9,783 research outputs found
Spiral-like structure in nearby clusters of galaxies
X-ray data analysis have found that fairly complex structures at cluster
centres are more common than expected. Many of these structures have similar
morphologies, which exhibit spiral-like substructure. It is not yet well known
how these structures formed or are maintained. Understanding the origin of
these spiral-like features at the centre of some clusters is the major
motivation behind this work. We analyse deep \textit{Chandra} observations of
15 nearby galaxy clusters (0.01 0.06), and use X-ray temperature and
substructure maps to detect small features at the cores of the clusters. We
detect spiral-like features at the centre of 7 clusters: A85, A426, A496, Hydra
A cluster, Centaurus, Ophiuchus, and A4059. These patterns are similar to those
found in numerical hydrodynamic simulations of cluster mergers with non-zero
impact parameter. In some clusters of our sample, a strong radio source also
occupies the inner region of the cluster, which indicates a possible connection
between the two. Our investigation implies that these spiral-like structures
may be caused by off-axis minor mergers. Since these features occur in regions
of high density, they may confine radio emission from the central galaxy
producing, in some cases, unusual radio morphology.Comment: 14 pages, 3 figures, accepted for publication in A&A (Nov 17, 2009
Quantum dynamics of the Li+HF-->H+LiF reaction at ultralow temperatures
Quantum mechanical calculations are reported for the
Li+HF(v=0,1,j=0)-->H+LiF(v',j') bimolecular scattering process at low and
ultralow temperatures. Calculations have been performed for zero total angular
momentum using a recent high accuracy potential energy surface for the X 2A'
electronic ground state. For Li+HF(v=0,j=0), the reaction is dominated by
resonances due to the decay of metastable states of the Li...F-H van der Waals
complex. Assignment of these resonances has been carried out by calculating the
eigenenergies of the quasibound states. We also find that while chemical
reactivity is greatly enhanced by vibrational excitation the resonances get
mostly washed out in the reaction of vibrationally excited HF with Li atoms. In
addition, we find that at low energies, the reaction is significantly
suppressed due to the formation of rather deeply bound van der Waals complexes
and the less efficient tunneling of the relatively heavy fluorine atom.Comment: 24 pages, 8 figures, 1 table, submitted to J. Chem. Phy
XMM-Newton/SDSS: star formation efficiency in galaxy clusters and constraints on the matter density parameter
It is believed that the global baryon content of clusters of galaxies is
representative of the matter distribution of the universe, and can, therefore,
be used to reliably determine the matter density parameter Omega_m. This
assumption is challenged by the growing evidence from optical and X-ray
observations that the total baryon mass fraction increases towards rich
clusters. In this context, we investigate the dependence of stellar, and total
baryon mass fractions as a function of mass. To do so, we used a subsample of
nineteen clusters extracted from the X-ray flux limited sample HIFLUGCS that
have available DR-7 Sloan Digital Sky Survey (SDSS) data. From the optical
analysis we derived the stellar masses. Using XMM-Newton we derived the gas
masses. Then, adopting a scaling relation we estimate the total masses. Adding
the gas and the stellar mass fractions we obtain the total baryonic content
that we find to increase with cluster mass, reaching 7-year Wilkinson Microwave
Anisotropy Probe (WMAP-7) prediction for clusters with M_500 = 1.6 x 10^{15}
M_sun. We observe a decrease of the stellar mass fraction (from 4.5% to ~1.0%)
with increasing total mass where our findings for the stellar mass fraction
agree with previous studies. This result suggests a difference in the number of
stars formed per unit of halo mass, though with a large scatter for low-mass
systems. That is, the efficiency of star formation varies on cluster scale that
lower mass systems are likely to have higher star formation efficiencies. It
follows immediately that the dependence of the stellar mass fraction on total
mass results in an increase of the mass-to-light ratio from lower to higher
mass systems. We also discuss the consequences of these results in the context
of determining the cosmic matter density parameter Omega_m.Comment: Accepted for publication in ApJ, 11 pages, 5 figures.
http://stacks.iop.org/0004-637X/743/1
The optical/X-ray connection: ICM iron content and galaxy optical luminosity in 20 galaxy clusters
X-ray observations of galaxy clusters have shown that the intra-cluster gas
has iron abundances of about one third of the solar value. These observations
also show that part (if not all) of the intra-cluster gas metals were produced
within the member galaxies. We present a systematic analysis of 20 galaxy
clusters to explore the connection between the iron mass and the total
luminosity of early-type and late-type galaxies, and of the brightest cluster
galaxies (BCGs). From our results, the intra-cluster medium (ICM) iron mass
seems to correlate better with the luminosity of the BCGs than with that of the
red and blue galaxy populations. As the BCGs cannot produce alone the observed
amount of iron, we suggest that ram-pressure plus tidal stripping act together
to enhance, at the same time, the BCG luminosities and the iron mass in the
ICM. Through the analysis of the iron yield, we have also estimated that SN Ia
are responsible for more than 50% of the total iron in the ICM. This result
corroborates the fact that ram-pressure contributes to the gas removal from
galaxies to the inta-cluster medium, being very efficient for clusters in the
temperature range 2 < kT (keV)< 10Comment: Accepted for publication in MNRAS (11 pg, 9 figures and 3 tables
Accuracy of Author Names in Bibliographic Data Sources: An Italian Case Study
We investigate the accuracy of how author names are reported in bibliographic records excerpted from four prominent sources: WoS, Scopus, PubMed, and CrossRef. We take as a case study 44,549 publications stored in the internal database of Sapienza University of Rome, one of the largest universities in Europe. While our results indicate generally good accuracy for all bibliographic data sources considered, we highlight a number of issues that undermine the accuracy for certain classes of author names, including compound names and names with diacritics, which are common features to Italian and other Western languages
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