Reproducing the entropy structure in galaxy groups

We carry out a comparison between observations and hydrodynamic simulations of entropy profiles of groups and clusters of galaxies. We use the Tree+SPH GADGET code to simulate four halos of sizes in the M_500 = 1.0 - 16.e13 h^-1 Msun range, corresponding to poor groups up to Virgo-like clusters. We concentrate on the effect of introducing radiative cooling, star formation, and a variety of non-gravitational heating schemes on the entropy structure and the stellar fraction. We show that all the simulations result in a correct entropy profile for the Virgo-like cluster. With the heating energy budget of ~0.7 keV/particle injected at z_h=3, we are also able to reproduce the entropy profiles of groups. We obtain the flat entropy cores as a combined effect of preheating and cooling, while we achieve the high entropy at outskirts by preheating. The resulting baryon fraction locked into stars is in the 25-30% range, compared to 35-40% in the case of no preheating. Heating at higher redshift, z_h=9, strongly delays the star-formation, but fails to produce a sufficiently high specific entropy.Comment: 5 page, A&A in pres

The dynamical intracluster medium: a combined approach of observations and simulations

Current high resolution observations of galaxy clusters reveal a dynamical intracluster medium (ICM). The wealth of structures includes signatures of interactions between active galactic nuclei (AGN) and the ICM, such as cavities and shocks, as well as signatures of bulk motions, e.g. cold fronts. Aiming at understanding the physics of the ICM, we study individual clusters by both, deep high resolution observations and numerical simulations which include processes suspected to be at work, and aim at reproducing the observed properties. By comparing observations and simulations in detail, we gain deeper insights into cluster properties and processes. Here we present two examples of our approach: the large-scale shock in the Hydra A cluster, and sloshing cold fronts.Comment: 4 pages, to appear in proceedings of "The Monster's fiery breath" held in Madison, June 2009, eds. S. Heinz and E. Wilcots, version with full resolution pictures at http://www.faculty.iu-bremen.de/eroediger/PAPERS/roediger_e_madison.pd

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<0.05). Survival rate was boosted significantly (p<0.05) with dead yeast and not significantly (p>0.05) with the fungal isolate. None of the treatments induced significant increments in mean weight (p<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<0,05). La sobrevida mejoró significativamente (p<0,05) con la levadura muerta y sin significancia (p>0,05) con el hongo vivo. Ninguno de los tratamientos induce incrementos significativos del peso medio (p<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

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

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

X-Ray surface brightness and gas density fluctuations in the Coma cluster

X-ray surface brightness fluctuations in the core ($650 \times 650$ kpc) region of the Coma cluster observed with XMM-Newton and Chandra are analyzed using a 2D power spectrum approach. The resulting 2D spectra are converted to 3D power spectra of gas density fluctuations. Our independent analyses of the XMM-Newton and Chandra observations are in excellent agreement and provide the most sensitive measurements of surface brightness and density fluctuations for a hot cluster. We find that the characteristic amplitude of the volume filling density fluctuations relative to the smooth underlying density distribution varies from 7-10% on scales of $\sim$500 kpc down to $\sim$5% at scales $\sim$ 30 kpc. On smaller spatial scales, projection effects smear the density fluctuations by a large factor, precluding strong limits on the fluctuations in 3D. On the largest scales probed (hundreds of kpc), the dominant contributions to the observed fluctuations most likely arise from perturbations of the gravitational potential by the two most massive galaxies in Coma, NGC4874 and NGC4889, and the low entropy gas brought to the cluster by an infalling group. Other plausible sources of X-ray surface brightness fluctuations are discussed, including turbulence, metal abundance variations, and unresolved sources. Despite a variety of possible origins for density fluctuations, the gas in the Coma cluster core is remarkably homogeneous on scales from $\sim$ 500 to $\sim$30 kpc.Comment: published in MNRA

Radio galaxy feedback in X-ray selected groups from COSMOS: the effect on the ICM

We quantify the importance of the mechanical energy released by radio-galaxies inside galaxy groups. We use scaling relations to estimate the mechanical energy released by 16 radio-AGN located inside X-ray detected galaxy groups in the COSMOS field. By comparing this energy output to the host groups' gravitational binding energy, we find that radio galaxies produce sufficient energy to unbind a significant fraction of the intra-group medium. This unbinding effect is negligible in massive galaxy clusters with deeper potential wells. Our results correctly reproduce the breaking of self-similarity observed in the scaling relation between entropy and temperature for galaxy groups.Comment: Accepted for publication in the Astrophysical Journal. 12 Page

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