The Extended Spatial Distribution of Globular Clusters in the Core of the Fornax Cluster
R. D'Abrusco, M. Cantiello, M. Paolillo, V. Pota, N.R. Napolitano, L. Limatola, M. Spavone, A. Grado, E. Iodice, M. Capaccioli, R. Peletier, G. Longo, M. Hilker, S. Mieske, E.K. Grebel, T. Lisker, C. Wittmann, G. van de Ven, G. Fabbiano
vversion February 22, 2016: fm
Preprint typeset using L A TEX style emulateapj v. 5/2/11
THE EXTENDED SPATIAL DISTRIBUTION OF GLOBULAR CLUSTERS IN THE CORE OF THE FORNAXCLUSTER
R. D’Abrusco , M. Cantiello , M. Paolillo , V. Pota , N.R. Napolitano , L. Limatola , M. Spavone ,A. Grado , E. Iodice , M. Capaccioli , R. Peletier , G. Longo , M. Hilker , S. Mieske , E.K. Grebel ,T. Lisker , C. Wittmann , G. van de Ven & G. Fabbiano version February 22, 2016: fm ABSTRACTWe report the discovery of a complex extended density enhancement in the Globular Clusters(GCs) in the central ∼ . ◦ ) ( ∼ .
06 Mpc ) of the Fornax cluster, corresponding to ∼
50% ofthe area within 1 core radius. This overdensity connects the GC system of NGC1399 to most ofthose of neighboring galaxies within ∼ . ◦ ( ∼
210 kpc) along the W-E direction. The asymmetricdensity structure suggests that the galaxies in the core of the Fornax cluster experienced a livelyhistory of interactions that have left a clear imprint on the spatial distribution of GCs. The extendedcentral dominant structure is more prominent in the distribution of blue GCs, while red GCs showdensity enhancements that are more centrally concentrated on the host galaxies. We propose thatthe relatively small-scale density structures in the red GCs are caused by galaxy-galaxy interactions,while the extensive spatial distribution of blue GCs is due to stripping of GCs from the halos of coremassive galaxies by the Fornax gravitational potential. Our investigations is based on density maps ofcandidate GCs extracted from the multi-band VLT Survey Telescope (VST) survey of Fornax (FDS),identified in a three-dimensional color space and further selected based on their g -band magnitudeand morphology. Subject headings: galaxies: clusters: individual (Fornax) - galaxies: evolution - galaxies: individual(NGC1399) INTRODUCTION
In the hierarchical ΛCDM paradigm the most massivegalaxies grow through mergers and accretions of multi-ple smaller galaxies (Springel et al. 2005). These inter-actions leave their footprints in the galaxies’ dynamics,kinematics, chemistry and morphology, and in particularin galaxy halos (e.g. Zolotov et al. 2010) where dynam-ical timescales are longer than at small galactocentricdistances. In this context, historically much attentionhas been paid to the properties of the globular clus-ter systems (GCSs) of the galaxies (Brodie & Strader2006). In the framework of the two-phase galaxy for-mation model (e.g. Oser et al. 2010; Rodriguez-Gomezet al. 2015), GCs trace both the in situ star formationand the accretion phases. Recently it has been shownthat the spatial distribution of the GC systems of mas-sive early-type galaxies (e.g. D’Abrusco et al. 2015; Blomet al. 2014; D’Abrusco et al. 2014a,b, 2013b) has inho-mogeneities that may reflect the host’s accretion history.This approach complements the study of the GCS kine- University of Naples Federico II, C.U. Monte SantAngelo,Via Cinthia, 80126, Naples, Italy INAF-Astronomical Observatory of Teramo, Via Maggini,64100, Teramo, Italy INAF - Astronomical Observatory of Capodimonte, viaMoiariello 16, Naples, I-80131, Italy Kapteyn Astronomical Institute, University of Groningen,PO Box 72, 9700 AB Groningen, The Netherland European Southern Observatory, Karl-Schwarzschild-Strasse2, 85748 Garching bei M¨unchen, Germany Astronomisches Rechen-Institut, Zentrum f¨ur Astronomieder Universit¨at Heidelberg, M¨onchhofstrasse 12-14, 69120 Hei-delberg, Germany Harvard-Smithsonian Center for Astrophysics, 60 GardenStreet, Cambridge, MA 02138, USA matics (e.g. Strader et al. 2011; Coccato et al. 2013;Napolitano et al. 2014; Pota et al. 2015a,b).Deep, multi-band optical imaging data covering largeareas of the sky can be used to reconstruct the projected2D distribution of GCs within nearby clusters of galax-ies. The spatial distribution of GCs in the Virgo cluster,for instance, has been studied using both Sloan DigitalSky Survey (Lee et al. 2010) and the Canada-France-Hawaii Telescope data (Durrell et al. 2014, Next Gen-eration Virgo Survey collaboration). In this paper wediscuss the properties of the 2D spatial distribution ofcandidate GCs in the central region of the Fornax clus-ter using Fornax Deep Survey (FDS) data taken with theVST. THE DATA AND CATALOG EXTRACTION
