Constraining the ages of the fireballs in the wake of the dIrr galaxy VCC1217 / IC3418

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 Astrophysic

Radio continuum spectra of galaxies in the Virgo cluster region

New radio continuum observations of galaxies in the Virgo cluster region at 4.85, 8.6, and 10.55 GHz are presented. These observations are combined with existing measurements at 1.4 and 0.325 GHz. The sample includes 81 galaxies were spectra with more than two frequencies could be derived. Galaxies that show a radio-FIR excess exhibit central activity (HII, LINER, AGN). The four Virgo galaxies with the highest absolute radio excess are found within 2 degrees of the center of the cluster. Galaxies showing flat radio spectra also host active centers. There is no clear trend between the spectral index and the galaxy's distance to the cluster center.Comment: 13 pages, 12 figures. Accepted for publication in A&

A radial mass profile analysis of the lensing cluster MS2137-23

We reanalyze the strong lens modeling of the cluster of galaxies MS2137-23 using a new data set obtained with the ESO VLT. We found the photometric redshifts of the two main arc systems are both at z=1.6. After subtraction of the central cD star light of the HST image we found that only one object lying underneath has the expected properties of the fifth image associated to the tangential arc. We improve the previous lens modelings of the central dark matter distribution of the cluster, using an isothermal model with a core (IS) and the NFW-like model with a cusp. Without the fifth image, the arc properties together with the shear map profile are equally well fit by the and by an IS and a sub-class of generalized-NFW mass profiles having inner slope power index in the range 0.7<alpha<1.2. Adding new constrains provided by the fifth image favors IS profiles that better predict the fifth image properties. A model including cluster galaxy perturbations or the the stellar mass distribution does not change our conclusions but imposes the M/L_I of the cD stellar component is below 10 at a 99% confidence level. Using our new detailed lensing model together with Chandra X-ray data and the cD stellar component we finally discuss intrinsic properties of the gravitational potential. Whereas X-ray and dark matter have a similar shape at various radius, the cD stellar isophotes are twisted by 13 deg. The sub- arc-second azimuthal shift we observe between the radial arc position and the predictions of elliptical models correspond to what is expected from a mass distribution twist. This shift may result from a projection effect of the cD and the cluster halos, thus revealing the triaxiality of the system.Comment: Final version accepted in A&

The census of nuclear activity of late-type galaxies in the Virgo cluster

The first spectroscopic census of AGNs associated to late-type galaxies in the Virgo cluster is carried on by observing 213 out of a complete set of 237 galaxies more massive than M_dyn>10^{8.5} solar masses. Among them, 77 are classified as AGNs (including 21 transition objects, 47 LINERs and 9 Seyferts), and comprize 32% of the late-type galaxies in Virgo. Due to spectroscopic incompleteness at most 21 AGNs are missed in the survey, so that the fraction would increase up to 41%. Using corollary Near-IR observations, that enable us to estimate galaxies dynamical masses, it is found that AGNs are hosted exclusively in massive galaxies, i.e. M_dyn\gsim 10^{10} solar masses. Their frequency increases steeply with the dynamical mass from zero at M_dyn\approx10^{9.5} solar masses to virtually 1 at M_dyn>10^{11.5} solar masses. These frequencies are consistent with the ones of low luminosity AGNs found in the general field by the SDSS. Massive galaxies that harbor AGNs commonly show conspicuous r-band star-like nuclear enhancements. Conversely they often, but not necessarily contain massive bulges. Few well known AGNs (e.g. M61, M100, NGC4535) are found in massive Sc galaxies with little or no bulge. The AGN fraction seems to be only marginally sensitive to galaxy environment. We infer the black hole masses using the known scaling relations of quiescent black holes. No black holes lighter than $\sim 10^6$ \msol are found active in our sample.Comment: The paper contains 13 figures and 5 tables; accepted for publication in MNRA

The Dark UNiverse Explorer (DUNE): Proposal to ESA's Cosmic Vision

The Dark UNiverse Explorer (DUNE) is a wide-field space imager whose primary goal is the study of dark energy and dark matter with unprecedented precision. For this purpose, DUNE is optimised for the measurement of weak gravitational lensing but will also provide complementary measurements of baryonic accoustic oscillations, cluster counts and the Integrated Sachs Wolfe effect. Immediate auxiliary goals concern the evolution of galaxies, to be studied with unequalled statistical power, the detailed structure of the Milky Way and nearby galaxies, and the demographics of Earth-mass planets. DUNE is an Medium-class mission which makes use of readily available components, heritage from other missions, and synergy with ground based facilities to minimise cost and risks. The payload consists of a 1.2m telescope with a combined visible/NIR field-of-view of 1 deg^2. DUNE will carry out an all-sky survey, ranging from 550 to 1600nm, in one visible and three NIR bands which will form a unique legacy for astronomy. DUNE will yield major advances in a broad range of fields in astrophysics including fundamental cosmology, galaxy evolution, and extrasolar planet search. DUNE was recently selected by ESA as one of the mission concepts to be studied in its Cosmic Vision programme.Comment: Accepted in Experimental Astronom

The Arecibo Galaxy Environment Survey V : The Virgo Cluster (I)

