A Strong-Lensing Model for the WMDF JWST/GTO Very Rich Cluster Abell 1489
Adi Zitrin, Ana Acebron, Dan Coe, Patrick L. Kelly, Anton M. Koekemoer, Mario Nonino, Rogier A. Windhorst, Brenda Frye, Massimo Pascale, Tom Broadhurst, Seth H. Cohen, Jose M. Diego, Steven L. Finkelstein, Rolf A. Jansen, Rebecca L. Larson, Haojing Yan, Mehmet Alpaslan, Christopher J. Conselice, Alex Griffiths, Louis-Gregory Strolger, J. Stuart B. Wyithe
DDraft version July 24, 2020
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A Strong-Lensing Model for the WMDF JWST/GTO Very Rich Cluster Abell 1489
Adi Zitrin, Ana Acebron, Dan Coe, Patrick L. Kelly, Anton M. Koekemoer, Mario Nonino, Rogier A. Windhorst, Brenda Frye, Massimo Pascale, Tom Broadhurst,
8, 9, 10
Seth H. Cohen, Jose M. Diego, Steven L. Finkelstein, Rolf A. Jansen, Rebecca L. Larson, Haojing Yan, Mehmet Alpaslan, Christopher J. Conselice, Alex Griffiths, Louis-Gregory Strolger, andJ. Stuart B. Wyithe Physics Department, Ben-Gurion University of the Negev, P.O. Box 653, Be’er-Sheva 84105, Israel Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA School of Physics and Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455, USA INAF - Osservatorio Astronomico di Trieste, Via Tiepolo 11, I-34131 Trieste, Italy School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404, USA Department of Astronomy, Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ, 85721, USA Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA Department of Theoretical Physics, University of the Basque Country UPV/EHU, E-48080 Bilbao, Spain Donostia International Physics Center (DIPC), 20018 Donostia-San Sebastian (Gipuzkoa), Spain Ikerbasque, Basque Foundation for Science, E-48011 Bilbao, Spain Instituto de F´ısica de Cantabria (CSIC-UC). Edificio Juan Jord´a. Avda Los Castros s/n. 39005 Santander, Spain Department of Astronomy, The University of Texas at Austin, Austin, TX 78712 Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA Center for Cosmology and Particle Physics, Department of Physics, New York University, New York, NY 10012, USA School of Physics and Astronomy, The University of Nottingham, University Park, Nottingham, NG7 2RD, UK School of Physics, University of Melbourne, Parkville, VIC 3010, Australia (Received; Revised; Accepted)
Submitted to ApJABSTRACTWe present a first strong-lensing model for the galaxy cluster RM J121218.5+273255.1 ( z = 0 . Planck data, respectively; and its optical luminosity distribution implies a very largelens, following mass-to-light scaling relations. Based on these properties it was chosen for the WebbMedium Deep Fields (WMDF) JWST/GTO program. In preparation for this program, RMJ1212was recently imaged with GMOS on Gemini North and in seven optical and near-infrared bands withthe
Hubble Space Telescope . We use these data to map the inner mass distribution of the cluster,uncovering various sets of multiple images. We also search for high-redshift candidates in the data,as well as for transient sources. We find over a dozen high-redshift ( z (cid:38)
6) candidates based on bothphotometric redshift and the dropout technique. No prominent ( (cid:38) σ ) transients were found in thedata between the two HST visits. Our lensing analysis reveals a relatively large lens with an effectiveEinstein radius of θ E (cid:39) ± (cid:48)(cid:48) ( z s = 2), in broad agreement with the scaling-relation expectations.RMJ1212 demonstrates that powerful lensing clusters can be selected in a robust and automated wayfollowing the light-traces-mass assumption. Corresponding author: Adi [email protected] a r X i v : . [ a s t r o - ph . GA ] J u l Zitrin et al.
Keywords: dark matter – galaxies: clusters: general – galaxies: clusters: individual: Abell 1489 –gravitational lensing: strong – galaxies: high redshift INTRODUCTIONStrong lensing by galaxy clusters has both enabledstudies of the dark matter distribution in cluster cores(Kneib & Natarajan 2011; Bartelmann 2010, for re-views), and, a magnified view into the high-redshiftgalaxies, often not accessible otherwise (e.g., Franx et al.1997; Frye & Broadhurst 1998; Ellis et al. 2001; Bradleyet al. 2008; Coe et al. 2013; Zheng et al. 2012; Hashimotoet al. 2018).Deep cluster-lensing campaigns with
Hubble , suchas the Cluster Lensing and Supernova with Hubble(CLASH; Postman et al. 2012) and the ReionizationLensing Cluster Survey (RELICS; Coe et al. 2019), havesupplied hundreds of high-redshift (z (cid:38)
6) galaxies in theheart of the reionization era (Bradley et al. 2014; Salmonet al. 2020a). The Hubble Frontier Fields (HFF; Lotzet al. 2017) cluster lensing survey targeted six of themost prominent lensing clusters known (with Einsteinradii of ∼ (cid:48)(cid:48) –55 (cid:48)(cid:48) – for z s (cid:39) M UV (cid:39) −
16 at z (cid:39) Planck clusters (e.g., Planck Collaboration et al.2016) imaged in the RELICS program. However, thereappear to be many more massive optically selected richclusters in the sky that are not necessarily bright enoughin X-ray or SZ to be included in these samples, but theirprojected matter distribution is concentrated enough toform a large strong lens (see, e.g., Wong et al. 2012).Such cases (see also Umetsu 2020 section 6.2) include thefamous Abell 370 HFF cluster with θ E (cid:39) (cid:48)(cid:48) (Richardet al. 2010); CL0024+1654, with θ E (cid:39) (cid:48)(cid:48) (Zitrin et al.2009); or PLCK G165.7+67.0 – that despite its namingwas not in fact chosen based on its SZ signal, yet showsan impressive abundance of lensed features (Frye et al.2019).The JWST Medium-Deep Fields GTO program(WMDF; PI: Windhorst) has chosen to capitalize onsuch cases and, in addition to various gas-selected clus-ters that are well-known prominent lenses, set to observea few other clusters chosen based on a mix of differ-ent probes, including the rich, redMaPPer galaxy clus-ter RM J121218.5+273255.1 ( z = 0 .
