We present distance estimates for eleven peculiar Virgo cluster spiral galaxies based on measurements of the stellar kinematics of their central 2 kpc. Stellar circular velocities were obtained using two-integral dynamical models. Distances were obtained by comparing, at each radius, the stellar circular velocities with synthetic H_alpha rotation curves derived from NIR Tully-Fisher relations.The results show that most of our galaxies are located within 4 Mpc of the core of the cluster. Three of these galaxies, previously classified as "low rotator galaxies" or with "Truncated/Compact" H_alpha radial distributions, have stellar kinematics-based distances that are discrepant with HI-based distances by at least 60%, and are likely to be located within the virial radius of the cluster. These discrepancies appear due to very truncated gas distributions plus non-circular gas motions or gas motions not in the plane of the stellar disk, perhaps as the result of gravitational interactions. Our results show that environmental effects can significantly reduce the measured HI linewidths for some disturbed cluster galaxies, thus affecting the accurate determination of distances based on gas kinematics methods.
The oxygen and nitrogen abundances in the HII regions of the nine Virgo spirals of the sample from Skillman et al (1996) and in nine field spiral galaxies are re-determined with the recently suggested P - method. We confirm that there is an abundance segregation in the sample of Virgo spirals in the sense that the HI deficient Virgo spirals near the core of the cluster have higher oxygen abundances in comparison to the spirals at the periphery of the Virgo cluster. At the same time both the Virgo periphery and core spirals have counterparts among field spirals. We conclude that if there is a d…
We present new measurements of chemical abundances in H II regions in spiral galaxies of the Virgo cluster and a comparison of Virgo galaxies and field spirals. With these new data there now exist nine Virgo spirals with abundance measurements for at least four H II regions. Our sample of Virgo galaxies ranges from H I deficient objects near the core of the cluster to galaxies with normal H I properties, far from the cluster core. We investigate the relationship between H I disk characteristics and chemical abundances to determine whether dynamical process that remove gas from the disk, such a…
The massive star formation properties of 55 Virgo Cluster and 29 isolated S0-Scd bright (M(B) < -18) spiral galaxies are compared via analyses of R and Halpha surface photometry and integrated fluxes as functions of Hubble type and central R light concentration (bulge-to-disk ratio). In the median, the total normalized massive star formation rates (NMSFRs) in Virgo Cluster spirals are reduced by factors up to 2.5 compared to isolated spiral galaxies of the same type or concentration, with a range from enhanced (up to 2.5 times) to strongly reduced (up to 10 times). Within the inner 30% of the …
We describe the various Halpha morphologies of Virgo Cluster and isolated spiral galaxies, and associate the Halpha morphologies with the types of environmental interactions which have altered the cluster galaxies. The spatial distributions of Halpha and R-band emission are used to divide the star formation morphologies of the 52 Virgo Cluster spirals into several categories: normal (37%), anemic (6%), enhanced (6%), and (spatially) truncated (52%). Truncated galaxies are further subdivided based on their inner star formation rates into truncated/normal (37%), truncated/compact (6%), truncated…
The measurement of precise galaxy distances by Cepheid observations out to the distance of the Virgo cluster is important for the determination of the Hubble constant ($H_0$). The Virgo cluster is thereby often used as an important stepping stone. The first HST measurement of the distance of a Virgo galaxy (M100) using Cepheid variables provided a value for $H_0=80(\pm 17)$ km/s/Mpc (Freedman et al. 1994). This measurement was preceeded by a ground based study of the Virgo spiral NGC4571 (Pierce et al. 1994) formally providing $H_0= 87\pm7$ km/s/Mpc. These determinations rely on the accuracy w…
Quantitative measures of central light concentration and star formation activity are derived from R and Halpha surface photometry of 84 bright S0-Scd Virgo Cluster and isolated spiral galaxies. For isolated spirals, there is a good correlation between these two parameters and assigned Hubble types. In the Virgo Cluster, the correlation between central light concentration and star formation activity is significantly weaker. Virgo Cluster spirals have systematically reduced global star formation with respect to isolated spirals, with severe reduction in the outer disk, but normal or enhanced act…
Narrow-band Halpha and broadband R images and radial profiles are presented for 63 bright spiral galaxies in the Virgo Cluster. The sample is complete for Sb-Scd galaxies with B magnitude less than 12 and inclination less than 75 degrees. Isophotal radii, disk scalelengths, concentration parameters, and integrated fluxes are derived for the sample galaxies.
