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With the aim of providing the complete demography of galaxies in the local Universe, including their nuclear properties, we present SPRING, a complete census of local galaxies limited to the spring quarter of the Northern sky (10h< RA <16h; 0< Dec <65). The SPRING catalogue is a flux- and volume-limited sample (r < 17.7 mag, cz < 10000 km/s) of 30597 galaxies, including the Virgo, Coma and A1367 clusters. To inspect possible secular and environmental dependencies of the various nuclear excitation properties (SF vs. AGN), we perform a multidimensional analysis by dividing the sample according to (i) their position in the (NUV-i) vs. M* diagram,(ii) local galaxy density, (iii) stellar-mass, (iv) halo-mass of the group to which galaxies belong, and (v) neutral Hydrogen content. We present a new calibration of the optical diameter-based HI-deficiency parameter employing a reference sample of isolated galaxies. At intermediate distances between Virgo and Coma, we identify a ring-like structure of galaxies constituted by three large filaments. The fraction of HI-deficient galaxies within the filament suggests that filaments are a transitioning environment between field and cluster in terms of HI content. We classify the nuclear spectra according to the four-line BPT and the two-line WHAN diagrams, and investigate the variation in the fraction of AGN with stellar-mass, as well as their colours and environments. In general, we observe that the mass-dependency of the fraction of Seyfert nuclei is little sensitive to the environment, whereas the fraction of star-forming nuclei is a steeper function of M* in lower-density environments and in blue-cloud galaxies. We find that the fraction of LINERs depends on galaxy colour and, for logM* > 9.5-10, increases in galaxies belonging to the green valley., Comment: 26 pages, 22 figures. Accepted for publication in Astronomy & Astrophysics

We present an analysis of the kinematics and ionization conditions in a sample composed of seven star-forming galaxies undergoing ram-pressure stripping in the A1367 cluster, and the galaxy ESO137-001 in the Norma cluster. MUSE observations of two new galaxies in this sample, CGCG097-073 and CGCG097-079, are also presented. This sample is characterized by homogeneous integral field spectroscopy with MUSE and by a consistent selection based on the presence of ionised gas tails. The ratio [OI]/H${\alpha}$ is consistently elevated in the tails of these objects compared to what observed in unperturbed galaxy disks, an ubiquitous feature which we attribute to shocks or turbulent phenomena in the stripped gas. Compact star-forming regions are observed in only $\approx$ 50% of the tails, implying that specific (currently unknown) conditions are needed to trigger star formation inside the stripped gas. Focusing on the interface regions between the interstellar and intracluster medium, we observe different line ratios that we associate to different stages of the stripping process, with galaxies at an early stage of perturbation showing more prominent signatures of elevated star formation. Our analysis thus demonstrates the power of a well selected and homogeneous sample to infer general properties arising from ram-pressure stripping inside local clusters., Comment: 19 pages, 14 figures. Accepted for publication in MNRAS

Recent studies have highlighted the potential significance of intracluster medium (ICM) clumping and its important implications for cluster cosmology and baryon physics. Many of the ICM clumps can originate from infalling galaxies, as stripped interstellar medium (ISM) mixing into the hot ICM. However, a direct connection between ICM clumping and stripped ISM has not been unambiguously established before. Here we present the discovery of the first and still the only known isolated cloud (or orphan cloud, OC) detected in both X-rays and H$\alpha$ in the nearby cluster Abell 1367. With an effective radius of 30 kpc, this cloud has an average X-ray temperature of 1.6 keV, a bolometric X-ray luminosity of $\sim 3.1\times 10^{41}$ erg s$^{-1}$ and a hot gas mass of $\sim 10^{10}\ {\rm M}_\odot$. From the MUSE data, the OC shows an interesting velocity gradient nearly along the east-west direction with a low level of velocity dispersion of $\sim 80$ km/s, which may suggest a low level of the ICM turbulence. The emission line diagnostics suggest little star formation in the main H$\alpha$ cloud and a LI(N)ER-like spectrum, but the excitation mechanism remain unclear. This example shows that the stripped ISM, even long time after the initial removal from the galaxy, can still induce the ICM inhomogeneities. We suggest that magnetic field can stabilize the OC by suppressing hydrodynamic instabilities and thermal conduction. This example also suggests that at least some ICM clumps are multi-phase in nature and implies that the ICM clumps can also be traced in H$\alpha$. Thus, future deep and wide-field H$\alpha$ survey can be used to probe the ICM clumping and turbulence., Comment: 16 pages, 9 figures, 2 tables, MNRAS, in press, minor changes with abstract/conclusion the same

The impact of ram pressure stripping on galaxy evolution is well known. Recent multi-wavelength data have revealed many examples of galaxies undergoing stripping, often accompanied with multi-phase tails. As energy transfer in the multi-phase medium is an outstanding question in astrophysics, galaxies in stripping are great objects to study. Despite the recent burst of observational evidence, the relationship between gas in different phases in the tails is poorly known. Here we report a strong linear correlation between the X-ray surface brightness and the H$\alpha$ surface brightness of the diffuse gas in the stripped tails at $\sim$ 10 - 40 kpc scales, with a slope of $\sim$ 3.5. This discovery provides evidence for the mixing of the stripped interstellar medium with the hot intracluster medium as the origin of the multi-phase tails. The established relation in stripped tails, also in comparison with the likely related correlations in similar environments like galactic winds and X-ray cool cores, provides an important test for models of energy transfer in the multi-phase gas. It also indicates the importance of the H$\alpha$ data to study clumping and turbulence in the intracluster medium., Comment: Published on Nature Astronomy on Dec. 13, 2021, https://www.nature.com/articles/s41550-021-01516-8; results updated with more MUSE data, region updates and more discussion; conclusions unchanged

