3,036 research outputs found
HI tomographic imaging of the Cosmic Dawn and Epoch of Reionization with SKA
We provide an overview of 21cm tomography of the Cosmic Dawn and Epoch of
Reionization as possible with SKA-Low. We show why tomography is essential for
studying CD/EoR and present the scales which can be imaged at different
frequencies for the different phases of SKA- Low. Next we discuss the different
ways in which tomographic data can be analyzed. We end with an overview of
science questions which can only be answered by tomography, ranging from the
characterization of individual objects to understanding the global processes
shaping the Universe during the CD/EoRComment: 14 pages, 3 figures. Accepted for publication in the SKA Science Book
'Advancing Astrophysics with the Square Kilometre Array', to appear in 2015.
PoS(AASKA14)01
Wide-field LOFAR-LBA power-spectra analyses:Impact of calibration, polarization leakage and ionosphere
Contamination due to foregrounds, calibration errors and ionospheric effects pose major challenges in detection of the cosmic 21 cm signal in various Epoch of Reionization (EoR) experiments. We present the results of a study of a field centered on 3C196 using LOFAR Low Band observations, where we quantify various wide field and calibration effects such as gain errors, polarized foregrounds, and ionospheric effects. We observe a 'pitchfork' structure in the power spectrum of the polarized intensity in delay-baseline space, which leaks into the modes beyond the instrumental horizon. We show that this structure arises due to strong instrumental polarization leakage (∼30%) towards Cas A which is far away from primary field of view. We measure a small ionospheric diffractive scale towards CasA resembling pure Kolmogorov turbulence. Our work provides insights in understanding the nature of aforementioned effects and mitigating them in future Cosmic Dawn observations
The Sloan Lens ACS Survey. IX. Colors, Lensing and Stellar Masses of Early-type Galaxies
We present the current photometric dataset for the Sloan Lens ACS (SLACS)
Survey, including HST photometry from ACS, WFPC2, and NICMOS. These data have
enabled the confirmation of an additional 15 grade `A' (certain) lens systems,
bringing the number of SLACS grade `A' lenses to 85; including 13 grade `B'
(likely) systems, SLACS has identified nearly 100 lenses and lens candidates.
Approximately 80% of the grade `A' systems have elliptical morphologies while
~10% show spiral structure; the remaining lenses have lenticular morphologies.
Spectroscopic redshifts for the lens and source are available for every system,
making SLACS the largest homogeneous dataset of galaxy-scale lenses to date. We
have developed a novel Bayesian stellar population analysis code to determine
robust stellar masses with accurate error estimates. We apply this code to
deep, high-resolution HST imaging and determine stellar masses with typical
statistical errors of 0.1 dex; we find that these stellar masses are unbiased
compared to estimates obtained using SDSS photometry, provided that informative
priors are used. The stellar masses range from 10^10.5 to 10^11.8 M and
the typical stellar mass fraction within the Einstein radius is 0.4, assuming a
Chabrier IMF. The ensemble properties of the SLACS lens galaxies, e.g. stellar
masses and projected ellipticities, appear to be indistinguishable from other
SDSS galaxies with similar stellar velocity dispersions. This further supports
that SLACS lenses are representative of the overall population of massive
early-type galaxies with M* >~ 10^11 M, and are therefore an ideal
dataset to investigate the kpc-scale distribution of luminous and dark matter
in galaxies out to z ~ 0.5.Comment: 20 pages, 18 figures, 5 tables, published in Ap
Femtosecond Demagnetization and Hot Hole Relaxation in Ferromagnetic GaMnAs
We have studied ultrafast photoinduced demagnetization in GaMnAs via
two-color time-resolved magneto-optical Kerr spectroscopy. Below-bandgap
midinfrared pump pulses strongly excite the valence band, while near-infrared
probe pulses reveal sub-picosecond demagnetization that is followed by an
ultrafast (1 ps) partial recovery of the Kerr signal. Through comparison
with InMnAs, we attribute the signal recovery to an ultrafast energy relaxation
of holes. We propose that the dynamical polarization of holes through -
scattering is the source of the observed probe signal. These results support
the physical picture of femtosecond demagnetization proposed earlier for
InMnAs, identifying the critical roles of both energy and spin relaxation of
hot holes.Comment: 7 pages, 6 figure
