744 research outputs found
X-ray Bright Active Galactic Nuclei in Massive Galaxy Clusters I: Number Counts and Spatial Distribution
We present an analysis of the X-ray bright point source population in 43
massive clusters of galaxies observed with the Chandra X-ray Observatory. We
have constructed a catalog of 4210 rigorously selected X-ray point sources in
these fields, which span a survey area of 4.2 square degrees. This catalog
reveals a clear excess of sources when compared to deep blank-field surveys,
which amounts to roughly 1 additional source per cluster, likely Active
Galactic Nuclei (AGN) associated with the clusters. The excess sources are
concentrated within the virial radii of the clusters, with the largest excess
observed near the cluster centers. The average radial profile of the excess
X-ray sources of the cluster are well described by a power law (N(r) ~ r^\beta)
with an index of \beta ~ -0.5. An initial analysis using literature results on
the mean profile of member galaxies in massive X-ray selected clusters
indicates that the fraction of galaxies hosting X-ray AGN rises with increasing
clustercentric radius, being approximately 5 to 10 times higher near the virial
radius than in the central regions. This trend is qualitatively similar to that
observed for star formation in cluster member galaxies.Comment: 18 Pages, 10 Figures, Submitted to MNRAS. Please contact Steven
Ehlert ([email protected]) for higher resolution figures. Updated to
reflect small changes requested by referee. This version has been accepted
into MNRA
Extreme AGN Feedback and Cool Core Destruction in the X-ray Luminous Galaxy Cluster MACS J1931.8-2634
We report on a deep, multiwavelength study of the galaxy cluster MACS
J1931.8-2634 using Chandra X-ray, Subaru optical, and VLA 1.4 GHz radio data.
This cluster (z=0.352) harbors one of the most X-ray luminous cool cores yet
discovered, with an equivalent mass cooling rate within the central 50 kpc is
approximately 700 solar masses/yr. Unique features observed in the central core
of MACSJ1931.8-2634 hint to a wealth of past activity that has greatly
disrupted the original cool core. We observe a spiral of relatively cool,
dense, X-ray emitting gas connected to the cool core, as well as highly
elongated intracluster light (ICL) surrounding the cD galaxy. Extended radio
emission is observed surrounding the central AGN, elongated in the east-west
direction, spatially coincident with X-ray cavities. The power input required
to inflate these `bubbles' is estimated from both the X-ray and radio emission
to reside between 4 and 14e45 erg/s, putting it among the most powerful jets
ever observed. This combination of a powerful AGN outburst and bulk motion of
the cool core have resulted in two X-ray bright ridges to form to the north and
south of the central AGN at a distance of approximately 25 kpc. The northern
ridge has spectral characteristics typical of cool cores and is consistent with
being a remnant of the cool core after it was disrupted by the AGN and bulk
motions. It is also the site of H-alpha filaments and young stars. The X-ray
spectroscopic cooling rate associated with this ridge is approximately 165
solar masses/yr, which agrees with the estimate of the star formation rate from
broad-band optical imaging (170 solar masses/yr). MACS J1931.8-2634 appears to
harbor one of most profoundly disrupted low entropy cores observed in a
cluster, and offers new insights into the survivability of cool cores in the
context of hierarchical structure formation.Comment: 19 pages, 15 figures, 5 tables. Accepted by MNRAS for publication
September 30 201
The Diverse Nature of Optical Emission Lines in Brightest Cluster Galaxies: IFU Observations of the Central Kiloparsecs
We present integral field spectroscopy of the nebular line emission in a
sample of 9 brightest cluster galaxies (BCGs). The sample was chosen to probe
both cooling flow and non-cooling flow clusters, as well as a range of cluster
X-ray luminosities. The line emission morphology and velocity gradients suggest
a great diversity in the properties of the line emitting gas. While some BGCs
show evidence for filamentary or patchy emission (Abell 1060, Abell 1668 and
MKW3s), others have extended emission (Abell 1204, Abell 2199), while still
others have centrally concentrated emission (Abell 2052). We examine diagnostic
line ratios to determine the dominant ionization mechanisms in each galaxy.
Most of the galaxies show regions with AGN-like spectra, however for two BCGs,
Abell 1060 and Abell 1204, the emission line diagnostics suggest regions which
can be described by the emission from young stellar populations. The diversity
of emission line properties in our sample of BCGs suggests that the emission
mechanism is not universal, with different ionization processes dominating
different systems. Given this diversity, there is no evidence for a clear
distinction of the emission line properties between cooling flow and
non-cooling flow BCGs. It is not always cooling flow BCGs which show emission
(or young stellar populations), and non-cooling flow BCGs which do not.Comment: 23 pages, 23 figures, accepted for publication in MNRAS. Full
resolution images are online http://web.ipac.caltech.edu/staff/louis
Cell-based Approaches to Joint Surface Repair : A Research Perspective
The authors are grateful for support to their research from Arthritis Research UK (grants 19271, 19429, 19667, 20050). None of the authors received any funding related to the writing of this manuscript, and the funding bodies did not play any role in the writing of the manuscript or decision to submit the manuscript for publication.Peer reviewedPublisher PD
Crying and feeding problems in infancy and cognitive outcome in preschool children born at risk : a prospective population study
Objective: To investigate whether regulatory problems, i.e., crying and feeding problems in infants > 3 months of age, predict cognitive outcome in preschool children born at risk even when controlled for confounding factors.
