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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

31 pages, 18 figures, 3 tables, submitted; The impact of ram pressure stripping (RPS) on galaxy evolution has been studied for over forty years. Recent multi-wavelength data have revealed many examples of galaxies undergoing RPS, often accompanied with multi-phase tails. As energy transfer in the multi-phase medium is an outstanding question in astrophysics, RPS galaxies are great objects to study. Despite the recent burst of observational evidence, the relationship between gas in different phases in the RPS tails is poorly known. Here we report, for the first time, a strong linear correlation between the X-ray surface brightness (SB$_{\rm X}$) and the H$\alpha$ surface brightness (SB$_{\rm H\alpha}$) of the diffuse gas in the RPS tails at $\sim$ 10 kpc scales, as SB$_{\rm X}$/SB$_{\rm H\alpha} \sim$ 3.6. This discovery supports the mixing of the stripped interstellar medium (ISM) with the hot intracluster medium (ICM) as the origin of the multi-phase RPS tails. The established relation in stripped tails, also in comparison with the likely similar correlation in similar environments like X-ray cool cores and galactic winds, provides an important test for models of energy transfer in the multi-phase gas. It also indicates the importance of the H$\alpha$ data for our understanding of the ICM clumping and turbulence.

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$��$ 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$��$ 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$��$. Thus, future deep and wide-field H$��$ survey can be used to probe the ICM clumping and turbulence., 16 pages, 9 figures, 2 tables, MNRAS, in press, minor changes with abstract/conclusion the same

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 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, 1 page, 1 figure

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 �� [NII] to H�� lines and the equivalent width (EW) of H�� versus [NII]/H�� (WHAN diagnostic introduced by Cid Fernandes and collaborators) after correcting H�� for underlying absorption. The obtained spectra are made available in machine readable format via the Strasbourg Astronomical Data Center (CDS) and NED., 8 pages, 6 Figures, 4 Tables, accepted for publication in Astronomy & Astrophysics

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 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., 22 pages, 8 figures. A&A accepted. Atlas available upon request

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS) is a complete blind survey of the Virgo cluster covering ∼40 sq. deg in the far UV (FUV, λeff = 1539 Å Δλ = 442 Å) and ∼120 sq. deg in the near UV (NUV, λeff = 2316 Å, Δλ = 1060 Å). The goal of the survey is to study the ultraviolet (UV) properties of galaxies in a rich cluster environment, spanning a wide luminosity range from giants to dwarfs, and regardless of prior knowledge of their star formation activity. The UV data will be combined with those in other bands (optical: NGVS; far-infrared - submm: HeViCS; HI: ALFALFA) and with our multizone chemo-spectrophotometric models of galaxy evolution to make a complete and exhaustive study of the effects of the environment on the evolution of galaxies in high density regions. We present here the scientific objectives of the survey, describing the observing strategy and briefly discussing different data reduction techniques. Using UV data already in-hand for the central 12 sq. deg we determine the FUV and NUV luminosity functions of the Virgo cluster core for all cluster members and separately for early- and late-type galaxies and compare it to the one obtained in the field and other nearby clusters (Coma, A1367). This analysis shows that the FUV and NUV luminosity functions of the core of the Virgo clusters are flatter (α ∼ -1.1) than those determined in Coma and A1367. We discuss the possible origin of this difference. © 2011 ESO.

International audience; The Next Generation Virgo Cluster Survey (NGVS) is a CFHT MegaPrime large program to survey the Virgo Cluster from its core to virial radius, for a total coverage of 104 square degrees. Over the next four years, the survey will perform deep imaging (10 sigma detection for point sources of 25.7 mag in the g-band) in five band-passes (u*,g',r',i',z'), thereby superceding all optical studies of this uniquely important system. The program's main scientific objectives are: the characterization of the faint-end shape of the galaxy luminosity function, the characterization of galaxy scaling relations over a factor 107 in mass, the cluster/intracluster medium/galaxy connection, the role of environmental effects in galaxy evolution,and the fossil record of star formation and chemical enrichment in dense environments. Numerous ancillary projects - from a survey of the Galactic halo to a cosmic shear measurement of the matter power spectrum on large scales - will also be enabled. Details about the survey can be found at http://astrowww.phys.uvic.ca/ lff/NGVS.html

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.