Deep Effelsberg HI spectra of the one-armed, bright Virgo cluster spiral galaxy NGC 4254 are presented.Five different positions were observed in the 21 cm HI line with the Effelsberg 100-m telescope: one in the center and 4 located one HPBW to the NE, NW, SW, and SE, respectively, from the galaxy center. The spectra are compared to existing deep VLA observations, and the single dish and interferometric HI data are used to constrain a dynamical model which includes the effects of ram pressure. The peculiar, one-armed spiral pattern of NGC 4254 and its distorted and kinematically perturbed atomi…
A study of the distribution of barred and nonbarred disk galaxies in the Virgo cluster is presented in an attempt to use the frequency and spatial distribution of galaxies with specific morphological features to study the efficiency of various environmental effects on the evolution of disk galaxies in clusters. The velocity distribution of the barred spirals in the Virgo region is clearly different than that of the nonbarred spirals, suggesting that barred spirals are more common in the main condensation of the cluster. A sample cleansed of galaxies not belonging to the main cluster condensati…
Using the Effelsberg radio telescope at 4.85GHz and 8.35 GHz we discovered large symmetric lobes of polarized radio emission around the strongly HI deficient Virgo cluster spiral galaxy NGC4569. These lobes extend up to 24 kpc from the galactic disk. Our observations were complemented by 1.4 GHz continuum emission from existing HI observations. This is the first time that such huge radio continuum lobes are observed in a cluster spiral galaxy. The eastern lobe seems detached and has a flat spectrum typical for in-situ cosmic ray electron acceleration. The western lobe is diffuse and possesses …
We have measured the strengths of the [C II] 158 micron, [N II] 122 micron, and CO (1 - 0) lines from five low blue luminosity spiral galaxies in the Virgo Cluster, using the Infrared Space Observatory and the NRAO 12m millimeter telescope. Two of the five galaxies have high L([C II)]/L(CO) and L(FIR)/L(CO) ratios compared to higher mass spirals. These two galaxies, NGC 4294 and NGC 4299, have L([C II])/L(CO) ratios of >14,300 and 15,600, respectively, which are similar to values found in dwarf irregular galaxies. This is the first time that such enhanced L([C II])/L(CO) ratios have been found…
We report on high-resolution interferometer observations of the 12CO(J=1-0) emission in the central 5 kpc region of the Seyfert 2 galaxy NGC 4501. The observations were made using the Nobeyama Millimeter Array during a long-term CO line survey of Virgo spirals. The major features are: (1) a nuclear concentration with a radius of r~5'' (390 pc), which is resolved into double peaks, and (2) spiral arms which extend out from the nuclear region. The nuclear component has a mass of 1.3x10^8 Mo, which corresponds to ~3.5% of the dynamical mass, and shows a slight non-circular motion. The double peak…
We present the results of the stellar and ionized gas kinematics of 13 bright peculiar Virgo cluster galaxies. The stellar velocity field are mostly consistent with a rotation pattern, but some of them shows interesting features such as; S-shaped stellar isovelocity contours in NGC 4064, and signatures of kinematical distinct components in NGC 4429, and NGC 4698. This latter galaxy and NGC 4424 exhibit extremely low (V/sigma)* values suggesting that these galaxies are the result of mergers. The ionized gas velocity fields are more disturbed than the stellar velocity fields, displaying non-circ…
We show that the mean percentage of stellar light re-radiated by dust is ~30 percent for the Virgo Cluster late-spirals measured with ISOPHOT by Tuffs et al. (2002). A strong dependence of this ratio with morphological type was found, ranging from typical values of ~15 percent for early spirals to up to ~50 percent for some late spirals. The extreme BCDs can have even higher percentages of their bolometric output re-radiated in the thermal infrared. Luminosity correction factors for the cold dust component are given for general use in converting far-infrared (FIR) luminosities derived from IRA…
