First observation of the thermal Sunyaev-Zel'dovich effect with kinetic inductance detectors

16 Pages·2014·5.57 MB·English

A&A569,A66(2014) Astronomy
DOI:10.1051/0004-6361/201322902 &
(cid:13)c ESO2014 Astrophysics
First observation of the thermal Sunyaev-Zel’dovich
effect with kinetic inductance detectors
R.Adam1,B.Comis1,J.F.Macías-Pérez1,A.Adane2,P.Ade3,P.André4,A.Beelen5,B.Belier6,A.Benoît7,
A.Bideaud3,N.Billot8,N.Boudou7,O.Bourrion1,M.Calvo7,A.Catalano1,G.Coiffard2,A.D’Addabbo7,14,
F.-X.Désert9,S.Doyle3,J.Goupy7,C.Kramer8,S.Leclercq2,J.Martino5,P.Mauskopf3,13,F.Mayet1,
A.Monfardini7,F.Pajot5,E.Pascale3,L.Perotto1,E.Pointecouteau10,11,N.Ponthieu9,V.Revéret4,L.Rodriguez4,
G.Savini12,K.Schuster2,A.Sievers8,C.Tucker3,andR.Zylka2
1 LaboratoiredePhysiqueSubatomiqueetdeCosmologie,UniversitéJosephFourierGrenoble1,CNRS/IN2P3,
InstitutPolytechniquedeGrenoble,53ruedesMartyrs,38026Grenoble,France
e-mail:[email protected]
2 InstitutdeRadioAstronomieMillimétrique(IRAM),38402Grenoble,France
3 AstronomyInstrumentationGroup,UniversityofCardiffCF103XQ,UK
4 LaboratoireAIM,CEA/IRFU,CNRS/INSU,UniversitéParisDiderot,CEA-Saclay,91191Gif-Sur-Yvette,France
5 Institutd’AstrophysiqueSpatiale(IAS),CNRSandUniversitéParisSud,91405Orsay,France
6 Institutd’ÉlectroniqueFondamentale(IEF),UniversitéParisSud,91405Orsay,France
7 InstitutNéel,CNRSandUniversitédeGrenoble,25ruedesMartyrs,38042Grenoble,France
8 InstitutdeRadioAstronomieMillimétrique(IRAM),Granada,Spain
9 InstitutdePlanétologieetd’AstrophysiquedeGrenoble(IPAG),CNRSandUniversitédeGrenoble,38042Grenoble,France
10 Université de Toulouse, UPS-OMP, Institut de Recherche en Astrophysique et Planétologie (IRAP), 31028 Toulouse Cedex 4,
France
11 CNRS,IRAP,9Av.colonelRoche,BP44346,31028ToulouseCedex4,France
12 UniversityCollegeLondon,DepartmentofPhysicsandAstronomy,GowerStreet,LondonWC1E6BT,UK
13 SchoolofEarthandSpaceExplorationandDepartmentofPhysics,ArizonaStateUniversity,Tempe,AZ85287,USA
14 DipartimentodiFisica,SapienzaUniversitàdiRoma,PiazzaleAldoMoro5,00185Roma,Italy
Received23October2013/Accepted1July2014
ABSTRACT
Context.ClustersofgalaxiesprovidevaluableinformationontheevolutionoftheUniverseandlargescalestructures.Recentcluster
observations via the thermal Sunyaev-Zel’dovich (tSZ) effect have proven to be a powerful tool to detect and study them. In this
context,highresolutiontSZobservations(∼tensofarcsec)areofparticularinteresttoprobeintermediateandhighredshiftclusters.
Aims.ObservationsofthetSZeffectwillbecarriedoutwiththemillimeterdual-bandNIKA2camera,basedonkineticinductance
detectors(KIDs)tobeinstalledattheIRAM30-mtelescopein2015.Todemonstratethepotentialofsuchaninstrument,wepresent
tSZobservationswiththeNIKAcameraprototype,consistingoftwoarraysof132and224detectorsthatobserveat140and240GHz
witha18.5and12.5arcsecangularresolution,respectively.
Methods.TheclusterRXJ1347.5-1145wasobservedsimultaneouslyat140and240GHz.Weusedaspectraldecorrelationtechnique
toremovetheatmosphericnoiseandobtainamapoftheclusterat140GHz.Theefficiencyofthisprocedurehasbeencharacterized
throughrealisticsimulationsoftheobservations.
Results.Theobserved140GHzmappresentsadecrementattheclusterpositionconsistentwiththetSZnatureofthesignal.Weused
thismaptostudythepressuredistributionoftheclusterbyfittingagNFWmodeltothedata.Subtractingthismodelfromthemap,
weconfirmthatRXJ1347.5-1145isanongoingmerger,whichconfirmsandcomplementsprevioustSZandX-rayobservations.
Conclusions.Forthefirsttime,wedemonstratethetSZcapabilityofKIDbasedinstruments.TheNIKA2camerawith∼5000detec-
torsanda6.5arcminfieldofviewwillbewell-suitedforin-depthstudiesoftheintraclustermediuminintermediatetohighredshifts,
whichenablesthecharacterizationofrecentlydetectedclustersbythePlancksatellite.
Key words. instrumentation: detectors – techniques: high angular resolution – galaxies: clusters: individual: RX J1347.5-1145 –
galaxies:clusters:intraclustermedium
1. Introduction tracethestellarpopulationsinthemembergalaxies.Theirradio
emission is related to the acceleration of charged particles, and
Galaxy clusters are the largest gravitationally bound objects in thelensingofbackgroundobjectsprovidessurfacemassdensity
the Universe. Their formation strongly depends on the con- measurements from multi-band optical and infrared data. See
tent and the history of the Universe within the framework of Böhringer & Werner (2010); Gal (2006); Oliver et al. (2012);
a bottom-up scenario (e.g., Kravtsov & Borgani 2012), where Feretti et al. (2012); Kneib & Natarajan (2011) for reviews on
there is merging of small clusters to form larger ones. They thedifferentclusterobservables.
areclassicallyprobedusingX-rayproducedviabremsstrahlung The thermal Sunyaev-Zel’dovich (tSZ) effect (Sunyaev &
emission of the electrons in the intracluster medium (ICM) but Zel’dovich1972,1980),whichconsistsoftheinverseCompton
arealsomeasuredintheopticalandinfraredwavelengths,which scatterofcosmicmicrowavebackground(CMB)photonsonhot
ArticlepublishedbyEDPSciences A66,page1of16
A&A569,A66(2014)
electrons in the ICM, can be used as a complementary method thencomparedtootherexperimentsinSect.7.Throughoutthis
toprobegalaxyclusters(seeBirkinshaw1999;Carlstrometal. paper, we assume a flat ΛCDM cosmology according to the
2002,foradetailedreviewonthetSZeffect).Three-dimensional lastest Planck results (Planck Collaboration XVI 2014) with
information on the cluster may be inferred using the character- H0 =67.11kms−1Mpc−1,ΩM =0.3175,andΩΛ =0.6825.
isticdependencesofX-ray(sensitivetotheline-of-sightintegral
of the density squared and the square root of the temperature)
2. PreviousobservationsofRXJ1347.5-1145
and tSZ (sensitive to the integrated pressure along the line-of-
sight)withthepropertiesoftheICM.Thisgivesamoreaccurate The object RX J1347.5-1145 is among the clusters that have
picturethanX-rayortSZalone,especiallyinthecaseofmerg- been intensively observed at several wavelengths and the most
ingsystems(Basuetal.2010).Inaddition,unlikeotherobserva- widelystudiedusingtSZatsub-arcminresolution.Itisamassive
tionalapproaches,thetSZsignalisnotaffectedbycosmological intermediateredshiftgalaxyclusteratz = 0.4516undergoinga
dimming.Onlytheangularsizeoftheobservedclusterdepends mergingevent.
on the distance to the source. High angular resolution tSZ ob- This cluster is the most luminous X-ray cluster of galax-
servations are therefore of particular interest to probe structure ies known to date (e.g. Allen et al. 2002). It was discov-
formationathighredshift. ered in the ROSAT X-ray all-sky survey (Voges et al. 1999)
The resolutions of the main current instruments measur- and has been the object of many studies in X-ray (Schindler
ing the tSZ effect are of the order of the arcmin. It is larger et al. 1995, 1997; Allen et al. 2002; Gitti & Schindler 2004,
than 5 arcmin for the Planck satellite (Planck Collaboration I 2005; Gitti et al. 2007b,a; Ota et al. 2008), optical (Cohen
2014) and about 1 arcmin for the South Pole Telescope (SPT; & Kneib 2002; Verdugo et al. 2012), infrared (Zemcov et al.