35; RMJ1212 here-after; also known as Abell 1489, RXC J1212.3+2733, orCL1212+2733), as identified in the Sloan Digital SkySurvey (SDSS; York et al. 2000) data. RMJ1212 wasprovisionally chosen for WMDF mainly as an optically-selected strong lens based on the following properties:it is amongst the 0.1% richest clusters in the redMaP-Per catalog (Rykoff et al. 2014, λ = 158 . ± .
03 inthe public redMaPPer sdss dr8 v6.3 catalog , rank-ing 33 rd out of over ∼ ,
000 clusters); it has a highecliptic latitude ( b (cid:38) ◦ ) minimizing zodiacal near-infrared background light (an important considerationfor JWST high-redshift targets); it had a prominentlensing strength, and large Einstein radius of ∼ (cid:48)(cid:48) ±
20% predicted from mass-to-light rescaling of SDSS clus-ters (Zitrin et al. 2012); its preliminary velocity disper-sion estimate from few measured cluster members in http://risa.stanford.edu/redmapper/ L analysis of RMJ1212 ∼
900 km/s; and given that it issignificantly detected in X-ray (e.g., 6.13 σ in ROSAT;or an estimated mass of M = 10 . ± . × M (cid:12) ,Mantz et al. 2010), and SZ (10.09 σ in Planck ; an SZmass proxy of M = 7 . ± . × M (cid:12) , PlanckCollaboration et al. 2016).Following these promising properties, we targetedRMJ1212 with GMOS on Gemini-N in imaging modeand detected various sets of potentially multiply im-aged galaxies (see Fig. 1). Since space data is typicallyrequired to verify the tentative identification of multi-ple images, RMJ1212 was also recently imaged with the Hubble Space Telescope in seven bands (see Fig. 2 and § HST visits of the cluster. Updated lens models,including with spectroscopic redshifts for the multipleimages , and extending out to the weak-lensing regime,are planned for future work (Pascale et al., in prepara-tion ).The paper is organized as follows: In § § §
4, and con-cluded in §
5. Throughout this work we use a ΛCDMcosmology with Ω M = 0 .
3, Ω M = 0 .
7, and H = 70km/s/Mpc. Unless otherwise stated, we generally useAB magnitudes (Oke & Gunn 1983), and errors are 1 σ . OBSERVATIONS AND DATA REDUCTIONThe galaxy cluster RMJ1212 was imaged in queuemode with GMOS on Gemini-N (program ID: GN-2019A-Q-903, PI: Zitrin) on 2019 March 12, in the g (8 × r ( (cid:39) . × s ) bands, and on 2019 April04, in the i (8 × s ) band. Data were retrieved from theGemini archive and reduced using standard procedureswith the Gemini Iraf pipeline. Astrometry, based onSDSS, was obtained using
Scamp (Bertin 2006). Theimages, after background subtraction, were coadded us-ing
Swarp (Bertin et al. 2002), and zero points for the g,r,i stacks were obtained via a comparison with SDSS. this is only somewhat lower than the cut for the SZ-selectedRELICS sample, 8 . × M (cid:12) . Spectroscopic observations were already in queue forGMOS/Gemini-North before the telescope shut down onMarch 2020 due to the COVID-19 pandemic, and were eventu-ally completed on June 2020 after the writing of this manuscript.These will be reduced and incorporated in a future model.
