70 research outputs found
Close companions to Brightest Cluster Galaxies: Support for minor mergers and downsizing
We identify close companions of Brightest Cluster Galaxies (BCGs) for the
purpose of quantifying the rate at which these galaxies grow via mergers. By
exploiting deep photometric data from the CFHTLS, we probe the number of
companions per BCG (Nc) with luminosity ratios down to those corresponding to
potential minor mergers of 20:1. We also measure the average luminosity in
companions per galaxy (Lc). We find that Nc and Lc rise steeply with luminosity
ratio for both the BCGs, and a control sample of other bright, red, cluster
galaxies. The trend for BCGs rises more steeply, resulting in a larger number
of close companions. For companions within 50kpc of a BCG, Nc= 1.38+/-0.14 and
Lc=(2.14+/-0.31)x10^(10)L_sun and for companions within 50kpc of a luminosity
matched control sample of non-BCGs, Nc=0.87+/-0.08 and
Lc=(1.48+/-0.20)x10^(10)L_sun. This suggests that the BCGs are likely to
undergo more mergers compared to otherwise comparable luminous galaxies.
Additionally, compared to a local sample of luminous red galaxies, the more
distant sample presented in this study (with redshifts between 0.15-0.39,)
shows a higher Nc, suggesting the younger and smaller BCGs are still undergoing
hierarchical formation. Using the Millennium Simulations we model and estimate
the level of contamination due to unrelated cluster galaxies. The contamination
by interloping galaxies is 50% within projected separations of 50kpc, but
within 30kpc, 60% of identified companions are real physical companions. We
conclude that the luminosity of bound merger candidates down to luminosity
ratios of 20:1 could be adding as much as 10% to the mass of a typical BCG over
0.5Gyr at redshifts of z~0.3.Comment: 10 pages, 7 figures. Accepted and to be published in MNRA
The Origin of the Cosmic Soft X-Ray Background: Optical Identification of an Extremely Deep ROSAT Survey
We present the results of the deepest optically identified X-ray survey yet
made. The X-ray survey was made with the ROSAT PSPC and reaches a flux limit of
1.6x10^-15 erg cm^-2 s^-1 (0.5--2.0 keV). Above a flux limit of 2x10^-15 erg
cm^-2 s^-1 we define a complete sample of 70 sources of which 59 are
identified. Some (5) other sources have tentative identifications and in a
further 4 the X-ray error-boxes are blank to R=23 mag. At the brighter flux
levels (>= 10^-14 erg cm^-2 s^-1) we confirm the results of previous less deep
X-ray surveys with 84% of the sources begin QSOs. At fainter fluxes, however,
the survey is dominated by a population of galaxies with narrow optical
emission lines (NELGs). In addition, a number of groups and clusters of
galaxies are found at intermediate fluxes. Most of these are poor systems of
low X-ray luminosity and are generally found at redshifts of > 0.3. Their
numbers are consistent with a zero evolutionary scenario, in contrast to the
situation for high luminosity clusters at the same redshift. We discuss the
significance of these results to the determination of the cosmic soft X-ray
background (XRB) and show that at 2x10^-15 erg cm^-2 s^-1, we have resolved
more than 50% of the background. We also briefly consider the probable
importance of NELG objects to the residual background and look at some of the
properties of these unusual objects.Comment: 28 pages, LaTeX, 17 figures from 32 postscript files. Uses mn.sty and
epsf.sty. Accepted by MNRAS. Revised version now contains data table. For
more information see http://www.astro.soton.ac.uk/~amn/UKdee
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Insiders, Outsiders, and the Struggle for Consecration in Cultural Fields: A Core-Periphery Perspective
Building on recent research emphasizing how legitimacy depends on consensus among audiences about candidates’ characteristics and activities, we examine the relationship between cultural producers’ (candidates) position in the social structure and the consecration of their creative work by relevant audiences. We argue that the outcome of this process of evaluation in any cultural field, whether in art or science, is a function of (1) candidates’ embeddedness within the field, and (2) the type of audience—that is, peers versus critics—evaluating candidates’ work. Specifically, we hypothesize that peers are more likely to favor candidates who are highly embedded in the field, whereas critics will not show such favoritism. We find support for these hypotheses in the context of the Hollywood motion picture industry
