6,792 research outputs found

    PICACS: self-consistent modelling of galaxy cluster scaling relations

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    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

    A reliable data collection/control system

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    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

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

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    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/

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

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    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 ∼10\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%60\% due to its variability (ignoring any statistical noise). This is larger than the characteristic variability of the population by a factor of 2\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 2\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

    The evolution of the cluster X-ray scaling relations in the WARPS sample at 0.6<z<1.0

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    The X-ray properties of a sample of 11 high-redshift (0.6<z<1.0) clusters observed with Chandra and/or XMM are used to investigate the evolution of the cluster scaling relations. The observed evolution of the L-T and M-L relations is consistent with simple self-similar predictions, in which the properties of clusters reflect the properties of the universe at their redshift of observation. When the systematic effect of assuming isothermality on the derived masses of the high-redshift clusters is taken into account, the high-redshift M-T and Mgas-T relations are also consistent with self-similar evolution. Under the assumption that the model of self-similar evolution is correct and that the local systems formed via a single spherical collapse, the high-redshift L-T relation is consistent with the high-z clusters having formed at a significantly higher redshift than the local systems. The data are also consistent with the more realistic scenario of clusters forming via the continuous accretion of material. The slope of the L-T relation at high-redshift (B=3.29+/-0.38) is consistent with the local relation, and significantly steeper then the self-similar prediction of B=2. This suggests that the non-gravitational processes causing the steepening occurred at z>1 or in the early stages of the clusters' formation, prior to their observation. The properties of the intra-cluster medium at high-redshift are found to be similar to those in the local universe. The mean surface-brightness profile slope for the sample is 0.66+/-0.05, the mean gas mass fractions within R2500 and R200 are 0.073+/-0.010 and 0.12+/-0.02 respectively, and the mean metallicity of the sample is 0.28+/-0.16 solar.Comment: 23 pages, 17 figures. Accepted for publication in MNRAS. Revised to match accepted version: reanalysed data with latest calibrations, several minor changes. Conclusions unchange

    High angular resolution observation of the Sunyaev-Zel'dovich effect in the massive z=0.83 cluster ClJ0152-1357

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    X-ray observations of galaxy clusters at high redshift (z>0.5) indicate that they are more morphologically complex and less virialized than those at low-redshift. We present the first subarcmin resolution at 18 GHz observations of the Sunyaev-Zel'dovich (SZ) effect for ClJ0152-1357 using the Australia Telescope Compact Array. ClJ0152-1357 is a massive cluster at redshift z=0.83 and has a complex structure including several merging subclumps which have been studied at optical, X-ray, and radio wavelengths. Our high-resolution observations indicate a clear displacement of the maximum SZ effect from the peak of X-ray emission for the most massive sub-clump. This result shows that the cluster gas within the cluster substructures is not virialised in ClJ0152-1357 and we suggest that it is still recovering from a recent merger event. A similar offset of the SZ effect has been recently seen in the `bullet cluster' by Malu et al. This non-equilibrium situation implies that high resolution observations are necessary to investigate galaxy cluster evolution, and to extract cosmological constraints from a comparison of the SZ effect and X-ray signals.Comment: 5 pages, 4 figures, submitted to ApJ

    Do historical changes in parent-child relationships explain increases in youth conduct problems?

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    The coincidence of historical trends in youth antisocial behavior and change in family demographics has led to speculation of a causal link, possibly mediated by declining quality of parenting and parent-child relationships. No study to date has directly assessed whether and how parenting and parent-child relationships have changed. Two national samples of English adolescents aged 16-17 years in 1986 (N = 4,524 adolescents, 7,120 parents) and 2006 (N = 716 adolescents, 734 parents) were compared using identical questionnaire assessments. Youth-reported parental monitoring, expectations, and parent-child quality time increased between 1986 and 2006. Ratings of parental interest did not change. Parenting differences between affluent and disadvantaged families narrowed over time. There was thus little evidence of a decline in quality of parenting for the population as a whole or for disadvantaged subgroups. Parent-reported youth conduct problems showed a modest increase between 1986 and 2006. Findings suggested that the increase in youth conduct problems was largely unrelated to observed change in parent-child relationships

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

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    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

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    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
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