A color composite image of these data is shown in Figure1, right panel .In preparation for the WMDF JWST/GTO program,and in order to construct a detailed lens model, iden-tify high-redshift candidates, and form baseline obser-vations for future transient detection, RMJ1212 was re-cently observed with
Hubble for five orbits (programID: 15959, PI: Zitrin). The cluster was observed fora total of about 1 orbit in each of the F435W (1934s),F606W (1904s), and F814W (1934s) filters with the
Ad-vanced Camera for Surveys (ACS) Wide Field Channel(WFC) ; and for a total of about 1 / Wide-Field Camera 3 -infrared channel (WFC3/IR) . One F140W exposure suf-fered from a guiding problem. To fix this, the readout( ∼ s ) in which the drift was detected was discarded,and not used in constructing the final images. Observa-tions were divided into two visits, both to relax schedul-ing constraints, and to allow – albeit at low probability– for transient searches, and were carried out on 2020March 16 and 2020 March 25.Mosaic images for all the HST exposures were pro-duced from the calibrated exposures by running theMosaicDrizzle pipeline (Koekemoer et al. 2011), spe-cialized for this proposal and updated to use the lat-est drizzlepac routines, achieving milliarcsecond-level as-trometric alignment across all the different filters forACS/WFC and WFC3/IR. Two sets of mosaics wereproduced, at scales of 0 . (cid:48)(cid:48)
03 and 0 . (cid:48)(cid:48)
06 per pixel, with allthe pixels aligned to the same astrometric grid, withNorth up, and registered onto the Gaia DR2 referenceframe. The 0 . (cid:48)(cid:48)
03 mosaics are most useful for study-ing fine morphological details, especially since they sub-sample the native ACS pixel scale, while the 0 . (cid:48)(cid:48)
06 mo-saics are more generally useful for producing catalogsacross both WFC3/IR and ACS, which we describe inthis section.Throughout we work with several photometric cata-logs. First, for the lens model, we need a list of potentialcluster members and their photometry. We run
SEx-tractor (Bertin & Arnouts 1996) version 2.25.0 on theF814W band, and then in dual mode on all other HSTimages with the F814W as the detection image. Clus-ter members are identified following the red-sequence ina color-magnitude diagram, where we use the F606W-F814W color versus the F814W magnitude. Membersare chosen within ± .
15 mag from this sequence (definedas ( mag F W − mag F W ) = 0 . ∗ mag F W + 0 . mag F W = 22 .
5. The list ofcluster members is then examined visually, and updatedas needed (we also include an apparently foreground,
Zitrin et al.
Figure 1.
Preliminary lensing properties of RMJ1212 from ground-based data.
Left: prediction for the shape and size of thecritical area in RMJ1212 based solely on our mass-to-light scaling relation of SDSS selected clusters (Zitrin et al. 2012; whitelines mark the critical curves for z s = 2). The lens was predicted to be large, with an Einstein radius of ∼ (cid:48)(cid:48) . The typicalerror in this estimate is about 20%. Right: the Gemini/GMOS deep gr observations of RMJ1212. Marked on the image arecandidate multiply imaged galaxy families as identified prior to the HST data (the i band observations were not yet available atthe time of the candidate multiple image identification and hence were not included). Their location follows nicely the criticalcurves predicted, suggesting that indeed RMJ1212 is a prominent lens, but HST observations were required to corroborate this,secure these identifications and construct a credible lens model for the cluster, which are our goals here. z phot (cid:39) . back size = 16, detect minarea =8, detect thresh = 1, analysis thresh = 1 . deblend nthresh = 16 to improve source detection.Note that all magnitudes are measured and given here-after in isophotal apertures, and corrected for galacticextinction.We also show here a smoothed X-ray map takenwith Chandra in 2003, January 11 (Obs. ID 5767, PI:Vikhlinin), with an exposure time of 15.0 ks. We use thehigh resolution ACIS Primary data product, smoothedwith a 20-pixel Gaussian. These X-ray data are onlyused qualitatively to show the X-ray centroid (Fig. 3).The reduced
HST images, combined color images andcatalogs, are made publicly available online . The lensmodel now detailed is also available in the same library. SL MODELING OF RMJ1212We use here the Light-Traces-Mass (LTM) lens mod-eling code of Zitrin et al. (2009, 2015, and referencestherein), which is especially useful for the analysis of newlenses as it is inherently capable of guiding the detection ∼ koekemoer/zitrin/RMJ1212 L analysis of RMJ1212 Figure 2.