Carlstrom et al. 2011) and the Atacama Cosmology Telescope 2007), tSZ (Pointecouteau et al. 1999; Komatsu et al. 1999,
(ACT;Kosowsky2003).Higherresolutioninstruments,suchas 2001; Pointecouteau et al. 2001; Kitayama et al. 2004; Mason
MUSTANG(∼8arcsecresolutionat90GHz;Masonetal.2010; et al. 2010; Korngut et al. 2011; Zemcov et al. 2012; Plagge
Korngut et al. 2011), may suffer from filtering of large-scale et al. 2013), and multiwavelength analysis (Bradacˇ et al. 2008;
structures due to the atmospheric noise removal when observ- Miranda et al. 2008; Johnson et al. 2012). From ROSAT X-ray
ing at a single frequency band. High redshift tSZ observations, observations, this cluster was thought to be a dynamically old
therefore,needanewgenerationofinstruments.TheNewIRAM relaxedcool-coreclusterwithanextremelystrongcoolingflow,
KIDArrays(NIKA)isaprototypeofahigh-resolutioncamera due to its very spherical morphology and peaked X-ray pro-
based on kinetic inductance detectors (KIDs; Day et al. 2003; file (ROSAT; Schindler et al. 1995, 1997). However, high an-
Calvo et al. 2010) in development for millimeter wave astron- gularresolutiontSZobservationshaveprovedRXJ1347.5-1145
omy (Monfardini et al. 2011). It consists of two arrays of 132 to be an ongoing merger due to the measurement of an exten-
and224detectors,whichobserveat140and240GHzwithres- sion toward the southeast (SE) with respect to the X-ray cen-
olutions of 18.5 and 12.5 arcsec, respectively. Due to the char- ter (Pointecouteau et al. 1999; Komatsu et al. 2001; Kitayama
acteristic spectral distortion of the CMB photons induced by etal.2004).ThisillustrateshowtSZandX-ray(andotherwave-
the tSZ effect, NIKA is an ideal instrument for high resolution lengths) observations are complementary. More recent X-ray
tSZ observations. Indeed, the tSZ signal is strongly negative at (Chandra; Allen et al. 2002) and lensing (Miranda et al. 2008)
140GHzandpositivebutclosetozeroat240GHz.TheNIKA observations are consistent with this interpretation and show a
prototypehasalreadybeensuccessfullytestedduringfourobser- cleardetectionoftheSEextension.
vation campaigns (Monfardini et al. 2010, 2011) at the Institut HighresolutiontSZmapsofRXJ1347.5-1145,suchasthe
de Radio Astronomie Millimétrique (IRAM) 30-m telescope at 90 GHz 8 arcsec (smoothed to 10 arcsec) resolution map of
Pico Veleta, Granada, Spain. These observations have demon- MUSTANG (Mason et al. 2010), have confirmed the presence
strated performances comparable to state-of-the-art bolometer of a strong SE extension. It is interpreted as being due to a hot
arraysoperatingatthesewavelengths,suchasGISMO(Staguhn gas that is heated by the merging of a subcluster crossing the
et al. 2008). The final camera, NIKA2, will contain 1000 and main,originallyrelaxed,systemfromthesouthtothenortheast
4000detectorsat140and240GHz,respectively,andshouldbe (NE),whichisperpendiculartotheline-of-sight.TheSEexten-
operationalin2015. sioncoincideswitharadiomini-halo(Gittietal.2007a),which
We report the first observation of a galaxy cluster via the indicatesthepresenceofnon-thermalelectrons,thatunderliesa
tSZ effect here using the NIKA prototype. It has been imaged non-thermalcontributiontothetotalpressure.Opticalobserva-
during the fifth observation campaign of NIKA in November tions have also confirmed this scenario with the detection of a
2012. The targeted source is the massive intermediate redshift massiveellipticalgalaxy,whichislocated20arcsecontheeast
galaxy cluster RXJ1347.5-1145 at z = 0.4516. It has been se- sideoftheX-raycenter,whilethecentralellipticalgalaxyofthe
lected for both its tSZ intensity and angular size with the latter mainclusterremainsattheX-raypeaklocation(Cohen&Kneib
being comparable to the field of view of the NIKA prototype. 2002).
Moreover, RXJ1347.5-1145 is known to be a complex merg- The temperature profile of RX J1347.5-1145 varies from
ingsystemthatweaimatcharacterizingfurtherwithrespectto ∼6 keV in its core to ∼20 keV at 80 arcsec and decreases to
previousworksatscalesintherangeof20to200arcsec. ∼9 keV on the outer part of the cluster (120−300 arcsec form
This paper is organized as follows. In Sect. 2, we give thecore).ThemaximumtemperatureislocatedattheSEexten-
the status of the previous observations of RXJ1347.5-1145. In sion,reachingk T ∼ 25keV(Otaetal.2008).TheComptony
B e
Sect. 3, we provide a brief description of the NIKA camera parameterhasbeenmeasuredtobey (cid:39) 10−3 (Pointecouteau
max
and give an overview of the observations that is carried out etal.1999).
during the November 2012 campaign at the IRAM 30-m tele- The object RX J1347.5-1145 hosts a well-known radio
scope. Section 4 describes the tSZ dedicated data analysis and sourcewithin3arcsecoftheX-raycenterinthecentralelliptical
its validation on simulations is reported in Sect. 5. We present galaxy.Duetothiscontamination,thelocationofthetSZmax-
the map of RXJ1347.5-1145 in Sect. 6 and the results on the imumisstilldebated.Currentsingledishobservationsarecon-
pressure profile for this cluster of galaxies. These results are sistentwiththetSZemissionoftheSEextensionbeingstronger
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R.Adametal.:FirsttSZobservationwithKID
thanthatattheclusterX-raycenter.However,takingadvantage
of the intrinsic point source removal power of interferometric
data,Plaggeetal.(2013)claimthatitisonlyasecondarymax-
imum.ThepointsourcehastobetakenintoaccountinthetSZ
analysis. According to Pointecouteau et al. (2001), the source
follows the spectrum F = (77.8 ± 1.7)ν−0.58±0.01 mJy. For
ν GHz
NIKA, this corresponds to 4.4 ± 0.3 and 3.2 ± 0.2 mJy at
140and240GHz,respectively.
Finally,inadditiontothecentralradiosource,Zemcovetal.
