arXiv:1405.5013v2 [astro-ph.CO] 15 Jun 2015 estv oteaciuesaeeiso u ocutr a clusters to due emission arcminute-scale the to sensitive eeto ucini asta,freape X-ray-select example, for than, ( mass samples in function selection ra L) ihaglrrslto of resolution angular with (LA), Array .C Perrott C. Y. estvt osrcue pto up structures to sensitivity epeetosrain n nlsso apeo 2 galax 123 of sample a of analysis and observations present We aeo la,admc esrdhf-eedn (above redshift-dependent less much and clean, a of tage cl etrs aiga nua eouinof resolution arcminute angular viewing an for having optimised ar- features, (SA), two scale Array of consists Small AMI the UK. rays: Cambridge, near situated is which uye e’oih1972 Zel’dovich & Sunyaev rud10 around 2008 2009 2004 ( al. quantities et observable Silva optical with or tightly X-ray more example, correlates for ‘flux’ than, SZ the that predict tions 2014 ossigo lsessann esit pto up redshifts spanning clusters of consisting eouin rmncmae othe to compared rad arcmin ground-based 3 a resolution, (AMI), Imager Microkelvin Arcminute the aaou r en olwdu ihotcl ai n X-ra informati properties. and their multi-wavelength t radio fully provide in understand optical, to clusters with order Universe; in up the telescopes followed in being inv structure are for of tool catalogue powerful growth very the potentially gating a therefore is alogue mrvdpstoa siae,adacnitnyceko t on check consistency a and estimates, positional improved ht GF)mdl edtc 9o h lses eueteAM the use We clusters. the the of by 99 detect We model. (GNFW) White 27glx lsesdtce i h uye-e’oih( Sunyaev-Zel’dovich the via detected clusters galaxy 1227 The Introduction 1. clusters galaxies: X-rays: nawdrrneo nua clsta r rsn nAIdata AMI in present words. are Key than scales angular of a range careful wider provided a clusters individual on for model GNFW the in osrit,epcal o high for especially constraints, rsuepol hp sdt oe h lses eso tha show We clusters. the model to used shape profile pressure coe 7 2018 17, October ⋆ Astrophysics & Astronomy n rmteAciueMcoevnIae o 9glx clus galaxy 99 for Imager Microkelvin Arcminute the from and .G Pooley G. G. orsodn uhr .C ert,[email protected] Perrott, C. Y. author: Corresponding h rmnt irkli mgr(AMI; Imager Microkelvin Arcminute The oprsno uye-e’oihmaueet from measurements Sunyaev-Zel’dovich of Comparison Planck sada-ra nefrmtrdsge o Zstudies, SZ for designed interferometer dual-array a is ) , date to SZ in catalogue cluster all-sky deepest the is This ). .Arnaud M. .F Mac´ıas-P´erez F. J. Planck nuoe l 2012 al. et Angulo .Comis B. lnkClaoainX 2014 XX Collaboration Planck 14 2 M aelt aarlaeo 03icue aaou of catalogue a included 2013 of data-release satellite omlg:observations Cosmology: ⋆ loihsPwlSae n M3 efidthat find We MMF3. and PowellSnakes algorithms .Olamaie M. , 2 ⊙ .D .Saunders E. D. R. , 18 17 o10 to .Dahle H. , , .Ashdown M. , ole l 2005 al. et Motl 15 18 M .B Melin J.-B. , ⊙ 2 , 13 .Rumsey C. , Zslce ape aeteadvan- the have samples SZ-selected . a ta.2012 al. et Kay .Democles J. , e ) Planck ≈ 16 aucitn.ms˙2 no. manuscript ff , 0aci nsae n h Large the and scale; in arcmin 10 2 2 c ( ect .Aussel H. , , 16 SRcutr.W efr iuain oso htti a b can this that show to simulations perform We clusters. -SNR , .P Schammel P. M. , Planck 6 − aa 2006 Nagai lnkClaoainXXIX Collaboration Planck .Pointecouteau E. , 2 aais lses general clusters: Galaxies: .L Brown L. M. , ≈ 17 .Douspis M. , 0ace,wihi in- is which arcsec, 30 ;i diin simula- addition, in ); em f51 rmn h M bevtostu rvd vali provide thus observations AMI The arcmin. 5–10 of beams .The ). 17 .Barrena R. , (A ≈ ffi , ,admse of masses and 1, itoscnb on fe h references) the after found be can liations ≈ gai tal. et Aghanim Planck 2 15 rmnand arcmin 3 wr tal. et Zwart , 10 .Feroz F. , 24 11 .F Scott F. P. , efitd‘ie ( ‘size’ fitted he , .Harrison D. , 4 14 tnini adt h eeeaisbtenprmtr,bu parameters, between degeneracies the to paid is ttention .W Pratt W. G. , eevd;Accepted ; Received M aacncntanthe constrain can data AMI t , Zcat- SZ z oitreoee.AIpoie nidpnetmeasuremen independent an provides AMI interferometer. io 8 e.g. .Bikmaev I. , k ln ocretycntanalprmtr simultaneousl parameters all constrain correctly to alone ≈ lsesfo h 2013 the from clusters y Y nto on mass dis nd ABSTRACT esti- tot 0.3) SZ, oiinletmtst hc h oiinletmtsan estimates positional the check to estimates positional I 2 .J .Grainge B. J. K. , da he ed − ausa esrdb M r isddwwrswt epc t respect with downwards biased are AMI by measured as values y - 2 , aais lses nrcutrmedium intracluster clusters: Galaxies: .W Shimwell W. T. , 12 17 it of width fteisrmn,see instrument, the of ealteaayi fteAIdt nSection in data AMI the of analysis the detail rasoeaea eta rqec of frequency central sources. a radio at confusing operate subtract arrays and characterise to used h su fvrainfo h uiesl oe described model ‘universal’ the from variation of issue the Sections and results, the of examples Section criteria. detection our Section In signal. SZ the the describe describe briefly to Section used in model and the reduction, line data Section and In observations sample. AMI cluster the of selection the the