Astronomy&Astrophysicsmanuscriptno.VerganiHGz2LE1c (cid:13)cESO2017 January11,2017 = The chemical enrichment of long-GRB nurseries up to z 2 S.D.Vergani1,2,3,J.Palmerio2,R.Salvaterra4,J.Japelj5,F.Mannucci6,D.A.Perley7,P.D’Avanzo3,T.Krühler8,M. Puech1,S.Boissier9,S.Campana3,S.Covino3,L.K.Hunt6,P.Petitjean2,andG.Tagliaferri3 1 GEPI, Observatoire de Paris, PSL Research University, CNRS, Univ. Paris Diderot, Sorbonne Paris Cité, Place Jules Janssen, F-92195Meudon,France;e-mail:susanna.vergani@obspm.fr 2 Institutd’AstrophysiquedeParis,UniversitéParis6-CNRS,UMR7095,98bisBoulevardArago,F-75014Paris,France 3 INAF-OsservatorioAstronomicodiBrera,viaE.Bianchi46,I-23807Merate,Italy 4 INAF-IASFMilano,viaE.Bassini15,I-20133,Milano,Italy 5 INAF-OsservatorioAstronomicodiTrieste,viaG.B.Tiepolo11,I-34131Trieste,Italy 6 INAF-OsservatorioAstrofisicodiArcetri,LargoE.Fermi5,I-50125Firenze,Italy 7 7 DarkCosmologyCentre,NielsBohrInstitute,UniversityofCopenhagen,JulianeMariesVej30,DK-2100Copenhagen,Denmark 1 8 Max-Planck-InstitutfürextraterrestrischePhysik,Giessenbachstraße,D-85748Garching,Germany 0 9 AixMarseilleUniv,CNRS,Laboratoired’AstrophysiquedeMarseille,F-13388,Marseille,France 2 Received;accepted n a J ABSTRACT 9 Aims.Weinvestigatetheexistenceofametallicitythresholdfortheproductionoflonggamma-raybursts(LGRBs). Methods.WeusedthehostgalaxiesoftheSwift/BAT6sampleofLGRBs.Weconsideredthestellarmass,starformationrate(SFR), E] andmetallicitydeterminedfromthehostgalaxyphotometryandspectroscopyuptoz=2andusedthemtocomparethedistribution ofhostgalaxiestothatoffieldgalaxiesinthemass-metallicityandfundamentalmetallicityrelationplane. H Results. WefindthatalthoughLGRBsalsoformingalaxieswithrelativelylargestellarmasses,thelargemajorityofhostgalax- . ies have metallicities below log(O/H) ∼ 8.6. The extension to z = 2 results in a good sampling of stellar masses also above h Log(M /M )∼9.5 and provides evidence that LGRB host galaxies do not follow the fundamental metallicity relation. As shown p ∗ (cid:12) bythecomparisonwithdedicatednumericalsimulationsofLGRBhostgalaxypopulation,theseresultsarenaturallyexplainedby - o theexistenceofamild(∼0.7Z(cid:12))thresholdfortheLGRBformation.Thepresentstatisticsdoesnotallowustodiscriminatebetween r differentshapesofthemetallicitycutoff,buttherelativelyhighmetallicitythresholdfoundinthisworkissomewhatindisagreement t tomostofthestandardsingle-starmodelsforLGRBprogenitors. s a Keywords. Gamma-rayburst:general–Galaxies:abundances–Galaxies:starformation [ 1 v 1. Introduction PortegiesZwart2013;Kellyetal.2014;Perleyetal.2016b),it 2 hasbeenoneofthemoststudiedinthepastasthemetalcontent 1 Ithasbeenestablishedthatlonggamma-raybursts(LGRBs)are of the progenitor star is considered to play a major role in the 3 2linkedtotheexplosionsofmassivestars,bothfromthestudiesof formation of a LGRB explosion. Single-star evolution models 0theirhostgalaxyformationsites(Fruchteretal.2006;Svensson predictthatthemetallicityofLGRBprogenitorsshouldbevery .et al. 2010) as well as from detections of accompanying super- low(e.g.,Hirschietal.2005;Yoon&Langer2005;Woosley& 1 