(2007)havereportedthepresenceoftwoinfraredgalaxies.The
first one (Z1 hereafter) is located at about 60 arcsec from the
X-raycenterinthesouthwestdirectionwithafluxof15.1mJy
(as measured with a signal to noise of 5.1) at 850 µm and
125 ± 34 mJy at 450 µm. The second source (Z2 hereafter)
is located closer to the X-ray center at about 20 arcsec on the
northeast side. However, it is only detected at 850 µm with a
flux of 11.4 mJy (measured with a signal to noise of 4.7). The
Fig.1. Elevation (dashed green) and azimuth (solid red) offset scans.
best-fitvalueat450µmis10 ± 32mJy.Thecontaminationof
The center is represented by a black dot and has coordinates
thesesourcesintheNIKAbandsisestimatedandaccountedfor (RA,Dec)=(13h47m32s,−11◦45(cid:48)42(cid:48)(cid:48)).The140GHzarrayisalsorep-
inouranalysis,asdiscussedinSect.4.2.4.
resentedbyblackcrosses,whichcorrespondtothepositionofeachKID
inthefocalplane(gapsinthearraycorrespondtoinvaliddetectors).
3. ObservationswithNIKA
3.1. BriefoverviewoftheNIKAcameraduringthecampaign The KIDs used here are Hilbert dual-polarization designed
ofNovember2012 LEKIDpixels(LumpedElementKID;Doyleetal.2008;Roesch
etal.2012),whicharerealizedon180µmand275µmthickness
TheNIKAcameraconsistsoftwoarraysofKineticInductance
siliconsubstrateat240and140GHz,respectively.Thedetector
Detectors (KIDs) with maximum transmissions at 140 and
resistivity is larger than 5000 Ω cm for both wavelengths. The
240GHz.NinetypercentofthetotaltransmissionoftheNIKA
detectorsarecooleddowntoabout100mKwitha4He−3Hedi-
bandpasses (see Fig. 2) is in the range 127–171 GHz for
lutioncryostat.
140GHzand196–273GHzfor240GHzbands.Therespective
More details on the NIKA prototype setup can be found
angular resolutions (FWHM) are 18.5 and 12.5 arcsec with ef-
fectivefieldsofviewof1.8×1.8and1.0×1.0arcmin.Thepitch inCatalanoetal.(2014).
betweenpixelsis2.3mmat140GHzand1.6mmat240GHz.
Thiscorrespondstoaneffectivefocalplanesamplingof0.77Fλ 3.2. Observingstrategyofthetargetedgalaxyclusters
and 0.8 Fλ at 140 and 240 GHz, respectively. In this particular
campaign, the first band (140 GHz) was used with 127 detec- Galaxy clusters are weak extended sources when seen through
torshavingameaneffectivesensitivityof29mJys1/2 perbeam the tSZ effect, making their observations challenging. For this
(19 mJys1/2 per beam for the best 20% of all pixels), and the study,wehaveselectedRXJ1347.5-1145,whichisaninterme-
secondband(240GHz)had91detectorswithameaneffective diateredshiftclusteratz=0.4516.TheobjectRXJ1347.5-1145
sensitivity of 55 mJys1/2 per beam (37 mJys1/2 per beam for isamongthemostluminoustSZsourcesinthesky,anditisalso
thebest20%ofallpixels).Thisunexpectedpoorsensitivityand compactenoughtohaveanangularsizecomparabletothefield
thesmallnumberofavailabledetectorsforthe240GHzbandis ofviewoftheNIKAcamera.
due to the dysfunction of a cold amplifier during this observa- As shown in Fig. 1, the cluster signal is scan-modulated
tioncampaign.Usingonlyeightdetectorsofthe240GHzarray, but there is no wobbling involved. Raster scans are made of
we obtain the expected mean effective sensitivity measured to constant elevation subscans or constant azimuth subscans. For
be 22 mJys1/2 per beam. Despite the constant improvement in the latter, only the low azimuth part of the field was cov-
sensitivity over the the last campaigns (Monfardini et al. 2010, ered due to an error in the control software. Both of them are
2011; Calvo et al. 2013), the sensitivity of the instrument was 6 min 20s scans that are made of 19 subscans separated by
limitedbydetectorcorrelatednoisecomingfromelectronicand 10arcsecsteps.Scansalongtheazimuthdirectionarecentered
skynoiseresiduals.Fortheaveragedbackgroundduringobser- at(RA,Dec)=(13h47m32s,−11◦45(cid:48)42(cid:48)(cid:48)),whichsamplearect-
vations,theexpectedphotonnoiseis5mJys1/2 at140GHzand angularregionof360 × 180arcsec(azimuth×elevation),while
7mJys1/2at240GHz. scansalong theelevation samplearegion of180 × 180arcsec
Unliketraditionalbolometricinstruments,NIKAusesKIDs. and are centered on a point 90 arcsec away from (13h47m32s,
TheKIDsaresuperconductingresonatorswhoseresonancefre- −11◦45(cid:48)42(cid:48)(cid:48)),whichrotateswiththeparallacticangle.Thescan
quency(∼1−2.5GHz)changeslinearlywiththeabsorbedopti- velocityisabout15arcsecs−1.Thedetailedintegrationtimesare
calpower(seeforexampleSwensonetal.2010).Eachresonator giveninTable1withthecorrespondingatmosphericopacities.
can be modeled by a complex transfer function in frequency
with a real part I (in-phase) and imaginary part Q (quadrature;
3.3. Pointing,calibration,bandpasses,andbeam
Grabovskijetal.2008).BymeasuringIandQataconstantfre-
quency(definedforeachdetectorbytheelectronics)asafunc- Uranusobservationswereusedtoreconstructbeammaps(pro-
tion of time, we can reconstruct the shift of the resonance fre- jectionofthearrayontheskyandmeasureofindividualdetector
quency,asdescribedinCalvoetal.(2013).Thismethodallows beams)forbothwavelenghts.Nearbyquasarswereusedforde-
ustoobtainaccuratephotometrytobebetterthan10%. termining pointing corrections. The pointing root mean square
A66,page3of16
A&A569,A66(2014)
Table1.Meanzenithopacity,on-sourceintegrationtime,andperiodofthedayforthethreedaysofthecampaignofNovember2012.
Nov.21st Nov.22nd Nov.23rd
τ 0.14 0.18 0.053
140GHz
τ 0.17 0.22 0.046
240GHz
Timerange 8:27amto11:43am 8:16amto12:01pm 8:11amto10:59am
Integrationtime 2h29min 3h00min 2h29min
Unflaggedintegrationtime 50min 2h35min 2h23min
Notes.Thetotalintegrationtimeis5h47min.Themeanopacityratioisτ /τ (cid:39) 1.2.
240GHz 140GHz
Table2.MaincontributionstotheabsoluteerroroftheNIKAdatafor
the140GHzband.
Systematicuncertainty Errorpercentage
Brightnesstemperaturemodel 5%
Pointsourcecalibration 15%
Secondarybeamsfraction 45%±10%
Bandpasses 2%
180arcsec,andfindanoverallfactorequalto1.45(seeCatalano
etal.2014,foramoredetaileddescription).Fromthedispersion
over different observations of Uranus, we estimate the uncer-
taintiesonthesolidangleofthemainbeamtobeabout4%.We
obtain 10% uncertainties for the full beam by also considering
uncertaintiesonthesidelobes.