Multiple images and critical curves for RMJ1212. Shown is an RGB color-composite image from the 7-band HSTdata. Multiple-image sets are marked on the image and the critical curves from our model are overlaid in light blue for a sourceat a redshift similar to that of the main arc (system 1; z phot ∼ . red for a source redshift of z s (cid:39)
10. Bright clustermembers, some of whose parameters were individually optimized in the minimization (see text), are noted with A, B, C and D. of multiple-image sets (Carrasco et al. 2020). More com-plete details of the formalism can be found in the abovereferences, and we give here only a broad outline.The deflection field is modeled as a sum of three com-ponents. The first component maps the projected massdensity distribution of the cluster galaxies, modeled eachwith a simple power-law ( q ) surface-mass density, scaledwith the galaxy’s luminosity and normalized to a de- sired lensing distance, or redshift, by some factor ( K ).The second component is the dark matter map whichis obtained by smoothing the galaxy map with a Gaus-sian kernel of width S . The two components are thenadded with a relative weight k gal , reflecting the ratioof luminous to dark matter. The third component, con-tributing only to the deflection field, but not to the massdensity, is an external shear of strength γ ex and position Zitrin et al. angle φ ex , which allows for greater effective elongationof the critical curves and accounts for the contributionof larger-scale structure. The model thus comprises sixmain parameters: q, S, K, k gal , γ ex and φ ex .We often introduce ellipticites and position angles aswell as central cores for a few key cluster members,such as the brightest (and thus most massive) galax-ies. These can either be set as fixed, or be minimizedas well (adding, correspondingly, to the number of freeparameters). In addition, it is often beneficial to leavethe relative weight (i.e., the relative mass-to-light ratio)of some key galaxies free as well. Similarly, the lens-ing distance (i.e., essentially, redshift) of systems withpoorly constrained redshifts can also be left to be freelyoptimized.The optimization of the model is carried out by min-imizing, using a χ function, the distance between mul-tiple images and their positions predicted by the model.This is done via a Monte-Carlo Markov Chain witha Metropolis-Hastings algorithm (e.g., Hastings 1970).We also include some annealing in the procedure, andthe chain typically runs for several thousand steps afterthe burn-in stage. Errors are calculated from the sameMarkov chain.For modeling RMJ1212 we start with all galaxiesfixed, and construct a simple model minimized by twosets of obvious multiple images: images 1.1+1.2, and im-ages 4.1+4.2, fixing them to their best-fit photometricredshifts (Table 1). With this preliminary model we it-eratively predict the location of counter images and findadditional systems by sending notable arclets across thefield to the source plane and back, probing a range ofredshifts. In total, we find 31 likely multiple images andcandidates of about 8-10 background sources (systems 1,2 and 3 may correspond to a single background object).With these, we construct the final model presented here.To anchor the model we fix the redshift of all systemsto roughly their average, or typical, best BPZ value,listed in Table 1 as well (although some minor differ-ences may exist due to updates to the catalog; theseonly weakly affect the derived D ls /D s ratio). We leavethe weight of the four central brightest cluster galaxies(BCGs A,B,C,D in Fig. 2) free, and allow for ellipticityfor the brightest two (A and B). For the southern BCGaround which system 6 appears, BCG “B”, we allow theellipticity to vary around its values measured from SEx-tractor. No cores are incorporated for cluster galaxies,aside from this southern one, for which we allow a smallcore. In total, the model includes 13 free parameters,optimized using uniform flat priors. Image position un-certainties were adopted to be 0.5 (cid:48)(cid:48) , whereas for systems Figure 3.
Projected mass density of RMJ1212. We show κ ,the surface mass density distribution in units of the criticaldensity for strong lensing, for the source redshift adopted forthe main arc ( z s = 2 .
7; systems 1, 2, 3). Overlaid blackcontours follow a smoothed X-ray map from Chandra. Cap-ital letters A, B, C and D mark the four central BCGs as inFig. 2. From the lensing analysis (and its resulting κ mapshown) it becomes apparent that the main mass concentra-tion in centered on galaxy B, in agreement with the X-raycontours, and despite galaxy A being comparable in opticalbrightness (and in fact slightly brighter, see §
1, 3, and 6, we adopted 0.1 (cid:48)(cid:48) (to give them more weightin the modeling). RESULTS AND DISCUSSION4.1.
Lens modeling
The resulting best-fit model has an rms of 1 (cid:48)(cid:48) .44 inreproducing the position of multiple images. Such valuesare typical for LTM models of moderately complex, largelenses. The reproduction of multiple images is excellent,and a few examples are given in Fig. 4.The projected mass density map of the best-fit modelis shown in Fig. 3. An interesting point to noteis that while galaxy A in Fig. 2 is slightly brighter( mag F W = 17 .
37 AB) than galaxies B ( mag F W =17 .
68 AB) and C ( mag F W = 17 .
93 AB), the lattertwo seem to represent locations of much greater concen-
L analysis of RMJ1212 black contours ).The corresponding critical curves of the best-fit modelare overlaid on an image of the cluster in Fig. 2, wheremultiple images are marked as well. The effective Ein-stein radius we find is relatively large, 31 . ± . (cid:48)(cid:48) fora source at z s = 2, where the effective Einstein radiusis defined as the radius of the area enclosed within thecritical curves if it were a circle. The mass in that crit-ical area is 1 . ± . × M (cid:12) . Errors on the Ein-stein radius and mass are nominal, systematic values,reflecting typical errors seen between different models;the statistical uncertainties are somewhat smaller. Forthe assigned redshift of systems 1-3, z s = 2 .
