The 3D soft X-ray cluster-AGN cross-correlation function in the ROSAT NEP survey

X-ray surveys facilitate investigations of the environment of AGNs. Deep Chandra observations revealed that the AGNs source surface density rises near clusters of galaxies. The natural extension of these works is the measurement of spatial clustering of AGNs around clusters and the investigation of relative biasing between active galactic nuclei and galaxies near clusters.The major aims of this work are to obtain a measurement of the correlation length of AGNs around clusters and a measure of the averaged clustering properties of a complete sample of AGNs in dense environments. We present the first measurement of the soft X-ray cluster-AGN cross-correlation function in redshift space using the data of the ROSAT-NEP survey. The survey covers 9x9 deg^2 around the North Ecliptic Pole where 442 X-ray sources were detected and almost completely spectroscopically identified. We detected a >3sigma significant clustering signal on scales s<50 h70^-1 Mpc. We performed a classical maximum-likelihood power-law fit to the data and obtained a correlation length s_0=8.7+1.2-0.3 h_70-1 Mpc and a slope gamma=1.7$^+0.2_-0.7 (1sigma errors). This is a strong evidence that AGNs are good tracers of the large scale structure of the Universe. Our data were compared to the results obtained by cross-correlating X-ray clusters and galaxies. We observe, with a large uncertainty, that the bias factor of AGN is similar to that of galaxies.Comment: 4 pages, 2 figure, proceedings of the Conference "At the edge of the Universe", Sintra Portugal, October 2006. To be published on the Astronomical Society of the Pacific Conference Series (ASPCS

Levaduras autóctonas como factores de crecimiento en Rhamdia quelen: primeras aproximaciones

Rhamdia quelen is an autochthonous fish used for aquaculture in the Northeast of Argentina. Antibiotics as growing factors in fish production had been criticized in the last years and the use of microorganisms emerged as a putative replacement. The aim of this study was to isolate autochthonous yeasts from R. quelen and to evaluate the effect of the administration over biometrical parameters of larvae under intensive culture system. Fungi were isolated from the digestive tract of wild specimens, phenotypically identified and evaluated on their ability to exert beneficial properties. One selected fungal isolate was administered, four times a day, dead or alive at 1 or 2% together with balanced feed to R. quelen larvae for 15 days. aftertreatment larvae were counted and weighted in order to obtain the values of survival, mean weight and total biomass. Only four Candida tropicalis isolates were obtained. None of them expressed beneficial properties. One fungal isolate was randomly selected for in vivo assays. Results indicated that only dead yeast at 1% induced a significant increment of biomass when compared with the control group (p&lt;0.05). Survival rate was boosted significantly (p&lt;0.05) with dead yeast and not significantly (p&gt;0.05) with the fungal isolate. None of the treatments induced significant increments in mean weight (p&lt;0.05). These results allowed us to propose  the treatment with dead yeast at 1% as a growing factor for R. quelen, considering this microorganism as an effective prebiotic in the aquaculture of this specie.Rhamdia quelen es un pez autóctono cultivado en el nordeste argentino. El uso de antibióticos como factores de crecimiento en acuicultura fue criticado en los últimos años y la administración de microorganismos surgió como una opción posible. El objetivo de este trabajo fue aislar levaduras autóctonas de R. quelen y evaluar el efecto de su administración sobre parámetros biométricos de larvas en cultivo intensivo. Los hongos se aislaron del tracto digestivo de especímenes de vida silvestre, se identificaron fenotípicamente y se evaluaron en cuanto a la expresión de propiedades benéficas. Se seleccionó una de las cepas y se administró cuatro veces por día, muerta o viva al 1 o 2% junto con el alimento balanceado durante 15 días. Luego del tratamiento las larvas se contaron y pesaron para obtener los valores de sobrevida, peso medio y biomasa. Sólo se obtuvieron cuatro aislamientos de Candida tropicalis. Ninguno expresó propiedades benéficas y uno fue elegido al azar para los ensayos in vivo. Solo la levadura muerta al 1% incrementó significativamente la biomasa en comparación con el control (p&lt;0,05). La sobrevida mejoró significativamente (p&lt;0,05) con la levadura muerta y sin significancia (p&gt;0,05) con el hongo vivo. Ninguno de los tratamientos induce incrementos significativos del peso medio (p&lt;0,05). Estos resultados nos permiten proponer al tratamiento con levadura muerta al 1% como un factor de crecimiento para R. quelen, considerando al microorganismo como un prebiótico efectivo para su uso en esta especie