The sky maps (also for Uranus maps prior to calibration)
Fig.2. Normalized 140 GHz (solid red line) and 240 GHz (solid or- are corrected for atmospheric absorption using elevation scans,
angeline)instrumentalbandpasses.Thetotalatmospherictransmission or skydips (see Catalano et al. 2014, for further details). In our
isalsogivenasasolidgreenlinefor1mmofprecipitablewatervapor, case, the resonance frequencies of the detectors are measured
according to the Pardo model (Pardo et al. 2002). The oxygen (dash-
versus the optical load, which depends on the zenith opacity
dottedlightblue)andthewatervapor(dasheddarkblue)contributions
andtheelevation.Thisgivesthezenithopacityasafunctionof
arerepresented.
theresonancefrequencyofthedetectors,whichismeasuredfor
each scan. The opacity can then be corrected to good accuracy
by accounting for the air mass at the elevation of the source.
errorisestimatedtobe∼3arcsec(Catalanoetal.2014).Thisis Furthermore, different atmospheric conditions lead to changes
small compared to the beam and has a negligible impact in the in the beam pattern of the instrument that also affect the abso-
caseofextendedsourcessuchasRXJ1347.5-1145.
lute calibration accuracy (Catalano et al. 2014). From the dis-
WealsousedUranusforabsolutepointsourcefluxcalibra- persion of the recovered flux of Uranus, which was observed
tion. The flux of the planet was inferred from a frequency de- several times with different opacities during the campaign, we
pendent model of the planet brightness temperature taken from estimate an overall accuracy of 15% (Catalano et al. 2014) for
Moreno (2010). The Uranus brightness temperatures are typi- thecalibrationprocedure.
cally 113 K at 140 GHz and 94 K at 240 GHz. This model is
To summarize, the list of the main systematic uncertainties
integratedovertheNIKAbandpassesforeachchannel,anditis
in the 140 GHz band are listed in Table 2. The total calibra-
assumedtobeaccurateatthe5%level.Thefinalabsolutecali-
tionuncertaintyonthefinaldataatthemaplevelisestimatedto
brationfactorisobtainedbyfittingtheamplitudeofaGaussian
be16%.
function of fixed angular size on the reconstructed maps of
Uranus (representing the main beam). We neglect the angular
diameterofUranus,3.54arcsecatthetimeoftheobservations,
4. ThermalSunyaev-Zel’dovichdedicateddata
when it is compared to the size of the main beam, since the
analysisandmapmaking
convolution of the corresponding disk with a Gaussian of 12.5
and18.5arcsecfullwidthathalfmaximum(FWHM)broadens 4.1. ThermalSunyaev-Zel’dovichdata
our beam by only 0.17 arcsec at 240 GHz and 0.12 arcsec at
140GHz. Inthenon-relativisticlimit,thetSZeffectresultsinadistortion
oftheCMBblack-bodyspectrum,whoseintensityfrequencyde-
Scaleslargerthan180arcsec,whichcorrespondtothescan
pendenceisgivenby(Birkinshaw1999)
size,werenotmeasuredwithNIKA.ByintegratingtheUranus
fluxupto100arcsec,weobservethatthetotalsolidanglecov-
x4ex (cid:18) (cid:18)x(cid:19)(cid:19)
ered by the beam, which includes the power in the side lobes, g(x)=− 4−xcoth , (1)
is larger than the Gaussian best-fit of the main beam by a fac- (ex−1)2 2
tor of 1.32. Scales larger than 100 arcsec are noise dominated
on the Uranus map. Thus, using recent measurements of the wherex= hν isthedimensionlessfrequency;histhePlanck
kBTCMB
IRAM30-meterbeampatternwithEMIR(Krameretal.2013), constant,k theBoltzmannconstant,νtheobservationfrequency
B
weextrapolatetheangularprofileofthebeamfrom100arcsecto and T the temperature of the CMB. The induced change in
CMB
A66,page4of16
R.Adametal.:FirsttSZobservationwithKID
intensityrelativetoprimaryCMBintensityI reads 4.2. Timeordereddataanalysis
0
δI Themainstepsforprocessingthetimeordereddata(TOD)are
tSZ =yg(x), (2)
I listedbelow.
0
whereyistheComptonparameter.Thelattermeasurestheinte- – Loading raw data, including the telescope parameters, the
gratedelectronicpressureP alongtheline-of-sight reconstructionoftheprojectionofthearrayonthesky,and
e
theatmosphericopacity.
(cid:90)
σ
y= T P dl. (3) – CalibratingtheTOD,includingopacitycorrection.
m c2 e – Flagginginvaliddetectors.
e
– Flaggingcosmicrayimpactsonthedetectors.
Theparameterσ istheThomsoncrosssection,m istheelec-
T e – Decorrelatingatmosphericandelectronicnoise.
tron mass, and c the speed of light. The tSZ spectral distortion
– Filtering low frequencies and removing lines produced by
is null at 217 GHz, negative below this frequency, and positive
thepulsetubeofthecryostatwithanotchfilter.
above.
– Makingmapusinginversevarianceweighting.
The unit conversion coefficients between Jy/beam and
Compton parameter y are −11.8 ± 1.2 and +2.2 ± 0.6 at 140 In the following, we give details on specific points of the
and 240 GHz, respectively, for the NIKA prototype. These co- analysis.
efficientsarecomputedbytakingtheoveralltransmissionofthe
instrumentandthemeasuredtotalbeamwiththeirrespectiveer-
4.2.1. Rawdata
rorsintoaccount.TheComptonparameteryisfirstconvertedto
Jy/srusingEq.(2)andthenconvertedtoJy/beamusingthean- TherawTODcorrespondtothereal(I (t),in-phase)andimagi-
k
gular coverage of the beam. We assume a pure non-relativistic nary(Q (t),quadrature)partsofthetransferfunctionofthesys-
k
tSZspectrum. tem(arrayandtransmissionline),whicharesampledonprede-
As the expected tSZ signal is small (up to ∼10 mJy/beam), finedfrequencytonesk atanacquisitionrateof23.842Hz.We
theNIKArawdataaredominatedbyinstrumentalnoiseandat- alsocomputetheaveragemodulationofthesequantitieswithre-
mosphericemission.WemodelthesignalmeasuredbyaKIDk, specttotheinjectedfrequency(typicallyafewkHz),whichare
whichoperatesattheobservingfrequencybandνb (140GHzor notedδIk(t)andδQk(t).Thesefourquantitiesareusedtorecon-
240GHz)as structtheshiftoftheresonancefrequencyδf (t),whichprobes
0k
d (ν ,t)=S (ν ,t)+N (t)+E(ν ,t)+A(ν ,t). (4) theopticalpowerabsorbedbyadetector(seeCalvoetal.2013,
k b k b k b b for more details). To monitor the electronic noise and possible
The astrophysical signal (essentially tSZ) S (ν ,t) is time- variations of the transfer function of the transmission line, the
k b
dependentthroughthescanningstrategy.Furthermore,itvaries latter is also sampled with tones that are placed off-resonance
withthefrequencyband(Eq.(2))andwiththedetectorkbecause (withnocorrespondencetoanydetector),whichareinsensitive
ofitslocationinthefocalplane.ThevariableN (t)istheuncor- toopticalpower.
k
relateddetectornoiselimitingthesensitivitiesgiveninSect.3.1. InthecaseoftheNIKAprototype,somedetectorsaresub-
Thecorrelatedelectronicnoise,E(ν ,t),iswellcharacterizedby ject to cross talk and are not used for this analysis. Bad detec-
b
an identical common-mode for the detectors of the same band tors are also flagged on the basis of the statistical properties of
(Bourrionetal.2011).Asweuseindependentreadoutelectron- theirnoise.Inparticular,weuseskewnessandkurtosistests,in
ics for the two bands, the electronic noise is uncorrelated be- addition to testing the stationarity of the noise. Some TODs,
tweenbands.Finally,bysplittingthefrequencyandtimedepen- which are affected by baseline jumps due to the coupling with
dance,theatmosphericcontributioncanbemodeledas ambient magnetic fields, are also excluded. These rejected de-
tectors are not used in the following. For the observations of
A(νb,t)=aeHl2O(νb)AeHl2O(t) + aeOl2(νb)AeOl2(t) RXJ1347.5-1145, the number of detectors used in the analysis
+afluc (ν )Afluc (t). (5) is81at140GHzand45at240GHz.