Radio continuum observations at 20 and 6 cm of the highly inclined Virgo spiral galaxy NGC 4522 are presented. Both, 20 and 6 cm total emission distributions are asymmetric with an extended component to the west where extraplanar atomic gas and Halpha emission are found. The 6 cm polarized emission is located at the eastern edge of the galactic disk. Its peak is located about 1 kpc to the east of the total emission peak. We argue that this phenomena is a characteristic feature for cluster galaxies which are experiencing significant pressure from the intracluster medium. The degree of polarizat…
We found high molecular fractions ($f_{\rm mol}$; ratio of the molecular to total gas surface densities) in three of five Virgo spiral galaxies in spite of their low total gas column density, based on $^{12}$CO$(J=1-0)$ observations with the Nobeyama 45 m telescope equipped with a multi-beam receiver, BEARS. We interpret this as a result of environmental effects. Combining the CO data with HI data, the relationship between the surface density of the total gas (HI plus H$_2$) and $f_{\rm mol}$ indicates that the three galaxies near the cluster center have larger $f_{\rm mol}$ values than expect…
We discuss HI and optical evidence for ongoing ICM-ISM interactions in 6 HI-deficient Virgo cluster spiral galaxies. One of the clearest cases is the highly inclined Virgo galaxy NGC 4522, which has a normal stellar disk but a truncated gas disk, and lots of extraplanar gas right next to the gas truncation radius in the disk. Unusually strong HI, H-alpha and radio continuum emission are all detected from the extraplanar gas. The radio continuum polarized flux and spectral index peak on the side opposite the extraplanar gas, suggesting ongoing pressure by the ICM. Four other HI-deficient edge-o…
Because of its proximity the Virgo Cluster is an excellent target for studying interactions of galaxies with the cluster environment. Both the high-velocity tidal interactions and effects of ram pressure stripping by the intracluster gas can be investigated. Optical and/or \ion{H}{i} observations do not always show effects of weak interactions between galaxies and their encounters with the cluster medium. For this reason we searched for possible anomalies in the magnetic field structure in Virgo Cluster spirals which could be attributed to perturbations in their gas distribution and kinematics…
The scale lengths of the old stars and ionized gas distributions are compared for similar samples of Virgo Cluster members and field spiral galaxies via Halpha and broad R-band surface photometry. While the R-band and Halpha scale lengths are, on average, comparable for the combined sample, we find significant differences between the field and cluster samples. While the Halpha scale lengths of the field galaxies are a factor of 1.14 +- 0.07 longer on average than their R-band scale lengths, the Halpha scale lengths of Virgo Cluster members are on average 20% smaller than their R-band scale len…
Deep Effelsberg 100-m HI observations of 5 HI deficient Virgo spiral galaxies are presented. No new extended HI tail is found in these galaxies. The already known HI tail north of NGC 4388 does not significantly extend further than a WSRT image has shown. Based on the absence of HI tails in a sample of 6 Virgo spiral galaxies and a balance of previous detections of extraplanar gas in the targeted galaxies we propose a global picture where the outer gas disk (beyond the optical radius R_25) is removed much earlier than expected by the classical ram pressure criterion. Based on the two-phase nat…
(Abridged) We present an analysis of the stellar populations of the gas-stripped outer disks of ten Virgo Cluster spiral galaxies, utilizing SparsePak integral field spectroscopy on the WIYN 3.5m telescope and GALEX UV photometry. The galaxies in our sample show evidence for being gas-stripped spiral galaxies, with star formation within a truncation radius, and a passive population beyond the truncation radius. We find that all of the galaxies with spatially truncated star formation have outer disk stellar populations consistent with star formation ending within the last 500 Myr. The synthesis…
The results of an analysis of the substructure of 1 degree field galaxies of the Virgo cluster by means of the S-tree technique developed by Gurzadyan et al, are represented. The existence of 3 main subgroups is shown and their dynamical parameters are obtained. The mass centers of the subgroups appear to be aligned in the direction parallel to the elongation of the Virgo cluster. The morphological analysis shows some domination of dwarf galaxies in the subgroup A containing M 87, and existence of two spiral galaxies N4425 and N4461; the latter fact can be crucial for the estimation of the dis…
