M. Lpez-Caniego Cavendish Laboratory University of Cambridge Detection of Point Sources in Maps of...

M. López-Caniego

Cavendish LaboratoryUniversity of Cambridge

Detection of Point Sources in Maps of the Cosmic Microwave Background Radiation

using Linear Filters

Outline

M. López-Caniego Cavendish Laboratory University of Cambridge

Introduction

Study the performance of three different filters detecting point sourcesat the 9 Planck frequency channels:

Matched Filter Mexican Hat Wavelet Mexican Hat Wavelet 2

Application of these results to WMAP data:

.- WMAP 3yr Non-Blind Analysis: NEWPS Catalogue of 380 PS

.- WMAP 5yr Blind + Non-Blind Analysis: NEWPS-5yr Catalague 516 PS

Detection of SZ clusters using the Matched Multifilter Conclusions

INTRODUCTION


INTRO

INTRODUCTION


INTRO

One of the main objectives of Planck will be to produce a map of the Cosmic Microwave Background radiation (CMB), a relic radiation from the Big Bang that was produced when the Universe was only 350.000 years old. In particular, we are interested in the so-called anisotropies of the CMB, fluctuations of 1 part in a million from the mean temperature field of 2.73 Kelvin.

The detection of extragalactic point sources in maps of the Cosmic Microwave Background is very important:

• Our knowledge of the populations of galaxies at frequencies >5 GHz is very poor. In particular, in the range of frequencies observed by Planck.

• The resolved and unresolved point sources contaminate the data and we need to do something with them (mask, substract,calibrate the effect etc).

When Planck is launched and starts sending data, it will yield a wealth of information about EPS, but untill then we have to work with the best all-sky available data, WMAP.

Several methods to detect point sources have been proposed:

.- Bayesian methods

.- Linear filters (Matched Filters, Mexican Hat Wavelets 1 & 2, Scale Adaptive…)

.- Combination of Linear Filters + Bayesian Detectors

We are comparing some these methods with realistic Planck Simulations within thePlanck WG2 and CSI (Cambridge-Santander-IPAC (Caltech)) collaboration (G. Rocha)

INTRODUCTION


INTRO

Comparison of filters for the detection of point sourceson Planck Simulations


Comparison of filters for the detection of point sources in Planck simulationsLópez-Caniego, M.; Herranz, D.; González-Nuevo, J.; Sanz, J. L.; Barreiro, R. B.; Vielva, P.; Argüeso, F.; Toffolatti, L..2006, MNRAS, 370, 2047L

INTRO PLANCK SIMULATIONS

The Simulations: Freq (GHz) # Im Size FWHM (‘) Pix Size (‘)

30 145 128x128 33.0 6.0’

44 145 128x128 24.0 6.0

70 145 256x256 14.0 3.0

100 145 256x256 9.5 3.0

143 145 512x512 7.1 1.5

217 145 512x512 5.0 1.5

353 145 512x512 5.0 1.5

545 145 512x512 5.0 1.5

857 145 512x512 5.0 1.5



Simulations: Galactic components and SZ Clusters (Reference Sky)

1. Thermal Dust 2. Synchrotron

3. Free-Free 4. SZ Clusters



Simulations: Foregrounds patch extraction70 GHz Foregrounds map

We obtained 12 patches that will be used in the simulations



Simulations: noise reduction and large scale structure removal

+ =

=



A) The Matched Filter

Filters: Matched Filter & Wavelets



B) The Mexican Hat Wavelet FamilyMHW and MHW2 (1st / 2nd order Laplacian of the Gaussian)

Gaussian, MHW, MHW2 & CMHW in Real and Fourier space:

Filters: Comparison of the MHW1 and MHW2 with the MF



Filters: Ringing effects with the Matched FIlterFilters: Ringing effects MF vs. MWH2


• Theoretically the matched filter is optimal (among the class of linear filters) in the sense of signal-to-noise ratio amplification

• In practice, implementation issues degrade the performance


Another example of dramatic border effects introduced by the a very bright source in the edge of the patch after being filtered with a Matched Filter.

Further work need to be done to improve the estimation of the P(k).

Filters: Ringing effects with the Matched FIlterFilters: Ringing effects MF vs. MWH2



Results



• We have compared the performance of three filters (MHW1, MHW2, MF) when dealing with the detection of point sources in maps of the CMB.

