Spectroscopy!in!the!Era!of!LSST!

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1 SpectroscopyintheEraofLSST ThomasMatheson(NOAO),XiaohuiFan(Arizona),RichardGreen(Arizona),Alan McConnachie(NRCDHIA),JeffNewman(Pittsburgh),KnutOlsen(NOAO),Paula Szkody(Washington),&W.MichaelWoodDVasey(Pittsburgh) 1.Introduction TheLargeSynopticSurveyTelescope(LSST)representsasignificantchangeinthe strategiesemployedbyu.s.astronomerstostudythecosmos.thesurveywill imagetheavailablesouthernskyeverythreetofourdays,switchingamongthesix filters(ugrizy)overtenyearstoachievedepthanduniformity.thefourmain scientificgoalsoftheprojectare:1)characterizethenatureofdarkenergy,2) illuminatethestructureofthemilkyway,3)performacensusofthesolarsystem, and4)discovertransientandvariableobjects.thesegoalscanbeachievedwithin thecontextoftheprojectitself,buteachofthemcanbegreatlyenhancedwiththe

2 additionofaspectroscopiccomponent.moreover,spectroscopicfollowdupwill enableanevenbroaderrangeofscientificuseoflsst. TobeginthediscussionofthespectroscopiccapabilitiesdesiredforLSSTfollowDup, thenationalopticalastronomyobservatory(noao)hostedatwoddayworkshop (April11D12,2013)inTucson.Therewereoversixtyattendeesrepresentingawide rangeofusastronomicalinterests,includingpublicandprivateuniversities,federal facilities,andinternationalobservatories.plenarysessionsgaveanoverviewofthe LSSTprojectitself,aswellasabroadvisionoftheastronomicallandscapein2020, nearthestartoftheoperationsphaseoflsst.breakoutsessionswereorganizedby sciencetopic.eachsessionhadafacilitatortoguidediscussionandprovide feedbacktotheentireworkshop.thefourareaswere:timedomainscience, Galacticstructureandstellarpopulations,galaxiesandAGN,anddarkenergyand cosmology.therewerenotenoughattendeeswithinterestinthesolarsystemto conveneasessiononthattopic. Thegoalofthebreakoutsessionswastoidentifyspectroscopiccapabilitiesthat eachscienceareawouldliketohavetofollowdupoflsstdiscoveries.thefocuswas onscienceddrivenneeds,withbriefsciencecasestobeincluded.nospecificbudget constraintswereapplied,butattendeeswereremindedtoberealisticintheir expectations.thecapabilitiestoconsiderwerenotjustneworrepurposed instruments.theparticipantsineachsessionwerealsoencouragedtoexplorenew facilities,observingmodes,timedallocationmodes,andsoftwareinfrastructureto assistwithtargetselectionandscheduling.inaddition,theycouldalsodescribe precursorexperimentsthatmightguidelsstfollowdup.forallcapabilities,the needforspecificitywasemphasized. Duringthesessions,atablewasdevisedasawaytocharacterizethespecificneeds forindividualsciencecases(seeappendix1forexamplesfromeachbreakout session).thisincludedsuchinformationasthenecessaryspectralresolution, wavelengthcoverage,densityoftargets(singlevs.multidobjects),depth(aperture), numberoftargets,andmanyothers.eachsessioncontributedexamplesto demonstratetheutilityofsuchatable.thistableisstillaworkinprogress,butcan serveasaframeworkforfuturediscussionsofspectroscopiccapabilities. Section2includesthereportsfromthebreakoutsessions.Section3synthesizesthe capabilitiesfromthebreakoutsessionsandassessesthecommondesires. 2.-Reports-from-Breakout-Sessions- 2.1TimeDomain(PaulaSzkodyfacilitator) TheLSSTprojectpresentsatremendouschallengetoastronomersinterestedin timeddomainscience.thevolumeanddataratewillbeunprecedented.current timeddomainprojects(e.g.,palomartransientfactory,catalinarealdtimetransient

3 Survey,PANDStarrs,LaSillaDQUEST,Skymapper)couldsaturateavailable spectroscopicfacilitiesnow,andlsstwillonlyaddtothedemand. PriortothestartofthemainLSSTsurvey,atimedomainecosystemmustbe establishedandtestedtoenablethecapabilitytosortrareandunusualphenomena fromnormalknownvariableobjects.thiswillrequireprecursorcommunity programs(currentlyandincludinglsstitselfduringcommissioning)using2d8m classtelescopesoversmallareasoftheskytoidentifynormaltransients,witha cadencefrom15secondsto6monthsandfilterssimilartothosetobeusedbylsst. Thelightcurvesobtainedneedtobefollowedupwithlowresolutionspectrafor positiveidentificationandtrainingofclassificationschemaandtosetupanevent broker(softwareinfrastructurethatcanfilteralerts).inaddition,testingofrapid responseoftelescopesuponalertsoftransientobjectsisneeded.- Atthestartofthe10DyearLSSTsurvey,theeventbrokermustbecapableof distinguishingknown/unknowntransientsfromthealertstream.thelsstproject expects10 6 alertspernight(whereanalertisdefinedasa5σdifferencefroma referenceimage).thisdwarfstheavailablespectroscopicresources.manyofthese eventswillnotrequirespectroscopicfollowdup,andcertainlymostwillnotrequire immediatespectroscopicobservation.butsomeobjectswithshortlifetimeswill needtobeobservedrapidly.thebrokerwillhavetowinnowthealertstreamdown toafeasiblenumber,ontheorderofonehundredobjects.withoutasoftware infrastructuretosortthealerts,theopportunitytothoroughlystudyrareand unusualeventsdiscoveredbylsstwillbelost. Rapid(sameday,orevensamehour)alertsneedtobeissuedforfaintandfast objectssuchas.iasn,cadrichtransients,grbsandligotargets.theapproximately ~100objects/nightthatthebrokerdeemsinterestingwillneedlowDresolution (R~100D500)spectrawithinstrumentssuchasFLOYDS 1 orthesed 2 machineon2m (toreachr~20magobjects)and4m(toreachr~22mag)telescopes.thelowd resolutionspectrawillprovidemoreinformationforfurthercharacterizationofthe alerts.thiswillnarrowtheoptimumtargetlistofthemostinteresting/unusual objectstoabout10/night. Achangeofobservatoryoperationmodesoverallaperturesfrom2D30mwillbe neededtoenablespectraondemand,whichcouldbededicatedfacilities(optimum), queueschedulingortoointerrupts.- Inordertounderstandthenatureofvariability,obtainradialvelocitiesformasses, determinemetallicity,temperatureandgravity,wewillneedmoderateresolution (R~3000D5000)withwidewavelengthcoverage(theatmosphericcutofftotheK band)on4d8mclasstelescopesofafewthousandselectedtargetsperyeardownto g,r~23magandabout100peryearona20d30mtelescopeforevenfainterobjects

