PICACS: self-consistent modelling of galaxy cluster scaling relations

In this paper, we introduce PICACS, a physically-motivated, internally consistent model of scaling relations between galaxy cluster masses and their observable properties. This model can be used to constrain simultaneously the form, scatter (including its covariance) and evolution of the scaling relations, as well as the masses of the individual clusters. In this framework, scaling relations between observables (such as that between X-ray luminosity and temperature) are modelled explicitly in terms of the fundamental mass-observable scaling relations, and so are fully constrained without being fit directly. We apply the PICACS model to two observational datasets, and show that it performs as well as traditional regression methods for simply measuring individual scaling relation parameters, but reveals additional information on the processes that shape the relations while providing self-consistent mass constraints. Our analysis suggests that the observed combination of slopes of the scaling relations can be described by a deficit of gas in low-mass clusters that is compensated for by elevated gas temperatures, such that the total thermal energy of the gas in a cluster of given mass remains close to self-similar expectations. This is interpreted as the result of AGN feedback removing low entropy gas from low mass systems, while heating the remaining gas. We deconstruct the luminosity-temperature (LT) relation and show that its steepening compared to self-similar expectations can be explained solely by this combination of gas depletion and heating in low mass systems, without any additional contribution from a mass dependence of the gas structure. Finally, we demonstrate that a self-consistent analysis of the scaling relations leads to an expectation of self-similar evolution of the LT relation that is significantly weaker than is commonly assumed.Comment: Updated to match published version. Improvements to presentation of results, and treatment of scatter and covariance. Main conclusions unchange

Mental health of Irish students: Self-criticism as a complete mediator in mental health attitudes and caregiver identity

Mental health is a concern in the Republic of Ireland, and in particular mental health of higher education students is challenging. Further, their poor mental health may be negatively impacted by their negative mental health attitudes and caregiver identity, which can yield high self-criticism and low self-reassurance. Accordingly, this study aimed to (i) elucidate the relationships among these five constructs, and (ii) assess the impact of self-criticism and self-reassurance in the relationship (a) between mental health attitudes and mental health, and (b) between caregiver identity and mental health. One-hundred twenty-nine Irish undergraduate students completed self-report measures regarding these constructs. Correlation and path analyses were conducted. Overall all variables were related to each other, in particular family-related shame subscales were strongly related to mental health problems. In path analysis, self-criticism completely mediated the relationship between mental health attitudes and mental health, while self-reassurance did not. Likewise, self-criticism also completely mediated the relationship between caregiver identity and mental health, while self-reassurance did not. The findings suggest the importance of self-criticism to their mental health. While current literature highlights the importance of mental health attitudes such as stigma and caregiver identity such as low self-awareness, our results indicated that it was their self-criticism that predicted poor mental health. Their mental health may be more effectively improved by targeting self-criticism. Compassion training, peer-support groups, and reframing were recommended to counter self-criticism. Our findings will help educators and researchers to identify an alternative and effective means to improve mental health in Irish students.N/

A reliable data collection/control system

The Cal Poly Space Project requires a data collection/control system which must be able to reliably record temperature, pressure and vibration data. It must also schedule the 16 electroplating and 2 immiscible alloy experiments so as to optimize use of the batteries, maintain a safe package temperature profile, and run the experiment during conditions of microgravity (and minimum vibration). This system must operate unattended in the harsh environment of space and consume very little power due to limited battery supply. The design of a system which meets these requirements is addressed

Chandra Measurements of a Complete Sample of X-ray Luminous Galaxy Clusters: the Gas Mass Fraction

We present Chandra X-ray measurements of the gas mass fraction out to r500 for a complete sample of the 35 most luminous clusters from the Brightest Cluster Sample and the Extended Brightest Cluster Sample at redshift z=0.15-0.30. The sample includes relaxed and unrelaxed clusters, and the data were analysed independently using two pipelines and two different models for the gas density and temperature. We measure an average of fgas(r500) = 0.163 +/- 0.032, which is in agreement with the cosmic baryon fraction (Omega_b / Omega_M = 0.167 +/- 0.006) at the 1-sigma level, after adding the stellar baryon fraction. Earlier studies reported gas mass fractions significantly lower than the cosmic baryon fraction at r500, and in some cases higher values that are consistent with the cosmic baryon fraction towards the virial radius.In this paper we show that the most X-ray luminous clusters in the redshift range z=0.15-0.30 have a gas mass fraction that is consistent with the cosmic value at r500.Comment: MNRAS submitted, comments welcome; 23 pages, 57 figure

The Effect of Single Nucleotide Polymorphisms (SNPs) in Toll-Like Receptors -2, -4, -9, and CD14 Genes in an African-American Population with Chronic Periodontitis