Sunyaev-Zel'dovich observations of galaxy clusters out to the virial radius with the Arcminute Microkelvin Imager
We present observations using the Small Array of the Arcminute Microkelvin
Imager (AMI; 14-18 GHz) of four Abell and three MACS clusters spanning
0.171-0.686 in redshift. We detect Sunyaev-Zel'dovich (SZ) signals in five of
these without any attempt at source subtraction, although strong source
contamination is present. With radio-source measurements from high-resolution
observations, and under the assumptions of spherical -model,
isothermality and hydrostatic equilibrium, a Bayesian analysis of the data in
the visibility plane detects extended SZ decrements in all seven clusters over
and above receiver noise, radio sources and primary CMB imprints. Bayesian
evidence ratios range from 10^{11}:1 to 10^{43}:1 for six of the clusters and
3000:1 for one with substantially less data than the others. We present
posterior probability distributions for, e.g., total mass and gas fraction
averaged over radii internal to which the mean overdensity is 1000, 500 and
200, r_200 being the virial radius. Reaching r_200 involves some extrapolation
for the nearer clusters but not for the more-distant ones. We find that our
estimates of gas fraction are low (compared with most in the literature) and
decrease with increasing radius. These results appear to be consistent with the
notion that gas temperature in fact falls with distance (away from near the
cluster centre) out to the virial radius.Comment: 18 pages, 10 figures, submitted to MNRAS (updated authors and fixed
Figure 1
2023 roadmap for potassium-ion batteries
The heavy reliance of lithium-ion batteries (LIBs) has caused rising concerns on the sustainability of lithium and transition metal and the ethic issue around mining practice. Developing alternative energy storage technologies beyond lithium has become a prominent slice of global energy research portfolio. The alternative technologies play a vital role in shaping the future landscape of energy storage, from electrified mobility to the efficient utilization of renewable energies and further to large-scale stationary energy storage. Potassium-ion batteries (PIBs) are a promising alternative given its chemical and economic benefits, making a strong competitor to LIBs and sodium-ion batteries for different applications. However, many are unknown regarding potassium storage processes in materials and how it differs from lithium and sodium and understanding of solid–liquid interfacial chemistry is massively insufficient in PIBs. Therefore, there remain outstanding issues to advance the commercial prospects of the PIB technology. This Roadmap highlights the up-to-date scientific and technological advances and the insights into solving challenging issues to accelerate the development of PIBs. We hope this Roadmap aids the wider PIB research community and provides a cross-referencing to other beyond lithium energy storage technologies in the fast-pacing research landscape
A GMRT multifrequency radio study of the isothermal core of the poor galaxy cluster AWM 4
We present a detailed radio morphological study and spectral analysis of the
wide-angle-tail radio source 4C +24.36 associated with the dominant galaxy in
the relaxed galaxy cluster AWM 4. Our study is based on new high sensitivity
GMRT observations at 235 MHz, 327 MHz and 610 MHz, and on literature and
archival data at other frequencies. We find that the source major axis is
likely oriented at a small angle with respect to the plane of the sky. The
wide-angle-tail morphology can be reasonably explained by adopting a simple
hydrodynamical model in which both ram pressure (driven by the motion of the
host galaxy) and buoyancy forces contribute to bend the radio structure. The
spectral index progressively steepens along the source major axis from 0.3 in the region close to the radio nucleus to beyond 1.5 in the lobes.
The results of the analysis of the spectral index image allow us to derive an
estimate of the radiative age of the source of 160 Myr. The cluster
X-ray emitting gas has a relaxed morphology and short cooling time, but its
temperature profile is isothermal out to at least 160 kpc from the centre.