• We have performed 145 simulations (area: half sky) with the characteristics of the 9 Planck frequencies.

• We have found that the MHW2 and the MF outperform the MHW1 in several aspects.

• The MHW2 is comparable to the MF in almost every aspect.

• The “problematics” with the MF in the plane and in particular on the sphere make this result a very important one. One can deal with most of these problematics on a one-by-one approach.



Conclusions:

A new radio source catalogue obtained with the MHW2 from the three-year WMAP data


Non-blind Catalog of Extragalactic Point Sources from the Wilkinson Microwave Anisotropy Probe (WMAP) First 3 Year Survey Data. López-Caniego, M.; González-Nuevo, J.; Herranz, D.; Massardi, M.; Sanz, J. Luis; De Zotti, G.; Toffolatti, L.; Argüeso, F. ApJS, 2007, Volume 170, Issue 1, pp. 108-125.

Blind and Non-Blind source detection in WMAP 5-year mapsMassardi, M.; López-Caniego, M.; González-Nuevo, J.; Herranz, D.; De Zotti, G.; Sanz, J. L.; Submited to MNRAS.

INTRO PLANCK SIMULATIONS WMAP-3yr NON-BLIND

What are the advantages/disadvantanges of a BLIND and NON-BLIND search:

NON-BLIND:- The position of the object is known, and only the flux must be estimated.- Better estimation of the noise in the vicinity of the source- Catalogues produced in this way may be easily be incomplete, depending on the selection criterion used to construct them:

– surveys at other frequencies (mostly low frequency).– different angular resolution.– variability, observation at different epochs– Low freq surveys may miss strong inverted sources.– High resolution experiments may miss extended sources, etc.

BLIND:2 additional parameters for the source position must be found, and below a certain flux level the number false objects that appear as point sources increases rapidly, affecting the reliability.

Two complementary approaches : BLIND or NON-BLIND



WMAP Team has produced 3 catalogues of point sources:– (WMAP1) 1 year data: detected 208 sources (Bennett C. L., et al., 2003, ApJS, 148, 97).

– (WMAP3) 3 years data: detected 323 sources (Hinshaw et al. ApJS 170, 228-334, 2007)

– (WMAP5) 5 years data: detected 390 sources (Wright et al. 2008 ApJS submited).

Nie & Zhang 2007: clean the 1st year maps and look for sources in the residual maps. 101 sources, 26 (25) of them new to WMAP1 (WMAP3).

Chen & Wright 2008: combine the 61 and 94 maps to cancel the CMB, detected 31 (64 in 3 yrs data) sources, 21 of them new to WMAP3.

Wright 2008: using the same method as before, detected 99 sources outside |b|>10, 64 in WMAP5, 17 new, 17 Galactic and 1 unidentified object.

Some recent BLIND works detecting Point Sources in WMAP:



Recent NON-BLIND works detecting Point Sources in WMAP:

Lopez-Caniego et al. 2007: NEWPS catalogue using WMAP 3 year data


Our NON-BLIND approach in the WMAP 3 year data:




• Non-blind: positions of known sources observed at low frequency surveys.




A complete sample at 5 GHz is generated from other catalogues:

1,980,491 sources at 5 GHz with positions and fluxes above ~5 mJy and spectral indexes

A subsample of 4050 objects with flux > 500 mJy 5 GHz is selected as our Initial Catalogue (IC)






• Local approach: filters that are specific for the statistical properties of the neighbourhood of the sources




Filtering with the MHW2 at the optimal scale for each flat patch








• Better beam modelling: symmetrized radial beam profiles instead of idealized Gaussian beams




http://lambda.gsfc.nasa.gov/product/map/current/m_images.cfm

WMAP 3rd year symmetrized radial beam profiles








• Better beam modelling: symmetrized radial beam profiles instead of idealized Gaussian beams

• Selection criterion: in order to obtain complete sample of extragalactic point sources down to a fixed flux detection threshold




For each position in the initial catalog:

* A flat patch centered at such position is obtained

* Each patch is filtered with the MHW2:

Determination of the optimal scale maximum amplification

minimum variance

* Local noise estimation in a corona around the center of the patch

* Look for peaks above a certain SNR

* Estimate the flux density of these peaks

NEWPS 3yr Non-Blind: Local filtering and noise estimation



(4050 Obj.) Initial Catalogue

WMAP 3yr 323 obj Catalogue

25 Missed Objs.

297Common Objs.

