density substructures of the cluster. Their position in the velocity space indicates that they are virialised within the cluster; thus, they are Virgo members since its formation. They have been shaped by gravitational perturbations occurring within the infalling groups that later form the cluster (pre-processing). On the contrary, low-mass star-forming systems are extremely rare in the inner regions of the Virgo cluster A, where the density of the intergalactic medium is at its maximum. Our ram pressure str

We present a resolved dust analysis of three of the largest angular size spiral galaxies, NGC 4501 and NGC 4567/8, in the Herschel Virgo Cluster Survey (HeViCS) science demonstration field. Herschel has unprecedented spatial resolution at far-infrared wavelengths and with the PACS and SPIRE instruments samples both sides of the peak in the far infrared spectral energy distribution (SED). We present maps of dust temperature, dust mass, and gas-to-dust ratio, produced by fitting modified black bodies to the SED for each pixel. We find that the distribution of dust temperature in both systems is in the range ∼19-22 K and peaks away from the centres of the galaxies. The distribution of dust mass in both systems is symmetrical and exhibits a single peak coincident with the galaxy centres. This Letter provides a first insight into the future analysis possible with a large sample of resolved galaxies to be observed by Herschel. © 2010 ESO.

Passive early-type galaxies (ETGs) provide an ideal laboratory for studying the interplay between dust formation around evolved stars and its subsequent destruction in a hot gas. Using Spitzer-IRS and Herschel data we compare the dust production rate in the envelopes of evolved AGB stars with a constraint on the total dust mass. Early-type galaxies which appear to be truly passively evolving are not detected by Herschel. We thus derive a distance independent upper limit to the dust grain survival time in the hostile environment of ETGs of <46±25 Myr for amorphous silicate grains. This implies that ETGs which are detected at far-infrared wavelengths have acquired a cool dusty medium via interaction. Given likely time-scales for ram-pressure stripping, this also implies that only galaxies with dust in a cool (atomic) medium can release dust into the intra-cluster medium. © ESO 2010.

We use the science demonstration phase data of the Herschel Virgo Cluster Survey to search for dust emission of early-type dwarf galaxies in the central regions of the Virgo cluster as an alternative way of identifying the interstellar medium. We present the first possible far-infrared detection of cluster early-type dwarf galaxies: VCC781 and VCC951 are detected at the 10(sigma) level in the SPIRE 250 mu m image. Both detected galaxies have dust masses of the order of 10(5) M-circle dot and average dust temperatures approximate to 20 K. The detection rate (less than 1%) is quite high compared to the 1.7% detection rate for Hi emission, considering that dwarfs in the central regions are more Hi deficient. We conclude that the removal of interstellar dust from dwarf galaxies resulting from ram pressure stripping, harassment, or tidal effects must be as efficient as the removal of interstellar gas.

By combining Herschel-SPIRE observations obtained as part of the Herschel Virgo Cluster Survey with 21 cm Hi data from the literature, we investigate the role of the cluster environment on the dust content of Virgo spiral galaxies. We show for the first time that the extent of the dust disk is significantly reduced in Hi-deficient galaxies, following remarkably well the observed "truncation" of the Hi disk. The ratio of the submillimetre-to-optical diameter correlates with the Hi-deficiency, suggesting that the cluster environment is able to strip dust as well as gas. These results provide important insights not only into the evolution of cluster galaxies but also into the metal enrichment of the intra-cluster medium.

High sensitivity 21-cm H I line observations with an rms noise level of similar to 0.5 mJy were made of 35 spiral galaxies in the Coma Supercluster, using the refurbished Arecibo telescope, leading to detection of 25 objects. These data, combined with the measurements available in the literature, provide the set of H I data for 94% of all late-type galaxies in the Coma Supercluster with an apparent photographic magnitude m(p) <= 15.7 mag. We confirm that the typical scale of H I deficiency around the Coma cluster is 2 Mpc, i.e. one virial radius. Comparing the H I mass function (HIMF) of cluster with non-cluster members of the Coma Supercluster we detected a shortage of high Hi mass galaxies among cluster members that can be attributed to the pattern of H I deficiency found in rich clusters.

We present a multiwavelength analysis of a compact group of galaxies infalling at high speed into the dynamically young cluster Abell 1367. Peculiar morphologies and unusually high H alpha emission are associated with two giant galaxies and at least ten dwarfs/extragalactic HII regions, making this group the region with the highest density of star formation activity ever observed in the local clusters. Moreover H alpha imaging observations reveal extraordinary complex trails of ionized gas behind the galaxies, with projected lengths exceeding 150 kpc. These unique cometary trails mark the gaseous trajectory of galaxies, witnessing their dive into the hot cluster intergalactic medium. Under the combined action of tidal forces among group members and the ram-pressure by the cluster ambient medium, the group galaxies were fragmented and the ionized gas was blown out. The properties of this group suggest that environmental effects within infalling groups may have represented a preprocessing step of the galaxy evolution during the high redshift cluster assembly phase.

High sensitivity (rms noise similar to0.5 mJy) 21-cm HI line observations were made of 33 galaxies in the Virgo cluster, using the refurbished Arecibo telescope, which resulted in the detection of 12 objects. These data, combined with the measurements available from the literature, provide the first set of H. data that is complete for all 355 late-type (Sa-Im-BCD) galaxies in the Virgo cluster with m(p) less than or equal to 18.0 mag. The Virgo cluster HI mass function (HIMF) that was derived for this optically selected galaxy sample is in agreement with the HIMF derived for the Virgo cluster from the blind HIJASS HI survey and is inconsistent with the Field HIMF. This indicates that both in this rich cluster and in the general field, neutral hydrogen is primarily associated with late-type galaxies, with marginal contributions from early-type galaxies and isolated H. clouds. The inconsistency between the cluster and the field HIMF derives primarily from the difference in the optical luminosity function of late-type galaxies in the two environments, combined with the HI deficiency that is known to occur in galaxies in rich clusters.

We report on a complete CCD imaging survey of 226 elliptical galaxies in the North-East quadrant of the Virgo cluster, representative of the properties of giant and dwarf elliptical galaxies in this cluster. We fit their radial light profiles with the Sersic r(1/n) model of light distribution. We confirm the result of Graham & Guzman ( 2003, AJ, 125, 2936) that the apparent dichotomy between E and dE galaxies in the luminosity -[mu](e) plane no longer appears when other structural parameters are considered and can be entirely attributed to the onset of "core" galaxies at B-T similar to - 20.5 mag. When "core" galaxies are not considered, E and dE form a unique family with n linearly increasing with the luminosity. For 90 galaxies we analyze the B - I color indices, both in the nuclear and in the outer regions. Both indices are bluer toward fainter luminosities. We find also that the outer color gradients do not show any significant correlation with the luminosity. The scatter in all color indicators increases significantly toward lower luminosities, e.g. galaxies fainter than B-T similar to - 15 have a B - I spread > 0.5 mag.