in clusters the of all size. observe angular to smaller AMI measure of and used as fainter have signals average, on SZ be, the to m finding AMI as by telescopes, parameters two cluster the the by of sured consistency the the check from to selected order clusters 11 of sample Planck a AP2013) on here from h lse aaee siae rdcdb M otoepro those to AMI by by produced duced estimates parameter cluster the n ihrrslto Zmp falrenme of number large estimate a positional of maps improved SZ higher-resolution of, and validation provide furthe AP2013 to in (b) found discrepancies purp two the investigate serves to This (a) redshift). low very wit at observable those easily (excluding declinations at are that catalogue SZ e eetos ehr rsn hs bevtosadora our and them. observations of these ysis present here We detections. ter , 16 .A Rubi˜no-Mart´ın A. J. , θ 7 s , .Hempel A. , 1 n flx ( ‘flux’ and ) .B¨ohringer H. , napeiu ae,( paper, previous a In h ae sognsda olw.I Section In follows. as organised is paper The al ees aaou a olwdu ihAIin AMI with up followed was Catalogue Release Early ≈ Planck 2 . H,dvddit i hnes o ute details further For channels. six into divided GHz, 4.5 , 16 2 , , 15 5 14 .J Titterington J. D. , Planck Y .P Hobson P. M. , , α 8 tot , 19 23 nSection In . and aaeesi h eeaie aar,Fekand Frenk Navarro, Generalised the in parameters ) .Burenin R. , .Hurier G. , Planck 14 β aaou fSnavZldvc ore with sources Sunyaev-Zel’dovich of catalogue , wr tal. et Zwart 8 aaeesdsrbn h hp fteprofile the of shape the describing parameters .Stolyarov V. , xlie ydvainfo h ‘universal’ the from deviation by explained e lnkadAIClaoain 2013 Collaborations AMI and Planck 11 2 aaaayi n eciei more in describe and analysis data 5 .N Lasenby N. A. , 21 .Khamitov I. , , euesmltost investigate to simulations use we 2 4.4 20 .M Waldram M. E. , .Carvalho P. , − ( aino h lse detections, cluster the of dation otissm representative some contains 2008 omcbcgon radiation background Cosmic 2 , 16 , 21 4.4.6 ). n .Sutton D. and , n eursinformation requires one t ≈ y. 22 5Gzwt band- a with GHz 15 , 2 7 , 12 .Kneissl R. , 16 ro-asproduced error-bars d and ihhge angular higher with t , 16 .J MacTavish J. C. , 3 Planck 2 .Aghanim N. , .Chon G. , edsrb the describe we 4.4.7 4.3
2 c Planck Planck edescribe we S 2018 ESO including , the o 12 4 ters 9 , compare 16 , 3 eout- we 19 , 4.2 AMI h Planck , ,and r, for, s 2013 oses: clus- Both 11 nal- We ea- we , 16 in − d 1 - , , Y. C. Perrott et al.: Planck and AMI SZ measurements for 99 galaxy clusters
◦ ◦ Section 4, and in Section 5.3 we present results from reanalysing Table 1: Numbers of clusters in the 20 ≤ δ< 87 , Planck SNR the real data allowing the shape parameters in the model to vary. ≥ 5 sub-sample in various categories. Finally, we conclude in Section 6. Category Number of clusters Total 229 2. Selection of the cluster sample z ≤ 0.100 34 Automatic radio-source environment rejection 52 ◦ ◦ An initial selection cut of 20 ≤ δ < 87 was applied to sat- Manual radio-source environment rejection 20 isfy AMI’s ‘easy’ observing limits; although AMI can observe Included in sample 123 to lower declinations, increased interference due to geostation- GREY: A0001 IPOL 15772.689 MHZ A.FLATN.1 GREY: A0001 IPOL 15734.113 MHZ SA.OHGEO.1 ary satellites makes observing large samples below δ = 20◦ 100 150 200 200 400 600 800 1000 currently difficult. In addition, clusters with known redshifts of 54 25 z ≤ 0.100 were excluded since these have large angular sizes 20 and will be largely resolved out by AMI; although the brightest 15 of these will still be detectable, it will be difficult to constrain 10 their properties using AMI data. These initial cuts resulted in an 05 Declination (J2000) initial sample size of 337 with Planck SNR values ranging from 00
4.5 – 20. In this paper, we present results for the subset of the 53 55 sample with SNR ≥ 5; this reduces the sample to 195. Results 50
01 10 00 09 30 00 08 30 00 07 30 00 06 30 00 05 30 for the remaining clusters with 4.5 ≤ SNR < 5 will be released Right ascension (J2000) Grey scale flux range= 0.107 1.118 MilliRATIO at a later date. Grey scale flux range= 67.0 240.0 MicroJY/BEAM As in the optical, where confusion due to a bright star or a crowded field can affect the detection likelihood, a benign radio point source environment is important for AMI, but the requi- site benignness is difficult to quantify. In practice, the effect of the source environment on the detection potential of a cluster depends on many factors including the number, location and ori- entation of the sources with respect to each other and to the side- lobes of the primary and synthesised beams. Non-trivial source environments can create complex and overlapping sidelobe pat- terns which can create spurious sources or reduce the flux den- sity of real sources. In turn, the synthesised beam depends on uv-coverage, which changes for different δ and hour-angle cov- erage of observations of a given cluster. The primary beam is a function of frequency so the effect of a source at a given offset from the pointing centre also depends on its spectrum. These ef- fects are almost impossible to quantify in a systematic way. In