22 research outputs found
Joint constraints on galaxy bias and through the N-pdf of the galaxy number density
We present a full description of the N-probability density function of the
galaxy number density fluctuations. This N-pdf is given in terms, on the one
hand, of the cold dark matter correlations and, on the other hand, of the
galaxy bias parameter. The method relies on the assumption commonly adopted
that the dark matter density fluctuations follow a local non-linear
transformation of the initial energy density perturbations. The N-pdf of the
galaxy number density fluctuations allows for an optimal estimation of the bias
parameter (e.g., via maximum-likelihood estimation, or Bayesian inference if
there exists any a priori information on the bias parameter), and of those
parameters defining the dark matter correlations, in particular its amplitude
(). It also provides the proper framework to perform model selection
between two competitive hypotheses. The parameters estimation capabilities of
the N-pdf are proved by SDSS-like simulations (both ideal log-normal
simulations and mocks obtained from Las Damas simulations), showing that our
estimator is unbiased. We apply our formalism to the 7th release of the SDSS
main sample (for a volume-limited subset with absolute magnitudes ). We obtain and , for galaxy number density fluctuations in cells of a size of
Mpc. Different model selection criteria show that galaxy biasing is
clearly favoured.Comment: 25 pages, 9 figures, 2 tables. v2: Substantial revision, adding the
joint constraints with \sigma_8 and testing with Las Damas mocks. Matches
version accepted for publication in JCA
Isotropic Wavelets: a Powerful Tool to Extract Point Sources from CMB Maps
It is the aim of this paper to introduce the use of isotropic wavelets to
detect and determine the flux of point sources appearing in CMB maps. The most
suited wavelet to detect point sources filtered with a Gaussian beam is the
Mexican Hat. An analytical expression of the wavelet coefficient obtained in
the presence of a point source is provided and used in the detection and flux
estimation methods presented. For illustration the method is applied to two
simulations (assuming Planck Mission characteristics) dominated by CMB (100
GHz) and dust (857 GHz) as these will be the two signals dominating at low and
high frequency respectively in the Planck channels. We are able to detect
bright sources above 1.58 Jy at 857 GHz (82% of all sources) and above 0.36 Jy
at 100 GHz (100% of all) with errors in the flux estimation below 25%. The main
advantage of this method is that nothing has to be assumed about the underlying
field, i.e. about the nature and properties of the signal plus noise present in
the maps. This is not the case in the detection method presented by Tegmark and
Oliveira-Costa 1998. Both methods are compared producing similar results.Comment: 6 pages. Accepted for publication in MNRA
Point Source Detection using the Spherical Mexican Hat Wavelet on simulated all-sky Planck maps
We present an estimation of the point source (PS) catalogue that could be
extracted from the forthcoming ESA Planck mission data. We have applied the
Spherical Mexican Hat Wavelet (SMHW) to simulated all-sky maps that include
CMB, Galactic emission (thermal dust, free-free and synchrotron), thermal
Sunyaev-Zel'dovich effect and PS emission, as well as instrumental white noise.
