MNRAS 532, 2842–2859 (2024) https://doi.org/10.1093/mnras/stae1640 Advance Access publication 2024 July 3 MeerKAT obser v ations of starburst galaxies and AGNs within the core of XMMXCS J2215.9 −1738 at z = 1.46 D. Y. Klutse, 1 , 2 ‹ M. Hilton , 2 , 3 ‹ I. Heywood , 4 , 5 , 6 I. Smail , 7 A. M. Swinbank , 7 K. Knowles 5 , 6 and S. P. Sikhosana 1 , 2 1 Astrophysics Research Centre, University of KwaZulu – Natal, Westville Campus, Durban 4041, South Africa 2 School of Mathematics, Statistics & Computer Science, University of KwaZulu – Natal, Westville Campus, Durban 4041, South Africa 3 Wits Centre for Astrophysics, School of Physics, University of the Witwatersrand, Private Bag 3, Johannesburg 2050, South Africa 4 Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK 5 Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, P.O. Box 94, Makhanda 6140, South Africa 6 South African Radio Astronomy Observatory, 2 Fir Street, Black River Park, Observatory, Cape Town 7925, South Africa 7 Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK Accepted 2024 July 1. Received 2024 June 26; in original form 2024 April 18 A B S T R A C T We present the first detailed radio study of the galaxy cluster XMMXCS J2215.9 −1738 at z = 1.46 using MeerKAT L -band (1.3 GHz) observations. We combine our radio observation with archival optical and infrared data to investigate the star formation and active galactic nucleus (AGN) population within R 200 ( R = 0.8 Mpc) of the cluster centre. Using three selection criteria; the radio luminosity, the far-infrared radio ratio ( q IR ), and the mid-infrared colour, we distinguish galaxies with radio emission predominantly powered by star formation from that powered by AGNs. We selected 24 cluster members within R 200 in the MeerKAT image based on either their photometric or spectroscopic redshift. We classified 12/24 (50 per cent) as galaxies whose radio emission is dominated by star-formation activity, 6/24 (25 per cent) as intermediate star-forming galaxies, and 6/24 (25 per cent) as AGN-dominated galaxies. Using the radio continuum luminosities of the star-forming cluster galaxies, we estimated an integrated star formation rate (SFR) value of 1700 ± 330 M � yr −1 within R 200 . We derived a mass-normalized integrated SFR value of (570 ± 110) × 10 −14 yr −1 . This supports pre vious observ ational and theoretical studies that indicated a rapid increase in star formation activity within the core of high-redshift clusters. We also show that the high-AGN fraction within the cluster core is consistent with previous cluster observations at z > 1.5. Key words: galaxies: clusters: general – galaxies: clusters: individual: (XMMXCS J2215.9 −1738) – galaxies: star formation. 1 G o d e t e d w d 2 2 g l f � b S r g s e S X c d r A s a a 2 D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 I N T RO D U C T I O N alaxy clusters provide a powerful means to study the formation f large-scale structures, the evolution of galaxies, and the thermo- ynamics of the intergalactic medium. They also complement other xisting probes of structural growth over cosmological time due to heir high masses (Kravtsov & Borgani 2012 ). Environment plays a major role in galaxy evolution and this is vident via the relationship of star formation rate to local galaxy ensity. Star formation rate (SFR) in galaxies at z � 1.0 increases ith increasing galaxy density up to galaxy group scales, and then eclines in the denser regions of galaxy clusters (Kodama & Bower 001 ; Lewis et al. 2002 ; G ́omez et al. 2003 ; Blanton & Moustakas 009 ; Cluver et al. 2020 ; Pearson et al. 2021 ). Denser regions within alaxy clusters at z � 1.0 are mostly populated by elliptical and enticular galaxies (early-type galaxies) which show minimal star ormation activity in contrast to low-density regions mostly occupied E-mail: dianasmoke1@gmail.com (DYK); matt.hilton@wits.ac.za (MH) ( s o Published by Oxford University Press on behalf of Royal Astronomical Socie Commons Attribution License ( https:// creativecommons.org/ licenses/ by/ 4.0/ ), whi y star-forming spirals (late-type disc galaxies; Dressler et al. 1997 ; mith et al. 2005 ). Sev eral studies hav e suggested a rev erse in this order at higher edshifts (i.e. in some clusters at z > 1, the fraction of star-forming alaxies increases with galaxy density) leading to the so-called rever- al in the star formation density relation (Hayashi et al. 2010 ; Tran t al. 2010 ; Tadaki et al. 2012 ; Brodwin et al. 2013 ; Santos et al. 2015 ; mail 2024 ). For example, a study of the z = 1 . 56 galaxy cluster MMU J1007.4 + 1237 showed strong starburst activity within the luster core (Fassbender et al. 2011 ). Whilst Wang et al. ( 2016 ) etected nine star-forming cluster galaxies within the central 80 kpc egion of the X-ray detected cluster CL J1001 + 0220 at z = 2 . 5. Sub-millimetre Common User Bolometer Array 2 (SCUBA-2; ub-millimetre observation) study of the CL 0218.3 −0510 cluster t z = 1 . 6 by Smail et al. ( 2014 ) showed that active star formation ctivities take place outside the cluster core, whilst the outcome of a 4- μm (mid-infrared) observation of the same cluster from Tran et al. 2010 ) showed that this high-redshift cluster was actively forming tars. In contrast, an 850 μm SCUBA-2 continuum observations f eight X-ray-detected massive galaxy clusters at z ≈ 0 . 8 − 1 . 6 © 2024 The Author(s). ty. This is an Open Access article distributed under the terms of the Creative ch permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. http://orcid.org/0000-0002-8490-8117 http://orcid.org/0000-0001-6864-5057 http://orcid.org/0000-0003-3037-257X http://orcid.org/0000-0003-1192-5837 http://orcid.org/0000-0002-8452-0825 http://orcid.org/0000-0003-3199-1161 mailto:dianasmoke1@gmail.com mailto:matt.hilton@wits.ac.za https://creativecommons.org/licenses/by/4.0/ MeerKAT observations of XCS J2215 2843 s S t f e ( fi c o C f t r W t 2 g ( w s s c i m × b m w r J I t c = v h s ( o o a M P e a b h t a a e f i c r ( o s c s ( c b b d s g w o t L s J o b f d l I g o s l m i W c a = s u 2 T o a a o 2 T L r f d − d m B c c f D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 tudied by Cooke et al. ( 2019 ) revealed that the mass-normalized FR for clusters at 1 < z < 1 . 6 is a factor of 1 . 5 ± 0 . 3 lower than he field galaxies and they do not find any reversal for local star- ormation-rate-density (SFRD) relation in their study. In a study of ight submillimetre (850 μm) galaxy clusters at z = 1 . 6 − 2 . 0, Smail 2024 ) found a reversal in the local SFRD relation for clusters and elds at z = 1 . 8. There may be a wide range of star formation activity in galaxy lusters at z > 1. A narrow band imaging surv e y of the [ O II ] emitters f the CIG J0218.3 −0510 cluster at z = 1 . 62 using the Suprime- am on Subaru Telescope led to the detection of some very high-star ormation rate galaxies as well as some quiescent galaxies within he cluster core (Tadaki et al. 2012 ). Similarly, the study of a higher edshift cluster JKCS 041 at z = 1 . 8 (Andreon et al. 2009 ) using the ide Field Camera 3 of the Hubble Space Telescope showed that he cluster core was populated by quiescent galaxies. (Newman et al. 014 ). Studies have shown that galaxy mergers, interactions and active alactic nuclei (AGN) activities take place in high-redshift clusters Lotz et al. 2013 ; Alberts et al. 2016 ; Krishnan et al. 2017 ) but hether these processes lead to the enhancement or suppression of tar formation has not been conclusively established. The study of tar formation and AGNs in 11 spectroscopically selected massive lusters at 1.0 < z < 1.75 by Alberts et al. ( 2016 ) showed an increase n star formation rate, excess AGN activity and an increase in galaxy erger rate within the clusters at this high redshift. The central 24 24 kpc region within the cluster XDCP J0044.0 −2033 at z � 1.5 y Lepore et al. ( 2022 ) showed that high-star formation and gas-rich erger-driven nuclear activities take place in the cluster core (i.e. ithin ≈ 0.16 Mpc from the cluster centre). One well studied cluster to investigate starburst activity at high- edshift is XMMXCS J2215.9 −1738 at z = 1 . 46 (subsequently 2215, located at R.A. = 22 h 15 m 58 . s 5 and Dec. = 17 ◦38 ′ 02 ′′ ). t was one of the distant clusters with a well-developed structure o be disco v ered at X-ray wav elengths (Stanford et al. 2006 ). The luster’s velocity dispersion σv within a virial radius R 200 (i.e. R 0.8 Mpc) is 720 ± 110 kms −1 (Hilton et al. 2010 ), resulting in a irial mass of M cl = 3 × 10 14 M �. A SCUBA-2 surv e y found sev eral ighly star-forming galaxies in the cluster’s core with an integrated tar formation rate of ≈1400 M � yr −1 (Salpeter initial mass function IMF) assumed, Ma et al. 2015 ). Thus J2215 appears to be an example f a distant and highly star-forming galaxy cluster. Twelve [ O II ] emitting cluster members and four star forming dust- bscured ultra luminous infrared galaxies (ULIRGs) were detected t < 0.25 Mpc from the cluster centre by Hayashi et al. ( 2010 ) and a et al. ( 2015 ), respectively. A 24- μm Spitzer/Multiband Imaging hotometer for Spitzer (MIPS) cluster surv e y conducted by Hilton t al. ( 2010 ) resulted in the detection of three star-forming galaxies nd a potential AGN all located at R < 0.25 Mpc, suggesting that oth starburst and AGN activities take place in the cluster core at igher redshifts. There is also evidence of mergers between cluster galaxies within his high-redshift cluster; a surv e y of the core region of J2215 cluster t z = 1 . 