Influence of laser-excited electron distributions on the x-ray magnetic circular dichroism spectra: Implications for femtosecond demagnetization in Ni
In pump-probe experiments an intensive laser pulse creates non-equilibrium
excited electron distributions in the first few hundred femtoseconds after the
pulse. The influence of non-equilibrium electron distributions caused by a pump
laser on the apparent X-ray magnetic circular dichroism (XMCD) signal of Ni is
investigated theoretically here for the first time, considering electron
distributions immediately after the pulse as well as thermalized ones, that are
not in equilibrium with the lattice or spin systems. The XMCD signal is shown
not to be simply proportional to the spin momentum in these situations. The
computed spectra are compared to recent pump-probe XMCD experiments on Ni. We
find that the majority of experimentally observed features considered to be a
proof of ultrafast spin momentum transfer to the lattice can alternatively be
attributed to non-equilibrium electron distributions. Furthermore, we find the
XMCD sum rules for the atomic spin and orbital magnetic moment to remain valid,
even for the laser induced non-equilibrium electron distributions.Comment: 6 pages, 3 figure
Scintillation noise in widefield radio interferometry
In this paper, we consider random phase fluctuations imposed during wave
propagation through a turbulent plasma (e.g. ionosphere) as a source of
additional noise in interferometric visibilities. We derive expressions for
visibility variance for the wide field of view case (FOV deg) by
computing the statistics of Fresnel diffraction from a stochastic plasma, and
provide an intuitive understanding. For typical ionospheric conditions
(diffractive scale km at MHz), we show that the resulting
ionospheric `scintillation noise' can be a dominant source of uncertainty at
low frequencies ( MHz). Consequently, low frequency widefield
radio interferometers must take this source of uncertainty into account in
their sensitivity analysis. We also discuss the spatial, temporal, and spectral
coherence properties of scintillation noise that determine its magnitude in
deep integrations, and influence prospects for its mitigation via calibration
or filtering.Comment: Accepted versio
Християнські традиції паломництва в сучасній Білорусії (за матеріалами польових досліджень)
Іn the article are examined modern Christian traditions of pilgrimage in Byelorussia. There is given a characteristic of the features of the traditions of worship to the sainted places in the contemporary culture of Byelorussian ethnos, structure and functions of pilgrimage are investigated. The influence of pilgrim traditions on the ethnic processes is noted (consciousness of Belorussians). The author used the materials of the field ethnolographical expeditions as the main saurce of the investigation.У артыкуле разглядаюцца сучасныя хрысціянскія традыцыі паломніцтва ў Беларусі. Пад-час аналізу праблемы аўтарам выкарыстаны ў якасці асноўнай крыніцы матэрыялы палявых этнаграфічных экспедыцый. Даецца характарыстыка асаблівасцей традыцый пакланення святым месцам у сучаснай культуры беларускага этнасу, даследуюцца структура і функцыі паломніцтва. Адзначаны ўплыў паломніцкіх традыцый на этнічныя працэсы (самасвядомасць беларусаў)
Lens Galaxy Properties of SBS1520+530: Insights from Keck Spectroscopy and AO Imaging
We report on an investigation of the SBS 1520+530 gravitational lens system
and its environment using archival HST imaging, Keck spectroscopic data, and
Keck adaptive-optics imaging. The AO imaging has allowed us to fix the lens
galaxy properties with a high degree of precision when performing the lens
modeling, and the data indicate that the lens has an elliptical morphology and
perhaps a disk. The new spectroscopic data suggest that previous determinations
of the lens redshift may be incorrect, and we report an updated, though
inconclusive, value z_lens = 0.761. We have also spectroscopically confirmed
the existence of several galaxy groups at approximately the redshift of the
lens system. We create new models of the lens system that explicitly account
for the environment of the lens, and we also include improved constraints on
the lensing galaxy from our adaptive-optics imaging. Lens models created with
these new data can be well-fit with a steeper than isothermal mass slope (alpha
= 2.29, with the density proportional to r^-alpha) if H_0 is fixed at 72
km/s/Mpc; isothermal models require H_0 ~ 50 km/s/Mpc. The steepened profile
may indicate that the lens is in a transient perturbed state caused by
interactions with a nearby galaxy.Comment: 12 pages, 10 figures, submitted to Ap
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