order to apply at least consistent criteria across the whole sam- ple, the following criteria were applied based on LA observa- tions: clusters were discarded if there were radio sources of peak flux density S peak > 5mJy within 3arcmin of the pointing cen- tre, of S peak > 20mJy within 10arcmin of the pointing centre, or extended emission with fitted (deconvolved) major-axis size > 2arcmin and integrated flux density S int > 2mJy anywhere on the map; experience suggests that observation of the SZ signal in such clusters with AMI is unreliable. Clusters were discarded for source environment based either on existing observations or, for clusters that had not been previously observed with AMI, based on a short pre-screening observation carried out with the LA. It should be noted that some clusters which have been previ- ously observed and detected by AMI are excluded by these cuts; some of the new clusters discarded by this process may also be observable. In addition, clusters were visually inspected at various stages of the follow-up and analysis process, and some were rejected at later stages due to extra source environment problems such as extended emission not visible on the LA map, or very bright sources just outside the LA detection radius which affect the SA map due to the larger primary beam. Here we present results for the so obtained final sub-sample,which we will refer to as the SZ sample, consisting of 123 clusters. A breakdown of the numbers of clusters rejected for various reasons is shown in Table 1. The full list of clusters within the AMI observational bounds and their reason for rejection, if not part of the SZ sample, is given in Appendix A. In addition, as a service to the commu- Y. C. Perrott et al.: Planck and AMI SZ measurements for 99 galaxy clusters Ants * - * Stokes YY IF# 1 Chan# 3 - 8 Ants * - * Stokes YY IF# 1 Chan# 3 - 8
5 1.0 4
3
0.5 2
1 λ λ k 0 k 0.0 / / v v -1
-2 -0.5
-3
-4 -1.0 PSfrag replacements -5 PSfrag replacements 1.0 0.5 0.0 -0.5 -1.0 6 4 2 0 -2 -4 -6 u / kλ u / kλ (a) (b) Fig. 2: uv-coverages for a typical cluster observation at δ ≈ 54◦, for the AMI-LA (a) and SA (b). The colours indicate different channels. Note the different axis scales; the short baselines of the SA are designed for sensitivity to arcminute-scale cluster emission, while the longer baselines of the LA are insensitive to emission on this scale and are used to characterise and subtract the foreground radio sources.
+ Table 2: Assumed I Q flux densities of 3C286, 3C48 and and r ≫ rs respectively (Nagai et al. 2007). Following Arnaud 3C147. et al. (2010), we fix the slope parameters to their ‘universal’ values, γ = 0.3081, α = 1.0510, β = 5.4905 derived from the REXCESS sample (B¨ohringer et al. 2007). They are also fixed Channelν ¯/GHz S 3C286/Jy S 3C48/Jy S 3C147/Jy to these values in the Planck analysis. 3 13.88 3.74 1.89 2.72 Given this model, the integrated SZ surface brightness, or 4 14.63 3.60 1.78 2.58 integrated Compton-y parameter, for a cluster is given by 5 15.38 3.47 1.68 2.45 6 16.13 3.35 1.60 2.34 σ r = T ′ π ′2 ′, 7 16.88 3.24 1.52 2.23 Ysph(r) 2 Pe(r )4 r dr (2) 8 17.63 3.14 1.45 2.13 mec Z0 where σT is the Thomson scattering cross-section, me is the elec- tron mass, and c is the speed of light. This has an analytical solu- the LA continuum map, as described in Davies et al. (2011) and tion as r →∞, giving the total integrated Compton-y parameter Franzen et al. (2011), and sources that are detected at ≥ 3σ on at Ytot,phys as least three channel maps and are not extended have a spectral in- dex α fitted across the AMI band.SA data are binnedon a grid in 3−γ β−3 4πσ Γ α Γ α Y = T P r3 . (3) uv-space in order to reduce the memory required for subsequent tot,phys 2 0 s β−γ mec analysis. αΓ α With (γ, α, β) fixed, a cluster’s appearance on the sky 4. Analysing the SZ signal may be described using four (observational) parameters only: (x , y , θ , Y ), where x and y are the positional coordinates 4.1. Cluster model 0 0 s tot 0 0 for the cluster, θs = rs/DA is the characteristic angular scale of For consistency with the Planck catalogue, in this paper we as- the cluster on the sky (DA is the angular diameter distance to 2 sume the electron pressure profile Pe(r) of each cluster follows the cluster), and Ytot = Ytot,phys/DA is the SZ surface brightness a generalised Navarro-Frenk-White (NFW, Navarro et al. 1997) integrated over the cluster’s extent on the sky. model, which is given by (assuming spherical geometry) This model does not require any redshift information; physi- cal quantities such as rs and Ytot,phys can be recovered from θs and −γ α (γ−β)/α r r Ytot given a redshift. Alternatively, rX and MX for some overden- Pe(r) = P0 1 + , (1) sity radius X can be recovered given a redshift, a concentration rs ! " rs ! # parameter cX ≡ rX/rs and some model or scaling relationship where P0 is a normalisation coefficient, r is the physical radius, for translating Y into mass (e.g. Planck Collaboration XX 2014, rs is a characteristic scale radius, and the parameters (γ, α, β) de- Olamaie et al. 2012). Physical modelling will not be addressed scribe the slopes of the pressure profile at radii r ≪ rs, r ≈ rs, in this paper.
