A substructure analysis of the A3558 cluster complex

The "algorithm driven by the density estimate for the identification of clusters" (DEDICA, Pisani 1993, 1996) is applied to the A3558 cluster complex in order to find substructures. This complex, located at the center of the Shapley Concentration supercluster, is a chain formed by the ACO clusters A3556, A3558 and A3562 and the two poor clusters SC 1327-312 and SC 1329-313. We find a large number of clumps, indicating that strong dynamical processes are active. In particular, it is necessary to use a fully three-dimensional sample(i.e. using the galaxy velocity as third coordinate) in order to recover also the clumps superimposed along the line of sight. Even if a great number of detected substructures were already found in a previous analysis (Bardelli et al. 1998), this method is more efficient and faster when compared with the use of a wide battery of tests and permits the direct estimate of the detection significance. Almost all subclusters previously detected by the wavelet analyses found in the literature are recognized by DEDICA. On the basis of the substructure analysis, we also briefly discuss the origin of the A3558 complex by comparing two hypotheses: 1) the structure is a cluster-cluster collision seen just after the first core-core encounter; 2) this complex is the result of a series of incoherent group-group and cluster-group mergings, focused in that region by the presence of the surrounding supercluster. We studied the fraction of blue galaxies in the detected substructures and found that the bluest groups reside between A3562 and A3558, i.e. in the expected position in the scenario of the cluster-cluster collision.Comment: 10 pages with 12 encapsulated figures; MNRAS in pres

Image Scaling by de la Vallée-Poussin Filtered Interpolation

We present a new image scaling method both for downscaling and upscaling, running with any scale factor or desired size. The resized image is achieved by sampling a bivariate polynomial which globally interpolates the data at the new scale. The method’s particularities lay in both the sampling model and the interpolation polynomial we use. Rather than classical uniform grids, we consider an unusual sampling system based on Chebyshev zeros of the first kind. Such optimal distribution of nodes permits to consider near-best interpolation polynomials defined by a filter of de la Vallée-Poussin type. The action ray of this filter provides an additional parameter that can be suitably regulated to improve the approximation. The method has been tested on a significant number of different image datasets. The results are evaluated in qualitative and quantitative terms and compared with other available competitive methods. The perceived quality of the resulting scaled images is such that important details are preserved, and the appearance of artifacts is low. Competitive quality measurement values, good visual quality, limited computational effort, and moderate memory demand make the method suitable for real-world applications

Image Scaling by de la Vallée-Poussin Filtered Interpolation

We present a new image scaling method both for downscaling and upscaling, running with any scale factor or desired size. The resized image is achieved by sampling a bivariate polynomial which globally interpolates the data at the new scale. The method’s particularities lay in both the sampling model and the interpolation polynomial we use. Rather than classical uniform grids, we consider an unusual sampling system based on Chebyshev zeros of the first kind. Such optimal distribution of nodes permits to consider near-best interpolation polynomials defined by a filter of de la Vallée-Poussin type. The action ray of this filter provides an additional parameter that can be suitably regulated to improve the approximation. The method has been tested on a significant number of different image datasets. The results are evaluated in qualitative and quantitative terms and compared with other available competitive methods. The perceived quality of the resulting scaled images is such that important details are preserved, and the appearance of artifacts is low. Competitive quality measurement values, good visual quality, limited computational effort, and moderate memory demand make the method suitable for real-world applications

Regularity bounds by minimal generators and Hilbert function

Let $\rho_C$ be the regularity of the Hilbert function of a projective curve $C$ in \mbox {P}^n_K over an algebraically closed field $K$ and $\beta_1, \ldots, \beta_{n-1}$ be degrees for which there exists a complete intersection of type ($\beta_1, \ldots, \beta_{n-1}$) containing properly $C$. Then the Castelnuovo-Mumford regularity of $C$ is bounded above by max $\{\rho_C +1, \beta 1 + \ldots + \beta_n-1 -(n-1)\}$ .We investigate the sharpness of the above bound, which is achieved by curves algebraically linked to ones having degenerate general hyperplane section

K-band Properties of Well-Sampled Groups of Galaxies

We use a sample of 55 groups and 6 clusters of galaxies ranging in mass from 7 x 10^11 Msun to 1.5 x 10^15 Msun to examine the correlation of the Ks-band luminosity with mass discovered by Lin et al. (2003). We use the 2MASS catalog and published redshifts to construct complete magnitude limited redshift surveys of the groups. From these surveys we explore the IR photometric properties of groups members including their IR color distribution and luminosity function. Although we find no significant difference between the group Ks luminosity function and the general field, there is a difference between the color distribution of luminous group members and their counterparts (generally background) in the field. There is a significant population of luminous galaxies with H-Ks > 0.35 which are rarely, if ever, members of the groups in our sample. The most luminous galaxies which populate the groups have a very narrow range of IR color. Over the entire mass range covered by our sample, the Ks luminosity increases with mass as L ~ M^(0.64 +/- 0.06) implying that the mass-to-light ratio in the Ks-band increases with mass. The agreement between this result and earlier investigations of essentially non-overlapping sets of systems shows that this window in galaxy formation and evolution is insensitive to the selection of the systems and to the details of the mass and luminosity computations.Comment: 38 pages, 9 figures, 2 tables. Accepted for publication on Astronomical Journa