7, the light-blue curves shown in Fig. 2 have an effective θ E (cid:39) (cid:48)(cid:48) ,and for a source at z s = 10 (red curves therein), theyreach (cid:39) (cid:48)(cid:48) . These estimates will be revised once multi-ple image redshifts become available, and perhaps whenmore multiple images, especially around the northernend, are identified.It has been known that substantial substructure pro-jected near the core in merging clusters, as seen inRMJ1212, boosts the Einstein radius (Torri et al. 2004;Redlich et al. 2012). Searching for the largest andmost efficient lenses is important for a variety of stud-ies. Given the shape of the cosmological mass functionand the hierarchical mass build up, massive clusters arerarer, and their numbers have direct implications forstructure formation and evolution models, as well as forcosmological models. While a total mass does not guar-antee a large lens, overall the Einstein radius shouldincrease with the mass of the cluster (albeit with a largescatter), and predictions can be made for the univer-sal Einstein radius distribution based on an input massfunction, cosmology, and assumptions on the shape ofthe clusters (e.g. Oguri & Blandford 2009). In addi-tion, and especially as we prepare for the next genera-tion space telescope, JWST, a primary goal of which isdetecting the first galaxies, we wish to find those lensesthat maximize the high-redshift galaxy yield. Merginggalaxy clusters, especially those with elongated shapes,are known to have a boosted lensing cross section (e.g.,Meneghetti et al. 2003; Zitrin et al. 2013; Acebron et al.2019a), such as the HFF clusters (Lotz et al. 2017; Vega-Ferrero et al. 2019), and thus should be favorable for de-tecting high-redshift galaxies. On the other hand, somemassive clusters, despite being merging with many sub-clumps and comprising large Einstein radii, are not nec-essarily the most prolific in terms of high-redshift galax-ies (see for example Acebron et al. 2019b), but it is not yet clear if this is a result of cosmic variance, less avail-able area outside the critical curves to search for high-redshift dropouts (see also Oesch et al. 2015), or indi-cation of less a steep faint-end luminosity function thanwhat is needed to counter the magnification bias (e.g.,Broadhurst et al. 1995; Mashian & Loeb 2013). Ongo-ing surveys such as the BUFFALO survey (Steinhardtet al. 2020) mapping larger areas around the HubbleFrontier Fields clusters, should be helpful in answeringthis important question with HST , in the advent of nextgeneration telescopes.The largest gravitational lenses known to date (seethe list in Table 1 of Acebron et al. 2019b) have beenusually chosen for
HST observations based on their X-ray (MACS clusters and respective snapshot programs,Ebeling et al. 2010; CLASH, Postman et al. 2012) andand SZ signatures (RELICS, Coe et al. 2019; Acebronet al. 2019b; Paterno-Mahler et al. 2018; Cerny et al.2018), or following optical signatures such as giant arcs(e.g., Sharon et al. 2015). In contrast, and althoughRMJ1212 is “only” modestly large – note that it is largerthan the typical Hubble Frontier Field cluster – we stressthat RMJ1212 was designated as a potentially large lensin a computerized, blind search in ground-based datafollowing only the distribution and luminosity of clustermembers as input (Zitrin et al. 2012, using the SDSSGMBCG cluster catalog of Hao et al. 2010). Here weconfirm that, although somewhat smaller than the pre-liminary blind estimate of ∼ (cid:48)(cid:48) , it is indeed a promi-nent lens. In Fig. 1 we show the preliminary criticalcurves predicted by the methodology and mass-to-lightscaling of Zitrin et al. (2012). We can compare thesecurves to the final curves presented here in Fig. 2, de-rived using the HST data and careful multiple-imageidentification. Due to the overall successful assumptionthat light traces mass, the preliminary critical curves,derived from the SDSS data with no multiple imagesas input, are quite similar in shape to the final curvesin Fig. 2, passing in between multiple images as theyshould and making RMJ1212 another proof-of-conceptfor identifying the largest lenses directly in ground-basedand large sky surveys (Zitrin et al. 2012; Wong et al.2012; Stapelberg et al. 2019). This increasing abilityto approximate the projected mass distribution and thecorresponding lensing properties can be quite useful forupcoming surveys from the ground, or from space, suchas with Euclid or the Nancy Grace Roman Space Tele-scope (previously known as WFIRST).We can also compare the tentative multiple imageidentification in our ground-based Gemini data to thefinal identification presented here.
Hubble has the cru-cial combination of depth and high resolution – a much
Zitrin et al.
Figure 4.
Reproduction of multiple images by our model. We show the reproduction of system 1 (and 2 and 3), by lensingthe left side of the arc, image 1.1+2.1+3.1, to the source-plane and back through the lens; system 4, by lensing image 4.1 tothe source-plane and back; system 6, by lensing image 6.1 to the source-plane and back; system 8, by lensing image 8.3 tothe source-plane and back; and system 9, by lensing image 9.1 to the source-plane and back. For each system the upper rowshows the images in the data and the bottom row the reproduction by the model. Although some minor differences exist, theprediction of the model evidently reproduces the observed images well, strengthening their identification.
L analysis of RMJ1212 Table 1.