This work is an extension of the one presented in Vielva et al. (2001a). We
have developed an algorithm focused on a fast local optimal scale
determination, that is crucial to achieve a PS catalogue with a large number of
detections and a low flux limit. An important effort has been also done to
reduce the CPU time processor for spherical harmonic transformation, in order
to perform the PS detection in a reasonable time. The presented algorithm is
able to provide a PS catalogue above fluxes: 0.48 Jy (857 GHz), 0.49 Jy (545
GHz), 0.18 Jy (353 GHz), 0.12 Jy (217 GHz), 0.13 Jy (143 GHz), 0.16 Jy (100 GHz
HFI), 0.19 Jy (100 GHz LFI), 0.24 Jy (70 GHz), 0.25 Jy (44 GHz) and 0.23 Jy (30
GHz). We detect around 27700 PS at the highest frequency Planck channel and
2900 at the 30 GHz one. The completeness level are: 70% (857 GHz), 75% (545
GHz), 70% (353 GHz), 80% (217 GHz), 90% (143 GHz), 85% (100 GHz HFI), 80% (100
GHz LFI), 80% (70 GHz), 85% (44 GHz) and 80% (30 GHz). In addition, we can find
several PS at different channels, allowing the study of the spectral behaviour
and the physical processes acting on them. We also present the basic procedure
to apply the method in maps convolved with asymmetric beams. The algorithm
takes ~ 72 hours for the most CPU time demanding channel (857 GHz) in a Compaq
HPC320 (Alpha EV68 1 GHz processor) and requires 4 GB of RAM memory.Comment: 18 pages, 11 figures, revised version (minor changes). MNRAS
accepted; high quality color figures upon request to the author
A Bayesian non-parametric method to detect clusters in Planck data
We show how one may expect a significant number of SZ detections in future
Planck data without any of the typical assumptions needed in present component
separation methods, such as about the power spectrum or the frequency
dependence of any of the components, circular symmetry or a typical scale for
the clusters. We reduce the background by subtracting an estimate of the point
sources, dust and CMB. The final SZE map is estimated in Fourier space. The
catalogue of returned clusters is complete above flux 200 mJy (353 GHz) while
the lowest flux reached by our method is about 70 mJy (353 GHz). We predict a
large number of detections (about 9000) in 4/5 of the sky. This large number of
SZ detections will allow a robust and consistent analysis of the evolution of
the cluster population with redshift and will have important implications for
determining the best cosmological model.Comment: MNRAS accepted. Major changes made to match accepted version. Colour
figures attached as GIF files. 15 pages and 12 figures. High resolution
colour pictures can be obtained on request from the authors
([email protected]
Cosmological applications of a wavelet analysis on the sphere
The cosmic microwave background (CMB) is a relic radiation of the Big Bang
and as such it contains a wealth of cosmological information. Statistical
analyses of the CMB, in conjunction with other cosmological observables,
represent some of the most powerful techniques available to cosmologists for
placing strong constraints on the cosmological parameters that describe the
origin, content and evolution of the Universe. The last decade has witnessed
the introduction of wavelet analyses in cosmology and, in particular, their
application to the CMB. We review here spherical wavelet analyses of the CMB
that test the standard cosmological concordance model. The assumption that the
temperature anisotropies of the CMB are a realisation of a statistically
isotropic Gaussian random field on the sphere is questioned. Deviations from
both statistical isotropy and Gaussianity are detected in the reviewed works,
suggesting more exotic cosmological models may be required to explain our
Universe. We also review spherical wavelet analyses that independently provide
evidence for dark energy, an exotic component of our Universe of which we know
very little currently. The effectiveness of accounting correctly for the
geometry of the sphere in the wavelet analysis of full-sky CMB data is
demonstrated by the highly significant detections of physical processes and
effects that are made in these reviewed works.Comment: 17 pages, 8 figures; JFAA invited review, in pres
Detection of non-Gaussianity in the WMAP 1-year data using spherical wavelets
A non-Gaussian detection in the WMAP 1-year data is reported. The detection
has been found in the combined Q-V-W map proposed by the WMAP team (Komatsu et
al. 2003) after applying a wavelet technique based on the Spherical Mexican Hat
Wavelet (SMHW). The skewness and the kurtosis of the SMHW coefficients are
calculated at different scales. A non-Gaussian signal is detected at scales of
the SMHW around 4 deg (size in the sky of around 10 deg). The right tail
probability of the detection is approx. 0.4%. In addition, a study of
Gaussianity is performed in each hemisphere. The northern hemisphere is
compatible with Gaussianity, whereas the southern one deviates from Gaussianity
with a right tail probability of approx. 0.1%. Systematics, foregrounds and