Previous studies have revealed a population of galaxies in galaxy clusters with ram pressure stripped (RPS) tails of gas and embedded young stars. We observed 1.4 GHz continuum and HI emission with the Very Large Array in its B-configuration in two fields of the Coma cluster to study the radio properties of RPS galaxies. The best continuum sensitivities in the two fields are 6 and 8 $\mu$Jy per 4'' beam respectively, which are 4 and 3 times deeper than those previously published. Radio continuum tails are found in 10 (8 are new) out of 20 RPS galaxies, unambiguously revealing the presence of relativistic electrons and magnetic fields in the stripped tails. Our results also hint that the tail has a steeper spectrum than the galaxy. The 1.4 GHz continuum in the tails is enhanced relative to their H$\alpha$ emission by a factor of $\sim$7 compared to the main bodies of the RPS galaxies. The 1.4 GHz continuum of the RPS galaxies is also enhanced relative to their IR emission by a factor of $\sim$2 compared to star-forming galaxies. The enhancement is likely related to ram pressure and turbulence in the tail. We furthermore present HI detections in three RPS galaxies and upper limits for the other RPS galaxies. The cold gas in D100's stripped tail is dominated by molecular gas, which is likely a consequence of the high ambient pressure. No evidence of radio emission associated with ultra-diffuse galaxies is found in our data., Comment: 20 pages, 11 figures, accepted by MNRAS, matched with the accepted version

Multi-wavelength observations show that Abell 1367 (A1367) is a dynamically young cluster, with at least two subclusters merging along the SE-NW direction. With the wide-field XMM-Newton mosaic of A1367, we discover a previously unknown merger shock at the NW edge of the cluster. We estimate the shock Mach number from the density and temperature jumps as $M_{\rho}=1.21\pm0.08$ and $M_T=1.60\pm0.07$, respectively. This shock region also corresponds to a radio relic discovered with the VLA and GBT, which could be produced by the shock re-acceleration of pre-existing seed relativistic electrons. We suggest that some of the seed relativistic electrons originate from late-type, star-forming galaxies in this region., Comment: 5 pages, 1 figure, MNRAS Letters in press

We report new wide-field (~ 4 x 4 square arcmin) MUSE observations of the Blue Infalling Group (BIG), a compact group of galaxies located at a projected distance of ~ 150 kpc from the X-Ray centre of the A1367 cluster at z = 0.021. Our MUSE observations map in detail the extended ionized gas, primarily traced by H$\alpha$ emission, in between the members of the group. The gas morphology and its kinematics appear consistent with a tidal origin due to galaxy encounters, as also supported by the disturbed kinematics visible in one of the group members and the presence of tidal dwarf systems. A diffuse tail extending in the direction opposite to the cluster centre is also detected, hinting at a global ram-pressure stripping of the intra-group material as BIG falls inside A1367. Based on the analysis of spatially-resolved emission line maps, we identify multiple ionization mechanisms for the diffuse gas filaments, including in situ photoionization from embedded HII regions and shocks. Combining spatially resolved kinematics and line ratios, we rule out the association of the most massive galaxy, CGCG097-120, with the group as this system appears to be decoupled from the intragroup medium and subject to strong ram pressure as it falls into A1367. Through our new analysis, we conclude that BIG is shaped by pre-processing produced by gravitational interactions in the local group environment combined with ram pressure stripping by the global cluster halo., Comment: 19 pages, 12 figures, accepted for publication in MNRAS

We present the MUSE observations of UGC 6697, a giant (Mstar 10^{10} Msol) spiral galaxy infalling in the nearby cluster Abell 1367. During its high velocity transit through the intracluster medium (ICM), the hydrodynamical interactions with the ICM produce a ~ 100 kpc tail of ionized gas that we map with a mosaic of five MUSE pointings up to 60 kpc from the galaxy. CGCG 97087N, a small companion that lies at few arcminutes in projection from UGC 6697, is also suffering from the hydrodynamic action of the ICM of the cluster. Along the whole extent of the tail we detect diffuse H$\alpha$ emission and, to a lesser extent, H$\beta$, [OIII]$\lambda5007$, and [OI]$\lambda6300$. By comparing the kinematics and distribution of gas and stars (as traced by the CaII triplet) for both galaxies, we separate the ionized gas, as traced by the H$\alpha$ line, in a component still bound to the galaxy and a component that is stripped. We find that the "onboard" component shows low velocity dispersion and line ratios consistent with photoionization by hot stars. The stripped gas is more turbulent, with velocity dispersions up to > 100 km/s}, and is excited by shocks as traced by high values of [OI]/H$\alpha$ and [NII]/H$\alpha$ ratio. In the tail of UGC 6697 we identify numerous bright compact knots with line ratios typical of HII regions. These are distributed along the only streams of stripped gas retaining low velocity dispersions (< 35 km/s). Despite being in the stripped gas, their physical properties do not differentiate from normal HII regions in galactic disks. We find evidence of a past fast encounter between the two galaxies in the form of a double tail emerging from CGCG 97087N that connects with UGC 6697. This encounter might have increased the efficiency of the stripping process, leaving the stellar distribution and kinematics unaltered., Comment: Accepted for publication on A&A

We surveyed a central 0.6 deg^2 region of Abell 1367 cluster for extended ionized gas clouds (EIGs) using the Subaru prime-focus camera (Suprime-Cam) with a narrow-band filter that covers Halpha. We discovered six new EIGs in addition to five known EIGs. We also found that the Halpha tail from the blue infalling group (BIG) is extended to about 330 kpc in projected distance, which is about twice longer than previously reported. Candidates of star-forming blobs in the tail are detected. The properties of the EIG parent galaxies in Abell 1367 basically resemble those in the Coma cluster. A noticeable difference is that the number of detached EIGs is significantly fewer in Abell 1367, while the fraction of blue member galaxies is higher. The results suggest a difference in the evolutionary stage of the clusters; Abell 1367 is at an earlier stage than the Coma cluster., Comment: 31 pages, 22 figures(40 images), accepted by ApJ