Multiple Image SystemsID R.A DEC. z phot [95% C.I.] z model CommentJ2000.0 J2000.01.1 12:12:17.315 +27:33:04.24 2.743 [2.642 – 2.877] 2.701.2 12:12:16.983 +27:33:02.28 2.746 [2.610 – 2.776] ”1.3 12:12:21.881 +27:33:27.42 2.885 [2.744 – 3.105] ”2.1 12:12:17.346 +27:33:03.92 2.675 [2.554 – 2.739] ”2.2 12:12:16.971 +27:33:01.72 2.600 [2.518 – 2.719] ”2.3 12:12:21.881 +27:33:27.14 2.754 [2.588 – 2.978] ”3.1 12:12:17.217 +27:33:02.13 2.356 [2.097 – 2.546] ”3.2 12:12:17.148 +27:33:01.75 2.612 [2.446 – 2.739] ”4.1 12:12:19.028 +27:33:29.16 0.529 [0.151 – 0.706] 1.694.2 12:12:19.385 +27:33:28.81 1.698 [1.544 – 1.795] ”4.3 12:12:15.376 +27:33:04.16 1.617 [1.401 – 1.827] ”c5.1 12:12:17.948 +27:32:33.02 1.358 [1.168 – 1.417] —c5.2 12:12:17.810 +27:32:32.92 1.201 [1.143 – 1.352] —6.1 12:12:16.757 +27:32:50.82 1.455 [1.316 – 1.554] 1.346.2 12:12:18.374 +27:32:51.38 — ”6.3 12:12:18.393 +27:32:53.85 — ”6.4 12:12:18.232 +27:32:58.52 — ”6.5 12:12:21.006 +27:33:13.25 — ”c7.1 12:12:19.061 +27:33:24.68 2.377 [1.467 – 2.717] —c7.2 12:12:19.732 +27:33:23.64 2.120 [1.560 – 3.153] —c7.3 12:12:15.396 +27:32:57.20 1.151 [0.933 – 2.347] —8.1 12:12:18.615 +27:32:49.24 — 2.598.2 12:12:18.334 +27:33:03.27 — ”8.3 12:12:15.898 +27:32:49.08 2.187 [1.433 – 2.606] ”8.4 12:12:21.256 +27:33:18.93 2.304 [2.018 – 2.556] ”9.1 12:12:18.199 +27:33:43.28 3.254 [3.094 – 3.374] 3.359.2 12:12:20.552 +27:33:39.08 0.568 [0.132 – 3.189] ”9.3 12:12:15.295 +27:33:13.47 3.402 [3.224 – 3.503] ”c10.1 12:12:16.586 +27:33:36.49 2.578 [0.543 – 2.738] —c10.2 12:12:16.153 +27:33:29.88 0.928 [0.600 – 2.394] —c10.3 12:12:20.575 +27:33:49.15 2.615 [0.115 – 3.056] —
Note —Multiple images and candidates.
Column 1:
ID;
Column 2 & 3:
RightAscension and Declination, in J2000.0;
Column 4: best photometric redshift fromBPZ, and its 95% confidence interval;
Column 5: the redshift of the system asadopted for the modeling;
Column 6: comments. ”c” stands for candidate image,whose identification was less secure and it was not used in the minimization. Zitrin et al. better angular resolution than in typical ground-basedobservations (about ∼ . (cid:48)(cid:48) compared to ∼ (cid:48)(cid:48) ) – a keyfor securing the identification of multiple images, espe-cially in lack of spectroscopic redshifts. Nevertheless,two systems and one candidate system that we initiallyidentified in the GMOS data, guided by the location ofthe preliminary critical curves and following colors andsymmetry, survived the more careful inspection allowedby the HST data (at least partially, i.e., some counterimages may have been updated). The other two sys-tem candidates we marked on the Gemini data seem tobe wrong, emphasizing the need for space imaging forextensive multiple image identification. The HST dataallowed us to detect, in addition, several other systemsand multiple-image candidates, seen in Fig. 2.4.2.
High-redshift candidates
We take advantage of the multiband observations andsearch the field for high-redshift candidates. Given thatthe field was observed for only about half an orbit ineach WFC3/IR band, the target population are rela-tively, bright objects: the observing scheme was similarto that implemented in the RELICS program, designedto find bright (5 σ of AB 26.5 in the F160W band, forexample) lensed candidates across ∼
40 galaxy clusters.First, we search the RELICS-like BPZ catalog for ob-jects with a z best > .