VIVA HI observations of the Virgo spiral galaxy NGC 4501 are presented. The HI disk is sharply truncated to the southwest, well within the stellar disk. A region of low surface-density gas, which is more extended than the main HI disk, is discovered northeast of the galaxy center. These data are compared to existing 6cm polarized radio continuum emission, Halpha, and optical broad band images. We observe a coincidence between the western HI and polarized emission edges, on the one hand, and a faint Halpha emission ridge, on the other. The polarized emission maxima are located within the gaps b…
Monopole and dipole signatures of the peculiar velocity field as derived from the SFI sample of field spirals and the SCI and SC2 samples of cluster spirals are presented. The monopole exhibits no evidence of a `Hubble bubble' within 7000 km/s as suggested by Zehavi et al. (1998); the dipole of the reflex motion of the Local Group converges to the CMB dipole within less than 6000 km/s, and remains consistent with it, when referred to the reference frame constituted by the SC2 cluster sample, which extends to 20,000 km/s.
We present 12CO(J=2->1) and CO(J=3->2) observations of quiescent Virgo Cluster spiral galaxies with the KOSMA 3m submm telescope. The beam sizes of 80" at 345 GHz and 120" at 230 GHz are well suited for the investigation of global properties of Virgo Cluster galaxies. The observed sample was selected based on previous 12CO(J=1->0) detections by Stark et al. (1986), performed with the AT&T Bell Laboratory 7m telescope (beam size 100"). We were able to detect 18 spiral galaxies in 12CO(2->1) and 16 in 12CO(3->2). Beam matched observations of the lowest three 12CO transitions allow us to compare …
The Virgo cluster galaxy NGC 4522 is one of the best spiral candidates for ICM-ISM stripping in action. Optical broadband and H-alpha images from the WIYN telescope of the highly inclined galaxy reveal a relatively undisturbed stellar disk and a peculiar distribution of H-alpha emission. Ten percent of the H-alpha emission arises from extraplanar HII regions which appear to lie within filamentary structures >3 kpc long above one side of the disk. The filaments emerge from the outer edge of a disk of bright H-alpha emission which is abruptly truncated beyond 0.35R(25). Together the truncated H-…
New H-alpha Fabry-Perot interferometer observations of the Virgo cluster spiral galaxy NGC 4522 are presented. A velocity field up to a radius of 60'' was obtained. The observed rotation curve is symmetric. It is not perturbed in the inner disk. For radii >50'' it shows a solid body rotation. We compare these data with a numerical model which includes the effects of ram pressure stripping. The model can reproduce the main characteristics of the H-alpha emission distribution and velocity field. We therefore conclude that the stripping event which caused the HI deficiency and the distorted H-alp…
Despite many studies of the star formation in spiral galaxies, a complete and coherent understanding of the physical processes that regulate the birth of stars has not yet been achieved, nor a unanimous consent was reached, despite the many attempts, on the effects of the environment on the star formation in galaxies member of rich clusters. We focus on the local and global Schmidt law and we investigate how cluster galaxies have their star formation activity perturbed. We collect multifrequency imaging for a sample of spiral galaxies, member of the Virgo cluster and of the local field; we com…
(Abridged) The distances and HI contents of 161 spiral galaxies in the region of Virgo cluster are used to gain insight into the complicated structure of this galaxy system. The 3D galaxy distribution has been inferred from quality distance estimates obtained by averaging distance moduli based upon the TF relationship taken from eight published datasets previously homogenized. Previous findings that the spiral distribution is substantially more elongated along the line-of-sight than in the plane of the sky are confirmed by the current data. In addition, an important east-west disparity in this…