We present an observational study of the effect of bars on the gas component and on the star formation properties of their host galaxies in a statistically significant sample of resolved objects, the $Herschel$ Reference Sample. The analysis of optical and far--infrared images allows us to identify a clear spatial correlation between stellar bars and the cold-gas distribution mapped by the warm dust emission. We find that the infrared counterparts of optically identified bars are either bar--like structures or dead central regions in which star formation is strongly suppressed. Similar morphologies are found in the distribution of star formation directly traced by H$\alpha$ maps. The sizes of such optical and infrared structures correlate remarkably well, hinting at a causal connection. In the light of previous observations and of theoretical investigations in the literature, we interpret our findings as further evidence of the scenario in which bars drive strong inflows toward their host nuclei: young bars are still in the process of perturbing the gas and star formation clearly delineates the shape of the bars; old bars on the contrary already removed any gas within their extents, carving a dead region of negligible star formation., Comment: Accepted for publication in Astronomy and Astrophysics

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 profiles and color profiles. Unlike the SDSS pipeline, our procedure is not affected by the well known shredding problem and efficiently extracts Petrosian magnitudes for all galaxies. Hence we derived magnitudes even from the population of galaxies missed by the SDSS that 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 (0.2R{Pet} <=r<= 0.3R{Pet}) and outer, disk-dominated (r>=0.35R{Pet})) 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, consistently with the growing relevance of a bulge and/or a bar component above 10^{10} Modot., Comment: 18 pages, 12 figures, Accepted for publication by Astronomy & Astrophysics

We present a study of the physical properties of the disc and tail of ESO137-001, a galaxy suffering from extreme ram-pressure stripping during its infall into the Norma cluster. With sensitive and spatially-resolved MUSE spectroscopy, we analyse the emission line diagnostics in the tail of ESO137-001, finding high values of [NII]/H$\alpha$ and [OI]/H$\alpha$ that are suggestive of the presence of shocks in turbulent gas. However, the observed line ratios are not as strong as commonly seen in pure shock heating models, suggesting that other emission mechanisms may contribute to the observed emission. Indeed, part of the observed emission, particularly at close separations from the galaxy disc, may originate from recombination of photoionised gas stripped from the main body of ESO137-001. We also identify a large number of bright compact knots within in the tail, with line ratios characteristic of HII regions. These HII regions, despite residing in a stripped gas tail, have quite typical line ratios, densities, temperatures, and metallicity ($\sim0.7$ solar). The majority of these HII regions are embedded within diffuse gas from the tail, which is dynamically cool ($\sigma \sim 25-50\ \rm{km\ s^{-1}}$ ). This fact, together with a lack of appreciable gradients in age and metallicity, suggests that these HII regions formed in situ. While our analysis represents a first attempt to characterise the rich physics of the ESO137-001 tail, future work is needed to address the importance of other mechanisms, such as thermal conduction and magneto hydrodynamic waves, in powering the emission in the tail., Comment: 15 pages, 8 figures, 2 tables, modified to match MNRAS published version

Neutral hydrogen represents the major observable baryonic constituent of galaxies that fuels the formation of stars through the transformation in molecular hydrogen. The emission of the hydrogen recombination line Halpha is the most direct tracer of the process that transforms gas (fuel) into stars. We continue to present Halpha3 (acronym for Halpha-alpha-alpha), an extensive Halpha+[NII] narrow-band imaging campaign of galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA), using the instrumentation available at the San Pedro Martir observatory (Mexico). In only four years since 2011 we were able to complete in 48 nights the Halpha imaging observations of 724 galaxies in the region of the Coma supercluster 10^h < R.A. <16^h; 24^o < Dec. <28^o and 3900

With the advent of the next generation wide-field cameras it became possible to survey in an unbiased mode galaxies spanning a variety of local densities, from the core of rich clusters, to compact and loose groups, down to filaments and voids. The sensitivity reached by these instruments allowed to extend the observation to dwarf galaxies, the most "fragile" objects in the universe. At the same time models and simulations have been tailored to quantify the different effects of the environment on the evolution of galaxies. Simulations, models, and observations consistently indicate that star-forming dwarf galaxies entering high-density environments for the first time can be rapidly stripped from their interstellar medium. The lack of gas quenches the activity of star formation, producing on timescales of ${\sim}$1~Gyr quiescent galaxies with spectro-photometric, chemical, structural, and kinematical properties similar to those observed in dwarf early-type galaxies inhabiting rich clusters and loose groups. Simulations and observations consistently identify ram pressure stripping as the major effect responsible for the quenching of the star-formation activity in rich clusters. Gravitational interactions (galaxy harassment) can also be important in groups or in clusters whenever galaxies have been members since early epochs. The observation of clusters at different redshifts combined with the present high infalling rate of galaxies onto clusters indicate that the quenching of the star-formation activity in dwarf systems and the formation of the faint end of the red sequence is a very recent phenomenon., Comment: Invited review on Astronomy & Astrophysics Review, accepted for publication