H2O b H2O
Thefirstandthesecondtermsgivetheemissionchangeofwater
4.2.2. Calibration
vapor and oxygen due to the variation of the airmass with the
elevation. The third term, afluc (ν ) Afluc (t), gives the emission Theshiftoftheresonancefrequencyiscomputedforeachdetec-
change due to inhomogeneitHi2eOs inb theHw2Oater vapor distribution. tor. The absolute calibration from resonance frequency to flux
Wenotethataflucisimplicitlysettozerobecauseoftheassump- density is applied to these TODs. The beam is measured with
tion that the oOx2ygen is locally very homogeneous in the atmo- Uranus observations in atmospheric conditions that are simi-
sphere. It is also important to notice that the two bands are not larto thoseforthe RXJ1347.5-1145observations.The Uranus
sensitive to the same atmospheric components. The 140 GHz dataarefittedwithaGaussianfunctionofFWHMthatisequal
band is sensitive to the O 118 GHz line, while the 240 GHz to 12.5 and 18.5 arcsec at 240 and 140 GHz, respectively.
2
bandisalmostonlysensitivetowatervapor(Pardoetal.2002), An opacity correction is performed by multiplying the data by
(cid:0) (cid:1)
such that aaeeOll2((114400GGHHzz)) (cid:29) aaeeOll2((224400GGHHzz)). This can be observed in cexalpcuτlaνbt/iosnin(oefl)th,ewohpearceityelisisbathseedeolenvastkiyodnipofmtehaesusroeumrceen.tsT,haes
Fig.2,wheHr2eOweshowthebHa2OndpassesoftheNIKAprototypein brieflydescribedinSect.3.3(formoredetails,seeCatalanoetal.
red (140 GHz) and orange (240 GHz). The atmospheric trans- 2014).
missionisgivenfortheoxygen(lightbluedash-dottedline)and
water vapor (dark blue dashed line) contributions. The overall
4.2.3. Glitchremoval
atmospherictransmissionisgivenasagreensolidline,accord-
ingtothePardomodel(Pardoetal.2002).Traceconstituentsare Cosmic rays hitting the instrument induce glitches in the data.
neglectedhere(e.g.,ozone). The time response of KIDs is negligible compared to the
A66,page5of16
A&A569,A66(2014)
Fig.3.TOD(left)andtheirpowerspectra(right)foragivendetector.ThedatacorrespondstothecalibratedTODbefore(red)andafter(green)
theelectronicandatmosphericnoisedecorrelation.TheTODaredominatedbytheatmosphericnoiseatlowfrequencies,whichisresponsiblefor
theslowvariationsintheredTODandtheobviousriseofnoisebelow∼1Hzontheredpowerspectrum.Cosmicrayshittingtheinstrumentcan
beseenasspikesintheTODbuthavebeenremovedbeforecomputingthepowerspectra.Pulsetubefrequencylinesappearinthepowerspectrum
(e.g.the∼6Hzlineintherawpowerspectrum)andarenotchfiltered.Theelectronicnoisedominatesatfrequenciesbetween∼1and∼5Hzinthe
powerspectrumbeforedecorrelation.
sampling frequency, such that a cosmic ray impact appears as Wealsobuildatemplatefromahigh-passfilteredcommon-
apeakonasingledatasampleintheTOD.Wedetectaboutfour mode obtained from the TODs of the valid 140 GHz detectors.
glitchesperminute.Theyareremovedfromtheδf (t)TODsby Thishigh-passfilteristhecomplementtothepreviouslow-pass
0k
flaggingpeaksthatareabovefivetimesthestandarddeviationof filter such that their sum is equal to one for all frequencies.
theconsideredTOD.TheTODsareflaggedandinterpolatedat We linearly fit this template to each subscan of each 140 GHz
theglitchlocationsinordernottoaffectthedecorrelation.These detector TOD and remove it. As a consequence the correlated
flaggeddataarenotprojectedontomaps. electronicnoise,E(140GHz,t)isremovedatfrequencieslarger
thanthecutoff.Wenotethatthisdoesnotsignificantlyaffectthe
tSZsignalbecauseitisnotcorrelatedatthesehighfrequencies
4.2.4. Dual-banddecorrelation betweendetectorsastheyobservedifferentpositionsonthesky.
Typically,2Hzcorrespondstoabout8arcsecforthechosenscan
As discussed above the atmospheric contribution to the NIKA
speed(about15arcsecpersecond).
data, A(ν ,t), is essentially due to water vapor, to first order.
b
Therefore, it is expected to be the same for the two frequency Finally, we fit and remove a template that follows the ele-
bandsuptoanamplitudefactorA(240GHz, t)/A(140GHz, t)(cid:39) vation of the telescope from the TODs. Indeed, as the oxygen
5.Asaconsequence,wefirstusethe240GHzdatatobuildan componentoftheatmosphereisignoredinthedual-banddecor-
atmospheric template and remove it from the 140 GHz data by relation,itappearsasaresidualproportionaltotheelevationof
linearfitting.Thefitisperformedforeachsubscanandforeach thetelescope.
140GHzdetectorindependently.AsthetSZsignalat240GHz Themaindrawbackofthedual-banddecorrelationtechnique
issmallerbyafactorof5.5(seeunitconversionfactorsbetween isthepossiblecontaminationofthe140GHztSZreconstructed
Compton parameter and Jansky per beam in Sect. 4.1) with re- signal by other astrophysical components present at 240 GHz.
spect to the one at the 140 GHz band, the positive bias intro- First, we consider the kinematic Sunyaev-Zel’dovich (kSZ) ef-
ducedinthe140GHzdatabythetSZsignalpresentat240GHz fect,whichisduetotheoverallmotionofacluster(oritscom-
isnegligible(about27timessmaller). ponents)withrespecttotheCMBreferenceframeandfollowsa
As shown in the left panel of Fig. 3, where we present the pureblack-bodyspectrumattheCMBtemperature.ThekSZsig-
raw TOI signal for a typical KID at 140 GHz in red, the at- nalisalsoreducedbyafactorof∼5,suchthatitsfluxat240GHz
mospheric contribution is dominated by a low frequency com- should be larger than half the tSZ flux at 140 GHz to produce
ponent. These drifts correspond to the 1/f noise-like spectrum a non-negligible bias. This is not the case even for the most
with a knee frequency at about 1 Hz, which is presented in red extreme clusters, such as MACSJ0717.5+3745 (Mroczkowski
ontherightpanelofthefigure.Wethusapplyalow-passfilter etal.2012;Sayersetal.2013).Therefore,anykSZsignalpresent
to the atmospheric template that is deduced from the 240 GHz at240GHzisneglectedinthefollowinganalysis.
channel.Thisfilterremovesmostofthedetectorcorrelatedelec- We have also searched for dusty galaxies within the clus-
tronicnoiseinthe240GHzband,E(240GHz,t),whichdoesnot ter or gravitationally lensed submilimeter high-redshift back-
affectthe140GHzdata.Furthermore,itallowsustoreducethe ground objects that might also contaminate the signal at 140
intrinsichighnoiselevelofthe240GHzband,whichwasspe- and 240 GHz. As mentioned in Sect. 2, two of such sources
cifictotheNovember2012NIKAdataduetothecoldamplifier arepresentinRXJ1347.5-1145.Despitethehighlevelofnoise
disfunction and would otherwise pollute the 140 GHz cleaned in the 240 GHz NIKA data for this campaign, the first source,
data.Thelow-passfilterdoesnotaffectfrequenciessmallerthan Z1, (RA, Dec) = (13h47m27.6s, –11◦45(cid:48)54(cid:48)(cid:48)) is observed in
1.5Hzandsetsfrequencieslargerthan2Hztozero.Frequencies thisbandwithafluxof12.7mJy±6.2.Thesecondsource,Z2,
between1.5and2Hzareprogressivelyattenuatedusingacosine (RA,Dec)=(13h47m31.3s,–11◦44(cid:48)57(cid:48)(cid:48))isnotdetectedinthe
squaredcutoff. 240 GHz NIKA band, but we obtain an upper limit of 4.4 mJy
A66,page6of16
R.Adametal.:FirsttSZobservationwithKID
at 1σ. Using this information and the measured fluxes at 850 Table3.Valuesoftheparametersusedinthesimulation.