3 Y. C. Perrott et al.: Planck and AMI SZ measurements for 99 galaxy clusters
Note that in the Planck analysis, in order to impose a finite PwS positional errors in the sample are greater than 5arcmin. integration extent, Y5R500 (the SZ surface brightness integrated to MMF1 does not give positional error estimates, so clusters de- 5 × R500) is estimated rather than Ytot. For the ‘universal’ GNFW tected only by MMF1 are given the maximum 5arcmin error; parameter values, (with c500 = 1.177), the two quantities are some clusters detected by MMF3 (but not PwS) have positional equivalent to within 5%. errors > 5arcmin, but as will be shown in Section 4.4.6, MMF3 positional errors tend to be over-estimated. Model parameter estimation is performed in a fully Bayesian 4.2. Analysis of Planck data manner using the AMI in-house software package McADAM, in The Planck SZ catalogue is the union of the catalogues uv-space (see, e.g. Feroz et al. 2009b for more details). Bayes’ produced by three detection algorithms: MMF1 and MMF3, theorem states that which are multi-frequency matched-filter detection methods, Pr(D| Θ, H) Pr(Θ|H) and PowellSnakes (PwS), which is a Bayesian detection method. Pr(Θ|D, H) = , (4) Full details of these algorithms are provided in Melin et al. Pr(D|H) (2006), Carvalho et al. (2009), Carvalho et al. (2012) and Melin where Θ is a set of parameters for a model, H, and D is the data. et al. (2012). Since the PwS analysis methodology most closely Thus, the posterior probability distribution, Pr(Θ|D, H), is pro- matches the Bayesian analysis procedures used to analyse AMI portional to the likelihood, Pr(D| Θ, H), multiplied by the prior, data, we take cluster parameters produced by PwS as our pre- Pr(Θ|H). The normalising factor is the evidence, Pr(D|H) ≡ ferred ‘Planck’ values, followed by MMF3, and finally MMF1 Z. McADAM uses the nested sampler MultiNEST (Feroz & values where a particular cluster is not detected by all algo- Hobson 2008, Feroz et al. 2009a) to obtain the posterior distri- rithms. bution for all parameters, which can be marginalised to provide two- and one-dimensional parameter constraints. MultiNEST also calculates the evidence, which can be ig- 4.3. Analysis of AMI data nored for parameter estimation but is important for model selec- The model attempting to describe the AMI data is produced by tion, since it represents the probability of the data given a model a combination of the cluster model described above, the radio and a prior, marginalised over the the model’s parameter space: source environment as measured by the LA and a generalised Gaussian noise component comprising instrumental noise, con- Z = Pr(D| Θ, H) Pr(Θ|H)dDΘ, (5) fusion noise from radio sources below the detection threshold, Z and contamination from primordial CMB anisotropies. where D is the dimensionality of the parameter space. The prob- Each foreground radio source is modelled by the parameters ability of two different models given the data can be compared (xS , yS , S 0, α). Positions (xS , yS ) and initial estimates of the flux using their evidence ratio: density at a central frequency (S 0) are produced from the LA channel-averaged maps; for sources detected at ≥ 3σ on at least Pr(H |D) Pr(D|H ) Pr(H ) Z Pr(H ) 1 = 1 1 = 1 1 , (6) three of the individual channel maps, a spectral index α is also Pr(H |D) Pr(D|H ) Pr(H ) Z Pr(H ) fitted to the channel flux densities. The flux density and spec- 0 0 0 0 0 tral index of sources which are detected at ≥ 4σ on the SA map where Pr(H1)/ Pr(H0) is the a priori probability ratio for the are modelled simultaneously with the cluster; this accounts for two models. To assess the detection significance of a cluster, we possible source variability (although we attempt to observe clus- therefore perform two parameter estimation runs – one with the ters close in time on the two arrays, this is not always possible full cluster + radio source environmentmodel (H1), andone with due to different demands on the observing time of the arrays) only the radio source environmentmodel (the ‘null’ run, H0). We and inter-array calibration uncertainty. Flux densities are given set Pr(H1)/ Pr(H0) = 1 so that Z1/Z0 is a measure of the detec- a Gaussian prior with σ = 40%; where α has been fitted from tion significance for the cluster. This ratio takes into account the the LA data, a Gaussian prior with width corresponding to the varioussourcesofnoise as well asthe goodnessof fit of the radio fitting uncertainty is applied, otherwise a prior based on the 10C