novaemission(GRB-SN;seeCanoetal.2016forareview).Itis Heger2006):inthiswaytheprogenitorstarcanexpeltheouter 0 stillnotclearwhichconditionsgiverisetoLGRBsorwhatisthe envelope (hydrogen and helium are not observed spectroscopi- 7 1relation between the progenitors of LGRBs and those of other cally)withoutremovingtoomuchangularmomentumfromthe :explosionsresultingfromdeathsofmassivestars(e.g.,Metzger rapidly rotating core. Higher metallicity values are allowed in vetal.2015). the case of the models presented by Georgy et al. (2012), also Xi The progenitors of nearby core-collapse supernovae can be dependingonthedifferentprescriptionsbetweenthecouplingof directly identified as resolved stars in archived high-resolution surfaceandcoreangularmomentuminthestar.Alternatively,the r aimages of their birth places (Smartt 2015). However, LGRBs LGRBprogenitorscouldbecloseinteractingbinaries,inwhich have a lower occurrence rate (e.g., Berger et al. 2003; Guetta casethemetallicityisalessconstrainingfactor(e.g.,Fryeretal. &DellaValle2007)andareusuallyobservableatcosmological 2007;vandenHeuvel&Yoon2007).Strongobservationalcon- distances, for which their birth places cannot be resolved. Our straintsareclearlyneededtounderstandwhichoftheevolution- understanding ofLGRB progenitors thereforedepends onlink- arychannelscouldproduceaLGRB. ingthepredictionsofdifferentstellarevolutionmodelswiththe DifferentobservationalworksonLGRBhostgalaxiesinthe observed properties of LGRB multiwavelength emission (e.g., literaturehaveindeedrevealedthattheirmetallicitiesaremostly Schulzeetal.2011;Canoetal.2016)andtheirhostgalaxyenvi- subsolar (Modjaz et al. 2008; Levesque et al. 2010a; Graham ronment(seePerleyetal.2016aforareview).Inthiswork,we & Fruchter 2013; Vergani et al. 2015; Krühler et al. 2015; Per- focusonthelatter. ley et al. 2016b; Japelj et al. 2016). The evidence is corrobo- While metallicity is not the only factor that might affect rated by numerical simulations (e.g., Nuza et al. 2007; Camp- theefficiencyoftheLGRBproduction(e.g.,vandenHeuvel& isi et al. 2011; Trenti et al. 2015). In particular, Campisi et al. Articlenumber,page1of4 A&Aproofs:manuscriptno.VerganiHGz2LE1c (2011) studied LGRB host galaxies in the context of the mass Table1.Swift/BAT6sampleofLGRBhostgalaxiesat1 < z < 2with metallicitydetermination,visiblefromthesouthernhemisphere. metallicity(e.g.Tremontietal.2004)andfundamentalmetallic- ity (Mannucci et al. 2010, 2011) relations of field star-forming galaxiesbycombiningahigh-resolutionN-bodysimulationwith Hostgalaxy redshift Log(M(cid:63)/M(cid:12)) SFR Metallicity [M(cid:12)yr−1] 12+log(O/H) asemi-analyticmodelofgalaxyformation.Campisietal.