46 using the Atacama Large Millimetre Array (ALMA) nd the MUSE spectrograph on the Very Large Telescope by Stach t al. ( 2017 ) led to the detection of 14-mm sources within ≈0.5 Mpc rom the cluster centre. The result obtained by Stach et al. ( 2017 ) ndicated that there was an intense star formation within the cluster ore and evidence of a likely merger event taking place. The most ecent study of the J2215 cluster from the ALMA CO J = 2 − 1 line 0.4 arcsec resolution) and 870 μm continuum (0.2 arcsec resolution) bservation by Ikeda et al. ( 2022 ) has shown evidence of enhanced tar formation in the central region of the cluster, with 6 out of 17 luster members observed to be early-stage mergers. Observations have also shown that both quiescence galaxies and tar-forming systems reside within the cluster core; Hayashi et al. 2018 ) detected 12 quiescent and 27 star-forming galaxies within the ore of the J2215 cluster at z = 1.46 via the study of the ALMA and 3 data. The study of the J2215 cluster using the KMOS ( K- and Multi-Object Spectrograph) by Maier et al. ( 2019 ) led to the etection of apparently slow quenching systems and slightly lower tar formation activity within the cluster core. As noted abo v e, there hav e been sev eral studies of the J2215 alaxy cluster conducted at infrared and millimetre/submillimetre avelengths. Here, we present the first detailed radio observation f the J2215 galaxy cluster using the MeerKAT radio telescope. In his work, we combine archi v al optical and infrared data with new -band radio observations from MeerKAT to further investigate the tar formation, AGN and merger activities within the core of the 2215 cluster. This paper is structured as follows: We describe the MeerKAT bservations of the J2215 cluster, the data reduction process and riefly describe the optical and infrared archi v al observ ations used or this work in Section 2 . We describe the MeerKAT source etection, cluster membership classification scheme, and the radio uminosity and continuum star formation rate estimation in Section 3 . n Section 4 , we show the colour–magnitude relation of the cluster alaxies and their morphologies. In Section 5 , we characterize ur galaxy samples into normal star-forming galaxies, intermediate tar-forming galaxies, and AGNs using three indicators; the radio uminosity value, the far-infrared radio ratio ( q IR ) value, and the id-infrared colours. In Section 6 , we compare the AGN activity n the J2215 cluster core to other higher and low-redshift surv e ys. e discuss the star formation activity in J2215 and the evolution of lusters with redshift in Section 7 . We conclude this work by giving summary of the entire work done and the prospects in Section 8 . We assume a � cold dark matter cosmology with H 0 70 km s −1 Mpc −1 , �� = 0 . 7, and �m = 0 . 3. The AB magnitude ystem and the Chabrier ( 2003 ) IMF were used throughout this work nless stated otherwise. OBSERVATI ON A N D DATA R E D U C T I O N his work is based on the radio observation of the J2215 cluster btained from the MeerKAT telescope in combination with other rchi v al data. Sections 2.1 and 2.2 co v er the details of the MeerKAT observation nd data processing respectively, while we summarize the properties f the archi v al multiwavelength data used in this study in Section 2.3 . .1 MeerKAT obser v ations he J2215 galaxy cluster was observed in May 2019 using the -band receivers of the 64-dish MeerKAT telescope. The L -band eceiv er co v ers a frequenc y range of 856 − 1712 MHz with a central requency of 1284 MHz. The observation was conducted on two ifferent days, from 2019 May 11–12 between the hours of 02:16 10:20 UTC each day. A total of 61 antennas were in operation uring the observation. The 4096 (4K) channel wideband-coarse ode of the Square Kilometre Array Reconfigurable Application oard processing nodes correlator was used resulting in 209 kHz hannel resolution.The data was recorded in full polarization. The orrelator dump time was 8 s, and the data were acquired for all our polarization products, labelled as XX, XY, YX, and YY. The MNRAS 532, 2842–2859 (2024) 2844 D. Y. Klutse et al. M d a e f s ( c e 1 t o 2 D O t M t c t p R ‘ a m d S t a T t o o D e c B s f o a D a t o c o T f M E o s − t 1 c S V w ( d t = c 2 T d t t s A 6 b a S ( b i M C v b i 2 8 4 s 8 o t J i l i I s p r ( T i f P a e I a D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 ata set in measurement set format for the two-day observation is bout 5.2 TB with an approximate 2.6 TB measurement set obtained ach day. J1939 −6342 was used as the primary calibrator (i.e. or flux, delay, and bandpass calibration) while a much closer ource ( ≈ 13 degrees of the target source position), J2225 −0457 3C446) served as the secondary calibrator for amplitude and phase alibration. We observed the bandpass calibrator for 10 min after very two hours and two minutes on the gain calibrator after every 5-min target scan. In total, we spent ≈12 h on the target source and he total integration time for the entire observation is ≈16 h i.e. 8 h f total integration each day. .2 Data processing ata reduction was performed using a semi-automated pipeline, XKAT 1 (Heywood 2020 ). O XKAT comprises a set of python scripts hat incorporates other radio astronomical packages to process the eerKAT data. The first step in the OXKAT pipeline was to duplicate he MS (main sequence) and average to 1024 channels to make the ontinuum data processing easier i.e. faster with shorter computation ime. The primary calibrator was then re-phased to the correct osition via the CASA (McMullin et al. 2007 ) task FIXVIS . The known adio Frequency Interference (RFI) channels documented in the MeerKAT-Cookbook’ were flagged, other flags were also applied to ll the fields using the CASA task FLA GD ATA (i.e. manual, clip, quack ode) while auto-flaggers were applied to only the calibrators. We erived model data visibilities for the primary calibrator defined by tev ens–Re ynolds 2016 flux density scale (Partridge et al. 2016 ). We derive an intrinsic model for the secondary calibrator based on he primary calibrator and further derived delay ( K), bandpass ( B), nd gain ( G ) calibrations from the primary and secondary calibrators. he gain solutions were then applied to all the calibrators and the arget. K , B, and G corrections are derived iteratively, with rounds f residual flagging in between. The calibrated target data was split ut into individual MS, with the reference calibrated data in the ATA column of the new MS. We then imaged the radio continuum mission with WSCLEAN (Offringa et al. 2014 ) in Stokes I and then onducted one round of phase and then amplitude self-calibration. Imaging was performed using a cell size of 1.1 arcsec, and a riggs weighting of −0 . 3. Due to the presence of a ≈4.6 Jy extended ource 2MASX J22142575 −1701362 located at ≈ 0.7 degrees away rom our target (see Fig. 1 ), we performed a peeling operation n the ‘troublesome source’ in our field. This involved modelling nd subtracting using CUBICAL (Kenyon et al. 2018 ). We exploit DFACET (Tasse et al. 2018 ) on the residual visibility with the best vailable cleaning mask from the previous WSCLEAN run (cropped to he appropriate DDFACET image size i.e. 10125 × 10125 pixels) to btain a sky model and then defined the directions that will form the entres of the tesselated sk y. We deriv ed the gain solutions for each f the tesselated sky models using KILLMS (Tasse 2014 ; Smirnov & asse 2015 ). Further, we re-ran DDFACET to apply the gain corrections derived rom the KILLMS run and also the primary beam correction. The eerKAT L -band primary beam model was generated using the IDOS software (Asad et al. 2019 ). The primary beam has a diameter f ≈1.4 ◦. The resulting 1284 MHz image has a synthesized beam ize of 6 . 01 arcsec × 5 . 26 arcsec with a positional angle, PA of 10.4 degrees and an rms noise level of ≈3.5 μJy beam −1 . This is he most sensitive radio observation of the cluster to date. NRAS 532, 2842–2859 (2024) https:// github.com/ IanHeywood/ oxkat 2 We determined the accuracy of the astrometry of our image by omparing the coordinates of the MeerKAT sources (10 890, see ection 3.1 ) with its closest counterpart in the JVLA (Karl G. Jansky ery Large Array) map (298 sources). The processed JVLA map ith a sensitivity of ≈7.5 μJy beam −1 was obtained from Ma et al. 2015 ). The source extraction was done following the same procedure escribed in Section 3.1 . The mean offset of the 275 counterparts in he JVLA map was � RA = ( −0 . 22 arcsec ± 0 . 61 arcsec ) and � Dec ( −0 . 11 arcsec ± 0 . 61 arcsec which is insignificant so we did not orrect the astrometry. .3 Archi v al multiwav elength obser v ations o study the multiwavelength properties of the radio sources etected in the cluster we made use of archi v al images, pho- ometry or catalogues from submillimetre/far-infrared data from he SCUBA-2 (Ma et al. 2015 ), submillimetre/millimetre ob- ervations from Atacama Large Millimetre/Sub-millimetre Array, LMA band 3 (Hayashi et al. 2010 ), ALMA 1.25 mm (Band- ) observation (Stach et al. 2017 ), optical data from the Hub- le Space Telescope ( HST ), Advanced Camera for Surv e ys, ACS nd infrared data from the Multi-Object Infrared Camera and pectrograph, MOIRCS mounted on the 8.2 m Subaru telescope Hilton et al. 2009 ), the Infrared Array Camera (IRAC) on- oard the Spitzer Space Telescope (Fazio et al. 2004 ), the mid- nfrared (24- μm) observations of the cluster obtained using the IPS (Hilton et al. 2010 ), and the PACS (Photodetecting Array amera and Spectrometer) onboard the Herschel Space Obser- atory . 