4 Thecadenceofthesespectrawilldependontheobject,withspectraobtainedover daysdmonthstofollowthedevelopmentofsnandnovae,overdaysforgrbs,over weeksforaccretiondisksystemsandovermonthsforagn.overthecourseofthe survey,about10000spectraofsn,200novae,dozensofaccretiondisktransitions andafewagnwillbeneededtoaccomplishscienceonthoseobjects.- LongDtermspectralfollowDup(after1D5yearsofthesurveywhenlightcurvesof particularvariableobjectsarecomplete)willbeneededtodeterminestellar populationstatistics,stellarevolution,odditiesofvariousclassesofvariables, parameterslikemetallicitythatvaryacrossourgalaxyandthedifferencesbetween galaxies.oncethefrequencyanddistributionofvarioustargetsisdetermined,the costs/benefitsofmultidobjectvs.singledobjectorsmallfieldifucanbedetermined. Thenumberofspectrawilldependonthespecifictypeoftarget,e.g.,several thousandforcepheids,severalhundredfortheendproductsofclosebinary evolution.moderateresolutionon4d8mtargetscanbeusedforrvworkdownto r~22magforemissionlineobjects,20d30mtoreachobjectsinothergalaxies.- 2.2GalacticStructure(KnutOlsenfacilitator) ThediscoveryspaceenabledbyLSSTforGalacticstructureandstellarpopulations isbig,withthesciencemakingparticularuseofthealldskycoverage,thelargedepth ofthecoaddedsurvey,thecapabilitytodetectlargenumbersofvariablesastracers ofstructureandpopulations(e.g.rrlyraeoutto400kpc),andtheabilityoflsst tomeasureparallaxesandpropermotionsatfaintmagnitudes.andwhileitistrue thatthediscoverypotentialoflsstbyitselfistremendous,inalmostallcasesitis alsoeasytoseehowspectroscopyprovidesenormousaddedbenefit,e.g.,through theadditionoflinedofdsightvelocities,measurementofstellarabundances,orother detailedinformationonindividualsources. Thegroup sdiscussionontheneedforspectroscopytofollowuplsstdiscoveries beganbyidentifyingseveralbroadthemesofparticularimportancetoourscientific interests.thegroupthennarrowedthediscussiontotwothatappearedtodrivethe spectroscopicrequirementsmoststrongly:1)galacticstructureand2)thestellar populationsofthesolarneighborhood.specificsciencecasesaredescribedinthe subsectionsthatfollow.insummary,thegroupidentifiedcompellingcasesfor severalkindsofspectrographs: Massivelymultiplexedopticalspectrographs,onarangeofaperturesizes, including4dm,8d10dm,andlargertelescopes,coveringarangeofresolution fromr~ ,000. Moderatelymultiplexedand/orsingleDobjectopticalspectrographson8D10D morlargertelescopes,withresolutionsr~10,000andhigher HighDresolutionsingleDobjectnearinfraredspectrographs,withR~40,000 50,000,on8D10Dmorlargertelescopes

5 LowDresolutionsingleDobjectnearinfraredspectrographs,withR~2,000,on 4Dmorlargertelescopes Thegroupalsoidentifiedthepotentialutilityoftargetednarrowbandimaging followdupasacomplementtospectroscopy,whichpointstotheneedforfurther considerationoftheimagingandphotometricfollowdupneedsintheeraoflsst. Finally,wenotedthatmanyoftheGalacticstructurethemesdiscussedbythegroup echothosefoundinthefeasibilitystudyreportforthenextgenerationcfht ( Galacticstructure LSSTenablesanenormousdiscoveryspaceforthestudyofGalacticstructure.From photometryofthecoaddedimages,lsstwillbeabletouseoldmainsequence turnoff(msto)starsasprobesofstructureoutto~200kpc,or~4 further(~16 largervolume)thanforplanneddecamsurveys;thelonglifetimesofmstostars makethemusefulfortracingstructureswithequivalentsurfacebrightnessof 35 magarcsec D2.LSSTwillbeabletofollowRRLyraeout~400kpc,probingthe structureoftheintergalacticregionbetweenthemilkywayandm31.weidentified severalspecificsciencequestionsintheareaofgalacticstructurethatwould particularlybenefitfromspectroscopy WhatistheaccretionhistoryoftheGalaxy? AsdescribedbyFreeman&BlandDHawthorn(2002,ARA&A,40,487)intheirreview articlethe*new*galaxy,weareenteringanagewhereweanticipatehavingthe abilitytopiecetogethertheearlyaccretionhistoryofthegalactichaloandthick diskbyidentifyingthestarsthatremainofthefragmentsfromwhichthese componentsformed.lsstbyitselfwillbeanexcellenttoolforidentifyingspatial structures,likethenowwelldknownsagittariusstream,thatarethesignaturesof recentgalacticsatelliteaccretionevents.butstarsleftoverfromsuchevents becomemixedthroughoutthegalaxythroughdynamicalinteractionoverseveral Gyr(e.g.Helmi&White1999,MNRAS,307,495),requiringadditionalphaseDspace informationtoidentifythefragmentsfromwhichtheycame.usinggiants, horizontalbranchstars,subgiants,andmstostarsaspotentialtracers, spectroscopyoflargesamplesofstarscanaddmeasurementsoflinedofdsight velocities,bulkmetallicities([fe/h]),alphadelementabundances([α/h]),carbon abundances([c/fe]),andabundancesofkeyindividualelements.whencombined withpropermotionsfromgaiaandlsst,wewillbeabletoconstructthefull dynamicalandchemicalphasespaceofthestellarsamplesandbegintoidentify individualearlystellarsystems.thecharacteristicmassofthefragmentsthatwe willbeabletoidentifywillbelimitedbythesamplesize;withasampleof10 7 thick diskstarsand10 6 halostars,wewouldtypicallyhave~10starseachfroma populationoffragmentswithcharacteristicmassof10 4 Msun.Withsmallersamples, wewouldonlybesensitivetothemoremassivefragments.

6 Theclearneedforthissciencecaseismultiobjectspectroscopy,onarangeof aperturesizes.thetypicalobservingdepthwillber~22andfainter,probinga volumeof40kpcradiuswithmstostars,100kpcwithhbstars,and400kpcwith RGBstars.TheS/Nneedsrangefrom<10formeasurementofvelocitieswith<10 kms D1 accuracy,to~20formeasurementsof[fe/h],[α/h],and[c/fe],~30for individualαdelements,and50d100forarangeofotherelements.resolutionneeds alsovary,withr~2000d5000adequateforvelocitiesandthecoarserabundance measurements,andr~20,000orhigherforthemostdetailedabundancework. Mostofthelinesofinterestareintheopticalwavelengthrange. Severalquestionsimportanttothesciencecasewerenotimmediatelyansweredby thegroup,including: Howhotastellartracercanweeffectivelyuse?Measurementsof abundancesaremoredifficultathighertemperaturesasspectrallines becomefewerandnondlteeffectscreepin,whilevelocitiesbecomeless accuratewithbroaderlines. Whatisthesweetspotforthevelocityerror?Moreaccuratevelocitieswill givefinerdynamicalresolution(thoughatsomepointrandommotionsinthe populationsthemselvesmakehigheraccuracyunnecessary),whilecoarser velocitymeasurementscanmakeuseoflowers/nspectraandpoorer resolution,yieldinglargersamples. Howdoweefficientlyselecttargets?Thesciencecasetargetsthethickdisk andhalocomponentsspecifically,buttheseaccountfor<~10%ofthe Galaxy sstellarmass.efficientselectioniskeyformakingthebestuseof telescopetime. Howmanydifferentsamplesareneeded?Weareunlikelytobeableto collecteverytypeofmeasurement(velocitiesandabundances)foreverystar inthesample,becauseoftherangeofbrightness,resolution,ands/n requirements. Howaccuratelycanwemeasurethephotometry?Highphotometric accuracytranslatesdirectlytoimprovedtargetselectionefficiencyand accuracyofabundancesanddistanceestimates Whatistheshapeofthedarkmatterhalo? Theshapeofthedarkmatterhalo(itsradialdensityprofileandangular dependence)isakeyingredienttoanymodeloftheformationofthegalaxy. MeasuringtheDMhaloshaperequiresalargenumberofstellartracersdistributed alloverthesky,withvelocitymeasurementswithaccuracy<10kms D1 and,where available,propermotionsforconstructing3ddorbits.redgiantswithr~22would allowustoprobethedmhalooutto~400kpc.