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", To appear in "A long walk through astronomy". RevMexAA

We use Halpha and FUV GALEX data for a large sample of nearby objects to study the high mass star formation activity of normal late-type galaxies. The data are corrected for dust attenuation using the most accurate techniques at present available, namely the Balmer decrement and the total far-infrared to FUV flux ratio. The sample shows a highly dispersed distribution in the Halpha to FUV flux ratio indicating that two of the most commonly used star formation tracers give star formation rates with uncertainties up to a factor of 2-3. The high dispersion is due to the presence of AGN, where the UV and the Halpha emission can be contaminated by nuclear activity, highly inclined galaxies, for which the applied extinction corrections are probably inaccurate, or starburst galaxies, where the stationarity in the star formation history required for transforming Halpha and UV luminosities into star formation rates is not satisfied. Excluding these objects we reach an uncertainty of ~50% on the SFR. The Halpha to FUV flux ratio increases with their total stellar mass. If limited to normal star forming galaxies, however, this relationship reduces to a weak trend that might be totally removed using different extinction correction recipes. In these objects the Halpha to FUV flux ratio seems also barely related with the FUV-H colour, the H band effective surface brightness, the total star formation activity and the gas fraction. The data are consistent with a Kroupa and Salpeter initial mass function in the high mass stellar range and imply, for a Salpeter IMF, that the variations of the slope cannot exceed 0.25, from g=2.35 for massive galaxies to g=2.60 in low luminosity systems. We show however that these observed trends, if real, can be due to the different micro history of star formation in massive galaxies with respect to dwarf., Comment: Accepted for publication on ApJ

Aims. The present work is aimed at studying the distribution of galaxies of different types and luminosities along different structural scaling relations to see whether massive and dwarf ellipticals have been shaped by the same formation process.Methods. This exercise is done by comparing the distribution of Virgo cluster massive and dwarf ellipticals and star forming galaxies along the band effective surface brightness and effective radius vs. absolute magnitude relations and the Kormendy relation to the predictions of models tracing the effects of ram-pressure stripping on disc galaxies entering the cluster environment and galaxy harassment.Results. Dwarf ellipticals might have been formed from low luminosity, late-type spirals that recently entered into the cluster and lost their gas because of a ram-pressure stripping event, stopping their star formation. The perturbations induced by the abrupt decrease of the star formation activity are sufficient to modify the structural properties of disc galaxies into those of dwarf ellipticals. Galaxy harassment induces a truncation of the disc and generally an increase of the effective surface brightness of the perturbed galaxies. The lack of dynamical simulations of perturbed galaxies spanning a wide range in luminosity prevents us from deriving any firm conclusion on a possible harassment-induced origin of the low surface brightness dwarf elliptical galaxy population inhabiting the Virgo cluster.Conclusions. Although the observed scaling relations are consistent with the idea that the distribution of elliptical galaxies along the mentioned scaling relation is due to a gradual variation with luminosity of the Sersic index , the comparison with models indicates that dwarf ellipticals might have been formed by a totally different process to giant ellipticals. © 2008 ESO.

We investigate the dependence of the total-IR (TIR) to ultraviolet (UV) luminosity ratio method for calculating the UV dust attenuation A(UV) from the age of the underlying stellar populations by using a library of spectral energy distributions for galaxies with different star formation histories. Our analysis confirms that the TIR/UV versus A(UV) relation varies significantly with the age of the underlying stellar population: that is, for the same TIR/UV ratio, systems with low specific star formation rate (SSFR) suffer a lower UV attenuation than starbursts. Using a sample of nearby field and cluster spiral galaxies, we show that the use of a standard (i.e. age-independent) TIR/UV versus A(UV) relation leads to a systematic overestimate up to 2 mag of the amount of UV dust attenuation suffered by objects with low SSFR and in particular H i-deficient star-forming cluster galaxies. This result points out that the age-independent TIR/UV versus A(UV) relation cannot be used to study the UV properties of large samples of galaxies including low star-forming systems and passive spirals. Therefore, we give some simple empirical relations from which the UV attenuation can be estimated taking into account its dependence on the age of the stellar populations, providing a less biased view of UV properties of galaxies. © 2008 The Authors.