2 A summary of the archi v al observ ations can be found elow. SCUBA-2 450 μm and 850 μm : The J2215 cluster was observed n band 1 using the SCUBA-2 camera by Ma et al. ( 2015 ) between 013 July and August. The total observation time of the 450 and 50 μm surv e ys was 8 h (i.e. 12 scans and each scan lasted for 0 min). For detailed information on data reduction and imaging, ee Ma et al. ( 2015 ). The resulting noise level of the 450 and the 50 μm data was 5.4 and 0.63 mJy beam −1 , respectively. ACS/ HST : The J2215 galaxy cluster was among the 25 clusters bserved during the HST type Ia Supernovae search observed with he Wide Field Channel of the ACS mounted on the HST from 2005 uly to 2006 December. The total integration time for the observation n the i 775 band was 3320 s (resulting in a 5 σ point source magnitude imit of ≈ 25 . 1 ) whilst a total of 16 935 s exposure time was recorded n the z 850 band (reaching a deeper magnitude limit of ≈26.0). nformation on the observation is reported by Dawson et al. ( 2009 ), ee also Hilton et al. ( 2009 ) for detailed information on the data rocessing. MOIRCS/Subaru : Observation of the J2215 cluster was car- ied out with the Multi-Object Infrared Camera and Spectrograph MOIRCS, Ichikawa et al. 2006 ) mounted on the Subaru telescope. he 5 σ point source limiting magnitude from the J and K s -band mage was 24. More detailed information on the observation can be ound in Hilton et al. ( 2009 ). IRAC/Spitzer : The IRAC imaging of J2215 was obtained through rogramme 50 333 using all four channels (Ch1-Ch4: 3.6, 4.5, 5.8, nd 8.0 μm) on 2008 July 12. The total observation time was 1500 s xposures. The 5 σ point source magnitude limit obtained from the RAC catalogue was ≈23 mag (Ch1 and Ch2) and ≈20 mag (Ch3 nd Ch4) (see Hilton et al. 2010 for details). https:// irsa.ipac.caltech.edu/ Missions/ herschel.html https://github.com/IanHeywood/oxkat https://irsa.ipac.caltech.edu/Missions/herschel.html MeerKAT observations of XCS J2215 2845 Figure 1. Left panel: an ≈ 70 arcmin × 50 arcmin zoom-in image of the radio continuum image produced from MeerKAT’s L -band observation with the image before peeling displayed (rms noise value = 3.9 μJy beam −1 ). The very bright ≈4.6 Jy source is visible in the image (indicated with ≈4.0 ′ radius magenta circle) and the target source is located at a distance of 0.7 ◦ (indicated with a 2.75 ′ × 2.75 ′ cyan box). Right panel: same as the left panel but the very bright ≈4.6 Jy source has been mitigated after the peeling operation. The o v erall image has been well impro v ed after the peeling process (rms noise value = 3.5 μJy beam −1 ). 2 s 2 w r c b w w v l ( t a T 0 t o e t A t P w i m a 0 v C o o ≈ t a i N a J 2 T u fi p E e c b l a H 3 3 W M ( o t u M p 1 t o M 1 i D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 MIPS/Spitzer obser v ation : The target cluster w as observed on 008 June 21 before the IRAC observation was conducted via the ame proposal. The total integration time for the observation was 7 000 s. The 50 per cent completeness limit of the 24 μm observation as estimated to be 70 μJy at 5 σ . Detailed information about data eduction and photometry can be found in Hilton et al. ( 2010 ). ALMA (BAND 3) : A CO( J = 2–1) emission line surv e y of the luster was by carried out by Hayashi et al. ( 2017 ) using ALMA in and 3 in 2016 May. The total integration time for the observation as 3.12 h. Data reduction and processing were done using CASA ith a standard pipeline. The mosaicked 3D cubes with five different elocity resolutions 50, 100, 200, 400, and 600 km s −1 yielded noise evels of 0.17, 0.12, 0.11, 0.12, and 0.12 mJy beam −1 , respectively see Hayashi et al. 2017 for detailed information). ALMA (BAND 6) : The CO( J = 5–4) observations of the core of he J2215 were carried out by Stach et al. ( 2017 ) using forty-two 12 m ntennae on 2016 June 19 under the project ID: 2015.1.00575.S. he six pointing observations yielded a synthesized beam size of . 66 arcsec × 0 . 47 arcsec (PA = 78 ◦). The rms noise recorded for he final mosaicked image was 48 μJy beam −1 . Detailed information n the data acquisition and reduction process can be found in Stach t al. ( 2017 ). PACS Herschel 100 μm (green) and 160 μm (Red) : We obtained he J2215 PACS 100 and 160 μm data from the Herschel Science rchive. We conducted aperture photometry at the positions of he detected MeerKAT sources (see Section 3.1 below) using the HOTOUTILS package (Bradley et al. 2016 ). Fluxes were extracted ithin aperture sizes 6 arcsec and 12 arcsec for the 100 and 160 μm mages, respectively. The noise in the images was estimated using the edian absolute deviation of the data in source-free regions using pertures of 6 arcsec and 12 arcsec. We obtained a noise level of .2 and 0.3 mJy at 100 and 160 μm, respectively. Comparing our alues to that of the catalogue from the Herschel /PACS Point Source atalogue (HPPSC) via the Herschel User Provided Data Products 2 , ur values are consistent with that of the HPPSC (i.e. a median ratio f ≈1 for both bands). Ho we ver, our v alues are higher by a factor of 3 and 2 for the green and red bands, respectively, with reference o the values obtained by Ma et al. ( 2015 ) even after conducting perture photometry using similar aperture sizes used in that work .e. 4.2 arcsec and 8.5 arcsec for the green and red bands, respectively. ote that Ma et al. ( 2015 ) erroneously treat the 100 μm PACS data s if it were 70 μm data, although no 70 μm PACS observations of 2215 exist in the archive. .4 Photometric redshifts he photometric redshift catalogue from Hilton et al. ( 2009 ) was sed in this work. Hilton et al. ( 2009 ) used the EAZY spectral template tting code of Brammer, van Dokkum & Coppi ( 2008 ) to estimate the hotometric redshift for the cluster galaxies. A default option within AZY was selected to fit a linear combination of all of the spectral nergy distribution templates to the cluster galaxies available in the atalogue within a redshift range of 0 < z < 4. The K−magnitude ased Bayesian redshift prior used in the code resulted in a maximum ikelihood redshift estimate z p and this estimated redshift value was dopted as the photometric redshift of the J2215 cluster galaxies, see ilton et al. ( 2009 ) for detailed information. ANALYSI S .1 MeerKAT source detection e extracted sources with > 4 σ detection significance from the eerKAT image using the Python Blob Detector and Source Finder PyBDSF ; Mohan & Rafferty 2015 ) resulting in an initial catalogue f 10 892 radio sources. We performed a ‘ne gativ e peak analysis test’ o quantify the level of noise contamination similar to the approach sed by Patil et al. ( 2019 ). This was accomplished by inverting the eerKAT continuum map and re-running PyBDSF using the same arameters we used for the original source extraction. We detected 54 ne gativ e sources as compared to the > 10 K sources detected in he original map which corresponds to a false positive detection rate f ≈1.4 per cent. We estimated a 4 σ flux detection limit of 14 μJy from the eerKAT image which translates to a limiting luminosity value of .5 ×10 23 WHz −1 at the cluster redshift of z = 1 . 46. This luminosity s equi v alent to SFR = 46 M �yr −1 when assuming the Bell ( 2003 ) MNRAS 532, 2842–2859 (2024) 2846 D. Y. Klutse et al. M T able 1. The MeerKAT -detected cluster galaxies within 0.8 Mpc of the cluster centre. Columns: (1) The ID numbers of each source in the MeerKAT L -band image selected as a cluster member; (2) MeerKAT pointing coordinates of each galaxy the units of right ascension (R.A.) are in hours, minutes, and seconds; (3) the units of declination (Dec) are in degrees, arcminutes, and arcseconds; (4) the observed flux measured in μJy; (5) radio luminosities are measured in WHz −1 ; (6) the Far Infrared Radio Luminosity Ratio; (7) star formation rates measured in M � yr −1 . Note that these estimates will not be reliable for galaxies where the radio emission is primarily due to the presence of an AGN; (8) radial distance of sources measured with respect to the cluster X-ray position measured in Mpc. The potential radio AGNs are marked with asterisks ( ∗) whilst objects blended in the MeerKAT radio image are denoted by the obelisk mark ( † ). (1) (2) (3) (4) (5) (6) (7) (8) MKT ID R.A. Dec. F 1 . 3 L 1 . 