We present high-angular-resolution (1".5 - 5") interferometer observations of the \co emission in the central region of the SA(s)c galaxy NGC 4254. The observations were obtained using the Nobeyama Millimeter-wave Array (NMA) during the course of a long-term CO line survey of Virgo spirals. We present the spectra, channel maps, integrated intensity distributions, velocity fields, position--velocity diagrams, and compare the data with various optical images. The rotation velocity is already finite at the nucleus, or at least it rises steeply to 80 km/s within the central 1", indicating the exis…
We present a detailed study of the peculiar HI-deficient Virgo cluster spiral galaxies NGC 4064 and NGC 4424, using $^{12}$CO 1-0 interferometry, optical imaging and integral-field spectroscopic observations, in order to learn what type of environmental interactions have afected these galaxies. Optical imaging reveals that NGC 4424 has a strongly disturbed stellar disk, with banana-shaped isophotes and shells. NGC 4064, which lies in the cluster outskirts, possesses a relatively undisturbed outer stellar disk and a central bar. In both galaxies H-alpha emission is confined to the central kilop…
We present cosmological simulations which closely mimic the real Universe within 100Mpc of the Local Group. The simulations, called Constrained Simulations, reproduce the large-scale density field with major nearby structures, including the Local Group, the Coma and Virgo clusters, the Great Attractor, the Perseus-Pices, and the Local Supercluster, in approximately correct locations. The MARK III survey of peculiar velocities of the observed structures inside 80Mpc/h sphere is used to constrain the initial conditions. Fourier modes on scales larger then 5Mpc/h are dominated by the constraints,…
Deep observations of 6cm polarized radio continuum emission of 8 Virgo spiral galaxies are presented. All galaxies show strongly asymmetric distributions of polarized intensity with elongated ridges located in the outer galactic disk. Such features are not found in existing observations of polarized radio continuum emission of field spiral galaxies, where the distribution of 6cm polarized intensity is generally relatively symmetric and strongest in the interarm regions. We therefore conclude that most Virgo spiral galaxies and most probably the majority of cluster spiral galaxies show asymmetr…
We report the detection of extended low radio frequency continuum emission beyond the optical disk of the spiral galaxy NGC 4254 using the Giant Metrewave Radio Telescope. NGC 4254, which has an almost face-on orientation, is located in the outskirts of the Virgo cluster. Since such extended emission is uncommon in low inclination galaxies, we believe it is a signature of magnetised plasma pushed out of the disk by ram pressure of the intracluster medium as NGC 4254 falls into the Virgo cluster. The detailed spectral index distribution across NGC 4254 shows that the steepest spectrum alpha < -…
We present VLA HI observations at ~20"=1.5 kpc resolution of the highly inclined, HI-deficient Virgo cluster spiral galaxy NGC 4522, which is one of the clearest and nearest cases of ongoing ICM-ISM stripping. HI is abundant and spatially coincident with the stellar disk in the center, but beyond R = 3 kpc the HI distribution in the disk is sharply truncated and the only HI is extraplanar, and all on the northwest side. The kinematics and the morphology of the HI appear more consistent with ongoing stripping, and less consistent with gas fall-back which may occur long after peak pressure. Much…
We study the old problem of the uniqueness of chemical evolution models. We showed in Molla et al. (1999) that multiphase models for three Virgo cluster galaxies were able to reproduce the observed radial distributions of spectral indices Mg2 and Fe52. But those models may fit the present-epoch radial distributions with different star formation histories. The two spectral indices are in turn affected by the well known age-metallicity degeneracy which prevents the disentagling of age and metallicity for single stellar populations. In this work we face both issues by analyzing a set of multiphas…
