3,010 research outputs found
Effect of reheating on predictions following multiple-field inflation
We study the sensitivity of cosmological observables to the reheating phase
following inflation driven by many scalar fields. We describe a method which
allows semi-analytic treatment of the impact of perturbative reheating on
cosmological perturbations using the sudden decay approximation. Focusing on
-quadratic inflation, we show how the scalar spectral index and
tensor-to-scalar ratio are affected by the rates at which the scalar fields
decay into radiation. We find that for certain choices of decay rates,
reheating following multiple-field inflation can have a significant impact on
the prediction of cosmological observables.Comment: Published in PRD. 4 figures, 10 page
A Deep Radio Survey of Abell 2125 III: The Cluster Core - Merging and Stripping
We use radio, near-IR, optical, and X-ray observations to examine dynamic
processes in the central region of Abell 2125. In addition to the central
triple, including members of both major dynamical subsystems identified from a
redshift survey, this region features a galaxy showing strong evidence for
ongoing gas stripping during a high-velocity passage through the gas in the
cluster core. The disk galaxy C153 exhibits a plume stretching toward the
cluster center seen in soft X-rays by Chandra, parts of which are also seen in
[O II] emission and near-UV continuum light. HST imaging shows a distorted
disk, with star-forming knots asymmetrically distributed and remnant spiral
structure possibly defined by dust lanes. The stars and ionized gas in its disk
are kinematically decoupled, demonstrating that pressure stripping must be
important, and that tidal disruption is not the only mechanism at work.
Comparison of the gas properties seen in the X-ray and optical data on the
plume highlight significant features of the history of stripped gas in the
intracluster medium. The nucleus of C153 also hosts an AGN, shown by the weak
and distorted extended radio emission and a radio compact core. The unusual
strength of the stripping signatures in this instance is likely related to the
high relative velocity of the galaxy with respect to the intracluster medium,
during a cluster/cluster merger, and its passage very near the core of the
cluster. Another sign of recent dynamical events is diffuse starlight
asymmetrically placed about the central triple in a cD envelope. Transient and
extreme dynamical events as seen in Abell 2125 may be important drivers of
galaxy evolution in the cores of rich clusters.Comment: 36 pages, 16 figures, accepted AJ, paper with full resolution figures
is available at http:www.aoc.nrao.edu/~fowen/papers/a2125/a2125paper3.ps.g
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
The Far-Infrared/Radio Correlation in Nearby Abell Clusters
A comprehensive study of the effect of the cluster environment on the far-
infrared (FIR)/radio correlation in nearby Abell clusters is presented. Using
the cluster radio galaxy database from Miller & Owen (2001) and optical
spectroscopy and high resolution radio images to remove AGN, we assess the
FIR/radio correlation of cluster galaxies from the centers of the clusters out
well past the classical Abell radius. The FIR/radio correlation is shown to
hold quite well for star forming galaxies, and the FIR and radio fluxes for
cluster AGN are also well correlated. In the case of AGN, the relative radio-
to-FIR fluxes are greater and the scatter in the correlation is larger than
those seen for star forming galaxies. We also find that there is a rare but
statistically significant excess of star forming galaxies with enhanced radio
emission in the centers of the clusters, and that the degree of this
enhancement is typically a factor of two or three. The FIR/radio correlation
for cluster star forming galaxies is also tested against line-of-sight velocity
relative to the cluster systemic velocities, but no significant correlation is
found. While the radial dependence of the FIR/radio correlation is consistent
with the model wherein ram pressure increases the cluster galaxies' magnetic
field strengths through compression, the velocity data do not confirm this
model. Although a contribution from ram pressure can not be ruled out, the
thermal pressure due to the ICM alone is an equally viable alternative. The
high resolution radio images largely reject the hypothesis that the increased
radio emission arises from an AGN component, strengthening the claim that the
change in the correlation is caused by a change in the environment of the
galaxies.Comment: 26 pages, including 5 figures (uses AASTeX 5.0). Accepted for
publication in the Astronomical Journa
The Metallicity of Pre-Galactic Globular Clusters: Observational consequences of the first stars
We explore a scenario where metal-poor globular clusters (GCs) are enriched
by the first supernovae in the Universe. If the first stars in a 10^7 Msun dark
halo were very massive (>180 Msun), then a pair instability supernova from a
single massive star can produce sufficient iron to enrich 10^6 Msun of
pristine, primordial gas to [Fe/H] ~ -2. In such a scenario, where a single
massive star acts as a seed for halo GCs, the accurate abundance analysis of GC
stars would allow a direct measurement of the Population III initial mass.