4 q IR SFR R (J2000) (J2000) ( μJy) (10 23 WHz −1 ) (M � yr −1 ) (Mpc) 5242 ∗ 22:16:04.79 −17:37:52.5 102 ± 8 10.6 ± 0.8 2.37 ± 0.25 336 ± 26 0.76 5307 22:16:03.75 −17:37:10.4 24 ± 7 2.5 ± 0.8 2.53 ± 0.37 81 ± 24 0.77 5332 ∗ 22:16:03.10 −17:38:39.3 197 ± 8 20.4 ± 0.8 1.74 ± 0.39 650 ± 26 0.64 5336 22:16:03.26 −17:39:09.0 18 ± 7 1.9 ± 0.7 1.95 ± 1.0 60 ± 23 0.80 5373 22:16:02.50 −17:37:56.5 40 ± 9 4.2 ± 1.0 1.76 ± 0.35 133 ± 31 0.49 5442 † 22:16:00.88 −17:38:31.7 77 ± 7 8.0 ± 0.7 2.48 ± 0.22 254 ± 22 0.38 5443 † 22:16:00.59 −17:38:35.3 61 ± 6 6.3 ± 0.6 2.55 ± 0.22 201 ± 20 0.38 5469 ∗ 22:16:00.30 −17:37:50.7 174 ± 12 18.1 ± 1.3 1.85 ± 0.42 576 ± 40 0.24 5470 ∗† 22:15:59.67 −17:37:59.2 125 ± 11 13.0 ± 1.2 2.45 ± 0.35 412 ± 37 0.14 5492 22:16:00.29 −17:38:58.7 21 ± 8 2.2 ± 0.8 2.19 ± 0.26 70 ± 26 0.52 5517 † 22:15:59.75 −17:38:17.0 47 ± 7 4.9 ± 0.8 2.48 ± 0.24 154 ± 24 0.19 5551 † 22:15:59.10 −17:37:41.5 69 ± 11 7.2 ± 1.1 2.45 ± 0.34 228 ± 35 0.19 5574 ∗ 22:15:58.13 −17:38:18.3 108 ± 10 11.2 ± 1.1 2.21 ±40.41 356 ± 34 0.14 5618 ∗† 22:15:57.27 −17:37:55.8 140 ± 11 14.5 ± 1.1 2.01 ± 0.33 462 ± 35 0.16 5619 † 22:15:57.70 −17:37:45.6 66 ± 8 6.9 ± 0.8 2.31 ± 0.37 219 ± 25 0.17 5642 22:15:57.30 −17:37:07.1 42 ± 9 4.3 ± 1.0 2.18 ± 0.5 137 ± 30 0.49 5675 22:15:56.95 −17:38:05.9 28 ± 9 2.9 ± 0.9 2.32 ± 0.38 92 ± 30 0.19 5685 22:15:56.75 −17:37:22.2 29 ± 8 3.0 ± 0.8 2.26 ± 0.59 96 ± 25 0.40 5766 † 22:15:55.01 −17:38:03.7 73 ± 14 7.6 ± 1.5 2.50 ± 0.45 242 ± 47 0.42 5790 22:15:54.73 −17:38:13.0 30 ± 8 3.1 ± 0.9 – 99 ± 27 0.46 5793 22:15:54.65 −17:38:54.8 29 ± 8 3.0 ± 0.8 2.55 ± 0.27 96 ± 27 0.64 5810 22:15:54.37 −17:37:41.1 23 ± 7 2.4 ± 0.7 – 76 ± 22 0.53 5837 22:15:53.80 −17:37:32.9 21 ± 7 2.2 ± 0.7 2.49 ± 0.34 71 ± 22 0.62 5872 22:15:52.86 −17:37:11.8 74 ± 7 7.7 ± 0.7 2.19 ± 0.22 244 ± 23 0.80 r C 3 W p 2 m W p w m r w i m w ( C c H a 2 t o t g t o J p d S 3 W C l m o B b C e r o a l l D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 elation between radio continuum luminosity and SFR assuming a habrier ( 2003 ) IMF. .2 XMMXCS J2215.9 −1738 cluster membership classification e cross-matched the MeerKAT source catalogue with the archi v al hotometric (Hilton et al. 2009 ) and spectroscopic (Hilton et al. 010 ) redshift catalogues of J2215 at z = 1.46 using a cross- atching radius of 6.0 arcsec to determine their cluster membership. e selected galaxies as cluster members within R 200 based on their hotometric or spectroscopic redshifts. For the photometric selection, e adopted a similar redshift cutoff that was used to define the cluster embership in Hilton et al. ( 2009 ) (i.e. cluster galaxies within the edshift range 1.27 < z p < 1.65 were assumed to be cluster members) hilst sources having spectroscopic redshifts = 1.46 ± 3 σ (where σ s the line-of-sight velocity dispersion) were also selected as cluster embers. We also cross-matched the MeerKAT source catalogues ith catalogues obtained from [ O II ] emitters via the narrow band NB) observation of the J2215 cluster at z = 1.46 using the Suprime- am on the Subaru Telescope. Two sources were selected from the ross-match between the NB912 (NB912 � = 9139 Å, � � = 134 Å; ayashi et al. 2010 , 2011 ), one source was detected using the NB921 nd seven sources using the NB 912 + 921 catalogues (Hayashi et al. 014 ). In total, we detected 24 cluster members within 0.8 Mpc of he cluster centre (see Table 1 and Fig. 2 ). The median angular size f the selected sources presented in Table 1 is ≈ 7 ′′ which suggests NRAS 532, 2842–2859 (2024) hat the majority of our selected radio sources are barely resolved iven a synthesized beam size of ≈ 6 arcsec. We further cross-matched these 24 cluster members detected in he MeerKAT image with catalogues from other archi v al infrared bservations as described in Section 2.3 . The final sample of the 2215 cluster members in the MeerKAT L -band and their counter- arts in other archi v al observ ations are summarized in T able 2 . W e iscuss how the far-infrared and radio luminosities were derived in ections 3.3 and 3.4 , respectively. .3 SED fitting with CIGALE e performed spectral energy distribution (SED) fitting using IGALE V2022.0 (Yang et al. 2022 ) to derive the far-infrared (IR) uminosity values of the cluster members. We used the following odels; the delayed star formation history model (see equation 4 f Boquien et al. 2019 ), the single stellar populations model of ruzual & Charlot ( 2003 ), the nebular emission template adopted ased on Inoue ( 2011 ), dust attenuation templates based on the harlot & Fall ( 2000 ) model, dust emission template of Draine t al. ( 2014 ), AGN models from Stalevski et al. ( 2016 ), and galaxy adio synchrotron emission based on the radio-infrared correlation f Helou, Soifer & Rowan-Robinson ( 1985 ). CIGALE V2022.0 lso models the AGN components of galaxies using the radio- oudness parameter (Ballo et al. 2012 ) and assumes an AGN power- aw SED within the wavelength range 0.01–100 cm. The fitting MeerKAT observations of XCS J2215 2847 Figure 2. A zoom-in of the MeerKAT radio map centred on the cluster members. The positions of the cluster members and the ID numbers of the sources in Table 1 are shown with circles and numbers, respectively. The ≈6 arcsec synthesized beam size is displayed in the lower-left corner of the image. p t l t A ( t M d c fi v S t w a o ( w e fl d t o t f m s V v c χ r d SED fitting with CIGALE V2022.0 . D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 arameters we used in this work are listed in Table B1 . One of he output parameters derived from the SED fitting was the infrared uminosity. Comparing the infrared luminosity values derived after fitting he models to the observed SEDs (i.e. optical to radio bands, see ppendix A ) to that of the counterpart values in table 2 of Ma et al. 2015 ) we observed that the infrared luminosity v alues deri ved in his work are about a factor of 2.4 higher than that estimated in a et al. ( 2015 ). We probed further and realized that the J2215 ata was taken using the 100 and the 160 μm filters of the PACS amera onboard the Herschel Space Telescope and not the 70 μm lters presented in Ma et al. ( 2015 ) and therefore the luminosity alues they obtained after the SED fit are likely to be in error (see ection 2.3 ). We also fitted the SED models to only the mid-infrared o the radio data (the exact bands used in Ma et al. 2015 ) to ascertain hether the inclusion of the optical and near-infrared bands had ny impact on the results generated, we obtained a median ratio f 1.6 which is still higher than the value obtained in Ma et al. 2015 ). We also compared the MeerKAT flux densities reported in this ork to those of the nine detected JVLA sources reported in Ma t al. ( 2015 ). We find a median flux ratio of 1.34, with the MeerKAT ux densities being higher on average. Ho we ver, only 6/9 of the etected JVLA sources reported on in Ma et al. ( 2015 ) are considered o be cluster members in our work, and as indicated in Table 1 , all f these are either blended in the MeerKAT image, or are thought o be AGN, which may explain the higher MeerKAT flux densities or these sources. We hav e v erified that the MeerKAT flux density easurements in our catalogue are within 5 per cent on average of ources detected in the NRAO VLA Sk y Surv e y (Condon et al. 1998 ). We show in Appendix B examples of SED fitting using CIGALE 2022.0 , the goodness of the fit is measured via the reduced χ2 alue. The median reduced χ2 value is 1.9 for all galaxies selected as luster members. In total, 17/24 (71 per cent) sources had a reduced 2 value of less than 3. Whilst 20/24 (83 per cent) sources had educed χ2 value less than 5. This implies that the observed SED ata are reasonably well-fitted with the models we selected for the MNRAS 532, 2842–2859 (2024) 2848 D. Y. Klutse et al. M Table 2. We compare the sources detected in the MeeKAT L -band image to other archi v al observ ations. Columns: (1) Same as in Table 1 ; (2) source ID numbers from the SCUBA-2 observation compiled by Ma et al. ( 2015 ); (3) ACS/ HST (Hilton et al. 2009 ); (4) 24 μm MIPS/Spitzer observation (Hilton et al. 2010 ); (5) ALMA (Band 3; Hayashi et al. 2017 ); (6) ALMA (Band 6; Stach et al. 2017 ); (7) KMOS (Chan et al. 2018 ); (8) morphology E = elliptical, S0 = lenticular, Sp = spiral, Irr = irregular Hilton et al. (see Section 3.2 of 9 for details); (9) log 10 M ∗[M �]; the logarithmic expression of the cluster galaxy stellar mass. (1) (2) (3) (4) (5) (6) (7) (8) (9) MKT ID M15ID H9ID H10ID HY17ID ST17ID C18 Morph log 10 M ∗[M �] Notes 5242 ∗ 10 709 – – – – Sp + Irr 11.11 ± 0.06 – 5307 – 460 – – – – Sp + Irr 9.58 ± 0.09 – 5332 ∗ 2 1022 – – – – Sp + Irr 9.72 ± 0.15 – 5336 – 1201 – – – – Sp + Irr 9.61 ± 0.08 – 5373 – 728 – – – – Sp + Irr 10.63 ± 0.11 – 5442 † 3 983 – ALMA.B3.16 – – Sp + Irr 11.02 ± 0.12 NB921 [O II ] 5443 † – 1004 – – – 575 E 9.81 ± 0.13 – 5469 ∗ – 692 53 ALMA.B3.14 5 1011 E 11.06 ± 0.10 NB912 [O II ] 5470 ∗† 6 747 – ALMA.B3.06 9 930 Sp + Irr 11.49 ± 0.07 NB921 [O II ] 5492 – 1130 – ALMA.B3.17 – – Sp + Irr 11.29 ± 0.05 NB912 + NB921 [O II ] 5517 † – 874 – ALMA.B3.13 12 724 – 11.01 ± 0.09 – 5551 † – 614 – ALMA.B3.11 2 1118 E 11.03 ± 0.05 NB912 + NB921 [O II ] 5574 ∗ 4 884 899 ALMA.B3.05 13 732 – 9.82 ± 0.16 NB921 [O II ] 5618 ∗† 13 734 35 ALMA.B3.07 7 940 Sp + Irr 9.64 ± 0.02 NB912 + NB921 [O II ] 5619 † – 653 – ALMA.B3.09 – 1038 Sp + Irr 11.25 ± 0.11 NB912 + NB921 [O II ] 5642 – 419 – – – – E 9.48 ± 0.13 NB912 + NB921 [O II ] 5675 – 786 39 ALMA.B3.12 – 829 Sp + Irr 10.65 ± 0.25 NB912 [O II ] 5685 – 529 529 – – 1261 Sp + Irr 10.93 ± 0.08 – 5766 † – 777 – – – 798 S0 9.85 ± 0.06 – 5790 – 863 – – – – – – – 5793 – 1118 1118 – – 412 – 11.27 ± 0.08 – 5810 – 658 – – – – – – – 5837 – 571 – – – – – 10.41 ± 0.14 – 5872 – 446 – – – – – 11.52 ± 0.09 – 3 T s l o t a 1 L w F u b S w 1 l ( T r i v a 1 4 O A g m g l 2 e t o t w m W t c 4 W m t d ( o D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 .4 Radio luminosities and continuum star formation rates he observed 1.3 GHz radio flux F 1 . 3 , obtained from the MeerKAT urv e y was scaled to the rest frame 1.4 GHz ( F 1 . 4 ) using a power aw with a slope ( α) of −0.8 (i.e. F 1 . 4 = ( ν1 . 4 /ν1 . 3 ) α×F 1 . 3 , this value f α is assumed for non-thermal radio emissions, Bell 2003 ) and hen converted the F 1 . 4 into a rest-frame 1.4 GHz luminosity ( L 1 . 4 ) ssuming a spectral index ( α) dependent K -correction factor (Condon 992 ; Karim et al. 2011 ), 1 . 4 = 9 . 52 × 10 12 × F 1 . 4 D 2 L 4 π (1 + z) 1 + α , (1) here, D L is the luminosity distance in Mpc, L 1 . 4 in units of WHz −1 , 1 . 4 in units of μJy, and z = 1.46. We converted the L 1 . 