(2011) GRB080413B 1.1012 9.3 2.1+3.1 8.4+0.2 findthataverylowmetallicitycutisnotnecessarytoreproduce GRB090926B 1.2427 10.28 26+−119.2 8.44−+00..218 the observed relations. However, previous observational works GGRRBB006611102017∗∗ 11..32166203 190..2321 454.8.2−+−+14411..889 88.1.56+−+−00.000...2911083 present one or more of the following issues: (i) they are based GRB071117∗ 1.3293 <10.12 >2−.810 8.4−+00..0165 onincompletebiasedsamples(e.g.,Levesqueetal.2010a);(ii) GRB100615A 1.3979 9.27 8.6+13.9 8.14−+00.0.296 theyarebasedonstellarmassesdirectlydeterminedfromobser- GGRRBB007600330066 11..45956957 1100.5.53 1170.61−++−48.214348.6 89..4152−+−+0000....20012888 vations, but on metallicities inferred from the mass-metallicity GRB080605 1.6408 10.53 47.0−+1117 8.46−+00..4028 relation(e.g.,Perleyetal.2016b);(iii)theyusemetallicitiesdi- GRB080602 1.8204 9.99 125.0−+11245 8.56−+00.0.28 rectlydeterminedfromtheobservations,butdonotconsiderthe GRB060814 1.9223 10.82 54.0+−8695 8.38+−00..134 −19 −0.28 stellarmasses(e.g.:Krühleretal.2015);and(iv)theyarebased Notes.There are 4 LGRBs in the 1 < z < 2 sample for which we on samples limited to small redshift ranges (e.g.,0 < z < 1) as couldnotdeterminethemetallicityoftheirhostgalaxies:GRB050318, inJapeljetal.(2016). GRB050802, GRB060908, and GRB091208B. Indeed, there are no In this paper we study the metallicity of the host galaxies usefulspectratothispurposeforthehostgalaxiesofGRB091208Band of the complete Swift/BAT6 sample (Salvaterra et al. 2012) of GRB050318. For the host galaxies of GRB050802 and GRB060908 LGRBs at z < 2, visible from the southern hemisphere. Com- we obtained X-shooter spectroscopy (Prog. ID: 097.D-0672; PI: S.D. bining the observed properties with simulations, we study their Vergani),butthespectradonotshowsufficientemissionlinestoallow behaviorinthestellarmass-metallicityrelation(MZ)andfun- themetallicitydetermination. damentalmetallicityrelation(FMR).Afterthedescriptionofthe ∗:fromnew/unpublishedX-shooterobservationspresentedinthispaper (seeTable3). sampleandnewdata(Section2),wepresenttheresultsinSec- tion3anddiscusstheminSection4. Allerrorsarereportedat1σconfidenceunlessstatedother- wise.Weuseastandardcosmology(PlanckCollaborationetal. exceptionofthehostgalaxiesofGRB071117andGRB080602, 2014):Ωm = 0.315,ΩΛ = 0.685,andH0 = 67.3kms−1 Mpc−1. which are not part of the Perley et al. (2016b) sample, and for Thestellarmassesandstarformationrates(SFR)aredetermined which we determined the stellar masses using Spitzer observa- usingtheChabrierinitialmassfunction(Chabrier2003). tionsandthesameprescriptionasPerleyetal.(2016b).Thehost ofGRB071117liesveryclose(∼2(cid:48)(cid:48))toaredgalaxy,and,therefore,thespatialresolutionoftheSpitzerobservationsallowedus 2. Thesample to obtain only an upper limit on its infrared flux. We therefore Our sample is composed of the 27 host galaxies of the also performed a spectral energy distribution fitting using the Swift/BAT6 complete sample of LGRBs at z < 2 with declina- host galaxy photometry (see Table 2) following the same pre- tion Dec< 30◦. As the spatial distribution of GRB is isotropic, scriptionsasVerganietal.