1,070 research outputs found
Structure and Evolution of Galaxy Clusters: Internal Dynamics of ABCG 209 at z~0.21
We study the internal dynamics of the rich galaxy cluster ABGC 209 on the
basis of new spectroscopic and photometric data. The distribution in redshift
shows that ABCG 209 is a well isolated peak of 112 detected member galaxies at
z=0.209, characterised by a high value of the line-of-sight velocity
dispersion, sigma_v=1250-1400 Km/s, on the whole observed area (1 Mpc/h from
the cluster center), that leads to a virial mass of M=1.6-2.2x10^15 M_sun
within the virial radius, assuming the dynamical equilibrium. The presence of a
velocity gradient in the velocity field, the elongation in the spatial
distribution of the colour-selected likely cluster members, the elongation of
the X-ray contour levels in the Chandra image, and the elongation of cD galaxy
show that ABCG 209 is characterised by a preferential NW-SE direction. We also
find a significant deviation of the velocity distribution from a Gaussian, and
relevant evidence of substructure and dynamical segregation. All these facts
show that ABCG 209 is a strongly evolving cluster, possibly in an advanced
phase of merging.Comment: 26 pages, 14 figures. A&A in pres
On Simulating Liouvillian Flow From Quantum Mechanics Via Wigner Functions
The interconnection between quantum mechanics and probabilistic classical
mechanics for a free relativistic particle is derived in terms of Wigner
functions (WF) for both Dirac and Klein-Gordon (K-G) equations. Construction of
WF is achieved by first defining a bilocal 4-current and then taking its
Fourier transform w.r.t. the relative 4-coordinate. The K-G and Proca cases
also lend themselves to a closely parallel treatment provided the Kemmer-
Duffin beta-matrix formalism is employed for the former. Calculation of WF is
carried out in a Lorentz-covariant fashion by standard `trace' techniques. The
results are compared with a recent derivation due to Bosanac.Comment: 9 pages, Latex; email: [email protected]
Optical Mass Estimates of Galaxy Clusters
We evaluate in a homogeneous way the optical masses of 170 nearby clusters
(z< 0.15). The sample includes both data from the literature and the new ENACS
data (Katgert et al. 1996, 1998). On the assumption that mass follows the
galaxy distribution, we compute the masses of each cluster by applying the
virial theorem to the member galaxies. We constrain the masses of very
substructured clusters (about 10% of our clusters) between two limiting values.
After appropriate rescaling to the X-ray radii, we compare our optical mass
estimates to those derived from X-ray analyses, which we compiled from the
literature (for 66 clusters). We find a good overall agreement. This agreement
is expected in the framework of two common assumptions: that mass follows the
galaxy distribution, and that clusters are not far from a situation of
dynamical equilibrium with both gas and galaxies reflecting the same underlying
mass distribution. We stress that our study strongly supports the reliability
of present cluster mass estimates derived from X-ray analyses and/or
(appropriate) optical analyses.Comment: 13 pages, 7 eps figures, tables are not included, USE LaTeX2e !!,
accepted by Ap
Ages and Metallicities of Star Clusters and Surrounding Fields in the Outer Disk of the Large Magellanic Cloud
We present Washington system C,T_1 CMDs of 13 star clusters and their
surrounding fields which lie in the outer parts of the LMC disk. Ages are
determined by means of the magnitude difference between the giant branch clump
and the turnoff, while metallicities are derived from the location of the giant
and subgiant branches as compared to fiducial star clusters. We find that in
most cases the stellar population of each star cluster is quite similar to that
of the field where it is embedded. Three particular fields present remarkable
properties: (i) The so far unique cluster ESO121-SC03 at ~9 Gyr has a
surrounding field which shares the same properties. (ii) The field surrounding
the far eastern intermediate age cluster OHSC37 is noteworthy in the sense that
we do not detect any evidence of LMC stars. (iii) The fields of SL388 and SL509
present CMDs with a secondary clump ~0.45 mag fainter than the dominant
intermediate age clump, suggesting a stellar population component located
behind the LMC disk at a distance comparable to that of the SMC. The mean
metallicity derived for the intermediate age outer disk clusters is
=-0.7 and for their surrounding fields =-0.6. These values are
significantly lower than found by Olszewski et al. (1991, AJ, 101, 515) for a
sample of clusters of similar age, but are in good agreement with several
recent studies. A few clusters stand out in the age--metallicity relation in
the sense that they are intermediate age clusters at relatively low metallicity
([Fe/H]~-1).Comment: LaTeX, to be published in July, 1998 Astronomical Journa
Improving the mass determination of Galactic Cepheids
We have selected a sample of Galactic Cepheids for which accurate estimates
of radii, distances, and photometric parameters are available. The comparison