7 Thespectrographrequirementsforthissciencecaseareessentiallyidenticaltothat of becausethegoalistoonlymeasurevelocities,mostoftheworkcouldbe donethroughmultiobjectspectroscopyon4dmdclasstelescopes.resolutionneeds arer~2000d5000.thisscienceprojectcouldeasilypiggybackonthemore demandingobservationsneededforstudyingtheaccretionhistoryofthegalaxy WhatdoesthepopulationofDMsubhaloslooklike? Inahierarchicalstructureformationscenario,theGalactichaloisexpectedtobe populatedbyhundredsoflowermassdarkmattersubhalos.whilethenumberof dwarfsatellitesknowntoresideinthegalactichalocontinuestoriseasnew systemsarediscovered,thereremainfarfewerdwarfsatellitesthanwouldbe predictedifalldmsubhaloshostedstellarsystems.ifalargepopulationofmissing darksatellitesexists,theonlywaytodetectthemwillbetoobservetheir gravitationaleffectonvisiblematter.apromisingmethod,enabledbylsst s preciseanddeepphotometry,istoidentifycoldstreamsinthehaloandlookfor velocityperturbationsfromdarksubhalosnearby.themostusefulstreamsarethe coldestones,suchasthetidaltailsaroundtheglobularclusterpalomar5,which haveavelocitydispersionof~2kms D1 (Odenkirchenetal.2009,AJ,137,3378).The projectwouldusethedeeplsstphotometrytoidentifywellddefinedstellarstreams withpotentialsubstructure(e.g.ibataetal.2002,mnras,332,915;johnstonetal. 2002,ApJ,570,656;Carlberg2009,ApJL,705,223),andselect~1000targetsper streamforspectroscopy.inordertomaximizethenumberoftargets,wewilluse thebaseofthergb,subgiantstars,andmstostarsasnecessary,fortypical magnitudesofr~20. Themostfundamentalspectrographrequirementistobeabletomeasurevelocities withprecision<1kms D1,whichdemandsR~10000orbetter.Therelativelyfaint magnitudesthatarelikelyneededandrequiredmediumtolargesamplesizeswould bebestservedbymultiobjectspectroscopyon8d10dmclasstelescopes.becausewe wouldbetargetingrelativelynarrowstreams,thefieldofviewofthese spectrographsneednotbeparticularlylarge,although~1degreefieldofview wouldbehelpfulinimprovingthetargetingefficiency. Questionsforexploration: Howmanystreamsareneededinordertohavealikelyprobabilityof detectingatleastonedmsubhalo? Giventhemassspectrumanddistancesoflikelydetectedstreams,whatis themagnitudedistributionoftargetsgivenarequirementof~1000sources perstream? HowlongisthemetalDpoortailoftheGalactichalo? ThemostmetalpoorstarsintheGalactichaloprovideavaluablewindowintothe earlyhistoryoftheuniverse,astheirchemicalabundancepatternsreflectthe

8 productsofatmostafewgenerationsofchemicalenrichment.findingthestars thatoccupytheextremeofthemetaldpoortailcouldprovideaviewoftheveryfirst generationsofsupernovae,perhapseventhoseproducedbythefirstpopulationiii stars.thechallengeinfindingthemistoidentifytheseveryrarestarsfromthe backgroundseaofmuchmorenumerousmetaldrichstars.lsstcolorswillprovide theroughfirstcut,whileamassivelowdresolutionspectroscopicsurveyonamidd sizedtelescopewouldbeneededtoprovideasecondcut.oncepromising candidatesareidentified,theywouldbefollowedbyhighdresolutionhighs/n observationsonlargetelescopes.thetargetstarsneednotbefaint,andassuch representpotentiallowdhangingfruit. Forselectingthemostpromisingcandidates,lowresolution(R<2000)spectroscopy withs/n~20isneeded,ofaslargeasampleofstarsaspossible,beginningwiththe brightest(r<~17)stars.thefirststagethuscallsforhighlymultiplexed spectroscopyon4dmdclasstelescope.thisdemandforlowresolutionspectroscopy couldbesignificantlyreducedbyefficientuseofnarrowbandimagingtargetingthe CalciumH&KlinesandtheGband.Oncethecandidatesareidentified,singleobject, highdresolution(r>20000)spectroscopyon8d10dmclasstelescopesisneededto studytheabundancesofindividualelementswithhighprecision TheSolarNeighborhood LSST spreciseastrometryovera10dyearbaselineacrossthefullsouthernsky makesitapowerfultoolforconstructingacompleteinventoryofthesolar neighborhoodoutto~200pcthroughparallaxmeasurements.whilegaia sregime willbetoprovideastrometryforstarsbrighterthanr~20,lsstwillprovidefar superiorperformanceforthefaintendofthewhitedwarfcoolingsequenceand substellardwarfs.thehugevolumewithinwhichwecanstudybrowndwarfswith LSSTwill,whencombinedwithspectroscopy,allowustoaddresssomeexciting fundamentalquestionsaboutthem Whatarethemassesofbrowndwarfs? Directknowledgeofstellarmassesacrossabroadrangeoftemperaturesis fundamentaltomodelingandunderstandingtheircharacteristics.forbrown dwarfs,thenumberofobjectswithmassesmeasureddirectlyfromtheir gravitationalinfluenceisverysmall.thelargenumberofbrowndwarfsthatlsst willdiscoverwithinthesolarneighborhoodwillturnupmanyinbinarysystems, wherewewillhavetheopportunitytomeasuretheirmassesdirectly.measuring massesinbinarysystemsrequiresrepeatspectroscopicmeasurementsinorderto associatethevelocitycurvesofthebinarycomponentswiththeirorbits. Spectroscopicmeasurementsineclipsingbinarysystemswillbeparticularly valuableformeasuringstellarparameters.

9 Becauseoftheirloweffectivetemperatures,browndwarfspectrapeakinthenearD infrared.giventheirlowmasses,weneedvelocityaccuracyof50d100ms D1 to detectthevelocitywiggles,correspondingtoaneardinfraredspectrographwith R~40,000 50,000.InordertoachieveS/N~10forsinglesourceswithK~15,the spectrographwillneedtobeonan8d10dmorlargertelescope Whatisthenatureofweatheronbrowndwarfs? Thecooltemperaturesofbrowndwarfatmospheresleadtocomplexatmospheric chemistryandbehavior,includingweather.studyingandunderstandingsuch phenomenaisimportantbothformodelingbrowndwarfsandforunderstanding thephysicsofplanetaryatmospheres.lsstwilldiscoveralargenumberofbrown dwarfsthroughparallax,aswellasprovidemeasurementsofthephotometric variabilityassociatedwithatmosphericchanges.spectroscopyofthebrowndwarfs, linkedtothephotometricvariability,wouldbeinvaluableforunderstandingthe phenomena. LowDresolution(R~1000),nearinfraredspectroscopywithS/N 20issufficientfor monitoringthebroadmolecularanddustdcloudgeneratedspectralfeaturesin browndwarfatmospheres.withtypicalsourcemagnitudesofk~15,the spectroscopyneeds4dmtelescopesorlarger. 2.3GalaxiesandAGN(XiaohuiFanfacilitator) TheoverarchingscientificmotivationfortheGalaxiesandAGNbreakoutsession wasunderstandingtheassembly,starformation,andchemicalenrichmenthistories ofgalaxies,theinteractionofgalaxieswiththeigm,thecodevolutionofsmbhsand theirfeedback,allasafunctionofevolvinglssenvironment&cosmictime.the followingsciencecasesillustratethecapabilitiesdesiredtopursuethesetopics AMassiveRedshiftSurvey ThiswouldencompassalargeDscalesamplingofarangeofenvironmentsand redshiftsforchemicalevolution,starformationrate,mass,etc.itwouldneed severalsdssvolumesfordifferentredshiftsliceswithapproximatelyonemillion galaxieswithdiagnosticqualityspectroscopy.thiswouldentailcoverageofanarea of1d3degreesindiameterwith~1000fibersandthespectralresolutiontosplit[o II](velocitysigmaof30km/s,i.e.,R~4000).Coverageofthefaintestredshiftbins requires10dmclasstelescopeswithadequates/nforphysicaldiagnostics(100sof nightson10mclasstelescopes) TopologyofReionizationSurvey(ToRS) Reionizationendedatz 6.5andwasprobablyduetophotoDionizationfrom galaxies.itmightwellhavebeeninhomogeneous,duetoclusteringofionizing sources.lsstwilldetectandmaptheangulardistributionofuvdbrightgalaxiesout