The FDS data analyzed in this letter were acquiredas Guaranteed Time Observations for the surveys FOr-nax Cluster Ultra-deep Survey (FOCUS; P.I. R. Peletier)and VST Early-type GAlaxy Survey (VEGAS; P.I. M.Capaccioli), based on observations taken at the ESO LaSilla Paranal Observatory. Imaging in the u , g , r and i filters was performed with the 2.6-m ESO VLT SurveyTelescope (VST) at Cerro Paranal in Chile (Schipani etal. 2012). VST is equipped with the wide field cameraOmegaCAM (Kuijken 2011), whose field of view covers1 × ◦ ) in the [0.3, 1.0] µ m wavelength range, with meanpixel scale of 0 . (cid:48)(cid:48) /pixel.The images used in this letter cover 7 partially over-lapping fields centered on the core of the Fornax cluster,for a total of ∼ . ◦ ) . Images were acquired using the step-dither strategy, consisting of a cycle of short expo-sures alternately centered on the field and on contiguousregions adjacent to the field. This approach, adopted in a r X i v : . [ a s t r o - ph . GA ] F e b other photometric surveys (e.g. Ferrarese et al. 2012), al-lows an accurate estimate of the sky background aroundbright and extended galaxies. For each field, we ob-tained 76 exposures of 150s in the u -band, 54s in the g and r bands and 35s in the i -band, for a total exposuretime of 3.17, 2.25 and 1.46 hours respectively, reachingS/N ∼
10 at 23 . , . , . , . u , g , r and i , respectively, with no sig-nificant spatial variations. The average seeing and thefield-to-field standard deviation are 1 . (cid:48)(cid:48) ± . (cid:48)(cid:48)
08 in the g -band and 0 . (cid:48)(cid:48) ± . (cid:48)(cid:48)
07 in the r band. Other bands displaycomparable variations over the observed fields.The image reduction was performed with the VST-Tube imaging pipeline (see Capaccioli et al. 2015and Iodice et al. 2016 for descriptions of the pipelineand the observing strategy). The photometric analy-sis of the images followed the prescriptions in Cantielloet al. (2015). We extracted the catalog of all sourcesby independently running SExtractor (Bertin & Arnouts1996) in each filter. To improve the detection of sourcesaround bright galaxies, we modeled and subtracted thegalaxies using the IRAF ellipse routine and ran SEx-tractor on a 6 × (cid:48) ) cutouts of the frame centered onthe extended sources. We obtained aperture magnitudeswithin a 8-pixel diameter ( ∼ . (cid:48)(cid:48)
68 at OmegaCAM reso-lution), and applied aperture corrections to infinite ra-dius calculated with the growth curves of bright iso-lated point-like sources, independently for each band andpointing (Cantiello et al. 2015).The catalogs in the four bands were matched with a 0 . (cid:48)(cid:48) ∼ . · sources. The techniques used to obtain thecatalog of sources will be described in a forthcoming pa-per (Cantiello et al. 2016). Corrections for Galactic fore-ground extinction were applied following Draine (2003)and the Schlafly & Finkbeiner (2011) reddening map. SELECTION OF CANDIDATE GCS
We designed a new method that employs multi-wavelength photometry and a sample of bona fide con-firmed GCs for the selection of candidate GCs. The con-firmed GCs are used to model the region of the three-dimensional (3D) color space occupied by GCs (here-inafter, the locus ). The main steps required to extractthe candidate GCs from the general catalog of sourcesare: • Select sources located within the GC 3D color space locus ; • Apply magnitude cuts to the color-selected sourcesand discard extended sources;GCs occupy a well-defined region in the optical colorspace (Rhode & Zepf 2001; Pota et al. 2013). We definethe locus as the smallest compact region in the 3D spacegenerated by the Principal Components (PCs) associatedwith their optical colors u − g , g − r and r − i (zero centeredand scaled to unity variance), containing a fixed fractionof training set GCs. Modeling the GC locus in the PCspace ensures the simplest possible geometry by virtue ofthe definition of PCs itself (see D’Abrusco et al. 2013b). Only photometric sources detected in all bands locatedwithin the PC space locus are considered. Moreover, weselect only sources whose “color-error ellipsoid” (ellip-soids with semi-axes equal to the PC-transformed uncer-tainties on each color) intersects the locus for ≥