We present MUSE observations of ESO137-001, a spiral galaxy infalling towards the center of the massive Norma cluster at z~0.0162. During the high-velocity encounter of ESO137-001 with the intracluster medium, a dramatic ram-pressure stripping event gives rise to an extended gaseous tail, traced by our MUSE observations to >30 kpc from the galaxy center. By studying the H-alpha surface brightness and kinematics in tandem with the stellar velocity field, we conclude that ram pressure has completely removed the interstellar medium from the outer disk, while the primary tail is still fed by gas from the inner regions. Gravitational interactions do not appear to be a primary mechanism for gas removal. The stripped gas retains the imprint of the disk rotational velocity to ~20 kpc downstream, without a significant gradient along the tail, which suggests that ESO137-001 is fast moving along a radial orbit in the plane of the sky. Conversely, beyond ~20 kpc, a greater degree of turbulence is seen, with velocity dispersion up to >100 km/s. For a model-dependent infall velocity of ~3000 km/s, we conclude that the transition from laminar to turbulent flow in the tail occurs on timescales >6.5 Myr. Our work demonstrates the terrific potential of MUSE for detailed studies of how ram-pressure stripping operates on small scales, providing a deep understanding of how galaxies interact with the dense plasma of the cluster environment., Comment: 10 pages, 6 figures. MNRAS in press

We present the refurbished GOLDMine galaxy site (http://goldmine.mib.infn.it) superseding the one operating since 2002 (Gavazzi et al. 2003). Data for 9704 galaxies selected with r<17.7 mag from the SDSS, belonging to the Cancer cluster, Local supercluster, Coma supercluster, Hercules, A2197 and A2199 clusters are included., Comment: 1 page, 1 figure

The NGVS-IR project (Next Generation Virgo Survey - Infrared) is a contiguous near-infrared imaging survey of the Virgo cluster of galaxies. It complements the optical wide-field survey of Virgo (NGVS). The current state of NGVS-IR consists of Ks-band imaging of 4 deg^2 centered on M87, and J and Ks-band imaging of 16 deg^2 covering the region between M49 and M87. In this paper, we present the observations of the central 4 deg^2 centered on Virgo's core region. The data were acquired with WIRCam on the Canada-France-Hawaii Telescope and the total integration time was 41 hours distributed in 34 contiguous tiles. A survey-specific strategy was designed to account for extended galaxies while still measuring accurate sky brightness within the survey area. The average 5\sigma limiting magnitude is Ks=24.4 AB mag and the 50% completeness limit is Ks=23.75 AB mag for point source detections, when using only images with better than 0.7" seeing (median seeing 0.54"). Star clusters are marginally resolved in these image stacks, and Virgo galaxies with \mu_Ks=24.4 AB mag arcsec^-2 are detected. Combining the Ks data with optical and ultraviolet data, we build the uiK color-color diagram which allows a very clean color-based selection of globular clusters in Virgo. This diagnostic plot will provide reliable globular cluster candidates for spectroscopic follow-up campaigns needed to continue the exploration of Virgo's photometric and kinematic sub-structures, and will help the design of future searches for globular clusters in extragalactic systems. Equipped with this powerful new tool, future NGVS-IR investigations based on the uiK diagram will address the mapping and analysis of extended structures and compact stellar systems in and around Virgo galaxies., Comment: 23 pages, 18 figures. Accepted for publication in ApJS

We obtained long-slit optical spectra of the nuclear regions of 376 galaxies in the local Universe using the 1.5m Cassini telescope of Bologna Observatory. Of these spectra, 164 were either never taken before by the Sloan Digital Sky Survey (SDSS), or given by the Nasa Extragalactic Database (NED). With these new spectra, we contribute investigating the occurrence of active galactic nuclei (AGNs). Nevertheless, we stress that the present sample is by no means complete, thus, it cannot be used to perform any demographic study. Following the method presented in Gavazzi et al. (2011), we classify the nuclear spectra using a six bin scheme: SEY (Seyfert), sAGN (strong AGN), and wAGN (weak AGN) represent active galactic nuclei of different levels of activity; HII accounts for star-forming nuclei; RET (retired) and PAS (passive) refer to nuclei with poor or no star-formation activity. The spectral classification is performed using the ratio of 6584 {\lambda} [NII] to H{\alpha} lines and the equivalent width (EW) of H{\alpha} versus [NII]/H{\alpha} (WHAN diagnostic introduced by Cid Fernandes and collaborators) after correcting H{\alpha} for underlying absorption. The obtained spectra are made available in machine readable format via the Strasbourg Astronomical Data Center (CDS) and NED., Comment: 8 pages, 6 Figures, 4 Tables, accepted for publication in Astronomy & Astrophysics

We present the analysis of Halpha3, an Halpha imaging survey of 409 galaxies selected from the HI Arecibo ALFALFA Survey in the Local Supercluster, including the Virgo cluster. We explore the relations between the stellar mass, the HI mass and the current, massive SFR of nearby galaxies in the Virgo cluster and we compare them with those of isolated galaxies in the Local Supercluster, disentangling the role of the environment in shaping the star formation properties of galaxies at the present cosmological epoch. We investigate the relationships between atomic neutral gas and newly formed stars in different environments, across many morphological types, and over a wide range of stellar masses adopting an updated calibration of the HI deficiency parameter. Studying the mean properties of late-type galaxies in the Local Supercluster, we find that galaxies in increasing local galaxy density conditions (or decreasing projected angular separation from M87) show a significant decrease in the HI content and in the mean specific star formation rate, along with a progressive reddening of their stellar populations. The gradual quenching of the star formation occurs outside-in, consistently with the predictions of the ram pressure model. Once considered as a whole, the Virgo cluster is effective in removing neutral hydrogen from galaxies, and this perturbation is strong enough to appreciably reduce the SFR of its entire galaxy population. An estimate of the present infall rate of 300-400 galaxies per Gyr in the Virgo cluster is obtained from the number of existing HI-rich late-type systems, assuming 200-300 Myr as the time scale for HI ablation. If the infall process has been acting at constant rate this would imply that the Virgo cluster has formed approximately 2 Gyr ago, consistently with the idea that Virgo is in a young state of dynamical evolution., Comment: 13 pages, 10 figures, 4 tables, A&A accepted, language edited