We present large-area maps of the CO J=3-2 emission obtained at the James Clerk Maxwell Telescope for four spiral galaxies in the Virgo Cluster. We combine these data with published CO J=1-0, 24 micron, and Halpha images to measure the CO line ratios, molecular gas masses, and instantaneous gas depletion times. For three galaxies in our sample (NGC 4254, NGC4321, and NGC 4569), we obtain molecular gas masses of 7E8-3E9 Msun and disk-averaged instantaneous gas depletion times of 1.1-1.7 Gyr. We argue that the CO J=3-2 line is a better tracer of the dense star forming molecular gas than the CO J…
A dynamical model including ram pressure stripping is applied to the strongly HI deficient Virgo spiral galaxy NGC 4522. A carefully chosen model snapshot is compared with existing VLA HI observations. The model successfully reproduces the large-scale gas distribution and the velocity field. However it fails to reproduce the large observed HI linewidths in the extraplanar component, for which we give possible explanations. In a second step, we solve the induction equation on the velocity fields of the dynamical model and calculate the large scale magnetic field. Assuming a Gaussian distributio…
Many observations indicate that dark matter dominates the extra-galactic Universe, yet no totally dark structure of galactic proportions has ever been convincingly identified. Previously we have suggested that VIRGOHI 21, a 21-cm source we found in the Virgo Cluster using Jodrell Bank, was a possible dark galaxy because of its broad line-width (~200 km/s) unaccompanied by any visible gravitational source to account for it. We have now imaged VIRGOHI 21 in the neutral-hydrogen line and find what could be a dark, edge-on, spinning disk with the mass and diameter of a typical spiral galaxy. Moreo…
IRAM 30m 12CO(1-0) and 12CO(2-1) HERA observations are presented for the ram-pressure stripped Virgo spiral galaxy NGC 4522. The CO emission is detected in the galactic disk and the extraplanar gas. The extraplanar CO emission follows the morphology of the atomic gas closely but is less extended. The CO maxima do not appear to correspond to regions where there is peak massive star formation as probed by Halpha emission. The presence of molecular gas is a necessary but not sufficient condition for star formation. Compared to the disk gas, the molecular fraction of the extraplanar gas is 30% low…
We expand our pervious numerical study of the properties of the stellar velocity distribution within the disk of a two-armed spiral galaxy by considering spiral stellar density waves with different global Fourier amplitudes, C_2. We confirm our previous conclusion that the ratio σ_1:σ_2 of smallest versus largest principal axes of the stellar velocity ellipsoid becomes abnormally small near the outer edges of the stellar spiral arms. The extent to which the stellar velocity ellipsoid is elongated (as compared to the unperturbed value typical for the axisymmetric disk) increases with the streng…
Some of the peculiar features of the periodic velocity-field structure for OB associations can be explained by using the model of Roberts and Hausman (1984), in which the behavior of a system of dense clouds is considered in a perturbed potential. The absence of statistically significant variations in the azimuthal velocity across the Carina arm, probably, results from its sharp increase behind the shock front, which is easily blurred by distance errors. The existence of a shock wave in the spiral arms and, at the same time, the virtually free motion of OB associations in epicycles can be reco…
Peculiar velocities thoughout the region of the local supercluster are reconstructed by two different orbit-retracing methods. The requirement of the optimal correlation between the radial components of reconstructed velocities and the observed peculiar velocities derived from our extensive new catalog of distances puts stringent constraints on the values of the cosmological parameters. Our constraints intersect those from studies of microwave background fluctuations and statistical properties of galaxy clustering: the ensemble of constraints are consistent with Omega_m=0.22\pm 0.02. While mot…
We have completed a survey of 30 Virgo cluster galaxies in the Halpha emission-line using Fabry-Perot interferometry. The goal of the survey is to obtain a high angular resolution sample of velocity fields of spirals and to study the environmental effects on their kinematics and dynamics.