Aims. We are using the Arecibo Legacy Fast ALFA survey (ALFALFA), which is covering 17% of the sky at 21 cm, to study the HI content of early-type galaxies (ETG) in an unbiased way. The aim is to get an overall picture of the hot, warm and cold ISM of ETG, as a function of galaxy mass and environment, to understand its origin and fate, and to relate it to the formation and evolution history of these objects. Methods. This paper deals with the first part of our study, which is devoted to the 8-16 deg. declination strip in the Virgo cluster. In this sky region, using the Virgo Cluster Catalogue (VCC), we have defined an optical sample of 939 ETG, 457 of which are brighter than the VCC completeness limit at BT = 18.0. We have correlated this optical sample with the catalogue of detected HI sources from ALFALFA. Results. Out of the 389 ETG from the VCC with BT ≤ 18.0, outside the 1 deg. region of poor HI detection around M 87, and corrected for background contamination of VCC galaxies without a known radial velocity, only 9 galaxies (2.3%) are detected in HI with a completeness limit of 3.5 and 7.6 × 107 M ⊙ of HI for dwarf and giant ETG, respectively. In addition 4 VCC ETG with fainter magnitudes are also detected. Our HI detection rate is lower than previously claimed. The majority of the detected ETG appear to have peculiar morphology and to be located near the edges of the Virgo cluster. Conclusions. Our preliminary conclusion is that cluster ETG contain very little neutral gas, with the exceptions of a few peculiar dwarf galaxies at the edge of the ETG classification and of very few larger ETG, where the cold gas could have a recent external origin. © ESO 2007.

The recent evidence of a peculiar distribution of X-ray sources in the elliptical galaxy NGC 4261 reported by Zezas et al. has prompted us to study this galaxy combining archive X-ray and optical observations, from Chandra, INT, and HST. We find that a sizable fraction of the X-ray sources has a globular cluster as optical counterpart. This together with the shape of the luminosity function of the X-ray sources suggest that they are accreting low-mass binaries. We further show a remarkable similarity in the anisotropy of the projected spatial distributions of the optical and X-ray sources, which leads us to conclude that the spatial anisotropy of the X-ray sources in NGC 4261 is due to the anisotropy of the globular cluster population. © 2006 International Astronomical Union.

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=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., 25 pages, 18 figures; accepted for publication in the Astrophysical Journal

The molecular gas mass in nearby galaxies is generally estimated using (CO)-C-12(1-0) line intensities and assuming the X conversion factor between I(CO) and N(H-2) measured in the solar neighborhood. It is however known that this X conversion factor is not universal since it changes with metallicity, cosmic ray density and UV radiation field. Far-IR data in the spectral range 100-1000 mum can be used to estimate the molecular gas content of late-type galaxies in an independent way of CO line measurements once a metallicity-dependent dust to gas ratio is assumed, allowing a direct estimate of X. This exercise is presented here for a large sample of galaxies with available multifrequency data. X spans from similar to 10(20) mol cm(-2) (K km s(-1))(-1) in giant spirals to similar to 10(21) mol cm(-2) (K km s(-1))(-1) in dwarf irregulars

We present a deep wide field Halpha imaging survey of the central regions of the two nearby clusters of galaxies Coma and Abell 1367, taken with the WFC at the INT 2.5m telescope. We determine for the first time the Schechter parameters of the Halpha luminosity function (LF) of cluster galaxies. The Halpha LFs of Abell 1367 and Coma are compared with each other. Typical parameters of phi approximate to 10(0.00+/-0.07) Mpc(-3), L-* approximate to 10(41.25+/-0.05) erg sec(-1) and alpha approximate to -0.70+/-0.10 are found for both clusters

We present the distribution of a statistical sample of nearby galaxies in the kappa -space (kappa (1) proportional tolog M, kappa(2) proportional tolog I (e) (3) M /L, kappa(3) proportional tolog M /L ). Our study is based on near-IR (H -band: lambda =1.65 mum) observations, for the first time comprising early- and late-type systems. Our data confirm that the mean effective dynamical mass-to-light ratio M /L of the E+S0+S0a galaxies increases with increasing effective dynamical mass M , as expected from the existence of the Fundamental Plane relation. Conversely, spiral and Im/BCD galaxies show a broad distribution in M /L with no detected trend of M /L with M , the former galaxies having M /L values about twice larger than the latter, on average. For all the late-type galaxies, the M /L increases with decreasing effective surface intensity I (e) , consistent with the existence of the Tully-Fisher relation. These results are discussed on the basis of the assumptions behind the construction of the kappa -space and their limitations. Our study is complementary to a previous investigation in the optical (B -band: lambda =0.44 mum) and allows us to study wavelength dependences of the galaxy distribution in the kappa -space. As a first result, we find that the galaxy distribution in the kappa(1) -kappa(2) plane reproduces the transition from bulgeless to bulge-dominated systems in galaxies of increasing dynamical mass. Conversely, it appears that the M /L of late-types is higher (lower) than that of early-types with the same M in the near-IR (optical). The origins of this behaviour are discussed in terms of dust attenuation and star formation history