We present the analysis of Halpha3, an Halpha imaging survey of galaxies selected from the HI ALFALFA Survey in the Coma Supercluster. By using the Halpha line as a tracer of the "instantaneous" star formation, complemented with optical colors from SDSS we explore the hypothesis that a morphological sequence of galaxies of progressively earlier type, lower gas-content exists in the neighborhood of the Coma cluster, with specific star formation activity decreasing with increasing local galaxy density and velocity dispersion. In the dwarf regime (8.5<\log(M*)< 9.5) we identify a 4-step sequence of galaxies with progressively redder colors, i.e. of decreasing specific star formation, from (1) HI-rich Late-Type Galaxies belonging to the blue-cloud exhibiting extended plus nuclear star formation, (2) HI-poor LTGs with nuclear star formation only, (3) HI-poor galaxies with no star formation either extended or nuclear, but with nuclear Post-Star-Burst signature,(4) Early-type Galaxies in the red-sequence, with no gas or star formation on all scales. Along this sequence the quenching of the star formation proceeds radially outside-in. The progression toward redder colors found along this "morphological" (gas content) sequence is comparable to the one obtained increasing the local galaxy density, from the cosmic filaments (1,2), to the rich clusters (2,3,4). In the dwarf regime we find evidence for evolution of HI-rich LTGs into ETGs, passing through HI-poor and PSB galaxies, driven by the environment. We identify ram-pressure as the mechanism most likely responsible for this transformation. We conclude that infall of low-mass galaxies has proceeded for the last 7.5 Gyr building up the Coma cluster at a rate of approximately 100 galaxies per Gyr., Comment: 16 pages, 15 figures, 3 tables, A&A accepted, language edited

We present the analysis of the galaxy structural parameters from Halpha3, an Halpha narrow-band imaging follow-up survey of ~800 galaxies selected from the HI ALFALFA Survey in the Local and Coma Superclusters. Taking advantage of Halpha3 which provides the complete census of the recent star-forming, HI-rich galaxies in the local universe, we aim to investigate the structural parameters of both the young (<10 Myr) and the old (>1 Gyr) stellar populations. By comparing the sizes of these stellar components we investigated the spatial scale on which galaxies are growing at the present cosmological epoch and the role of the environment in quenching the star-formation activity. We computed the concentration, asymmetry, and clumpiness structural parameters. To quantify the sizes we computed half-light radii and a new parameter dubbed EW/r. The concentration index computed in the r band depends on the stellar mass and on the Hubble type, these variables being related since most massive galaxies are bulge dominated thus most concentrated. Going toward later spirals and irregulars both the concentration index and the stellar mass decrease. Blue Compact dwarfs represent an exception since they have similar stellar mass but they are more concentrated than dwarf irregulars. The asymmetry and the clumpiness increase along the spiral sequence then they decrease going into the dwarf regime, where the light distribution is smooth and more symmetric. When measured on Halpha images, the CAS parameters do not exhibit obvious correlations with Hubble type. We found that the concentration index is the main parameter that describes the current growth of isolated galaxies but, for a fixed concentration, the stellar mass plays a second order role. At the present epoch, massive galaxies are growing inside-out, conversely the dwarfs are growing on the scale of their already assembled mass., Comment: 16 pages, 11 Figures, 4 Tables, A&A accepted, Final version sent to the publisher

Aims. We study the dust content of a large optical input sample of 910 early-type galaxies (ETG) in the Virgo cluster, extending also to the dwarf ETG, and examine the results in relation with those on the other cold ISM components. Methods. We searched for far-infrared emission in all galaxies of the input sample using the 250 micron image of the Herschel Virgo Cluster Survey (HeViCS). This image covers a large fraction of the cluster. For the detected ETG we measured fluxes in 5 bands from 100 to 500 micron, and estimated the dust mass and temperature with modified black-body fits. Results. Dust is detected above the completeness limit of 25.4 mJy at 250 micron in 46 ETG, 43 of which are in the optically complete part of the input sample. In addition dust is present at fainter levels in another 6 ETG. We detect dust in the 4 ETG with synchrotron emission, including M 87. Dust appears to be much more concentrated than stars and more luminous ETG have higher dust temperatures. Dust detection rates down to the 25.4 mJy limit are 17% for ellipticals, about 40% for lenticulars (S0 + S0a) and around 3% for dwarf ETG. Dust mass does not correlate clearly with stellar mass and is often much more than that expected for a passive galaxy in a closed-box model. The dust-to-stars mass ratio anticorrelates with galaxy luminosity, and for some dwarf ETG reaches values as high as for dusty late-type galaxies. In the Virgo cluster slow rotators appear more likely to contain dust than fast ones. Comparing the dust results with those on HI from ALFALFA, there are only 8 ETG detected both in dust and in HI in the HeViCS area; 39 have dust but only an upper limit on HI, and 8 have HI but only an upper limit on dust. The locations of these galaxies in the cluster are different, with the dusty ETG concentrated in the densest regions, while the HI rich ETG are at the periphery., Comment: Accepted by Astronomy and Astrophysics; modified to reflect the on-line forthcoming version on the A&A web site