10 toz 7,withthemain(wide)surveyreachingbrighterthanL*galaxiesatz=6D7and fainterthanl*atz 5.ThedeepDdrillingfieldsreachfainterthanL*atallredshifts. SpectroscopicfollowupofLSSTimagingwillgiveanapproximatemapofthe3DUV luminositydensity.thisspectroscopywillmeasurethe3ddistributionofthe brightergalaxiesandcanbecorrelatedwithmuchdensersamplingoflsst photometricsamplestofaintermagnitudes(faintergalaxiesalmostcertainly dominatetheemissionofionizingphotons).measurementsfromz 7toz 3D4 willmaptheevolutionofclusteringanditsrelationtouvemission.thisreaches lowerluminositiesandmuchhigherspace/surfacedensitiesatlowerredshiftsand permitsextrapolationbackwardintothereionizationera. TheToRSsurveywillrequireoptical( 1μm)spectratom=26D27,withthegoalof detectinglyα,lydbreak,andismuvabsorptionlinesformeasuringredshifts. SpectroscopicresolutionofR~1000wouldbeadequate,buthigherresolution wouldbebettertoimprovetheefficiencyofdetectinglinesthroughtheohsky forest.asecondarygoalwillbetomeasurethelyαemissionfraction(whichis sensitivetotheneutraligm)vs.therestdframeuvluminosity.multislit spectrographswouldbefavoredtomatchtothehighsourcedensityatveryfaint magnitudes(surfacedensitiesof~few/arcmin2atz 6D7,~10/arcmin2atz<5) whileretaininghighthroughput.thesurveywillrequire~severaldeg 2 inorderto samplethescaleofreionizationbubbles,whichisroughly1degree(150mpccod moving)atz=7.thisprojectwoulduse~50nightswithgmacsongmt TheRegionsofHighestOverdensity LSSTwillfindmany(~tens)ofregionsofhighoverdensity,particularlyathigher redshifts.theseareuniqueenvironmentsforearlyassemblyofgalaxiesandstrong inflows.tostudytheseregions,onewouldneedcoverageof~10arcminute diameterareastomeasure10d100objectsperregion,withhighenoughspectral resolutiontosplitthe[oii]linepair(velocityerror<30km/s,i.e.,r~400). Coverageofthehighestzbinsto26thmagrequiresa20Dmclasstelescope.The spectraneedtohaves/nadequateforphysicaldiagnosticsandthustensofnights on10mclasstelescopes LyAlphaBlobs WhataretheLymanAlphablobsandwhatphasedotheyrepresentintheformation ofgalaxies,groups,andclusters?tostudythiswillrequireidentificationofalarge sampleoflabsatz~2d5.weexpect<1persquaredegree.thespectroscopic requirementsforidentificationincludesingleobjectspectroscopyover3200å 1µm withhighdthroughputinthebluebeingessential.thiswouldrequire~100d200 nightsonan8mclasstelescope.followdupsciencewouldrequireneardir spectroscopy(togetrestdframeopticallinediagnostics,wherepossible)withsingle objectslitspectroscopyacceptable,butifupreferred.inaddition,opticalifu spectroscopywouldprovidespatiallyresolvedlineratiosandkinematics.itwould alsobeusefultohaveasmallfield(10arcmind1degree)followdupmultidobject

11 spectroscopytounderstandtheenvironment,andpossibly2dspectropolarimetry. TocalibratephotoDz sforthelbgpopulation,onewouldwantmosoptical spectroscopyofsamplesof~100sto1000soflbgsforredshiftsintherangeofthe LABredshifts(z~2D5) DwarfSatelliteGalaxies LCDMpredictsfarmoredwarfsthanobservedinLocalGroup,butwestillhave incompleteunderstandingoffaintdwarfsbeyondthelocalgroup.thechallengeis inseparatingobservationallythosetruedwarfswithinthevirialradiusfrom background, slightlymoreluminousgalaxies.therearetensofparentgalaxiesat distancesof10d15mpc,withtensoffaintdwarfsperhosttobeculledfrom10,000 faintgalaxiespersquaredegree.forspectroscopicstudy,onewouldneedcoverage of1d3degreediameterwith~1000fibersandaccuraterv sforr~24(r=2000).ten thousandbackgroundobjectsperhostisbasedonphotodz.thismanysources wouldrequiremultipleconfigurationsoffibermos.foradditionalfollowdup spectroscopytogetphysicalpropertiesoftruedwarfsforinternalvelocity dispersionandabundances,onewouldneedr> IGMTomography BackgroundAGNsanddistantgalaxiesdiscoveredbyLyalphaemissionorLybreak energydistributionscanprovidehighdensityprobesforthe3ddstructureof inflowingandoutflowinggasfromgalaxiesintheforeground,aswellasits associationwithindividualobjects.tostudythisproblem,onewouldneed10d arcminfov,moscoverageofi=25.5sourceswiths/n~10,hundredsofobjectswith accuratevelocities(r~2000),andcoveragefrom0.4d1.0µmforrestdframeuv observationsat2<z<5.thiswouldrequire20hoursperfieldovertensoffieldsto coverarangeofoverdensitiesandredshifts QuasarRedshiftSurveys OneoftheleastwellDknownaspectsoftheAGN(bolometric)luminosityfunctionis thecontributionofobscuredagnandthelowdluminosityendoftheunobscured population.theformerextractsnuclearinformationfromgalaxyredshiftsurveys andmultidwavelengthassociationofobjectsfromothersurveys.unobscured objectsarederivedfromthefaintestobjectscapturedbythelsstdepth.thelarge sampleallowsdeterminationofevolutioninclustering,distributionofeddington ratios,andrelationofbhgrowthtogalaxygrowth.thisbuildsonmsddesiand currentsurveys.thisrequiresawavelengthcoverageof0.38d1.26um,r~1000d 2000,andS/N~10forvelocitywidths.Alimitofi=24gives500persquaredegree over10,000squaredegrees ReverberationMapping