WMAP

11 5 dets. out 2514 non det. 5 Objs.

258 Common 5 dets.39 non detected 5

If, for example, we look at the 23 GHz 5SubCatalogue (SC)

80 new 5 detected objectsfrom IC in WMAP

Total: 349 (80+258+11) 5 at 23 GHz


The NEWPS 3yr source catalogue: Summary of the results


The NEWPS 3yr source catalogue: Summary of the results

• Galactic cut | b | < 5 deg & LMC (5 deg).

• Bright Galactic objects outside the previously introduced cut are removed.

Why?: Sources in the WMAP catalogues are not 5 at all frequencies: 5 in at least one and at least >2 in the other

NEWPS5: all sources are 5


98 NEW 5SOURCES


One Step further: NEWPS 5yr Blind + Non-Blind Approach

Combine the power of both techniques, the Blind and Non-Blind approach.

Divide the sky into flat patchesFilter with the MHW2 Detect objetcs SNR > 5 and estimate SMake histogram of the fluxes of sourcesFlag area around 5% brightest sourcesFlag a border around the patchEstimate noise from unflagged pixels

Using a list of known positions:For every object, a patch centered in this posiiton is obtainedFilter with the MHW2 Detect objetcs SNR > 5 and estimate SMake histogram of the fluxes of sourcesFlag area around 5% brightest sourcesFlag a border around the patchEstimate noise from unflagged pixelsONLY in a CORONA around the object


INTRO PLANCK SIMULATIONS WMAP-3yr NON-BLIND WMAP-5yr BLIND+NON-BLIND

Simple Blind Detection (SB): Non-Blind Detection (NB)

We have used the BSS (Massardi et al. 2008) to study the flux estimation, completeness and reliability of our blind+non-blind approach, in WMAP 5 year data in the same area covered by AT20G.

The BSS: Bright Source Sample is a subsample of 320 objects observed by Australian Telescope 20 GHz Survey (AT20G), 294 of them with |b|>5° and <-15°, (194 S>1 Jy).

It is a complete sample down to S20=0.5 Jy, and the observations are contemporary to WMAP.

Results from the comparison at 23 GHz channel with SNR > 5:

125140 (114) # detected BSS obj (common to NB)

41 (15+9+17)

SB

-New sources

NB


The BSS: testing the Blind + Non-Blind Approach


Error in the estimation of the flux: good agreement above aprox. 840mJy


The Bright Source Sample: Flux density estimation


Systematic overestimation of the fluxes in WMAP databelow 840 mJy.

840 mJy


The Bright Source Sample: Reliability

Simple Blind: 41 new ps not in BSS: 15 extragalactic 9 Galactic

17 no counterpart (14 |b|<20 deg)


A cut of |b| > 10 deg will remove most of the contaminated regions, but some valuable regions as well.

The usual |b|>5 deg cut is a better compromise between removing contaminated regions and preserving clean ones.

We have produced a noise map at 23 GHz corresponding to HEALPix nside=32 using the noise estimations of the individual sources in the SB.

We can make a “noise mask”, removing the |b|<5 deg regions. The median of the remaining pixels outside this cut is <>= 169 mJy.




We can make a “noise mask”, removing the |b|<5 deg regions. The median of the remaining pixels outside this cut is <>= 169 mJy.

|b|<5°

Dropping areas with > 1.5 median = 253 mJy at 23 GHz removes 17 Objects, 9 of which where doubtful. If the remaining 8 objects where actually spurious, the sample reliability will be 95.5%.







Threshold at1.5<>= 253 mJy

Considering only SB detections, the completeness is 89% above 1 Jy.

Considering the combination of the SB+NB, increases to 91%.

Taking these results into account, we propose a recipe to do the PS Detection in the full-sky maps of WMAP 5yr.


The Bright Source Sample: Completeness


Blind and Non-Blind detection in WMAP 5-year data: Recipe

The analysis of the BSS provides a recipe to study the WMAP 5yr and to update NEWPS-3yr to NEWPS-5yr catalogue

– Carry out a Simple Blind detection over the full sky maps

– Generate noise maps of the mean noise values per pixel for nside=32 (pixel) and compute the median excluding the |b|<5 deg (median).

– Generate a mask with all the pixels with noise level > 1.5 median

– Consider all the sources outside the mask and SNR > 5 as true detections.