For 89 galaxies, mostly spirals, in the Virgo cluster region, we have obtained optical long-slit major axis spectra of the ionized gas. We find: (1) One-half of the Virgo galaxies we observed have regular rotation patterns, while the other 50% exhibit kinematic disturbances ranging from mild to major. Velocity complexities are generally consistent with those resulting from tidal encounters or accretion events. Since kinematic disturbances are expected to fade within ~10^9 years, many Virgo galaxies have experienced several significant kinematic disturbances during their lifetimes. (2) A few Vi…
The presence on the Virgo cluster outskirts of spiral galaxies with gas deficiencies as strong as those of the inner galaxies stripped by the intracluster medium has led us to explore the possibility that some of these peripheral objects are not newcomers. A dynamical model for the collapse and rebound of spherical shells under the point mass and radial flow approximations has been developed to account for the amplitude of the motions in the Virgo I cluster (VIC) region. According to our analysis, it is not unfeasible that galaxies far from the cluster, including those in a gas-deficient group…
A catalog of ionized gas velocity fields for a sample of 30 spiral and irregular galaxies of the Virgo cluster has been obtained by using three-dimensional optical data. The aim of this survey is to study the influence of high density environments on the gaseous kinematics of local cluster galaxies. Observations of the Halpha line by means of Fabry-Perot interferometry have been performed at the Canada-France-Hawaii, ESO 3.6m, Observatoire de Haute-Provence 1.93m and Observatoire du mont Megantic telescopes at angular and spectral samplings from 0.4" to 1.6" and 7 to 16 km/s. A recently develo…
The 2MFGC catalog we have used contains 18020 galaxies selected from the extended objects in the 2MASS infrared sky survey as having apparent ratios of the axes b/a<0.3. Most of them are spiral galaxies of later morphological types whose disks are seen almost edge-on. The individual distances to the 2724 2MFGC galaxies with known rotation velocities and radial velocities are determined using a multiparameter infrared Tully-Fisher relation. A list of the distances and peculiar velocities of these galaxies is presented. The collective motion of the 2MFGC galaxies relative to the cosmic microwave…
We present the initial results from SPITSOV, the Spitzer Survey of Virgo, which includes MIPS and IRAC observations for a carefully selected sample of 44 Virgo cluster spiral and peculiar galaxies. SPITSOV is part of a multiwavelength campaign to understand the effects of the cluster environment on galaxy evolution. These Virgo galaxies are different from galaxies outside of clusters, since most of them have been significantly modified by their environment. The SPITSOV data can serve the community as the Spitzer sample of nearby cluster spiral galaxies, a complement to the SINGS data for nearb…
Dark Matter supposedly dominates the extragalactic, yet no totally dark structure of galactic proportions has ever been convincingly identified. Earlier (Minchin et al. 2005) we suggested that VIRGOHI 21, a 21-cm source we found in the Virgo Cluster at Jodrell Bank using single-dish observations (Davies et al. 2004), was probably such a dark galaxy because of its broad line-width (~ 200 km/s) unaccompanied by any visible gravitational source to account for it. Now we have managed to image VIRGOHI 21 in the neutral-hydrogen line, and indeed we find what appears to be a dark, edge-on, spinning d…
We present a new method for studying the star formation history of late-type, cluster galaxies undergoing gas starvation or a ram-pressure stripping event by combining bidimensional multifrequency observations with multi-zones models of galactic chemical and spectrophotometricevolution. This method is applied to the Virgo cluster anemic galaxy NGC 4569. We extract radial profiles from recently obtained UV GALEX images at 1530 and 2310 A, from visible and near-IR narrow (Halpha) and broad band images at different wavelengths (u, B, g, V, r, i, z, J, H, K), from Spitzer IRAC and MIPS images and …
We present results from an ongoing survey dedicated to the ionized gas kinematics of Virgo cluster spiral galaxies using Fabry-Perot interferometry. Our goal is to study the environmental effects on galaxy evolution in the Virgo cluster. We report here on the Halpha distribution map and velocity field of NGC 4438, the prototype of an interacting galaxy near the centre of the cluster.
