2,156 research outputs found
Tracing the Warm Hot Intergalactic Medium in the local Universe
We present a simple method for tracing the spatial distribution and
predicting the physical properties of the Warm-Hot Intergalactic Medium (WHIM),
from the map of galaxy light in the local universe. Under the assumption that
biasing is local and monotonic we map the ~ 2 Mpc/h smoothed density field of
galaxy light into the mass density field from which we infer the spatial
distribution of the WHIM in the local supercluster. Taking into account the
scatter in the WHIM density-temperature and density-metallicity relation,
extracted from the z=0 outputs of high-resolution and large box size
hydro-dynamical cosmological simulations, we are able to quantify the
probability of detecting WHIM signatures in the form of absorption features in
the X-ray spectra, along arbitrary directions in the sky. To illustrate the
usefulness of this semi-analytical method we focus on the WHIM properties in
the Virgo Cluster region.Comment: 16 pages 11 Figures. Discussion clarified, alternative methods
proposed. Results unchanged. MNRAS in pres
Effective-Field-Theory Approach to Top-Quark Production and Decay
We discuss new physics in top-quark interactions, using an effective field
theory approach. We consider top-quark decay, single top production, and
top-quark pair production. We identify 15 dimension-six operators that
contribute to these processes, and we compute the deviation from the Standard
Model induced by these operators. The results provide a systematic way of
searching for (or obtaining bounds on) physics beyond the Standard Model.Comment: 24 pages, 12 figures; references added, typos correcte
Revealing the Warm-Hot Intergalactic Medium with OVI Absorption
Hydrodynamic simulations of growth of cosmic structure suggest that 30-50% of
the total baryons at z=0 may be in a warm-hot intergalactic medium (WHIM) with
temperatures ~10^5-10^7K. The O VI \lambda \lambda 1032, 1038 absorption line
doublet in the FUV portion of QSO spectra provides an important probe of this
gas. Utilizing recent hydrodynamic simulations, it is found that there should
be ~5 O VI absorption lines per unit redshift with equivalent widths >= 35 mA,
decreasing rapidly to ~0.5 per unit redshift at >= 350 mA. About 10% of the
total baryonic matter or 20-30% of the WHIM is expected to be in the O VI
absorption line systems with equivalent width >= 20 mA; the remaining WHIM gas
may be too hot or have too low metallicity to be detected in O VI. We find that
the simulation results agree well with observations with regard to the line
abundance and total mass contained in these systems. Some of the O VI systems
are collisionally ionized and some are photoionized, but most of the mass is in
the collisionally ionized systems. We show that the gas that produces the O VI
absorption lines does not reside in virialized regions such as galaxies,
groups, or clusters of galaxies, but rather has an overdensity of 10-40 times
the average density. These regions form a somewhat connected network of
filaments. The typical metallicity of these regions is 0.1-0.3Zsun.Comment: accepted to ApJ Letters; full color Figure 1 may be obtained at
http://astro.princeton.edu/~cen/PROJECTS/p2/p2.html (at the bottom of the
page
Heating of the intergalactic medium due to structure formation
We estimate the heating of the intergalactic medium due to shocks arising
from structure formation. Heating of the gas outside the collapsed regions,
with small overdensities () is considered here,
with the aid of Zel'dovich approximation. We estimate the equation of state of
this gas, relating the density with its temperature, and its evolution in time,
considering the shock heating due to one- density peaks as being the
most dominant. We also estimate the mass fraction of gas above a given
temperature as a function of redshift. We find that the baryon fraction above
K at is . We estimate the integrated Sunyaev-Zel'dovich
distortion from this gas at present epoch to be of order .Comment: 5 pages (3 figs), To appear in MNRAS (pink pages
Constraints on Non-standard Top Quark Couplings
We study non-standard top quark couplings in the effective field theory
approach. All nine dimension-six operators that generate anomalous couplings
between the electroweak gauge bosons and the third-generation quarks are
included. We calculate their contributions at tree level and one loop to all
major precision electroweak observables. The calculations are compared with
data to obtain constraints on eight of these operators.Comment: 26 pages, 2 figure
Recovery of multiple parameters in subdiffusion from one lateral boundary measurement
This work is concerned with numerically recovering multiple parameters simultaneously in the subdiffusion model from one single lateral measurement on a part of the boundary, while in an incompletely known medium. We prove that the boundary measurement corresponding to a fairly general boundary excitation uniquely determines the order of the fractional derivative and the polygonal support of the diffusion coefficient, without knowing either the initial condition or the source. The uniqueness analysis further inspires the development of a robust numerical algorithm for recovering the fractional order and diffusion coefficient. The proposed algorithm combines small-time asymptotic expansion, analytic continuation of the solution and the level set method. We present extensive numerical experiments to illustrate the feasibility of the simultaneous recovery. In addition, we discuss the uniqueness of recovering general diffusion and potential coefficients from one single partial boundary measurement, when the boundary excitation is more specialized
The most ancient spiral galaxy: a 2.6-Gyr-old disk with a tranquil velocity field
We report an integral-field spectroscopic (IFS) observation of a
gravitationally lensed spiral galaxy A1689B11 at redshift . It is the
most ancient spiral galaxy discovered to date and the second kinematically
confirmed spiral at . Thanks to gravitational lensing, this is also
by far the deepest IFS observation with the highest spatial resolution (
400 pc) on a spiral galaxy at a cosmic time when the Hubble sequence is about
to emerge. After correcting for a lensing magnification of 7.2 0.8, this
primitive spiral disk has an intrinsic star formation rate of 22 2
yr, a stellar mass of 10 and a
half-light radius of kpc, typical of a main-sequence
star-forming (SF) galaxy at . However, the H\alpha\ kinematics show a
surprisingly tranquil velocity field with an ordered rotation ( =
200 12 km/s) and uniformly small velocity dispersions ( = 23 4 km/s and = 15 2 km/s).