PA design and statistical analysis through X-par driven load-pull and EM simulations

Modeling the active device is a key step for the successful statistical analysis of power amplifiers: the nonlinear model must not only depend on the most relevant device fabrication parameters, but should also work accurately in source/load-pull analysis, since variations of the passive embedding network effectively act as a load-pull at the active device ports. We demonstrate that the X-parameter model extracted from physics-based nonlinear TCAD simulations is extremely accurate for load-pull analysis. The X-parameter model is coupled to electromagnetic simulations to assist the variability-aware design of a GaAs MMIC X-band power amplifier (PA): concurrent variations of the active device doping and of the capacitor dielectric layer thickness are considered as the main contributions to PA variability. Two possible output matching networks, with distributed or semi-lumped design, are compared: already for moderate doping variations the PA output power spread is dominated by the active device variability, while passive network variations are always the relevant contribution to PA efficiency

Global Assessment of PA variability through concurrent Physics-based X-parameter and Electro-Magnetic simulations

The novel technique introduced in [1] is exploited to address a full variability analysis of a GaAs MMIC X-band power amplifier, including the statistical variations of several technological parameters, both in the active and passive components. The active device is modelled by means of X-parameters, directly extracted from physics-based analysis. A non-50 O X-Par model is used to take into account the input port mismatch with respect to the conventional 50 O reference. The scattering parameters of the passive structures are extracted from accurate electromagnetic simulations and then imported into the circuit simulator through data intercharge files (e.g. MDIF or CITIfile) as a function of the most important MMIC fabrication parameters, e.g. the thickness of the MIM capacitor dielectric layer. The analysis shows that more than 10% of output power variations can be ascribed to the concurrent MIM and doping variations in conventional GaAs MMIC technology

Spectroscopy of moderately high-redshift RCS-1 clusters

We present spectroscopic observations of 11 moderately high-redshift (z~0.7- 1.0) clusters from the first Red-Sequence Cluster Survey (RCS-1). We find excellent agreement between the red-sequence estimated redshift and the spectroscopic redshift, with a scatter of 10% at z>0.7. At the high-redshift end (z>~0.9) of the sample, we find two of the systems selected are projections of pairs of comparably rich systems, with red-sequences too close to discriminate in (R-z') colour. In one of these systems, the two components are close enough to be physically associated. For a subsample of clusters with sufficient spectroscopic members, we examine the correlation between B_gcR (optical richness) and the dynamical mass inferred from the velocity dispersion. We find these measurements to be compatible, within the relatively large uncertainties, with the correlation established at lower redshift for the X-ray selected CNOC1 clusters and also for a lower redshift sample of RCS-1 clusters. Confirmation of this and calibration of the scatter in the relation will require larger samples of clusters at these and higher redshifts. [abridged]Comment: AJ accepted. 30 pages, 7 figures (figure 5 reduced quality

The Galaxy Populations of X-Ray Detected, Poor Groups

(Abridged) We determine the quantitative morphology and star formation properties of galaxies in six nearby X-ray detected, poor groups using multi-object spectroscopy and wide-field R imaging. We measure structural parameters for each galaxy by fitting a PSF-convolved, two component model to their surface brightness profiles. To compare directly the samples, we fade, smooth, and rebin each galaxy image so that we effectively observe each galaxy at the same redshift (9000 km/s) and physical resolution (0.87h^(-1) kpc). We compare results for the groups to a sample of field galaxies. We find that: 1) Galaxies spanning a wide range in morphological type and luminosity are well-fit by a de Vaucouleurs bulge with exponential disk profile. 2) Morphologically classifying these nearby group galaxies by their bulge fraction (B/T) is fairly robust on average, even when their redshift has increased by up to a factor of four and the effective resolution of the images is degraded by up to a factor of five. 3) The fraction of bulge-dominated systems in these groups is higher than in the field (~50% vs. ~20%). 4) The fraction of bulge-dominated systems in groups decreases with increasing radius, similar to the morphology-radius (~density) relation observed in galaxy clusters. 5) Current star formation in group galaxies is correlated with significant morphological asymmetry for disk-dominated systems (B/T<0.4). 6) The group galaxies that are most disk-dominated (B/T<0.2) are less star forming and asymmetric on average than their counterparts in the field.Comment: Accepted for publication in the Astrophysical Journal (26 pages + 12 figures); Figs 1 & 2 also available at http://www.ucolick.org/~vy/astronomy/groups_figs.tar.g