(2015),andfoundlog(M /M )∼9.9. (cid:63) (cid:12) this restriction does not introduce any bias in our results. The choice to select only the LGRBs that are well observable from Table2.ObservedABmagnitudes(correctedbytheMilkyWayextinc- the southern hemisphere was due to the availability of the X- tion)ofGRB071117hostgalaxy. shooterspectrograph(Vernetetal.2011)attheESOVLT(Very LargeTelescope)facilities,which,thankstoitswidewavelength Hostgalaxy g r i z K GRB071117 24.4±0.1 24.7±0.2 24.8±0.3 >24.4 22.9±0.2 coverage,makespossiblethedetectionoftheemissionlinesnec- essarytodeterminetheSFRandmetallicityofthehostgalaxies Notes.The g, r, i, z magnitudes have been determined from GROND at z < 2. In particular, metallicity is available for 81% of the (Greiner et al. 2008) observations, whereas for the K value we used sample (an estimate of the metallicity was not possible for five VLT/HAWKIobservations(Prog.ID:095.D-0560;P.I.:S.D.Vergani). hostgalaxiesonly). As the original Swift/BAT6 sample is selected essentially TheSFRvaluesweretakenfromKrühleretal.(2015)with onlyonthebasisoftheLGRBpromptγ-rayflux,andnoother theexceptionofthehostgalaxiesofGRB061007,GRB061121 selectioncriterionisappliedwhengatheringthegalaxysample and GRB071117, not included in that work. We obtained the (exceptthesouthernhemispherevisibility),oursampledoesnot VLT/X-shooter spectroscopy of these three host galaxies (ESO suffer of any flux bias. Indeed, no correlation has been found programs 095.D-0560 and 085.A-0795, PI: S.D. Vergani and between the prompt γ-ray emission and host galaxy properties H.Flores,respectively).Weprocessedthespectrausingversion (seee.g.:Levesqueetal.2010b;Japeljetal.2016).Furthermore, 2.6.0oftheX-shooterdatareductionpipeline(Modiglianietal. darkburstsarecorrectlyrepresentedinthesample(seeMelandri 2010),followingtheproceduresdescribedinJapeljetal.(2015). etal.2012).Therestrictiontothesouthernhemisphereatz < 2 The measured emission line fluxes are reported in Table3. We maintainsthiscondition,with26%ofLGRBofthesamplebeing determinetheSFRfromtheHαfluxes(correctedbytheextinc- dark. tion determined through the Balmer ratio), with the same pre- Forthepartofthesampleatz<1,Verganietal.(2015)and scriptionsasKrühleretal.(2015). Japeljetal.(2016)reportthetableswiththeobjectsinthesample Following the same prescription as in Japelj et al. (2016), andtheirproperties(includingstellarmasses,SFRandmetallic- wedeterminedthemetallicityoftheobjectsinthesamplewith ity).TherestrictiontotheDec<30◦ excludesGRB080430and the Maiolino et al. (2008) method on the strong emission line GRB080319Bfromthesampleusedinthiswork. fluxesreportedintheliterature(Piranomonteetal.2015;Krühler The properties (redshift, stellar mass, SFR, and metallicity) etal.2015)oronthosemeasuredbyus;intherelevantcases,the ofthe1 < z < 2partofthesamplearereportedinTable1.The results are consistent within errors to those already reported in stellar masses were taken from Perley et al. (2016b), with the theliterature. Articlenumber,page2of4 S.D.Verganietal.:Thechemicalenrichmentoflong-GRBnurseriesuptoz=2 3. TheFMRandMZrelation host galaxies for which the relevant lines to use this metallicity indicator are available. The resulting MZ plot confirms the avoidanceofsuper-solarmetallicityandtheshiftofhighstellar masshostgalaxiestowardlowermetallicitythanthosefoundfor generalstar-forminggalaxypopulationsatsimilarstellarmasses andredshifts. We stress that the five galaxies in the sample for which we couldnotdeterminethemetallicity(GRB050318,GRB050525, GRB050802, GRB060908, and