Search results for "Galaxy cluster"
showing 10 items of 76 documents
THE ORIENTATION OF GALAXIES IN GALAXY CLUSTERS
2010
We present an analysis of the spatial orientations of galaxies in the 247 optically selected rich Abell clusters, having in the considered area at least 100 members. We investigated the relation between angles giving information about galaxy angular momenta and the number of members in each structure. The position angles of the galaxy major axes, as well as two angles describing the spatial orientation of galaxy plane were tested for isotropy, by applying three different statistical tests. It is found that the values of statistics increase with the amount of galaxies' members, which is equivalent to the existence of the relation between anisotropy and number of galaxies in cluster. The sear…
Constraints on cosmological models from strong gravitational lensing systems
2012
Strong lensing has developed into an important astrophysical tool for probing both cosmology and galaxies (their structure, formation, and evolution). Using the gravitational lensing theory and cluster mass distribution model, we try to collect a relatively complete observational data concerning the Hubble constant independent ratio between two angular diameter distances $D_{ds}/D_s$ from various large systematic gravitational lens surveys and lensing by galaxy clusters combined with X-ray observations, and check the possibility to use it in the future as complementary to other cosmological probes. On one hand, strongly gravitationally lensed quasar-galaxy systems create such a new opportun…
Multimodality in galaxy clusters from SDSS DR8: substructure and velocity distribution
2012
We search for the presence of substructure, a non-Gaussian, asymmetrical velocity distribution of galaxies, and large peculiar velocities of the main galaxies in galaxy clusters with at least 50 member galaxies, drawn from the SDSS DR8. We employ a number of 3D, 2D, and 1D tests to analyse the distribution of galaxies in clusters: 3D normal mixture modelling, the Dressler-Shectman test, the Anderson-Darling and Shapiro-Wilk tests and others. We find the peculiar velocities of the main galaxies, and use principal component analysis to characterise our results. More than 80% of the clusters in our sample have substructure according to 3D normal mixture modelling, the Dressler-Shectman (DS) te…
The Near-Infrared Surface Brightness Distribution of NGC4696
2006
We present H-band observations of the elliptical galaxy NGC4696, the brightest member of the Centaurus cluster of galaxies. We have measured its light profile, using a two-dimensional fitting algorithm, out to a radius of 180 arcsec (37 h^{-1}_{70} kpc). The profile is well described by a de Vaucouleurs law, with an effective radius of 35.3 +/- 1.0 h^{-1}_{70} kpc. There is no need for the extra free parameter allowed by a Sersic law. Allowing for a variation of 0.3% in the sky level, the profile obtained is compatible with data from 2MASS. The profile shows no sign of either a truncation or an extended halo.
Mean-field correlations in the core of rich galaxy clusters
1991
We develop a theory for the contribution to the clustering correlation function from gravitational interactions of neighboring pairs of galaxies in clusters. This is based on the «Hypernetted Chain Equation», a self-consistent integral equation relating the correlation function to the interaction potential.
The rich young cluster NGC 6530: a combined X-ray-optical-infrared study
2006
We present a combined X-ray, optical, and IR (2MASS) study of NGC 6530, complementing our previous studies of this cluster. We consider different indicators of IR excesses, which can be taken as an indicator of circumstellar disks and therefore of pre-main-sequence status. We used reddening-free indices to ensure that our results are unaffected by highly irregular, differential reddening. More than the study of the JHK bands alone (33 IR-excess stars found), we found it useful to compare various optical and IR colors, finding overall 333 stars with optical-IR excess. In the field of the previously studied Chandra ACIS-I observation, we found 196 stars with optical-IR excess, of which 120 ha…
XMM-Newton survey of two upper Scorpius regions
2006
We study X-ray emission from young stars by analyzing deep XMM-Newton observations of two regions of the Upper Scorpius association, having an age of 5 Myr. Based on near infrared and optical photometry we identify 22 Upper Scorpius photometric members among the 224 detected X-ray sources. We derive coronal properties of Upper Scorpius stars by performing X-ray spectral and timing analysis. The study of four strong and isolated stellar flares allows us to derive the length of the flaring loops. Among the 22 Upper Scorpius stars, 13 are identified as Upper Scorpius photometric members for the first time. The sample includes 7 weak-line T Tauri stars and 1 classical T Tauri star, while the na…
Multiscaling Properties of Large-Scale Structure in the Universe
1995
The large-scale distribution of galaxies and galaxy clusters in the universe can be described in the mathematical language of multifractal sets. A particularly significant aspect of this description is that it furnishes a natural explanation for the observed differences in clustering properties of objects of different density in terms of multiscaling, the generic consequence of the application of a local density threshold to a multifractal set. The multiscaling hypothesis suggests ways of improving upon the traditional statistical measures of clustering pattern (correlation functions) and exploring further the connection between clustering pattern and dynamics.
Exploring Mergers of Galaxy Clusters in a Cosmological Context
2010
We present results of an Eulerian Adaptive Mesh Refinement (AMR) hydrodynamical and N-body simulation in a ΛCDM cosmology. The simulation incorporates common cooling and heating processes, a phenomenological description of the star formation and supernovae feedback. A specific halo finder has been designed and applied in order to extract a sample of galaxy clusters directly obtained from the simulation without considering any resimulating scheme. We have studied the evolutionary history of the cluster halos, and classified them in three categories depending on the merger events they have undergone. We pay special attention to discuss the role of merger events as a source of feedback and reh…
Current status of modified gravity
2014
We revisit the cosmological viability of the Hu-Sawicki modified gravity scenario. The impact of such a modification on the different cosmological observables, including gravitational waves, is carefully described. The most recent cosmological data, as well as constraints on the relationship between the clustering parameter ${\ensuremath{\sigma}}_{8}$ and the current matter mass-energy density ${\mathrm{\ensuremath{\Omega}}}_{m}$ from cluster number counts and weak lensing tomography, are considered in our numerical calculations. The strongest bound we find is $|{f}_{R0}|l3.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ at 95% C.L. Forthcoming cluster surveys covering $10\text{ …