642 research outputs found
The optical and near-infrared properties of nearby groups of galaxies
We present a study of the optical (BRI) and near-infrared (JHK) luminosity
fuctions (LFs) of the GEMS sample of 60 nearby groups of galaxies between
0<z<0.04, with our optical CCD photometry and near-IR photometry from the 2MASS
survey. The LFs in all filters show a depletion of galaxies of intermediate
luminosity, two magnitudes fainter than L*, within 0.3 R{500} from the centres
of X-ray faint groups. This feature is not as pronounced in X-ray bright
gropus, and vanishes when LFs are found out to R{500}, even in the X-ray dim
groups. We argue that this feature arises due to the enhanced merging of
intermediate-mass galaxies in the dynamically sluggish environment of low
velocity-dispersion groups, indicating that merging is important in galaxy
evolution even at z~0.Comment: to appear in the proceedings of the ESO workshop "Groups of Galaxies
in the Nearby Universe", Santiago, Dec 5-9, 2005. Eds. I. Saviane, V. Ivanov,
& J. Borissova (Springer Verlag); 5 page
XMM-Newton study of 0.012<z<0.024 groups. I: Overview of the IGM thermodynamics
We study the thermodynamic properties of the hot gas in a sample of groups in
the 0.012-0.024 redshift range, using XMM-Newton observations. We present
measurements of temperature, entropy, pressure and iron abundance.
Non-parametric fits are used to derive the mean properties of the sample and to
study dispersion in the values of entropy and pressure. The scaling of the
entropy at 0.2r500 matches well the results of Ponman et al. (2003). However,
compared to cool clusters, the groups in our sample reveal larger entropy at
inner radii and a substantially flatter slope in the entropy in the outskirts,
compared to both the prediction of pure gravitational heating and to
observations of clusters. This difference corresponds to the systematically
flatter group surface brightness profiles, reported previously. The scaled
pressure profiles can be well approximated with a Sersic model with n=4. We
find that groups exhibit a systematically larger dispersion in pressure,
compared to clusters of galaxies, while the dispersion in entropy is similar.Comment: 11 pages, MNRAS in press, the 25 page version with all 176 figures
included is at ftp://ftp.xray.mpe.mpg.de/people/alexis/2dxgs_astroph.ps.g
Plastic zone evolution during fatigue crack growth: Digital image correlation coupled with finite elements method
International audienceNonlinearities effects at the crack tip, due to the elastic-plastic material behavior , impact the crack growth rate and path. This paper is devoted to the study of the plastic zone evolution in the crack tip region. The methodology relies on coupling an elastic-plastic Finite Elements Method (FEM) model and experimental displacements measured by Digital Image Correlation (DIC). These latter are introduced as Dirichlet boundary conditions in the finite elements analysis. The considered FEM domain is constant, i.e. the same mesh with a centered crack is moved to each new crack tip position deduced from DIC. The new boundary conditions are updated and the residual stresses and plastic strains of the former computation are interpolated and actualized on the mesh shifted to the new crack tip position in order to incorporate them in the numerical model. The coupling method allowed applying experimental boundary conditions in order to be as close as possible to real experimental conditions and to observe the plasticity evolution from small to large scale yielding conditions. A fatigue test was conducted to validate the proposed approach. The identification residues are proved to be lower than those obtained with an experimental displacements projection onto Williams' series basis, which is a method commonly used with DIC. The coupling results present an attractive similarity with Irwin's model regardless of the crack length. Thus, the definition of the mask needed for the displacements fields projection on Williams' model can be deduced with a reliable estimate of Irwin's plastic radius
The unusual morphology of the intragroup medium in NGC 5171
We present the results of a 24 ks XMM-Newton observation of the NGC 5171
group of galaxies. NGC 5171 is unusual in that it is an X-ray bright group (L >
10^42 erg/s), with irregular contours which are not centred on a bright galaxy.