50% ofits volume.The training set used in this letter is the sample ofNGC1399 spectroscopically confirmed GCs (Schuberthet al. 2010, A and B), covering ∼ . ◦ ) around thehost. The GCs locus contains all the contiguous cells ofa regular lattice with at least one training set member.The number of cells of the lattice, i.e. the spatial resolu-tion of the grid along each PC axis is set such that theaverage density per cell over the region of the PC spaceconsidered is ∼
1. Empty cells surrounded by cells con-taining members of the training set are included in the locus to obtain a simply connected geometry. Figure 1shows the projections of the PC space GC locus on threecolor-color diagrams.We apply a brightness selection on the g -band magni-tude and a size selection to the color-selected sources. Weexclude sources brighter than m g = 20 to avoid contam-ination by stars and ultra-compact dwarf galaxies (cp.Mieske et al. 2008). Sources fainter than m g = 23, thefaintest g -band magnitude of the FDS counterparts ofthe training set GCs, are also discarded. Since GCsat the distance of the Fornax cluster appear mostlyas unresolved sources with the VST spatial resolution,we employ the SExtractor CLASS ST AR parameter toselect star-like sources . Based on the distribution ofthe Schuberth et al. (2010) GCs, we required that can-didate GCs have CLASS ST AR ≥ .
3. We checked thatour selection is consistent with the different techniquebased on the position of the sources in the m (8pxl) g vs∆ m g = m (8pxl) g − m (4pxl) g plane (see Jennings et al. 2014),where the g -band magnitudes are measured within fixedapertures of 4 and 8 pixels. We found differences for lessthan 3% of the candidate GCs selected.We required the PC locus to contain 95% of the train-ing set. The “observed” recovery rate is slightly smaller( ∼ g -band mag-nitude and “CLASS STAR” parameter. We estimatethe background of our selection as the density of allsources in two regions of ∼ . ◦ ) located along theborders of the observed frame and devoid of bright galax-ies. Since these regions are placed within 1 Fornax virialradius (Drinkwater et al. 2001), the background popula-tion is likely composed of both contaminants (stars andgalaxies) and GCs. The average total density of back-ground sources is 0.05 ± − (0.03 ± ± THE CATALOG OF CANDIDATE GCS
The catalog of candidate GCs contains ∼ g − i histogram is bimodal (as expected given thetraining set color distribution). The best-fit parameter The CLASS STAR parameter is estimated by a neural networktrained on 10 photometric parameters extracted from simulated im-ages. The extension index produced by the neural network rangesbetween 0 and 1 (Bertin & Arnouts 1996).
Table 1
Left) Loadings, standard deviations and variance fractions of the PCs associated with the colors of the training set; Mid) Lower andupper boundaries for all parameters used for the selection; Right) Number of red, blue GCs and parameters of the best-fit Gaussians. PC PC PC Parameter Lower Upper Blue Redboundary boundary u − g PC -1.56 1.92 N GCs ∼ . · ∼ . · g − r PC -0.47 0.41 µ ( g − i ) r − i PC -0.12 0.11 σ ( g − i ) σ m g
20 23 σ (%) CLASS STAR of the two Gaussians are shown in Table 1 (right). Weadopted the g − i = 0 .
85 threshold to separate red fromblue candidate GCs, yielding ∼ ∼
37% of the total) and ∼ ∼ ∼ .
5, 1.5 magnitudes brighter than the aver-age g -band turnover of the GCLF m ( g ) T O = 24 (Villegaset al. 2010; Jord´an et al. 2007). While the g − i dis-tribution (bottom-right panel in Figure 1) is consistentwith those in Bassino et al. (2006) and Kim et al. (2013),our catalog is dominated by the blue component of theGCs population because the FDS data, unlike the Schu-berth et al. (2010) training set, cover a wide area of thecluster at large distances from the hosts, where GCs areoverwhelmingly blue (cp. Durrell et al. 2014). The cross-match of our catalog with the deeper ( m lim V = 23 .