Therefore we seek evidence of energy ejection from the central AGN to prevent
catastrophic cooling. We find that the energy injected by 4C +24.36 in the form
of synchrotron luminosity during its lifetime is far less than the energy
required to maintain the high gas temperature in the core. We also find that it
is not possible for the central source to eject the requisite energy in the
intracluster gas in terms of the enthalpy of buoyant bubbles of relativistic
fluid, without creating discernible large cavities in the existing X-ray
XMM-Newton observations.Comment: 15 pages, 12 figures, accepted for publication in Ap
Breast cancer prognostic classification in the molecular era: the role of histological grade
Breast cancer is a heterogeneous disease with varied morphological appearances, molecular features, behavior, and response to therapy. Current routine clinical management of breast cancer relies on the availability of robust clinical and pathological prognostic and predictive factors to support clinical and patient decision making in which potentially suitable treatment options are increasingly available. One of the best-established prognostic factors in breast cancer is histological grade, which represents the morphological assessment of tumor biological characteristics and has been shown to be able to generate important information related to the clinical behavior of breast cancers. Genome-wide microarray-based expression profiling studies have unraveled several characteristics of breast cancer biology and have provided further evidence that the biological features captured by histological grade are important in determining tumor behavior. Also, expression profiling studies have generated clinically useful data that have significantly improved our understanding of the biology of breast cancer, and these studies are undergoing evaluation as improved prognostic and predictive tools in clinical practice. Clinical acceptance of these molecular assays will require them to be more than expensive surrogates of established traditional factors such as histological grade. It is essential that they provide additional prognostic or predictive information above and beyond that offered by current parameters. Here, we present an analysis of the validity of histological grade as a prognostic factor and a consensus view on the significance of histological grade and its role in breast cancer classification and staging systems in this era of emerging clinical use of molecular classifiers. © 2010 BioMed Central Lt
Imaging biomarker roadmap for cancer studies.
Imaging biomarkers (IBs) are integral to the routine management of patients with cancer. IBs used daily in oncology include clinical TNM stage, objective response and left ventricular ejection fraction. Other CT, MRI, PET and ultrasonography biomarkers are used extensively in cancer research and drug development. New IBs need to be established either as useful tools for testing research hypotheses in clinical trials and research studies, or as clinical decision-making tools for use in healthcare, by crossing 'translational gaps' through validation and qualification. Important differences exist between IBs and biospecimen-derived biomarkers and, therefore, the development of IBs requires a tailored 'roadmap'. Recognizing this need, Cancer Research UK (CRUK) and the European Organisation for Research and Treatment of Cancer (EORTC) assembled experts to review, debate and summarize the challenges of IB validation and qualification. This consensus group has produced 14 key recommendations for accelerating the clinical translation of IBs, which highlight the role of parallel (rather than sequential) tracks of technical (assay) validation, biological/clinical validation and assessment of cost-effectiveness; the need for IB standardization and accreditation systems; the need to continually revisit IB precision; an alternative framework for biological/clinical validation of IBs; and the essential requirements for multicentre studies to qualify IBs for clinical use.Development of this roadmap received support from Cancer Research UK and the Engineering and Physical Sciences Research Council (grant references A/15267, A/16463, A/16464, A/16465, A/16466 and A/18097), the EORTC Cancer Research Fund, and the Innovative Medicines Initiative Joint Undertaking (grant agreement number 115151), resources of which are composed of financial contribution from the European Union's Seventh Framework Programme (FP7/2007-2013) and European Federation of Pharmaceutical Industries and Associations (EFPIA) companies' in kind contribution
A galaxy-scale fountain of cold molecular gas pumped by a black hole
We present ALMA and MUSE observations of the Brightest Cluster Galaxy in Abell 2597, a nearby (z = 0:0821) cool core cluster of galaxies. The data map the kinematics of a three billion solar mass filamentary nebula that spans the innermost 30 kpc of the galaxy’s core. Its warm ionized and cold molecular components are both cospatial and comoving, consistent with the hypothesis that the optical nebula traces the warm envelopes of many cold molecular clouds that drift in the velocity field of the hot X-ray atmosphere. The clouds are not in dynamical equilibrium, and instead show evidence for inflow toward the central supermassive black hole, outflow along the jets it launches, and uplift by the buoyant hot bubbles those jets inflate. The entire scenario is therefore consistent with a galaxy-spanning “fountain”, wherein cold gas clouds drain into the black hole accretion reservoir, powering jets and bubbles that uplift a cooling plume of low-entropy multiphase gas, which may stimulate additional cooling and accretion as part of a self-regulating feedback loop. All velocities are below the escape speed from the galaxy, and so these clouds should rain back toward the galaxy center from which they came, keeping the fountain long-lived. The data are consistent with major predictions of chaotic cold accretion, precipitation, and stimulated feedback models, and may trace processes fundamental to galaxy evolution at effectively all mass scale
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