We present a deep wide field Halpha imaging survey of the central regions of the two nearby clusters of galaxies Coma and Abell 1367, taken with the WFC at the INT 2.5 m telescope. We determine for the first time the Schechter parameters of the Halpha luminosity function (LF) of cluster galaxies. The Halpha LFs of Abell 1367 and Coma are compared with each other and with that of Virgo, estimated using the B band LF by Sandage et al. (1985) and a L(Halpha) vs. M-B relation. Typical parameters of phi* approximate to 10(0.00+/-0.07) Mpc(-3), L* approximate to 10(41.25+/-0.05) erg s(-1) and alpha approximate to -0.70 +/- 0.10 are found for the three clusters. The best fitting parameters of the cluster LFs differ from those found for field galaxies, showing flatter slopes and lower scaling luminosities L*. Since, however, our Halpha survey is significantly deeper than those of field galaxies, this result must be confirmed on similarly deep measurements of field galaxies. By computing the total SFR per unit volume of cluster galaxies, and taking into account the cluster density in the local Universe, we estimate that the contribution of clusters like Coma and Abell 1367 is approximately 0.25% of the SFR per unit volume of the local Universe.

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., LaTex, 24 pages, 12 figures, accepted for publication on Astronomical Journal

L'evoluzione delle galassie puo' essere vista come l'effetto cumulativo di due grandi classi di processi differenti: processi interni legati alla genetica della galassia e processi legati all'ambiente in cui esse risiedono. In questa tesi affronto entrambi gli aspetti dell'evoluzione delle galassie. Tra i processi interni alle galassie, ho approfondito gli effetti che le barre stellari hanno sulla componente gassosa delle galassie e le conseguenze sulla loro evoluzione. Dimostro che le barre influenzano sia il gas ionizzato che il gas freddo al'interno di due campioni: (i) il campione Halpha3, tratto da una survey di immagini Halpha di galassie selezionate in HI dalla survey ALFALFA nel supercluster Locale e in quello di Coma; (ii) il campione HRS di 323 galassie osservato con il satellite Herschel in banda FIR, che traccia le polveri e quindi il gas freddo. Grazie ai dati di Halpha3 e' infatti stato possibile verificare che, a parita' di massa, le galassie barrate della sequenza principale hanno minori livelli di SFR rispetto ai puri dischi. Proponiamo un semplice modello evolutivo in cui la crescita di una barra influenza fortemente l'evoluzione di una galassia: dalle simulazioni e' ormai chiaro che l'effetto dinamico della barra trascina il gas all'interno del raggio di corotazione verso il centro dove si addensa, raffredda e puo' scatenare intensi episodi di formazione stellare. Dopodiche' la regione occupata dalla barra non forma piu' stelle e diventa rossa. Nel campione HRS troviamo le prove dello svuotamento del gas dalla regione della barra ispezionando le immagini FIR del campione HRS. Dopodiche' ho cercato le prove del prematuro invecchiamento della regione occupata dalla barra nelle proprieta' medie delle popolazione stellari di un campione di migliaia di immagini di galassie locali prese dalla SDSS in band g e i. Per analizzarle, ho sviluppato una procedura automatica per l'analisi della fotometria in diverse bande delle galassie SDSS e di fittare con ellissi le isofote. In questo modo abbiamo estratto magnitudini, profili di brillanza, di colore, di ellitticita' e P.A. Ho poi sviluppato un algoritmo che riconosce automaticamente le galassie barrate del sample sulla base dei loro profili di elliticita' e P.A. L'analisi ha rivelato che in generale le galassie a disco sviluppano una regione rossa al loro centro la cui importanza dipende dalla loro massa. Analizzando le sole galassie barrate si conclude che queste contribuiscono in maniera fondamentale alle proprieta' medie dei colori delle galassie a spirale. In una seconda parte, il lavoro e' dedicato ai risultati delle osservazioni prese con l'IFU MUSE. Con questo strumento abbiamo osservato la galassia UGC-6697 nell'ammasso A1367. La galassia sta attraversando il cluster ad alta velocita' e la sua componente gassosa e' affetta dalla pressione idrodinamica esercitata dal mezzo dell'ammasso. Grazie a procedure python da me sviluppate, si e' potuto studiare in dettaglio il campo di velocita' del gas della galassia che rivela diverse componenti lungo la linea di vista. Comparandolo con la cinematica delle stelle, abbiamo separato una componente ancora associata al potenziale della galassia da una componente di gas strappato alla galassia. L'analisi delle due componenti rivela che la ionizzazione del gas strappato al potenziale e' sostenuta da shocks e ha una dinamica turbolenta