source and cluster models. survey is applied (Davies et al. 2011). Sources detected at < 4σ Fig. 3 shows the distribution of ∆ ln(Z) values in the SZ on the SA map are subtracted directly based on the LA values of sample. It is also useful to define discrete ‘detection’ and ‘non- S 0 and α (or the median of the 10C prior where α has not been detection’ categories based on the continuous evidence ratio val- fitted) initially. If the cluster position output from the analysis ues. We follow Jeffreys (1961) in taking ∆ ln(Z) = 0 as the has directly-subtracted sources within 3arcmin, the analysis is boundary between detections and non-detections. We also de- repeated with those sources also modelled. The positions of the fine an additional boundary ∆ ln(Z) = 3 between ‘moderate’ sources are always fixed to their LA values as the LA has higher and ‘clear’ detections, where ‘moderate’ detections are cases positional precision. where the data are more consistent with the presence of a cluster In the cluster model, x0 and y0 are the offsets in RA and δ than not, but there is not enough information in the data to con- from the pointing centre of the SA observation; for previously- strain the model parameters well. For symmetry, we also define known clusters with existing AMI data, the pointing centre is a boundary at ∆ ln(Z) = −3 to indicate cases where the cluster the X-ray position of the cluster, while for new clusters it is the model is strongly rejected by the data. These boundaries were Planck position. Gaussian priors are used on x0 and y0, centred chosen empirically, by inspecting final maps and posterior dis- on the Planck position (i.e. offset from the pointing/phase ref- tributions. The four categories are listed in Table 3. erence centre, if the pointing centre is the X-ray position) and with width given by the Planck positional uncertainty up to a 4.3.1. Prior on Y and θ maximum of 5arcmin; larger priors allow the detection algo- tot s rithm to fix on noise features toward the edges of the SA pri- The priors assigned to Ytot and θs in AP2013 and used for the mary beam, which has a FWHM of ≈ 20arcmin. In practice, no Planck PwS analysis are based on marginalised distributions of
4 PSfrag replacements
PSfrag replacements Y. C. Perrott et al.: Planck and AMI SZ measurements for 99 galaxy clusters
Number of clusters Number of clusters 20 0 20 40 -20 -10 0 10 20 15
10 0 5 0.5 0.1 0.1 Number of clusters 1 2 0 0 20 40 60 80 100 120 0.01 0.01 arcmin
∆ ln(Z) /
0 tot Fig. 3: The distribution of evidence ratio values in the SZ sam- 0.5 Y 0.001 0.001 ple, with the division into detection categories given in Table 3 1 indicated by red vertical lines. 2 5 10 20 40 2 5 10 20 40 θs / arcmin θs / arcmin (a) (b) Table 3: The evidence difference (∆ ln(Z)) boundaries used for categorising clusters as clear detections, moderate detections, Fig. 4: (a) shows the sampled distribution (red histogram), and non-detections and clear non-detections, and the number of clus- the two-dimensional elliptical Gaussian fit to the Ytot vs θs dis- ters in each category in the SZ sample. tribution in log-space (black lines, enclosing 68% and 95% of the probability). (b) shows the residuals with respect to the sim- Category ∆ ln(Z) boundaries Number ulated distribution. Note that the colour-axis scales are different. Clear detection (Y) ∆ ln(Z) ≥ 3 79 Moderate detection (M) 0 ≤ ∆ ln(Z) < 3 20 Non-detection (N) −3 ≤ ∆ ln(Z) < 0 21 Clear non-detection (NN) ∆ ln(Z) < −3 3 Some representative examples from each category are dis- cussed in the following. In each case, two foreground-source- Ytot and θs in a simulated population of clusters generated ac- subtracted maps are shown; both are produced using natural cording to the Jenkins mass function (Jenkins et al. 2001), as weighting, and the second also has a Gaussian weighting func- described in Carvalho et al. (2012). The parameterisation func- tion with the 30% point at 600 λ applied (the ‘uv-tapered’ map). tions for these priors are listed in Table 4. These priors ignore, This taper downweights the longer baselines, which are only however, the correlation between Ytot and θs; in addition, they sensitive to small-angular-scale features, making the extended take into account the Planck selection function only in assuming cluster more visible. The symbols × and + show the positions minimum and maximum cutoffs in each parameter. of subtracted sources, respectively either modelled in McAdam To produce a better approximation to the true distribution of or directly