between their pulsation masses, based on new Period-Mass-Radius (PMR)
relations, and their evolutionary masses, based on both optical and NIR
Color-Magnitude (CM) diagrams, suggests that pulsation masses are on average of
the order of 10% smaller than the evolutionary masses. Current pulsation masses
show, at fixed radius, a strongly reduced dispersion when compared with values
published in literature.The increased precision in the pulsation masses is due
to the fact that our predicted PMR relations based on nonlinear, convective
Cepheid models present smaller standard deviations than PMR relations based on
linear models. At the same time, the empirical radii of our Cepheid sample are
typically accurate at the 5% level. Our evolutionary mass determinations are
based on stellar models constructed by neglecting the effect of mass-loss
during the He burning phase. Therefore, the difference between pulsation and
evolutionary masses could be intrinsic and does not necessarily imply a problem
with either evolutionary and/or nonlinear pulsation models. The marginal
evidence of a trend in the difference between evolutionary and pulsation masses
when moving from short to long-period Cepheids is also briefly discussed. The
main finding of our investigation is that the long-standing Cepheid mass
discrepancy seems now resolved at the 10% level either if account for canonical
or mild convective core overshooting evolutionary models.Comment: 14 pages, 4 postscript figures, accepted for publication on ApJ
Letter
Entropy scaling in galaxy clusters: insights from an XMM-Newton observation of the poor cluster A1983
An XMM-Newton observation of the cool (kT=2.1 keV) cluster A1983, at z=0.044,
is presented. Gas density and temperature profiles are calculated for the inner
500 h_{50}^{-1} kpc (~0.35 r_200). The outer regions of the surface brightness
profile are well described with a beta model with beta=0.74, but the central
regions require the introduction of a second component. The temperature profile
is flat at the exterior with a slight dip towards the centre. The total mass
profile, calculated assuming hydrostatic equilibrium, is consistent with an NFW
profile, but with a low concentration parameter c=3.75 +/- 0.74. The M/L_B
ratio profile shows that, at large scale, light traces mass to a reasonable
extent, and the M/L_B ratio at 0.35 r_200 is consistent with the trends with
mass observed in the optical. The M_Fe/L_B ratio is about two times less than
that observed for a cluster at 5 keV. The gas mass fraction rises rapidly to
level off at ~200 kpc; the value at 0.35 r_200 is ~8%. The scaling properties
of the emission measure profile are consistent with the empirical relation
\mgas \propto \Tx^{1.94}, and not with the self-similar relation \mgas \propto
\Tx^{1.5}. Comparison of the entropy profile of A1983 with that of the hot
cluster A1413 shows that the profiles are well scaled using the empirically
determined relation S \propto \Tx^{0.65}, suggesting that the slope of the S-T
relation is shallower than in the self-similar model. The form of the entropy
profiles is remarkably similar, and there is no sign of a larger isentropic
core in the cooler cluster. These data provide powerful agruments against
preheating models. In turn, there is now increasing observational support for a
trend of f_gas with system mass, which may go some way towards explaining the
observed scaling behaviour. (Abridged.)Comment: Final refereed version to appear in A&A; Figs 2, 7, 11 and 12 are low
re
Anthropic pressures on Nature 2000 Sites: recommendations and monitoring criteria for the pollution emergency response activities within the Orbetello lagoon
Lâelevato valore naturalistico e socioeconomico
di un Sito Natura 2000 richiede che tutte le
attivitĂ antropiche che si svolgono al suo interno
(es. pesca, turismo, trasporti, attivitĂ industriali,
etc.) siano gestite in maniera tale da non pregiudicare
le specie e gli habitat per i quali lâarea Ăš
stata designata. Molti di questi Siti sono ambienti
di transizione, ovvero zone che costituiscono il
passaggio naturale tra terra e mare. La loro
posizione di interfaccia tra questi due ambienti li
rende ecosistemi unici e biologicamente molto
produttivi, sede di meccanismi di regolazione dei processi interattivi della biosfera nelle due
fasi, terrestre e marina. In alcuni Siti la presenza
di attivitĂ antropiche diffuse e prolungate nel
tempo ha portato al riscontro di stati di
contaminazione elevata, fino allâinclusione di
queste zone, o parti di esse, tra i Siti di bonifica
di Interesse Nazionale (SIN). Il presente lavoro
descrive le linee di indirizzo e le attivitĂ di
monitoraggio da attuare per la salvaguardia della
salute pubblica e dellâambiente nel corso degli
interventi di messa in sicurezza di emergenza
predisposti nellâarea lagunare antistante lâarea
industriale Ex Sitoco, allâinterno della perimetrazione
del SIN di Orbetello, incluso in un Sito di
Importanza Comunitaria. Le matrici ambientali
potenzialmente a rischio a causa dellâesecuzione
di tali interventi sono: acqua, sedimento,
biocenosi acquatiche, avifauna, uomo.
