25,764 research outputs found
Detection and extraction of signals from the epoch of reionization using higher-order one-point statistics
Detecting redshifted 21-cm emission from neutral hydrogen in the early Universe promises to give direct constraints on the epoch of reionization (EoR). It will, though, be very challenging to extract the cosmological signal (CS) from foregrounds and noise which are orders of magnitude larger. Fortunately, the signal has some characteristics which differentiate it from the foregrounds and noise, and we suggest that using the correct statistics may tease out signatures of reionization. We generate mock data cubes simulating the output of the Low Frequency Array (LOFAR) EoR experiment. These cubes combine realistic models for Galactic and extragalactic foregrounds and the noise with three different simulations of the CS. We fit out the foregrounds, which are smooth in the frequency direction, to produce residual images in each frequency band. We denoise these images and study the skewness of the one-point distribution in the images as a function of frequency. We find that, under sufficiently optimistic assumptions, we can recover the main features of the redshift evolution of the skewness in the 21-cm signal. We argue that some of these features ¿ such as a dip at the onset of reionization, followed by a rise towards its later stages ¿ may be generic, and give us a promising route to a statistical detection of reionization
Sharp weighted estimates for multi-frequency Calder\'on-Zygmund operators
In this paper we study weighted estimates for the multi-frequency
Calder\'{o}n-Zygmund operators associated with the frequency set
and modulus of continuity
satisfying the usual Dini condition. We use the modern method of domination by
sparse operators and obtain bounds for the exponents of and characteristic
Integral field unit spectroscopy of 10 early type galactic nuclei: I - Principal component analysis Tomography and nuclear activity
Most massive galaxies show emission lines that can be characterized as
LINERs. To what extent this emission is related to AGNs or to stellar processes
is still an open question. In this paper, we analysed a sample of such galaxies
to study the central region in terms of nuclear and circumnuclear emission
lines, as well as the stellar component properties. For this reason, we
selected 10 massive ( > 200 km/s) nearby (d < 31 Mpc) galaxies and
observed them with the IFU/GMOS (integral field unit/Gemini Multi-Object
Spectrograph) spectrograph on the Gemini South Telescope. The data were
analysed with principal component analysis (PCA) Tomography to assess the main
properties of the objects. Two spectral regions were analysed: a yellow region
(5100-5800 A), adequate to show the properties of the stellar component, and a
red region (6250-6800 A), adequate to analyse the gaseous component. We found
that all objects previously known to present emission lines have a central
AGN-type emitting source. They also show gaseous and stellar kinematics typical
of discs. Such discs may be co-aligned (NGC 1380 and ESO 208 G-21), in
counter-rotation (IC 1459 and NGC 7097) or misaligned (IC 5181 and NGC 4546).
We also found one object with a gaseous disc but no stellar disc (NGC 2663),
one with a stellar disc but no gaseous disc (NGC 1404), one with neither
stellar nor gaseous disc (NGC 1399) and one with probably ionization cones (NGC
3136). PCA Tomography is an efficient method for detecting both the central AGN
and gaseous and stellar discs. In the two cases (NGC 1399 and NGC 1404) in
which no lines were previously reported, we found no evidence of either nuclear
or circumnuclear emission, using PCA Tomography only.Comment: 26 pages, 17 figures, accepted for publication in MNRA
Light cone effect on the reionization 21-cm power spectrum
Observations of redshifted 21-cm radiation from neutral hydrogen during the
epoch of reionization (EoR) are considered to constitute the most promising
tool to probe that epoch. One of the major goals of the first generation of low
frequency radio telescopes is to measure the 3D 21-cm power spectrum. However,
the 21-cm signal could evolve substantially along the line of sight (LOS)
direction of an observed 3D volume, since the received signal from different
planes transverse to the LOS originated from different look-back times and
could therefore be statistically different. Using numerical simulations we
investigate this so-called light cone effect on the spherically averaged 3D
21-cm power spectrum. For this version of the power spectrum, we find that the
effect mostly `averages out' and observe a smaller change in the power spectrum
compared to the amount of evolution in the mean 21-cm signal and its rms
variations along the LOS direction. Nevertheless, changes up to 50% at large
scales are possible. In general the power is enhanced/suppressed at large/small
scales when the effect is included. The cross-over mode below/above which the
power is enhanced/suppressed moves toward larger scales as reionization
proceeds. When considering the 3D power spectrum we find it to be anisotropic
at the late stages of reionization and on large scales. The effect is dominated
by the evolution of the ionized fraction of hydrogen during reionization and
including peculiar velocities hardly changes these conclusions. We present
simple analytical models which explain qualitatively all the features we see in
the simulations.Comment: 15 pages, 15 figures, 4 tables, moderate revision, added results on
anisotropies in the power spectra arising from the light cone effect and a
discussion on the foreground subtraction effect. MNRAS (in press
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