The low gas velocity dispersion is similar to local spiral galaxies and is
consistent with the classic density wave theory where spiral arms form in
dynamically cold and thin disks. We speculate that A1689B11 belongs to a
population of rare spiral galaxies at that mark the formation epoch
of thin disks. Future observations with JWST will greatly increase the sample
of these rare galaxies and unveil the earliest onset of spiral arms.Comment: 18 pages, 13 figures, 1 table; accepted for publication in Ap
Dual-Frequency Observations of 140 Compact, Flat-Spectrum Active Galactic Nuclei for Scintillation-Induced Variability
The 4.9 GHz Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey
detected a drop in Interstellar Scintillation (ISS) for sources at redshifts z
> 2, indicating an apparent increase in angular diameter or a decrease in flux
density of the most compact components of these sources, relative to their
extended emission. This can result from intrinsic source size effects or
scatter broadening in the Intergalactic Medium (IGM), in excess of the expected
(1+z)^0.5 angular diameter scaling of brightness temperature limited sources
due to cosmological expansion. We report here 4.9 GHz and 8.4 GHz observations
and data analysis for a sample of 140 compact, flat-spectrum sources which may
allow us to determine the origin of this angular diameter-redshift relation by
exploiting their different wavelength dependences. In addition to using ISS as
a cosmological probe, the observations provide additional insight into source
morphologies and the characteristics of ISS. As in the MASIV Survey, the
variability of the sources is found to be significantly correlated with
line-of-sight H-alpha intensities, confirming its link with ISS. For 25
sources, time delays of about 0.15 to 3 days are observed between the
scintillation patterns at both frequencies, interpreted as being caused by a
shift in core positions when probed at different optical depths. Significant
correlation is found between ISS amplitudes and source spectral index; in
particular, a large drop in ISS amplitudes is observed at spectral indices of <
-0.4 confirming that steep spectrum sources scintillate less. We detect a
weakened redshift dependence of ISS at 8.4 GHz over that at 4.9 GHz, with the
mean variance at 4-day timescales reduced by a factor of 1.8 in the z > 2
sources relative to the z < 2 sources, as opposed to the factor of 3 decrease
observed at 4.9 GHz. This suggests scatter broadening in the IGM.Comment: 30 pages, 14 figures, accepted for publication in the Astronomical
Journa
Rewritable nanoscale oxide photodetector
Nanophotonic devices seek to generate, guide, and/or detect light using
structures whose nanoscale dimensions are closely tied to their functionality.
Semiconducting nanowires, grown with tailored optoelectronic properties, have
been successfully placed into devices for a variety of applications. However,
the integration of photonic nanostructures with electronic circuitry has always
been one of the most challenging aspects of device development. Here we report
the development of rewritable nanoscale photodetectors created at the interface
between LaAlO3 and SrTiO3. Nanowire junctions with characteristic dimensions
2-3 nm are created using a reversible AFM writing technique. These nanoscale
devices exhibit a remarkably high gain for their size, in part because of the
large electric fields produced in the gap region. The photoconductive response
is gate-tunable and spans the visible-to-near-infrared regime. The ability to
integrate rewritable nanoscale photodetectors with nanowires and transistors in
a single materials platform foreshadows new families of integrated
optoelectronic devices and applications.Comment: 5 pages, 5 figures. Supplementary Information 7 pages, 9 figure
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