In a 5 hour Halpha exposure of the N-W region of the Coma cluster with the 2.1m telescope at SPM (Mx) we discovered a 65 kpc cometary emission of ionized gas trailing behind the SBab galaxy NGC 4848. The tail points in the opposite direction of the cluster center, in the same direction where stripped HI has been detected in previous observations. The galaxy shows bright HII regions in an inner ring-like pattern, where the star formation takes place at the prodigious rate of 8.9 Msun/yr. From the morphology of the galaxy and of the trailing material, we infer that the galaxy is suffering from ram pressure due to its high velocity motion through the cluster IGM. We estimate that 4 x 10^9 Msun of gas is swept out from the galaxy forming the tail. Given the ambient conditions in the Coma cluster (rho = 6.3 x 10^-27 g/cm^3; sigma_vel = 940 km/s) simulations predict that the ram pressure mechanism is able to remove such an amount of gas in less than 200 Myr. This, combined with the geometry of the interaction, indicating radial infall into the cluster, leads to the conclusion that NGC 4848 is caught in its first passage through the dense cluster environment., Comment: 7 pages, 2 figures, 3 tables, Accepted for publication in Astronomy and Astrophysics (18.07.12)

We present Halpha3 (acronym for Halpha-alpha-alpha), an Halpha narrow-band imaging survey of ~400 galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) in the Local Supercluster, including the Virgo cluster. By using hydrogen recombination lines as a tracer of recent star formation, we aim to investigate the relationships between atomic neutral gas and newly formed stars in different environments (cluster and field), morphological types (spirals and dwarfs), and over a wide range of stellar masses (~10^7.5-10^11.5 Msun). We image in Halpha+[NII] all the galaxies that contain more than 10^7 Msun of neutral atomic hydrogen in the sky region 11^h < R.A. <16^h 4^o < Dec. <16^o; 350< cz <2000 km/s using the San Pedro Martir 2m telescope. This survey provides a complete census of the star formation in HI rich galaxies of the local universe. We present the properties of the galaxy sample, together with Halpha fluxes and equivalent widths. We find an excellent agreement between the fluxes determined from our images in apertures of 3 arcsec diameter and the fluxes derived from the SDSS spectral database. From the Halpha fluxes corrected for galactic and internal extinction and for [NII] contamination we derive the global star formation rates (SFRs)., Comment: 22 pages, 8 figures. A&A accepted. Atlas available upon request

Context: We study the peculiar interacting galaxy system of VCC1249/M49 located in the core of the Virgo B subcluster. Owing to a recent interaction between the dwarf galaxy VCC1249 and the halo gas of the gE M49, neutral hydrogen has been displaced from the interstellar medium of this dwarf into the Virgo ICM. Observations also reveal multiple compact star-forming regions that are embedded in this HI cloud, with a projected separation up to 13 kpc from VCC1249 in the northwest direction. Aims: Motivated by recent NUV imaging from GUViCS of the VCC1249/M49 system that shows significant ongoing/recent star formation in the compact regions, we aim to constrain the origin of these outlying HII regions with a multi-wavelength approach. Methods: Using deep optical (u, g, i, z) imaging from NGVS and new Halpha imaging obtained at the San Pedro Martir observatory together with Keck long-slit spectroscopy, we characterize the SFR, ages, and metallicity of VCC1249 and its outlying compact regions. Moreover, we analyze the color and luminosity profile of the galaxy to investigate its recent interaction with M49. Results: Our new observations indicate that VCC1249 underwent a recent interaction with M49 in which both ram-pressure stripping and tidal interaction occured. The joint action of the two mechanisms led to the removal of the HI gas from the ISM of VCC1249, while the gravitational tides triggered the stellar tail and counter-tail of VCC1249. Our SED analysis reveals that the star formation in this galaxy was truncated around 200 Myr ago and that the outlying HII regions were born in situ about 10 Myr ago out of pre-enriched gas removed from the dwarf galaxy. These observations also reveal that interactions between central and satellite galaxies similar to the one between VCC1249/M49 may be an effective way of dispersing metals into the halos of massive galaxies., Comment: 19 pages, 17 figures; one co-author added

To investigate the dependence of the occurrence of active galactic nuclei (AGNs) on local galaxy density, we study the nuclear properties of ~5000 galaxies in the Coma Supercluster whose density spans 2 orders of magnitude from the sparse filaments to the cores of the rich clusters. We obtained optical spectra of the nuclei of 177 galaxies using the 1.5m Cassini telescope, which are added to the 4785 spectra available from SDSS (DR7) to fill-in the incomplete coverage by SDSS of luminous galaxies. We perform a spectral classification of the nuclei of galaxies (with a completeness of 98% at r<17.77), classifying the nuclear spectra in six classes: three of them (SEY, sAGN, LIN) refer to AGNs and the remaining three (HII, RET, PAS) refer to different stages of starburst activity. To perform such classification, we use the WHAN diagnostic, after correcting Halpha by 1.3 A for underlying absorption. We find that 482 (10%) of 5027 galaxies host an AGN: their frequency strongly increases with increasing luminosity of the parent galaxies, such that 32% of galaxies with Log(i-Lum)<10.2 (Solar) harbor an AGN at their interior. In addition to their presence in luminous galaxies, AGNs are also found in red galaxies with < 1.15 \pm 0.15 mag. The majority of SEY and sAGN (strong AGNs) are associated with luminous late-type (or S0a) galaxies, while LIN (weak AGNs) and RET ("retired"), are mostly found among E/S0as. The number density of AGNs, HII region-like, and retired galaxies is found to anti-correlate with the local density of galaxies, such that their frequency drops by a factor of two near the cluster cores, while the frequency of galaxies containing passive nuclei increases by the same amount towards the center of rich clusters. The dependence of AGN number density on the local galaxy density is greater than the one implied by morphology segregation alone., Comment: 15 pages, 10 figures, 4 tables. Accepted for publication in A&A