4 into SFR sing the calibration of the Far Infrared Radio Correlation (FIRRC) y Bell ( 2003 ) scaled to a Chabrier IMF (Karim et al. 2011 ), i.e. FR (M � yr −1 ) = ⎧ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎩ 3 . 18 × 10 −22 L 1 . 4 , L 1 . 4 > L c , 3 . 18 × 10 −22 L 1 . 4 0 . 1 + 0 . 9 ( L 1 . 4 L c )0 . 3 , L 1 . 4 � L c , (2) here L c is the radio luminosity of an L ∗ galaxy (i.e. 6 . 4 × 0 21 WHz −1 ). Bell ( 2003 ) sees the need to distinguish between low- uminous and high-luminous star-forming galaxies since non-thermal low-luminous) galaxies may have their SFR rate underestimated. hough the MeerKAT observation mostly exploits the non-thermal adio regime, our radio luminosities mostly fall abo v e the L c threshold .e. L 1 . 4 ≥ 10 23 WHz −1 and also fall below radio luminosity ( L rad ) alue of 10 25 WHz −1 where radio emissions at L rad � 10 24 −25 WHz −1 NRAS 532, 2842–2859 (2024) re mostly dominated by radio loud AGNs (Miller, Peacock & Mead 990 ; Yun, Reddy & Condon 2001 ). M O R P H O L O G I E S A N D O P T I C A L C O L O U R S F R A D I O SOURCES IN J 2 2 1 5 GN host galaxies can be identified via their colours and morpholo- ies. Previous colour–magnitude relation studies have shown that ost galaxies found on the red sequence or blue cloud are normal alaxies (Baldry et al. 2004 ) whilst the majority of the AGNs are ocated in the green valley (Nandra et al. 2007 ; Schawinski et al. 010 ; Povi ́c et al. 2012 ; Wang et al. 2017 ; Gu et al. 2018 ; Lacerda t al. 2020 ). The green valley represents a transitional region between he blue cloud (mostly populated by late-type galaxies having spiral r irregular morphologies) and the red sequence (populated by early- ype galaxies having elliptical or lenticular morphologies). In this ork, we investigated the position of the MeerKAT-detected cluster embers on the colour–magnitude diagram and their morphologies. e describe the morphological classification in Section 4.1 and he position of the morphologically classified radio galaxies on the olour–magnitude diagram in Section 4.2 . .1 Morphological classification e used the catalogue of morphologically classified J2215 cluster embers in Hilton et al. ( 2009 ) for this work. We cross-matched he catalogue in Hilton et al. ( 2009 ) with that of the MeerKAT- etected cluster members within a radius of 6 arcsec. In Hilton et al. 2009 ) morphological classification of the galaxies was performed n magnitudes brighter than z 850 ≤ 24 via visual inspection by MeerKAT observations of XCS J2215 2849 Figure 3. The postage stamp images of the selected members of the J2215 cluster within a radius of 0.8 Mpc of the original X-ray cluster position. The source ID number presented in Table 1 is located in the upper left corner of each extracted postage stamp image. The cross marker represents the MeerKAT source position. Each set of the postage stamp images was taken from the MeerKAT L -band image (left panel), the JVLA L -band image in A configuration (Ma et al. 2015 ) (middle panel) and the Hubble Space Telescope ACS z 850 -band image (right panel image from which the initial classification of the cluster galaxy morphology was performed in Hilton et al. 2009 ). The MeerKAT and JVLA postage stamp images are 40 arcsec, whilst the HST image is 3.75 arcsec on a side with east at the left. fi t T g s d c s i s p ( f ( l D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 ve human classifiers under four different morphological bins i.e. he elliptical (E), lenticular (S0), spiral (S), and irregular (Irr). hey determined the morphologies using an existing training set of alaxies compiled by Postman et al. ( 2005 ) from the morphological tudies of high-redshift cluster galaxies i.e. q0.8 < z < 1.3. An in- epth description of the morphological classification of the J2215 luster galaxies can be found in Hilton et al. ( 2009 ). The postage tamp images of the selected galaxies from the MeerKAT L -band mage listed in Table 1 can be seen in Fig. 3 . Each set of the postage tamp images was taken from the MeerKAT L -band image (left anel), the JVLA L -band image in A configuration (Ma et al. 2015 ) middle panel) and the z 850 -band counterpart images (right panel) rom which the initial morphologies were determined by Hilton et al. see section 3.2 of Hilton et al. 2009 ). Only 17/24 MeerKAT-detected cluster members had their morpho- ogical counterparts in the Hilton et al. ( 2009 ) catalogue, 7/24 did MNRAS 532, 2842–2859 (2024) 2850 D. Y. Klutse et al. M Figure 4. Caption as per Fig. 3 . n d s w 1 s 4 F o i c a d t t r u b c S o o b h b i m t 3 w t e g 5 5 T t i f c s s D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 ot hav e an y morphological classification. Out of the 17 MeerKAT- etected cluster members having morphological classification 12 had piral/irregular morphology (6/12–SFGs, 2/6–ISFGs, 4/6–AGNs) hilst five had elliptical/lenticular galaxy morphology (3/12–SFGs, /6–ISFGs, and 1/6–AGNs). Therefore, the majority of the MeerKAT ources correspond to host galaxies with late-type morphologies. .2 Colour–magnitude relation ig. 5 shows the ( z 850 − J ) colour versus magnitude ( J ) diagram f all cluster members selected in the MeerKAT L -band radio mage that had counterparts in the optical and infrared catalogue ompiled by Hilton et al. ( 2009 ). The solid black line shows fit to the colour–magnitude relation of the early-type galaxies etected in Hilton et al. ( 2009 ) i.e. the red sequence. We show he early-type galaxies (i.e. Elliptical/lenticular–E + S0) and late- ype galaxies (spiral/irregular–Sp + Irr) with circles and stars, espectively, whilst sources without morphological classification and ncertain morphologies are shown as diamond markers. The red, lue, and black markers signify MeerKAT-detected cluster members lassified as AGNs, star-forming galaxies (SFGs), and intermediate FGs (ISFGs), respectively (see Section 5 ). A significant number of ur sources fall below the red sequence line i.e. in the blue cloud. The majority of these sources are blue and faint, ho we ver, three utliers with source IDs #5332, #5242, and #5872 are blue but very NRAS 532, 2842–2859 (2024) right compared to the other cluster members. IDs #5332 and #5242 ave dual morphologies i.e. spiral/irregular suggesting that they are lended in the infrared image ( J ) (Hilton et al. 2009 ) and the JVLA mage (see Figs 3 and 4 ) thus their photometry and estimated SFR ay not be reliable. We also classified them as radio AGNs based on he three selection schemes mentioned in Section 5 . Also, we detected both early-type and late-type galaxies within - σ of the red sequence in this work (Fig. 5 ). The elliptical galaxies ithin the red sequence of J2215 are very bright ( J < 22.5) compared o other ellipticals outside the red sequence. Is it likely that J2215 is xperiencing the final episode of star formation within its early-type alaxies? CLASSI FI CATI ON O F R A D I O S O U R C E S .1 Mid-infrared colour–colour criteria he mid-infrared photometry provides a robust approach to the iden- ification of A GNs. A GN SEDs are redder than star-forming galaxies n the mid-infrared bands where stellar populations dominate the red, alling portion of the stellar spectra. Stern et al. ( 2005 ) found that simple mid-infrared colour criteria ould robustly separate AGNs from normal star-forming galaxies and tars (this method could identify > 90 per cent of spectroscopically elected quasars and Seyfert 1 galaxies). MeerKAT observations of XCS J2215 2851 Figure 5. The z 850 − J colour–magnitude diagram of all the selected cluster members detected in the MeerKAT L -band image located within 0.8 Mpc of the cluster centre. Elliptical/lenticular (E + S0) galaxies are shown as circles; spiral/irregular galaxies (Sp + Irr) with stars; galaxies without any morphological classification are marked with a diamond shape (None). The filled markers signify the MeerKAT sources classified as AGNs whilst the thick and thin unfilled markers represent SFGs and ISFGs, respectively. The solid line denotes the red sequence path derived from a fit to the colour– magnitude relation of the elliptical/lenticular galaxies (early-type) detected in Hilton et al. ( 2009 ). The dotted dashed lines show the 3- σ deviations abo v e and below the red sequence. It can be seen that the majority of our cluster members are located below the red sequence line and 12 out of the 17 MeerKAT-detected cluster members with morphological classification have spiral/irregular morphology ( ≈71 per cent). This may imply that the majority of all the MeerKAT-detected cluster galaxies may be actively forming stars irrespective of whether they have been classified as AGNs, ISFGs or SFGs. Figure 6. The IRAC colour–colour plot of the selected cluster members detected with the MeerKAT telescope, with some sources falling within the ‘AGN zone’ (shaded re gion). Ov erlaid are two evolutionary tracks of spectral templates from the library of Polletta et al. ( 2007 ); a starburst galaxy (M82) and an active galaxy (Seyfert 2) as they are redshifted from z = 0 (the crosses in each template track) to z = 2 (the open end of each track). The majority of the cluster members are all located outside the AGN wedge which implies that using only the IRAC colour–colour plot as diagnostic tool, the majority of the radio emission is mostly powered by star-formation activity rather than AGNs. s c o f o = c Figure 7. The distribution of q IR (Far Infrared Radio Luminosity Ratio) for all sources in the MeerKAT/FIR sample (hashed histogram). The black vertical dashed line denotes the mean q IR value, < q IR > greater than 2 for the entire MeerKAT/FIR sample (i.e. < q IR > = 2 . 