We present 21 cm observations of a 10 $\times$ 2 degree region in the Virgo cluster, obtained as part of the Arecibo Galaxy Environment Survey. 289 sources are detected over the full redshift range (-2,000 $<$ $v$$_{hel}$ $<$ + 20,000 km/s) with 95 belonging to the cluster ($v$$_{hel}$ $<$ 3,000 km/s). We combine our observations with data from the optically selected Virgo Cluster Catalogue (VCC) and the Sloan Digital Sky Survey (SDSS). Most of our detections can be clearly associated with a unique optical counterpart, and 30% of the cluster detections are new objects fainter than the VCC optical completeness limit. 7 detections may have no optical counterpart and we discuss the possible origins of these objects. 7 detections appear associated with early-type galaxies. We perform HI stacking on the HI-undetected galaxies listed in the VCC in this region and show that they must have significantly less gas than those actually detected in HI. Galaxies undetected in HI in the cluster appear to be really devoid of gas, in contrast to a sample of field galaxies from ALFALFA.Comment: 23 pages, 22 figures, 4 table

SARCS strong lensing galaxy groups: I - optical, weak lensing, and scaling laws

We present the weak lensing and optical analysis of the SL2S-ARCS (SARCS) sample of strong lens candidates. The sample is based on the Strong Lensing Legacy Survey (SL2S), a systematic search of strong lensing systems in the photometric Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The SARCS sample focuses on arc-like features and is designed to contain mostly galaxy groups. We briefly present the weak lensing methodology that we use to estimate the mass of the SARCS objects. Among 126 candidates, we obtain a weak lensing detection for 89 objects with velocity dispersions of the Singular Isothermal Sphere mass model ranging from 350 to 1000 km/s with an average value of 600km/s, corresponding to a rich galaxy group (or poor cluster). From the galaxies belonging to the bright end of the group's red sequence (M_i<-21), we derive the optical properties of the SARCS candidates. We obtain typical richnesses of N=5-15 galaxies and optical luminosities of L=0.5-1.5e+12 Lsol (within a radius of 0.5 Mpc). We use these galaxies to compute luminosity density maps, from which a morphological classification reveals that a large fraction of the sample are groups with a complex light distribution, either elliptical or multimodal, suggesting that these objects are dynamically young structures. We finally combine the lensing and optical analyses to draw a sample of 80 most secure group candidates, i.e. weak lensing detection and over-density at the lens position in the luminosity map, to remove false detections and galaxy-scale systems from the initial sample. We use this reduced sample to probe the optical scaling relations in combination with a sample of massive galaxy clusters. We detect the expected correlations over the probed range in mass with a typical scatter of 25% in the SIS velocity dispersion at a given richness or luminosity, making these scaling laws interesting mass proxie

Enhanced lensing rate by clustering of massive galaxies: newly discovered systems in the SLACS fields

[Abridged] We exploit the clustering of massive galaxies to perform a high efficiency imaging search for gravitational lenses. Our dataset comprises 44 fields imaged by the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS), each of which is centered on a lens discovered by the Strong Lens ACS Survey (SLACS). We compare four different search methods: 1) automated detection with the HST Archive Galaxy-scale Gravitational Lens Survey (HAGGLeS) robot, 2) examining cutout images of bright galaxies (BGs) after subtraction of a smooth galaxy light distribution, 3) examining the unsubtracted BG cutouts, and 4) performing a full-frame visual inspection of the ACS images. We compute purity and completeness and consider investigator time for the four algorithms, using the main SLACS lenses as a testbed. The first and second algorithms perform the best. We present the four new lens systems discovered during this comprehensive search, as well as one other likely candidate. For each new lens we use the fundamental plane to estimate the lens velocity dispersion and predict, from the resulting lens geometry, the redshifts of the lensed sources. Two of these new systems are found in galaxy clusters, which include the SLACS lenses in the two respective fields. Overall we find that the enhanced lens abundance (30^{+24}_{-8} lenses/degree^2) is higher than expected for random fields (12^{+4}_{-2} lenses/degree^2 for the COSMOS survey). Additionally, we find that the gravitational lenses we detect are qualitatively different from those in the parent SLACS sample: this imaging survey is largely probing higher-redshift, and lower-mass, early-type galaxies.Comment: submitted to ApJ; 19 pages, 12 figure

UV properties of early-type galaxies in the Virgo cluster

We study the UV properties of a volume limited sample of early-type galaxies in the Virgo cluster combining new GALEX far- (1530 A) and near-ultraviolet (2310 A) data with spectro-photometric data available at other wavelengths. The sample includes 264 ellipticals, lenticulars and dwarfs spanning a large range in luminosity (M(B)<-15). While the NUV to optical or near-IR color magnitude relations (CMR) are similar to those observed at optical wavelengths, with a monotonic reddening of the color index with increasing luminosity, the (FUV-V) and (FUV-H) CMRs show a discontinuity between massive and dwarf objects. An even more pronounced dichotomy is observed in the (FUV-NUV) CMR. For ellipticals the (FUV-NUV) color becomes bluer with increasing luminosity and with increasing reddening of the optical or near-IR color indices. For the dwarfs the opposite trend is observed. These observational evidences are consistent with the idea that the UV emission is dominated by hot, evolved stars in giant systems, while in dwarf ellipticals residual star formation activity is more common.Comment: 5 pages, 2 figures, 1 table. Accepted for publication in Astrophysical Journal Letter

Deepest Near-IR Surface Photometry of Galaxies in the Local Sphere of Influence

We present near-IR, deep (4 mag deeper than 2MASS) imaging of 56 Local Volume galaxies. Global parameters such as total magnitudes and stellar masses have been derived and the new near-IR data combined with existing 21cm and optical B-band data. We present multiwavelength relations such as the HI mass-to-light ratio and investigate the maximum total baryonic mass a galaxy can have.Comment: 4 pages, 3 figures, To be published in the proceedings of "Galaxies in the Local Volume", ed. B. Koribalski, H. Jerje