A complex of Halpha emitting blobs with strong FUV excess is associated to the dIrr galaxy VCC1217 / IC3418 (Hester et al. 2010), and extends up to 17 Kpc in the South-East direction. These outstanding features can be morphologically divided into diffuse filaments and compact knots, where most of the star formation activity traced by Halpha takes place. We investigate the properties of the galaxy and the blobs using a multiwavelength approach in order to constrain their origin. We collect publicly available data in UV and Halpha and observe the scene in the optical U,g,r,i bands with LBT. The photometric data allows to evaluate the star formation rate and to perform a SED fitting separately of the galaxy and the blobs in order to constrain their stellar population age. Moreover we analyze the color and luminosity profile of the galaxy and its spectrum to investigate its recent interaction with the Virgo cluster. Our analysis confirms that the most plausible mechanism for the formation of the blobs is ram pressure stripping by the Virgo cluster IGM. The galaxy colors, luminosity profile and SED are consistent with a sudden gas depletion in the last few hundred Myr. The SED fitting of the blobs constrains their ages in < 400 Myr., Comment: 10 pages, 11 figures, accepted for publication in Astronomy and Astrophysics

With the aim of quantifying the contribution of the environment on the evolution of galaxies at z=0 we have used the DR7 catalogue of the Sloan Digital Sky Survey (SDSS) to reconstruct the 3-D distribution of 4132 galaxies in 420 square degrees of the Coma supercluster, containing two rich clusters (Coma and A1367), several groups, and many filamentary structures belonging to the "Great Wall", at the approximate distance of 100 Mpc. At this distance the galaxy census is complete to Mi=-17.5 mag, i.e. approx 4 mag fainter than M*. The morphological classification of galaxies into early- (ellipticals) and late-types (spirals) was carried out by inspection of individual SDSS images and spectra. The density around each galaxies was determined in cylinders of 1 Mpc radius and 1000 km s^-1 half length. The color-luminosity relation was derived for galaxies in bins morphological type and in four thresholds of galaxy density-contrast, ranging from delta{1,1000} <= 0 (UL = the cosmic web); 0 < delta{1,1000} <= 4 (L = the loose groups); 4 < delta{1,1000} <= 20 (H = the large groups and the cluster's outskirts) and delta{1,1000} > 20 (UH = the cluster's cores). The fraction of early-type galaxies increases with the log of the over-density. A well defined "red sequence" composed of early-type galaxies exists in all environments at high luminosity, but it lacks of low luminosity (dwarf) galaxies in the lowest density environment. Conversely low luminosity isolated galaxies are predominantly of late-type. In other words the low luminosity end of the distribution is dominated by red dE galaxies in clusters and groups and by dwarf blue amorphous systems in the lowest density regions. At z=0 we find evidence for strong evolution induced by the environment (Nurture). Transformations take place mostly at low luminosity when star forming dwarf galaxies inhabiting low density environments migrate into amorphous passive dwarf ellipticals in their infall into denser regions. The mechanism involves suppression of the star formation due to gas stripping, without significant mass growth, as proposed by Boselli et al. (2008a). This process is more efficient and fast in ambients of increasing density. In the highest density environments (around clusters) the truncation of the star formation happens fast enough (few 100 Myr) to produce the signature of post-star-burst in galaxy spectra. PSB galaxies, that are in fact found significantly clustered around the largest dynamical units, represent the remnants of star forming isolated galaxies that had their star formation violently suppressed during their infall in clusters in the last 0.5-1.5 Gyrs, and the progenitors of future dEs., Comment: 14 pages, 14 figures, Astronomy and Astrophysics, in press

We use a sample of 47 homogeneous and high sensitivity CO images taken from the Nobeyama and BIMA surveys to demonstrate that, contrary to common belief, a significant number (~40%) of HI-deficient nearby spiral galaxies are also depleted in molecular hydrogen. While HI-deficiency by itself is not a sufficient condition for molecular gas depletion, we find that H2 reduction is associated with the removal of HI inside the galaxy optical disk. Those HI-deficient galaxies with normal H2 content have lost HI mainly from outside their optical disks, where the H2 content is low in all galaxies. This finding is consistent with theoretical models in which the molecular fraction in a galaxy is determined primarily by its gas column density. Our result is supported by indirect evidence that molecular deficient galaxies form stars at a lower rate or have dimmer far infrared fluxes than gas rich galaxies, as expected if the star formation rate is determined by the molecular hydrogen content. Our result is consistent with a scenario in which, when the atomic gas column density is lowered inside the optical disk below the critical value required to form molecular hydrogen and stars, spirals become quiescent and passive evolving systems. We speculate that this process would act on the time-scale set by the gas depletion rate and might be a first step for the transition between the blue and red sequence observed in the color-magnitude diagram., Comment: 12 pages, 9 figures, accepted for publication in ApJ

The study of PopI and PopII indicators in galaxies has a profound impact on our understanding of galaxy evolution. Their present (z=0) ratio suggests that the star formation history of galaxies was primarily dictated by their global mass. Since 1989 Luis Carrasco and I spent most of our sleepless nights gathering H_alpha and near infrared surface photometry of galaxies in the local Universe and focused most of our scientific career on these two indicators trying to convince the community that the mass was the key parameter to their evolution. We were unsuccessful, until in 2004 the Sloan team rediscovered this phenomenon and named it "downsizing", Comment: To appear in "A long walk through astronomy". RevMexAA