36 ± 0 . 04). The black vertical dot–dashed line represents the threshold below which sources are classified as radio excess AGN i.e. q IR = 1.68 adopted from Del Moro et al. ( 2013 ). We compared our work with other surv e ys of high-redshift galaxies from the ALESS surv e y of the sub-millimetre galaxies in the Extended Chandra Deep Field South observation with ALMA 870 μm and JVLA (dotted histogram, Swinbank et al. 2014 ) and the GOODS-Herschel (North) field with the VLA, 24 μm Spitzer/MIPS, Chandra X-ray, and Herschel infrared data (star-filled histogram, Del Moro et al. 2013 ). All the MeerKAT/FIR sources fall within the radio normal region using only the q IR criterion. A s S q c r n p t t [ c T a A 2 5 T d e i ( q w l u S ( h D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 We adopted the same approach from Stern et al. ( 2005 ). Fig. 6 hows the mid-infrared colour–colour plot of the MeerKAT-detected luster members obtained from the IRAC catalogue. We show an v erlay of two non-evolving tracks of spectral templates obtained rom the library of Polletta et al. ( 2007 ) co v ering a wav elength range f 8–1000 μm. The figure shows these tracks as they evolve from z 0 to z = 2. The shaded region depicts the area within the colour– olour space dominated by broad-lined AGNs (Stern et al. 2005 ). ny source located outside the ‘AGN wedge’ is likely to be a normal tar-forming galaxy or another type of AGN apart from quasars and eyfert 1 (since the mid-infrared colour criteria can identify only uasars and Seyfert 1 efficiently; Stern et al. 2005 ). From Fig. 6 , it an be observed that at least five cluster members fall within this egion, IDs: #5492, #5442, #5517, #5551, and #5469. Sources with o IRAC data were not included in the colour–colour AGN diagnostic lot. i.e. 8/24 cluster members did not have IRAC photometry for the wo longest wavelength IRAC channels (i.e. 5.8 and 8.0 μm) because he IRAC images at those bands are shallow. Due to the large error bars in both the [3.4] − [4.5] and [5.8] − 8.0] colours we can not draw a firm conclusion based on only this riterion (i.e. the mid-infrared colour–colour AGN diagnostic plot). he Far-Infrared Radio Luminosity Ratio, q IR and the FIRRC are lternatives to distinguish normal star-forming galaxies from radio GN via the so-called ‘radio excess’ approach (Del Moro et al. 013 ). .2 Far-Infrared Radio Luminosity Ratio he Far Infrared Radio Luminosity Ratio, q IR value is used to istinguish normal star-forming galaxies from AGNs (Del Moro t al. 2013 ; Delvecchio et al. 2021 ; Radcliffe et al. 2021 ). This q IR s defined similarly to Condon ( 1992 ), Bell ( 2003 ), Magnelli et al. 2015 ), Calistro Rivera et al. ( 2017 ), and Algera et al. ( 2020 ) as: IR = log 10 ( L IR 3 . 75 × 10 12 ) − log 10 ( L 1 . 4 ) , (3) here L 1 . 4 is the rest-frame radio luminosity. L IR is the total infrared uminosity obtained from the best-fitting model to the observed SED sing galaxy dust emission templates from Draine et al. ( 2014 ), see ection 5.3 for details. Fig. 7 shows the q IR distribution of all the MeerKAT/far-infrared FIR) selected cluster members (i.e. hashed histogram) and other igh-redshift field galaxies from the VLA/ALMA 870- μm obser- MNRAS 532, 2842–2859 (2024) 2852 D. Y. Klutse et al. M Figure 8. The FIRRC for all the J2215 MeerKAT/FIR galaxies located within 0.8 Mpc of the cluster centre. It can be seen that all the MeerKAT radio normal star-forming galaxies 18/24 (solid star markers) and the radio loud AGNs 6/24 (solid square markers) are all located within the radio normal region i.e. below the radio excess AGN fit. We compare our work with other high-redshift galaxies from the GOODS- North field (Del Moro + 2013 radio excess star-forming galaxies–plus symbol; Del Moro et al. 2013 ) and the ECDFS star-forming galaxies (Swinbank + 2014 SFG–cross marker; Swinbank et al. 2014 ). The dashed and dotted–dashed lines represent the best-fitting models to the radio excess star-forming galaxies and AGNs from Del Moro et al. ( 2013 ), respectively. v ( b 1 w d a s ‘ i g 5 A o i f 1 2 f o g L o S d e f c s m o o t f 5 W i s p o I 1 6 B a 2 A i c D d r t a a s l G o g t t f c a r z fi a o 7 7 O r s e 4 N T t t D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 ations (dotted histogram; Swinbank et al. 2014 ) and VLA/24- μm star-filled histogram, Del Moro et al. 2013 ). The cutoff/separation oundary adopted from Del Moro et al. ( 2013 ) was defined at q IR = .68 (the black vertical dot–dashed line). Sources with q IR > 1.68 ere defined as ‘radio normal’ whilst those below the cutoff were efined to be ‘radio excess’ sources. The ‘radio normal’ sources ccording to Del Moro et al. ( 2013 ) are mostly dominated by tar-forming galaxies and low-luminous radio AGNs, whilst the radio excess’ sources are most likely to be dominated by AGNs. Comparing our work with other high-redshift field galaxy surv e ys n Fig. 7 , it can be seen that, all the MeerKAT/FIR detected cluster alaxies fall within the radio normal region. .3 Far-infrared radio correlation lthough there is a v ast dif ference between the emission mechanism f radio (synchrotron) and infrared galaxies (dust re-emission), there s a tight correlation between the radio and FIR luminosities of star- orming galaxies (Helou et al. 1985 ; Condon, Anderson & Helou 991 ; Yun et al. 2001 ; Bell 2003 ; Appleton et al. 2004 ; Ivison et al. 010 ; Basu et al. 2015 ; Algera et al. 2020 ). The FIRRC has been ound to be well correlated for several galaxy samples irrespective f their stellar activities or morphology excluding radio-loud active alaxies or some other interacting galaxies (Lisenfeld & V ̈olk 2010 ; isenfeld et al. 2015 ). Previous works have established the validity f the FIRRC out to z ≈ 2 (Garrett 2002 ; Appleton et al. 2004 ; argent et al. 2010a , b ; Algera et al. 2020 ), with only a few uncertain eviations at higher redshifts ( 3 ≤ z ≤ 6 ) (Murphy 2009 ; Seymour t al. 2009 ; Shen et al. 2022 ). The FIRRC for all the J2215 members rom the MeerKAT L -band surv e y (this work) and its FIR counterpart an be seen in Fig. 8 . We compare our work with other high-redshift radio excess tar-forming galaxies from the GOODS-Herschel North field (plus arker; Del Moro et al. 2013 ) and the ALMA LESS (ALESS) surv e y f sub-millimetre Extended Chandra Deep Field South (ECDFS) bservation (cross marker; Swinbank et al. 2014 ) in Fig. 8 . All of NRAS 532, 2842–2859 (2024) he MeerKAT/FIR sources are located within the radio normal star- orming region. .4 Source classification e employed three selection criteria to distinguish SFGs from AGNs .e. sources with L 1 . 4 < 10 24 WHz −1 , q IR values > 1.68 and finally ources detected outside the IRA C A GN zone were all considered as otential SFG candidates. Ho we ver, sources that passed at least two ut of the three selection criteria mentioned earlier are considered SFGs otherwise, they are selected as AGNs. In total, we classified 2/24 sources as SFGs, 6/24 as ISFGs, and 6/24 as AGNs. A G N A CTI VI TY WI THI N J 2 2 1 5 ased on the three selection criteria described in Section 5 we classify ll the other non-SFGs as potential AGNs i.e., 6/24 this implies that 5 per cent of the MeerKAT sources that are cluster members are GN hosts and there is a possibility of a higher AGN activity ongoing n the core of this high-redshift cluster. Alberts et al. ( 2016 ) found that in a sample of ≈250 galaxy lusters obtained from the IRAC Shallow Cluster Surv e y and IRAC istant Cluster Surv e y at 0.5 < z < 2, AGN-composite (moderately ominated AGN fraction) cluster galaxies increased with respect to edshifts abo v e the field galaxies at 1.0 < z < 1.5. They attributed he rise in the AGN-composite cluster galaxies at these redshifts to conducive cluster environment that allows black hole growth or ctivities. Also, a multiwavelength study of AGNs using three different election criteria i.e. mid-IR colour, radio luminosity, and X-ray uminosity of galaxy clusters in the 8 . 5 ◦ × 8 . 