12 TheresponseofthebroadDlineregiontocontinuumvariationscreatesrelationof luminosityandlinewidthallowingmassdeterminationforthecentralbh.todate, thishasbeenaccomplishedonlyforlowdluminosityagnsandthenstrongly extrapolatedtohigherluminosityagns.thereisapossibilitythismightbeauseful distanceindicatorforcosmology.therearetwoapproaches,eitheran opportunistictriggerforstrongvariabilityorregularmonitoringofknownagnin thedeepddrillingfield(s).thisrequiressingleobjectcoverageforanalldskytrigger, MOScoverageofD1.5degdiameter(deepDdrilling),~1000fibers,andaccurateRV s forr~24(r>1000).therewouldbemonitoringspectroscopyforthedeepddrilling field(s)andnewsequencesforstrongvariablesatfirsttrigger RareClassesofAGN Special,astrophysicallyinterestingclassesofquasars/AGNwillturnupgiventhe LSSTareaanddepth.Forexample,quasarsatz>6testearlyBHgrowthandare reionization/igmprobes.therewillbe~100z>7.2quasarsaty<24overthelsst survey.forthesetargets,anxdshooterdtypeinstrument(0.8d2.5micron),r~2000, singletarget,highs/n,on10mclasstelescopewouldserve.forz>~6quasars,at Y<24therewillbeoneobjectevery1D3persquaredegree,or~1perPFSFOV. ThesecouldbeobservedaspartofwideDareagalaxy/quasarspectroscopicsurvey withr~2000andmoderatedtodhighs/non6d10mclasstelescopes.otherexamples includerarebalstostudyfeedback,quasarstronglenses,andultraluminoushighdz galaxies.tofindthese,oneneedstodeveloptargetselectionbefore/during commissioningwithlsstdtypefilter/depth/cadence KeyCapabilities Consideringtheabovesciencecase,thechiefcapabilitiesarehighlymultiplexed spectroscopicsurveysandraredobjectfollowup.forthehighdmultiplex spectroscopicsurveys,onewouldlike6.5d10mclasstelescopeswithwidedfieldhighd multiplexingoptical/irspectrographsoflowdtodmoderateresolution(r<=4000). Thesewouldbededicatedsurveyswithmillionsoftargets.IRcapability (realisticallyuptojband)isimportantformanysciencecases.exceptfor reverberationmapping,followdupisnottimesensitive.msddesiandpfswill providemuchofthiscapability,butthereisanoticeablemismatchbetweenthe currentlyplannedfacilitiesandthelsstfootprint. ForrareobjectsandstructurefollowDup,thenecessarycapabilitiesarea 20mclasstelescopewithasingle/multislit/IFUspectrographandaFOV<~10 arcmin.theresolutioncouldbelowdtodmoderate(r<=4000)formostapplications, butr~30000forigmabundance.ircapability(ideallywithcontinuouscoverage suchasxdshooter)isimportantformanysciencecases.uvcoverageisimportant forigmtomography.notethatthereisnoxdshootertypeinstrumentamongfirstd generationinstrumentsontheelts.

13 OtherusefulcapabilitiesincludeanefficientIFUforhighspatialresolutionandrapid followdupsingleobject/ifuwithbroadwavelengthcoverage.inaddition,abroker fortransientalertstoidentifypossibleagn,especiallyflaringagn,isimportant, alongwithothersoftwaredevelopmentfortargetselectionandimageprocessing.a precursorsurveywithdecamandacomplementaryirsurveywouldhelpto facilitatelsstfollowdup. 2.4DarkEnergyandCosmology(MichaelWoodDVaseyfacilitator) TheWeakLensingandLargeDScaleStructuregroupidentifiedseveralcompelling sciencecaseswithdifferentspectroscopicneeds: A)Asurveyof>100,000brightobjects(galaxies+QSOs)over>100sq.deg.from 0<z<3.5forhighDprecisioncrossDcorrelationcalibrationofphotoDz's;R~4000, µm B)Asurveyof~20, ,000faint(22<i<25)galaxiesfrom0<z<3.5with highestpossibleredshiftsuccessrateforphotometricredshifttraining,spanning widearea;r~4000, µm.Thiswouldbesupplementedbyobservationsof i~25abmaggalaxiesthatdonotyieldsecureredshiftsatfirstpass,including: Longerexposuresforobjectsthatfailedtoyieldredshifts JWSTNIRSPECorWFIRSTIFUspectraof~1,000ofthegalaxies SpectroscopyusingOHsuppressiontechnologycouldpotentiallyyield significantbenefits,althoughthosehavenotbeenrealizedasofcurrent generationinstruments. C)Aclustercosmologysurveyinvolving: 2500spectraofredgalaxiesinclusters.Thespectroscopictargetswouldbe 2D3galaxiesfromeachof1000clustersinevenlydistributedbinsfrom 0<z<1.5,withresolutionR~4000andcoveragefrom µmfor100km/s accuracy. Redshiftsfor>200objectsperclusterin10galaxyclustercandidates between0<z<1.5formodifiedgalaxytests.thespectroscopywouldhave resolutionr~4000andcover µm. D)AstronglensingcosmologysurveyusingadaptiveopticsDcorrectedIFU spectroscopyfor~1000stronglenssystemson20/30mclasstelescopes.the spectrographwouldhaver~2000,wavelengthcoverage1 2µm,a5"fieldofview, and0.05"sampling. E)AnSNIacosmologysurveycomprisedof10,000SNIaspectraatwavelengths µmwithR~ ,whichwouldbetimeDsensitive;and200,000SNhost galaxyspectra,alsoatwavelengths µmbutwithR~4000,whichwouldnot betimedsensitive.

14 2.4.1PhotometricRedshiftstoenableDarkEnergyandCosmologyStudieswith LSST AsLSSTisaphotometricsurvey,photometricredshiftsandclassificationwillimpact allmajorextragalacticsciencecases.manyofthetopicsofcosmological investigationswithlsstrequiretheinferenceofredshiftsandtypesofobjects basedonthelsstimagingdata.therobustandaccuratecalibrationofthese inferencesrequiresspectroscopicobservationsofsignificantsubsamples CosmologywithGalaxyClusteringandWeakLensing WeakLensingStory Theweakgravitationallensingofdistantgalaxiesdependsonthedistributionof matterintheuniverseandsoissensitivetodarkenergythroughitseffectonthe growthofstructures.theacceleratedexpansionoftheuniversethatiscausedby darkenergyopposesthegravitationalattractionthatwouldotherwiseleadtothe increasedclumpingofdarkmatterstructures.themagnitudeoftheweaklensing signaldependsondistancestoboththelensandthesource.theefficiencyofthe lensingchangesslowlywithredshiftandthusrelativelywideredshiftbinscanbe usedtostudytheevolutionoftheweaklensingsignal. Thismeanstheaccuracyofindividualphotometricredshiftsarenotveryimportant, butthedistributionofphotometricredshifterrorsmustbeknowntohighprecision. Forweaklensingwerequireanaccurateestimationofthedistributionoftrue redshiftswithineachphotometricredshiftbin GalaxyClustering/LSSStory ForlargeDscalestructuremeasurements,understandingandquantifyingtheoverall uncertaintiesingalaxyphotometricredshiftestimateswillbeimportantfor measurementofgalaxydgalaxylensing.baryonacousticoscillations(bao)imprinta standardrulerthatcanbemeasuredfromthegalaxytwodpointcorrelationfunction. ThismeasurestheangulardiameterdistanceandtheHubbleparameter.BAO measurementswillbeperformedbysplittingthegalaxysampleonebyoneintoa seriesofredshiftshells.thisrequiresphotoredshiftsoftheindividualobjects accurateenoughtoenablecleanseparationofbins.overlapinredshiftshells resultingfromuncertaintieswillleadtocrossdbincorrelations Challenges Therearetwomainchallenges.First,obtainingahighlyaccuratecalibrationof photometricredshifts("calibration").themeanredshiftandredshiftspread (sigma)oflsstsamplesmusteachbeknownto<~0.003(1+z)forweaklensing andbaodarkenergyinferencenottobedegraded.second,producingthehighestd qualityphotometricredshiftsforeveryobject("training").minimizingthe