and 450 µm (see Sect. 2), we estimate the expected flux of the
sources at 140 GHz. Assuming dust temperatures in the range Parameter Value
of15−20Kanddustspectralindexesβ intherangeof1.5−2, v 1 m/s
d H2O
weobtain0.85mJyat140GHzfortheZ1source.Forthesec- h 3000 m
H2O
ondsource,Z2,wearenotabletofitatypicaldustspectrumand αH2O –1.35
only compute an upper limit of the flux at 140 GHz by assum- τ140GHz 0.1
τ 0.12
ing a Rayleigh-Jeans spectrum at low frequency and using the (cid:16) 240(cid:17)GHz
240GHzestimatedflux.Weobtainanupperlimitat140GHzof (cid:16)FH2O(cid:17)140GHz 28 Jy/beam
0.65mJy.Inthecontextofdual-banddecorrelation,the240GHz F 110 Jy/beam
fluxes are scaled down by (cid:39)5, and they are diluted by another F H(12O4024G0HGHzz) 14 Jy/beam/K
el
factor of (cid:39)5 due the averaging over all the 240 GHz detectors, F (240GHz) 35 Jy/beam/K
el
which observe the source at different time samples. As uncer- Tatmo 233 K
taintiesontheestimatedfluxforbothsourcesandatbothwave- E0(1Hz,140GHz) 38 mJy/beam
E (1Hz,240GHz) 76 mJy/beam
lengthsarelarge,wechoosenottosubtractthemdirectlyinthe 0
β –0.25
TODbuttoaccountfortheminthefinalanalysis,as discussed
N (140GHz) 29 mJys1/2
inSect.7.5. 0
N (240GHz) 57 mJys1/2
0
R 0.065s−1
g
4.2.5. Fourierfiltering
Notes.Seetextfordetails.
Frequencylines(e.g.at∼6Hz)areinducedbythepulsetubeof
thecryostatandobservedintheTODpowerspectra(seeFig.3,
right panel). They are flagged and set to zero. In addition, we
applyahigh-passfiltertoremovecorrelatednoiseatfrequencies TheparametersusedinthesimulationaregiveninTable3and
lower than the subscan because no tSZ signal is present there. arerepresentativeoftheweatherconditionsfortheobservations
Wealsoremovelowfrequency(below0.05Hz)sineandcosine describedinthispaper.
fromthedatatofurthersubtractcorrelatednoisecontamination.
5.1.1. Atmosphericcontribution
4.3. Mapmaking
The atmospheric contribution A(ν ,t) is simulated as described
b
Finally, we construct surface brightness maps by projecting inSect.4.
and averaging the signal from all KIDs on a pixelized map at The water vapor fluctuations (i.e., afluc × Afluc (t)) are ob-
140GHz.Theprojecteddataareweightedaccordingtothelevel tained by simulating a map of water Hv2aOpor aHn2iOsotropy that
of noise of each detector using inverse variance weighting. To passes in front of the telescope aperture with a speed v
removepossibleoffsetsintheTOD,wesubtractthemeanvalue at an altitude h above the telescope. The power spectrHu2mO
of each TODs, and we take the zero level as the mean of the of this map is aH2pOower law with slope α . The amplitudes
externalpartofthemap,wherenosignalisdetected. of the atmospheric fluctuations are thenHn2oOrmalized to have
a standard deviation over the time of the scan equal to σ =
(cid:16) (cid:16) (cid:17)(cid:17)
F 1−exp − τ ,whereτisthezenithopacity,eltheel-
4.4. Pointsourcesubtraction H2O sin(el)
evation,andF isthereferenceflux.
The object RX J1347.51145 hosts a radio point source lo- H2O
The contribution of the elevation terms, both from H O
2
cated within 3 arcsec of the X-ray center that has a flux of
andO ,issimulatedas
2
4.4 ± 0.3mJyand3.2 ± 0.2mJyat140and240GHz,respec-
(cid:32) (cid:32) (cid:33) (cid:32) (cid:33)(cid:33)
tively(Pointecouteauetal.2001).Thepointsourceissubtracted τ τ
in the TODs at both frequencies before the processing, so that del(t) = FelTatmo exp −sin((cid:104)el(cid:105)) −exp −sin(el) · (6)
itdoesnotbiastheanalysis.WediscussinSect.7.5howuncer-
taintiesonthepointsourcesubtractionaffectthefinalresults. The parameter T is the temperature of the atmosphere, and
atmo
F isareferencefluxthatismeasuredatbothfrequenciesusing
el
5. Validationoftheanalysis skydips.
Wepresenttwoindependentvalidationsoftheanalysispipeline.
Thefirstofthemisbasedonadetailedsimulationoftheobser-
5.1.2. Electronicnoise
vationofatSZclusterwithknownphysicalparametersandtyp-
ical atmospheric and electronic noise. The second one is based The electronic noise E(ν ,t) is simulated as a common mode
b
on the observation of a faint cluster that allow us to show that with a power spectrum slope β and an amplitude E . This
0
the tSZ detection is not an artifact of the data analysis and/or common-modeisidenticalforalldetectorsinagivenfrequency
acquisition. bandbutdiffersforthetwobandssincetheelectronicsisnotthe
same.Thespectrumslopeisthesameforthetwobands,butthe
amplitudeishigherat240GHzthanat140GHz(seeTable3).
5.1. Simulation
To test the pipeline as described in Sect. 4, we simulate the
5.1.3. Uncorrelatednoise
NIKA observations of a cluster and construct the TODs by
takingalltermsofEq.(4)intoaccount,whichincludestheatmo- We also simulate a total uncorrelated noise term, N (t), in-
k
spheric contamination, the electronic noise, and the tSZ signal. dependently for each detector. This term accounts for various
A66,page7of16
A&A569,A66(2014)
white noise contributions, including photon noise, spontaneous Table 4. Generalized Navarro, Frenk, and White parameters used to
Cooperpairbreakingduetothermalnoisefluctuationsandelec- simulatethecompactanddiffuseclusters.
tronicwhitenoise.Forthepurposeofthesimulations,wekeep
thisnoisecontributionindependentoftheobservingconditions. Compactcluster Diffusecluster
However,fortherealobservations,wefindthatthewhitenoise
α 1.2223 1.2223
level is coupled to the atmospheric conditions. This is mainly
β 5.4905 5.4905
duetothebroadeningoftheresonancesforlargeopticalloads,
γ 0.7736 0.7736
and it is not accounted for in the simulations. Similarly, we do r (kpc) 383 800
s
not account for photon noise variations induced by changes in θ (arcmin) 1.1 2.3
s
the optical load. For the sake of simplicity, the total root mean P (keV/cm3) 0.5 0.18
0
square of the uncorrelated noise is assumed to be identical for Bestfitθ (arcmin) 1.048±0.042 2.019±0.075
s
alldetectorsofthesamearray. BestfitP (keV/cm3) 0.449±0.052 0.150±0.010
0
Notes. The choice of the slope parameters is given in Sect. 6.3. The
5.1.4. Glitches lasttwolinesprovidetherecoveredmarginalizedbestfitprofileofthe
simulatedclusters.
GlitchesaresimulatedwitharateR .Theyonlyaffectindividual
g
samplesintheTODs(i.e.,theKIDresponseismuchfasterthan
thesamplingfrequency)andsimultaneouslyaffectallKIDsofa
the same scanning strategy, as in the case of RXJ1347.5-1145
givenarray(i.e.,glitchesareassumedtogeneratephononsthat
observations of NIKA during the Run 5. The focal plane and
hitalltheKIDsofthearray).Theamplitudesoftheglitchesare
thenumberofdetectorsarealsothesame.Theclustersarecen-
generated using a Gaussian spectrum with a standard deviation
teredatthetSZsignalmaximumdecrementthatweobserveon
of1.3Jy/beam,asobservedinthemeasuredTODs.
