VANZELLA, ErosErosVANZELLACASTELLANO, MARCOMARCOCASTELLANOMENEGHETTI, MASSIMOMASSIMOMENEGHETTIMERCURIO, AMATAAMATAMERCURIOCaminha, G. B.G. B.CaminhaCUPANI, GuidoGuidoCUPANICALURA, FrancescoFrancescoCALURAChristensen, L.L.ChristensenMERLIN, EmilianoEmilianoMERLINRosati, P.P.RosatiGronke, M.M.GronkeDijkstra, M.M.DijkstraMIGNOLI, MarcoMarcoMIGNOLIGILLI, RobertoRobertoGILLIDe Barros, S.S.De BarrosCaputi, K.K.CaputiGrillo, C.C.GrilloBalestra, I.I.BalestraCRISTIANI, StefanoStefanoCRISTIANINONINO, MarioMarioNONINOGIALLONGO, EmanueleEmanueleGIALLONGOGRAZIAN, AndreaAndreaGRAZIANPENTERICCI, LauraLauraPENTERICCIFONTANA, AdrianoAdrianoFONTANACOMASTRI, AndreaAndreaCOMASTRIVignali, C.C.VignaliZamorani, G.G.ZamoraniBrusa, M.M.BrusaBergamini, P.P.BergaminiTOZZI, PaoloPaoloTOZZI2020-07-242020-07-2420170004-637Xhttp://hdl.handle.net/20.500.12386/26622We study the spectrophotometric properties of a highly magnified (μ ≃ 40{--}70) pair of stellar systems identified at z = 3.2222 behind the Hubble Frontier Field galaxy cluster MACS J0416. Five multiple images (out of six) have been spectroscopically confirmed by means of VLT/MUSE and VLT/X-Shooter observations. Each image includes two faint ({m}<SUB>{UV</SUB>}≃ 30.6), young (≲ 100 Myr), low-mass (< {10}<SUP>7</SUP> {M}<SUB>☉ </SUB>), low-metallicity (12 + Log(O/H) ≃ 7.7, or 1/10 solar), and compact (30 pc effective radius) stellar systems separated by ≃ 300 pc after correcting for lensing amplification. We measured several rest-frame ultraviolet and optical narrow ({σ }<SUB>v</SUB>≲ 25 km s<SUP>-1</SUP>) high-ionization lines. These features may be the signature of very hot (T> {{50,000}} K) stars within dense stellar clusters, whose dynamical mass is likely dominated by the stellar component. Remarkably, the ultraviolet metal lines are not accompanied by Lyα emission (e.g., C IV/Lyα > 15), despite the fact that the Lyα line flux is expected to be 150 times brighter (inferred from the Hβ flux). A spatially offset, strongly magnified (μ > 50) Lyα emission with a spatial extent ≲ 7.6 kpc<SUP>2</SUP> is instead identified 2 kpc away from the system. The origin of such a faint emission could be the result of fluorescent Lyα induced by a transverse leakage of ionizing radiation emerging from the stellar systems and/or may be associated with an underlying and barely detected object (with {m}<SUB>{UV</SUB>}> 34 de-lensed). This is the first confirmed metal-line emitter at such low-luminosity and redshift without Lyα emission—suggesting that, at least in some cases, a non-uniform covering factor of the neutral gas might hamper the Lyα detection. <P />Based on observations collected at the European Southern Observatory for Astronomical research in the southern hemisphere, under ESO programmes P095.A-0840, P095.A-0653, and P186.A-0798.STAMPAenArticle10.3847/1538-4357/aa74ae2-s2.0-85021144824000403167700003https://iopscience.iop.org/article/10.3847/1538-4357/aa74ae2017ApJ...842...47VFIS/05 - ASTRONOMIA E ASTROFISICA