15 uncertaintyinthemeasurementofthephotometricdredshiftofanindividualgalaxy willhavesignificantscientificbenefitsforbaoandclusterstudiesofdarkenergy,as wellasgalaxyclustering/environmentstudies.thesrdrequirementisthatlsst shoulddeliversigma_z<0.02(1+z)forperfecttemplateknowledge.anoptimal trainingsetshouldbringusasclosetothislimitasfeasible. ForCalibration,therequirementsforLSSandweaklensingsciencewithLSSTcanbe metusingcrossdcorrelationcalibrationtechniquesthatrelyonusingaspectroscopic samplethatspanstheredshiftrangeofandoverlapsinskycoveragewitha photometricsample.whilethelsstgoldsampleofgalaxieswillgodowntoi<25.3 ABmagouttoz~3.5,thespectroscopiccrossDcorrelationsamplenecessaryto characterizeredshiftdistributions(bothmeanredshiftsandstandarddeviations)at thelevelrequiredfordarkenergyinferenceneedonlyspantheredshiftrange,but notnecessarilyproperties,ofthegoldsample.thusredshiftsforthemostmassive galaxiesandmostluminousquasarsatagivenredshiftaresufficient.because robustredshiftidentificationiskey,sufficientresolutiontosplitthe[oii]doubletis necessary.thisimplies100,000brightobjects(r<23.5)from0<z<3.5withr>4000 over0.4µmd1.0µm. ForTraining,theaccuracyofclusteringmeasurements(includingBAOdarkenergy constraints),clusteridentification,andconstraintsontheimpactofintrinsic alignmentsonweaklensingwillallbeimprovedastheerrorsinindividualdobject photometricredshiftsgetsmaller.thelsstsystemisbeingdesignedtobecapable ofdeliveringagoldsampleperdobjectphotometricredshiftaccuracy(withperfect knowledgeofsedtemplates)ofσz<0.02(1+z).thecloserwecancometoanideal trainingset,thecloserwewillbetoachievingthiserrorlevelforallobjects.oneof themajorconcernsisobtainingsecureredshiftsforafairsampleofgalaxiesforall SEDtypesandredshifts.>1%errorratesinthecalibrationredshiftsamplewould yieldunacceptablesystematicerrorsinphotodzcalibration.existingsurveysto i~22.5haveachievedsecureredshiftsfor40%d70%oftargets,withsomefailures broadlydistributedincolorspaceandothersconcentratedinlimitedregions. Galaxytypesthatarenotrepresentedintheredshifttrainingsamplecannotbe reliablyusedformanytypesofscientificinquiry.anidealtrainingsetwould includeasetofstatisticallycomplete(i.e.notsystematicallyincompleteforanyclass ofgalaxies),securespectroscopicredshiftsfor20, ,000faintobjectsi<25.3 from0<z<3.5.maximalwavelengthcoverageisdesirable;0.4d1umwouldbethe minimumuseful,whiledeepcoveragefrom0.37d2.0µmwouldbeideal.aminimum resolutionofr~4000willbeneededtosplitthe[oii]3727adoublet,greatly enhancingthesetofgalaxieswithsecureredshifts.thisalsoappliestothesnia hostgalaxies.oforder objectsmayrequiretheequivalentofJWST NIRSPECspectroscopytoyieldredshifts.SignificantadvancesinOHsuppressionin multidobjectspectroscopywouldyieldsignificantgainsforgrounddbasedeffortsin supportofthesegoals.anideal,completetrainingsamplewouldallowlsst calibrationneedstobemetwithoutrelyingoncrossdcorrelationtechniques.

16 ObservingMode ForeachofthesephotometricDredshiftcalibrationneeds,largesurveyprogramswill beappropriateandnecessarytocompleteandenabletheseprojects.thesesurveys couldlastaslongas5oreven10years;becauseitisfeasibletogeti<25.3 photometryover>100squaredegreeswithfacilitiesnowbeingcommissioned, theseeffortscanbeginwellbeforelsstisondsky TypeIaSupernovaCosmology IdealandperfectlyaccurateandcalibratedSNeIacouldmeasurerelativedistances intheuniverseto0.07%per0.1redshiftbin(7%/sqrt(10,000)).however,weare currentlylimitedbythesystematicsofthecalibration(δw~0.08),thetreatmentof supernovacoloranddust(δw~0.05),andconcernsofpotentialevolutionofsnia propertieswithredshift(δwunknown). Thecurrentknownlimitingsystematiciscalibrationofthephotometricsystems. LSSTwillhaveaselfDcalibratedsampleofSNeIarangingfrom0.1<z<1.0.TheLSST calibrationto1%willreducetheδwcontributionto(δw~0.02).theinvestigation ofcoloranddustwillrequiresignificantuv,optical,andnirimagingand spectroscopyintheyearsupto2022.apotentialoutcomeofthesestudiesisthat SNeIawillhavetobematchedupbygalaxypropertiestobettercontrolforthe likelydustencounteredbythesnialightinthehostgalaxyaswellasanoverall correlationwithprogenitormetallicityandotherproperties.wearethereforemost concernedaboutpotentialsystematicsthathavenotasyetbeenrevealed. Variationsinintrinsicsupernovapropertieslikelycomefromtheirbinaryevolution andmetallicity.themetallicity,andpotentiallybinaryfraction/separationimfare likelytobefunctionsofthestellarformationhistorywherethesupernovaisformed. Acentralconcernisthatthesedistributionsandpropertiesmayevolvewith redshift.butthegrossnatureofthisconcernshouldsimilarlybewellmatchedby thegrosstracingofthepropertiesofthehostgalaxy.wethusstronglydesire spectroscopyofthehostgalaxyofeverysupernovaofalltypes(ia,coredcollapse, etc.).thiswillhelpsolidifyphotometricdclassification/redshiftofthesupernovae, andprovideawaytomapthepropertiesofsupernovaeasafunctionofredshift. ThelargenumberofLSSTSNeIawillallowforselectionofidealsubsamples.The selectionofthesesubsampleswillquitelikelyrequireinformationaboutthehost galaxy.metallicityofthegalaxy(bothgasdphaseandstellar)willlikelybeakey tracer,alongwithestimateofratesofrecentstarformation(last200myr). TypeIasupernovaecosmologywillthussignificantlybenefitfromspectraof ~10,000supernovaeatgivenphases.Thesespectrawillbedistributedfrom 0.1<z<0.9with19<i<24.Thiswouldbesubdividedintothreesets.SetAwould have5,000forspectraatmaximumlight.setbwouldhave2,500spectratofollow