The global spectrum is adequately described by a single temperature APEC model
with T = 0.96 +/- 0.04 keV, and Z = 0.13 +/- 0.02 Zsol, in good agreement with
previous ROSAT data. We find the X-ray contours are centred on a bright ridge
of emission stretching from the BGG to a nearby galaxy. Spectral mapping
reveals this ridge to be both cool (T ~ 1.1 keV) and metallic (Z ~ 0.4 Zsol) in
comparison to its surrounding, suggesting it is the result of a tidal
interaction between the two galaxies. Optical data reveals the member galaxies
to have a high velocity dispersion (sigma = 494 +/- 99 km/s), and a
significantly non-Gaussian velocity distribution, suggesting the group is in
the process of merging. A region of hot gas with T = 1.58 +/- 0.36 keV is found
to the West of the bright central ridge, and we interpret this as shock-heating
resulting from the merging. A further region of emission to the South-East of
the bright central ridge, with T = 1.14 +/- 0.13 keV, is probably associated
with a background group, four times more distant.Comment: 10 pages, 8 figures, to be published in MNRA
A New Window of Exploration in the Mass Spectrum: Strong Lensing by Galaxy Groups in the SL2S
The existence of strong lensing systems with Einstein radii (Re) covering the
full mass spectrum, from ~1-2" (produced by galaxy scale dark matter haloes) to
>10" (produced by galaxy cluster scale haloes) have long been predicted. Many
lenses with Re around 1-2" and above 10" have been reported but very few in
between. In this article, we present a sample of 13 strong lensing systems with
Re in the range 3"- 8", i.e. systems produced by galaxy group scale dark matter
haloes, spanning a redshift range from 0.3 to 0.8. This opens a new window of
exploration in the mass spectrum, around 10^{13}- 10^{14} M_{sun}, which is a
crucial range for understanding the transition between galaxies and galaxy
clusters. Our analysis is based on multi-colour CFHTLS images complemented with
HST imaging and ground based spectroscopy. Large scale properties are derived
from both the light distribution of the elliptical galaxies group members and
weak lensing of the faint background galaxy population. On small scales, the
strong lensing analysis yields Einstein radii between 2.5" and 8". On larger
scales, the strong lenses coincide with the peak of the light distribution,
suggesting that mass is traced by light. Most of the luminosity maps have
complicated shapes, indicating that these intermediate mass structures are
dynamically young. Fitting the reduced shear with a Singular Isothermal Sphere,
we find sigma ~ 500 km/s and an upper limit of ~900 km/s for the whole sample.
The mass to light ratio for the sample is found to be M/L_i ~ 250 (solar units,
corrected for evolution), with an upper limit of 500. This can be compared to
mass to light ratios of small groups (with sigma ~ 300 km/s and galaxy clusters
with sigma > 1000 km/s, thus bridging the gap between these mass scales.Comment: A&A Accepted. Draft with Appendix images can be found at
http://www.dark-cosmology.dk/~marceau/groups_sl2s.pd
The XMM-LSS survey: the Class 1 cluster sample over the initial 5 square degrees and its cosmological modelling
We present a sample of 29 galaxy clusters from the XMM-LSS survey over an
area of some 5deg2 out to a redshift of z=1.05. The sample clusters, which
represent about half of the X-ray clusters identified in the region, follow
well defined X-ray selection criteria and are all spectroscopically confirmed.
For all clusters, we provide X-ray luminosities and temperatures as well as
masses. The cluster distribution peaks around z=0.3 and T =1.5 keV, half of the
objects being groups with a temperature below 2 keV. Our L-T(z) relation points
toward self-similar evolution, but does not exclude other physically plausible
models. Assuming that cluster scaling laws follow self-similar evolution, our
number density estimates up to z=1 are compatible with the predictions of the
concordance cosmology and with the findings of previous ROSAT surveys. Our well
monitored selection function allowed us to demonstrate that the inclusion of
selection effects is essential for the correct determination of the evolution
of the L-T relation, which may explain the contradictory results from previous
studies. Extensive simulations show that extending the survey area to 10deg2
has the potential to exclude the non-evolution hypothesis, but that constraints
on more refined ICM models will probably be limited by the large intrinsic
dispersion of the L-T relation. We further demonstrate that increasing the
dispersion in the scaling laws increases the number of detectable clusters,
hence generating further degeneracy [in addition to sigma8, Omega_m, L(M,z) and
T(M,z)] in the cosmological interpretation of the cluster number counts. We
provide useful empirical formulae for the cluster mass-flux and mass-count-rate
relations as well as a comparison between the XMM-LSS mass sensitivity and that
of forthcoming SZ surveys.Comment: Accepted for publication by MNRAS. Full resolution images as well as
additional cluster data are available through a dedicated database at
http://l3sdb.in2p3.fr:8080/l3sdb
The evolution of galaxy groups and of galaxies therein
Properties of groups of galaxies depend sensitively on the algorithm for
group selection, and even the most recent catalogs of groups built from
redshift-space selection should suffer from projections and infalling galaxies.