Accretion onto the Supermassive Black Hole in M87

Chandra X-ray observations of the giant elliptical galaxy M87 resolve the thermal state of the hot interstellar medium into the accretion (Bondi) radius of its central 3 10^9 Msun black hole. We measure the X-ray gas temperature and density profiles and calculate the Bondi accretion rate, Mdot_Bondi \sim 0.1 Msun/yr. The X-ray luminosity of the active nucleus of M87 observed with Chandra is L_{x, 0.5-7 \keV} \sim 7 \times 10^{40}erg/s. This value is much less than the predicted nuclear luminosity, L_{Bondi} \sim 5 \times 10^{44} erg/s, for accretion at the Bondi rate with a canonical accretion radiative efficiency of 10%. If the black hole in M87 accretes at this rate it must do so at a much lower radiative efficiency than the canonical value. The multiwavelength spectrum of the nucleus is consistent with that predicted by an advection-dominated flow. However, as is likely, the X-ray nucleus is dominated by jet emission then the properties of flow must be modified, possibly by outflows. We show that the overall energetics of the system are just consistent with the predicted Bondi nuclear power. This suggests that either most of the accretion energy is released in the relativistic jet or that the central engine of M87 undergoes on-off activity cycles. We show that, at present, the energy dumped into the ISM by the jet may reduce the accretion rate onto the black hole by a factor \propto (v_j/c_s)^{-2}, where v_j is the jet velocity and c_s the ISM sound speed, and that this is sufficient to account for the low nuclear luminosity.Comment: emulateapj.sty, revised version, accepted by Ap

Feedback under the microscope II: heating, gas uplift, and mixing in the nearest cluster core

Using a combination of deep 574ks Chandra data, XMM-Newton high-resolution spectra, and optical Halpha+NII images, we study the nature and spatial distribution of the multiphase plasma in M87. Our results provide direct observational evidence of `radio mode' AGN feedback in action, stripping the central galaxy of its lowest entropy gas and preventing star-formation. This low entropy gas was entrained with and uplifted by the buoyantly rising relativistic plasma, forming long "arms". These arms are likely oriented within 15-30 degrees of our line-of-sight. The mass of the uplifted gas in the arms is comparable to the gas mass in the approximately spherically symmetric 3.8 kpc core, demonstrating that the AGN has a profound effect on its immediate surroundings. The coolest X-ray emitting gas in M87 has a temperature of ~0.5 keV and is spatially coincident with Halpha+NII nebulae, forming a multiphase medium where the cooler gas phases are arranged in magnetized filaments. We place strong upper limits of 0.06 Msun/yr on the amount of plasma cooling radiatively from 0.5 keV and show that a uniform, volume-averaged heating mechanism could not be preventing the cool gas from further cooling. All of the bright Halpha filaments appear in the downstream region of the <3 Myr old shock front, at smaller radii than ~0.6'. We suggest that shocks induce shearing around the filaments, thereby promoting mixing of the cold gas with the ambient hot ICM via instabilities. By bringing hot thermal particles into contact with the cool, line-emitting gas, mixing can supply the power and ionizing particles needed to explain the observed optical spectra. Mixing of the coolest X-ray emitting plasma with the cold optical line emitting filamentary gas promotes efficient conduction between the two phases, allowing non-radiative cooling which could explain the lack of X-ray gas with temperatures under 0.5 keV.Comment: to appear in MNRA

The C4 Clustering Algorithm: Clusters of Galaxies in the Sloan Digital Sky Survey

We present the "C4 Cluster Catalog", a new sample of 748 clusters of galaxies identified in the spectroscopic sample of the Second Data Release (DR2) of the Sloan Digital Sky Survey (SDSS). The C4 cluster--finding algorithm identifies clusters as overdensities in a seven-dimensional position and color space, thus minimizing projection effects which plagued previous optical clusters selection. The present C4 catalog covers ~2600 square degrees of sky with groups containing 10 members to massive clusters having over 200 cluster members with redshifts. We provide cluster properties like sky location, mean redshift, galaxy membership, summed r--band optical luminosity (L_r), velocity dispersion, and measures of substructure. We use new mock galaxy catalogs to investigate the sensitivity to the various algorithm parameters, as well as to quantify purity and completeness. These mock catalogs indicate that the C4 catalog is ~90% complete and 95% pure above M_200 = 1x10^14 solar masses and within 0.03 <=z <= 0.12. The C4 algorithm finds 98% of X-ray identified clusters and 90% of Abell clusters within 0.03 <= z <= 0.12. We show that the L_r of a cluster is a more robust estimator of the halo mass (M_200) than the line-of-sight velocity dispersion or the richness of the cluster. L_r. The final SDSS data will provide ~2500 C4 clusters and will represent one of the largest and most homogeneous samples of local clusters.Comment: 32 pages of figures and text accepted in AJ. Electronic version with additional tables, links, and figures is available at http://www.ctio.noao.edu/~chrism/c

Coherent interactions and long term evolution of ultrafast transients in a semiconductor laser

