A statistical investigation of the radio emission of clusters : role of AGNs

0.21 MB·English

by  J. Lanoux

Mem.S.A.It.Vol.75,282
(cid:13)c SAIt 2008 Memoriedella
A statistical investigation of the radio emission
of clusters : role of AGNs
J.Lanoux1,2,E.Pointecouteau1,2 andM.Giard1,2
1
1
0 (1) Universite de Toulouse (UPS-OMP), Institut de Recherche en Astrophysique et
2
Planetologie

n (2)CNRS,UMR5277,9Av.colonelRoche,BP44346,F31028Toulousecedex4,France
a e-mail:[email protected]
J

6
2 Abstract. Radioemissioninthedirectionofgalaxyclustersisduetotheindividualemis-
sionofAGNs,andtothediffusenon-thermalemissionoftheintraclustermedium(ICM).

] ThepopulationofAGNsinclustersiscorrelatedtotheoverallhaloproperties,andlikely
O
impactstheirevolutions.Inordertobetterunderstandthisconnection(whichwillalsoleads
C toconstraintsonthenon-thermalICMemissionforlowermasssystems),weareconducting
. astatisticalanalysisoftheradioemissioninthedirectionofalargenumberofX-rayclus-
h ters.Bymeansoftheirstackedradioemission,weareinvestigatingtheradioluminosities
p inclustersof galaxieswithrespect totheir mass,withthegoal tobetter understand their
- linktoandtheirimprintontheintra-clustergasphysics.
o
r
t Key words. Radio: galaxies: clusters – X-rays: galaxies: clusters – Radio: galaxies –
s
Intergalacticmedium–Diffuseradiation–Cosmology:observations
a
[

1
1. Introduction first to show the existing correlation between
v
0 radio and X-ray luminosities in such clus-
The ICM is mainly constituted of dif-
1 ters.Thiscorrelationwasconfirmedbysubse-
fuse hot gas that cools down via thermal
0 quentworkssuchasGiovanninietal.(2009)or
5 Bremsstrahlung emission observed at X-ray Brunettietal.(2009).
1. wavelengths. But it is also populated by non- Here,weinvestigatedthiscorrelationdown
thermalrelativisticelectronsobservedatradio
0 to a lower mass regime of clusters, together
wavelengths due do their synchrotron emis-
1 with the contributionof AGNs to the total ra-
1 sion.Theradionon-thermalemissionofgalaxy dioluminosity.Sofar,wehavebeenlimitedby
: clustersisduetopoint-likesources(AGNs,ra- the sensitivity of radio surveysto directly de-
v
diogalaxies)anddiffuseextendedsources(ha-
i tectdiffuseemission.
X los, relics, mini-halos, e.g. Ferrarietal. 2008
Therefore,weinvestigatedthecorrelations
forareview).
r by means of statistical and stacking tools ap-
a Diffuse radio emission has now been ob-
plied to X-ray (RASS) and radio (NVSS) all-
served in a few tens of massive merging sky surveys. We used the Meta-Catalogue of
galaxy clusters. Liangetal. (2000) were the
X-ray detected Clusters of galaxies (MCXC,
1743 clusters, Piffarettietal. 2011). From
Sendoffprintrequeststo:J.Lanoux maps extracted at each cluster position, we
Lanoux:Astatisticalinvestigationofclustersradioemission:roleofAGNs 283
Wefoundthatthesummedradioluminosi-
tiesofselectedpointsourceswithinR com-
500
pares very well to the total integrated radio
luminosities within this aperture. This likely
showsthatthecomponentofpointsources(i.e.
AGNs)isdominantinouraperture.
Thisconclusionisreinforcedbythestrong
L − L correlation we found for radio lumi-
R X
nosities associated to AGNs only for a sub-
sample of 374 galaxy clusters of the MCXC
with redshift z < 0.1 (Figure 1, bottom). We
deriveaslopeof∼1.4compatiblewiththepre-
viouscorrelationfoundfortotalintegratedra-
dio luminosities. This strengthened our result
foraflatter L −L withrespecttothecorre-
R X
lationfoundfordiffuseradioemissioninclus-
ters.
3. ConclusionandPerspectives
We have probe the radio emission of a large
numberofX-rayclusters,andwehaveshown
thatthere is a strong L −L correlation,and
R X
thattheradioluminosityismainlycontributed
Fig.1. LR−LX correlationsfortotalintegratedra- byAGNsinclusters.
dioluminositieswithinR andforluminositiesof
500 Theprovidedstatisticalconstraintswillal-
pointsourcesonly(top).L −L correlationforra-
R X lowustofurtherinvestigatetheoverallnature
dio luminosities of AGNsfor a sub-sample of 374
of the radio emission seen in the direction of
clusterswithredshiftz<0.1(bottom).
galaxyclusters.
computed count rates and fluxes within R .
500
References
We derivedcorrespondingX-rayandradiolu-
minosities. From the NVSS source catalogue Akritas, M. G. and Bershady, M. A. 1996,
(Condonetal.1998)andthe2MASSextended ApJ,470,706
source catalogue (Jarrettetal. 2000), we se- Brunetti,G.,Cassano,R.,Dolag,K.,andSetti,
lected AGNs associated with clusters and we G.2009,A&A,507,661
derivedtheirsummedradioluminositieswithin Condon,J.J.,Cotton,W.D.,Greisen,E.W.,et
R500 for each cluster. We then fitted the LR − al.1998,AJ,115,1693
LX correlationswithBCESregressionmethod Ferrari, C., Govoni, F., Schindler, et al. 2008,
(Akritasetal.1996). SpaceSci.Rev.134,93
Giovannini,G.,Bonafede,A.,Feretti,L.,etal.
2009,A&A,507,1257
2. Results
Jarrett,T.H.,Chester,T.,Cutri,R.,etal.2000,
We found a L − L correlation with a slope AJ,119,2498
R X
of ∼1.2 for total integrated radio luminosities Liang, H., Hunstead, R. W., Birkinshow, M.,
within R (Figure 1, top). This slope is flat- andAndreani,P.2000,ApJ,544,686
500
tercomparedtootherworkswhichinvestigated Piffaretti, R., Arnaud, M., Pratt, G. W.,
the relation between detected diffuse radio Pointecouteau,E.,& Melin, J. 2011,A&A,
emissions and L (i.e. ∼2.1 for Brunettietal. submitted[arXiv:astro-ph/1007.1916]
X
2009or∼1.7forGiovanninietal.2009).