subtracted based on LA values. shows the AMI clusters expected to be detected by Planck, we used the results (McAdam-determined) position of the cluster, and the 1×σPlanck of the Planck completeness simulation (Planck Collaboration positional error radius is shown as a circle. Contours are plotted XXIX 2014, Section 3.1 and 3.2, Fig. 9). This simulation was at ±(2, 3, 4,..., 10)× the r.m.s. noise level (measured using the produced by drawing a cluster population from the Tinker mass aips task imean), and dashed contours are negative. The synthe- function (Tinker et al. 2008), and converting the redshifts and sised beam is shown in the bottom left-hand corner. We empha- masses to Y500 and θ500 observable quantities using the scaling sise that these maps are only shown for visual inspection and relations in Planck Collaboration X (2011). This cluster popu- to assess the residual foreground contamination; all parameter lation was injected into the real Planck data assuming GNFW estimation is done in uv-space. pressure profiles with the shape parameters varying according Posterior distributions for position offset, cluster model pa- to results from Planck Collaboration Int. V (2013) and a simu- rameters and the flux densities of the closest radio sources to the lated union catalogue was created by running the Planck detec- cluster centre are also shown; in these plots the units are arc- 2 tion pipelines on the simulated dataset in the usual manner; see sec on the sky for offset in RA (x0) and δ (y0), arcmin for Ytot, Planck Collaboration XXIX (2014) for more details. arcmin for θs and mJy for radio source flux densities. The blue We noted that the resulting two-dimensional distribution in (pink) areas correspond to regions of higher (lower) probabil- θs and Ytot in log-space was elliptical in shape with roughly ity density. The Ytot-θs posterior distribution is shown separately Gaussian distribution along the principal axes and performed a with solid black lines for the AMI constraints overlaid with that two-dimensional Gaussian fit to the distribution, parameterised obtained by PwS using Planck data for the cluster in red, as well by width and offset in x = log10(θs), width and offset in y = as the AMI prior (black dashed lines). The joint constraint is log10(Ytot), and angle φ measured clockwise from the y-axis. The shown in yellow where appropriate. In all cases, the contours best-fit parameters are listed in Table 4, and the fit and residuals mark the 68% and 95% confidence limits in the posterior or prior with respect to the simulated population are shown in Fig. 4. We probability distributions. Similar maps and posterior distribution use this fit to the simulated population as our prior on θs and Ytot. plots for the entire sample are available online at http://www. astro.phy.cam.ac.uk/surveys/ami-planck/. 4.4. Results 4.4.1. Clear detections In the SZ sample, 79 are clear detections, 20 are moderate de- tections, 21 are non-detections and 3 are clear non-detections. A Abell 2218 (PSZ1 G097.72+38.13) summaryof the results for each cluster in the sample is presented Abell 2218 (Abell 1958) is an extremely well-known cluster and in Appendix A. one of the earliest SZ detections (e.g. Birkinshaw et al. 1978,
5 Y. C. Perrott et al.: Planck and AMI SZ measurements for 99 galaxy clusters Table 4: Priors used on profile fit parameters
Parameter Prior type Parameters Limits −x2/2σ2 x0, y0 Gaussian, e σ = max(5 arcmin,σPlanck) - −a Ytot (old) Power-law, x a = 1.6 0.0005 < x < 0.2 −λx θs (old) Exponential, λe λ = 0.2 1.3 < x < 45
2D elliptical Gaussian x0 = 0.6171,σx = 0.1153, Ytot, θs (new) in x = log10(θs), y0 = −2.743,σy = 0.2856, 1.3 <θs ◦ y = log10(Ytot) φ = 40.17
CONT: A0001 IPOL 15801.167 MHZ Aca.ICL001.1 CONT: A0001 IPOL 15801.167 MHZ Aca.ICL001.1
Birkinshaw et al. 1984, Jones et al. 1993). It lies at redshift 66 25 66 25 z = 0.171 (Kristian et al. 1978). It has been observedPSfrag by replacements AMI previously as part of the LoCuSS sample (Rodr´ıguez-Gonz´alvez 20 20 et al. 2012) and was also in AP2013. It has the highest Planck 15 4 5 15 4 5 SNR in the final subsample and is also well-detected by AMI 3 3 with ∆ ln(Z) = 34. Fig. 5 shows that the cluster is resolved by 10 10 Declination (J2000) Declination (J2000) AMI as the depth of the decrement increases inPSfrag the uv replacements-tapered PSfrag replacements map, and structure can be clearly seen in the naturally-weighted 05 05 map. The posterior distributions (Fig. 6) show good constraints 00 00 in both position and the cluster