– Carry out a Non-Blind search on the maps at the positions of the NEWPS-3yr-3 sample.

- Combine results from both methods



Areas with pixel > 1.5 median have been excluded.

516 different sources: 480 EPS, 20 GS, 16 unidentified - at least 96.9% reliable

In the region covered by NEWPS, WMAP has 388 PS: 356 SNR >5 and 32 SNR < 5

NEWPS-5yr has 164 new sources not in WMAP-5yr: from em, only 16 may be false

We recover the 64 objects of Chen & Wright (08) and the objects by Nie & Zhang (07)

Summary of the properties of the NEWPS-5yr 5 catalogue




NEWPS-5yr Number Counts


We have studied the efficiency in source detection and flux density estimation of a Blind+Non-Blind approach based on the MHW2 applied on WMAP 5yr.

Using the ATC20G Bright Source Sample (Massardi et al. 2008) we have beenable to estimate the completeness, reliability and accuracy of the flux densityDetermination for the samples obtained with the blind and the non-blind approach.

The flux density are unbiased down to 840 mJy where we overestimate theFluxes (a manfestation of the Eddington bias). This will affect the number counts,but it can be corrected using high resolution surveys that go below WMAPdetection limit, AT20G (Massardi 08, Ricci 04) and 9C (Waldram, 03).

At higher flux density, most candidates to be spurious are low Galactic |b|<20 deg.

Excluding objects in contaminated areas ( > 1.5 median outside |b|>5) the numberof dubious objects reduces by half. If all of them are spurious, reliability 95.5%


Conclusions


In the full-sky study:

Blind finds 488 sources (|b|>5, noise > 1.5 median)Non-Blind finds 28 additinal sources

Total: 516 (480+20+16 ) sources with SNR > 5 compared with the 388 objects in the WMAP-5yr catalogue.

From the 516, since only 16 of them are dubious, then the reliability at least 96.9%.

Conclusions



Planck expects to detect aproximately 2500-3000 clusters of galaxies in 2/3 of the sky.The SZ effect induces a characteristic spectral distortion in the CMB produced by inverse Compton scattering of CMB photons during their passage through hot ionized gas, mainly in the inner regions of clusters of galaxies.

Detection of Sunyaev Zel’dovich clusters on flat patches:


INTRO PLANCK SIMULATIONS WMAP-3yr NON-BLIND WMAP-5yr BLIND+NON-BLIND SZ CONCLUSIONS

The Matched Multifilter

This filter works with 9 patches of the sky centered in the same position, producing a weighted sum (taking into account the frequency dependance) of the 9 patches. Then the code looks for candidates above a certain SNR producing a list of objects to be analysed.

Then, each of the candidates is analized individually in an iterative procedure trying to estimate its size.

This code is being used to detect clusters in Planck simulations produced at the full Planck resolution.



Herranz et al., 2002, MNRAS,Vol 336, 1057-1068




Weighted sum of the previous nine patches taking into account thefrequency dependence of the SZ in the filtering and weighting process


In these works we have approached the problem of point source detection in maps of the Cosmic Microwave Background using linear filters :

• We have tested the MHW1 and MHW2 against the MF in realistic simulations for the 9 Planck frequencies (the Planck Reference Sky and PS based on the lates models)

• The MHW2 at the optimal scale is comparable to the MF but easier to implement.

• We have used the MHW2 in real data from WMAP to construct a new catalogue of extragalactic point sources to complement WMAP result.

• This was a non-blind approach with initial catalogue of 4050 objects already observed at 5 GHz.

• Estimated their flux at the WMAP frequencies.

• Constructed a 3 and 5 subcatalogues of objects, 25% of them not included in WMAP


Final Conclusions and General Remarks for Planck


Final Conclusions and General Remarks for Planck

Using the WMAP 5-years data we have combined the power of a blind + non-blind approach to create a new catalogue of point sources.

The result of this combination is a catalogue with 500 sources SNR > 5, 164 of them are new to WMAP 5yr catalogue. A similar strategy could be used for Planck.

These studies are preparatory work for Planck.

We have shown that the MWH2 code is performing well, we have installed it in the LFI and HFI DPCs and we are now in the process of installing it in the ERCSC pipeline.

There is room for improvement in the high Planck frequencies



M. Lpez-Caniego Cavendish Laboratory University of Cambridge Detection of Point Sources in Maps of...

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