Following the discovery of spiral structure in IC3328 (Jerjen et al.~2000), we present further evidence that a sizable fraction of bright early-type dwarfs in the Virgo cluster are genuine disk galaxies, or are hosting a disk component. Among a sample of 23 nucleated dwarf ellipticals and dS0s observed with the Very Large Telescope in $B$ and $R$, we found another four systems exhibiting non-axisymmetric structures, such as a bar and/or spiral arms, indicative of a disk (IC0783, IC3349, NGC4431, IC3468). Particularly remarkable are the two-armed spiral pattern in IC0783 and the bar and trailin…
We present a systematic search for disks in 476 Virgo cluster early-type dwarf (dE) galaxies. Disk features (spiral arms, edge-on disks, or bars) were identified by applying unsharp masks to a combined image from three bands (g, r, i), as well as by subtracting the axisymmetric light distribution of each galaxy from that image. 14 objects are unambiguous identifications of disks, 10 objects show 'probable disk' features, and 17 objects show 'possible disk' features. The number fraction of these galaxies, for which we introduce the term dEdi, reaches more than 50% at the bright end of the dE po…
We compare infrared Tully-Fisher (TF) distances and peculiar velocities derived for spiral galaxies from the two largest datasets: the 2MASS selected Flat Galaxy Catalog, 2MFGC [19, 20] and the Arecibo General Catalog with I-band photometry, SFI++ [30,7]. These samples contain peculiar velocities for ~3000 and ~4000 objects, respectively. Based on a sub-sample of ~1000 common deeply inclined galaxies, we reach the following conclusions. Irrespective to high (SFI++) or low (2MFGC) quality of the used photometric data, about 10% of the galaxies in both samples deviate considerably from the main …
Spiral galaxies that are deficient in neutral Hydrogen are observed on the outskirts of the Virgo cluster. If their orbits have crossed the inner parts of the cluster, their interstellar gas may have been lost through ram pressure stripping by the hot X-ray emitting gas of the cluster. We estimate the maximum radius out to which galaxies can bounce out of a virialized system using analytical arguments and cosmological N-body simulations. In particular, we derive an expression for the turnaround radius in a flat cosmology with a cosmological constant that is simpler than previously derived expr…
The origin of the deficiency in neutral Hydrogen of 13 spiral galaxies lying in the outskirts of the Virgo cluster is reassessed. If these galaxies have passed through the core of the cluster, their interstellar gas should have been lost through ram pressure stripping by the hot X-ray emitting gas of the cluster. We analyze the positions of these HI-deficient and other spiral galaxies in velocity-distance plots, in which we include our compilation of velocity-distance data on 61 elliptical galaxies, and compare with simulated velocity-distance diagrams obtained from cosmological N-body simulat…
We report on work done by the Virgo consortium, an international collaboration set up in order to study the formation and evolution of Large Scale Structure using N-body simulations on the latest generation of parallel supercomputers. We show results of 256^3 particle simulations of the formation of clusters in four Dark Matter models with different cosmological parameters. Normalizing the models such that one obtains the correct abundance of rich clusters yields an interesting result: The peculiar velocities of the clusters are almost independent of Ω, and depend only weakly on Γ, the shape p…
In order to investigate dynamical properties of spiral galaxies in the Hickson compact groups (HCGs), we present rotation curves of 30 galaxies in 20 HCGs. We found as follows. 1) There is not significant relation between dynamical peculiarity and morphological peculiarity in HCG spirals. 2) There is no significant relation between the dynamical properties and the frequency distribution of nuclear activities in HCG spirals. 3) There are no significant correlations between the dynamical properties of HCG spirals and any group properties (i.e., the size, the velocity dispersion, the galaxy numbe…
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 fr…