5 ◦ Boots field by alametz et al. ( 2009 ) showed that a higher fraction of AGN is bserved in cluster centres than in the field at z � 1.0. Further, Martini et al. ( 2013 ) studied the AGN evolution of 13 alaxy clusters from the Spitzer/IRAC Shallow Cluster Surv e y and heir surrounding field galaxies at 1 < z < 1.5. They observed that here was an order of magnitude increase in the evolution of AGN raction in clusters from 0 < z < 1.25 than in the field of these lusters whilst a reverse is seen at lower redshift i.e. AGN fraction is factor of ≈6 times higher in the field than in the clusters at lower edshift. High-redshift studies of two proto-clusters and field galaxies at > 2 showed an increase in AGN fractions in proto-cluster than in eld galaxies (Lehmer et al. 2009 ; Digby-North et al. 2010 ). Giv en the abo v e e xamples in relation to the high-redshift clusters nd their AGN fraction, the J2215 galaxy cluster is no different from ther higher redshift clusters investigated by previous surveys. STAR F O R M AT I O N AC TI VI TY WI THI N J 2 2 1 5 .1 Star formation rate versus stellar mass bservations suggest a rough correlation between the star formation ates in galaxies and their stellar mass ( M ∗), the so-called ‘main equence’ (Brinchmann et al. 2004 ; Elbaz et al. 2007 ; Noeske t al. 2007 ). This correlation claimed to hold from z = 0 to z = (Brinchmann et al. 2004 ; Daddi et al. 2007 ; Elbaz et al. 2007 ; oeske et al. 2007 ; Pannella et al. 2009 ; Schreiber et al. 2015 ). his has resulted in the ‘dual mode’ of star formation evolution i.e. he normal star-forming mode and the starburst mode depending on he position of the galaxy in the SFR–M ∗ plot although there are MeerKAT observations of XCS J2215 2853 Figure 9. The SFR versus M ∗ of the SFGs (solid squares) and the interme- diate SFGs (solid triangle) detected in the J2215 MeerKAT image. The solid line represents the best-fit to the MS relations derived from observations in literature (i.e. equation 28 of Speagle et al. 2014 ) at the cluster redshift ( z = 1.46). The ±0.3 dex scatter about the adopted MS fit to our data is represented as the blue dotted line. The 4- σ radio flux detection limit equi v alent to an SFR value of 46 M � yr −1 is represented as the black horizontal dashed line. i 2 t s 2 a w i 2 w w o o i F f c s o t m o p s a e m ( g o m t a a a o h m r g t a t i w l m w i g 7 W g m a t r ∑ v c m e h r w p μ s n C a v e 1 g t h S t t 7 W c M f v D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 ncreasing doubts about the reality of this distinction (Elbaz et al. 018 ; Puglisi et al. 2021 ). Galaxies found within the ‘main sequence’ region are termed he ‘normal star-forming’ galaxies, whilst those abo v e the main equence regions are termed the ‘star -b urst’ galaxies (Elbaz et al. 011 ). The ‘normal star-forming’ mode is associated with the gas ccretion process (Dekel, Sari & Ceverino 2009 ; Dav ́e et al. 2010 ) hilst the ‘starburst’ mode is often associated with the major merger nteractions (Daddi et al. 2010 ; Genzel et al. 2010 ; Rodighiero et al. 011 ). In Fig. 9 , we show how the SFR of the cluster galaxy varies ith the galaxy stellar mass. The stellar masses used in the work ere obtained by fitting SED models described in Section 3.3 to the bserved data. The majority of the SFGs and ISFGs are located on r abo v e the best-fit to the MS relations derived from observations n literature (black line; Speagle et al. 2014 ). It can also be seen in ig. 9 that, our SFR detection limit of 46 M � yr −1 lies abo v e the MS or all but the most massive galaxies in our sample. Coogan et al. ( 2018 ) showed that only 2/8 of the Cl J1449 + 0856 luster galaxies at z = 2 were found to reside abo v e the main equence relation (see fig. 8 of that paper) although the majority f the cluster galaxies exhibited starburst-like characteristics. A similar trend was also observed by Smith et al. ( 2019 ) during he study of CLJ1449 at z = 2. They found that most of the cluster embers lay within the MS region (see fig. 10 of that paper) with nly a few cluster galaxies located about a factor of 2 or 3 abo v e the redicted MS region at the cluster redshift. They suggested that the tarburst activities within those cluster galaxies could be caused by merger event and this goes to support the claim made by Coogan t al. ( 2018 ) that the star-formation activity of the same cluster is ostly merger-driven. ‘Starb urst’ galaxies ha v e also been observ ed by Hung et al. 2013 ) via visual morphological analysis of the 2084 COSMOS field alaxies (Herschel-PACS and SPIRE observation) at z = 0–1.5 they bserved that about 50 per cent of the galaxies were undergoing a erging process and these systems were seen to be deviating from he main sequence relation supporting the claim that galaxies that re located abo v e the MS relation are mostly merging systems. The y lso observed that some main sequence galaxies ( ≈18 per cent) were lso undergoing merging events. Is it possible that the majority f J2215 cluster galaxies are undergoing a merger episode at this igh redshift? This is because in Fig. 9 it can be observed that the ajority of the cluster galaxies fall on or abo v e the main sequence elation. Also, in a CO (2–1) emission line surv e y of the J2215 cluster alaxies conducted by Hayashi et al. ( 2017 ) they showed that, two of he cluster galaxies located at R ≈ 0.5 Mpc were undergoing a merger ctivity (i.e. # ALMA.B3.15 and # ALMA.B3.16 – this is visible as wo bulges in the intensity maps of the individual cluster galaxies n Fig. 3 of 14 , the # ALMA.B3.16 counterpart is # 5442 in this ork). Again, Ik eda et al. ( 2022 ) classified six out of 17 CO emitters ocated within ≈0.5 Mpc of the J2215 cluster centre as early-stage ergers i.e. #ALMA.B3.06, #ALMA.B3.09, and #ALMA.B3.16 hich correspond to IDs #5470, #5619, and #5442, respectively, n this work. Therefore J2215 may be undergoing a high rate of alaxy-to-g alaxy merger episode at this high redshift. .2 Integrated star formation rate e estimated a cluster-wide integrated star formation rate for 12/24 alaxies selected to be star forming based on the three criteria entioned in Section 5.4 . This resulted in ∑ SFR = 1700 ± 330 M � yr −1 at � 0.8 Mpc nd 1100 ± 210 at � 0.5 Mpc for 7/24 SFGs. Our measurement of he integrated SFR is approximately two times higher than the value eported by Ma et al. ( 2015 ) within 0.8 Mpc of the cluster centre i.e. SFR value of 800 + 360 −250 M � yr −1 but it is in agreement with the alue reported by Stach et al. ( 2017 ) (i.e. 840 M � yr −1 within the entral ≈0.5 Mpc of the J2215 cluster). The integrated SFR that we obtain for J2215 is of similar agnitude to that seen in other clusters at similar redshift. Santos t al. ( 2014 ) obtained an ∑ SFR value of 780 ± 90 M � yr −1 for a igh-redshift cluster at 1.62 (i.e. CLG0218.3 −0510) within 0.5 Mpc adius. Tran et al. ( 2010 ) also estimated an ∑ SFR of ≈1370 M � yr −1 ithin < 0.5 Mpc of the same cluster at that redshift emphasizing the ossibility of an underestimation due to the low sensitivity of the 24- m image, which implies that there may be a possibility of higher tar formation activity ongoing in this high-redshift cluster that has ot been captured. The 0.5 Mpc central region of another high-redshift cluster LJ1449 at z = 2 was also seen to be actively forming stars with n ∑ SFR value of 470 ± 120 M � yr −1 (Smith et al. 2019 ). Similar alues were also estimated within the core of this cluster by Strazzullo t al. ( 2018 ) and Coogan et al. ( 2018 ). Cooke et al. ( 2019 ) estimated a median ∑ SFR = 750 ± 90 M � yr −1 within 1 Mpc of the cluster centre of eight submillimetre alaxy clusters at z ≈ 0.8–1.6. This value is also in agreement with he residual field contamination corrected integrated SFR of eight igh-redshift ( z = 1.6–2.0) submillimeter galaxy clusters studied by mail ( 2024 ) i.e. a median ∑ SFR = 530 ± 80 M � yr −1 . All these high-redshift galaxy cluster studies give an indication hat there is indeed an increase in the star formation activity within he core of some high-redshift clusters at z = 1.5 and beyond. .3 Mass–normalized integrated SFR e determined the mass-normalized integrated SFR for all the 12/24 luster members classified as non-AGNs, adopting a cluster mass cl of 3 × 10 14 M � from Ma et al. ( 2015 ) and an integrated star- ormation rate of ∑ SFR of 1700 ± 330 M � yr −1 . We obtained a alue of ∑ (SFR)/ M cl = (570 ± 110) × 10 −14 yr −1 . MNRAS 532, 2842–2859 (2024) 2854 D. Y. Klutse et al. M Figure 10. The ∑ (SFR)/ M cl − z relation for low- and high-redshift clusters. The solid line depicts the evolutionary model for the number density of star- forming ULIRGs radio sources out to z ≈ 1.5 that follows the (1 + z) 7 − z relation (Cowie et al. 2004 ; Geach et al. 2006 ). The dashed line represents the best-fitting model to the ∑ (SFR)/ M cl of massive galaxy clusters studied in Smail ( 2024 ) (i.e. (1 + z) 5 . 5 − z; Webb et al. 2013 ). The dash–dotted line denotes the best-fitting model to the observed ∑ (SFR)/ M −z (the integrated star formation rate per unit total halo mass) relation for the nine cluster sample detected by Popesso et al. ( 2012 ) including a blind extrapolation of the best-fitting model beyond the observed cluster redshifts (i.e. 0 . 15 < z < 0 . 85). All the power-law models have been normalized at z = 0.8 and all measurements have been scaled to an equi v alent FIR luminosity limit of 10 12 L � where necessary to ensure a uniform comparison with other high-redshift clusters studied in Smail ( 2024 ). All three power-law models converge at the normalization redshift ( z = 0 . 8) ho we v er be yond that redshift the ∑ (SFR)/ M cl increases sharply with high z for the Cowie et al. ( 2004 ) and Smail ( 2024 ) model with a relatively uniform pattern for the Popesso et al. ( 2012 ) model which deviates by a factor of ≈3 and 2 below the Cowie et al. ( 2004 ) and Smail ( 2024 ) model, respectively. The wider deviations from the two models at higher redshifts may be due to insufficient data at higher redshifts to better represent the best-fitting model beyond the redshift range of the nine cluster sample investigated by Popesso et al. ( 2012 ). f C a o 2 r z r l o 0 c m w l F b p S i p s a e b m b i g ( i 1 8 W M r i t s q f 1 ( i m m ( 2 i ( r g a c h e i h a A A W t A C c S a h S ( o M t o o D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 Previous works have suggested that the critical epoch of star ormation is at z ≈ 1.4; a study conducted via the IRACS Shallow luster Surv e y rev ealed that abo v e z = 1 . 