Introduction The interaction of short optical pulses with laser cavity modes is important in, for example, formation of mode-locked pulse trains, optical clock recovery, and external optical feedback The spatio-temporal dynamics of the electric field may be calculated from Maxwell&apos;s equations using a finite-difference time-domain (FDTD) method. Coupling a Lorentzian resonance allows an approximate model of the optical gain We consider a class of recent experiments in which a short optical pulse is injected into a semiconductor laser diode, allowing a study of the pulse-cavity interactions on time-scales shorter than the cavity roundtrip time. In addition to the expected pulse broadening and relaxation oscillations, new phenomena such as stable, long-lived &apos;dark pulses&apos; were observed Numerical Methods We have coupled an FDTD calculation of the electric field with multiple Lorentzian resonances which approximate the spectral dependence of the semiconductor gain. Results and discussion During the propagation of a short pulse through a population-inverted semiconductor a region of depleted gain is left behind the injected pulse. For a laser under CW operation this region of depleted gain can evolve into a long lived &apos;dark pulse&apos;

Hubble Space Telescope Weak-lensing Study of the Galaxy Cluster XMMU J2235.3-2557 at z=1.4: A Surprisingly Massive Galaxy Cluster when the Universe is One-third of its Current Age

We present a weak-lensing analysis of the z=1.4 galaxy cluster XMMU J2235.3-2557, based on deep Advanced Camera for Surveys images. Despite the observational challenge set by the high redshift of the lens, we detect a substantial lensing signal at the >~ 8 sigma level. This clear detection is enabled in part by the high mass of the cluster, which is verified by our both parametric and non-parametric estimation of the cluster mass. Assuming that the cluster follows a Navarro-Frenk-White mass profile, we estimate that the projected mass of the cluster within r=1 Mpc is (8.5+-1.7) x 10^14 solar mass, where the error bar includes the statistical uncertainty of the shear profile, the effect of possible interloping background structures, the scatter in concentration parameter, and the error in our estimation of the mean redshift of the background galaxies. The high X-ray temperature 8.6_{-1.2}^{+1.3} keV of the cluster recently measured with Chandra is consistent with this high lensing mass. When we adopt the 1-sigma lower limit as a mass threshold and use the cosmological parameters favored by the Wilkinson Microwave Anisotropy Probe 5-year (WMAP5) result, the expected number of similarly massive clusters at z >~ 1.4 in the 11 square degree survey is N ~ 0.005. Therefore, the discovery of the cluster within the survey volume is a rare event with a probability < 1%, and may open new scenarios in our current understanding of cluster formation within the standard cosmological model.Comment: Accepted to ApJ for publication. 40 pages and 14 figure

The supernova rate-velocity dispersion relation in the interstellar medium

We investigate the relationship between the velocity dispersion of the gas and the SN rate and feedback efficiency in the ISM. We explore the constancy of the velocity dispersion profiles in the outer parts of galactic disks at~6-8 km s^-1, and the transition to the starburst regime. Our results show that a) SN driving leads to constant velocity dispersions of sig~6 km s^-1 for the total gas and sigHI~3 km s^-1 for the HI gas, independent of the SN rate, for values of the rate between 0.01-0.5 the Galactic rate R_{G},b) the position of the transition to the starburst regime at SFR/Area~5*10^-3-10^-2 M_sol yr^-1 kpc^-2 observed in the simulations, is in good agreement with the transition to the starburst regime in the observations, c) for the high SN rates, no HI gas is present in the simulations box, however, for the total gas velocity dispersion, there is good agreement between the models and the observations,d) at the intermediate SN rates R/R_{G}~0.5-1, taking into account the thermal broadening of the HI line helps reach a good agreement in that regime between the models and the observations,e) for R/R_{G}<0.5, sig and sigHI fall below the observed values by a factor of~2. However, a set of simulation with different values of epsilon indicates that for larger values of the supernova feedback efficiencies, velocity dispersions of the HI gas of the order of 5-6 km s^{-1} can be obtained, in closer agreement with the observations. The fact that for R/R_{G}<0.5, the HI gas velocity dispersions are a factor ~2 smaller than the observed values could result from the fact that we might have underestimated the SN feedback efficiency. It might also be an indication that other physical processes couple to the stellar feedback in order to produce the observed level of turbulence in galactic disks.Comment: 44 pages, 22 figures. Accepted to Ap

The Herschel Virgo Cluster Survey: I. Luminosity functions

We describe the Herschel Virgo Cluster Survey (HeViCS) and the first data obtained as part of the Science Demonstration Phase (SDP). The data cover a central 4x4 sq deg region of the cluster. We use SPIRE and PACS photometry data to produce 100, 160, 250, 350 and 500 micron luminosity functions (LFs) for optically bright galaxies that are selected at 500 micron and detected in all bands. We compare these LFs with those previously derived using IRAS, BLAST and Herschel-ATLAS data. The Virgo Cluster LFs do not have the large numbers of faint galaxies or examples of very luminous galaxies seen previously in surveys covering less dense environments.Comment: Letter accepted for publication in A&A (Herschel special issue