We report the results of an HI blind survey of 80deg^2 of the Virgo cluster, based on the 08deg < delta < 16 deg strip of ALFALFA, the Arecibo Legacy Fast ALFA Survey. 187 HI sources of high significance are found providing a complete census of HI sources in this region of the Virgo cluster (-1000 10^7.5-8 M_sun. 156/187 (83%) sources are identified with optical galaxies from the Virgo Cluster Catalogue (Binggeli et al. 1985), all but 8 with late-type galaxies. Ten sources are not associated with optical galaxies and were found to correspond to tidally-disrupted systems (see Kent et al. 2007 and Haynes, Giovanelli and Kent 2007). The remaining 21 (11%) are associated with galaxies that are not listed in the Virgo Cluster Catalogue. For all sources with an optical counterpart in the Sloan Digital Sky Survey, we analyzed i-band SDSS plates to measure optical structural parameters. We find that in the Virgo cluster: i) HI inhabits galaxies that are structurally similar to ordinary late-type galaxies; ii) their HI content can be predicted from their optical luminosity; iii) low surface brightness galaxies have low optical luminosity and contain small quantities of neutral hydrogen; iv) low surface brightness, massive Malin1 type galaxies are comfortably rare objects (less than 0.5%); v) there are no "dark-galaxies" with HI masses M_HI > 10^7.5-8 M_sun; vi) less than 1% of early-type galaxies contain neutral hydrogen with M_HI>10^7.5-8 M_sun (di Serego Alighieri et al. 2007)., Comment: 10 pages, 10 Postscript figures, accepted for publication in Astronomy and Astrophysics (25/01/2008) - Replaced to fit A&A vers. 6.1

Chandra images of the elliptical galaxy NGC4261 have revealed an anisotropy in the spatial distribution of the off-nuclear X-ray sources, interpreted by Zezas et al. as evidence of an association with a young stellar population. Our independent analysis of archive X-ray (Chandra) and optical (INT and HST) observations confirms the anisotropy of the X-ray sources but conducts to a different interpretation for their origin. We find that nearly half of the X-ray sources are associated to a globular cluster (optical counterpart) suggesting that they are accreting low-mass X-ray binaries. Where color index information is available, the X-ray sources are found to reside in red (metal-rich) systems. The luminosity function of the X-ray sources is also consistent with the one drawn from a population of Low Mass X-ray Binaries. We further investigate the properties of the sample of point-like sources obtained from archival optical images that we suggest are good globular cluster candidates and for which we find that the projected spatial distribution is non-homogeneous. In addition, we show that the distributions of the optical and X-ray populations are very similar, which leads us to conclude that the spatial anisotropy of the X-ray sources in NGC4261 is mostly a reflection of the anisotropy of the globular cluster population., Comment: 16 pages, 9 figures, accepted for publication in ApJ main journal

Drift-scan mode (3600-6800 A) spectra with 500

As a result of an extensive observational campaign targeting the Virgo cluster, we obtained integrated (drift-scan mode) optical spectra and multiwavelength (UV,U,B,V,H) photometry for 124 and 330 galaxies, respectively, spanning the whole Hubble sequence, and with m_p<=16 (M_p<=-15). These data were combined to obtain galaxy SEDs extending from 2000 to 22000 A. By fitting these SEDs with synthetic ones derived using Bruzual & Charlot population synthesis models we try to constrain observationally the SFH of these galaxies. Assuming a Salpeter IMF and an analytical form for the SFH, the fit free parameters are: the age (T) of the star formation event, its characteristic time-scale (tau) and the initial metallicity (Z). We test the (simplistic) case where all galaxies have a common age T=13 Gyr, exploring a SFH with "delayed" exponential form, thus allowing for an increasing SFR with time. This SFH is consistent with the full range of observed SEDs, provided that the characteristic time-scale tau is let free to vary between 0.1 and 25 Gyr and Z between 1/5 and 2.5 Z solar. Elliptical galaxies (including dEs) are best fitted with short time scales (tau~3 Gyr) and Z varying between 1/5 and 1 Z solar. The model metallicity is found to increase with H band luminosity. Spiral galaxies require that both tau and Z correlate with H band luminosity: low mass Im+BCD have sub-solar Z and tau>=10 Gyr, whereas giant spirals have solar metallicities and tau~3 Gyr, consistent with ellipticals. Moreover we find that the SFH of spirals depends upon the presence at their interior of fresh gas capable of sustaining the star formation. In fact the residuals of the tau vs. L_H relation depend significantly on the HI content. HI deficient galaxies have shorter tau than spirals with normal HI content., Comment: 25 pages, 18 figures; accepted for publication in the Astrophysical Journal

We have collected a large body of NIR (H band), UV (2000 A) and Halpha measurements of late-type galaxies. These are used, jointly with spectral evolutionary synthesis models, to study the initial mass function (IMF) in the mass range m > 2 Mo. For spirals (Sa-Sd), Magellanic irregulars (Im) and blue compact dwarfs (BCD), our determination is consistent with a Salpeter IMF with an upper mass cutoff M_up = 80 Mo. The history of star formation and the amount of total gas (per unit mass) of galaxies are found to depend primarily on their total masses (as traced by the H band luminosities) and only secondarily on morphological type. The present star formation activity of massive spirals is up to 100 times smaller than that average over their lifetime, while in low mass galaxies it is comparable to or higher than that at earlier epochs. Dwarf galaxies have presently larger gas reservoirs per unit mass than massive spirals. The efficiency in transforming gas into stars and the time scale for gas depletion (10 Gyrs) are independent of the luminosity and/or of the morphological type. These evidences are consistent with the idea that galaxies are coeval systems,that they evolved as closed-boxes forming stars following a simple, universal star formation law whose characteristic time scale is small (1 Gyr) in massive spirals and large (10 Gyr) in low mass galaxies. A similar conclusion was drawn by Gavazzi and Scodeggio (1996) to explain the colour-magnitude relation of late-type galaxies. The consequences of this interpretation on the evolution of the star formation rate and of the gas density per comoving volume of the Universe with look-back time are discussed., Comment: LaTex, 24 pages, 12 figures, accepted for publication on Astronomical Journal