AIM: to determine if a relationship exists between TLR-2, TLR-4, TLR-9, or CD14 polymorphisms and risk for developing chronic periodontal disease in an African-American population. This is the first study conducted to determine role of SNPs in TLR genes and CD14 gene in a periodontally-diseased African-American population. Additionally, this is the first study to assess the role of TLR-9 polymorphism in periodontitis patients. METHODS: A total of 130 subjects were involved in the study. The chronic periodontitis (CP) group contained 73 subjects, and the healthy control (NP) group 57subjects. Genotyping was performed in TLR2 (G2408A), TLR4 (A896G),TLR9 (T1486C) and CD14 (C260T) genes by TaqMan® allelic discrimination using Assay-by-DesignSM SNP Genotyping Assays (Applied Biosystems). Accuracy of genotyping was confirmed by known DNA samples of each genotype and by Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) analyses on selected samples. Fisher’s exact test and chi-square analyses were performed to compare genotype and allele frequencies. Within disease groups, we investigated whether SNPs were related to disease severity by step-wise logistic regression adjusted for age, gender, and smoking status. RESULTS: There was a significant difference in the distribution of specific TLR9 (T1486C) genotypes between the periodontally diseased group versus the control group. Expression of TT genotype was more prevelant in periodontally-diseased individuals compared to periodontally-healthy subjects (p\u3c0.0001) whereas individuals expressing C allele of the TLR9 SNP (CC&CT) were more frequently found in the control group after adjusting for age, gender, and smoking status (p\u3c0.0001) There was no statistically significant difference in the distribution of genotypes between groups for any other TLRs or CD14 polymorphism. CONCLUSION: Based on findings of this study, homozygocity for the T allele of TLR 9 polymorphism was related to chronic periodontal disease susceptibility in African Americans. Additionally, presence of the C allele at TLR-9 appeared to confer resistance to periodontal destruction. Our results showed that specific SNPs in TLR-2, -4 and CD14 genes are not related to periodontitis in African Americans

On the connection between giant radio halos and cluster mergers

The frequently observed association between giant radio halos and merging galaxy clusters has driven present theoretical models of non-thermal emission from galaxy clusters, which are based on the idea that the energy dissipated during cluster-cluster mergers could power the formation of radio halos. To quantitatively test the merger-halo connection we present the first statistical study based on deep radio data and X-ray observations of a complete X-ray selected sample of galaxy clusters with X-ray luminosity > 5x 10^44 erg/s and redshift 0.2<z< 0.32. Using several methods to characterize cluster substructures, namely the power ratios, centroid shift and X-ray brightness concentration parameter, we show that clusters with and without radio halo can be quantitatively differentiated in terms of their dynamical properties. In particular, we confirm that radio halos are associated to dynamically disturbed clusters and cluster without radio halo are more "relaxed", with only a couple of exceptions where a disturbed cluster does not exhibit a halo.Comment: 5 pages, 1 figure, ApJ Letter in pres

The X-ray Variability of AGN and its Implications for Observations of Galaxy Clusters

The detection of new clusters of galaxies or the study of known clusters of galaxies in X-rays can be complicated by the presence of X-ray point sources, the majority of which will be active galactic nuclei (AGN). This can be addressed by combining observations from a high angular resolution observatory (such as Chandra) with deeper data from a more sensitive observatory that may not be able to resolve the AGN (like XMM). However, this approach is undermined if the AGN varies in flux between the epochs of the observations. To address this we measure the characteristic X-ray variability of serendipitously detected AGN in 70 pairs of Chandra observations, separated by intervals of between one month and thirteen years. After quality cuts, the full sample consists of 1511 sources, although the main analysis uses a subset of 416 sources selected on the geometric mean of their flux in the pairs of observations, which eliminates selection biases. We find a fractional variability that increases with increasing interval between observations, from about 0.25 for observations separated by tens of days up to about 0.45 for observations separated by $\sim 10$ years. As a rule of thumb, given the precise X-ray flux of a typical AGN at one epoch, its flux at a second epoch some years earlier or later can be predicted with a precision of about $60\%$ due to its variability (ignoring any statistical noise). This is larger than the characteristic variability of the population by a factor of $\sqrt{2}$ due to the uncertainty on the mean flux of the AGN due to a single prior measurement. The precision can thus be improved with multiple prior flux measurements (reducing the $\sqrt{2}$ factor), or by reducing the interval between observations to reduce the characteristic variability.Comment: 13 pages, 7 figures; accepted for publication in the Open Journal of Astrophysics; full data table included with source files; comments welcom

Application of ERTS-1 imagery to the harvest model of the US Menhaden fishery

Preliminary results of an experiment to demonstrate the utility of ERTS-1 imagery for providing significant information to the harvest model of the menhaden industry are reported. Fisheries and related environmental data were obtained discontinuously throughout the 1973 menhaden (a surface schooling, coastal species) fishing season in Mississippi Sound. The unexpected complexity of the physical environment in Mississippi Sound precluded simplistic analysis of fish/environment relationships. Preliminary indications are that an association does exist between fish availability and differences in water transparency (turbidity) within the Sound. A clearer relationship is developing between major turbid features, imaged by ERTS-1 and location of successful fishing attempts. On all occasions where relatively cloudfree ERTS-1 overflight days coincided with fishery activity, overlays of catch location of ERTS-1 images show an association of school position with interfaces between imaged turbid features. Analysis is currently underway to determine persistence of such associations in an attempt to define minimum satellite return time necessary to maintain continuity of associations

Development of a reliable and reproducible phantom manufacturing method using silica microspheres in silicone

Optically scattering phantoms composed of silica microspheres embedded in an optically clear silicone matrix were manufactured using a previously developed method. Multiple problems, such as sphere aggregation, adsorption to the cast, and silicone shrinkage, were, however, frequently encountered. Solutions to these problems were developed and an improved method, incorporating these solutions, is presented. The improved method offers excellent reliability and reproducibility for creating phantoms with uniform scattering coefficient. We also present evidence of decreased sphere aggregation