7) Kimet al. (2013) sample of
U BV I -photometry selected can-didate GCs in a 36 (cid:48) × (cid:48) region around NGC1399 returns ∼
70% of common GCs. We also recover ∼
85% of thekinematically confirmed GCs from Bergond et al. (2007). MAPS OF THE SPATIAL DISTRIBUTION OF GCS
We determined the density maps of the spatial distri-bution of candidate GCs applying the K-Nearest Neigh-bor (KNN) method (see Dressler 1980; D’Abrusco et al.2013a) on a regular grid covering the observed region.KNN density, defined as d K = K/ ( π · r K ), is directlyproportional to the neighbor index K and inversely pro-portional to the area of the circle defined by the distanceof the K -th closest source to the center of the grid cells,where the density is calculated. The parameter K wasvaried over the interval [3 ,
9] (see D’Abrusco et al. 2015,for a discussion on the choice of K ). This strategy pro-vides a non-zero density in each cell of the grid, includingthose not containing candidate GCs. K is a measure ofthe richness and size expressed in number of members,of the structures to which the density map is sensitiveto. Maps with small K are dominated by compact den-sity structures, while large K ’s highlight more extendedstructures. In the following, we will discuss K = 9 mapsto focus on the features of the distribution of candidateGCs on large spatial scales. Since background contri- bution to the catalog of candidate GCs is only knownstatistically, the shapes and areas of the density struc-tures discussed henceforth are to be considered approxi-mations.The significance of the density structures is calculatedas the complement to the probability of the number ofcandidate GCs observed within the structure of beingcaused by fluctuations of the background population,which we assume to follow the Poisson statistics. Fordensity structures located within other overdensities, thesignificance has been determined relative to poissonianfluctuations of a population with density equal to thedensity of all candidate GCs in the underlying densitystructure. By assuming that background sources are in-dependent, our estimates are lower limits to the real sig-nificances of the density structures. In the case of en-hancements including compact GCSs, the contributionof the hosts’ GC population is accounted for by remov-ing all the sources within a circle containing 95% of theGCS population centered on each galaxy. We assumea power-law radial density profile with slope from theliterature when available or fixed to α = − ∼ . ◦ ) (A). The significance of this structure is > . ∼
30% of all candi-date GCs, (35% /
65% red/blue), corresponding to ∼ ∼
9% of totalnumber of red candidate GCs in our catalog.Other galaxies associated with noticeable overdensi-ties are NGC1374 (B), NGC1380 (C), NGC1427 (D) andNGC1336 (E) in agreement with earlier works on theirGCSs (Kissler-Patig et al. 1997a,b), while ESO358G059and NGC1428 lack visible density enhancements. Twospatial features not associated to bright galaxies areclearly visible in the density map of all candidate GCs:a large enhancement of circular shape (F, > . ∼ . ◦ NE of NGC1399; and a hook-shaped structure(G, > . ∼ . ◦ SE of the NGC1404 over-density and seemingly connected to the structure Athrough the NGC1427A density enhancement. Outsidethe core region, excluding the structures of the NGC1427,NGC1336 and NGC1380 GCSs, the distribution of can-didate GCs is featureless and homogeneous on spatialscales ≥ . ◦ , except for a ∼ . × . ◦ ) region cen-tered on R.A. ≈ . ◦ and Dec ≈ − ◦ almost devoid ofcandidate GCs ( > . − . . . . . g − r l l l lll ll l lll ll l l lll lll ll llll ll lll l ll lll lll ll lll l ll ll ll ll ll lll lll ll lll l ll lll lll lll lllllllll ll l ll llllll ll ll lll l ll l lll lll ll ll ll lllll l lll ll lll llll ll ll ll ll lll ll ll l l ll llllll lllll lll l l ll l llllllll lll ll ll llll lll ll llll l ll ll lll lll l l ll l llll ll lll lllll ll lll ll ll lll ll ll lllll lll llll l lll lll lll ll ll −0.5 0.0 0.5 1.0 1.5 2.0 2.5 g−i l ll llllll llllll l lll llll l llll ll lllll l lll lll llll ll ll ll ll ll ll ll ll ll ll lll l ll l ll ll llll lllllllll lll ll ll llll ll lllll llll lllll l llllll l llll ll ll llll l llll ll ll ll l l lllll llll ll llllll ll ll l llll lll l llllllll lll ll lll llllll ll llll l ll ll lll ll ll llll l lll l llll lll ll l lll l ll ll lll ll ll lllll lll ll ll llll lll ll l ll ll −1 0 1 2 3 − . . . . . u−g r − i l l l lll ll l lll ll l l lll lll ll llll ll lll l ll lll lll ll lll l ll ll ll ll ll lll lll ll lll l ll lll lll lll lllllllll ll l ll llllll ll ll lll l ll l lll lll ll ll ll lllll l lll ll lll llll ll ll ll ll lll ll ll l l ll llllll lllll lll l l ll l llllllll lll ll ll llll lll ll llll l ll ll lll lll l l ll l llll ll lll lllll ll lll ll ll lll ll ll lllll lll llll l lll lll lll ll ll g−i Figure 1.