uncertainties in the estimation of the cosmological parameters are carefully
studied in order to identify the possible source of non-Gaussianity. The
detected deviation from Gaussianity is not found to be caused by systematic
effects: 1) each one of the Q, V and W receivers shows the same non-Gaussianity
pattern, and 2) several combinations of the different receivers at each
frequency band do not show this non-Gaussian pattern. Similarly, galactic
foregrounds show a negligible contribution to the non-Gaussian detection:
non-Gaussianity is detected in all the WMAP maps and no frequency dependence is
observed. Moreover, the expected foreground contribution to the combined WMAP
map was added to CMB Gaussian simulations showing a behaviour compatible with
the Gaussian model. Influence of uncertainties in the CMB power spectrum
estimation are also quantified. Hence, possible intrinsic temperature
fluctuations (like secondary anisotropies and primordial features) can not be
rejected as the source of this non-Gaussian detection.Comment: 33 pages, 14 figures. Revised to match version accepted for
publication in Ap
Constraints on f_nl and g_nl from the analysis of the N-pdf of the CMB large scale anisotropies
[Abridged] In this paper we explore a local non-linear perturbative model up
to third order as a general characterization of the CMB anisotropies. We focus
our analysis in large scale anisotropies. At these angular scales, the
non-Gaussian description proposed in this work defaults (under certain
conditions) to an approximated local form of the weak non-linear coupling
inflationary model. In particular, quadratic and cubic terms are governed by
the non-linear coupling parameters f_nl and g_nl, respectively. The extension
proposed in this paper allows us to directly constrain these non-linear
parameters. Applying the proposed methodology to WMAP 5-yr data, we obtain -5.6
x 10^5 < g_nl < 6.4 x 10^5, at 95% CL. This result is in agreement with
previous findings obtained for equivalent non-Gaussian models and with
different non-Gaussian estimators. A model selection test is performed,
indicating that a Gaussian model is preferred to the non-Gaussian scenario.
When comparing different non-Gaussian models, we observe that a pure f_nl model
is the most favoured case, and that a pure g_nl model is more likely than a
general non-Gaussian scenario. Finally, we have analyzed the WMAP data in two
independent hemispheres, in particular the ones defined by the dipolar pattern
found by Hoftuft et al. 2009. We show that, whereas g_nl is still compatible
with zero for both hemispheres, it is not the case for f_nl (with a p-value
0.04). However, if anisotropy of the data is assumed, the distance between the
likelihood distributions for each hemisphere is larger than expected from
Gaussian and anisotropic simulations, also for g_nl (with a p-value of 0.001 in
the case of this parameter). This result is an extra evidence for the CMB
asymmetries previously reported in WMAP data.Comment: 15 pages, 9 figures, accepted for publication in MNRAS. Corrections
made to match the final versio
The Mexican Hat Wavelet Family. Application to point source detection in CMB maps
We propose a new detection technique in the plane based on an isotropic
wavelet family. This family is naturally constructed as an extension of the
Gaussian-Mexican Hat Wavelet pair and for that reason we call it the Mexican
Hat Wavelet Family (MHWF). We show the performance of these wavelets when
dealing with the detection of extragalactic point sources in cosmic microwave
background (CMB) maps: a very important issue within the most general problem
of the component separation of the microwave sky. Specifically, flat
two-dimensional simulations of the microwave sky comprising all astrophysical
components plus instrumental noise have been analyzed for the channels at 30,
44 and 70 GHz of the forthcoming ESA's Planck mission Low Frequency Instrument
(LFI). We adopt up-to-date cosmological evolution models of extragalactic
sources able to fit well the new data on high-frequency radio surveys and we
discuss our current results on point source detection by comparing them with
those obtained using the Mexican Hat Wavelet (MHW) technique, which has been
already proven a suitable tool for detecting point sources. By assuming a 5%
reliability level, the first new members of the MHWF, at their ``optimal
scale'', provide three point source catalogues on half of the sky (at galactic
latitude |b|> 30) at 30, 44 and 70 GHz of 639, 387 and 340 extragalactic
sources, respectively. The corresponding flux detection limits are 0.38, 0.45
and 0.47 Jy . By using the same simulated sky patches and at the same
frequencies as before, the MHW at its optimal scale provides 543, 322 and 311
sources with flux detection limits of 0.44, 0.51 and 0.50 Jy, respectively (5%
reliability level). These results show a clear improvement when we use the new
members of the MHWF and, in particular, the MHW2 with respect to the MHW.Comment: 11 pages and 4 figures. Accepted for publication on MNRA