4 activ e star formation ctivities are dominant within the cluster core and the reverse is bserved below this redshift (e.g., Brodwin et al. 2013 ; Alberts et al. 014 ). This trend can be visualized in Fig. 10 where the ∑ (SFR)/ M cl − z elation for some high-redshift clusters nearly follows the (1 + z) 7 − relation. i.e. the evolutionary model for the number density for adio star-forming galaxies whose luminosity values correspond to ocal ULIRGs from z ≈ 0–1.5 proposed by Cowie et al. ( 2004 ). The black dash–dotted line denotes the best-fitting model to the bserved ∑ (SFR)/ M cl − z relation for the nine cluster sample ( z = .15–0.85) studied by Popesso et al. ( 2012 ). Comparing our work with previous surv e ys of high-redshift lusters one can see that J2215 generally follows the ‘higher ass-normalized integrated SFR at higher redshift’ trend. When e correct our measurements to a corresponding FIR luminosity imit of ≥ 10 12 L � and normalize all the power-law models in ig. 10 at z = 0.8 following Smail ( 2024 ) the ∑ (SFR)/ M cl value ecomes a factor of ≈4.4, 1.7, and 3.5 higher than the value redicted by the Popesso et al. ( 2012 ), Cowie et al. ( 2004 ) and mail ( 2024 ) relation, respectively. The J2215 cluster at z = 1.46 s in relatively better agreement with the Cowie et al. ( 2004 ) ower law and also consistent with the submillimetre value of the ame cluster studied by Cooke et al. ( 2019 ). Again, J2215 was mong the two highest star forming clusters studied by Cooke NRAS 532, 2842–2859 (2024) t al. ( 2019 ). They also suggested that the mild evidence of a inomial velocity distribution of the cluster (Hilton et al. 2010 ) ay be due to cluster to cluster merger event and that event may e responsible for the extremely high-star formation rate recorded n their work. Should this claim be true then J2215 may be under- oing a ‘twin’ merger event i.e. cluster galaxy to galaxy merger see Section 7.1 ) and cluster to cluster merger event. This may mply that J2215 is at the peak of its star-formation phase at z = .46. SUMMARY e have studied star formation and AGN activity within the XM- XCS J2215.9 −1738 cluster at z = 1.46 using MeerKAT L -band adio data. We combined the radio data with other archi v al optical and nfrared data to study the star formation and AGN activities within he cluster. We use for the first time in the study of the cluster three election criteria; the radio luminosity, the far-infrared radio ratio IR and the mid-infrared colour, to classify sources as normal star- orming, intermediate star-forming, and AGN galaxies. We classified 2/24 (50 per cent) as SFGs and 6/24 (25 per cent) as ISFGs and 6/24 25 per cent) as radio AGNs. We further investigated the evolution of star-forming galaxies n clusters with redshifts. We achieved this by comparing the ass-normalized integrated SFR of the MeerKAT-detected cluster embers with other lower and higher redshift clusters. We observed that XMMXCS J2215.9 −1738 is consistent with the 1 + z) 7 − z relation proposed by (Cowie et al. 2004 ; Geach et al. 006 ) and these higher star formation activities occur within clusters n their youthful ages (high redshift) compared to their older ages low redshift). Finally, we also showed that most of the cluster members that are adio sources detected by MeerKAT at this high redshift are late-type alaxies. This also gives an indication that this cluster at z = 1.46 is ctively star forming. This work can be extended to impro v e upon the morphological lassification and the visual identification of merger events with igher resolution observations like that of the JWST . We hope to also mploy a more advanced technique to mitigate the blending effect n our MeerKAT radio images whilst we anticipate the arri v al of the igher resolution and more sensitive near future radio telescopes such s the MeerKAT extension project (MK + ) and the Square Kilometer rray. C K N OW L E D G E M E N T S e thank the referee for a number of useful suggestions that impro v ed his work. DYK acknowledges financial support from the South frican Radio Astronomy Observatory (SARAO) via the Human apital Development (HCD) programme. MH acknowledges finan- ial support from SARAO and the National Research Foundation of outh Africa. IS and AMS acknowledge STFC (ST/X001075/1). We cknowledge the use of the University of Kwazulu-Natal UKZNs’ igh-computing facility ( https:// www.acru.ukzn.ac.za/ ∼hippo/ ) and outh Africa’s National Integrated Cyberinfrastructure System NICIS) Centre for High performance computing facility (CHPC) for ur data processing. The primary data used for this work was from the eerKA T radio telescope. The MeerKA T telescope is operated by he South African Radio Astronomy Observatory, which is a facility f the National Research Foundation, an agency of the Department f Science and Innovation. https://www.acru.ukzn.ac.za/~hippo/ MeerKAT observations of XCS J2215 2855 D T t A a R A A A A A A B B B B B B B B B B B C C C C C C C C C C C D D D D D D D D D D E E E F F G G G G G G H H H H H H H H H H I I I I K K K K K L L L L L L L M M M M M M M M N N N O P P P P P P P P P R R D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 ATA AVAILABILITY he MeerKAT continuum data used in this work can be found in he MeerKAT data archive managed by the South African Radio stronomy Observ atory ( https://archi ve.sarao.ac.za/). The data are ssociated with proposal ID SCI-20190418-MH-01. EFERENCES lberts S. et al., 2014, MNRAS , 437, 437 lberts S. et al., 2016, ApJ , 825, 72 lgera H. S. 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The b black curve. The stellar attenuation and unattenuated models are shown a dust, and A GN emission models are also shown with the green, red, and o star-forming galaxies is shown as the brown curve. The red dots are the C served fluxes, whilst the green triangles represent the upper limit values f nfrared bands. We assumed the following upper limits: A 4 sigma upper l y – 85 μm), 5 sigma upper limit for the 24 μm Spitzer MIPS (0.070 mJy) a e of ≈23 mag (Ch1 and Ch2) and ≈20 mag (Ch3 and Ch4). The 5 sigma u mag. J band image is ≈24.4 whilst that of the K s – band is ≈24.5. D ow nloaded from PPENDIX A : SPECTRAL E N E R G Y DISTRI BU TI n Figs A1 , A2 we show the spectral energy distribution plots for est-fitting model for each of the cluster galaxies is shown as the s the yellow and the dashed blue curv e, respectiv ely. The nebular , range curv es, respectiv ely. The non-radio synchrotron emission for IGALE -generated model fluxes, the purple open circles show the ob or the radio sources that were not detected in either the optical or i imit for the SCUBA-2 sources (i.e. 21.6 mJy – 450 μm and 2.52 mJ nd for the IRAC channels we assumed a magnitude upper limit valu pper limit of the HST z 850 band is ≈ 26 mag and the i 775 band ≈25.1 MNRAS 532, 2842–2859 (2024) Figure A1. Spectral energy distributions of member galaxies of J2215. See Appendix A for details. https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 2858 D. Y. Klutse et al. MNRAS 532, 2842–2859 (2024) Figure A2. Spectral energy distributions of member galaxies of J2215. See Appendix A for details. D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw atersrand H ealth Sciences Library user on 06 Septem ber 2024 MeerKAT observations of XCS J2215 2859 A pcigale.ini’ configuration file. This ‘pcigale.ini’ file was run to generate several Values 10, 16, 27, 46, 77, 129, 215, 359, 599, 1000 Myr 1000, 1291, 1668, 2154, 2782, 3593, 4641, 5994, 7742, 10 000 Myr 5.0, 50.0, 500 Myr 0.0, 0.01, 0.05, 0.1, 0.25 1 (Chabrier) 0.02 0.014 0.2 0.8 m 0.15, 0.45, 0.60, 0.90, 1.20, 1.5, 1.8, 2.1, 2.4, 2.8, 0.50, 0.75 unger stars, i.e. μ 0.25, 0.50, 0.75, 0.44 0.47, 1.12, 2.5 0.10, 0.15, 0.20, 1.0 2.0, 3.0 7 GN axis 30, 70 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.8, 0.9 2.58 0.8 d the default v alues set by CIGALE V2022.0 T © P ( D ow nloaded from https://academ ic.oup.com /m nras/article/532/2/2842/7705620 by W itw ater PPENDIX B: CIGALE M O D E L PA R A M E T E R S Table B1. This table shows the model parameters and values set in the ‘ models to fit our observed SED. Module Parameter sfhdelayed e-folding time of the burst of star formation Stellar age Age of the last starburst Mass fraction of late starburst population Simple stellar population (bc03) Initial mass function (imf) Bruzual & Charlot ( 2003 ) Metallicity Nebular emission Gas metallicity Fraction of escaped photons Fraction of absorbed photons Dust attenuation V -band attenuation in the interstellar mediu dustattmodifiedCF00 (modified Charlot & Fall 2000 attenuation law) Attenuation ratio between older stars and yo = A ISM v /A BC v + A ISM v Dust emissions Mass fraction of PAH Minimum radiation field Power-law slope AGN model Average edge-on optical depth at 9.7 μm skirtor2016 Inclination, i.e. viewing angle w.r.t. to the A AGN fraction Galaxy radio synchrotron emission FIR/radio correlation coefficient spectral index a Note . F or parameters and their corresponding v alues that were not listed here, we use a For parameters relating to star-forming galaxies. his paper has been typeset from a T E X/L A T E X file prepared by the author. MNRAS 532, 2842–2859 (2024) 2024 The Author(s). ublished by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License https://cr eativecommons.or g/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. srand H ealth Sciences Library user on 06 Septem ber 2024 https://creativecommons.org/licenses/by/4.0/ 1 INTRODUCTION 2 OBSERVATION AND DATA REDUCTION 3 ANALYSIS 4 MORPHOLOGIES AND OPTICAL COLOURS OF RADIO SOURCES IN J2215 5 CLASSIFICATION OF RADIO SOURCES 6 AGN ACTIVITY WITHIN J2215 7 STAR FORMATION ACTIVITY WITHIN J2215 8 SUMMARY ACKNOWLEDGEMENTS DATA AVAILABILITY REFERENCES APPENDIX A: SPECTRAL ENERGY DISTRIBUTION PLOTS APPENDIX B: cigale MODEL PARAMETERS