Top and bottom left: projections of the PC color space locus model on three color-color diagrams (yellow lines). The FDScounterparts of the Schuberth et al. (2010) training set (green symbols) and the gray-scale density map of the general catalog of photometricsources are also shown. Bottom right: rescaled histograms of the g − i color of all candidate GCs (black), the training set (dashed) and theGaussians fitting the red and blue subclasses. quality in this area, but did not notice differences withthe other regions of the observed frame.The central overdensity associated with NGC1399 issignificantly more compact for red than for blue GCs.Although the accuracy of the density maps deteriorateswith smaller sample size, this difference is still evidentfor brighter magnitude-selected subsets of red and bluecandidate GCs. The structures F and G are not visiblein the density map of red candidate GCs but are stilldetected in the blue GC density map (with > .
9% and > .
5% significance, respectively), hinting to a possibleaccretion-related origin (e.g. Cˆot´e et al. 1998). The no-table differences of the NGC1380 and NGC1336 densitystructures for red and blue candidate GCs are caused bythe combined effects of the fixed g − i color threshold, thelow number of candidate GCs due to high galaxy back-ground levels, and the relative shallowness of the u -bandimages that favors the selection of blue candidate GCs.Moreover, near the edges of the surveyed region the KNNwith K = 9 may underestimate the density of compact,numerically small or extended, only partially covered GCsubpopulations.We produced additional density maps for the clustercore, using a finer grid. Figure 3 shows the maps forall, red and blue candidate GCs in a ∼ ◦ (R . A . ) × ∼ . ◦ (Dec . ) box roughly centered on NGC1399. Thestrong overdensity connecting NGC1399 and NGC1404along the SE-NW direction (H, > . . (cid:48) bona fide HST GCs in the cen-tral region of NGC1399 (Puzia et al. 2014; Jord´an etal. 2015), we find that the completeness of our catalogof candidate GCs increases from a minimum of ∼ . (cid:48) g -band surface brightness ∼
17 mag / ( (cid:48)(cid:48) ) , to ∼
55% at 1 . (cid:48) ∼
23 mag / ( (cid:48)(cid:48) ) ), and remains constant be-tween ∼
50% and ∼
55% with no evident trend up to ∼ . (cid:48) ∼
23 mag / ( (cid:48)(cid:48) ) ). For this reason, we cannot de-termine the nature of the deficit observed in Figure 3.Comparable completeness is measured near the centersof NGC1380, NGC1336 and NGC1387.On large spatial scales, the main NGC1399-NGC1404overdensity extends to the W joining with the density en-hancements associated with NGC1387 and NGC1381 (I, > . ∼ ◦ ) around NGC1399 and, inde-pendently, by Kim et al. (2013). The NGC1380B (L)and NGC1379 (M) density enhancements are isolated.The density map of red candidate GCs (Figure 3, mid)still shows a large overdensity in the core of the Fornaxcluster composed by two sub-concentrations centered on NGC1399 and NGC1404, connected by a lower densityvalley. The other bright galaxies in the field are not asso-ciated with clear density enhancements. In the densitymaps of blue candidate GCs, the central structure (N, > . DISCUSSION