model parameters. The two- 16 38 00 37 30 00 36 30 00 35 30 00 34 30 00 16 38 00 37 30 00 36 30 00 35 30 00 34 30 00 Right ascension (J2000) Right ascension (J2000) dimensional posterior distributions for the flux densities of the Cont peak flux = -1.2804E-03 JY/BEAM Cont peak flux = -1.8656E-03 JY/BEAM three most significant nearby sources are included in the plot; it (a) (b) can be seen that there is some correlation between the flux densi- Fig.5: SA source-subtracted map of A2218 with (a) natural ties of the sources and Ytot, i.e. lower values of the flux densities weighting and (b) a uv-taper. The r.m.s. noise levels are 131 and ff − allow lower values of Ytot, but this does not a ect the parameter 6163 µJy beam 1 respectively. The numbered sources have pos- constraints significantly. There is also some correlation between 6.2terior distributions for their flux densities plotted in Fig. 6. See the flux densities of the sources and the cluster position. The re- Section 4.4 for more details on the plots. maining two sources near the cluster centre are fainter and were 5 not modelled in the initial analysis since they appear at < 4σ 10 15 on the SA map; there is no evidence for degeneracy between 5 15 the flux densities of these sources and the cluster parameters. As 10 15 2 12 in AP2013 (see their Fig. 5), the PwS Ytot-θs posterior overlaps with the AMI posterior, but AMI finds the cluster to be smaller 30 9 / arcmin / 0 0 3 y and fainter than Planck (at low significance for this particular 10 6 -30 ×
cluster). 10 3 s Ytot is the total SZ signal of the cluster and corresponds to θ 5 4 6 8 10 12 the zero-spacing flux, which is not measured by an interferome- 15 3 θ / arcmin tot 10 ter; the constraints produced by AMI on Ytot therefore rely on Y
× 5 extrapolating the signal on the angular scales that AMI does measure (≈ 200 to 1200λ, corresponding to ≈ 15 to 3arcmin) 3 6 S to 0λ assuming a fixed profile. Since this is a relatively nearby, 5.5 2 large-angular-size cluster (i.e. θ500 inferred from the X-ray lu- 4 minosity is 6.4arcmin (B¨ohringer et al. 2000, Piffaretti et al. S 1.5 2011) corresponding to θs = 5.4arcmin for the ‘universal’ value
5 3 of c500 = 1.177, in agreement with the AMI constraint and S 2.5 slightly smaller than the preferred Planck value), much of the -20 20 60 -30 0 30 4 8 12 5 15 5.5 6 1.5 2 2.5 3 3 flux of the cluster exists on scales that are not measured by x0 y0 θs Ytot × 10 S 3 S 4 S 5 AMI. Ytot is therefore not well constrained and the Ytot-θs degen- eracy is large compared to that produced by Planck, which mea- Fig.6: AMI posterior distributions for A2218 and the Ytot-θs pos- sures Ytot directly. Nonetheless, the different degeneracy direc- terior overlaid with that obtained by Planck in red, and the prior tion means that combining the two posteriors results in a tighter as a black dotted line (upper right-hand corner). The joint con- constraint (assuming no systematic difference between the two straint is shown in yellow. See Section 4.4 for more details on instruments, which will be discussed in Section 4.4.7). the plots.
PSZ1 G060.12+11.42 This is a new, previously unconfirmed (at the time the catalogue the cluster. The source flux densities of the two nearest sources was published) cluster discovered by Planck at high SNR (7.2) are shown in the posterior distributions; there is no apparent de- and clearly detected by AMI with ∆ ln(Z) = 16. The source- generacybetween the source flux densities and any of the param- subtracted maps for the cluster are shown in Fig. 7, and the pos- eters. In this case, the posterior distributions for θs and Ytot are terior distributions in Fig. 8. Again, it is clear that AMI resolves very consistent with the PwS posteriors. The AMI and PwS de-
6 PSfrag replacements PSfrag replacements
0 0 0.1 0.1 0.2 0.2 0.3 0.3 0.4 0.4 0.5 0.5 0.6 0.6 0.7 0.7 0.8 0.8 0.9 0.9 1 1
8 0 0 0.5 5 1
0 0 0.5 5 1 10 0 0 0.5 5 1 10