mentre il gas ancora nel potenziale della galassia e' consistente con l'essere ionizzato dalle stelle nel disco ed e' caratterizzato da velocita' di dispersione basse. Le regioni di formazione stellare osservate nel gas al di fuori della galassia sono sistematicamente associate a regioni in cui il gas che le circonda ha basse velocita di dispersione. The evolution of galaxies can be thought as the result of the cumulative effects of two broad classes of processes: (i) secular (internal) processes determined by the very nature of the galaxy, and (ii) external processes that are determined by the environment in which the object is embedded. In this thesis I face both aspects of galaxy evolution. Among secular processes, I investigated the effects of stellar bars on the gaseous components of galaxies and their consequences on their evolution. In particular I show how bars affect both the ionized and cold gas in two different samples: the sample of the Halpha3 survey, an Halpha imaging survey of galaxies selected from ALFALFA in the Local and Coma superclusters; the Herschel Reference Sample, a representative sample of 323 local galaxies observed with the space-based Herschel observatory sensitive to the far-infrared emission of dust, a good tracer of cold gas. Owing to the Halpha3 data I demonstrate that main sequence barred galaxies have specific star formation rate suppressed with respect to pure disks. Here I propose a simple model in which bars drive the evolution of disk galaxies. Hydrodynamical simulations indeed show that a barred potential funnels the gas inside the corotation radius toward the center of the galaxy where it reaches high densities, cools and can be consumed by a burst of star formation. At the same time the dynamical torque of the bar keeps the gas outside the corotation radius in place, cutting the gas supply to the central region that consequently stops its star formation activity. Taking advantage of the images of the HRS sample, we show the evidences of such quenching. The aforementioned model is further tested by studying the stellar population properties of galaxies belonging to a sample of 6000 galaxies extracted from SDSS. To this aim, I designed in-house IDL codes that automatically perform aperture photometry and isophotal fitting recovering reliable magnitudes, colors, ellipticity, position angle (P.A.) and color profiles. The automatic procedure is complemented by an automatic bar finder able to extract a fairly pure sample of barred galaxies on the basis of their P.A. and ellipticity profiles. The analysis of color profiles show that disk galaxies have their central regions redder (therefore quenched) than their outer regions and that this is more evident at high mass. The high local bar fraction that we extrapolate as well as the analysis of the average color profile of barred galaxies shows the strong contribution of bars to the observed colors. In a second part, I present the work done in the field of environmental processes. The work is focused on the analysis of the observations, carried on with the IFU MUSE, of a system belonging to the nearby galaxy cluster A1367. These observations mosaicked the galaxies UGC-66967 and CGCG-97087N, two galaxies suffering ram pressure stripping and that have possibly interacted, as hinted by the presence of gas in the region between them. Owing to in-house automatic Python codes and by comparing the gas velocities to the stellar kinematics, we could separate the emission of the ionized gas in a stripped component and a component still attached to the potential of the galaxy. While the gas onboard the galaxy shows low velocity dispersions and ionizations states consistent with photoionization by stars, the stripped gas is more turbulent and ionized by shocks. The HII regions that formed in the tail of UGC-66967 (but are absent in the tail of CGCG-97087N) are systematically found in regions where the velocity dispersion of the gas is lower than 50 km/s, while the stripped gas show typical velocity dispersions about or greater than 100 km/s.

Galaxies are clusters of millions and billions of stars dynamically stable, with gas, dust and dark matter. They are the biggest isolated objects known in the Universe . Even though they are very complex systems, today we have a clear knowledge about their evolution and about their physical phenomena. Aside from the stellar component there is a gaseous component, principally neutral Hydrogen (HI), and dust that, although is not a significant component in terms of the mass, plays an important role on the absorption phenomena. Finally, cinematic and other kind of observations suggest the existence of a spheric dark matter halo, dominant in terms of mass and more extensive than the barionic component.