Methods: A prospective longitudinal study of children born in a geographically defined area in Germany. N = 4427 children of 6705 eligible survivors (66%) participated at all four assessment points (neonatal, 5, 20, and 56 months of age). Excessive crying and feeding problems were measured at 5 months. Mental development was assessed with the Griffiths Scale at 20 months, and cognitive assessments were conducted at 56 months. Neonatal complications, neurological, and psychosocial factors were controlled as confounders in structural equation modeling and analyses of variance.
Results: One in five infants suffered from single crying or feeding problems, and 2% had multiple regulatory problems, i.e., combined crying and feeding problems at 5 months. In girls, regulatory problems were directly predictive of lower cognition at 56 months, even when controlled for confounders, whereas in boys, the influence on cognition at 56 months was mediated by low mental development at 20 months. Both in boys and girls, shortened gestational age, neonatal neurological complications, and poor parent-infant relationship were predictive of regulatory problems at 5 months and lower cognition at 56 months.
Conclusion: Regulatory problems in infancy have a small but significant adverse effect on cognitive development
How special are Brightest Group and Cluster Galaxies?
We use the Sloan Digital Sky Survey to construct a sample of 625 brightest
group and cluster galaxies (BCGs) together with control samples of non-BCGs
matched in stellar mass, redshift, and color. We investigate how the systematic
properties of BCGs depend on stellar mass and on their privileged location near
the cluster center. The groups and clusters that we study are drawn from the C4
catalogue of Miller et al. (2005) but we have developed improved algorithms for
identifying the BCG and for measuring the cluster velocity dispersion. Since
the SDSS photometric pipeline tends to underestimate the luminosities of large
galaxies in dense environments, we have developed a correction for this effect
which can be readily applied to the published catalog data. We find that BCGs
are larger and have higher velocity dispersions than non-BCGs of the same
stellar mass, which implies that BCGs contain a larger fraction of dark matter.
In contrast to non-BCGs, the dynamical mass-to-light ratio of BCGs does not
vary as a function of galaxy luminosity. Hence BCGs lie on a different
fundamental plane than ordinary elliptical galaxies. BCGs also follow a steeper
Faber-Jackson relation than non-BCGs, as suggested by models in which BCGs
assemble via dissipationless mergers along preferentially radial orbits. We
find tentative evidence that this steepening is stronger in more massive
clusters. BCGs have similar mean stellar ages and metallicities to non-BCGs of
the same mass, but they have somewhat higher alpha/Fe ratios, indicating that
star formation may have occurred over a shorter timescale in the BCGs. Finally,
we find that BCGs are more likely to host radio-loud active galactic nuclei
than other galaxies of the same mass, but are less likely to host an optical
AGN. The differences we find are more pronounced for the less massive BCGs.Comment: Replaced with slightly modified version accepted by MNRAS. 28 pages,
25 figures. Version with full resolution figures available at
http://www.mpa-garching.mpg.de/~anja/bcgs_avdl.pd
The Social Acceptance of Carbon Dioxide Utilisation: A Review and Research Agenda
CO2 utilisation technologies—also called carbon dioxide utilisation (CDU) and carbon capture and utilisation (CCU)—convert CO2 via physical, chemical, or biological processes into carbon-based products. CO2 utilisation technologies are viewed as a means of helping to address climate change and broadening the raw material base for commodities that can be sold to generate economic revenue. However, while technical research and development into the feasibility of CO2 utilisation options are accelerating rapidly; at present, there has been limited research into the social acceptance of the technology and CO2-derived products. This review article outlines and explores three key dimensions of social acceptance (i.e., socio-political, market, and community acceptance) pertaining to innovation within CO2 utilisation. The article highlights the importance of considering issues of social acceptance as an aspect of the research, development, demonstration, and deployment process for CO2 utilisation and explores how key stakeholders operating on each dimension might affect the innovation pathways, investment, and siting decisions relating to CO2 utilisation facilities and CO2-derived products. Beyond providing a state-of-the-art review of current research into the social acceptance of CO2 utilisation, this article also outlines an agenda for future research in the field
Stellar population gradients in brightest cluster galaxies
We present the stellar population and velocity dispersion gradients for a
sample of 24 brightest cluster galaxies (BCGs) in the nearby Universe for which
we have obtained high quality long-slit spectra at the Gemini telescopes. With
the aim of studying the possible connection between the formation of the BCGs
and their host clusters, we explore the relations between the stellar