0 -100 0.5 -80 1 -60 0 -40 0.5 -20 1 -100 0 -80 0.5 -60 1 -40 -20 -100 0 -80 0.5 -60 1 -40 0 -20 0.5 1 0 -100 0.5 -50 1 -100 0 -50 0.5 -100 1 -50 -100 -50 0 0 0.5 0.5 1 0 0.5 4 4.5 1 5 0 0 0.5 5 1 0 0 5 0.5 10 1 -100 0 -80 0.5 -60 1 -40 0 -20 0.1 -100 0.2 -50 0.3 0 0.4 0.1 0.5 0.2 0.6 0.3 0.7 0.4 0.8 0.5 0.9 0.6 1 0.7 0 0.8 Y. C. Perrott et al.: Planck and AMI SZ0.5 measurements for 99 galaxy clusters 0.9 1 CONT: A0001 IPOL 15730.784 MHZ Aca.ICL001.1 CONT: A0001 IPOL 15730.784 MHZ Aca.ICL001.1 0 CONT: A0001 IPOL 15734.193 MHZ Aca.ICL001.1 CONT: A0001 IPOL 15734.193 MHZ Aca.ICL001.1 129 30 29 30 1 0.5 1 1.5 23 20 23 20 1 25 25 0 1.5 0.5 1 15 15 4 20 9 20 9 4.5 1 1 0 2 1 2 1 0.5 5 10 10 1 15 15 1 1.5Declination (J2000) Declination (J2000) Declination (J2000) 0 Declination (J2000) 0.5 05 05 4 10 10 4.5 1 PSfrag replacements PSfrag replacements PSfrag replacements 0 PSfrag replacements 5 00 00 0 05 05 0.5 5 1 18 59 45 30 15 00 58 45 30 15 00 57 45 18 59 45 30 15 00 58 45 30 15 00 57 45 21 23 15 00 22 45 30 15 00 21 45 30 21 23 15 00 22 45 30 15 00 21 45 30 Right ascension (J2000) Right ascension (J2000) 0 Right ascension (J2000) Right ascension (J2000) 1 Cont peak flux = -9.7653E-04 JY/BEAM Cont peak flux = -1.3182E-03 JY/BEAM Cont peak flux = 5.9762E-04 JY/BEAM Cont peak flux = 5.9791E-04 JY/BEAM 1.5 0.5 4 (a) (b) 1 (a) (b) 4.5 0 5Fig.7: SA source-subtracted map of PSZ1 G060.12+11.42 with 0.5Fig.9: SA source-subtracted map of ZW8503 with (a) natural 0 1 5(a) natural weighting and (b) a uv-taper. The r.m.s. noise levels 0weighting and (b) a uv-taper. The r.m.s. noise levels are 90 and − − 0are 96 and 131 µJy beam 1 respectively. The numbered sources 0.5122 µJy beam 1 respectively. The numbered sources have poste- 5 1 10have posterior distributions for their flux densities plotted in 0rior distributions for their flux densities plotted in Fig. 10. See 0Fig. 8. See Section 4.4 for more details on the plots. 0.5Section 4.4 for more details on the plots. 0.5 1
10 10.0 2 8 2 7.5 0 6 / arcmin / / arcmin / 3
8 3 100 5.0 10 10 0 0 4 × ×
-50 y y 0 -100 2 2.5 30 10 0 s s 0.5 θ θ 5 3 6 9 12 15 6 12 18 24 30 0 1 10 θ / arcmin θ / arcmin 0.5 0 0 1 0.5 10 tot 0 tot 4 1 6 Y Y 0.5 0 2 1 0 0.5 5 0 1 5 1 1 S 0.5 S 4.5 0 1 0.5 4.5 4 0 1 0.5 1.5 0 9
2 1.5 S 1 0.5 S 1 0 1 1 0.5 -100 -50 -100 -50 0 5 10 0 4 4 4.5 5 1 1.5 0 -100 0 0 100 10 30 2 6 10 4.5 5 1 1.5 1 0.5 x0 y0 θs Ytot S 1 S x0 y0 θs Ytot S 1 S 9 1 2
Fig.8: AMI posterior distributions for PSZ1 G060.12+11.42and Fig.10: AMI posterior distributions for ZW8503 and the Ytot-θs the Ytot-θs posterior overlaid with that obtained by Planck (upper posterior overlaid with that obtained by Planck (upper right hand right-hand corner). The joint constraint is shown in yellow. See corner). See Section 4.4 for more details on the plots. Section 4.4 for more details on the plots.
tion. The AMI map shows a good positional coincidence with generacies are in different directions, meaning that the joint con- the X-ray emission (Fig. 11) and also shows some substructure straints produced by combining the two are considerably tighter. within the cluster; if this is real, the spherical cluster model with the ‘universal’ pressure profile (derived from fits to relaxed clus- ters) may not provide a good fit and the extrapolated Y result 4.4.2. Moderate detections tot may be biased. ZW8503 (PSZ1 G072.78-18.70) ZW8503 is a well-known cluster at z = 0.143 (Allen et al. 4.4.3. Non-detections 1992) with a large angular size (θs ≈ 8arcmin as measured by Planck); it is therefore not too surprising that AMI does not de- PSZ1 G074.75-24.59 tect it well. A decrement at the phase centre is visible in the PSZ1 G074.75-24.59 is associated in the Planck catalogue with source-subtracted maps (Fig. 9), and a model with a cluster is ZwCl 2143.5+2014. Despite having an SNR of 6.1 and being favoured over one without by ∆ ln(Z) = 1.8, but Fig. 10 shows detected by all three of the Planck detection algorithms, it is not that there is not enough information in the AMI data to constrain detected by AMI, with an evidencedifference of ∆ ln(Z) = −2.6. the cluster parameters well, and the Ytot-θs posterior distribution Although there is some negative flux visible on the map, it is is strongly influenced by the prior (plotted as a black dotted line ruled out by the Planck positional prior (Fig. 12). for comparison). There is also significant degeneracy between the cluster parameters (x0, y0, θs,Ytot) and the flux densities of 2 Courtesy of the Chandra X-ray Observatory Center and the closest sources. The parameter space indicated by the Planck the Chandra Data Archive, http://cxc.cfa.harvard.edu/cda/ posterior is completely ruled out by the AMI posterior distribu- (ivo://ADS/Sa.CXO#obs/13379)
7 PSfrag replacements
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
-100 0 100 200
-100 0 100 -100 0 100
20 40 60 -100 0 100 200 -100 0 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Y. C. Perrott et al.: Planck and AMI SZ0 measurements for 99 galaxy clusters
CONT: A0001 IPOL 15733.883 MHZ Aca.OHGEO.1 5 0 10 20 30 10 23 18 0 12 16 5
10 2 14 20 9 40 12 / arcmin /
60 3 6 10 Declination (J2000) 10 ×