17 allsndlikeeventstoexplorecontaminationandclassification.setcwouldhave 2,500spectra(5x500)repeatedcoveragetomapoutfullcoveragearoundpeak. R~100issufficientforsupernovaclassificationastheseexplosiveeventshave broadfeatures,witheffectivevelocitywidthsfrom3,000d10,000km/s.it'spossible thattheabilitytopickupnarroweremissionlinesandabsorptionlinesmaybe relevantforstudiesofsniaenvironments.buthavingr~100capabilitiesonlarge aperturesmaybeveryhelpfulinefficientlyobtainingspectraofz~0.9sneia. IFUobservationswouldbepreferableifpossibletosimultaneouslyobservethe supernovaandhostgalaxy. Inaddition,spectraof100,000hostgalaxiesfrom0.1<z<0.9wouldbeuseful.The maindriverforr~4000forthehostgalaxiesistoobtainsufficientinformationon emissionandabsorptionlinestocharacterizethegasdphasemetallicityofthehost galaxiesandtosplitthe[oii]doublet. ThespecificobservingcapabilitiestopursuetheSNIascienceprogramincludea transientbrokertoidentifysntargets.forsinglesne,onewouldlikeasingledslitor IFU,highDthroughput,0.4D1.2µm,R~ spectrographona8D10mclass telescopeatthestartoflsstoperations.thiswouldbealongdtermprogramwhere targetswouldbeallocatedafewdaysaheadoftime.thereisnorequirementfor interrupts,butthereistheneedtobeabletochoosewhenagiventargetis observed.understandingtheselectioneffectsintroducedintargetselectionis criticaltothesuccessofcontamination/rate/typingstudies.thisneedstobe algorithmicanddeterministic.therewillbe~5targets/squaredegreeatatime. Nosignificantmultiplexadvantageislikelypossible,butcoordinationwithlarge galaxystudiesinthesameareamayyieldgains.forthehostsofsneia,the necessarycapabilitiesareamultidobjectspectrographwithwide(fewdegrees)fov, 0.4D1.0µm,R~4,000.Observationscouldwaituntilwellintothesurvey.AfiveDyear surveycouldobtainallofthehostgalaxyredshiftswith100d500targetspersquare degreeafterthefull10dyearlsstsurvey Cosmologywithgalaxyclusters Clustercosmologyreliesonphotometricredshiftstoidentifyconcentrationsof galaxies.lsstisanexquisitephotodz+lensingmachine,ideallysuitedtoabsolute masscalibration.itwillfindmanyopticalclustersatz<1.2.primarilyspectroscopic redshiftswouldaidphotodzaccuracyandenablethebestlensingcalibration.a secondusewillstudy``clean,''welldsettledclusterstotestgravity. Theprimarytoolfortheabsolutecalibrationofgalaxyclustermassesfor cosmologicalstudiesisweakgravitationallensing.workinthisareaisprogressing rapidly(e.g.vonderlindenetal.2013;applegateetal.2013)anditislikelythat withinthenext2d3yearsthesystematicsinmasscalibrationwiththismethodwill becomedominatedbyuncertaintiesinthephotodzsforgalaxiesintheclusterfields.

18 Mostofthegalaxiesthatenterclusterweaklensinganalysesarerelativelyfaint, i~25mag.wecurrentlyhaveanincompletepictureofhowwellphotodzcodes trainedonfieldpopulationsdescribefaintclustermembersinthisregime:dothe faintclustermembershavesimilarcolorstofieldgalaxies?doweneedtoadjustthe photodzpriorsforclusterfieldstoreflectthegreaterlikelihoodoffindingfaint galaxiesattheclusterredshift?thebestwaytoaddressthesequestionsisthrough comprehensive,deepspectroscopyofclusterfieldsoverarangeofclusterredshifts andalso,ideally,clustermasses. Ataminimum,thisworkrequirescomprehensivespectroscopyof~20clusterfields (2massbins,4redshiftbins,with2D3clustersperbin).UsingKECK,orsimilar8D 10mclassfacilities,weexpecttoattaingood(~75%)completenessdowntor~24 with1(ideally2)nightspercluster.toreachr~25,willrequire30mtelescopesand again1(ideally2)nightspercluster.intotal,thisimplies~20(ideally40)nightsof both10mand30mtelescopetime.otherpossibleinstrumentstoinitiatethiswork atbrightermagnitudes,withtheabilitytoefficientlytargetlargenumbersofobjects, includethelowddispersionprismatmagellan,aswellashstgrismsurveys(e.g. theglasssurvey) Cosmologywithstronglensing Stronglensingconstraintsoncosmologyrelyonhavingkinematicmass measurementsforhosts,aswellashighlyaccuratepositionmeasurementsforboth thehostandimages.highdspatialresolutionifuspectroscopycanfillboththese needs.weexpecttoidentify~1000'gold'highdqualitylensingsystemswithlsst. TheidealcapabilityforthispurposewouldbehighDstrehladaptiveopticIFU spectroscopyfor~1000stronglenssystemsusing20/30mclasstelescopeswith R~3000and1D2umcoverage.TherequiredfieldofviewisthetypicalsizeoftimeD delaylenses,3d4"onaside.asecondaryneedisforspectroscopyofthemore massiveobjectsover~fewarcminradiusfromthelensingsystemtoconstrainline ofsightconvergenceandshear.kinematicinformationwillbehelpfulfor establishingmasses.anidealsamplewouldconstitute100objects/lenssystem, observedwithspectralresolutionr>3000,over~5arcminradiusfieldofview, spanning0.4d1umwavelengthcoverageorbroader. 3.-Synthesis- - Thereareseveralcommoncapabilitiesacrossthevarioustopicsdiscussedatthe workshop.thisincludednotjustinstruments,butobservingmodesandsoftware infrastructure. 3.1SoftwareInfrastructure Althoughtimedomainscienceistheprimarybeneficiaryofabrokertosortthrough thealertsgeneratedbychangesinbrightness(orposition),thecosmologicaluseof

19 SNeIa,thestudyofAGNs,andthestudyofbrowndwarfweatherallwillrelyonthe abilitytorecognizeinterestingeventswhentheyhappen.foreachcase,thesignal hiddeninthenoiseofonemillionalertspernightwillbedifferent,buttheywillall requireasystemtowinnowalertsdonetotheonestheywillfindofinterest. Hiddenamongthosemillionalertswillberareandinterestingobjects,andthese willbelostwithoutaworkingbroker. 3.2Instruments 3.2.1LowDResolutionSpectrographs Althoughabrokerwillbeimportantfornarrowingdownthenumberofalertstoa reasonablenumber,therewillbesomeeventsthatwillrequiremoreinformationin ordertomakeadecision.fortrulytransientevents,whenanobjectappearswhere nonehasbefore,lsstwillprovideonlyamagnitudeatdiscovery.therewillbeno historytohelpcharacterizetheevent.fortheseobjects,arapid,lowdresolution spectrumcanprovidemoreinformation.becauseoftheirlowresolution(r~100d 500)andhighthroughput,theycanbedeployedonsmalleraperturefacilities(2D 4m).Asuiteofsuchspectrographsonarangeoftelescopeapertureswouldgreatly enhancetheidentificationofrareandinterestingobjectsinthelsstalertstream.it wouldalsohelptoidentifysneiaforcosmologicaluse,agnsforvariabilityand reverberationmapping SingleDObject,HighDThroughput,WideDWavelengthCoverageSpectrographs Formanyobjects,thedensityontheskyatanygiventimewillbelowenoughthat thereisnoadvantagetoamultidobjectspectrograph.whilethiswillapplymainlyto timeddomainevents,itisalsotrueofrarenondvariableobjects(suchashighdredshift AGNandgalaxies).Thegeneralrequirementforresolutionistosplitthe[OII] doublet,sor~3500,butthisisalsohighenoughtoseparatetheohnightskylines andthusproducebetterspectraoffaintobjectsintheinfradred.mosttimeddomain targetswillbeunknownandtheknowntargetswillcoverawideredshiftrange,so thewidestpossiblewavelengthcoverageisimportant.thiscoversfromthe atmosphericcutoffat0.32μmtothekband.asingleinstrumentthatencompasses allthesecapabilitiesmaybedifficult,butasuiteofinstrumentsdeployedonarange oftelescopeaperturesfrom4mto10mwouldfulfillmostoftheneed HighlyMultiplexedSpectrographs Therearemanysciencecasesfromacrossthebreakoutsessionsthatrequire spectraofmanythousandsofobjects.somewouldlikeordersofmagnitudemore. Theinstrumentswouldbewidefield,withafieldofviewof1D3degrees.There wouldbecapacityforhundreds(minimal)tothousands(highlydesirable)ofspectra inasingleobservation.thesecasesfocusmainlyonopticalwavelengths,butir capabilityisalsoimportant.