RXJ1347.5-1145.
5.1.5. Pulsetubelines
5.1.7. Validationofthepipelineonsimulateddata
Tosimulatethefrequencylinesgeneratedbythepulsetube,we
Afterprocessingthesimulateddata,werecoverthetwocluster
add cosine functions to the timeline that correspond to the typ-
maps (compact is labeled C and diffuse is labeled D). Figure 4
icalfrequenciesandamplitudesseeninthedata(seethepower
providestheinputmodelmaps,therecoveredmapsafterthepro-
spectrumoftherawdatainFig.3).
cessing,theresidualbetweentheinputmodelsandtherecovered
maps,andthebestfitmodelsoftherecoveredmaps.Thetopline
5.1.6. ThethermalSunyaevZel’dovichsignal correspondstothecompactclusterandthesecondtothediffuse
cluster. The clusters are detected with a signal-to-noise of the
WeusethegeneralizedNavarro,Frenk,andWhite(gNFW)pres-
order of 10 and are well mapped in both cases. The signal am-
sureprofile(Nagaietal.2007b)todescribetheclusterpressure
plitudeisslightlyreducedwithrespecttotheinputmaps.
distributionouttoasignificantfractionofthevirialradius.This
Using these maps, we compute the angular profiles of the
profileisgivenby
recovered clusters by evaluating the average flux value for a
set of concentric annuli. They are shown in Fig. 5, as green
P
P(r)= 0 , (7) and red dots for the compact and diffuse clusters, respectively.
(cid:16)r(cid:17)γ(cid:16)1+(cid:16)r(cid:17)α(cid:17)β−αγ Comparison with the input profiles is provided by solid lines
rs rs with similar colors. We also show the profiles recovered after
where P is a normalizing constant; α, β, and γ set the slope projectiononlytocheckzero-leveleffects(orangeandbluedia-
0
atintermediate,large,andsmallradiirespectively,andr isthe mondsforthecompactanddiffusecluster,respectively),thatis
s
characteristicradius.Thesameprofilecanbewritteninitsuni- theinputtSZsignalissimplyprojectedwithoutdecorrelationor
versal form (Arnaud et al. 2010) by relating the characteristic filtering.
radius to the concentration parameter c , r = r /c , with Firstofall,duetothescanningstrategy,thelargestangular
500 s 500 500
r the radius within which the mean density of the cluster is scalethatcanberecoveredinthemapis6arcmin,whichcorre-
500
equalto500timesthecriticaldensityoftheUniverseattheclus- sponds to the size of the observed map. In Fig. 5, we show the
ter redshift. The pressure normalization can then be written as profileofthediffusecluster(projectiononly,asbluediamonds)
P = P ×P ,whereP isanormalizationfactorand P is that reaches the zero-level at 3 arcmin, which is unlike the in-
0 500 0 0 500
theaveragepressurewithintheradiusr (relatedtotheaverage jectedprofilethatextendsfarther.Hence,thedataprocessingaf-
500
masswithinthesameradius,M ,byascalinglaw).Wefinally fects the map in the case of the diffuse cluster by reducing the
500
define θ = r /D the characteristic angular size, where D is measuredfluxupto25%ataradiiof∼1arcmin.Thiscanalsobe
s s A A
theangulardiameterdistanceofthecluster. observedontheresidualmapofthediffuseclusterthatispositive
Wesimulatetwodifferentkindsofclusters.Thefirstoneis around the cluster peak. In the case of the compact cluster, the
similartowhatweobserveforRXJ1347.5-1145intermsofam- amplitudeoftheprofileisnotaffectedbymorethan10%,andthe
plitudeandspatialextension(referredtoascompactinthefol- correspondingresidualmapisconsistentwithnoise.Concerning
lowing).Thesecondoneismorediffuse,butitspeakamplitude the shape of the reconstructed signal with respect to the input
isthesameasfortheprevious(referredtoasdiffusehereafter). one, we observe a flat transfer function for angular scales be-
The corresponding parametrization can be found in Table 4. tween0.4and4arcminforthecompactclustercase.Finally,the
Using these sets of parameters, we compute the Compton pa- remainingcorrelatednoisecanslightlycontaminatetheprofile,
rameter map according to Eq. (3) by integrating the pressure butitisnotsignificantonceaveragedonconcentricannuli.
along the line-of-sight. The map is then convolved with the in- WeusethesimulatedmapstofitthenormalizationP andthe
0
strumental beam and converted into surface brightness. We use characteristicradiusr ofthepressureprofile.Thisisdoneusing
s
A66,page8of16
R.Adametal.:FirsttSZobservationwithKID
Fig.4.GeneralizedNavarro,Frenk,andWhitesimulationsoftwoclustersprocessedthroughthepipeline.Thefirstone(compactcluster,asC)
is similar to the NIKA map of RXJ1347.5-1145 (top panels). The second (diffuse cluster, labeled D) is more extended (bottom panels). The
parametersusedintheclustersimulationsaregiveninTable4.Fromlefttoright,weshowtheinputmodelmaps,therecoveredmaps,theresidual
maps,andthebestfitmodelmapsoftherecoveredsignal.TheyarelabeledfromC1toC4andfromD1toD4forthecompactanddiffusecluster,
respectively.Themapsareshownuptoanoiselevelthatistwicetheminimalnoiselevelofthemap.Theeffectivebeamisshownonthebottom
leftcorner,accountingfortheinstrumentalbeamandanextra10arcsecGaussiansmoothingofthemaps.Thecontourscorrespondto3,–3,–6,and
–9mJy/beam,towhichweadd−1mJy/beamforthemodelmaps.Thecolorscalesrangefrom−13to13mJy/beam,exceptfortheresidualmaps
forwhichwehave−5to5mJy/beam.ThecenteroftheclustershasbeensimulatedatthetSZpeaklocationoftheNIKARXJ1347.5-1145map.
sourcemimickingthat,whichispresentintheRXJ1347.5-1145
cluster has been added to the simulated data. It has then been
removedduringtheprocessingbyassumingaflux3σlowerthan
theinjectedone.Theresultschangebylessthan1σforbothP
0
andr eitherforthediffuseorthecompactclustercase.
s
5.2. Mapoftheundetectedgalaxycluster
IDCSJ1426.5+3508
WehavealsoobservedIDCSJ1426.5+3508,afainthighredshift
(z = 1.75) cluster of galaxies. These observations corre-
spond to 5 h 41 min of unflagged on-source data in at-
mospheric conditions, which are slightly poorer but compa-
rable to those described in Table 1 for RXJ1347.5-1145.
For IDCSJ1426.5+3508, the expected tSZ decrement is
∼0.25mJy/beamat140GHzwithanangularsizeof∼2arcmin
(Brodwinetal.2012).We,therefore,donotexpectadetection,
Fig.5.Comparisonoftheprofilesinjectedinthesimulationandrecov- since its flux is below the standard deviation of the expected
ered at the end of the pipeline. The injected profiles are given as red noiseattheclusterlocationbyafactorof∼5.
(compactcluster)andgreen(diffusecluster)solidlines.Therecovered InFig.6,weshowthemapofIDCSJ1426.5+3508obtained
profiles are shown with dots of similar colors. We also show the re-
afterpipelinereduction.ThismapshowsnoevidenceoftSZsig-
coveredprofilesinthecaseofprojectiononlywithoutcorrelatednoise,
glitches,orpulsetubelinesincludedinthesimulation.Theyaregiven nal,anditisconsistentwithnoiseasexpected.Thiscanbecon-
asorange(compactcluster)andblue(diffusecluster)diamonds. sideredasanulltestthatallowsustoconcludethatthetSZsignal
observedintheRXJ1347.5-1145dataisnotduetoabiasinthe
analysis1.