We report a density structure in the spatial distri-bution of candidate GCs in a region ∼ . ◦ ) withinthe core of the Fornax cluster of galaxies, connect-ing NGC1399 to the surrounding galaxies NGC1404,NGC1387, NGC1381 and NGC1380B. Our findings ex-pand on the discovery by Bassino et al. (2006) of aGC bridge between NGC1399 and NGC1404. We used ∼ ugri imagescovering the central ∼ . ◦ ) of the cluster. The methodemployed for the selection of candidate GCs relies on themodeling of the locus occupied by confirmed GCs in the3D color space generated by ugri -bands photometry, andthe application of cuts on g -band magnitude and mor-phology.The dominant GC overdensity displays an intricatemorphology and is elongated on the WE direction. Asimilar asymmetry was observed, on scales of ∼ g -band light dis-tribution (Figure 4). This evidence suggests that themore massive NGC1399 may have stripped GCs fromNGC1387. We also highlighted two isolated densitystructures (F and G) with complex shapes mostly formedby blue GCs, whose origins could be related to accretionor stripping events. Other isolated galaxies (NGC1380,NGC1427, NGC1379 and NGC1336) are associated withdistinct, compact enhancements. On larger spatial scaleswe observe a featureless distribution of candidate GCs,barring few compact GCSs and one underdensity.The zoomed in density map of blue GCs (Figure 3, bot-tom) shows that NGC1381, NGC1379 and NGC1380Bare also connected to the main overdensity centeredon NGC1399. This result indicates that GC strippingmay not have been limited to NGC1387, as proposedby Bassino et al. (2006). Since the shapes of the densityenhancements in the map of red GCs, barring the evi-dent central overdensities associated to the GCSs of thesingle galaxies, are reminiscent of the structure linkingthe NGC1399-NGC1404 region to NGC1387, one mayspeculate that these galaxies have experienced strong in-teractions which may have disrupted the GCSs of nearbysatellites and/or gravitationally trapped relatively redintra-cluster GCs. The large-scale morphology of blueGCs observed in both the general and the zoomed den-sity maps may be explained with a different mechanism,namely the trapping in the potential well in the Fornaxcore of mostly blue GCs stripped by the tidal field of thecluster from hosts at small cluster-centric distances, as
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NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059
All GCsK = 9 l candidate GCsFCC galaxies B T = 9B T = 12B T = 15B T = 18B T = 21
56 55 54 53 52 − . − . − . − . − . D e c li na t i on [ D eg ] AAAAAAAAA BBBBBBBBBDDDDDDDDD llll l ll l l l l ll l lll l ll ll l l ll lllll ll l l lll ll l l lll l l l ll l ll ll ll lll ll ll l ll l lll ll ll ll l ll lll lll ll l ll l ll lll ll l l l ll lll ll l lll l lll l l ll ll ll ll l ll l ll l l l ll lll l ll ll ll ll l l ll l ll ll lll ll ll ll l llll l lll l l l ll l ll lll ll ll ll l lll l ll ll l l llllll ll ll ll lll l ll lll ll l lll l ll l ll ll l l lll l ll l lll l llll ll ll llll l ll llll ll l ll ll l l ll ll lll ll ll llll lll ll l ll l ll l ll l l ll lll l l ll l ll l ll ll llll l l ll lll ll ll llll ll ll l llll lll l lll l lll ll llll ll ll l ll lll l ll l lll lll ll l l ll l l l llll ll lll l l l l l ll lll l ll l ll ll lll l llll ll ll lll l ll ll l l ll l l ll ll l l ll l ll lll lll l ll lll l l l ll ll l llll ll ll l ll l lll ll ll l lll ll ll llll ll ll l l l l ll llll l l llll ll ll llll ll l l ll ll ll ll l l ll ll l ll lll ll ll ll l ll lll llll ll l l l ll ll lll lll ll ll ll ll ll lll ll ll l ll lll lll lll ll ll l l ll l lll l ll lll l ll llll ll ll lll lll l ll ll l lll l ll l ll l ll lll l lll lll ll lll ll lll l lll l ll ll l ll ll l ll ll l l lll lll lll l lll ll l ll ll ll ll ll l ll lll l llll llll lll l llll lll l lll llll ll l ll l ll ll l lllll ll ll lll l ll ll llll lll ll ll ll l ll l ll ll l lll l ll ll l lll ll ll l llll l l l ll ll ll l l ll lll llll lll ll l llll lll lllll llllll ll ll l l ll l l l llll ll l ll lllll l lll lll lllll l lll l l lll l l l ll llll llll ll l lll ll l ll lll l lll lll ll l ll ll ll lll lll llll l ll lllll lll l ll llll lll l llll ll lll l ll l ll ll l ll llll lll llll l l ll ll lllll l lll l ll ll llll l lll ll l ll ll llll lll l l
NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059
Red GCsK = 9 l red candidate GCsFCC galaxies B T = 9B T = 12B T = 15B T = 18B T = 21
56 55 54 53 52 − . − . − . − . − . Right Ascension [Deg] D e c li na t i on [ D eg ] AAAAAAAAADDDDDDDDD GGGGGGGGGFFFFFFFFF l l ll l ll llll ll ll ll ll l lll ll ll llll l ll lll l lll lll ll l ll lll ll ll lll l l l ll lll ll lll l ll ll l l ll ll ll ll ll l llll ll l lll lll ll ll ll l l lll llll lll ll l ll lllllll l ll l ll l ll ll ll lll ll lllll ll l l lll ll l ll ll ll lll l ll l ll ll l ll ll l lll l l lll l ll l ll l l ll llll lll lll l lll l lll lll l ll ll l lll l ll ll l lll l ll lll lll l lll ll l ll l ll lll lll llllll ll lll ll ll lll lll l lll ll ll l ll ll l lll ll l lll ll lll l ll l ll l ll l ll ll l lll lll llll l l l l lll l ll l ll lll ll ll lll l ll l lllll l ll l l lll l l ll l ll l lll ll l l ll lll l ll ll l ll ll ll l l lll ll ll l ll l ll ll lll ll l ll lll ll ll lll l l l ll ll ll l ll l lll ll l l ll l lll l lll l ll ll llll l ll lll l l l ll l ll l lll ll ll l lll ll l lll ll lll l ll l l l ll l ll l ll l ll l lll lll l l lll l l ll l l l l llll ll l ll l ll ll l l lll ll ll l l llll lll llll ll l l lll l lll l l ll l l lll ll l ll l lll l l l ll l l l ll ll lll ll l l ll ll ll ll l llll lll lll ll lll l ll ll l ll ll ll ll lll ll l ll llll ll lll l l llll l lll l l ll l l lll ll ll l l l ll l l lll l ll l lll l ll l lll l lll l ll llll l ll ll l ll l ll l lll l l ll l l llll ll l ll ll lll lll l ll l l ll l ll l lll l ll l l ll l l l l l llll ll ll l lllll l llll ll ll ll lll l l ll lll lll l ll ll ll ll l llll l ll ll lll ll llllll llll ll l l ll lll l lll l l ll lll ll llll l lll l llll ll l lll l ll l lll l ll ll l l llll ll ll ll ll ll lll ll l l ll ll lll l ll l ll ll l lll l l ll ll l llll ll l ll ll ll ll ll l ll ll l l lll lll ll lll l lll ll ll l l l l ll ll l lll ll lll ll ll lll lll l ll l l l l ll l l lll ll l lll ll ll ll l l lll ll l ll llll ll l ll llll ll l ll l ll lll ll l ll ll l lll l l ll l l ll l ll ll ll l ll lll ll l lll l ll lll ll l l ll lll lllll l llll ll l l llll l llll ll l l lll ll ll ll l lll l lll ll l ll llll ll lllll ll l ll l l ll llll l l ll l ll l lll l ll ll l ll lll ll l ll ll ll ll lll ll ll l ll l lll l ll l l ll l lll ll lll l ll ll lll lll l lll ll ll l lll l ll l ll l ll ll ll l lll ll l ll l ll l l lll l l l ll ll lll ll ll lll l ll l lll ll l llll l l ll llll lll ll l l lll l l l ll ll ll lll ll ll ll l ll lll ll ll lll l llll l ll l lllll l l ll ll l l lll l ll ll l ll ll lll lll ll l l ll lll l lll ll l l l l ll lll ll ll l ll ll l ll ll ll ll ll lll ll ll lll l lll l lll l ll l ll l ll lll ll lll ll ll ll ll l ll lll llll l l ll ll l l lll l lll l l lll ll ll ll ll ll l l lll ll llll l llll ll l ll l ll l l l ll ll l l ll ll l lll l l lll l l lll ll l ll lll ll lll l llll l l lll ll l lll ll lll l ll ll l l ll l lll ll lll l lll l l ll l lllll l l lll lll llll ll ll lll lll llll ll ll lll ll ll l ll llll ll l l lll llll ll llll lllll llll l lll l lllll l l ll lll ll l ll lll l ll ll lll lll llll llll
NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059 NGC1336NGC1374NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427ANGC1427NGC1428ESO358G059
Blue GCsK = 9 l blue candidate GCsFCC galaxies B T = 9B T = 12B T = 15B T = 18B T = 21 Figure 2.
