Cent Of Groups Research Articles

The localization of galaxy groups in close proximity to galaxy clusters using cosmic web nodes

ABSTRACT We investigate the efficacy of using the cosmic web nodes identified by the DisPerSE topological filament finder to systematically identify galaxy groups in the infall regions around massive clusters. The large random motions and infall velocities of galaxies in the regions around clusters complicate the detection and characterisation of substructures through normal group-finding algorithms. Yet understanding the co-location of galaxies within filaments and/or groups is a key part of understanding the role of environment on galaxy evolution, particularly in light of next-generation wide-field spectroscopic surveys. Here we use simulated massive clusters from TheThreeHundred collaboration and compare the derived group catalogues, (haloes with σv > 300 h−1 km s−1) with the critical points from DisPerSE, ran on haloes with more than 100 particles. We find that in 3D, 56 per cent of DisPerSE nodes are correctly identified as groups (purity) while 68 per cent of groups are identified as nodes (completeness). The fraction of matches increases with group mass and with distance from the host cluster centre. This rises to a completeness of 100 per cent for the most massive galaxy groups (M > 1014 M⊙) in 3D, or 63 per cent when considering the projected 2D galaxy distribution. When a perfect match occurs between a cosmic web node and a galaxy group, the DisPerSE node density (δ) serves as an estimate of the group’s mass, albeit with significant scatter. We conclude that the use of a cosmic filament finder shows promise as a useful and straightforward observational tool for disentangling substructure within the infall regions of massive clusters.

How to interpret measurements of diffuse light in stacked observations of groups and clusters of galaxies

ABSTRACT The diffuse light within galaxy groups and clusters provides valuable insight into the growth of massive cosmic structures. Groups are particularly interesting in this context, because they represent the link between galactic haloes and massive clusters. However, low surface brightness makes their diffuse light extremely challenging to detect individually. Stacking many groups is a promising alternative, but its physical interpretation is complicated by possible systematic variations of diffuse light profiles with other group properties. Another issue is the often ambiguous choice of group centre. We explore these challenges using mock observations for 497 galaxy groups and clusters with halo masses from $\sim 10^{12}$ to $1.5 \times 10^{15}\, \textrm {M}_{\odot }$ at redshift 0.1 from the Hydrangea cosmological hydrodynamic simulations. In 18 per cent of groups with at least five galaxies above $10^{9} \, \mathrm{M}_\odot$ in stellar mass, the r-band brightest galaxy is not the one at the centre of the gravitational potential; line-of-sight projections account for half of these cases. Miscentring does not significantly affect the ensemble average mass density profile or the surface brightness profile for our sample: even within ambiguously centred haloes, different centring choices lead to only a 1 per cent change in the total fraction of diffuse intra-group light, fIGL. We find strong correlations of fIGL with the luminosity of the central group galaxy and halo mass. Stacking groups in narrow bins of central galaxy luminosity will therefore make the physical interpretation of the signal more straightforward than combining systems across a wide range of mass.

Segregation effects according to the evolutionary stage of galaxy groups

Abstract We study segregation phenomena in 57 groups selected from the 2dF Percolation-Inferred Galaxy Groups (2PIGG) catalogue of galaxy groups. The sample corresponds to those systems located in areas of at least 80 per cent redshift coverage out to 10 times the radius of the groups. The dynamical state of the galaxy systems was determined after studying their velocity distributions. We have used the Anderson–Darling test to distinguish relaxed and non-relaxed systems. This analysis indicates that 84 per cent of groups have galaxy velocities consistent with the normal distribution, while 16 per cent of them have more complex underlying distributions. Properties of the member galaxies are investigated taking into account this classification. Our results indicate that galaxies in Gaussian groups are significantly more evolved than galaxies in non-relaxed systems out to distances of ∼4R200, presenting significantly redder (B−R) colours. We also find evidence that galaxies with MR≤−21.5 in Gaussian groups are closer to the condition of energy equipartition.

Surveillance programme for Campylobacterspecies in Swedish brooilers, July 2001 to June 2002

A total of 20,599 samples from 4133 slaughter groups representing about 71 million broilers slaughtered between July 1, 2001 and June 30, 2002 were tested for Campylobacter species. From each...

Computer analysis of the orthogonal electrocardiogram and vectorcardiogram in 939 cases with hypertensive cardiovascular disease

Orthogonal ECG's (Frank system) were recorded from 939 male patients with hypertensive cardiovascular disease (HCVD) and were compared with records from 229 normal subjects, matched for age, race, and sex. The hypertensive subjects were divided into three clinical groups: (1) patients without cardiac enlargement by chest x-ray and no history of congestive heart failure (CHF), (2) patients with cardiac enlargement but without past or present CHF, and (3) patients with cardiac enlargement and one or more episodes of CHF. A sustained blood pressure level of 150 90 mm. Hg or more was present in all cases. First an attempt was made to identify optimal scalar and vectorial ECG measurements for discriminating between HCVD and normal, testing a total of 333 variables. With four scalar measurements at a specificity level of 95 per cent, 24 per cent of Group 1, 37 per cent of Group 2, and 44 per cent of Group 3 could be correctly classified. Vector measurements were found mostly redundant. Using linear discriminant function analysis and a likelihood ratio test with 13 different ECG variables at a level of specificity of 95 per cent, it was possible to identify correctly 53 per cent, 75 per cent, and 87 per cent of Groups 1, 2, and 3, respectively. Comparison of results with other reports on ECG changes caused by left ventricular overload (LVO) suggested that the degree of LVO in HCVD, even in the most advanced Group 3, was considerably less than that reported in patients with valvular heart disease with the only exception of terminal cases with HCVD who had come to autopsy. Antihypertensive therapy was considered as one factor which might have contributed to this finding. Multivariate ECG analysis was found an efficient means for diagnostic classification, leading to results which equalled those reported for multiple dipole analysis. As compared to scalar or vector measurements, either used individually or in combination, the multivariate technique exceeded all of these methods for LVO diagnosis by a wide margin when specificity was kept at a constant level.

The Initial Period of Artificial Pneumothorax: The Effect of Para-Aminosalicylic Acid and Dihydrostreptomycin on the Frequency of Pleural Effusion and on Pulmonary Function

An investigation is presented of the effect of antimicrobial agents on artificial pneumothorax therapy. Three groups of patients were observed for six months after the induction of pneumothorax: A) One hundred sixteen consecutive pneumothoraces without specific medication—the control cases. B) Eighty-two consecutive pneumothoraces in which all but seven of the patients had received para-aminosalicylic acid both before and after induction. C) Eighty-five consecutive pneumothoraces with PAS and dihydrostreptomycin given in combination both before and after induction. 1) A free space was found at induction or was obtained after adhesion section in 42 per cent of group A, 57 per cent of group B, and 56 per cent of group C. 2) “Spontaneous” pleural effusions formed in 15 per cent of group A, 9 per cent of group B, and 5 per cent of group C. 3) Adhesion section was followed by pleural effusion in 23, 18, and 15 per cent of the respective groups. 4) Pleural effusion persisted for more than two months in 27, 15 and 7 per cent. 5) Empyema developed in 3 per cent of the patients in group A but in none in groups B and C. 6) Impairment of ventilatory function due to pleural effusion was observed in 16 per cent of group A; in a number of these cases the impairment was severe. In groups B and C only 11 and 5 per cent showed any functional damage and this was invariably slight. 7) In addition to antimicrobial agents the patients in groups B and C who developed pleural effusion were treated with the writer's technique of “guided symphysis” and this contributed to the lack of functional impairment.