GRB091208B) are all faint galaxies, not hosting dark GRBs, and with stellar masses log(M /M )< 9.2 (three of these galaxies have log(M /M )< ∗ (cid:12) ∗ (cid:12) 8.7;seeVerganietal.2015;Perleyetal.2016b).Asuper-solar metallicity for a large portion of these host galaxies is there- foreextremelyunlikely.Fortwoofthesegalaxies(GRB050525 and GRB050802) SFR limits are available (Japelj et al. 2016; Palmerio et al. in preparation). Under the conservative hypoth- esis that they follow the FMR relation, we can derive limits on their metallicities from their SFR and stellar masses of 12+log(O/H)<8.1,8.4,respectively. Wefurther investigatetheimplications ofour observational resultsbycomparingthemwiththeexpectationsofadedicated numerical simulation of the LGRB host galaxy population presented in Campisi et al. (2009, 2011), coupling high resolution numerical simulation of dark matter with the semi-analytical models of galaxy formation described in De Lucia & Blaizot (2007). Previous work (De Lucia et al. 2004) has shown that thesimulatedgalaxypopulationprovidesagoodmatchwiththe observed local galaxies properties and relations among stellar mass,gasmassandmetallicity.Moreover,Campisietal.(2011) shows that the simulations nicely reproduce the observed FMR ofSDSSgalaxiesanditsspread.FollowingCampisietal.(2011) wecomputetheexpectednumberofLGRBshostedineachsim- Fig.1. Toppanel:MZplot.Thedotscorrespondtothehostgalaxies ulatedgalaxy,assumedtobeproportionaltothenumberofshort- oftheSwift/BAT6sampleofLGRBsatz < 2,colorcodeddepending living massive stars (i.e., star particles less than 5 × 107 yr in ontheirredshiftasshownintherightbar.Thelinescorrespondtothe age),applyingdifferentmetallicitythresholds(Z )fortheGRB relationsfoundforfieldgalaxiesattheredshiftindicatednexttoeach th line. Bottom panel: The FMR plane. The dots correspond to the host progenitor,withprobabilityequaltoonebelowZthandzerooth- galaxies of the Swift/BAT6 sample of LGRBs at z < 2, color coded erwise.WeconstructtheFMRofsimulatedhostsintheredshift depending on their redshift as shown in the right bar. The gray line range z = 0.3−2 and we determined the best-fit value of Z th corresponds to the FMR found by Mannucci et al. (2010, 2011). The by minimizing the χ2 against the BAT6 host data in the same darkbluecurveandareacorrespondtoFMRrelationandofitsquartiles redshift interval. The best-fit model (see Fig.1) is obtained for obtainedusingthesimulationofCampisietal.(2011).Thecyancurve Z = 0.73+0.08 Z (1σ errors). This is consistent with indirect andareacorrespondtothebest-fitmodelresults. th −0.07 (cid:12) results inferred from the distribution of the LGRB host stellar massesatz<1(Verganietal.2015)oroftheinfraredluminosi- In Fig.1 we plot the host galaxies of our sample in the MZ tiesoverawiderredshiftrange(Perleyetal.2016b). and FMR spaces. The dearth of high metallicity galaxies is ev- identaswellasthefactthattherearemoremassivegalaxiesat 4. Discussionandconclusions thehigherredshifts(1 0.1−0.2dex) are References unlikely(onthe basisoflow-redshift,spatiallyresolved LGRB Berger,E.,Cowie,L.L.,Kulkarni,S.R.,etal.2003,ApJ,588,99 host galaxies observations; Christensen et al. 2008; Levesque Campisi,M.A.,DeLucia,G.,Li,L.