5. Six objects pass this criterion.Two are designated as likely artifacts close ( < (cid:48)(cid:48) ) tothe edge of the WFC3 frame and are discarded. Theremaining four objects are listed in Table 2, and theirstamp images in different bands are shown in Fig. 5. Wethen take on a second approach. We adopt the Lyman-break technique and apply selection criteria searchingexplicitly for dropout galaxies. Specifically, we adopttwo sets of color criteria for the Lyman-break galaxyselection, as follows:The criteria used in Atek et al. (2014, ; hereafter criteriaA): • Redshift ∼ − > > (0.6 + 2.0*(F105W-F125W))(F105W-F125W) < • Redshift ∼ > > (0.3 + 1.6*(F125W-F140W))(F125W-F140W) < • Redshift ∼ − > > (0.8 + (F105W - F125W))(F105W - F125W) < • Redshift ∼ − > > (0.8 + (F140W - F160W))(F140W - F160W) < • Redshift ∼
10 selection:(F125W - F160W) > σ in all bandsbluewards of the break, as well as not detected by morethan 1.5 σ in a weighted-stack image consisting of allbands bluer than the break. We only consider objectsthat are at least 1 (cid:48)(cid:48) away from the edge of the WFC3frame, and adopt a SExtractor stellarity cut of < . σ in the combined, WFC3/IR detection image.We run these constraints by the RELICS-like ”wfc3ir”catalog. Three objects pass these criteria, and are listedin the second part of Table 2, and are shown in Fig.5. We then also run these constraints by the alterna-tive catalog we made for high-redshift source detection( §
2; note that the lower back size used here can leadto slightly different isophotal magnitudes compared tothe RELICS-like catalog). Fourteen high- z candidatespass these dropout selection criteria in this alternativecatalog. Following a visual inspection by eye we dis-card three of them as likely artifacts (two are buriedin the BCG light and one appears to be related to alower-redshift counterpart). Four out of the remaining11 overlap with candidates from the RELICS-like cat-alog (two from the photo- z selected and two from thedropout-selected) so that overall, seven more objects areadded to the list, listed in the third part of Table 2 andshown in Fig. 6, respectively. In total, we identify here14 tentative high-redshift candidates.We note that, as seen in Figs. 5–6, the objects se-lected via the dropout technique all have a photometric-redshift distribution that allows for a high-redshift solu-tion, but the best-fit suggests a lower redshift. In that L analysis of RMJ1212 (cid:48)(cid:48) from the predicted location of counter images.This practice indicates that objects ID8971 and ID311may be related, but no other obvious counter images arefound for other objects.We can compare the high- z yield to the high-redshiftnumber counts in the RELICS survey, where the imagingscheme (filter choice and depth) is similar. Salmon et al.(2020a) find 257, 57, and 8 candidate galaxies at z phot (cid:39)
6, 7, and 8, respectively, over 41 RELICS clusters, sothat the average per cluster is 6.3, 1.4, and 0.2 galaxiesat these redshifts, respectively, whereas the most prolificRELICS clusters can show above a couple-dozen candi-dates in total. In that sense, RMJ1212 seems to becomparable to, or somewhat stronger than the averageRELICS cluster field in terms of high- z number counts(although note the different selection methods). We em-phasize that our list is preliminary, and our candidates,especially the fainter and smaller ones, will need morecareful examination when more data is available. For ex-ample, the F160W (isophotal) magnitude distribution ofthe high- z candidates of Salmon et al. (2020a) concen-trates around AB 27, with relatively few objects aroundAB 28. Our candidates seem to concentrate close to AB28, comparable to the nominal depth limit ( (cid:39) σ at AB (cid:39) . Transients
Last, we also take advantage of the fact that the clus-ter was imaged in two different epochs to search fortransient sources such as potential supernovae or caus-tic crossing events. The WFC3-IR integrations throughthe F105W, F125W, F140W, and F160W wideband fil-ters were acquired first on March 16 2020, UT and atsecond epoch, nine days later, on March 25, 2020 UT(the ACS WFC imaging was acquired, by contrast, ata single epoch). We have searched the two epochs ofWFC3 IR imaging data for variable sources, includingsupernovae and microlensing events caused as the caus- tic magnification pattern in the source plane moves rel-ative to the stars in a magnified arc. While microlensingdue to a moving caustic pattern will, in general, causea continuous change in magnification, the characteris-tic time scale of microlensing peaks (e.g., Kelly et al.2018; Rodney et al. 2018; Chen et al. 2019; Kaurov et al.2019) should be approximately two weeks, which wasconfirmed by that of the Icarus event in MACS J1149(Kelly et al. 2018). According to the WFC3 ExposureTime Calculator (ETC), the 5- σ AB detection limitsare approximately 26.0 mag (F105W), 25.9 (F125W),25.9 (F140W), and 26.0 (F160W), after taking into ac-count the background-noise from the template image.For added sensitivity, we also carried out a search of thecoaddition of all WFC3 filters. Visual inspection andSExtractor searches, however, yield