Ă altresĂŹ importante valutare gli effetti che le
ipotetiche modifiche su microscala, apportate a
livello di ogni matrice, potrebbero causare nel
lungo periodo su macroscala.The high naturalistic and socio-economic value
of Natura 2000 sites requires that all human
activities performed within their borders (e.g.
fishing, tourism, transports, industrial activities)
are regulated. Indeed, the site management
should assure the effective safeguard of all
species and habitats of European interest
included in the protected area. A lot of such
sites are located in transitional environments,
that are areas characterised by a natural
progression from the terrestrial to the water
environments. Such environments include
unique and very productive habitats, and they
represent the regulation mechanisms of the
interactive processes of the terrestrial and
marine biosphere. In some sites, the presence
of human activities that are distributed both in
space and time has led to high levels of contamination,
that in some cases even required their
inclusion in Reclamation Sites of National
Interest (SIN). The present study describes the
planning and monitoring activities to be
performed in order to safeguard human and
environment health during the actions of MISE in the lagoonal area in front of the industrial area
Ex Sitoco, within the borders of the Orbetello
SIN, included in a SCI. The environmental
parameters that are potentially at risk due to
such activities are: water, sediment, water
biocenosis, birds, humans. Furthermore, it is
important to evaluate the effects that potential
variations at the microscale level may cause at
the macroscale level
Optical/X-ray/radio view of Abell 1213: A galaxy cluster with anomalous diffuse radio emission
Context. Abell 1213, a low-richness galaxy system, is known to host an
anomalous radio halo detected in data of the VLA. It is an outlier with regard
to the relation between the radio halo power and the X-ray luminosity of the
parent clusters. Aims. Our aim is to analyze the cluster in the optical, X-ray,
and radio bands to characterize the environment of its diffuse radio emission
and to shed new light on its nature. Methods. We used optical data from the
SDSS to study the internal dynamics of the cluster. We also analyzed archival
XMM-Newton X-ray data to unveil the properties of its hot intracluster medium.
Finally, we used recent data from LOFAR at 144 MHz, together with VLA data at
1.4 GHz, to study the spectral behavior of the diffuse radio source. Results.
Both our optical and X-ray analysis reveal that this low-mass cluster exhibits
disturbed dynamics. In fact, it is composed of several galaxy groups in the
peripheral regions and, in particular, in the core, where we find evidence of
substructures oriented in the NE-SW direction, with hints of a merger nearly
along the line of sight. The analysis of the X-ray emission adds further
evidence that the cluster is in an unrelaxed dynamical state. At radio
wavelengths, the LOFAR data show that the diffuse emission is ~510 kpc in size.
Moreover, there are hints of low-surface-brightness emission permeating the
cluster center. Conclusions. The environment of the diffuse radio emission is
not what we would expect for a classical halo. The spectral index map of the
radio source is compatible with a relic interpretation, possibly due to a
merger in the N-S or NE-SW directions, in agreement with the substructures
detected through the optical analysis. The fragmented, diffuse radio emissions
at the cluster center could be attributed to the surface brightness peaks of a
faint central radio halo.Comment: 14 pages, 16 figures, 5 tables. In press on Astronomy & Astrophysics.
Paper resubmitted after revision by the language edito
An HST/WFPC Survey of Bright Young Clusters in M31. II. Photometry of Less Luminous Clusters in the Fields
We report on the properties of 89 low mass star clusters located in the
vicinity of luminous young clusters (blue globulars) in the disk of M31. 82 of
the clusters are newly detected. We have determined their integrated magnitudes
and colors, based on a series of Hubble Space Telescope Wide Field/Planetary
Camera 2 exposures in blue and red (HST filters F450W and F814W). The
integrated apparent magnitudes range from F450W = 17.5 to 22.5, and the colors
indicate a wide range of ages. Stellar color-magnitude diagrams for all
clusters were obtained and those with bright enough stars were fit to
theoretical isochrones to provide age estimates. The ages range from 12 Myr to
>500 Myr. Reddenings, which average E(F450 - F814) = 0.59 with a dispersion of
0.21 magnitudes, were derived from the main sequence fitting for those
clusters. Comparison of these ages and integrated colors with single population
theoretical models with solar abundances suggests a color offset of 0.085
magnitudes at the ages tested. Estimated ages for the remaining clusters are
based on their measured colors. The age-frequency diagram shows a steep decline
of number with age, with a large decrease in number per age interval between
the youngest and the oldest clusters detected.Comment: 20 pages, 9 figure
LIGHT PHOTINOS AS DARK MATTER
There are good reasons to consider models of low-energy supersymmetry with
very light photinos and gluinos. In a wide class of models the lightest
-odd, color-singlet state containing a gluino, the , has a mass in the
1-2 GeV range and the slightly lighter photino, \pho, would survive as the
relic -odd species. For the light photino masses considered here, previous
calculations resulted in an unacceptable photino relic abundance. But we point
out that processes other than photino self-annihilation determine the relic
abundance when the photino and are close in mass. Including
\r0\longleftrightarrow\pho processes, we find that the photino relic
abundance is most sensitive to the -to-\pho mass ratio, and within model
uncertainties, a critical density in photinos may be obtained for an
-to-\pho mass ratio in the range 1.2 to 2.2. We propose photinos in the
mass range of 500 MeV to 1.6 GeV as a dark matter candidate, and discuss a
strategy to test the hypothesis.Comment: uuencoded compressed tar file containing 32 page LaTeX file and eight
postscript figure
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