-X.,Mao,S.,&Kang,X.2009,MNRAS, etal.2011;Kruhleretal.inpreparation),wecannotexcludethat 400,1613 they are at play in the couple of galaxies showing evidences of Campisi,M.A.,Tapparello,C.,Salvaterra,R.,Mannucci,F.,&Colpi,M.2011, MNRAS,417,1013 super-solarmetallicities(as,e.g.,inthecaseofGRB060306;see Cano,Z.,Wang,S.-Q.,Dai,Z.-G.,&Wu,X.-F.2016,ArXiv:1604.03549 alsoNiinoetal.2015).Theexistenceofsomesuper-solarhosts Chabrier,G.2003,PASP,115,763 may as well indicate, however, that the formation of LGRBs Christensen,L.,Vreeswijk,P.M.,Sollerman,J.,etal.2008,A&A,490,45 DeLucia,G.&Blaizot,J.2007,MNRAS,375,2 is also possible above the general threshold, although at much DeLucia,G.,Kauffmann,G.,&White,S.D.M.2004,MNRAS,349,1101 lowerrate.Applyingsmoothercutoffstothemetallicity,instead Fruchter,A.S.,Levan,A.J.,Strolger,L.,etal.2006,Nature,441,463 of the step function used here, shifts Z toward lower values Fryer,C.L.,Mazzali,P.A.,Prochaska,J.,etal.2007,PASP,119,1211 th depending on the functional shape used. The present statistics Georgy,C.,Ekström,S.,Meynet,G.,etal.2012,A&A,542,A29 Graham,J.F.&Fruchter,A.S.2013,ApJ,774,119 doesnotallowustodiscriminatebetweendifferentcutoffshapes, Greiner,J.,Bornemann,W.,Clemens,C.,etal.2008,PASP,120,405 therefore we do not go into further detail. We point out how- Guetta,D.&DellaValle,M.2007,ApJ,657,L73 ever that none of them succeed in reproducing the super-solar Hirschi,R.,Meynet,G.,&Maeder,A.2005,A&A,443,581 Japelj,J.,Covino,S.,Gomboc,A.,etal.2015,A&A,579,A74 metallicityvalue.ItshouldalsobestressedthattheGRB060306 Japelj,J.,Vergani,S.D.,Salvaterra,R.,etal.2016,A&A,590,A129 metallicityisveryuncertainwithprettylargeerrorbars. Kelly,P.L.,Filippenko,A.V.,Modjaz,M.,&Kocevski,D.2014,ApJ,789,23 Kennicutt,Jr.,R.C.,Bresolin,F.,&Garnett,D.R.2003,ApJ,591,801 The relatively high metallicity threshold found in this work Kewley,L.J.&Dopita,M.A.2002,ApJS,142,35 Kewley,L.J.&Ellison,S.L.2008,ApJ,681,1183 is much higher than required from standard collapsar models Kobulnicky,H.A.&Kewley,L.J.2004,ApJ,617,240 (but see Georgy et al. 2012). Binary stars are a possible solu- Krühler,T.,Malesani,D.,Fynbo,J.P.U.,etal.2015,A&A,581,A125 tion as progenitors, although detailed models studying the role Levesque,E.M.,Berger,E.,Soderberg,A.M.,&Chornock,R.2011,ApJ,739, 23 of metallicity on the fates of binary stars are missing. How- Levesque,E.M.,Kewley,L.J.,Berger,E.,&Zahid,H.J.2010a,AJ,140,1557 ever,itisimportanttonotethatthemetallicitiesdeterminedus- Levesque,E.M.,Soderberg,A.M.,Kewley,L.J.,&Berger,E.2010b,ApJ,725, ing strong emission lines are not absolute values (see Kewley 1337 López-Sánchez,Á.R.,Dopita,M.A.,Kewley,L.J.,etal.2012,MNRAS,426, &Ellison2008).Inourcase,theyarerelativetotheKewley& 2630 Dopita (2002) photoionization models on which the Maiolino Maiolino,R.,Nagao,T.,Grazian,A.,etal.2008,A&A,488,463 et al. (2008) method is based. On the one hand, some works Mannucci,F.,Cresci,G.,Maiolino,R.,Marconi,A.,&Gnerucci,A.2010,MN- seem to indicate that those models