population gradients and properties of the host clusters as well as the
possible connections between the stellar population gradients and other
properties of the galaxies. We find mean stellar population gradients (negative
{\Delta}[Z/H]/log r gradient of -0.285{\pm}0.064; small positive {\Delta}log
(age)/log r gradient of 0.069{\pm}0.049; and null {\Delta}[E/Fe]/log r gradient
of -0.008{\pm}0.032) that are consistent with those of normal massive
elliptical galaxies. However, we find a trend between metallicity gradients and
velocity dispersion (with a negative slope of -1.616{\pm}0.539) that is not
found for the most massive ellipticals. Furthermore, we find trends between the
metallicity gradients and K-band luminosities (with a slope of 0.173{\pm}0.081)
as well as the distance from the BCG to the X-ray peak of the host cluster
(with a slope of -7.546{\pm}2.752). The latter indicates a possible relation
between the formation of the cluster and that of the central galaxy.Comment: 23 pages, 18 figures, accepted for publication in MNRAS. arXiv admin
note: text overlap with arXiv:1104.2376v
Keep up the good work! An age-moderated mediation model of perceived job support for learning, negative age stereotypes and participation in employability enhancing activities predicting employees' intention to retire
In European nations, the aging of the workforce is a major issue which is increasingly addressed both in national and organizational policies in order to sustain older workers' employability and to encourage longer working lives. Particularly older workers' employability can be viewed an important issue as this has the potential to motivate them for their work and change their intention to retire. Based on lifespan development theories and Van der Heijden's ‘employability enhancement model’, this paper develops and tests an age-moderated mediation model (which refers to the processes that we want to test in this model), linking older workers' (55 years old and over) perceptions of job support for learning (job-related factor) and perceptions of negative age stereotypes on productivity (organizational factor), on the one hand, and their intention to retire, on the other hand, via their participation in employability enhancing activities, being the mediator in our model. A total of 2,082 workers aged 55 years and above were included in the analyses. Results revealed that the two proposed relationships between the predictors and intention to retire were mediated by participation in employability enhancing activities, reflecting two mechanisms through which work context affects intention to retire (namely ‘a gain spiral and a loss spiral’). Multi-Group SEM analyses, distinguishing between two age groups (55–60 and 61–65 years old), revealed different paths for the two distinguished groups of older workers. Employability mediated the relationship between perceptions of job support for learning and intention to retire in both age groups, whereas it only mediated the relationship between perceptions of negative age stereotypes and intention to retire in the 55–60 group. From our empirical study, we may conclude that employability is an important factor in the light of older workers' intention to retire. In order to motivate this category of workers to participate in employability enhancing activities and to work longer, negative age stereotypes need to be combated. In addition, creating job support for learning over the lifespan is also an important HR practice to be implemented in nowadays' working life
HTLV-1 and HIV-2 Infection Are Associated with Increased Mortality in a Rural West African Community
BACKGROUND: Survival of people with HIV-2 and HTLV-1 infection is better than that of HIV-1 infected people, but long-term follow-up data are rare. We compared mortality rates of HIV-1, HIV-2, and HTLV-1 infected subjects with those of retrovirus-uninfected people in a rural community in Guinea-Bissau. METHODS: In 1990, 1997 and 2007, adult residents (aged ≥15 years) were interviewed, a blood sample was drawn and retroviral status was determined. An annual census was used to ascertain the vital status of all subjects. Cox regression analysis was used to estimate mortality hazard ratios (HR), comparing retrovirus-infected versus uninfected people. RESULTS: A total of 5376 subjects were included; 197 with HIV-1, 424 with HIV-2 and 325 with HTLV-1 infection. The median follow-up time was 10.9 years (range 0.0-20.3). The crude mortality rates were 9.6 per 100 person-years of observation (95% confidence interval 7.1-12.9) for HIV-1, 4.1 (3.4-5.0) for HIV-2, 3.6 (2.9-4.6) for HTLV-1, and 1.6 (1.5-1.8) for retrovirus-negative subjects. The HR comparing the mortality rate of infected to that of uninfected subjects varied significantly with age. The adjusted HR for HIV-1 infection varied from 4.0 in the oldest age group (≥60 years) to 12.7 in the youngest (15-29 years). The HR for HIV-2 infection varied from 1.2 (oldest) to 9.1 (youngest), and for HTLV-1 infection from 1.2 (oldest) to 3.8 (youngest). CONCLUSIONS: HTLV-1 infection is associated with significantly increased mortality. The mortality rate of HIV-2 infection, although lower than that of HIV-1 infection, is also increased, especially among young people
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