no credible ( (cid:38) σ )transients either at the locations of the prominent arcsor at other locations in the imaging footprint. Nev-ertheless, as the cluster shows several arcs that clearlystraddle the critical curves, such as the blue star-formingsystems 1-3, or systems 4 and c5, it should in principlebe useful for future caustic crossing searches. SUMMARYWe presented a SL model for the very rich redMaP-PER galaxy cluster RMJ1212 (also known as Abell 1489,RXC J1212.3+2733, or CL1212+2733), in preparationfor the WMDF JWST/GTO program ( θ E (cid:39) ± (cid:48)(cid:48) ( z s = 2), and θ E (cid:39) ± (cid:48)(cid:48) ( z s = 10).We searched the data for high-redshifts candidates.We found four candidate high-redshift objects ( z (cid:38) Zitrin et al. here reveals a somewhat ( ∼ Hubble
L analysis of RMJ1212 T a b l e . H i g h - R e d s h i f t C a nd i d a t e s I D R . A D E C . m a g F W m a g F W m a g F W m a g F W m a g F W m a g F W m a g F W z p h o t [ % C . I .] µ J . J . I D : : . + : : . . ± . . ± . . ± . . ± . . ± . . ± . . [ . . ] . ± . I D : : . + : : . . ± . . ± . . ± . . ± . . [ . . ] . ± . I D a , b : : . + : : . . ± . . ± . . ± . . ± . . ± . . ± . . [ . . ] . ± . I D a , b : : . + : : . . ± . . ± . . ± . . ± . . ± . . [ . . ] . ± . I D b : : . + : : . — . ± . . ± . . ± . . ± . . ± . . ± . . [ . . ] . ± . I D b : : . + : : . — . ± . . ± . . ± . . ± . . ± . . ± . . [ . . ] . ± . I D a , b : : . + : : . — . ± . . ± . . ± . . ± . . ± . . ± . . [ . . ] . ± . I D b : : . + : : . . ± . — . ± . . ± . . ± . . ± . . ± . . [ . . ] . ± . I D a , b : : . + : : . . ± . . ± . . ± . . ± . . ± . . ± . . ± . . [ . . ] . ± . I D a , b : : . + : : . — . ± . . ± . . ± . . ± . . ± . . ± . . [ . . ] . ± . ∗ I D a , b : : . + : : . — . ± . . ± . . ± . . ± . . ± . . ± . . [ . . ] . ± . I D b : : . + : : . — . ± . . ± . . ± . . ± . . ± . . ± . . [ . . ] . ± . I D a , b : : . + : : . — . ± . . ± . . ± . . ± . . ± . . ± . . [ . . ] . ± . ∗ I D a , b : : . + : : . — . ± . . ± . . ± . . ± . . ± . . ± . . [ . . ] . ± . N o t e — H i g h - r e d s h i f t( z (cid:38) ) ga l a xy c a nd i d a t e s . C o l u m n : I D ; C o l u m n & : R i g h t A s c e n s i o n a nd D e c li n a t i o n ,i n J . ; C o l u m n - : i s o ph o t a l m ag n i t ud e s a nd a ss o c i a t e dun c e r t a i n t y m e a s u r e db y S o u r c e - E X t r a c t o r ; C o l u m n : b e s t ph o t o m e t r i c r e d s h i f t f r o m B P Z , a nd i t s % c o nfid e n c e i n t e r v a l; C o l u m n : a pp r o x i m a t e m ag n i fi c a t i o nb y t h e m o d e l, a d o p t i n g t h e r e l e v a n t ph o t o m e t r i c o r d r o p o u t - s e l e c t i o n r e d s h i f t . ∗ D i v e r g i n g v a l u e ss u gg e s tt h e o b j e c t i s c l o s e t o t h e c r i t i c a l c u r v e s , h i g h l y m ag n i fi e d bu t w i t hp oo r l y c o n s t r a i n e d m ag n i fi c a t i o n . T h e fi r s t p a r t o f t h e T a b l e a r e o b j e c t ss e l e c t e db y c o n s i d e r i n g e n t r i e s w i t h z p h o t > . i n t h e a u t o m a t e d R E L I C S - li k e c a t a l og . T h e s e c o ndp a r t o f t h e T a b l e a r e o b j e c t s t h a t p a ss e d t h e d r o p o u t - s e l e c t i o n c r i t e r i a i n t h e R E L I C S - li k e c a t a l og ( w i t hn o ph o t o m e t r i c r e d s h i f t c u t ; s ee § . ) , a nd t h e t h i r dp a r t a r e o b j e c t s t h a t p a ss e d t h e d r o p o u t - s e l e c t i o n c r i t e r i a i n o u r a l t e r n a t i v e , d e s i g n a t e d c a t a l og . N o t e t h i s c a t a l og u s e dd i ff e r e n t S E x t r a c t o r p a r a m e t e r ss o t h e i s o ph o t a l m ag n i t ud e s c a nb e s li g h t l y (t y p i c a ll y ∼ . − . m ag ) d i ff e r e n t c o m p a r e d t o t h e R E L I C S - li k e c a t a l og . F o r e a c h ga l a xy w e n o t e w h i c h c r i t e r i a i t p a ss e d ( ”a” = A o r ” b ” = B ) , a nd f o r w h i c h r e d s h i f t( ”67” s t a nd s f o r z ∼ − ; ”78” f o r z ∼ − , ”8” f o r z ∼ , e t c . ) . Tw oo f t h e p h o t o − z s e l e c t e d ga l a x i e s w e r e a l s o r e c o v e r e db y t h e d r o p o u t s e l e c t i o n . S ee t e x t f o r m o r e d e t a il s . Zitrin et al.
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L analysis of RMJ1212 ID25:ID244:ID311:ID613:ID544:ID1000:ID1024:Figure 5.
High-redshift candidates. Each row corresponds to a different object in the RELICS-like catalog, in the same orderas in Table 2. For each object we show stamp images in the seven different bands, as well as in a combined optical (both ingrey-scale and in a composite RGB image from the ACS bands), and combined RGB optical+infrared image. The first fourobjects are photo- z selected and the rest of the objects were selected with the dropout technique and are undetected bluer ofthe Lyman break. Each stamp is 3 . (cid:48)(cid:48) × . (cid:48)(cid:48) in size. Also shown is the photometric-redshift distribution for each object. Zitrin et al.
ID117:ID304:ID732:ID821:ID897:ID958:ID998:Figure 6.
Same as Fig. 5, but for dropout-selected candidates from our second catalog.
L analysis of RMJ121217