Top to bottom: K = 9 density maps of the spatial distribution of all, red and blue candidate GCs. All structures discussedin the text are highlighted and labeled. All maps display contours at ten log-spaced densities levels (normalized to peak) starting at 0.05,FCC galaxies (diamonds) size-coded according to their B T magnitude and the background regions. Density in the shaded region may beunderestimated because of border effects. predicted by simulations (Ramos et al. 2015).Our conclusions are constrained by the limits of thetraining set and the depth of the photometric data.As the survey nears completion, the new data acquiredwill be used to improve our analysis and provide a de-tailed assessment of the performance of our selection us-ing a larger, more homogenous sample of spectroscop-ically selected (P.I. Capaccioli, ID 094.B-0687; Pota etal. 2016) GCs covering 1( ◦ ) around NGC1399, observedin the context of the FDS project. 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D e c li na t i on [ D eg ] IIIIIIIIILLLLLLLLL MMMMMMMMMHHHHHHHHH l lll l ll ll l lll lll l l lll ll ll ll lll l l lll l lll ll llll l ll lll l l ll ll l lllll l lll ll l ll l ll lll ll ll ll lllll ll l ll ll l ll lll ll l ll ll l l ll l lll ll l lll lll llll l lllll ll ll l lll llll ll l ll l ll lll l l ll ll lll ll l ll l ll ll ll l lll l l ll lll ll lll l lll l ll l ll l lll l ll ll ll ll lll ll ll l ll lll lll llll l lll ll ll ll ll llll l l lll l ll l lll l ll ll lll l lll ll ll lll lll ll l ll ll l ll l ll ll ll l llll l lll l ll ll llll lll l ll lll ll ll l ll lll ll l ll ll ll l lll ll ll lll l ll ll ll ll ll l l ll l l llllll ll ll l l ll ll l l ll ll l lll l l ll ll l ll l l ll ll l l ll ll llll lll lll l l lll l ll ll lllll l l ll l l ll lll ll l l l ll ll l l ll ll lll l l llll lll llll ll ll ll lll llll l ll lll lll l l lll lll l l lll ll lll l l ll llll lll l lll lllll lll ll l lll ll l lll ll ll ll l ll ll lll ll ll ll lll lll l ll l ll l ll ll l ll l l l ll l lll ll l ll lll ll ll ll lll ll ll llll l lll l lll l ll l l ll ll lll ll ll l l l ll ll ll l ll ll l l ll ll lll ll ll ll ll l lll l l ll ll l l ll llll ll lll l lll lll ll l lll ll l lll lll l lll l llll l ll lll ll l ll llll l l ll ll ll l l ll lllll l ll l lll llll lll l ll lll lll l ll ll l lll llll l lll l lll llll l lll l lll llll l lll lll ll l l lll lll l ll l l llll ll ll ll l
NGC1379NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A l candidate GCsFCC galaxies B T = 9B T = 12B T = 15B T = 18B T = 21 All GCsK = 9 − . − . − . − . − . − . D e c li na t i on [ D eg ] lll l ll l ll ll lll l l lll l lll lll l ll ll l l ll ll l l ll ll llll l l lll lll llll llll ll l lll l ll l ll l ll lll ll ll ll ll lll l ll lll lll ll ll ll ll l ll l lll lll ll ll l l l lll lll l ll ll lll ll lll ll ll l lll l lll ll ll lll l ll llllll lll ll l ll l l ll l lll l ll l l lll ll l l ll lll ll ll llll lll llll l llll lll l l ll l l lll ll llll lll lll ll ll lll l ll l l l ll l lll ll l ll l lll ll l ll ll lll ll l ll ll l l ll lll ll ll l ll lll ll lll l ll ll l lll l ll llll l ll ll l lll lll ll ll l lllll l ll lll ll ll ll l llll l NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A l red candidate GCsFCC galaxies B T = 9B T = 12B T = 15B T = 18B T = 21 Red GCsK = 9 − . − . − . − . − . − . Right Ascension [Deg] D e c li na t i on [ D eg ] NNNNNNNNN l lll lll lll lll lll l l l ll ll ll ll lll l ll l llll ll l ll ll l ll lllll lll ll l ll l ll l lll ll lllll ll ll ll ll lll ll l ll ll ll lll ll ll l l ll l ll lll ll l l lll ll lll l l ll ll ll lll llll l ll ll llll l l llll l ll ll lll ll ll ll ll ll ll ll ll ll ll ll lll l lll ll l ll ll l ll ll ll ll l l ll l ll ll l l ll l ll ll l ll l ll ll llll ll llll ll ll ll lllll l l ll l ll ll l l ll ll lll ll ll ll lll llll lll lll l l lll ll ll ll lll lll l ll lll ll l lll ll ll ll ll ll ll lll lll l ll l ll l ll ll lll ll ll ll llll l lll l ll ll l l lll ll ll l ll ll l l lll ll l lll l l ll ll l ll lll ll l lll lll l lll l llll l lll l ll l l ll l ll l l ll lllll lll llll ll ll lll lll ll llll l lll lll ll ll lll llll l l ll ll ll ll l ll l
NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A NGC1379NGC1380NGC1381NGC1387NGC1380BNGC1396NGC1399NGC1404NGC1427A l blue candidate GCsFCC galaxies B T = 9B T = 12B T = 15B T = 18B T = 21 Blue GCsK = 9
Figure 3.
As in Figure 2, zoomed in on the core of the Fornax cluster.
22 23 24 25 26 27 28 29 30 31 32
NGC1404 NGC1399 NGC1396 NGC1387
Figure 4. K =9 isodensity contours and all candidate GCs overplotted to the FDS gg