20 ForthemultiDobjectcases,thereislesscommonalitywhenitcomestoresolution. MostextragalacticprogramsandsomeGalacticstructuresciencecoulduselowDtoD moderateresolutionsofr~1000d3000.thegalacticscienceprogramsalsodesire higherresolutionsofr~20,000d30,000.thesewouldbedeployedontelescopes withaperturesof4mto10m,withthelargertelescopestakingmostofthedemand SingleDObjectHighDResolutionOpticalandNearDIRSpectrographs ForGalacticscience,availabilityofhighDresolutionopticalandnearDIR spectrographsonthelargesttelescopesisveryimportant.highdresolutionoptical spectrographs,withr~20,000andhigher,areparticularlyimportantformeasuring thepropertiesoftherareextremelymetaldpoorstarsinthegalactichalo,from whichwewillhaveauniquewindowintotheearlyuniverse.highdresolutionneard IRspectrographs,withR~40,000 50,000,arecriticalforderivingmassesof ultracooldwarfsinlowmassbinarysystems. 3.3Facilities Buildingnewfacilitiesisanexpensiveproposition,sorepurposingexistingfacilities maybetheanswertomeetingtheneedforspectroscopicfollowdupintheeraof LSST.Fromallthesciencecases,itisclearthatthereisaneedforarangeof apertures.smalleraperturesfrom2d4mcanhelpwithclassificationandstudyof thebrighterendoflsstdiscoveries.the6.5d10mtelescopesaremoresuitedtothe followdupofthebulkofthetargetsfoundbylsst. Inaddition,theoperationofthesefacilitiesmayneedtochange.Dedicated operationsthatarematchedtospecificsciencegoalswillmoredirectlyenable followdupoflssttargets.thisway,schedulingandtimeallocationcanbeadapted tothemostefficientuseofthesefacilities.itmaybeeasiertodedicatesmaller aperturefacilities,butthevolumeandrateoflssttargetssuggeststhatdedicated largerfacilitieswouldalsobevaluable. 3.4Timing LSSTisscheduledtobeginoperationsin2022,sodesignandconstructionofsome instrumentshastostartnow.thesurvey,though,willlastfortenyears.giventhe lengthoftheproject,noteveryfollowdupcapabilityhastoexistatthestartof operations.raretransientsareunlikelytobeuniformlydistributedoverthesurvey, sothecapabilitiestodiscernandstudythemmustbeinplaceoncelsstbegins producingalerts. Forstaticobjects,thefollowDupcanoccuronamoreleisurelytimeDscale.The massivelymultiplexedspectrographscanbeonskywellintotheperiodoflsst operations.infact,itmaytakeseveraliterationsofdatadcatalogreleaseinorderto producethesamplesthatareofinterest,sotheremaybelittleornoscientificgain inhavingthesecapabilitiesearlyinlsstoperations.

21 AsthevarioussciencegoalsoftheLSSTprojecthavedifferentoperationaltimelines forfollowdup,thisallowsforthedevelopmentofastrategicplanforcapability designandconstruction.inaddition,thisspreadsthecostofthesecapabilitiesover alongertime,allowingforamoreconsistentapproachtofunding. 4.-Acknowledgments- - Wewishtothanktheparticipantsinthisworkshop(listedinAppendix2)fortheir valuablecontributions,aswellascontributionsfromindvidualswhocouldnot attend,includingsteveallenandrachelmandelbaum.wewouldalsoliketothank themembersoftheorganizingcommittee,toddboroson,steveheathcote,ken Hinkle,JoanNajita,andSteveRidgway. - -

22 Appendix-1.-Spectroscopy-Summary-Table Thistablerepresentsaninitialattempttocharacterizeparametersforindividual projectsthatwillfollowuplsstdiscoveries.itisnotmeanttobeexhaustive,but illustrative.itcanbetheframeworkthatguidesfuturediscussion. Problem a Depth b S/N c d R e Target f Area g Comments Superluminous SNe 16 <r<25 > µm deg 2 entire LSST footprint Cataclysmic variables 16 <r<25 > µm deg 2 entire LSST footprint Galaxy stellar dynamics 16 <r< µm ,000 deg 2 Galaxy stellar abundances: [Fe/H], [ /Fe], [C/Fe] 16 <r< µm ,000 deg 2 individual elements 16 <r< µm ,000 deg 2 all individual elements 16 <r< µm 20, ,000 deg 2 Brown dwarf masses K 15 > µm 50,000 18,000 deg 2 Brown dwarf weather K 15 > µm 5,000 18,000 deg 2 Massive galaxy survey 20 <i<25 > µm deg deg 2 Topology of reionization survey zab > 5 (for Ly line) µm up to 10 arcmin 2 1 deg 2 Dwarf satellite galaxies r<24 continuum > 10 for RV Å ,000 deg 2 few deg 2 IGM tomography i<25 26 continuum S/N Å arcmin 2 FOV 10 arcmin Quasar redshift survey i< deg 2 10,000 deg 2 Reverberation mapping r< > deg 2 one field (1-2 deg 2 ) z > 6 quasars (other rare AGN) Y < µm > 2000 single object entire LSST footprint Ly blobs i< Å 2000 single object entire LSST footprint Weak Lensing/LSS cross-corr. cal. 20 <i< µm deg deg 2 Weak Lensing/LSS photo-z train. 22 <i< µm deg deg 2 Weak Lensing/LSS supplemental i µm deg deg 2 Cluster Cosmology photo-z cal. 22 <i< µm deg deg 2 Strong Lensing cosmology i µm /10 deg deg 2 SNIa Cosmology: SN follow-up gri mag µm deg deg 2 SNIa Cosmology: Host follow-up 20 <i<25 mag µm deg deg 2 Problem Min. Desired Target # Visits k Cadence l When m Comments Sample Sample E ciency j Size h Size i Superluminous SNe few 100 few several 3-4 days start of LSST Cataclysmic variables several variable start of LSST Galaxy stellar dynamics Throughout Galaxy stellar abundances: [Fe/H], [ /Fe], [C/Fe] Throughout individual elements Throughout all individual elements subset subset 1 Throughout Brown dwarf masses 1 Throughout Brown dwarf weather 1 Throughout Massive galaxy survey few 10 5 a few million 1 1 static static needs to be done for a number of redshift bins Topology of reionization survey , static static for several di erent redshift bins Dwarf satellite galaxies 10 fields few tens of fields 1 static static higher R for velocity dispersion IGM tomography 10 fields few tens of fields 1 static static Quasar redshift survey ,000 static static Reverberation mapping deep drilling co-eval with LSST start of LSST z>6 quasars (other rare AGN) ,000 static static X-shooter-like Ly blobs static static near UV; near-ir ; IFU Weak Lensing/LSS cross-corr. cal. 50, ,000 1 static static Any bright objects Weak Lensing/LSS photo-z train. 20, ,000 1 static static faint galaxies Weak Lensing/LSS supplemental static static Likely JWST or WFIRST+IFU Cluster Cosmology photo-z cal static static Strong Lensing cosmology selective static IFU: samp. over 5 00 x5 00. prob. 20m/30m SNIa Cosmology: SN follow-up 5,000 10,000 1 selective start of LSST SNIa Cosmology: Host follow-up 100, ,000 1 static static a Particular astronomical question or source. b Brightness ranges of targets. c Desired signal-to-noise ratio. d Desired wavelength coverage. e Resolution. f Target density (multi- vs. single-object spectroscopy, background). g Necessary survey area. h Minimum number of targets. i Desired number of targets. j Desired target selection e ciency (purity). k Number of visits per target. l Desired cadence. m When is capability needed relative to the start of LSST operations.