Markov chain Monte Carlo (MCMC) techniques that are fur-
therdetailedinSect.6.3(whenappliedontheRXJ1347.5-1145
data). The recovered parameters can be compared to the in- 6. Results
put ones to estimate filtering effects and possible biases. Once
6.1. RXJ1347.5-1145asobservedbyNIKA
marginalized, we find that the recovered parameters are within
1σoftheinputsforbothP0(10%)andrs(5%)inthecaseofthe Figure 7 presents the RXJ1347.5-1145 tSZ map obtained with
compactcluster.Forthediffusecluster,wefindthatP0andrsare theNIKAprototype.Theradiosourceissubtractedintheright
underestimatedby2.7(17%)and3.7(12%)σ,respectively.The
MCMCbestfitmapsaregiveninpanelsC4andD4ofFig.4. 1 WeuseIDCSJ1426.5+3508foranulltestbecausewedonothave
Theeffectoftheradiopointsourcesubtraction(seeSect.4.4) observationsofwell-knownemptyfieldsthatwouldbettersuitsucha
hasalsobeencheckedviathesimulations.Todoso,aradiopoint nulltestfortheNIKARun5campaign.
A66,page9of16
A&A569,A66(2014)
NIKARXJ1347.5-1145mapwithpreviousobservationsisfur-
therdiscussedinSect.7.
6.2. RXJ1347.5-1145profile
Figure 9 gives the flux profile as a function of the an-
gular distance that is extracted from the tSZ map in
Fig. 7. In the case of RXJ1347.5-1145, the tSZ barycen-
ter and the X-ray center do not coincide due to the on-
going merger. We compare the profile computed from the
X-ray center, (RA, Dec) = (13h47m30.59s, −11◦45(cid:48)10.1(cid:48)(cid:48)),
to the tSZ peak that is taken to be at the coordinates
(RA, Dec) = (13h47m31s, −11◦45(cid:48)30(cid:48)(cid:48)) from the maximum
decrement of the NIKA map. The error bars have been com-
putedfromsimulatednoisemapswithstatisticalpropertiesesti-
matedusingthehalf-differencemappresentedontheleftpanel
ofFig.8.
The right panel in Fig. 9 compares the profile of
RXJ1347.5-1145fromtheX-raycenterinthreedifferentareas:
Fig.6. Map at 140 GHz of the undetected galaxy cluster
thenorthwest,thenortheast,andthesouth.Itshowstheincrease
IDCSJ1426.5+3508.
inthermalpressureinthesouthernregion,wherethesubclump
(merging) is observed in X-ray and tSZ (Sect. 2). This is due
to the compression of the hot gas within the merging process,
panelbutnotintheleftpanel.Theassociateddifferencemapof whichincreasesthetemperatureandthusthepressure(deepen-
separatedequivalentsubsamples(Jack-Knife),whichisnormal- ing the tSZ decrement at 140 GHz). We note that the southern
izedbyafactorof2topreservethestatisticalpropertiesofthe extensioncoincideswiththepresenceofaradiomini-halo(see
noiseinthetSZmap,isgivenintheleftpanelofFig.8.Wealso the work by Gitti et al. 2007a), which implies the presence of
presentonthemiddlepanelofFig.8thehistogramofthepixel non-thermalelectronsthatcouldunderlineanon-thermalcontri-
values.Theoutsidecontourofthemapsshownisdefinedbythe butiontothetotalpressure(notseeninthetSZsignal).Wealso
limitwherethestatisticalnoiselevel,whichincreasestowardthe notethattheradiosourcehasbeensubtractedbeforethecalcu-
edgesofthefullmap,equalstwicetheminimumnoiselevelof lationoftheprofiles.
the inner region. The bottle-like shape of the cut-off is due to
thescanstrategydetailedinSect.3.2.
6.3. Modelingoftheclusterpressureprofile
Theinhomogeneityofthenoisecanbeseendirectlyonthe
halfdifferencemapinFig.8.Thisisevenmoreobviousonthe The object RXJ1347.5-1145 has been intensively studied in
histogramplotthatprovidesthenoisedistributionintwodiffer- X-rays, which have revealed a fairly regular cluster at a large
ent regions of the half difference map and on the standard de- scaledowntothecenterinthenorthdirectionwithalowcentral
viationmap.Weobservethatthestandarddeviationonthetwo entropy (Cavagnolo et al. 2009). The contrast with the south-
regions is significantly different, (cid:104)σ(cid:105) = 0.99 mJy/beam on the ern part, which exhibits a tSZ and X-ray extension, suggests
east sideand (cid:104)σ(cid:105) = 1.42 mJy/beam onthe west side. Fromthe that RXJ1347.5-1145 was a spherical, relaxed cool-core clus-
half difference map, we estimate the overall root mean square ter that is undergoing the merging of a subcluster on its south-
of the noise in the cluster map to (cid:104)σ(cid:105) = 1.11 mJy/beam. This ern part. We, therefore, aim at quantifying the tSZ South East
is obtained by fitting the histogram of the pixel value with a extension detected with the NIKA prototype by modeling and
Gaussiandistribution.ThecontoursoverplottedonthetSZmaps subtractingthesignalcomingfromtherelaxedregion,whichis
of Fig. 7 correspond to 3, −3, −6, and −9 mJy/beam with the locatedonthenorthern-westsideoftheX-raycenter.Wemodel
noiselevelbeing1σ (cid:27) 1mJy/beamattheclusterlocation.The thetSZsignalbyconsideringagNFWprofile(Eq.(7)),whichis
beamisshownonthebottomleftcornerofthemap,accounting centeredattheX-raypositionofthesystem,whoseinner,outer,
forboththe18.5arcsecinstrumentalbeamandtheextra10arc- andintermediateslopes(γ,β,α)havebeensetequaltothecool-
secGaussiansmoothingofthemap(i.e.,21arcsec).Intermsof core best-fitting values of Arnaud et al. (2010) (γ = 0.7736,
cc
the Compton parameter, the sensitivity of the NIKA pro√totype βcc = 5.4905, αcc = 1.2223). The best-fitting values of P0
cameraduringthecampaignofNovember2012is∼10−4 hfor and θ are obtainedusing aMCMC approach.The sequenceof
s
onebeamand1σ. random samples, known as the chain, has been built by imple-
The maps in Fig. 7 clearly show the tSZ decrement menting the Metropolis-Hasting algorithm (Chib & Greenberg
that reaches up to (cid:39)10σ. The signal is extended, and 1995), which means that the parameter space is explored with
its maximum does not coincide with the X-ray center, a trial step drawn from a symmetric probability distribution.
(RA, Dec) = (13h47m30.59s, −11◦45(cid:48)10.1(cid:48)(cid:48)). It corresponds Convergenceofthechainsischeckedbyincludingthetestpro-
to the shock location, even for the radio point source sub- posedbyGelman&Rubin(1992).
tracted map, which agrees with other single-dish observations. The parameters P and θ have been constrained by mask-
0 s
As mentioned in Sect. 2, these results do not agree with those ing the southeast extension. The mask has been defined as a
from CARMA interferometric RXJ1347.5-1145 observations half ring on the southern part of the cluster, centered on the
(Plagge et al. 2013). The tSZ maximum corresponds to (cid:39)10−3 X-ray peak with inner and outer radii set to 10 and 80 arcsec,
inunitsofComptonparametery,asexpectedforthisclusterac- respectively. By masking the hottest region of the system, the
cording to Pointecouteau et al. (1999). The consistency of the constraintsobtainedonthebestfitparametersaremainlydriven
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