Using the latest theoretical yields for zero metallicity stars in the mass
range 140-260 Msun, we find that the metals expelled from a ~230 Msun star are
consistent with [Si/Fe] and [Ca/Fe] observed in GC stars. However, no single
star in this mass range can simultaneously explain all halo GC heavy-element
abundance ratios, such as [V/Fe], [Ti/Fe] and [Ni/Fe]. These require a
combination masses for the Population III stellar progenitors. The various
observational consequences of this scenario are discussed.Comment: 5 pages, 2 figures, accepted for publication in ApJ Lette
Researching "British [Muslim] Values": Vernacular politics, digital storytelling, and participant researchers
This article reflects on methodological decisions, strategies, and challenges from a recent interdisciplinary project on the relationship between âBritish valuesâ and Islam. The project employed digital storytelling to access âeverydayâ conceptions and constructions of this contentious relationship. The research was undertaken by participant researchers recruited from Muslim communities in the UKâs East Anglia region, working with academics from media studies and political science. In this article we offer a detailed account of key moments relating especially to recruitment, retention, and the production of digital content. It offers two contributions. First, methodological guidance for researchers interested in combining participatory research with digital storytelling. And, second, rationale for so doing given the methodologyâs scope for producing rich visual content with capacity (i) to deepen and disrupt established knowledge, and (ii) to change the views, ideas and aspirations of those involved in the contentâs creation
A Comprehensive Radio and Optical Study of Abell 2256: Activity from an Infalling Group
Abell 2256 is a nearby (z~0.06), rich cluster of galaxies with fascinating
observed properties across a range of wavelengths. Long believed to represent a
cluster merger, recent X-ray and optical results have suggested that in
addition to the primary cluster and subcluster there is evidence for a third,
poorer system. We present wide-field, high sensitivity 1.4 GHz VLA radio
observations of Abell 2256 in conjunction with optical imaging and additional
spectroscopy. Over 40 cluster radio galaxies are identified, with optical
spectroscopy indicating the emission source (star formation or AGN) for most of
them. While the overall fraction of galaxies exhibiting radio emission is
consistent with a large sample of other nearby clusters, we find an increase in
the activity level of galaxies belonging to the third system (hereafter, the
``Group''). Specifically, the Group has relatively more star formation than
both the primary cluster and main subcluster. The position of the Group is also
coincident with the observed cluster radio relic. We suggest that the Group
recently (~0.3 Gyr) merged with the primary cluster and that this merger, not
the ongoing merger of the primary and the main subcluster, might be responsible
for many of the unusual radio properties of Abell 2256. Furthermore, the
greater star formation activity of the Group suggests that the infall of groups
is an important driver of galaxy evolution in clusters.Comment: 21 pages plus 13 JPEG figures; to appear in the Astronomical Journa
Moments of the Virtual Photon Structure Function
The photon structure function is a useful testing ground for QCD. It is
perturbatively computable apart from a contribution from what is usually called
the hadronic component of the photon. There have been many proposals for this
nonperturbative part of the real photon structure function. By studying moments
of the virtual photon structure function, we explore the extent to which these
proposed nonperturbative contributions can be identified experimentally.Comment: LaTeX, 16 pages + 14 compressed and uuencoded postscript figures,
UMN-TH-1111/9
Constraints on UV Absorption in the Intracluster Medium of Abell 1030
We present results from an extensive HST spectroscopic search for UV
absorption lines in the spectrum of the quasar B2~1028+313, which is associated
with the central dominant galaxy in the cluster Abell~1030 (). This is
one of the brightest known UV continuum sources located in a cluster, and
therefore provides an ideal opportunity to obtain stringent constraints on the
column densities of any cool absorbing gas that may be associated with the
intracluster medium (ICM). Our HST spectra were obtained with the FOS and GHRS,
and provide continuous coverage at rest-frame wavelengths from to
4060~\AA, thereby allowing the investigation of many different elements and
ionization levels. We utilize a new technique that involves simultaneous
fitting of large numbers of different transitions for each species, thereby
yielding more robust constraints on column densities than can be obtained from
a single transition. This method yields upper limits of cm on the column densities of a wide range of molecular, atomic
and ionized species that may be associated with the ICM. We also discuss a
possible \Lya and C IV absorption system associated with the quasar. We discuss
the implications of the upper limits on cool intracluster gas in the context of
the physical properties of the ICM and its relationship to the quasar.Comment: Astrophysical Journal, in press, 19 pages, includes 5 PostScript
figures. Latex format, uses aas2pp4.sty and epsfig.sty file
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