The cosmo-dynamical evolution of groups from initial Hubble expansion to
collapse and virialization leads to a fundamental track (FT) in
virial-theorem-M/L vs crossing time. The increased rates of mergers, both
direct and after dynamical friction, in groups relative to clusters, explain
the higher fraction of elliptical galaxies at given local number density in
X-ray selected groups, relative to clusters, even when the hierarchical
evolution of groups is considered. Galaxies falling into groups and clusters
should later travel outwards to typically 2 virial radii, which is somewhat
less than the outermost radius where observed galaxy star formation
efficiencies are enhanced relative to field galaxies of same morphological
type. An ongoing analysis of the internal kinematics of X-ray selected groups
suggests that the radial profiles of line of sight velocity dispersion are
consistent with isotropic NFW distributions for the total mass density, with
higher (lower) concentrations than LambdaCDM predictions in groups of high
(low) mass. The critical mass, at M200 ~ 10^13 M_sun is consistent with
possible breaks in the X-ray luminosity-temperature and Fundamental Plane
relations. The internal kinematics of groups indicate that the M-T relation of
groups should agree with that extrapolated from clusters with no break at the
group scale. The analyses of observed velocity dispersion profiles and of the
FT both suggest that low velocity dispersion groups (compact and loose, X-ray
emitting or undetected) are quite contaminated by chance projections.Comment: Invited review, ESO workshop "Groups of Galaxies in the Nearby
Universe", held in Santiago, Chile, 5-9 December 2005, ed. I. Saviane, V.
Ivanov & J. Borissova, 16 page
URBAN CENTER. Una casa di vetro per le politiche urbane.
Nella cultura di governo della cittĂ , il termine "Urban Center" (o "Casa della cittĂ ") designa una serie di strutture il cui denominatore comune risiede nello svolgimento di attivitĂ di servizio per le comunitĂ urbane ai fini di soddisfare la crescente domenda di democrazia partecipativa e deliberativa nei processi di trasformazione degli insediamenti. Traendo spunto dalla storicizzazione del fenomeno e dal confronto tra i consolidati modelli statunitensi e le recenti esperienze in Italia, il volume si interroga sulla maturazione delle missioni dell' "Urban Center" nel passaggio da asettico spazio di informazione a luogo provilegiato per la costruzione trasparente di politiche urbane condivise.
Il percorso logico del volume si sviluppa seguendo un fil rouge articolato in quattro parti.
Il primo blocco si apre con due tematiche che costituiscono dialetticamente la cornice di riferimento entro cui puĂČ essere correttamente collocata la questione degli UC: lâurbanistica partecipata e il marketing urbano.
Nella seconda parte attraverso lo studio di casi si ricostruisce il quadro delle articolate declinazioni statunitensi di Urban Center, consolidatesi in diversi decenni di storia. Sono strutture fortemente caratterizzate e autonome per stile, missioni, obiettivi, prioritĂ , modalitĂ operative, ma allo stesso tempo accomunate da un equilibrato mix di passione civile e pragmatismo professionale.
Il terzo gruppo di saggi Ăš dedicato alla condizione attuale e di prospettiva degli UC in Italia, delineando criticamente una sorta di âmappa dinamicaâ delle diverse strutture attivate e in divenire, caratterizzate per soggetti ispiratori, missioni âstiliâ e protagonismo degli attori coinvolti.
Il cerchio delle riflessioni si chiude nella quarta parte discutendo la questione dellâinnovazione di metodo per la costruzione di un UC sia attraverso la dimensione teoretica che le potenzialitĂ operative.
Testi in italiano e inglese di B. Monardo (curatore), M.C. Bizzarri, E. Carmagnani, M. Carta, F. Ceci, P. Colarossi, L. De Bonis, A. Dina, A. De Rossi, D. Filippi, A. Giorgi, P. Laconte, F. Lovato, L. J. Osmond, R. Shiffman, O Tommasi, A. Uttaro; postfazione di M. Ricci
The Impact of Kidney Development on the Life Course: A Consensus Document for Action
Hypertension and chronic kidney disease (CKD) have a significant impact on global morbidity and mortality. The Low Birth Weight and Nephron Number Working Group has prepared a consensus document aimed to address the relatively neglected issue for the developmental programming of hypertension and CKD. It emerged from a workshop held on April 2, 2016, including eminent internationally recognized experts in the field of obstetrics, neonatology, and nephrology. Through multidisciplinary engagement, the goal of the workshop was to highlight the association between fetal and childhood development and an increased risk of adult diseases, focusing on hypertension and CKD, and to suggest possible practical solutions for the future. The recommendations for action of the consensus workshop are the results of combined clinical experience, shared research expertise, and a review of the literature. They highlight the need to act early to prevent CKD and other related noncommunicable diseases later in life by reducing low birth weight, small for gestational age, prematurity, and low nephron numbers at birth through coordinated interventions. Meeting the current unmet needs would help to define the most cost-effective strategies and to optimize interventions to limit or interrupt the developmental programming cycle of CKD later in life, especially in the poorest part of the world
A developmental approach to the prevention of hypertension and kidney disease: a report from the Low Birth Weight and Nephron Number Working Group
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