2,283 research outputs found
Spectroscopic Confirmation of the Cl 1604 Supercluster at z~0.9
We present spectroscopic confirmation of the Cl 1604 supercluster at z~0.9.
Originally detected as two individual clusters, Cl 1604+4304 at z = 0.90 and Cl
1604+4321 at z = 0.92, which are closely separated in both redshift and sky
position, subsequent imaging revealed a complex of red galaxies bridging the
two clusters, suggesting that the region contained a large scale structure. We
have carried out extensive multi-object spectroscopy, which, combined with
previous measurements, provides ~600 redshifts in this area, including 230
confirmed supercluster members. We detect two additional clusters that are part
of this structure, Cl 1604+4314 at z = 0.87 and Cl 1604+4316 at z = 0.94. All
four have properties typical of local clusters, with line-of-sight velocity
dispersions between 489 and 962 km/s. The structure is significantly extended
in redshift space, which, if interpreted as a true elongation in real space,
implies a depth of 93 Mpc. We examine the spatial and redshift distribution of
the supercluster members.Comment: Accepted to ApJ Letters. 4 pages with 3 figure
CMB Distortions from Superconducting Cosmic Strings
We reconsider the effect of electromagnetic radiation from superconducting
strings on cosmic microwave background (CMB) mu- and y-distortions and derive
present (COBE-FIRAS) and future (PIXIE) constraints on the string tension,
mu_s, and electric current, I. We show that absence of distortions of the CMB
in PIXIE will impose strong constraints on mu_s and I, leaving the possibility
of light strings (G mu_s < 10^{-18}) or relatively weak currents (I < 10 TeV).Comment: 10pages, 5 figures, Submitted to PRD, v2:References added, replaced
to match the PRD versio
Cosmological Constraints on Neutrino Injection
We derive general constraints on the relic abundances of a long-lived
particle which mainly decays into a neutrino (and something else) at
cosmological time scales. Such an exotic particle may show up in various
particle-physics models based on physics beyond the standard model. The
constraints are obtained from big-bang nucleosynthesis, cosmic microwave
background and diffuse neutrino and photon fluxes, depending on the lifetime
and the electromagnetic and hadronic branching ratios.Comment: 33 pages, 23 figure
Recommended from our members
Childhood Maltreatment Predicts Poor Economic and Educational Outcomes in the Transition to Adulthood.
ObjectivesTo test whether childhood maltreatment was a predictor of (1) having low educational qualifications and (2) not being in education, employment, or training among young adults in the United Kingdom today.MethodsParticipants were from the Environmental Risk (E-Risk) Longitudinal Twin Study, a nationally representative UK cohort of 2232 twins born in 1994 to 1995. Mothers reported on child maltreatment when participants were aged 5, 7, 10, and 12 years. Participants were interviewed about their vocational status at age 18 years.ResultsThe unadjusted odds of having low educational qualifications or of not being in education, employment, or training at age 18 years were more than 2 times greater for young people with a childhood history of maltreatment versus those without. These associations were reduced after adjustments for individual and family characteristics. Youths who reported having a supportive adult in their lives had better education outcomes than did youths who had less support.ConclusionsCloser collaboration between the child welfare and education systems is warranted to improve vocational outcomes for maltreated youths
Dynamical and photometric imprints of feedback processes on the early evolution of E/S0 galaxies
We show that the observed Velocity Dispersion Function of E/S0 galaxies
matches strikingly well the distribution function of virial velocities of
massive halos virializing at z > 1.5, as predicted by the standard hierarchical
clustering scenario in a \LambdaCDM cosmology, for a constant ratio sigma/V_vir
= 0.55 \pm 0.05, close to the value expected at virialization if it typically
occurred at z > 3. This strongly suggests that dissipative processes and later
merging events had little impact on the matter density profile. Adopting the
above sigma/V_vir ratio, the observed relationships between photometric and
dynamical properties which define the fundamental plane of elliptical galaxies,
such as the luminosity-sigma (Faber-Jackson) and the luminosity-effective
radius relations, as well as the M_BH-sigma relation, are nicely reproduced.
Their shapes turn out to be determined by the mutual feedback of star-formation
(and supernova explosions)and nuclear activity, along the lines discussed by
Granato et al. (2004). To our knowledge, this is the first semi-analytic model
for which simultaneous fits of the fundamental plane relations and of the
epoch-dependent luminosity function of spheroidal galaxies have been presented.Comment: 14 pages, 6 figures, submitted to Ap
The Dynamics of Abell 2125
We present 371 galaxy velocities in the field of the very rich cluster Abell
2125 (z~0.25). These were determined using optical spectroscopy collected over
several years from both the WIYN 3.5m telescope and NOAO Mayall 4m telescope.
Prior studies at a variety of wavelengths (radio, optical, and X-ray) have
indicated that A2125 is a likely cluster-cluster merger, a scenario which we
are able to test using our large velocity database. We identified 224 cluster
galaxies, which were subjected to a broad range of statistical tests using both
positional and velocity information to evaluate the cluster dynamics and
substructure. The tests confirmed the presence of substructures within the
Abell 2125 system at high significance, demonstrating that A2125 is a complex
dynamical system. Comparison of the test results with existing simulations
strengthens the merger hypothesis, and provides clues about the merger geometry
and stage. The merger model for the system can reconcile A2125's low X-ray
temperature and luminosity with its apparently high richness, and might also
explain A2125's high fraction of active galaxies identified in prior radio and
optical studies.Comment: 34 pages, including tables and 3 color figures; to appear in Ap
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