may overestimate oxygen RAS,408,2115 Mannucci,F.,Salvaterra,R.,&Campisi,M.A.2011,MNRAS,414,1263 abundances by ∼ 0.2-0.5dex compared to the metallicity de- Melandri,A.,Sbarufatti,B.,D’Avanzo,P.,etal.2012,MNRAS,421,1265 rived using the so-called direct Te method (see e.g., Kennicutt Metzger,B.D.,Margalit,B.,Kasen,D.,&Quataert,E.2015,MNRAS,454, etal.2003;Yinetal.2007).Ontheotherhand,otherworks(see 3311 Modigliani, A., Goldoni, P., Royer, F., et al. 2010, in Proc. SPIE, Vol. 7737, e.g.,López-Sánchezetal.2012;Nichollsetal.2012)foundthat ObservatoryOperations:Strategies,Processes,andSystemsIII,773728 the oxygen abundances determined using temperatures derived Modjaz,M.,Kewley,L.,Kirshner,R.P.,etal.2008,AJ,135,1136 fromcollisional-excitedlinescouldbeunderestimatedby∼0.2- Nicholls,D.C.,Dopita,M.A.,&Sutherland,R.S.2012,ApJ,752,148 0.3dex. In principle, the simulations should be independent of Niino,Y.,Nagamine,K.,&Zhang,B.2015,MNRAS,449,2706 Nuza,S.E.,Tissera,P.B.,Pellizza,L.J.,etal.2007,MNRAS,375,665 thesemodelsandthereforethecurvesderivedinthisworkfrom Osterbrock,D.E.1989,Astrophysicsofgaseousnebulaeandactivegalacticnu- simulationsshouldnotbeaffectedbythisissue. clei(MillValley,CA,UniversityScienceBooks) Perley,D.A.,Niino,Y.,Tanvir,N.R.,Vergani,S.D.,&Fynbo,J.P.U.2016a, TheZ ∼ 0.7 Z thresholdshouldnotbeconsidered,there- SpaceSci.Rev.[arXiv:1602.00770] th (cid:12) Perley,D.A.,Tanvir,N.R.,Hjorth,J.,etal.2016b,ApJ,817,8 fore,asanabsolutevalue.Nonetheless,tobeinagreementwith Piranomonte,S.,Japelj,J.,Vergani,S.D.,etal.2015,MNRAS,452,3293 themetallicities(Z≤0.2Z(cid:12))neededinmostLGRBsinglemas- PlanckCollaboration,Ade,P.A.R.,Aghanim,N.,etal.2014,A&A,571,A16 sive star progenitor models, all the metallicities presented here Salvaterra,R.,Campana,S.,Vergani,S.D.,etal.2012,ApJ,749,68 Schulze,S.,Klose,S.,Björnsson,G.,etal.2011,A&A,526,A23 shouldbesystematicallyoverestimated,mostofthembyatleast Smartt,S.J.2015,PASA,32[arXiv:1504.02635] ∼0.5dex. Svensson,K.M.,Levan,A.J.,Tanvir,N.R.,Fruchter,A.S.,&Strolger,L.-G. 2010,MNRAS,405,57 Tremonti,C.A.,Heckman,T.M.,Kauffmann,G.,etal.2004,ApJ,613,898 Acknowledgements. Thisworkisbasedinpartonobservationsmadewiththe Trenti,M.,Perna,R.,&Jimenez,R.2015,ApJ,802,103 SpitzerSpaceTelescope(programs90062and11116),whichisoperatedbythe vandenHeuvel,E.P.J.&PortegiesZwart,S.F.2013,ApJ,779,114 JetPropulsionLaboratory,CaliforniaInstituteofTechnologyunderacontract vandenHeuvel,E.P.J.&Yoon,S.-C.2007,Ap&SS,311,177 withNASA.SDVthanksM.Rodrigues,H.FloresandF.Hammerforuseful Vergani,S.D.,Salvaterra,R.,Japelj,J.,etal.2015,A&A,581,A102 discussions.JJacknowledgesfinancialcontributionfromthegrantPRINMIUR Vernet,J.,Dekker,H.,D’Odorico,S.,etal.2011,A&A,536,A105 2012201278X4FL002.TKacknowledgessupportfromaSofjaKovalevskaja Woosley,S.E.&Heger,A.2006,ApJ,637,914 AwardtoPatriciaSchady.WethanksG.CupaniforsharinghisexpertiseonX- Yin,S.Y.,Liang,Y.C.,Hammer,F.,etal.2007,A&A,462,535 shooterdatareduction. Yoon,S.-C.&Langer,N.2005,A&A,443,643 Articlenumber,page4of4

The chemical enrichment of long-GRB nurseries up to z=2

Similar The chemical enrichment of long-GRB nurseries up to z=2